# PPA v2 construction discussion



## morsel

Talk about building PPA v2 here.

Tangent's PPA v2 site
Morsel's PPA v2 site


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## individual6891

Are there alternative transistors you can use for the buffer stage? Some of those resistors are hard to source in europe, so a european transistor list might be handy.


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## Glassman

BD139/BD140 are easily found in Europe.. oh you probably meant the TO-92 parts.. instead of 2N5087/2N5088 you can use BC849/BC859 or BC850/BC860, the pinout is however slightly different.. another choice would be 2SC1815/2SA1015 if you can find them, these have the same pinout..


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## individual6891

Quote:


  Originally Posted by *Glassman* 
_BD139/BD140 are easily found in Europe.._

 

PN4392,2N5087,2N5088 aren't though


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## Glassman

instead of that JFET you can use for example some from the BF24x series with higher Idss, about 30-60mA is about right there.. they come in various pinout versions, you might find one that fits the PN4392 pinout, otherwise you have to bent legs.. oh and btw. PN4392 is the same as 2N4392 if that helps..


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## phobus

r24, r34 are 2.2 ohm resistors? Is there a mouser part number for that? I'm going to build one using the vishay dale resistors.

 thanks


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## Syzygies

Quote:


  Originally Posted by *phobus* 
_r24, r34 are 2.2 ohm resistors? Is there a mouser part number for that? I'm going to build one using the vishay dale resistors._

 

Yes, but Vishay Dale RN55's _start_ at 10 ohms, look at their datasheet.


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## phobus

doh. ok thanks.


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## sbelyo

Quote:


  Originally Posted by *phobus* 
_r24, r34 are 2.2 ohm resistors? Is there a mouser part number for that? I'm going to build one using the vishay dale resistors.

 thanks_

 

I found this.... It's not vishay but it's metal film and 1% and IN Stock

 660-MF1/4DLT52R2R21F from mouser

 Here's a vishay brand 1% metal film 2.21 ohm But it doesn't state the wattage.

 594-9B14064A2R21FCT Stock is coming


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## amb

Quote:


  Originally Posted by *Glassman* 
_oh and btw. PN4392 is the same as 2N4392 if that helps.._

 

PN4392 and 2N4392 are the same electrically, but in different packages and pinouts. PN4392 is plastic TO-92 while 2N4392 is metal can TO-18.


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## individual6891

Quote:


  Originally Posted by *amb* 
_PN4392 and 2N4392 are the same electrically, but in different packages and pinouts. PN4392 is plastic TO-92 while 2N4392 is metal can TO-18._

 

The 2N4392 is also a 1.8W device isn't it? Whereas PN4392 is 625mW


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## amb

Quote:


  Originally Posted by *individual6891* 
_The 2N4392 is also a 1.8W device isn't it? Whereas PN4392 is 625mW_

 

The TO-18 metal can has better heat dissipation than the plastic package hence the higher power rating. BTW the Vishay-Siliconix datasheet for these devices says the 2N is 1.8W as you state, but the PN is 350mW.


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## individual6891

Quote:


  Originally Posted by *amb* 
_The TO-18 metal can has better heat dissipation than the plastic package hence the higher power rating. BTW the Vishay-Siliconix datasheet for these devices says the 2N is 1.8W as you state, but the PN is 350mW._

 

Ahh you're right, Fairchild's datasheet says the PN4392 (TO-92) is 625mW, but it's surface mount equivalent MMBF4392 is 350mW... I guess different manufacturers datasheets can be all over 
	

	
	
		
		

		
		
	


	




 Well at the moment someone's ordering me some of the 2N5087/8 and PN4392 with their digi-key order to europe so yay 
	

	
	
		
		

		
		
	


	




 As for a replacement to the 2N5087 / 2N5088 available very easily  to the UK.. would:
BC337-40 : NPN, 2N5088 replacement
BC327-40 : PNP, 2N5087 replacement
 ...be appropriate?


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## amb

Quote:


  Originally Posted by *individual6891* 
_As for a replacement to the 2N5087 / 2N5088 available very easily  to the UK.. would:
BC337-40 : NPN, 2N5088 replacement
BC327-40 : PNP, 2N5087 replacement
 ...be appropriate?_

 

The BC550C/BC560C are better, and more favored in audio use. Note that these have reversed pinouts than the 2N5087/2N5088.


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## primer

Is there much of a difference between the "recommended" and the "alternate" part. Eg. Output transistor MJE243OS, BD139OS vs 511-BD139.


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## ppl

I would strongly advice you stick with the 2N5088 and 2N5087. Electrically the BC550C and BC560 will work but require rotation 180 to match pin out of the 2N devices. The 2SA1015 and its complement less suited electrically however have the base and emitter interchanged from the 2N types. See Below links to the data sheets. 
 2AS1015> http://www.alldatasheet.co.kr/datash...A/2SA1015.html
 2SC1815> http://www.alldatasheet.co.kr/datash...A/2SC1815.html
 2N5087 > http://www.alldatasheet.co.kr/datash...MI/2N5087.html
 2N5088 > http://www.alldatasheet.co.kr/datash...MI/2N5088.html
 BC550C> http://www.alldatasheet.co.kr/datash...LA/BC550B.html
 BC560C> http://www.alldatasheet.co.kr/datash...LA/BC560C.html
 BC337> http://www.alldatasheet.co.kr/datash...OLA/BC337.html
 BC327> http://www.alldatasheet.co.kr/datash...OLA/BC327.html
 MPS8099> http://www.alldatasheet.co.kr/datash...A/MPS8099.html
 MPS8599

 The selection of the 2N5087&2N5088 transistors was primarily based upon creating the ideal devices for use in the current Mirrors; however the high bandwidth and extremely high Gain at very low collector currents proved to provide a more stable buffer when operated at low quiescent currents, Moreover the low noise figure of These transistors have been used in the past in High gain Microphone and Magnetic phono preamps in both high end Equipment such as Mc-Intosh Preamplifiers and power amplifiers in addition to Mark Levenson. The low noise figure of 2-3 dB typical for the 2N5087&2N5088 are one of the primary reasons for there use in high gain low noise Audio circuits. Anyone that thinks these devices are not suitable for audio use or popular should perhaps look into this further

 The PN4392-PN4393 as well as the MPF4392-MPF4393 will interchange just fine. The Bias adjustment makes some tolerance on this transistor possible as long as the device you select has a min Idss of 30mA and your not looking at setting the output bias at 40 or so mA then things will be ok. Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices. The output transistors should all be matched in all three channels because of the symmetry created by the ground channel with respect to the right and left channel. 

 The output transistors allow some considerable flexibility. The default MJE243/253 provide the best solution for low impedance headphones as thay are of considerably higher current than the BD139 and BD140. However the BD139/140 pair have higher bandwidth with an ft of 190 typical vs 40 typical for the MJE243/253 at high currents the Hfe falls quicker on the 139/140 pair than the Mje’s so for low impedance headphones the Mje243 and 253 provide greater high frequency because the Hfe hold up better because of the higher current capacity of the devices. This is the paradox of BJT output transistor selection more power less fast devices. This is accounted for by providing driver transistors that have bandwidths of over 300 MHz at the currents they are operated at in the PPA v 2.0. However for you speed demons I might suggest the flowing transistors as output devices mind you the maximum short circuit current of these faster devices will be about 1 amp for a few seconds.
 BD139/140> http://www.alldatasheet.co.kr/datash...IPS/BD139.html
 KSA1220> http://www.alldatasheet.co.kr/datash...D/KSA1220.html
 KSC2690> http://www.alldatasheet.co.kr/datash...D/KSC2690.html
 2SC3421> http://www.alldatasheet.co.kr/datash...A/2SC3421.html
 2SA1358> http://www.alldatasheet.co.kr/datash...A/2SA1358.html

 The BD787/788 and the MJE 243/253 provide the best all around performance with load impedances lower than 50 ohms at bias currents above 20 mA throught the output transistors emitter resistor. Lower bias currents and or higher load impedances generally favor the lower current higher speed devices.
 BD787/788> http://www.alldatasheet.co.kr/datash...OLA/BD788.html
 MJE243/253> http://www.alldatasheet.co.kr/datash...LA/MJE243.html


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## individual6891

Thanks a lot for that very detailed post ppl. Decided to get some 2N5087/2N5088's shipped over with someone else's Digi-Key order in the end.

 Would they benefit from hfe matching?


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## primer

Thanks for that informative explanation, ppl. Trying to source everything from one vendor (Mouser) but wasn't sure of the alternatives.


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## tangent

Quote:


  Originally Posted by *individual6891* 
_Would [the driver transistors] benefit from hfe matching?_

 

...

  Quote:


  Originally Posted by *ppl* 
_Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices._


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## Vladco

What size of case do you recommend for board and steps? Which one from group buy?


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## individual6891

Option A can't fit a power supply with it.


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## tangent

Quote:


  Originally Posted by *Vladco* 
_What size of case do you recommend for board and steps? Which one from group buy?_

 

If you mean the MMM case group buy, I wouldn't use any of them. 2.5" is unnecessarily tall for a PPA. The standard 2" PAR Metals case that is otherwise spec'd the same as option B will work nicely. The "Tangent PPA" pics that I and others have linked to in that thread are of the 2" case with a custom FPE panel.


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## jamont

Will PPA v2 work well in the Hammond 1455N160X cases that was often used for v1? Is a ventilated case needed for v2?


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## tangent

Yes. No.


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## morsel

Has anyone completed their PPA v2 yet? We would love to hear from you.


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## tangent

Um, since the first ones went out on Friday, I'd be surprised to find that the first ones had even _arrived_ before today. Patience, Morsel.


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## thrice

Quote:


  Originally Posted by *morsel* 
_Has anyone completed their PPA v2 yet? We would love to hear from you._

 

Just got the boards yesterday and I am still getting a parts order ready for PPA V.2....there was another project distracting us ya know...
	

	
	
		
		

		
		
	


	




 Let me just say that the boards look great and wow..they are packed.

 Hopefully, I'll have one up and running in the next week.


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## steinchen

pcbs arrived today, much earlier than I expected 
	

	
	
		
		

		
		
	


	









 unfortunately I'm still waiting for an order with a few missing parts, so I'm not able to complete the build atm. I'll fetch the missing parts on Friday from a local shop, although prices are much higher there, because I don't want to wait another week. You can expect my first impressions next weekend.


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## Syzygies

Anyone notice that Newark lists the Elpac WM080-1950-760 as follows?

Newark Part # 16F126
_Power Supplies; Power Supply Type: External Power Supply; Terminal Type: 5 Pin DIN Connector; Size/Dimensions: 81.28 X 55.88 X 48.26 mm_

 To confirm anything as basic as the output voltage, one needs to consult the datasheet. The datasheet describes the outputs for this family as follows:
_Output connector: 5 pin DIN or barrel type (5.5 x 2.5 x 9.5mm)_

 I believe that the subtext here is: _"You're supposed to know that if the output only requires 2 wires, we'll use the barrel type. Otherwise, we'll use the DIN. Do you think we'd say which is which in the datasheet? Don't you think that if that was our disposition, we'd work with vendors who will type the correct connector into their part description, and will give you some idea of shipping costs before submitting an order?"_

 Just wondering, before ordering. This comes with a barrel connector, right? Anyone know an alternate vendor you'd rather have me support?


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## Syzygies

Tangent writes about _Choosing an Output Jack_:

  Quote:


 If the amp is putting out a significant voltage, Ohm's law tells us that current becomes infinite. Since the PPA's output buffers don't have output protection, this momentary short will likely fry the buffers. 
 

and goes on to not recommend 1/8" output jacks at all.

 I remember this point being a debate for PPAv1. I hoped/thought the debate would now be dead, but I take this issue seriously, as I've found that when an amp gets knocked around while traveling, an 1/8" output plug can get jostled part way out.

 My Etymotic 4p canalphones come with a 1/4" adapter, but it's not screw-on, so who's kidding who? We're in serious "penny-in-the-fusebox" territory here. Should the PPAv2 be described as not suitable for any headphones terminated with 1/8" jacks?

 I was thinking of equipping my PPAv2 with a locking 1/4" output jack _and_ a good 1/8" output jack such as the Tangent-recommended CUI SJ-43502PM (Digi-Key CP-43502PM), but with 50 or 75 ohms output resistance on the 1/8" jack.

 This accomplishes Ety 4p to 4s conversion and provides output protection.

 What is the minimum value that would provide adequate protection for the buffers? I understand all the "purity of sound" arguments against such a resistor, but the fact is that pretty much any headphones terminated in a 1/8" plug have reduced impedance to make them practical for the portable market, and sound better with some output resistance. Certainly _every_ 1/8" plug headphones I've tested.


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## amb

The PPAv2's output transistors are rated for continuous 1.5A (BD139/140) or 4A (MJE243/253). There are 2.2 ohm emitter resistors that would help limit the current in a short circuit. There is also current limiting in the PSU (The LM317 regulator for example will current-limit and shut down if the draw is over 1.5A). As long as you don't keep the short circuit condition persist over a long period of time while the music is playing loud, then there should be little risk of damage to the circuit. If you're really paranoid, add a fuse at the DC power input.


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## jamont

Quote:


  Originally Posted by *Syzygies* 
_Just wondering, before ordering. This comes with a barrel connector, right? Anyone know an alternate vendor you'd rather have me support?_

 

I'd get it from Allied rather than Newark. Newark really sucks. And yes it has a barrel connector.


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## tangent

Quote:


  Originally Posted by *Syzygies* 
_This comes with a barrel connector, right?_

 

Yes.

  Quote:


 Anyone know an alternate vendor you'd rather have me support? 
 

Allied Electronics.

  Quote:


  Originally Posted by *amb* 
_There is also current limiting in the PSU_

 

Yes, though I wonder if that is enough. There is no current limiting between the rail cap bank and the transistors. When that big bank discharges suddenly, what is the peak current? I suppose it depends on the output resistors.


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## Syzygies

Quote:


  Originally Posted by *amb* 
_There are 2.2 ohm emitter resistors that would help limit the current in a short circuit. There is also current limiting in the PSU (The LM317 regulator for example will current-limit and shut down if the draw is over 1.5A)._

 

Thanks, all.

 Shorts are most likely during travel. I've seen NiMH AA cells put out 6A in a short, though I'd guess that even my 1000 mAh AAA cells are incapable of 2.5A.

 Those 2.2 ohm resistors are only spec'd for 1/4 watt, they'd certainly see more than that in a short.

 For that matter, I just reread various of Tangent's voltage notes. I'm not coming away with a clear idea of the maximum watts my PPA is capable of putting into, say, a 10 ohm dummy load. I might have to measure this. To be safe, I'll extrapolate first from a bigger dummy load.

 People are going to use 1/8" plugs, perhaps in _"we're just kidding ourselves"_ 1/4" adapters. It would make sense to have a conservative recommendation here, for anyone who wants to add output resistance.


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## tangent

Quote:


 I've seen NiMH AA cells put out 6A in a short 
 

They should be able to do better than that. I've seen 9V _alkalines_ put out that kind of flash current. Surely a big cell like that can do better? Just dividing voltage by nominal impedance, I get 35A for Sanyo AAA NiMHs.

  Quote:


 Those 2.2 ohm resistors are only spec'd for 1/4 watt 
 

It's not yet covered in the docs, but you're supposed to use 2W resistors on the output, for precisely this reason. We allowed such large resistors there because we heard stories of people with PPL diamond buffer modules turning their 1/4W output resistors into fuses.

  Quote:


 I'm not coming away with a clear idea of the maximum watts my PPA is capable of putting into, say, a 10 ohm dummy load. 
 

No, there is indeed no way to get that number from what I've written so far. In fact, I think it's probably a complex problem, having to do with the hFEs of your transistors, supply voltage, and other such variables. You could use SPICE to simulate it.

 I did an informal test a few weeks ago and got many watts into a 32 ohm load. I don't have the data on me right now. It was "more than enough", so I haven't bothered to memorize it.


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## Syzygies

Quote:


  Originally Posted by *tangent* 
_Just dividing voltage by nominal impedance, I get 35A for Sanyo AAA NiMHs._

 

Thanks. My shorts were never intentional, just misguided late-night experiments with some circuitry in the way.

 While I wouldn't bet on your rule of thumb staying linear in a short circuit, it makes it clear that for purposes of this discussion, an NiMH battery pack might as well be viewed as capable of infinite current. Something else will give first.

 I'm upping the wattage of my 1/8" jack output resistors, to stay commensurate with the 2 watt, 2.2 ohm output resistors on board the PPAv2.

 As a rough rule of thumb, I'd say that additional R ohm output resistors should be rated for 4/R watts, e.g. 1/2 watt, 10 ohm output resistors can handle the same scenarios envisioned by the 2 watt, 2.2 ohm on board resistors.


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## steinchen

still a few caps missing, but my PPA v2 is up and running 
	

	
	
		
		

		
			





 two questions left for me atm:
 1) across which resistor do I have to measure the buffer bias ? R24 ? What is the default bias setting ? 50mA ?
 2) do I have to connect BBR with S2R for bass boost ? What does BBR stand for ? BBR = bass boost right (channel) ?


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## tangent

Quote:


  Originally Posted by *Syzygies* 
_While I wouldn't bet on your rule of thumb staying linear in a short circuit, it makes it clear that for purposes of this discussion, an NiMH battery pack might as well be viewed as capable of infinite current. Something else will give first._

 

Sure. Also keep in mind, my rough-and-ready 35A estimate is based on the pack impedance, and that is further reduced by the rail cap bank's parallel impedance. So while I'm not sure what the actual number is, I can't see that I'm greatly overstating the potential.

 I think you're right, though, that it's effectively infinite. To get 8A (the max peak the MJE243/253 allows) through 2.2 ohms, you need to put 17.6V across it. That just can't happen in a typical PPA. Ohm's Law poops out on you first. Now, that doesn't put us fully in the safe zone, because between that and the 4A continuous rating there's a danger zone. But I'm optimistic that the supply voltage and discharge current will be dropping at this time, so the ability to sustain more than 4A for a prolonged time should be difficult.

 The less studly BD139/140s would be easier to kill. In fact, I think it wouldn't be all that hard to kill them with 2.2 ohms of output resistance.

 It's worth pointing out that the resistor can easily die before the output transistor, even with 2W resistors. If you're somehow putting 4A through them, the wattage is 35.2W. Fortunately, film resistors tend to fail open; they're hard-to-replace fuses, in effect.

 During the PPAv2 development, we went through several design changes to the buffer, and at several points I had 10 ohms on the output. This will raise your distortion a bit but it will ameliorate these problems greatly. And because it's inside the feedback loop, it doesn't hurt as much as putting resistors inline with the output wires. That's why the distortion doesn't go up much.

  Quote:


 As a rough rule of thumb, I'd say that additional R ohm output resistors should be rated for 4/R watts, e.g. 1/2 watt, 10 ohm output resistors can handle the same scenarios envisioned by the 2 watt, 2.2 ohm on board resistors. 
 

Careful there. We didn't pick 2W through any special wisdom. It's just the largest value that fit in the space we had.


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## morsel

Hi steinchen,

 Measure output bias across the output resistors R24 or R34.
 Set bias to 30mA, or 10mA if using a battery board.
 Connect BBR with S2R for bass boost.


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## Syzygies

Quote:


  Originally Posted by *tangent* 
_We didn't pick 2W through any special wisdom. It's just the largest value that fit in the space we had._

 

It looks to me like PercyAudio's "MILLS Non-Inductive Wire Wound Resistors" MRA-5 (5 watts) $2.15 each in a range of nearby values, fits the spot. I'm about to go out, I'll check again. This resistor is highly regarded, if one believes their catalog copy!


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## steinchen

raised the bias to 30mA (= 66mV across R24 2.2Ohms), now Q24 / Q34 are getting warm but not hot, sound improved considerably

 it's 2 a.m. round here, I'll wire BBR tomorrow 

 DC offset: -0.4mV / 5mV (didn't match trannies out of lazyness)

 I suggest adding a setup-section to the PPA v2 pages (OpAmp bias, buffer bias, bass boost wiring, ... )

 I substituted Q3 with BF245C since I'm using AD843 which are drawing 13mA quiescent current. Using 2n5486 would require hand picking for IDDS > 13mA and pn4392 would have a significant lower noise isolation due to it's hig IDSS. Maybe you can add some words about that, too.

 first impression: nice clean sound, not that warm and rich like M³, rather analytical, but that has to be verified the next days with AB tests. Building cost should be much lower without monolithic buffers, a big step forward.

 PPA v2 is definitely a great amp. Thanks and regards to Morsel, Tangent and PPL


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## jamont

What should be considered in choosing the output transistors? Are the BD139/140 and MJE243/253 equally good in this circuit?


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## stadams

Quote:


  Originally Posted by *jamont* 
_What should be considered in choosing the output transistors? Are the BD139/140 and MJE243/253 equally good in this circuit?_

 

jamont,

 ppl addressed this earlier in post #16 I believe. He gives a good explanation between there differences and possible effects on the circuit.

 Later,


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## jamont

Quote:


  Originally Posted by *stadams* 
_ppl addressed this earlier in post #16 I believe. He gives a good explanation between there differences and possible effects on the circuit._

 

I'm going blind, thanks!


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## Syzygies

Quote:


  Originally Posted by *Syzygies* 
_It looks to me like PercyAudio's "MILLS Non-Inductive Wire Wound Resistors" MRA-5 (5 watts) $2.15 each in a range of nearby values, fits the spot._

 

Ok, this resistor is a bit long to fit cleanly, but there's room on the board for its body:






 Their other boutique resistors, the $7.50 "BE YAMAMURA Non-Inductive Wirewound Resistors", include a 2 watt resistor that makes only a slightly better fit:






 Then, back at the working class lunch counter, there's Mouser Xicon 2W 2.2OHMS 5% Small Metal Oxide Resistors, $0.19 each.

 The perhaps better Vishay Dale 2W 2.2ohm, Mouser 71-CCF02-J-2.2K, is non-stocked.

 Perhaps most promising is Vishay/BC components at Digi-Key, RES 2.2 OHM METAL FILM 2W 5% for $0.32 each. These have an L2 body dimension of 12mm, a tight but feasible fit with a board hole spacing of 0.5".

 I'm willing to buy 60 or 120 of these and do some matching, drop sets of 6 in the mail to people who PM me, but 5%, yikes, how close do we want to get?


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## jamont

Quote:


  Originally Posted by *Syzygies* 
_Then, back at the working class lunch counter, there's Mouser Xicon 2W 2.2OHMS 5% Small Metal Oxide Resistors, $0.19 each._

 

This part seems fine to me - I used it in the MMM and plan to use it in the PPA. Is there any point to using an overpriced boutique part here?


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## tangent

Quote:


 I'm willing to buy 60 or 120 of these and do some matching 
 

Do you have a 4-wire meter? If not, forget matching such low-value resistors. With my Fluke 189, I don't bother with anything from 10 ohms on down.


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## Glassman

well, on the other hand, my buffers use 1/4W smd 4R7 resistors in that place and I've sold lots of them and haven't heard of anyone with them fried or anything.. I'm plugging and unplugging headphones with music playing, even aloud, and there's absolutely no problem..


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## Syzygies

Quote:


  Originally Posted by *tangent* 
_If not, forget matching such low-value resistors._

 

Doesn't making voltage dividers and recording the midpoints work? I'd borrow a 9V trickle charge circuit for source. On the other hand, if there's no advantage...

 Edit: measure current using a constant voltage source, or voltage using a constant current source, either is better than 5% even on my sketchy meters?


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## jamont

Quote:


  Originally Posted by *tangent* 
_Do you have a 4-wire meter? If not, forget matching such low-value resistors. With my Fluke 189, I don't bother with anything from 10 ohms on down._

 

OK, I'll bite. I believe that a 4-wire meter would be necessary to measure the precise value of a given resistor, but why is it necessary for comparing several resistors, if the meter and cables are unchanged between comparisons? We don't care about the exact value of the measurement, only how it varies between resistors.


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## Syzygies

Tangent wrote in his Part Selection Guide:

  Quote:


 The ideal C2 setup is to make the three 'odd' capacitors 0.01*µF to 0.022*µF, and the two capacitors between these 0.1*µF to 0.22*µF. You can make them all the same value, but staggering these values gives better bypassing results.

 As a rule, the longer the capacitor is, the better, because you want as little lead length as you can reasonably get.

 Largest Part Size: 18mm × 6mm, 15mm pin spacing 
 

On the other hand, he gives parts numbers for all equal values, 10mm lead spacing.

 So here's a portion of my parts spreadsheet that I'm now thinking through:







 Am I ok going to the particular staggered caps shown in alt B? This introduces the MKP 418 line, any differences to concern me from the MKP 417 line?

 Am I ok going up to the smallest values that buys me a longer cap, i.e. just making the size breaks for 10mm and 15mm as shown in alt C?

 (The board has multiple C2 holes, so both 10mm and 15mm lead spacings fit cleanly, but 5mm would be a stretch, so to speak.)

 These caps are all on Digi-Key catalog p950. Balancing cap sizes, lead length, _ratio_ of capacitances for best performance, what is the optimal "even, odd" cap selection for C2, restricting to this catalog page?


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## phobus

Speaking of C2, does anyone know what type caps are in the picture on the PPAv2 web page? (Tangent would know obviously 
	

	
	
		
		

		
		
	


	




)


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## tangent

Quote:


 Doesn't making voltage dividers and recording the midpoints work? 
 

Yeah, a lot of work, though. If you really wanted to be clever, you could build a Wheatstone bridge instead.

  Quote:


 measure current using a constant voltage source, or voltage using a constant current source, either is better than 5% even on my sketchy meters? 
 

Depends on how 'constant' your sources are. It isn't uncommon for a quick-and-dirty CCS to have a 1% error, or more. If you're going to match resistors to 0.1%, that's not going to be good enough.

  Quote:


 why is it necessary for comparing several resistors, if the meter and cables are unchanged between comparisons? 
 

For one thing, down at such low values the varible contact resistance between the probes and the resistor leads is a big source of error.

This is also illuminating.

  Quote:


 does anyone know what type caps are in the picture on the PPAv2 web page 
 

Vishay-Somethingorother MKT 1813s. They're actually labelled ERO, but they were definitely sold under the Vishay name, from Mouser.


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## Syzygies

Quote:


  Originally Posted by *Syzygies* 
_Balancing cap sizes, lead length, ratio of capacitances for best performance, what is the optimal "even, odd" cap selection for C2, restricting to this catalog page?_

 

So I found myself revisiting Digi-Key page 950 for C5, and came up with these choices:

 C2 odd BC MKP 419 400V 10mm 0.022uF 2222 419 42203 BC2194-ND Digi-Key 0.50
 C2 even BC MKP 417 160V 10mm 0.22uF 2222 417 42204 BC2099-ND Digi-Key 0.65
 C5 BC MKP 416 63V 10mm 0.27uF 2222 416 42704 BC2064-ND Digi-Key 0.65

 This gives exactly the C2 values that tested best for Tangent, in pin spacings that cleanly fit the board holes, but at the expense of going to unnecessarily high voltages. C5 is the largest value cap that fits.

 On the other hand, Tangent made a recommendation with an unnecessarily high voltage, in choosing from the MKP 417 series rather than from the MKP 416 series for his uniform 0.1uF recommendation for C2. He usually has a good reason for these things; what am I missing? If MKP 416 is to be avoided, then I should change my C5 selection. 

 In trading off

 1. poor fit
 2. changing values from tested 
 3. increasing voltage rating

 I went with increasing voltage rating, to get a good fit with tested values. For other cap applications, I've read that wasted voltage rating can be undesireable, but in the absence of feedback from anyone who knows, I'm guessing that here this is the correct optimization.


----------



## individual6891

You know C2 and C5 don't _have_ to be polypropylenes, polyesters work equally fine (negligible audible difference) with a larger selection of parts..

 Wima MKS2 63V/1uF fit C5 wonderfully... though I don't know about US availability. BC have equivalent caps (but oh my god, they're not red).

 As for C2 the Vishay MKT1813 are also available from RS (for the europeans) as well as mouser.

 185-3990: 63V/0·22uF - L:11mm, Dia:5mm
 185-4123: 250V/0·022uF - L:11mm, Dia:5mm


----------



## morsel

I am a bit skeptical regarding this complex bypass capacitor arrangement. Clearly it won't hurt, but will it make a real world difference? Pretend I'm from Missouri and show me.


----------



## Syzygies

Quote:


  Originally Posted by *morsel* 
_I am a bit skeptical regarding this complex bypass capacitor arrangement._

 

I have no doubt Tangent measured something, maybe a person can't pick out one 2% difference blind, but pile on twenty of them? Amb tweaks till he gets a perfect square wave on his scope. I _don't want_ to ever hear a perfect square wave, with my Ety 4s phones I'd think one would make my ears bleed. However, I believe that there's merit to this design approach, simulators will never be able to "wire the last mile" here.

 I want to understand what I'm doing, but for me it always takes me much longer to pick parts than to build a working amp, so the cost here is that the question hung me up. If there had been an optimum parts selection posted for this tweak, I would have breezed by this question. Future builders won't see this as a big deal either way.

 I plan to post my parts list, not that I have any special knowledge, but I wish that everyone who posted a build pic would also post their parts list for others to use at their own risk. I'd start by loading in their work, _then_ thinking critically. Also more interesting to look at their parts choices than the colors of their caps.


----------



## Syzygies

So what hung me up in my most recent parts selection session were the C7 bass boost caps.

 In bass boost, Tangent writes:

  Quote:


 The Panasonic ECQP line will work well here, for instance; they go up to 0.12 µF without requiring lead bending. 
 

The datasheet for 

 C7 Bass boost film cap Panasonic ECGP 50V 0.12 µF ECQ-P1H124GZ P3124-ND Digi-Key 1.06

 lists maximum dimensions 17mm x 8.5mm. The following picture shows this outline; the smaller squares are 0.1":






 Morsel's bass boost calculator was the only one I could get working, and then only on a Windows box. My Mac is as fully loaded as possible, I believe that it can be used to cross-develop Java in Swahili for Windows 98, yet both bass boost calculators balked. For comparison, I have no difficulties using any other calculators on Tangent's site.

 (I have _Mathematica_ and know how to use it, so I really have no excuse here, the original bass boost threads are still around...)

 Morsel's calculator implies a bigger effect from my changing R4 to a 5.4x gain that Tangent's notes suggest will be the case. I've always avoided tone controls, I have no idea if a jacuzzi temperature should be 150F, so I just threw in the towel here and went with Tangent's part. I can always desolder after I hear it.


----------



## morsel

My bass boost calculator uses the correct equations, and so does amb's. Tangent still uses my 3 year old numerical approximation, which is not as accurate. If you are having problems on a Mac, make sure you are running a good up to date browser like Firefox or Mozilla.

 As for my comments about the PPA v2 odd/even cap scheme, I am suggesting there may be no real world difference even with a scope and RMAA.


----------



## ppl

Quote:


  Originally Posted by *morsel* 
_I am a bit skeptical regarding this complex bypass capacitor arrangement. Clearly it won't hurt, but will it make a real world difference? Pretend I'm from Missouri and show me. 
	

	
	
		
		

		
		
	


	


_

 



http://www.pa.msu.edu/hep/d0/ftp/run...pling_caps.pdf
http://www.avxcorp.com/docs/catalogs/caparray.pdf
http://www.analog.com/library/analog...5-02/avoiding/
http://www.latticesemi.com/lit/docs/...TOKEN=87373138
http://www.eetasia.com/ARTICLES/2004..._AMD_TAC01.pdf
http://www.xilinx.com/bvdocs/userguides/ug072.pdf


----------



## morsel

PPL, those references are fine and dandy, thanks for posting them, but they do not answer my basic point, which is whether the more complex odd/even bypassing arrangement makes a measurable real world difference in the PPA v2, as opposed to being a good idea on a purely theoretical basis.


----------



## tangent

Quote:


 Morsel's bass boost calculator was the only one I could get working 
 

Sorry, that's fixed now. I tested in Firefox and Safari on OS X.

  Quote:


 I have no doubt Tangent measured something 
 

No, ppl mentioned the idea, and I agreed with it on general principle. As Morsel says, it can't hurt and it may help, so I recommend it.

  Quote:


 Tangent still uses my 3 year old numerical approximation 
 

Not any more.

  Quote:


 as opposed to being a good idea on a purely theoretical basis. 
 

That argument would hold more water, Morsel, if it hurt to implement the idea. It doesn't, so why fight it?


----------



## morsel

It hurts in the sense that some people obsess, perhaps unnecessarily, about caps and buy more types of caps in order to comply with theories that may not have been clearly demonstrated to produce real world improvements in PPA v2. It is in my nature to try to keep things as simple as possible. I'm not saying the odd/even idea is bad or wrong, I'm asking for proof that it makes a difference.

 PS - your bass boost calculator does not handle bass boost gain < 6dB properly.


----------



## ppl

Wow just let Morsel define what Good theory is, as opposed to the many experts that wrote those articles I linked. Well moving along it is quite common knowledge even around hear that multiple values of bypassing operate most effectively at different frequencies the Big electrolytic start to poop out around 100 KHz and a noticeable rise in impedance is noted as low as a 500 HZ on some units. This is why we use smaller film caps in parallel to them. This same concept is carried to three levels as opposed to two levels if the mixed 0.1uF and something 10 times lower in value so this would be 0.01uf. Myself i tried 0.22uF and 0.022uF in addition to 0.56uF Teflon populating some C1 spots and so i have 4 levels of absolutely the best bypass arrangement both sonically as well as technically. This puts me at 4 that’s FOUR Levels of supply bypassing with the dielectric chosen so as to be most effective in its ideal frequency range. I will post a photo later of the innards of the Prototype showing the verity of the possible capacitor options that fit in the standard Hammond case on Version 1.916 anyway.


----------



## Glassman

I'm dealing now with board layout and supply decoupling for Spartan3 FPGA, so I've been reading some Xilinx application notes and this is exactly what I have found there.. it is important though not just to vary the value of the cap, but each cap should have different inductance, the smaller the cap is, the lower inductance you want, so picking 0.1 and 0.01 from the same line of caps does nothing in fact, each of the step has to have different parasitic inductance.. and yes it doesn't hurt using it this way of course.. on my buffers I rely upon 1uF polyester C2 caps on PPA board and use 0.1uF polypropylene on the buffer boards themselves..


----------



## tangent

Quote:


  Originally Posted by *Glassman* 
_picking 0.1 and 0.01 from the same line of caps does nothing in fact_

 

Not completely true. Yes, inductance also matters, but simply paralleling a lower-value cap will add another 'V' with a higher resonant point to the system.

 (If you've seen the impedance vs. capacity graphs in some datasheets, particularly film and ceramic types, you know what I mean about a 'V'.)


----------



## morsel

Relax PPL, I'm not trying to contradict established theory. I am quite familar with the concept of multiple values of capacitors for bypassing. The question is whether it will actually result in a real world improvement in PPA v2.

 Those of you with scopes and RMAA could try removing just the odd caps, then just the even caps, using all the same value, etc., and see if you can measure or hear a difference.

 Sorting the wheat from the chaff is an honorable and useful goal.


----------



## individual6891

Quote:


  Originally Posted by *ppl* 
_Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices. The output transistors should all be matched in all three channels because of the symmetry created by the ground channel with respect to the right and left channel. _

 

So I measured the hFE using a standard DMM, but the PNP transistors have a lower gain than the NPN devices, I suppose this is due to the way they are designed?

 Here are my tables (2N5088 on left, 2N5087 on right)... just trying to decide which ones to use:







 And for the PN4392...Only a small amount of the them put out over 30mA - is this a problem? They seem to hang around the 30mA mark.

 This is my 2N5486 list:






 Is around 17mA enough for the OPA637 for Q3? Looking at the datasheet, the specs say the chip uses 15mA max, but is there enough in my set of 2N5486s to provide enough? (with about 1mA bias).. Seems a bit borderline to me?!


----------



## morsel

The FET current sources only need to supply quiescent current + 1mA bias. Iq for OPA637 is 7mA, way under the 17mA Idss you measured. It is normal for PNP hfe to be lower than NPN hfe. The PN4392 Idss of 30mA is fine.


----------



## individual6891

Quote:


  Originally Posted by *morsel* 
_The FET current sources only need to supply quiescent current + 1mA bias. Iq for OPA637 is 7mA, way under the 17mA Idss you measured. It is normal for PNP hfe to be lower than NPN hfe. The PN4392 Idss of 30mA is fine._

 

Ahh, it said -/+7 typical and -/+7.5 max, so I presumed that it meant 15.. my bad


----------



## Glassman

Quote:


  Originally Posted by *tangent* 
_Not completely true. Yes, inductance also matters, but simply paralleling a lower-value cap will add another 'V' with a higher resonant point to the system.

 (If you've seen the impedance vs. capacity graphs in some datasheets, particularly film and ceramic types, you know what I mean about a 'V'.)_

 

the right part of the V won't change, just the left one, that sure shift the resonant frequency higher, but the overal impedance at that frequency will be about the same.. the point is to move the right part of V further to the right, in other words reduce the inductance.. using many smaller caps in parallel effectively reduce inductance..


----------



## bg4533

Quote:


  Originally Posted by *individual6891* 
_Ahh, it said -/+7 typical and -/+7.5 max, so I presumed that it meant 15.. my bad_

 

I think that means 7mA from the + rail and 7mA from the - rail. Each rail has its own jfet.


----------



## Clutz

So, I've read this thread a few times and have now become a little bit intimidated of assembling a PPA- it seems that a lot of rather more experienced DIYers than I are getting confused about assembling the PPA which makes me question whether or not I should attempt it (especially given the relative costs of building a PPA)

 I have ordered a Dynalo board (actually, two) and now I am afraid of trying to assemble that.

 So from some of the more experienced builders - after building three Cmoys and having a 4th laid out using a TLE2426 instead of the volage divider resistors - waiting to find somewhere I can buy TLE2426's in Vancouver (I don't want to order them online.. I don't know why..) - is doing a PPAv2 too advanced for me- esp. given the experienced DIYers haven't worked out the details yet?

 Thanks for your support.
 Cheers,
 Clutz


----------



## amb

Quote:


  Originally Posted by *Clutz* 
_is doing a PPAv2 too advanced for me- esp. given the experienced DIYers haven't worked out the details yet?_

 

LOL. What you read were experts chewing on some very fine points that "most people" could safely ignore. 
	

	
	
		
		

		
		
	


	




 Don't let that discourage you. The PPA is quite a step up from a cmoy but if you simply read through all of tangent's docs, get all the recommended parts and build the amp as-is, you should do just fine.


----------



## ppl

Quote:


  Originally Posted by *Glassman* 
_the right part of the V won't change, just the left one, that sure shift the resonant frequency higher, but the overal impedance at that frequency will be about the same.. the point is to move the right part of V further to the right, in other words reduce the inductance.. using many smaller caps in parallel effectively reduce inductance.._

 


 And we have a winner finaly someone that understands the finner points of the Art and yes folks its an art of decoupling


----------



## Syzygies

Quote:


  Originally Posted by *amb* 
_LOL. What you read were experts chewing on some very fine points that "most people" could safely ignore. 
	

	
	
		
		

		
			



_

 

Amen! So far for my amps I've been spending a month obsessing on parts lists, then a _very_ late evening assembling. I'm trying to shorten the month and lengthen the evening, as actually building is the fun part.

 There's a phenomenon in buying headphones (or many things) where one spends $25 then $50 then $100 then $200 then $400. Wish you had the money for $800 phones? You just spent it, dude, look back.

 Once you can solder cleanly and you know how big and how much, spend it and build it. As a rule, double what you think on both counts; the sound will be worth it.


----------



## ppl

Quote:


  Originally Posted by *Syzygies* 
_Amen! So far for my amps I've been spending a month obsessing on parts lists, then a very late evening assembling. I'm trying to shorten the month and lengthen the evening, as actually building is the fun part.

 There's a phenomenon in buying headphones (or many things) where one spends $25 then $50 then $100 then $200 then $400. Wish you had the money for $800 phones? You just spent it, dude, look back.

 Once you can solder cleanly and you know how big and how much, spend it and build it. As a rule, double what you think on both counts; the sound will be worth it._

 

Yes this i true but then again if we did not spend that interm amount on tweeks then we would be simply waisting mony on the $800.00 headphones and as obsessive compulsive types we could never really enjoy those new phones now can we Knowing full well that since we did not obtain that last 1% out ofthe rest of our rig that the Full potential of the new phones are not being utilised so we never will sleep and never can trust what we hear as true because the absolute has not been obtained elcewhare. darn ok time to look into some $2000 Headphones and perhapps a unique amplifire with High voltage running around your head to gain an additionial 1% that you lost in the first place so your really gonna be getting 2% inprovement rather than the 1% previously expecting. Heck thats twice the Goodness ain't it? now did we for get to mention that the decimil point of the illistration is now moved twards the right now our $800.00 Headphones are now gonna cost $8000.00 and our that $400.00 tweek just became $4000.00 and that $200.00 is now at $2000.00. What was that saying welcome to head-fi forget 
	

	
	
		
		

		
		
	


	




 about what?
 BTW Sony SA5000 $450 what a deal http://www.digitalfotoclub.com/sc/fr...ate=03_22_2005


----------



## SnoopyRocks

Quote:


  Originally Posted by *ppl* 
_And we have a winner finaly someone that understands the finner points of the Art and yes folks its an art of decoupling_

 

...and RF is black magic


----------



## phobus

Quick question.. What is R12 used to adjust?


----------



## amb

Quote:


  Originally Posted by *phobus* 
_Quick question.. What is R12 used to adjust?_

 

It's used to adjust the output transistors' bias (set the quiescent current). It's similar to the BIAS pot on the M³ amp. For the PPAv2, set the quiescent current to somewhere between 10mA to 30mA per channel (measure for 22mV to 66mV drop across the R24 and R34 resistors).


----------



## phobus

Thanks!


----------



## individual6891

Any word on sound quality? How does it compare to PPAv1 with intersils / with external diamond buffer?

 Any m³ comparisons too? 
	

	
	
		
		

		
		
	


	




 Very eager


----------



## phobus

Just finished mine yesterday and put it into a cigar box. I had to trim a bit off the end of the board to make it fit. Currently running with OPA627s at 1.8mA, and the quiescent current at 30mA per channel.

 Sounds great so far, but I'm going to let it burn in for a while before comparing it to my beloved M³. I don't know how fair that comparison would be anyways, since I've set the gain and bass boost values differently.

 Thanks very much to Team PPA!


----------



## individual6891

Holy Mack, that looks awesome 
	

	
	
		
		

		
		
	


	




 Can't wait for sound comparison


----------



## Edwood

Quote:


  Originally Posted by *ppl* 
_Yes this i true but then again if we did not spend that interm amount on tweeks then we would be simply waisting mony on the $800.00 headphones and as obsessive compulsive types we could never really enjoy those new phones now can we Knowing full well that since we did not obtain that last 1% out ofthe rest of our rig that the Full potential of the new phones are not being utilised so we never will sleep and never can trust what we hear as true because the absolute has not been obtained elcewhare. darn ok time to look into some $2000 Headphones and perhapps a unique amplifire with High voltage running around your head to gain an additionial 1% that you lost in the first place so your really gonna be getting 2% inprovement rather than the 1% previously expecting. Heck thats twice the Goodness ain't it? now did we for get to mention that the decimil point of the illistration is now moved twards the right now our $800.00 Headphones are now gonna cost $8000.00 and our that $400.00 tweek just became $4000.00 and that $200.00 is now at $2000.00. What was that saying welcome to head-fi forget 
	

	
	
		
		

		
		
	


	




 about what?
 BTW Sony SA5000 $450 what a deal http://www.digitalfotoclub.com/sc/fr...ate=03_22_2005_

 

With a 3% margin for error...... 
	

	
	
		
		

		
		
	


	




 -Ed


----------



## en480c4

Well, I finally got going on my amp.

 I haven't built anything since my CMoy, but have ridden shotgun while my friend Nate (n_maher) has put together some MINTS and PIMETAS. He's been busy with the Millet Hybrid board and we hadn't gotten to the PPA yet. So he went on vacation and left his Triple M with me... well about 5 minutes of listening to that was all the motivation I needed.

 Anyway, progress pics of the board pretty well popluated...











 The iPod's in the shot to give friends who haven't seen the board an idea of scale.

 Anyway, things went pretty well. I'll probably mount the Molex stuff tonight and then it will sit for a while 'til I can get some help wiring the compenents and getting going with the casework. It's going in a standard ParMetals case with STEPS and a crossfeed.

 Thanks to everyone who put this project together...


----------



## sbelyo

Laughing.... I'm just getting around to casing up my ppa 1.1 this week. I figue I'll wait until summer. By then everyone will be done arguing over caps, and transistors.

 Just my $0.02


----------



## tangent

Quote:


 By then everyone will be done arguing over caps, and transistors. 
 

I've been doing audio DIY for about four years now, and the argument was old when I got here.


----------



## sbelyo

Quote:


  Originally Posted by *tangent* 
_I've been doing audio DIY for about four years now, and the argument was old when I got here._

 

I knew that was coming.... alas in the next few weeks i'll be obsessing over caps and the like as well. However I only waste a day or two at the most. At some point you want to hear it work.

 Remeber the saying K.I.S.S. Keep It Simple Stupid


----------



## Chiels

About the power supply

 about the power supply, any recommendation?

 Do I have to separate the +12V and -12V DC ?
 (use 2 TREADs?)
 or I only have to use single source as +24V? 

 Is there any better choice instead of LM317?

 I am just quiet a new builder in DIY field.
 but I am really interested with PPA.


----------



## individual6891

Quote:


  Originally Posted by *Chiels* 
_About the power supply

 about the power supply, any recommendation?

 Do I have to separate the +12V and -12V DC ?
 (use 2 TREADs?)
 or I only have to use single source as +24V? 

 Is there any better choice instead of LM317?

 I am just quiet a new builder in DIY field.
 but I am really interested with PPA._

 

If you're dealing with the PPA, a single power supply set at +24V should do. The amp comes with an onboard rail splitter to create a virtual ground with respect to everything else, giving +12V and -12V


----------



## n_maher

Quote:


  Originally Posted by *individual6891* 
_Any m³ comparisons too? 
	

	
	
		
		

		
			





 Very eager 
	

	
	
		
		

		
		
	


	


_

 

My friend Ian, who posted pics of his partial PPA V2 earlier in this thread, just finished temporary wiring this afternoon. We hope to have a good, long sit down with his PPA and my M³ over the next week or so. We've got a couple of nice mid-fi sources to use (Denon DCM-560, Ipods with aps mp3's, Pioneer Elite DV-C36), decent cables and a good variety of phones (see my sig). We'll be putting together a comparison/review so look for a dedicated thread in the amp forum sometime soon. 

 Nate


----------



## Chiels

1. If I got STEP v1.1 , Is TREAD necessary ?
 Or I can just connect STEP to PPA ?

 2. Can TREAD connect to wall power directly?


----------



## n_maher

Quote:


  Originally Posted by *Chiels* 
_1. If I got STEP v1.1 , Is TREAD necessary ?_

 

No, TREAD is really just a portion of the STEPS board, modified a bit.
  Quote:


  Originally Posted by *Chiels* 
_Or I can just connect STEP to PPA ?_

 

 Yes, any STEPS would be fine to power a PPA, provided that you've tuned the output voltage to match whatever opamp you're using. To be on the safe side, you could just configure it for 24V which will work with most of the popular opamps.
  Quote:


  Originally Posted by *Chiels* 
_2. Can TREAD connect to wall power directly?
	

	
	
		
		

		
		
	


	


_

 

No, not directly. You need some sort of transformer to chance that AC voltage into DC voltage prior to the TREAD, do yourself a favor and reread the TREAD and STEPS docs. I know that it took me several reads to get somewhat comfortable with what each is meant to do.

 HTH,

 Nate


----------



## Megaptera

Quote:


 You need some sort of transformer to chance that AC voltage into DC voltage prior to the TREAD 
 

Slight correction: the transformer still puts out AC, just with a lower voltage than your AC power line has. The rectifier bridge, which is part of the TREAD, is what converts the AC to DC.


----------



## n_maher

Thanks for correcting that, I never get anything 100% right the first time 
	

	
	
		
		

		
		
	


	




 .


----------



## individual6891

Quote:


  Originally Posted by *Megaptera* 
_Slight correction: the transformer still puts out AC, just with a lower voltage than your AC power line has. The rectifier bridge, which is part of the TREAD, is what converts the AC to DC._

 

Well it produces a varying DC output. The smoothing capacitor that follows produces a smooth DC output with a small amount of ripple due to the capacitor discharging every cycle of the full wave DC. The regulator out of that turns the smooth DC into a regulated DC with very little ripple.


----------



## xtreme4099

theres a mod for the ppav2 if your using the ths4631 ...which requires the R9 pots around the opamps to be set to 0, allowing the ths opamps to get all the biasing current they want, but anyways the results are : 2-3x the soundstage -- detail goes up considerably --- speed attack -- all are greatly improved.

 Resistor changes are as follows : 

 R11 change from 1K to 220 ohm

 R34 R24 - 2 ohms are changed to 1 or 1.1ohm


----------



## silvalis

Q4 JFET:
 Is it possible to use a J108 JFET here (min Idss is 80mA)? I'm having a lot of difficulty locating a suitable nchannel jfet with a min Idss of 30mA in Australia. The next closest match is a J310, but that has a min Idss of 24mA.

 Are there any other suitable JFETs? I can't seem to find the PN4392/MPF4392 anywhere in Australia.


----------



## ppl

Quote:


  Originally Posted by *silvalis* 
_Q4 JFET:
 Is it possible to use a J108 JFET here (min Idss is 80mA)? I'm having a lot of difficulty locating a suitable nchannel jfet with a min Idss of 30mA in Australia. The next closest match is a J310, but that has a min Idss of 24mA.

 Are there any other suitable JFETs? I can't seem to find the PN4392/MPF4392 anywhere in Australia._

 

Yes however the 24 Ma Idss J310 will work with most all opamps except the THS4631 and AD843 these may requre the J108


----------



## myhui

Quote:


  Originally Posted by *xtreme4099* 
_theres a mod for the ppav2 if your using the ths4631 ..._

 

xtreme4099, can you tell us more about your teflon C1 caps?

 That's a first for me: large capacitance with teflon as dielectric.


----------



## ppl

Quote:


  Originally Posted by *myhui* 
_xtreme4099, can you tell us more about your teflon C1 caps?

 That's a first for me: large capacitance with teflon as dielectric._

 

Please don't Encourage him and give him an idea to add more teflon caps LOL


----------



## silvalis

If you Hfe match the large output transistors, what sort of spread is deemed "acceptable"? I've got three BD140s with a spread of 11 (172, 176, 183) and I'm not sure if I should get a few more or if I'm just being anal about Hfe matching.


----------



## ppl

Quote:


  Originally Posted by *silvalis* 
_If you Hfe match the large output transistors, what sort of spread is deemed "acceptable"? I've got three BD140s with a spread of 11 (172, 176, 183) and I'm not sure if I should get a few more or if I'm just being anal about Hfe matching._

 

 That is more than close enough what you should check is the matching between the BD139 and the BD140 complements. hear you will not find sutch a good match most of the time. however random fairchild devices are showing at least +/- 10-15% vs the typical +/- 50% one would expect.


----------



## silvalis

Between the BD140/139 pairs, I can't really get anything close. At the moment I have BD139 (143, 146, 146) and BD140 (172,176,183). Should I grab a few more and try for closer matches?

 Also, what's the best method of matching the buffer transistors (2n5087/5088)? 
 Should these be matched between complementary pairs and also between similar transistors within each buffer?


----------



## silvalis

I'm getting a thump through the L/R channels when I switch on/off. I'm currently using a transformer type 24V/1A reg supply.
 Could anyone speculate on the possible causes of this thump, if it will damage my headphones if i leave it connected when I turn on/off and how I can fix the problem?


----------



## tangent

Quote:


  Originally Posted by *silvalis* 
_I'm getting a thump through the L/R channels when I switch on/off._

 

This is probably normal. If you have access to a DSO, you can capture it. If it's just a volt or two, it's harmless.


----------



## ceRon

Quote:


  Originally Posted by *tangent* 
_This is probably normal. If you have access to a DSO, you can capture it. If it's just a volt or two, it's harmless._

 

but can it be avoided? though it is harmless to the headphone, i dont want to be shock whenever i switch it on or off


----------



## steinchen

it's depending from the opamp you're using, some pop very loud (especially opa637), some hardly at all (ad744).

 if you don't want to plug/unplug your cans every time you power on/off your amp you may consider building a muting delay, there are several designs out there in various boards. The latest one, the ε12 from amb, additionally incoporates an offset protection -> http://www5.head-fi.org/forums/showthread.php?t=119066


----------



## groovy2

delete meee


----------



## rhooper

So far the following setup seems to be stable:

 AD8610 x 3 and all other "default" parts available from Digikey or Tangent's audio shop, excluding the class a bias parts -- 5 x 470uF cerafine 25V.

 Power source: TREAD @ 24 VDC from a 24 VAC 200mA wall transformer that puts out 27 VAC unloaded.

 The regulator on the TREAD is running hot w/o a heatsink, but is still just barely touchable. Ouput voltage drops briefly when the PPAv2 is first powered up (and the TREAD LED dims), but otherwise it remains at constant brightness. (I assume that the high initial draw is the caps charging?)

 If I do my math right, 24V @ 200mA is 4.8 Watts, which is plenty for a PPAv2 driving Grado SR-80s, right?

 The PPAv2 sounds significantly better than my CMoy with the Grados. Right away I noticed considerbaly more fullness to the bass without the bass boost circuit installed. 

 Is that because of the discrete buffers? If I have it right, the buffer is there to provide the current the headphones need, and the opamps are there to provide the appropriate voltage?

 PS - Thanks to everyone who worked on the PPA design and its predecessors and successors (especially tangent and his detailled webpages)!


----------



## tangent

Quote:


  Originally Posted by *rhooper* 
_The regulator on the TREAD is running hot w/o a heatsink_

 

I coulda told ya that. 
	

	
	
		
		

		
			





 Or you could have found out for yourself in advance.

  Quote:


 Ouput voltage drops briefly when the PPAv2 is first powered up (and the TREAD LED dims) 
 

Absolutely normal. The regulator is dealing with a massive capacitive load during that period. Many regulators will completely fail to cope with your ~2500uF rail.

  Quote:


 If I do my math right, 24V @ 200mA is 4.8 Watts, which is plenty for a PPAv2 driving Grado SR-80s, right? 
 

That's misleading. There's no way you can deliver 4.8W to the headphones. The correct way to calculate wattage to the headphones deals in sinusoidal RMS output voltages from the amp, and takes into account clipping, and current limits in the amp's output stage.

  Quote:


 Is that because of the discrete buffers? 
 

That gives you the slam. The tightness in the bass is because of improved channel separation, lower supply impedance, etc. There are lots of things that make the PPA the PPA, not just the buffers. A PPA with BUF634s sounds better than a similarly-configured PIMETA.

  Quote:


 the opamps are there to provide the appropriate voltage? 
 

More or less. The pot is an attenuator, and the op-amp provides gain. Between the two, you adjust to overall amp gain to be what the phones need. If you knew the proper system gain in advance, you could do without the pot, and just set the gain appropriately.


----------



## Buzzerbro

I don’t know if this has been asked before and I can’t find the answer when doing a search. I am planning on building a PPAv2. For the bass boost pot, the 50k Alps Rk27 is suggested. I would like to know if a 100k pot would work for bass boost. Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost? 

 Regards,
 Buzzerbro


----------



## Clutz

Quote:


  Originally Posted by *Buzzerbro* 
_I don’t know if this has been asked before and I can’t find the answer when doing a search. I am planning on building a PPAv2. For the bass boost pot, the 50k Alps Rk27 is suggested. I would like to know if a 100k pot would work for bass boost. Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost? 

 Regards,
 Buzzerbro_

 

AFAIK it should be fine. All the pot does is take the place of R7 in the circuit, and there is no specific reason it couldn't be set to a value of 100k.


----------



## tangent

Quote:


  Originally Posted by *Buzzerbro* 
_Would anything on the PCB need to be changed to accommodate a 100k pot for bass boost?_

 

No, it will just give you a wider boost adjustment range. Maybe too wide to be useful, but that's for you to decide.


----------



## Buzzerbro

I almost have my PPA V2 put together. I am still waiting for my OPA627 chips to arrive which I will use on all 3 channels. 

 Is there some way to test the board with out the Opamps? Can I jumper the socket? Which pins would I connect in the diagram below?

 Thanks

 OPA627 pin configuration




Attachment 6886


----------



## jagrifen

I recently built the PPA v2 following tangent's guide. I've left the opamps out and left out the parts to bias into class A. I have also cleaned off all flux and trimmed the leads cleanly from the bottom. When I flip the power switch, the LED does not turn on, and I get about 2 volts at the supplies to the opamps. It seems there is a short somewhere, but I am not sure how to track it down efficiently. I have doen a visual inspection a number of times and can not locate any misplaced parts. I have also tried doing an in-circuit continuity test at each capacitor. One of the many transistors may be fried, but I hate to have to take them out one-by-one to track down the problem. Does anyone have any good troubleshooting methods? Any good ways to isolate the bad section?


----------



## Clutz

Is the protection diode in backwards?

 Take some pictures of it wioth a digital camera and post them. Get nice and close up, and pretty good resolution, so that we can look at it.


----------



## jagrifen

The diode is in correctly and functions properly. With the psu plugged in and switch off, i get 24V in all places up to the switch. When the switch is turned on, voltage drops to about 2 volts. I measured the current throught the diode to be .33 amps, which is the limit of the psu. I have tried another psu, and the same occurs.
 I am using four 470mF cerfine caps for C1. All are in correct polarity. The caps for C2 are not polarised. Do you think it matters that I do not have the opamps installed for this step? Does R12 need to be turned to a halfway point or something like that? Does the amplifier need a load?
 I am not sure how to post pictures on this website. I am told I am limited to a filesize of 25kb, which is not nearly large enough for a detailed picture. I can send the files via email unless someone has a better idea.


----------



## Clutz

How much capacitance do you have on the rails (C1)? 
 How do you have the switch wired up - is S1- jumpered, and S1+ is going to a SPST switch? 


 When you're trying to measure the voltage on the PPA board, have you tried measuring the voltage between the V- and V+ pads? What about measuring the voltage between the + and - pads on the capacitors?


----------



## n_maher

Quote:


  Originally Posted by *jagrifen* 
_ I can send the files via email unless someone has a better idea._

 

YGPM about the pictures.

 And as Clutz said I'd make sure you have the switch wired correctly, I did this on my first PPA and was dumbfounded as to why the LED wasn't at least lighting up 
	

	
	
		
		

		
			





.

 Nate


----------



## Clutz

jagrifen and I chatted for a while this afternoon. IT seems like something is shorting out, and I suspect there are problems with some of the transistors in the high current section, and possibly also Q3's. I'm a bit baffled by what's going on - I did my best to follow through the schematic and try to get him to read off voltages to me. Pretty much everything past V+/V- seems off.. and V+/V- only seems 'correct' when it's in the off position. 

 So.. yep. I still think that the switch is wired wrong, but I think there is also a short - and it's probably transistor related.


----------



## jagrifen

I promise, promise, promise, the switch is not reversed. I checked it with a meter before I soldered it, and I have checked it several times since, so as to not make an ass out of myself.
 Here are some stats from my earlier conversation with Clutz. I have used the recommended parts on Tangent's webpage
 Four C1 positions poplulated with cerafine 470uF 25V caps
 Five C2 positions poplulated with Vishay/Roderstein 0.1uF caps
 C4 positions populated with nichicon 220uF caps.
 24V DC between v+and v- with switch off
 2.6V DC between v+ and v- with switch on
 0.8V drop across D1 with switch on
 .2mV drop across RLED
 .33A through D1 with switch on
 .86VDC between opamp pins 4 and 7 with switch on
 0V drop across R8+ and r8- with switch on
 1.75VDC across C1 with switch on 
 1.75VDC across C2 with switch on
 PSU is rated at 24VDC to 0.33A
 All opamp positions are empty. Measurements were made regarding the ground channel with TLEG and C4G in place. I had removed the low-current power sections earlier to try and isolate the problem.
 Using a continuity meter, I found no DC shorts with the caps in-circuit.
 I really think I have some blown transistors, but I don't know how to test transistors in-circuit effectively. I have tried the diode test and looked for any transistor that behaves differently from the others, so unless they are all dead, I can not seem to find any that do not act like the other related transistors.
 I think that a transistor(s) is(are) or something else is shorting to ground (hence the .33A through D1).
 Does anyone know of a way to maybe isolate the problem to a specific channel or section?


----------



## Clutz

Here's another thought: What PSU are you using? Elpac? Some generic one with a TREAD?

 Could it be that the inrush current is overloading the PSU and causing it to trip out internally?


----------



## Clutz

The power flows in from the header, you place the probes at the V+/V- pads, and then after that comes the diode and holes for wiring up the power switch.
 So when you have the amp turned off 100% of the current (though not the entire 0.33A) is flowing through the DMM, so you're measuring the full 24 volts that your PSU is putting out. When you turn the PPA on, there is now a second path for the circuit - but the voltage you're measuring has dropped substantially - from 24 volts to 2.6 volts- a drop of 21.4 volts. 

 This really makes me wonder if it's something to do with your PSU. Can you get your hands on another wallwart to try it out, preferably something with a higher current output? 

 Second, I'm curious as to how you measured the current through D1 - did you unsolder it?


----------



## n_maher

Here are jagrifen's pics of the top and bottom of his PPA board. 

 Top





 Bottom


----------



## jagrifen

I unsoldered one leg of D1 to measure the current through it. I am using the Elpac power supply. I have tried another PSU I have lying around (15VDC 500mA). When I use it, I still get no LED but I get a slightly higher voltage between pins 4 and 7 and between v+ and v-(probably due to the higher current).


----------



## n_maher

[edit]*Are these progress pics or how the board sits right now?*

 Reason I ask, you're missing at least two of the TLEs and a couple of non-optional caps...

 Nate


----------



## Clutz

Are you sure that the LED is oriented correctly? LED's are diodes and thus they are polarized. If they were placed incorrectly then they would not light up at all.


----------



## jagrifen

LED is oriented with the longer leg through the square hole. I did try the other way just for kicks, no luck. I tried another LED to be sure, and still no light, but that is really only a symptom of a bigger issue. 
 As I mentioned before, I have removed two of the TLEs (and two C4s) to try and isolate the problem to a specific channel or section. Not the right choice, apparently.


----------



## n_maher

Quote:


  Originally Posted by *jagrifen* 
_As I mentioned before, I have removed two of the TLEs to try and isolate the problem to a specific channel or section._

 

D'oh, I guess I missed that. After that I go back to my suggestion of removing the switch from the circuit since all of your problems start there. Even if it's not the problem it at least totally eliminates it as a source. After you do that plug in your power source and do 2 things. One, measure the voltage at the PS caps (C1) and report your findings, two, feel (carefully) around the board for anything that is getting hot. I don't think you've said anything about any components heating up excessively. 

 Also, there is no good reason for your amp to be pulling 330mA in it's current state so yes, there may indeed be a short somewhere. The heat check may help find this as well.

 Keep the info coming,

 Nate


----------



## tangent

Quote:


  Originally Posted by *Buzzerbro* 
_Is there some way to test the board with out the Opamps?_

 

Not really, sorry. The op-amps establish a feedback loop that you need in order to set the buffer bias point correctly.


----------



## tangent

Quote:


  Originally Posted by *jagrifen* 
_I really think I have some blown transistors, but I don't know how to test transistors in-circuit effectively._

 

It's simple, actually: if you run 8W -- your supply's limit -- through a transistor, it gets hot right quick. Clearly there is a short, so if something's getting hot, you're one big step towards localizing the problem. If nothing's getting hot, the current must be going through a low-resistance path, so that would indicate something right around the power inputs.


----------



## jagrifen

I tracked down the problem to be a couple of blown Transistors. I used a power supply with a higher current and felt around to find some pretty hot components. I replaced the bad parts and finished wiring up the remainder of the board. Everything works fine and I will probably adjust the gain and the bias later next week when I have some time.
 Thanks to everyone who tried to help me out.


----------



## RJ2015

I've been listening using a PPAv2 for 6 months now. Initially the amp was configured to 20mA bias output and 1mA class A. I thought it sounded very good to start with. Yesterday I changed it to 30mA and 2 mA class A (just to experiment). Don't know it's part of me wanting to hear some differences, but I think the overall sound is a little more relaxed and a little less stressed. So far, I'm very positive about this change!

 Ralph


----------



## Buzzerbro

I am having an issue with my PPAV2. 

 If I have just one input connected, I get output on both channels. 

 The amp sounds fine but I am wondering why this is happening. Nothing gets hot in the amp. Here are some pics of it in this post.
http://www6.head-fi.org/forums/showp...&postcount=925

 I disconnect the crossfead completely in order to isolate the problem. 

 If anyone had any ideas it would be appreciated.


----------



## Clutz

Sounds like you have either your headphone out or input jacks miswired. It sounds to me like you may have one of your left or right channels (either input or output) connected to ground. Since ground is common to both the left and right channel inadvertantly connecting up a signal to the ground channel (either on the amp, or on the headphone itself) would result in sound coming out of both channels on the headphones themselves. 

 For the RCA inputs, the outer part of the connector is wired to ground, and the inner part of the connector is wired to the respective channel.

 The 1/8th" and 1/4" jacks are sometimes called tip-ring-sleeve jacks. The tip of the jack is the left channel, the ring of the jack is the right channel, and the sleeve is ground. It sounds to me like you've probably got either your left (or right) channel output connected to ground, and the ground output channel connected to the left (or right).


----------



## Buzzerbro

Thanks Clutz. You hit the nail on the head. I had the output Left and Ground switched. Its working fine now.


----------



## Buzzerbro

My buffer bias is 63mA. I am measuring the voltage at the 2.2Ω output resistors. When adjusting the bias trimmer, the lowest voltage I can get is 140mV. I can’t feel anything getting hot. 

 All channel measure the same. I am using MJE243/MJE253 on the output, the trim pot is 2k. My power supply is 20V and I have sound on the output. 

 Why can’t I adjust the buffer bias any lower?


----------



## steinchen

Quote:


  Originally Posted by *Buzzerbro* 
_Why can’t I adjust the buffer bias any lower?_

 

What JFET are you using for the buffer bias (Q4) ? pn4392 ? Did you happen to measure it's IDSS ? You could try a 5k pot on one channel to find out whether it's a IDSS prob.
 *edit*
 there must be something wrong, at 63mA the output transistors would get pretty hot. Did you measure the 140mV across the output resistors ?


----------



## Buzzerbro

In my amp, Q4 is PN4392. I will try to find a spare 5K pot. I am probing the output resistors and measuring millivolts. The output transistors don't get any hotter than the OPA627 chips even when playing music. Maybe I am reading the meter wrong.

 I will mess around with this tonight. Thanks Steinchen.

 *EDIT*
 Well I found the problem. I had 2k2 resistors for the output. 
	

	
	
		
		

		
		
	


	




 argh. I have some 2R7 resistors laying around and I will put those in Tonight. Again, thanks Steinchen.


----------



## Epicurean

Hello everyone!
 I'm in the process of building a PPAv2 and a STEPS. I have everything put together except for the C1s(suppressor caps) in the STEPS and the C2s in the PPA. Is it safe to try it out without these parts? I'll go buy the missing capacitors next week but I don't think I can wait that long to test the thing
	

	
	
		
		

		
		
	


	




 btw. the PPA is using OPA627s and BD139/140s as output transistors. STEPS at 24V.

 edit: Oh, I just noticed the C2's in the PPA are listed as NOT optional, so I guess I'll just have to wait then...


----------



## GeekGirl

Hello, I'm in the first stages of researching how to build a PPAv2. It's my first headphone amp (I'm not a beginner).

 I was wondering why I have not seen any discussions mentioning the risk of ESD (ElectroStatic Discharge). Op-amps (and any semiconductor) are affected by this, e.g. the AD8610 has a big warning on page 4 of the data sheet. Failure modes don't always just fry the device, performance degradation is also a symptom and very difficult to troubleshoot. It might be helpful if the risks of ESD and the proper handling procedures were emphasized, especially to beginners. On the other hand, am I overly concerned?

 Question: I was considering adding a 2nd input. Is this commonly done? I have a Sony CE-595 SACD/CD player and want to occassionally listen to my MP3 player. Is there anything I should be concerned about other than getting the input levels equal?


----------



## Epicurean

I'm putting the PPAv2 and the STEPS in the same case and I want to use only one power switch. I have the one recommended on tangents website but it has only 2 poles. So, can I connect only S1+ to the switch and keep the S1- jumpered?

  Quote:


  Originally Posted by *GeekGirl* 
_Hello, I'm in the first stages of researching how to build a PPAv2. It's my first headphone amp (I'm not a beginner).

 I was wondering why I have not seen any discussions mentioning the risk of ESD (ElectroStatic Discharge). Op-amps (and any semiconductor) are affected by this, e.g. the AD8610 has a big warning on page 4 of the data sheet. Failure modes don't always just fry the device, performance degradation is also a symptom and very difficult to troubleshoot. It might be helpful if the risks of ESD and the proper handling procedures were emphasized, especially to beginners. On the other hand, am I overly concerned?

 Question: I was considering adding a 2nd input. Is this commonly done? I have a Sony CE-595 SACD/CD player and want to occassionally listen to my MP3 player. Is there anything I should be concerned about other than getting the input levels equal?_

 


 GeekGirl, you should probably create a new thread about ESD, since people not interested in the ppa might not look in this thread. And that also means I don't have an answer to your question.


----------



## Epicurean

I just powered up the PPAv2 for the first time... and POOF it went
	

	
	
		
		

		
		
	


	




 First, nothing, even the led didn't light up, but then suddenly smoke started coming of the right channel output transistors. I found the problem immediately, which was an unsoldered(!!) middle leg of the Q33. I've no idea how I could've missed that since I doublechecked everything before powering up. And of course I don't have any spare output transistors. Oh well...


----------



## Clutz

Quote:


  Originally Posted by *Epicurean* 
_I just powered up the PPAv2 for the first time... and POOF it went
	

	
	
		
		

		
		
	


	




 First, nothing, even the led didn't light up, but then suddenly smoke started coming of the right channel output transistors. I found the problem immediately, which was an unsoldered(!!) middle leg of the Q33. I've no idea how I could've missed that since I doublechecked everything before powering up. And of course I don't have any spare output transistors. Oh well..._

 

The middle leg of Q33 might not've been soldered, but I don't think that's what caused the problem you had.


----------



## n_maher

I agree with Clutz, in all of the adventures I had with one of the PPA V2s that I built I never had an output tranny smoke. If it really happened after only a couple of seconds it must have been pulling serious juice through those and I'm shocked a resistor didn't go nuclear on your first. Are you sure it was an output tranny or was it just from that region of the PCB?

 Nate


----------



## Epicurean

Well, the thing is (being the newbie that I am), as soon as I noticed the problem, I soldered the Q33 in place, and there was one other pin nearby(I think it was a the q4) that looked a little bad which I also fixed(which might have caused the problem). Then I hoped everything was ok and I powered it up again (which probably wasn't very smart
	

	
	
		
		

		
		
	


	




) and the nothing was smoking or hot anymore. The output transistors AND the output resistors were a little dark in color however.

 How do you know if the resistors are wasted or not? My dmm still measures 2.2Ohm across them, but you can clearly see that they have been a little burnt.


----------



## Epicurean

I'm no good with transistor schematics, so could it be that without the q4 and q33 the current went kind of straight through the output resistors and output transistors? In that case I would only have to replace those, which would be nice.


----------



## n_maher

Quote:


  Originally Posted by *Epicurean* 
_I'm no good with transistor schematics, so could it be that without the q4 and q33 the current went kind of straight through the output resistors and output transistors? In that case I would only have to replace those, which would be nice._

 

Warning: if you chose to do the following you do so at your own risk...

 If it were me and my amp I'd probably replace the output resistors since I'm guessing that's what smoked. Even if they still measure fine they probably got a bit distressed by the whole ordeal and won't necessarily perform reliably in the future. After replacing said resistors I'd power up the amp and see what happens, I don't _think_ you can do much more in the way of dammage. If something/anything goes *poof* again you've got bigger problems and are in for what could be a long period of troubleshooting. Assuming nothing is on fire at this point I'd run through the typical PPA adjustments (op bias, buffer bias) and see if you can get those within spec. I'd be sure to check how hot the output trannies get on the damaged channel to see if they feel the same as the others. Note, if they got hot enough to smoke once it'd be a good idea to exercise some caution measuring the temperature. If all the trannies are uniformly warm I'd check DC offset and pick up your least favorite (hopefully cheap) cans and try it out. If it sounds bad it's probably time to order up some new output trannies and hope that this cures the problem.

 Best of luck and let us know how it goes.

 Nate


----------



## Epicurean

I took your advice n_maher and replaced the output resistors, hooked up my cheap phillips sbc-hp800 and powered up. It's amazing, but it works! At first there was only hiss in the right channel but since i have everything hooked up with alligator clips i rechecked them and the right channel was loose at one point. I haven't tried it with a good source and phones yet though, so I'm not sure if the output trannies are completely intact.


----------



## NeilR

I recently built an M3 and I discovered what was apparently a poor solder joint by running RMAA tests on the amp. The distortion on one channel was high- about 0.5%, where it should have been less than 0.01%. I would never have found that without testing. All the joints looked ok and I only fixed that issue by reflowing all the joints in the affected channel. If your trannies are impaired but basically functional, you may be able to find it by testing it with RMAA.

 If you have a good soundcard that can do a loopback, RMAA software is free. I had to buy an outboard Audio card for my laptop to make it work, but it was probably the cheapest way to do some more advanced testing than a simple DMM can provide.

 You can get that software here.


----------



## GeekGirl

Is bass boost common? I understand this is a topic that's left up to personal preference, but is it used in practice? It's simple enough to put in.

 What's a good cut-off frequency and level of boost 
	

	
	
		
		

		
			





 ? I'm using Audio-Technica ATH-A900's (closed circumaural). The PPAv2 schematic parts give a 6 dB boost with Fc = 220 Hz (tangent's on-line calculator, Micro-Cap is slightly different).


----------



## Clutz

I'd say it's reasonably common. For the $20 for the POT and cost of the capacitor, I'd say it's worth it. I'm using a 0.022uF cap instead of the default value suggested because I originally found the original value didn't provide enough of a boost for my liking at the time. 

 Man, I want to build a STEPS and an M^3. I'll lay off the M^3 until after my source improves substantially.. 
	

	
	
		
		

		
		
	


	




 That's where I should be putting my money.


----------



## NeilR

I use Senn HD-650's at home and Etymotic ER4-S on the road. I rarely use bass boost with the HD-650's; I always use it for the Etys. I'm trying to say that it is very dependent on your headphones and what you like. I think most people, for example, find the Etys to be a little thin on the low end.

 You might want to socket those two caps and buy a couple different values to experiment. That's what I did for my Pimeta; then when I built an M3 I knew what I wanted because the results are about the same in any of these feedback loop bass boosts. I used .22uf caps. That gave me a very low shelf, which is what I wanted because I was happy with the Ety's until the very low registers. That is a very subtle bass boost and some people that used a similar value have commented that they weren't even sure at first that it was working. Meaning it shouldn't make the bass go BOOM BOOM like consumer gear bass boosts sometimes do. You really need to try this yourself, though, to see what you like.


----------



## GeekGirl

Thanks, I'll experiment. It's a tough call to fine-tune, so I'll just get it roughed in. Too light a capacitance moves the corner frequency up into mid-range. Too much resistance increases both gain (shelf) and group delay to a few mS on the low end. 

 Time to pick values (0.1 uF / ~50K pot) and move to the active components. Was fun using Micro-Cap for the analysis, though.


----------



## kklee

I just finished building a PPA V2 using the recommended parts on Tangent's site. There were two areas where I used the listed alternate parts. BD139/140 in place of MJE243/253 (couldn't find any at the time) and OPA627 (sound preference) in place of AD8610. The buffer bias is set to 20mA and OpAmp bias is 1mA.

 The amp works great with higher impedance headphones (K701), but I would get a horrendous oscillation as soon as I used lower impedance (K81DJ, ER6i). Upping the buffer bias current to 30mA got rid of the oscillation, except for turning the amp on or off, where I would get a huge transient (offset/oscillation pulse > 2V!). I tried swapping out the OPA627 in the ground channel with an AD8610 and the amp settled right down (buffer bias @ 20mA).

 I've read that the MJE243/253 pairs are recommended for low impedance, so I've got some on order.

 I was wondering if somebody could shed some light on why I'm seeing this. Once I swap the buffer transistors out, will I be able to put the OPA627 back in the ground channel? I suppose I could just stay with high impedance cans for this amp, but I'm curious about this behaviour.

 Thanks,
 Ken


----------



## Clutz

I've experienced the same problem with my PPA and my AKG K24 or K26P headphones. I'm using the MJE243/253 combination, and I still had problems at the 20mA of buffer bias. in fact, I believe I also had difficulty at 30mA of bias.


----------



## steinchen

what output resistors did you use (R24/R34) ? If you picked 2R2 resistors it's a good idea to try 3R3 or 4R7 instead. What compensation cap did you pick for C6G (capacitance and type) ?


----------



## kklee

Quote:


  Originally Posted by *steinchen* 
_what output resistors did you use (R24/R34) ? If you picked 2R2 resistors it's a good idea to try 3R3 or 4R7 instead. What compensation cap did you pick for C6G (capacitance and type) ?_

 

I used 2R2, I've got some 4R7 on order to try out. As for C6, I used the spec'd part (Digikey 338-1061). Would it be worthwhile to up it to 100pF?


----------



## steinchen

not to 100pF but up to the recommended 33pF, pick a silvered mica or C0G ceramic multilayer cap


----------



## ppl

Most instability issues with all versions of PPA's are the quality of the Input RCA jacks the PPA absolutely requires a massive chassis as a ground due to the lack of a Ground plane. 100pF is ok in the Ground channel with OPA627 in. The opa627 really don’t like to be operated at unity gain and has allot less phase margin than the AD8610. While using higher value Emitter resistors on the output gains stability it is not the best method because it increces the output impedance and Distortion. I have used 1.1 ohm emitter resistors with OPA627/OPA637 combo biased at 25 mA with complete stability on about 12 different Headphones.


----------



## kklee

Quote:


  Originally Posted by *ppl* 
_Most instability issues with all versions of PPA's are the quality of the Input RCA jacks the PPA absolutely requires a massive chassis as a ground due to the lack of a Ground plane. 100pF is ok in the Ground channel with OPA627 in. The opa627 really don’t like to be operated at unity gain and has allot less phase margin than the AD8610. While using higher value Emitter resistors on the output gains stability it is not the best method because it increces the output impedance and Distortion. I have used 1.1 ohm emitter resistors with OPA627/OPA637 combo biased at 25 mA with complete stability on about 12 different Headphones._

 

It's in the spec'd Hammond chassis, which is grounded through the volume pot. I didn't have any RCA jacks on hand (they're on order), so the input is currently using an isolated 3.5mm jack with a 5G iPod as the source.

 I had an extra 10pF capacitor, so I tried tacking it in parallel with the existing C6 and found that the oscillations settled down a bit, but it still had an offset of 1.7V! I'll have to get a 100pF and try it.

 The OPA627 datasheet states that its supposed to be stable at unity gain, so I'm still wondering why it only has problems with low impedance headphones. Shouldn't the buffer circuit be isolating the impedance load from the opamp?

 ...Ken


----------



## ppl

Quote:


  Originally Posted by *kklee* 
_It's in the spec'd Hammond chassis, which is grounded through the volume pot. I didn't have any RCA jacks on hand (they're on order), so the input is currently using an isolated 3.5mm jack with a 5G iPod as the source.

 I had an extra 10pF capacitor, so I tried tacking it in parallel with the existing C6 and found that the oscillations settled down a bit, but it still had an offset of 1.7V! I'll have to get a 100pF and try it.

 The OPA627 datasheet states that its supposed to be stable at unity gain, so I'm still wondering why it only has problems with low impedance headphones. Shouldn't the buffer circuit be isolating the impedance load from the opamp?

 ...Ken_

 

No the first thing you do is hook up the RCA Jacks properly A SECURE CONECTION FROM THE INPUT GROUND TO THE CHASSIS IS MANDITORY NOT JUST RECOMENDED. Your grounding only at the pot is not what you were intructed to do on tangents site so why not wait intill you get your RCA jacks that are on order and after they are hooked up see if your instability goses away. The PPA is designed to work properly when built with the default parts and if it dose not first suspect builders error, Bad solder joints and flux left upon the PC board.. and again the Input ground on the PPA is not nice or desirable to be solidly grounded to the case. so ya you could use large caps in the ground channel and higher than recommended emitter resistors in the output to gain more stability than designed for however the PPA works quite well with your chosen Op amps if properly constructed and this includes removing all the flux from the PC Board. Remember the primary reason a DIY project or Electronic Kit don't work as designed is improper assembly


----------



## NeilR

Quote:


  Originally Posted by *ppl* 
_...A SECURE CONECTION FROM THE INPUT GROUND TO THE CHASSIS IS MANDITORY NOT JUST RECOMENDED. Your grounding only at the pot is not what you were intructed to do on tangents site..._

 

Hi ppl,

 Your statement above got me curious because I cannot find any reference in the build instructions to specifically ground the input to the case. For my recent PPA build, I don't think I isolated the jacks because they are inherently isolated and I didn't have any problems that would have lead me to ground them. Just curious...

 Regards,
 Neil


----------



## n_maher

Quote:


  Originally Posted by *NeilR* 
_Hi ppl,

 Your statement above got me curious because I cannot find any reference in the build instructions to specifically ground the input to the case._

 

Neil,

 I think ppl is referring to this quote, taken from the official PPA site.

  Quote:


 Connect the case and pot housing to signal ground. This helps shield the amp from hum and noise. Most cases are tied to signal ground and/or AC ground. Do not connect V+ or V- to the case instead of signal ground as it will short the rail if it touches another case, cable plug, or other grounded conductor. 
 

Hope that helps clear the confusion.

 Nate


----------



## NeilR

Quote:


  Originally Posted by *n_maher* 
_Neil,

 I think ppl is referring to this quote, taken from the official PPA site.



 Hope that helps clear the confusion.

 Nate_

 

OK... I understand that tieing signal ground to the case may help reduce hum or interference. I have never seen this discussed in the context of stability. I guess stability issues might be instigated by high frequency junk going through the signal inputs and amplified by the gain stage...

 Regards,
 Neil


----------



## kklee

As Neil pointed out, Tangent's instructions don't say anything about a requirement to ground the input. Even grounding the volume pot is optional as far as I can tell, I only did it because I've had hum issues before when I built a Pimeta.

 I unplugged the input from the PCB and still have the oscillation. Tried grounding the input jack, still oscillates. It's definitely NOT due to the input ground.

 I discovered that I still get oscillation with my ER6i, which is 16 ohm, so subbing the AD8610 for the OPA627 merely raised the low impedance/oscillation threshold so that the amp works with the K81DJ, 32 ohms.

 ...Ken


----------



## kklee

My oscillation problem's fixed (mostly). I replaced C6 with a 100pF ceramic cap and the amp is much more stable. I still get a little hiss with the ER6i's, but nothing as bad as before and no nasty on/off transients.

 I'm hoping that when the MJE243/253 and 4R7 that're on order show up, I'll have a perfect amp.

 Thanks for everyone's input and help with my problem.

 ...Ken


----------



## NeilR

I did some RMAA testing on my PPA V2 today (via M-Audio Firewire External Sound Card) and got some very strange results. I had a lot of trouble setting the gain properly, including solid crosstalk warnings. The distortion and noise tests were very bad and out of wack.

 I plugged in my headphones to listen to the RMAA's sample level setting tone and discovered that at full volume I got very loud hash that sounded like shortwave radio static. As I backed the volume down to 3 o'clock the hash instantly disappeared as if a switch had been thrown. At the 3 o'clock setting the amp tests spectacularly- noise level is -92.7 db (battery powered) and THD is 0.0014%.

 I cannot reproduce this problem except with RMAA. For example, using iTunes and the M-Audio device I can play at max volume with no indications of a problem. Nor can I reproduce this with my M3, for example, and RMAA.

 Anyone else experience a similar problem or have any WAGs as to the cause?


----------



## amb

NeilR, sounds like oscillation. As for why, it may have something to do with the fact that for RMAA, the output of the amp "sees" the line input of the sound card plus the interconnect cable going to it (instead of just headphones). The PPA does not have compensation caps in the L & R channels, relying instead on multiloop feedback. I don't know how much phase margin there is, but there may be enough capacitance there to cause the PPAv2 to misbehave.


----------



## NeilR

Thanks, amb. It is odd that it only happens with the volume control at full volume. I should mention that I have OPA637/OPA627 installed. I am about to solder down some AD8610's on browndogs and I'll try those. I'll also post some of the RMAA charts of the oscillations, which is also interesting because it is not just one or a few frequencies. I don't think I've ever seen a spectrum analysis posted here of a misbehaving amp.



  Quote:


  Originally Posted by *amb* 
_NeilR, sounds like oscillation. As for why, it may have something to do with the fact that for RMAA, the output of the amp "sees" the line input of the sound card plus the interconnect cable going to it (instead of just headphones). The PPA does not have compensation caps in the L & R channels, relying instead on multiloop feedback. I don't know how much phase margin there is, but there may be enough capacitance there to cause the PPAv2 to misbehave._


----------



## ppl

Quote:


  Originally Posted by *NeilR* 
_Thanks, amb. It is odd that it only happens with the volume control at full volume. I should mention that I have OPA637/OPA627 installed. I am about to solder down some AD8610's on browndogs and I'll try those. I'll also post some of the RMAA charts of the oscillations, which is also interesting because it is not just one or a few frequencies. I don't think I've ever seen a spectrum analysis posted here of a misbehaving amp._

 

 another small but Verry inportent item that i wanted in the PPA that never got installed is a small resistor on the hot side of the inputs hoever you can add one by using a 1K resistor from your RCa jack to the Amp L & R Inputs. This will prevent instability at max volume.


----------



## NeilR

Quote:


  Originally Posted by *ppl* 
_another small but Verry inportent item that i wanted in the PPA that never got installed is a small resistor on the hot side of the inputs hoever you can add one by using a 1K resistor from your RCa jack to the Amp L & R Inputs. This will prevent instability at max volume._

 

Thanks for the tip, PPL. Next time I uncase the amp I'll measure the resistance of the pot at the point the oscillations are eliminated.

 Can you provide an expanded technical reason why the resistor will eliminate the oscillation? Is it to kill any capacitance on the input cable?

 Regards,
 Neil


----------



## tangent

Quote:


  Originally Posted by *NeilR* 
_I did some RMAA testing on my PPA V2 today (via M-Audio Firewire External Sound Card) and got some very strange results. I had a lot of trouble setting the gain properly, including solid crosstalk warnings. The distortion and noise tests were very bad and out of wack._

 

amb's right, the amp's oscillating. The ground channel configuration is very cranky in this setup, because it's very easy to short the ground channel through the hookup configuration. The only way you're going to get reasonable results is to break the ground at the input or output; best to do it at the amp's input, since the output is a "stronger" ground, and so will have less trouble coping with cable capacitance and such.

 The RMAA tests you see on my site are very hard-won as result of this, which is why you'll find that I will resist most efforts to make me re-do them.


----------



## Epicurean

-


----------



## villekille

I just finished my ppa v2 and there might be a problem..
 the buffer bias is givinig me a head ache

 I adjust the trimmers R13 to get about 50mV across 2.2 ohm output resistor on all channels 
 ,if I measure the resistance of the trimmers,they are set at about 500 ohms in L and G channels but R is about 190 ohms! Why is it so as I have used same kind of components everywhere..

 another odd thing..If I plug in my senn PX100,the bias voltage on G channel goes down to about 35mV but L and R stay the same. If I plug in my ER-6i, even the left and right channels go down to about 32mV and G to 27mV is this normal


----------



## n_maher

Quote:


  Originally Posted by *villekille* /img/forum/go_quote.gif 
_I adjust the trimmers R13 to get about 50mV across 2.2 ohm output resistor on all channels 
 ,if I measure the resistance of the trimmers,they are set at about 500 ohms in L and G channels but R is about 190 ohms! Why is it so as I have used same kind of components everywhere._

 

I believe what you are seeing is exactly the function of the trimpots. They allow you to not only adjust the buffer bias but also to correct for variations between parts. I wouldn't worry about it a bit. 

  Quote:


 another odd thing..If I plug in my senn PX100,the bias voltage on G channel goes down to about 35mV but L and R stay the same. If I plug in my ER-6i, even the left and right channels go down to about 32mV and G to 27mV is this normal 
 

You've got me there, no idea what would cause the drop and I never tried to measure mine while headphones were plugged in. My advice, especially knowing how easy it is to short the output while adjusting the bias would be to leave well enough alone before something really unfortunate happens. 

 Nate


----------



## mik000000

I am having some trouble with my PPA.
 I had it running in the minimum config without the bass boost and it sounded excellent. I added the bass boost components and replaced the output jack at the same time. I go no sound and some strange voltage readings at the opamps. I realized the new jack was not isolating and had shorted input ground to output ground. 
 I removed the output jack and the voltage readings went back to normal. The amp worked until I went past about half volume and then it was very staticy with lout pops and crackles. 
 I replaced the ground opa627 with a spare opa132 (the only spare I had) and the staticy sound went away, but the overall sound is poor.
 I am also getting some odd readings.. I am using a steps for power at 24v. I get 9.5 v +/- at the opamps for the left and right channels but 10.5 on the ground channel.
 I also set the bias on the output transistors at 44mv and get:
 R34L – 44mv
 R24L – 64.8mv
 R34G – 44mv
 R24G – 44.8mv
 R34R – 44.1mv
 R24R – 22.6 mv

 Would shorting the input and output grounds have damaged the opamp? Any other likely damage? Any ideas of the source of the distortion?


----------



## funch

Is 111mA quiescent input current in a V2 too much? I just finished my amp, and everything checked out fine until I plugged in some cheap Sony 'phones to test, and all I got was a lot of hiss with the volume at zero. I've rechecked solder joints, etc. and can find nothing wrong so far. The amp board is not cased yet. Nothing gets hot at all. I have an Alps pot connected for the bass boost, but no C7 yet, and it's not class-A'd yet. Buffer bias is at 20mA. DC offset is excellent. I'm very careful when I build these amps, and never had any problems building a C-Moy, M3, Hagerman Bugle w/PS, and a Pimeta. This is frustrating.
	

	
	
		
		

		
			





 Any help would be appreciated.


----------



## tangent

Quote:


  Originally Posted by *mik000000* /img/forum/go_quote.gif 
_Would shorting the input and output grounds have damaged the opamp?_

 

Much more likely, you damaged the ground buffer. If not that, then one or more TLEs. That also explains the audio problems.


----------



## tangent

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Is 111mA quiescent input current in a V2 too much?_

 

Probably. Since you've accounted for 60 mA of it, that leaves ~50 mA for the op-amps plus assorted other things. The piggiest op-amps I'm aware of (AD843) aren't quite enough to soak all that up.

  Quote:


 I've rechecked solder joints, etc. and can find nothing wrong so far. The amp board is not cased yet. Nothing gets hot at all. I have an Alps pot connected for the bass boost, but no C7 yet 
 







 I wish you'd waited to install the second ALPS pot, like the documentation tells you. The bass boost reduces the amp's stability, and you've got an instability problem.

 The best you can do to try and patch over this potential problem is short both S2s, to take the pot out of the circuit.

 If that doesn't help, trace a signal through the circuit as discussed in my troubleshooting guide.

 Also, is C6 installed? What value did you use?


----------



## mik000000

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Much more likely, you damaged the ground buffer. If not that, then one or more TLEs. That also explains the audio problems._

 

thanks tangent. I will try the tle's first as i socketed those. if that does not do it, any way to tell which of the transistors is damaged without removing them?
 thanks for the help


----------



## tangent

Quote:


  Originally Posted by *mik000000* /img/forum/go_quote.gif 
_any way to tell which of the transistors is damaged without removing them?_

 

Not in any sane fashion. But in my limited experience repairing PPAv2s, a bad transistor in a buffer is likely to take down others, too, so it ends up being simplest to just replace everything in the channel. The exception is the output transistors, probably because they're much hardier.

 This is a difficult enough thing to do, with a serious risk of damaging the board, that it makes sense to test the buffer before you rebuild it. Just as in my previous post, I refer you to my troubleshooting page. If you have a scope, that would be ideal: if you see the test waveform visibly distorting, you can bracket the problem location.


----------



## funch

Please excuse my sorry computer skills; I don't know how to post the quotes. This reply is for tangent. 
 I do have C6G installed; it's a 100pF silver mica cap. I also forgot to list that I have an OPA627UA in the ground channel, and 2 OPA637AP's in L/R. 
 I realized that I only had the gain at 4.9, so I changed R4 to give me a gain of 11. I also jumpered both S2's per your suggestions.
 Now, the hiss isn't quite as bad (still very audible), and it will play music, but with a lot of crackling, which get worse as I add volume, so I guess I still have an instability issue. Time to up the learning curve. I'm one of those guys that's smart enough to get himself into trouble, but not smart enough to get himself out.
 (By the way, how did you know I have an instability issue? You've never met me! 
	

	
	
		
		

		
		
	


	




 )


----------



## tangent

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Please excuse my sorry computer skills; I don't know how to post the quotes._

 

What, you mean other than by clicking that big blue Quote button at the bottom of the post you want to quote? 
	

	
	
		
		

		
		
	


	




 To learn more, click on the links in the box at the bottom left of the page. ("vBCode", "Smileys", and "IMG")

  Quote:


 I realized that I only had the gain at 4.9, so I changed R4 to give me a gain of 11. I also jumpered both S2's per your suggestions.
 Now, the hiss isn't quite as bad (still very audible), and it will play music, but with a lot of crackling, which get worse as I add volume 
 

That definitely sounds like it's marginally unstable. Have you cleaned the flux off the board?


----------



## funch

Hey, no fair picking on the mentally infirmed
	

	
	
		
		

		
		
	


	




 Seriously, thanks. I'll have to spend some time figgerin' all this out.

 No, I haven't cleaned the board yet. Can I use rubbing alcohol, or do I need straight isopropyl? I used rubbing on my M^3 and it dulled the board, but the amp workes fine.

 I've noticed something else a little weird. At about one-third volume, there is a very small spot where all the noise goes away. Of course, it returns as I continue to increase the volume.

 I just tested the opamps in my M^3, and they all work fine. 

 Actually, at this point, I'm considering just replacing all the transistors and hope for the best. Other than a DMM, I don't have any other test equipment, so that may be my only fix. We'll see. No way I'm gonna dump this amp after all this!


----------



## n_maher

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Actually, at this point, I'm considering just replacing all the transistors and hope for the best. Other than a DMM, I don't have any other test equipment, so that may be my only fix. We'll see. No way I'm gonna dump this amp after all this!_

 

Take your time with the trannie replacement. I had to do it multiple times to the same PPA board and that amp survived just fine and is still producing wonderful sounding music nearly a year later. Also bear in mind that most, if not all of the truly expensive bits can be moved to a new pcb if something does go wrong.

 Best of luck,

 Nate


----------



## funch

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_Take your time with the trannie replacement. I had to do it multiple times to the same PPA board and that amp survived just fine and is still producing wonderful sounding music nearly a year later. Also bear in mind that most, if not all of the truly expensive bits can be moved to a new pcb if something does go wrong.

 Best of luck,

 Nate_

 

Thanks for the reply. It's both encouraging and a little disconcerting. May I ask why you had to do it multiple times?

 Allen


----------



## n_maher

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Thanks for the reply. It's both encouraging and a little disconcerting. May I ask why you had to do it multiple times?

 Allen_

 

Allen,

 For the full explanation see this thread. The short version of that story is that it was a PPA that a friend had built and while he was doing final adjustments on the buffers he shorted the ground channel output and it cooked that channel. So I rebuilt it once, got it all working and then did something really dumb. Thinking that I had once again managed to cook the ground channel I replaced all of the transistors a second time only to find that I'd tied V+ to IG and that the ground channel was fine all along. The good news for you in all of this is that it proves that the PPA pcb is rugged enough to handle *a lot* of soldering an de-soldering and that just about any problem with it can be fixed if you're up for the challenge.

 Be careful though, you just might wind up with a custom title as a result 
	

	
	
		
		

		
		
	


	




.

 Nate


----------



## villekille

Is it normal that there is a lot of background hiss with sensitive low impedance phones as Ety ER-6i (16 ohm)?

 I can't even plug them into my ears as the hiss is so loud..only way to get it down to a more reasonable level is to turn the ground channel buffer bias to 170mV and that's with 2.2ohm output resistors! And it's still uncomfortable to say at least. 

 With Senn PX-100 the hiss is nearly inaudible and the amp sounds great. 

 Another question about gain, my CDP has a loud output and I can just barely move the volume control on PPA as it gets too loud. The gain calc doesn't work on my computer but I tried to change R4 from 10K to 1K and it helped a little but not nearly enough..what should I do?


----------



## kklee

Quote:


  Originally Posted by *villekille* /img/forum/go_quote.gif 
_Is it normal that there is a lot of background hiss with sensitive low impedance phones as Ety ER-6i (16 ohm)?_

 

I had exactly the same problem when I built my PPA. It was oscillating when I plugged in any low impedance phones. Upping the bias would lessen it but not get rid of it. I played with C6G until I found a value that got rid of the oscillations. However, I don't remember what I ended up sticking in there.


----------



## n_maher

Quote:


  Originally Posted by *villekille* /img/forum/go_quote.gif 
_Is it normal that there is a lot of background hiss with sensitive low impedance phones as Ety ER-6i (16 ohm)?_

 

 Quote:


 Another question about gain, my CDP has a loud output and I can just barely move the volume control on PPA as it gets too loud. The gain calc doesn't work on my computer but I tried to change R4 from 10K to 1K and it helped a little but not nearly enough..what should I do? 
 

Is the hiss the same with the source connected and disconnected? What opamps are you using? And as kklee suggested the solution may lie in the value of C6G so what do you currently have in there?


----------



## villekille

The hiss is there with or without the source connected.. I have the recommended 10pF silver mica at C6G. I don't have any other silver micas so I tried to put a standard ceramic cap alongside that silver mica, 27pF and 100pF but with no effect. I also tried to desolder that silver mica completely and only with those ceramics but same hiss was there. Finally I took a 2200pF film cap but now there was LOTS of noise. Without a cap I was unable to plug in my headphones as the offset was many volts.

 I have used it with OPA134 x 3, OPA134 +OPA227 in G channel, and AD843 in L and R + OPA227 in G. 

 AD843 does not seem to be stable. If I'm running with a 12V supply it works but sometimes I get a many volts offset when I turn the amp on if the bass boost is on. With a 20V supply I haven't been able to use it because the offset is always there. Maybe it's because I have OPA134 or OPA227 in G channel as I have only two AD843s?


----------



## villekille

as a side note I have to say that the AD843 does sound good when it works, compared to OPA134 the bass is much better, deeper and more defined..that's so obvious that I'd soon like to get that setup working.


----------



## funch

OK, so I cleaned the flux from my board, and installed two 6.04K resistors in R4 = gain of 6.7. Hooked it all back up and tried it again with my 32 ohm HD497's. This time no hiss at idle, but as soon as I added volume, the hiss was back. It still plays music, but with the hiss and crackling. I've read post from a few others who experienced hiss/noise with low impedence cans, but not with high impedence, so I tried my HD 600's, and sure enough, it works great with the 600's.

 I'm so relieved that it works. I was begining to doubt myself on this one!

 So how does one get this amp to work with lower impedence 'phones? Or is it strictly an amp for high impedence 'phones?

 *Edit*
 I just hooked up the bass boost (pot and 0.1uF cap) and even with it at full turn, there's no problem. Happy, happy, joy, joy.


----------



## tangent

funch, villekille, there are posts earlier on in this thread with advice from ppl about dealing with instability. The AD843 is particularly unhappy in this amp in the default configuration. Low impedance loads are also risky, and combining them, as in villekille's case, is almost a guarantee of instability.

 Just off the top of my head, some of the advice had to do with:

 - smaller buffer input resistors
 - different values for output resistors
 - different choices for output transistors


----------



## kklee

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_- different values for output resistors_

 

That tweaked my memory. With my PPA problem, not only did I adjust C6G, I upped the output resistors to 4R7 as well.


----------



## funch

I'm wondering about my choice for C4. I used 100uF Muze KZ caps. Is this OK, or should I have used the recommended 220uF? I went with the smaller ones because I wanted a better cap, and the 220 wouldn't physically fit.


----------



## funch

Well, I just finished replacing the carbon 2R2 output resistors with some metal film 4R7 ones. Now, even with the volume turned all the way up and no input signal, there's no hiss or noise whatsoever. Quiet as a mouse, and, even with very little time on it, it sounds great.


----------



## villekille

I also changed the output resistors to 4R7 and the hiss is gone

 Can you check how many mA is the current at idle? Mine takes about 100 mA and the buffer bias is set to 15mA (72mV with 4,7 ohm output r), no class A biasing. Using opa134x2 + opa227. How can it be that high?


----------



## luvdunhill

Quote:


  Originally Posted by *villekille* /img/forum/go_quote.gif 
_I also changed the output resistors to 4R7 and the hiss is gone

 Can you check how many mA is the current at idle? Mine takes about 100 mA and the buffer bias is set to 15mA (72mV with 4,7 ohm output r), no class A biasing. Using opa134x2 + opa227. How can it be that high?_

 


 I had a hard time getting that particular combination working ;( I got noise at about 25% volume. Now that I have an oscilliscope and some testing tools, I'm going to try again, but FYI it didn't work out of the chute for me.


----------



## funch

Quote:


  Originally Posted by *villekille* /img/forum/go_quote.gif 
_I also changed the output resistors to 4R7 and the hiss is gone

 Can you check how many mA is the current at idle? Mine takes about 100 mA and the buffer bias is set to 15mA (72mV with 4,7 ohm output r), no class A biasing. Using opa134x2 + opa227. How can it be that high?_

 

I just realized that this question was probably for me. 




 In my previous post, I had measured my idle current at around 110mA. According to Tangent, it was probably high. But the amp is working fine, so I'm not going to worry about it. At least not until it goes boom, if it ever does. Nothing gets too hot, so I'm just going to enjoy the music.

 Speaking of which, I just changed the output resistors from 4R7 down to 3R3, and still no hiss, or noise with my 32 ohm HD497's, so that's where they're going to stay. I did this because in comparison with my M^3 through HD600's, the highs in the PPA were a little constricted with the larger resistors. Maybe some of that added distortion that Tangent talks about in his doc's. No such problem with the 3R3's. I suppose if someone wanted a smoother, less detailed sound, then they might prefer the 4R7's in the output. As for me, I'm 
	

	
	
		
		

		
		
	


	










.


----------



## DanP

I am new the Head-Hi and I am looking to build a PPA v2 amp with the battery board. I have been able to locate all of the parts except the MC33340P charge monitoring chip. This chip is out of stock every where. Does anyone know of a source for this part or a replacement part.

 Thanks


----------



## JDAPJ

Hi!

 I would like to know if anyone of u experts here could please explain this for me:

 In the instructions to PPA it says that Q4 should at least have a Idss of 30 mA.
 However, when I run it in a spiceprog and set the recommended Icq of 20 mA
 it seems to be enough with 5-10 mA to get the 40mV drop over 2.2 ohms.


 And to the next q:

 What is the real benefit of using currentmirrors instead of the simpler approach with a transistor+led+resistor ?

 Hope someone have the time to read this...

 Thanx!

 /PJ


----------



## amb

Quote:


  Originally Posted by *JDAPJ* /img/forum/go_quote.gif 
_In the instructions to PPA it says that Q4 should at least have a Idss of 30 mA.
 However, when I run it in a spiceprog and set the recommended Icq of 20 mA
 it seems to be enough with 5-10 mA to get the 40mV drop over 2.2 ohms._

 

It's because Q4 has a resistor and trimpot to set its current, and is not run "wide-open" at its Idss current. In order for the trimpot to have a useful adjustable range to suit device variations, Q4 should have an Idss much higher than its actual intended operating current.

  Quote:


 What is the real benefit of using currentmirrors instead of the simpler approach with a transistor+led+resistor ? 
 

It allows a single trimpot to set both the top and bottom currents. Using the transistor/LED/resistor scheme, you'd have to independently adjust the two CCSes, and it would be difficult to make them track each other.


----------



## JDAPJ

Now that was just what I needed to know, thanx a lot amb!

 Had my thoughts in this direction and you confirmed it, again thanks!

 /PJ


----------



## FallenAngel

Hey guys,

 I was debugging my PPAv2 tonight and couldn't get very far as I'm seeing the same thing over and over again.

 The amp sounds great but it's oscillating 
	

	
	
		
		

		
		
	


	




 Gain of 11 (freaking loud!)
 OPA637 on L/R = 7 x 7mA = 14mA
 OPA627 on G = 7 mA
 Buffers = 3 x 25mA = 75mA
 No Class-A
 No LED
 No Bass Boost (S2 jumpered, no second POT)

 Total = 91mA
*Reading = 140mA!*

 Where am I losing 50mA? 
	

	
	
		
		

		
		
	


	




 I also tried adjusting the buffer bias to 30mA each and I didn't get a total of 120mA, I still got 50mA over at about 165mA! I do think the amp sounds better this way.

 I used most of the recommended parts.
 - 2N8087/2N8088
 - MJE243/MJE253
 - 2.2Ohm output resistors (Yes, I know it would have been smarter to order a set of 3.3Ohm, but I haven't but will be considering it soon)
 - C6G is 33pF NP0/C0G ceramic.

 I read a little before that having the amp in a solid case is required and I got the same results when I was testing uncased as when I put it into the recommended Hammond.

 I think the solder job was ok, shouldn't have any cold joints, perhaps the opamp socket soldering is a little worse than it could since it's harder to have the pins in physical contact before soldering. This will be looked into and double checked as soon as I get a chance.

 1) What is the recommended way to connect the case to the board?
 2) What would you guys recommend doing next to track down the problem?

 Thanks in advance.


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_- C6G is 33pF NP0/C0G ceramic._

 

try 100pF and the oscillations should be gone


----------



## FallenAngel

Thanks Steinchen, I'll be replacing those as soon as I get my hands on a pair of 100pF NP0/C0G ceramics. I've got a few X7R but I was reading these aren't good enough in this position so I'll be ordering in a day or two (combining projects, eh).

 Yes, I said pair because I have 2 PPAv2 amps, both with similar parts and opamps except the second has BD139/BD40 output transistors and it is showing the EXACT same oscillation 
	

	
	
		
		

		
		
	


	




. Just my luck I guess.


----------



## steinchen

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I'll be replacing those as soon as I get my hands on a pair of 100pF NP0/C0G ceramics. I've got a few X7R but I was reading these aren't good enough in this position so I'll be ordering in a day or two (combining projects, eh)._

 

at least they should be good enough for a quick try to become sure that they are the source of your probs


----------



## FallenAngel

Well I just finally had a chance to play with these again.

 I redid most of the solder joints just to make sure it's alright. I also replaced the C6G with 100pF C0G/NP0 ceramic caps and unfortunately, I'm still seeing the exactly same current draw.

 I also accidentally (with fun outcomes) tried the amp without any opamps plugged in and strangely enough, I saw the exactly same current draw with no opamps! Totally confused 
	

	
	
		
		

		
			





 Here are pics of the board, perhaps one of you guys will see something funky that I missed. Hopefully 
	

	
	
		
		

		
		
	


	














 Thanks in advance!


----------



## Vladco

Are you sure what yours meter is reading properly? If I understand right if you got oscillations either something will overheat or DC offset will be big enough. You could put small resistor series with amp and check the voltage across it. 
 Vlad


----------



## FallenAngel

Quote:


  Originally Posted by *Vladco* /img/forum/go_quote.gif 
_Are you sure what yours meter is reading properly? If I understand right if you got oscillations either something will overheat or DC offset will be big enough. You could put small resistor series with amp and check the voltage across it. 
 Vlad_

 

Really not sure what you mean by putting a "resistor series with the amp to check voltage". The offset is basically non existent and nothing is hotter than it should be. Opamps are totally cool and the output transistors are warm, but nothing bad.

 I don't have any great meters, but I did check with 2 semi-cheap DMMs and both are giving me that current draw.


----------



## Vladco

If you got 2.2 Ohm or something like this resistor connect it between power source and amp and check voltage across resistor. Using the Ohm's law divide voltage by resistance to get current. Usually voltage reading on cheap DMM's is reasonably correct.
 Vlad


----------



## FallenAngel

Uhm... that's what I did to figure out that the current output of the buffers is 25mA with the voltage across the resistors is 55mV.

 3 Channels at 25mA each = 75mA and the 3 OPA627/OPA637 are 7mA each so it should be a total of less than 100mA. I'm getting 138mA current draw on the amp. Strangely enough, that's the same current draw as the amp is without the opamp chips.


----------



## FallenAngel

Hey guys,

 I had a chance to use a tone generator on this amp and measure the signal through the map as per Tangent's Basic Troubleshooting for Headphone Amplifiers. I got expected results through out the entire test except either my DMM's are screwy or some reason the output pin on the opamps show a slightly higher gain that I thought. I configured the gain for 11 because I'm using OPA637's but with a signal went form 0.1V to 1.6V. Gain of 16 is kind of strange, but I'm kind of thinking my DMM is just not accurate.

 Any other ideas of what I could try to figure out where I'm losing another 30mA?

 Thanks in advance


----------



## MdRex

I've got a question: If we choose not to have bass boost on our PPA (i.e. to omit R7) should we jumper R7?


----------



## Calroth

Quote:


  Originally Posted by *MdRex* /img/forum/go_quote.gif 
_I've got a question: If we choose not to have bass boost on our PPA (i.e. to omit R7) should we jumper R7?_

 

You could, but you're already jumpering the bass boost on/off switch (S2L and S2R), which has the same effect!


----------



## MdRex

Ah, Thanks I missed that step when reading the instruction.


----------



## steinchen

just shooting in the dark:
 - remove the R10 resistors, the class-A cascodes should be already disabled but that may be worth a try
 - remove the opamps and dial the bias of the output stages to zero. With no LED etc you should get zero current draw (and verify this way you don't got a short)


----------



## FallenAngel

Quote:


  Originally Posted by *steinchen* /img/forum/go_quote.gif 
_just shooting in the dark:
 - remove the R10 resistors, the class-A cascodes should be already disabled but that may be worth a try
 - remove the opamps and dial the bias of the output stages to zero. With no LED etc you should get zero current draw (and verify this way you don't got a short)_

 

Sounds like a plan, especially like the second idea, will try it tonight. Thanks!


----------



## FallenAngel

Just had a chance to play with this amp some more and here are the observations.

 I took all the opamps out, adjusted the bias to as low as it would go on each channel.
 Ground = 20mV = 9.1mA
 Right 16mV = 7.3mA
 Left 12mV = 5.5mA

 Total should be 22mA, I got a current draw of about 40 
	

	
	
		
		

		
		
	


	




 When I have all opamps installed and adjust the buffer bias from lowest to 25mA each, the DC offset changes from an initial -2.0mV / 0.8mV to is -2.3mV / 0.8mV on the other.

 Definitely funky stuff


----------



## n_maher

You mentioned earlier that your DMM's were "not so good" or something like that. How "not so good" are we talking here? I'd hate to see you spending this much time fighting a problem that might not exist.


----------



## MisterX

I was thinking the same thing.


----------



## FallenAngel

Not so good is the $20 MasterCRaft 052-0060-2 from Canadian Tire. It's a pretty basic meter, nothing fancy, but works well. The other is a cheap little one that has HFE testing so I don't have to bother making a circuit.

 The funky this was that both show the same value at about 135mA current draw when there should only be 100mA.


----------



## pobrecito

Hi, Does anyone know what is the lowest real world gain I could use with OPA637s in the left & right channels. I know that the data sheet states >=5. I'ld like to reduce the gain in order to allow for better use of the volume control.


----------



## MdRex

More questions:

 I read that the total capacitance of the power rail caps (C1) is kept at the range of 1000-2000 uF but I've seen many pictures of people adding 8 high capacity caps (say around 1000uF ea). Wouldn't that mean the total capacitance is around 8000uF and will there be any negative effects if the capacitance is >2000uF?

 Another thing, is it necessary to use caps from the same line in the power cap, I ask this because I have 6 Panasonic FC 220uF and 2 Nichicon Muse 1000uF cap and I was wondering if I could use them together on the power rail caps (C1)?

 If not, should I then use the 6 FC caps or the 2 Muse caps?

 Thanks!


----------



## Epicurean

Quote:


  Originally Posted by *pobrecito* /img/forum/go_quote.gif 
_Hi, Does anyone know what is the lowest real world gain I could use with OPA637s in the left & right channels. I know that the data sheet states >=5. I'ld like to reduce the gain in order to allow for better use of the volume control._

 

From what I've heard a gain of 8 is recommended. I tried a gain of 6 but it would turn unstable at random while listening, so I adjusted it to 10 and it works perfectly.

 IMHO, after extensive listening with OPA627,OPA637 and AD8610, I find the AD8610 to be the clear winner with no apparent faults, especially with senns. The OPAs do add some warmth, but the bass is off, sounds muddy and bloated in comparison to the AD8610. And yes I tried this with about a dozen different sources. This was also the case with DT990s '05 and every cheapo headphone I have laying around.


----------



## tangent

Quote:


  Originally Posted by *pobrecito* /img/forum/go_quote.gif 
_Does anyone know what is the lowest real world gain I could use with OPA637s in the left & right channels._

 

Don't push it. The 637 is notoriously difficult to make stable in the PPA in gains over 5 already. If you want to keep that same basic sound with a lower gain, switch to the 627...that's what it's for.

  Quote:


  Originally Posted by *MdRex* 
_I've seen many pictures of people adding 8 high capacity caps (say around 1000uF ea). Wouldn't that mean the total capacitance is around 8000uF and will there be any negative effects if the capacitance is >2000uF?_

 

As supply capacitance goes up, the power-up and -down thumps are larger, and it can overstress some power supplies. I have yet to see anyone A/B test a 2000uF PPA vs. a 8000uF one, so I still believe the audible advantage is nil. 2000uF is already an uncommonly large amount of capacitance for a headphone amp.

 You see PPAs with thousands of mics of rail capacitance in them only because it can be done, not because it gives some real advantage. We put 9 rail cap positions into the amp to account for boutique caps, which are often only 220uF in in the physical size required in the PPA. If we were designing for 1000uF caps, we'd have put 2 cap positions in there instead, and used the space for something else. We had ideas for lots more features we could have put in, if the space was there.

  Quote:


 I have 6 Panasonic FC 220uF and 2 Nichicon Muse 1000uF cap and I was wondering if I could use them together on the power rail caps (C1)? 
 

It'll be fine.

 But, why don't you save the FCs for another project? Just because the holes are there, doesn't mean you must fill them.


----------



## ppl

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Just had a chance to play with this amp some more and here are the observations.

 I took all the opamps out, adjusted the bias to as low as it would go on each channel.
 Ground = 20mV = 9.1mA
 Right 16mV = 7.3mA
 Left 12mV = 5.5mA

 Total should be 22mA, I got a current draw of about 40 
	

	
	
		
		

		
			





 When I have all opamps installed and adjust the buffer bias from lowest to 25mA each, the DC offset changes from an initial -2.0mV / 0.8mV to is -2.3mV / 0.8mV on the other.

 Definitely funky stuff 
	

	
	
		
		

		
		
	


	


_

 

IMHO your missing Ma is from mismatched Op-Amp Rail Isolation JFET's. If the Idss of each fet is different then the difference is expressed as excess current drain. If you have a set of op amp rail isolation FET's with mismatched Idss then any imbalance will simply Pull upon the output of the TLE-2426's causing a current to flow.

 The Bottom like is is you are building a PPA for portable use you want the lowest battery drain as possible, it is now required that the rail isolation fets be matched for Idss,It's not just a nice for battery operation. Having missed matched JFET's can added 10-50 Ma additional current drain. Oh Ya BTW matching transistors in the output stage while not required will reduce open loop Distortion up to 10 times.

 As with any DIY project the care in assembly quality of the solder joints and how cleen the PCB is all matter allot.


----------



## FallenAngel

Quote:


  Originally Posted by *ppl* /img/forum/go_quote.gif 
_IMHO your missing Ma is from mismatched Op-Amp Rail Isolation JFET's. If the Idss of each fet is different then the difference is expressed as excess current drain. If you have a set of op amp rail isolation FET's with mismatched Idss then any imbalance will simply Pull upon the output of the TLE-2426's causing a current to flow.

 The Bottom like is is you are building a PPA for portable use you want the lowest battery drain as possible, it is now required that the rail isolation fets be matched for Idss,It's not just a nice for battery operation. Having missed matched JFET's can added 10-50 Ma additional current drain. Oh Ya BTW matching transistors in the output stage while not required will reduce open loop Distortion up to 10 times.

 As with any DIY project the care in assembly quality of the solder joints and how cleen the PCB is all matter allot._

 


 Well that would definitely explain some things since I didn't match the Idss of the FETs.

 I did however match the output transistors for HFE so I'm hoping distortion (although I can't hear any) is kept at a minimum.

 Unfortunately though, that might not be the problem since I just removed all the rail isolation JFETs (Q3), matched new ones as closely as I could for IDSS (got the pairs within 1mA of each other, my PN4392's had quite a range, some at 28mA, others close to 50mA). The pairs I installed in this amp were 32.2/31.8, 42.2/41.9 and 46.5/46.3, I'm assuming it's only the pairs I need to match, not all together, right? After installing the new matched ones though, I still get 130mA (and slowly climbing at power-up) current draw when the buffers are set at 25mA.


----------



## ppl

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Well that would definitely explain some things since I didn't match the Idss of the FETs.

 I did however match the output transistors for HFE so I'm hoping distortion (although I can't hear any) is kept at a minimum.

 Unfortunately though, that might not be the problem since I just removed all the rail isolation JFETs (Q3), matched new ones as closely as I could for IDSS (got the pairs within 1mA of each other, my PN4392's had quite a range, some at 28mA, others close to 50mA). The pairs I installed in this amp were 32.2/31.8, 42.2/41.9 and 46.5/46.3, I'm assuming it's only the pairs I need to match, not all together, right? After installing the new matched ones though, I still get 130mA (and slowly climbing at power-up) current draw when the buffers are set at 25mA._

 

Remove ether the TLE2426 or the Rail JFET's and then remeasure the current drain what you should have done to eliminate this phantom current is see if any current is drawn when only the rail isolaten JFET's and the TLE2426 are installed no op amps no buffer parts then you would know where your phantom current is com9ong from and in your case its one of two issues (1) the JFET mismatch as previously described or you have mile oscillation in the output stage however this would also show up as an increase in voltage across your emitter resistors. In any event all anyone hear can do is suggest possible reasons for the malfunction it is up to you to investigate these.

 another thing to consider is the current the drivers and the Bias current generator of the output stage consume and this is about 1/4 the current you measure across the emiter resistors on the output transistors. measure the voltage drop across the 10 ohm emiter resistors for the driver transistors add that to your total.


----------



## MdRex

I've populated my PPAv2 board and after installing the OPAMP (AD744) I've got extremely high DC off set (several hundreds millivolt), the sound range from having the right channel only, no sound, to severe distortion. It's frustrating.


----------



## MdRex

I wonder if the problem is my output buffer stage. The transistors are not getting warm. I've only felt warmness in the MJE243/253

 I only hear severe distortion when I turn the volume up in the right channel, the left channel can barely be heard. I am using R4 to be 5.6K to lower gain and the rest of the parts are the same as what tangent has on his site.

 Can anyone help me please?


----------



## villekille

The current consumption seems like a common problem for the PPA. I have a PPA v2 with AD843 opamps and NO class A biasing, standard parts, 15V power supply and the current consuption is 163mA. 

 The output bias is set to 20mA if I have understood it right. (4.7 ohm resistors at R24/R34 and the voltage across them is 100 mV)

 I don't know where all that current goes but the amp sounds fine


----------



## villekille

I removed all opamps, and Q3s and the current draw was about 130mA. The buffer bias was set at 20mA. 

 Then I removed Q4s, one by one, and they all had about an equal effect. The current draw went down to 1.4 mA after removing all of the Q4s. 

 So each buffer consumes about 45 mA when the bias is set at 20mA..(voltage across a 4.7 ohm resistor is 100mV).
 There aren't any differences between the channels. That's more than 2 times the bias current!
 My Q4s are "2N4392".


----------



## MdRex

Is there any fool proof way to test if the buffer section is faulty? Someone offer their help please


----------



## squid

Hello everyone. I was hpoing someone could give me a clue whats happening with my ppav2. I have weird output bias currents: on left channel it wont go lower than 100 mA, on ground it wont go higher than 19 mA and on right channel its stuck on 6 mA. R12's have almost no effect on these currents. R32 and R33 have 10 volts across them, does not seem right either. Weird stuff start with buffer section, all voltages are fine before it.

 All using 24 Volts supply. Would greatly appreciate any comments.


----------



## Clutz

Double check that you have the correct value resistors in each of the positions. Also, you might want to consider taking some pictures of the top and bottom of your board (high quality photos in macro mode).


----------



## squid

Thanks Clutz, will do.


----------



## squid

I think I located the problem... but i broke transistor lead while desoldering it, so I cant try it right now


----------



## applegd

I am preparing the part list for my PPAv2, just wondering whether I need to match following transistors.

 1. Q1,Q2 for bias the op-amp into class A.
 As we have R9 as multiturn trim pot there, I am not sure how much difference matched transistor can make for Q1,Q2 position. 

 2. Q3 for power rail isolation.
 Match is needed here. 

 3. Q4 set bias point of the buffer
 We have R12 multiturn trim pot, I am not sure whether I need to match them.

 4. Q21-23,Q31-33 (Current mirror, buffer input transistors)
 I think Match is needed.

 5.Q24,Q34 Output transistor
 Match is needed.

 Please share your experience. If the match is need, I will need to buy (about 5 times)more stuff than I need. Thanks!


----------



## n_maher

The following is taken from this post.
  Quote:


  Originally Posted by *ppl* 
_Matching transistors are not mandatory however lower DC offset and perhaps better sound with slight measurable Right mark performance will be obtained with matched devices. The output transistors should all be matched in all three channels because of the symmetry created by the ground channel with respect to the right and left channel._

 

This officially qualifies as RTFM.

 Personally I've only used matched output transistors and never bothered with the others. None of the PPA's that I've built have had DC offset issues and have sounded pretty fantastic (IMO). YMMV


----------



## TzeYang

i don't think Q3 requires matching as long as you use something with a higher IDSS. PN4392 will work well as a substitute for the 2n5486.

 Q4 does not need matching. Most of the time, PN4392 as a lone jfet here has enough IDSS value.

 Yes, the last two should be matched. I personally think you can skip matching the output transistors, they are normally well matched due to their lower hFE. Plus PPA v2's design is already very stable even without parts matching.


----------



## dbfreak

I'm currently building a PPA v2 and would like to know if I should deviate from any of the resistor values listed on Tangent's Parts Selection List due to the fact I will be using low impedance headphones with the PPA (Grado SR225's which are 32 Ohms)?


----------



## FallenAngel

Quote:


  Originally Posted by *dbfreak* /img/forum/go_quote.gif 
_I'm currently building a PPA v2 and would like to know if I should deviate from any of the resistor values listed on Tangent's Parts Selection List due to the fact I will be using low impedance headphones with the PPA (Grado SR225's which are 32 Ohms)?_

 

Set a low gain, I guess. Look at ElvenCraft site as well, they have slightly different resistor values, but nothing major.


----------



## dbfreak

Thanks Fallen_Angel!


----------



## simply_BLACK

hi,
 i would like to know which opamp is better with ppav2. there r 2 opamps of my choice now which r opa627 and opa637. the sound signature that i;m looking is somehow transparent, not that bright yet not the laid back too. would prefer more details + warmth.. please suggest me other choices if u think it;s suitable too. thanks


----------



## FallenAngel

Quote:


  Originally Posted by *simply_BLACK* /img/forum/go_quote.gif 
_hi,
 i would like to know which opamp is better with ppav2. there r 2 opamps of my choice now which r opa627 and opa637. the sound signature that i;m looking is somehow transparent, not that bright yet not the laid back too. would prefer more details + warmth.. please suggest me other choices if u think it;s suitable too. thanks_

 

Had an interesting time reading that post, never understood why it's so much harder to type "are" and "you", but to each their own.

 You can't run OPA637 in Ground position, so you'll need to use something else there anyway, usually OPA627. This combination of OPA637 in Left/Right and OPA627 is very nice. AD8610 in all 3 was a little too analytical for my tastes. I got recommended AD8065 in Left/Right and AD8610 in Ground for Grados, still to try this one but considering that I really like AD8065 in my Pimeta, it should be a nice combination.


----------



## simply_BLACK

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Had an interesting time reading that post, never understood why it's so much harder to type "are" and "you", but to each their own.

 You can't run OPA637 in Ground position, so you'll need to use something else there anyway, usually OPA627. This combination of OPA637 in Left/Right and OPA627 is very nice. AD8610 in all 3 was a little too analytical for my tastes. I got recommended AD8065 in Left/Right and AD8610 in Ground for Grados, still to try this one but considering that I really like AD8065 in my Pimeta, it should be a nice combination._

 

thanks for the prompt reply. pardon my style of short-messaging..

 i'm going to use it for senn.. i do not need any opamp for the ground channel, so i'll just need a pair for Left/Right channel. i heard that 637 can be bright, i just afraid that the high may go too peaky for me.. the gain is at 11 because 637 needs high gain to be stable..

 by the way, how is AD8065 and AD8610 sound?


----------



## FallenAngel

Quote:


  Originally Posted by *simply_BLACK* /img/forum/go_quote.gif 
_thanks for the prompt reply. pardon my style of short-messaging..

 i'm going to use it for senn.. i do not need any opamp for the ground channel, so i'll just need a pair for Left/Right channel. i heard that 637 can be bright, i just afraid that the high may go too peaky for me.. the gain is at 11 because 637 needs high gain to be stable..

 by the way, how is AD8065 and AD8610 sound?_

 

Uhm... I think you do need an opamp in the ground channel. Please elaborate how you plan to skip it.

 AD8610 is very detailed, very clean highs, not too bassy. In the PPAv2, it was very bright for me.

 AD8065 is also detailed, but a little warner and the mids are beautiful. Bass is nice as well.

 I've never heard the OPA627/OPA637 as bright at all, I always thought they were detailed and somewhat more laid back than any of the AD chips I usually use.

 As for OPA637 requiring high gain, I have mine stable at a gain of 6.


----------



## simply_BLACK

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Uhm... I think you do need an opamp in the ground channel. Please elaborate how you plan to skip it.

 AD8610 is very detailed, very clean highs, not too bassy. In the PPAv2, it was very bright for me.

 AD8065 is also detailed, but a little warner and the mids are beautiful. Bass is nice as well.

 I've never heard the OPA627/OPA637 as bright at all, I always thought they were detailed and somewhat more laid back than any of the AD chips I usually use.

 As for OPA637 requiring high gain, I have mine stable at a gain of 6._

 

i'm not quite sure how is the topology since i ask kin0kin to make it for me. 
 anyway, i think that i'll probably go for 637. thanks


----------



## NelsonVandal

Quote:


  Originally Posted by *simply_BLACK* /img/forum/go_quote.gif 
_i'm going to use it for senn.. i do not need any opamp for the ground channel, so i'll just need a pair for Left/Right channel. i heard that 637 can be bright, i just afraid that the high may go too peaky for me.. the gain is at 11 because 637 needs high gain to be stable.._

 

I don't think you'll be happy with your amp without an opamp for the ground, even if you use high impedance phones. I don't have a PPA, but I've done some experimenting to find a sound I like. I've done "all I can" not to have to use opamps, still I recommend one in this position. I use HD650, and I find the sound a bit "hollow" with open loop buffer in ground position. At first I was impressed, but later on I found this defect annoying. I've found AD829 "comp pin out" to be very transparent as a ground channel opamp, but I guess some people would like a "snappier" sound.

  Quote:


 by the way, how is AD8065 and AD8610 sound? 
 

On the positive side - well balanced/neutral tonality (AD8610/20), very good staging (AD8610/20), detailed, snappy, punchy bass (AD8065/66). On the negative side - a bit harsh and sibilant and to my ears "unfriendly", AD8610/20 is a little to lean. They share the same sound signature "The Analog snap".


----------



## applegd

I matched all 2N5087s Hfe 330+/-0.5%, and matched all 2N5088 Hfe 390+/-0.5%. I think this is good enough.

 It looks like as long as the trannies are from same batch, most of them are within +/-15% range of one HFE value. This explained why some people can do fine without manual match at all. For my case, if I shoot the trannies in the dark without matching, I got 5% chance to get odd trannie which has much higher value than the rest.


----------



## applegd

Finally matched my Output tranies, got MJE253 exactly matched at HFE 150, got MJE243 matched at HFE 116+/-1%(actually 117 for both L and R, 115 for G).

 As I can see it is almost mission impossible to have same HFE for both MJE253bundle and MJE243 bundle. Same thing happened to my 2N5087 bundle and 2N5088 bundle.

 Hope the above HFE difference is not big deal, one thing I can say to myself.... the BJT match work is done, now my soldering iron is smoking.....


----------



## applegd

I bought RK27 pots from Tangent, so I know they must be Genuine. Then I ran some testing.

 I used Tangents's scale (http://tangentsoft.net/audio/misc/atten-meas-scale.pdf) and here are the results for my two RK27 pots' resistance between pin 2 and pin 3 for each channel respectively.

 Pot #1.
 Shaft Position(Degree): 0 60 150 240 300
 Channel L Resistance: 46.7K 46.2K 40.7K 18.2K 0
 Channel R Resistance: 46.2K 45.6K 40.2K 18.2K 0


 Pot #2.
 Degree: 0 60 150 240 300
 Channel L Resistance: 46.8K 46.4K 41K 18.8K 0
 Channel R Resistance: 46.8K 46.3K 40.6K 18.5K 0

 From above results, we can see the worst case of the channel mismatch can be up to 600 Ohm when resistance is around 45.6K, this looks not too good. I believe this is why some folks prefer the Stepped Attenuator.


----------



## tangent

In my tests, I measured voltage, not resistance, on purpose. Resistance tells you almost nothing by itself. What matters is the voltage division factor, which you test by comparing the voltage across the pot with the voltage at the wiper. I could do the math to convert your numbers to the voltage numbers, but it's much easier to tell you to go re-do your test using the correct methodology.


----------



## amb

^ What tangent said.

 If you then convert the voltage divider ratio differences into dB, you'll then get something much more meaningful. 600 ohms might seem like "a lot" of difference between the two sides of a 50K pot, but if you do the math, you'll find that the pot actually tracks very well (within a fraction of a dB) over much of its range, and then deviating to no more than 2dB at the lowest volume setting just before it goes mute.


----------



## applegd

Thanks very much! Tangent and AMB

 I will do some voltage testing later....


----------



## Soymilk

few questions on my build i just put together:

 the measurement for the voltage across the power resistors fluctuates +/- 1mV. is this normal, or should i be concerned?

 also, i'm getting a loud buzzing sound, but i haven't put in the pot yet. would adding the pot make the buzz go away? (i was curious to see if there would be any sound, i havent had time to get the pot on yet)

 last thing, i'm also getting a really loud pop when i turn the amp on (i can see the drivers of my ksc75 physically moving and hear it clearly when they're sitting on my desk), will this also be gone when i put the pot on, or is there something else?

 so far i've done the heat test (transistors get hot, opamps get warm) and i've measured my dc offset for both channels (it was ~1.2mV and 1.4mV, nothing to be concerned about). i also measured from ground to the v+ and v- pins of the L and R opamps (opa637 btw, gain is set to 6.somethinghigh, i was originally shooting for 7, which would use r4 = 6.4 ohms, but i could only find 6.2 ohm resistors) and they came out to be the same.

 tomorrow i'm going to add the pot, and if issues persist i'll measure the current draw and see if that's right or not.


----------



## tangent

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_the measurement for the voltage across the power resistors fluctuates +/- 1mV. is this normal, or should i be concerned?

 also, i'm getting a loud buzzing sound_

 

These are probably the same thing. Amps make sound with voltage, and there you are measuring voltage.

  Quote:


 i haven't put in the pot yet. would adding the pot make the buzz go away? 
 

Very likely. Without the pot, who knows what kind of nastiness the high-impedance inputs are picking up?

  Quote:


 will this also be gone when i put the pot on, or is there something else? 
 

Possible, but it would mean two things are going on, not one. A buzz is AC, and a pop is DC.

  Quote:


 i've measured my dc offset for both channels (it was ~1.2mV and 1.4mV, nothing to be concerned about 
 

Your loud pop symptom contradicts this. How exactly did you measure the offset? From where to where?

  Quote:


 opa637 
 

In all three channels, or just L & R, with a 627 in G?


----------



## Soymilk

i put on the pot, and the buzzing's now gone. opa637 l/r, opa627 ground. gain > 6.

 my pop isn't nearly as loud as it was before now too. i can still see the driver move, but i cant hear it unless they're on my ears, and even then it's not loud. i measured dc offset from og to ol and or.

 it seems like it works now, but i wanted to make sure and test everything i can before the weekend (i wont have access to this equipment anymore after this week). what is the quiescent current for the opa637/627 at 24V? i cant seem to find it in the datasheet on ti's website. i measured the amp's quiescent current and it was 160mA. my buffers are biased to 35mA each. are these opamps drawing enough to make up roughly 55mA of current? or is there something else that's drawing current that i'm forgetting to add? there is currently no class a biasing.


----------



## tangent

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_what is the quiescent current for the opa637/627 at 24V? i cant seem to find it in the datasheet on ti's website._

 

Sometimes there's no graph, only an entry in the main data table, because it doesn't vary much over voltage. It's around 6 mA, as I recall.

  Quote:


 are these opamps drawing enough to make up roughly 55mA of current? 
 

No. But I'm not certain the calculation for buffer current is correct. The only reason it's still on the site is because I haven't got a better formula to sub in.


----------



## Soymilk

oh, the buffers' current draw isnt just the bias? i was just using the bias for that, i'll go see what comes up in your calculator. and i saw the opa627/637 have a Iq of 7.5, so hopefully the buffers will be like 45mA each or something.

 edit - ok i think i had a brain fart when i was trying to figure out what the voltage should be across the output resistors to get a 35mA bias, i thought 58mV would yield 35mA w/ a 2.3ohm resistor :-\ so my buffers are actually currently biased to roughly 25mA, not 35.

 how should i calculate the current draw for the buffers? should i go look up the Iq for all of the transistors and add them together? where does the bias fit into this? cuz if it's just the bias current = buffer draw, then something's drawing way too much.

 edit again - also, should i still be worried about the pop, or is it normal? it isn't loud, but it's still definitely noticeable (when i have the headphones on).

 another thing: one of the transistors isn't getting as hot as the others (i think its the BD140 in the left channel). should i replace it? it still gets warm, just not hot. my left channel opa637 doesnt get as warm as the other two opamps either.


----------



## Soymilk

i adjusted the trim pots so that theres roughly 35mA through each channel, and wow it sounds noticeably better. the left opamp does get warm, dont know why i didnt think it was before, and i believe the output transistors are fine now too (i think my thinking it wasnt getting as hot was more because it isn't in close proximity with as many other parts, including another hot transistor like the middle ones). i did clean up the board a bit (cleaned off the flux), so that may have helped.

 anyways, so my build's done. when i find a camera i'll take pics of it and post it in the build thread 
	

	
	
		
		

		
		
	


	




 thanks for the help.


----------



## applegd

My PPAv2 with super matched components was done last night, the DC offset is 0.6mv, and 0.6mv for L, R respectively. I set opAMP class A bias to 3mA, Buffer Bias to 30mA, I am using OPA637BP for L&R, OPA627BP for G. My PPA's sounding is amazing, IMO it clearly beats the HR Desktop Portable with '06 MAX module(Side note: Please don't misinterpret this. I mean '06MAX is damn good, but my PPA is damn damn good. Although the comparison is not too fair here. 
	

	
	
		
		

		
		
	


	




 ) when they were all connected to my (little bit super version of) Sigma 22 PSU. I will run more testing in the next 3 days......


----------



## Ikon

Which way are the output transistors positioned? The board has a kind of marking (a thicker dash) on one side of the transistor "sign" printed on it, but does that mark the labeled or the metallic side of the transistor?

 Thanks for your answer(s)


----------



## MisterX

Image stolen from the Assembly guide. 

 (http://tangentsoft.net/audio/ppa/amp2/steps.html)







  Quote:


 does that mark the labeled or the metallic side of the transistor? 
 

Yes.


----------



## Ikon

Shame on me for not noticing that detail in the picture - thanks again


----------



## Ampersand

As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?


----------



## Ikon

Quote:


  Originally Posted by *Ampersand* /img/forum/go_quote.gif 
_As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?_

 

I don't think AD797 is unity gain stable, so it probably won't work in the ground channel. In the L/R channels, it will likely cause a dangerous amount of DC offset (depending on the set gain) as it is a bipolar input chip.

 In the PPA, you need FET input op-amps for the L/R channels unless you add extra input caps. In the ground channel, a bipolar input chip should also work, but it has to be unity gain stable. OPA132, for example, should work flawlessly in all channels (tangent has more examples on his op-amp page).

 It's not entirely impossible to adapt the PPA design to make AD797 work, but I'll leave that to the gurus.


----------



## Soymilk

Quote:


  Originally Posted by *Ampersand* /img/forum/go_quote.gif 
_As I can't get my hands on any 627/637's, I was thinking of using AD797 on L/R/G. Anyone try this? Or see some glaring problem with using these?_

 

i believe the AD8610 should work in L/R/G, unless you had some reason to not use them.

 edit - they dont come in a dip-8 package though, so you'll need to get an adapter for each one. tangent has them for sale on his site.


----------



## Ampersand

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_i believe the AD8610 should work in L/R/G, unless you had some reason to not use them.

 edit - they dont come in a dip-8 package though, so you'll need to get an adapter for each one. tangent has them for sale on his site._

 

I've used the AD8610 in a pimeta before and didn't really care for them. 

 Any word on when the 627/637 will be available again?


----------



## Ikon

I finally finished assembling my PPAv2 and a quick test with cheap earphones even revealed that it basically plays music, BUT my working voltages are seriously off. Measured at the C5 caps (which feed the op-amps), I get +/-5V und +/-6.5V on the left and right channels and, most strangely, +2/-0.6V on the ground channel. I guess it's pretty obvious that there is something quite wrong with the ground channel, but even the other voltages appear rather low given the fact that I'm feeding the amp 20V.

 Heat-wise, things stay pretty cool. The op-amps are hardly warming at all and the output transistors get just a little hot. I use OPA134s on all channels and also tried a LT1122 on the ground channel to check if that would change anything (it didn't). FYI, I had to pick some alternatives for a few of the transistors that should theoretically work (please ask if you need more info). Oh yeah, and I also added every optional cap that tangent has made room for on the board, just to be safe. 

 Can you help me, please?


----------



## n_maher

Check for a short between V+ and ground.


----------



## tangent

Quote:


  Originally Posted by *Ikon* /img/forum/go_quote.gif 
_Measured at the C5 caps_

 

Why not measure right at the op-amp power pins? They're a lot easier to get to, and it's more certain you're measuring the right thing.

 Also, are you measuring against IG or OG? It should be IG, for this measurement.

  Quote:


 Heat-wise, things stay pretty cool. 
 

What about current draw?

  Quote:


 alternatives for a few of the transistors that should theoretically work (please ask if you need more info) 
 

We can only decide if this is relevant if you give the part numbers.


----------



## dbfreak

In Tangent's "Parts Selection Guide," what exactly is meant by *Single Voltage or Dual Voltage Power Supply*?


----------



## MisterX

Single or dual is just a reference to polarity. 

 Single power supply = positive voltage and ground. 
 Dual power supply = positive voltage, ground, negative voltage

 Single voltage AC adapter -----> http://www.alliedelec.com/Cart/Produ...p?SKU=879-1080


----------



## luvdunhill

so, i'm finally getting around to tweaking my first real DIY project, my PPAv2. I recently added a AC wall-wart and a TREAD to my existing PPAv2, which sports crossfeed, battery pack, and bass boost. 

 I think my TREAD is dropping out of regulation, or I don't really understand what regulation means properly. Here are the numbers.

 I'm using a Triad 24 VAC @ 200mA which measures 26.81VAC unloaded (and unconnected). I did a bunch of research using Tangent's psu estimator to try and reduce the amount of heat dissipated by the TREAD, hence the above wall wart choice. Before, I was using a 24V Elpac DC power supply. Also, I wanted to be able to tweak the supply voltage via the TREAD to optimize the charger circuit, per Tangent's site. I don't have the exact battery pack specs, but it's fairly conservative and is one of the stock "recipes".

 So, when I hook up the TREAD, I get 26.50VAC at the wall wart and 25.00 VDC output and I get 33.3VDC across TP1-TP3, which represents the voltage after rectification. 

 Now, when I hook it up to the PPAv2, and turn the power switch off, the charger starts working. Now I get 22.94 VAC at the wall wart and 22.77 VDC at the TREAD output. Now, when I turn on the amp I get 21.56 VAC at the wall wart and 20.71 VDC at the TREAD. I believe I'm using 30mA biasing (the battery pack is kinda pointless when using the OPA627/OPA637 *and* 30mA biasing, but anyways)... the deal is, I don't think my battery pack is getting enough voltage to fully charge. 

 So, can I crank up the TREAD? Anyways, should it be regulating the voltage better than this?

 Thanks!


----------



## n_maher

You should try and measure the current draw of the PPA, it may be that you're trying to extract more than the wallwart has to offer. I don't think you should be drawing more than 200mA but that's just based on a rough approximation in my head and shouldn't be trusted. And you could certainly try dialing up the TREAD to see if the otuput voltage comes back up but I'm concerned about the drop in AC voltage output at the trafo, that doesn't seem right to me at all unless you're overloading it.


----------



## luvdunhill

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_You should try and measure the current draw of the PPA, it may be that you're trying to extract more than the wallwart has to offer. I don't think you should be drawing more than 200mA but that's just based on a rough approximation in my head and shouldn't be trusted. And you could certainly try dialing up the TREAD to see if the otuput voltage comes back up but I'm concerned about the drop in AC voltage output at the trafo, that doesn't seem right to me at all unless you're overloading it._

 

so, I think I figured it out... well, I did indeed measure and allow at least an extra 20% headroom for the current draw of the PPAv2, I forgot to figure in the charger 
	

	
	
		
		

		
			





 So, without the charger hooked up, I get 24.000 VDC turned off and 24.002 VDC turned on 
	

	
	
		
		

		
		
	


	




 With the charger hooked up, and the PPAv2 off, I get 25.46 VDC after the rectifier and 23.16 VDC after the regulator. Once I turn the amp on (with the charger) I get 20.82 VDC after the regulator and 27.52 VDC before. So, yeah, the charger is pulling too much current...

 so, next question is, how do I calculate this? Wouldn't this be 1.25 / R2, or 1.25V / 4.7 Ω = 266mA ?


----------



## tangent

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Wouldn't this be 1.25 / R2, or 1.25V / 4.7 Ω = 266mA ?_

 

Yes.


----------



## applegd

Just found one interesting thing on my PPAv2. I have two sets of Cardas RCA jacks for two independent inputs(INPUT#1, INPUT#2) and I put one NKK DPDT switch between them as Input signal selector before the input signal goes to PPAv2 circuit board. There is tiny "cross-talk" between my 2 sets of Cardas RCA Jacks, cross-talk between INPUT#1_L_channel and INPUT#2_L_channel, same thing happened between INPUT#1_R_channel and INPUT#2_R_Channel. But no cross-talk between L and R.

 Practically above cross-talk is not a big problem. When I am playing music on INPUT#1 while INPUT#2 has no signal input, then change NKK switch position from INPUT#1 to INPUT#2, I can not hear the music from INPUT#1 at this moment. Then I change the ALPS RK27 voulme pot to maximum volume position, I can hear the music playing at INPUT#1 but its volume is tiny.

 I checked the resistance between INPUT#1_L and INPUT#2_L, between INPUT#1_R and INPUT#2_R, the reading on my B+K 2706A DMM is OL(range is 20M Ohms). I think the problem might be in the NKK switch(Insulation Resistance is 1000M Ohms min @ 500V DC) or the RF effect.

 Anyone saw this kind of problem before? I will run more testing to isolate the root cause.


----------



## amb

applegd, if one set of inputs is open (no source connected) then it's not unusual to have the sort of crosstalk you describe when you switch to the unused input. A floating input will pick up all kind of stuff, including crosstalk from nearby wires, RFI, hum, and other garbage. As soon as you short it to ground, or connect a source, the problem should go away.


----------



## luvdunhill

Can I get any recommendations on how to stop some distortion on my PPAv2 when using my AKG K340s (400 ohm I believe)? I am using a gain of 10 and the OPA637/OPA627. I cannot get my HD650s to distort, but it's fairly easy with the K340 even at moderate listening. I'm assuming the problem is clipping, so should I try and lower the gain? What's the best way to track this down?


----------



## n_maher

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Can I get any recommendations on how to stop some distortion on my PPAv2 when using my AKG K340s (400 ohm I believe)? I am using a gain of 10 and the OPA637/OPA627. I cannot get my HD650s to distort, but it's fairly easy with the K340 even at moderate listening. I'm assuming the problem is clipping, so should I try and lower the gain? What's the best way to track this down?_

 

Once again I'm thinking that your problem is power supply related. The K340s, as I understand it, are both voltage and current hungry. So in reality instead of dialing the voltage down you'd want to up the bias current. I'd highly recommend picking up a different wallwart to try along with figuring out how to heatsink your TREAD differently if you're worried about cooking the reg.


----------



## LawnGnome

Well, my boards and parts should be arriving this week for a PPA V2 and a STEPS.

 I'm planning on putting the steps in the same case as the amp. It is the same dimensions as the tangent recommended one, except a few inches longer. I plan on putting the psu upside down in the top part of the case, so it is above the amp.

 Anyone see this as being a big problem? Should I build some more shielding?


----------



## luvdunhill

Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_Once again I'm thinking that your problem is power supply related. The K340s, as I understand it, are both voltage and current hungry. So in reality instead of dialing the voltage down you'd want to up the bias current. I'd highly recommend picking up a different wallwart to try along with figuring out how to heatsink your TREAD differently if you're worried about cooking the reg._

 

I'm running the buffers at 30mA here. Rereading tangents site, I'm not sure how much more I can up them without risking cooking them. When using the K340, my TREAD isn't dropping out of regulation anymore and presents a stable supply voltage to the opamps.

 I never quite know what people mean when they say a headphone is voltage or current hungry. Impedance is impedance, so stating this number should accurately describe the load. Unless "voltage/current hungry" is synonymous with high impendance, I'm confused by the term.


----------



## n_maher

I don't think impedance tells the whole story and realize that you're dealing with a two part headphone in the K340 with the electret and driver, right? I think that in addition to impedance you also need to consider the efficiency of the headphone and unfortunately I don't have the specs for the K340 at my fingertips. All I know is that with my Monica DAC (~1V output) and my PPA with a gain of 8 I could pretty much max the volume of the amp with my K340 and while it wouldn't clip I didn't think it was sounding it's best either. One more thing, I assume that you were measuring the current draw of your amp at idle, you might want to try it dynamicly while the amp is under load, I don't think this can hurt and given the low current capacity of your wallwart I wouldn't be at all surprised to find that it's running out of juice. 

 I did that type of measurement with my mini³ and it was pretty surprising to see how much the current demand varied.


----------



## applegd

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_applegd, if one set of inputs is open (no source connected) then it's not unusual to have the sort of crosstalk you describe when you switch to the unused input. A floating input will pick up all kind of stuff, including crosstalk from nearby wires, RFI, hum, and other garbage. As soon as you short it to ground, or connect a source, the problem should go away._

 

Amb, Thanks very much!! After I replace the 4G IPOD with my CD player for INPUT#2, this problem seem gone....


----------



## dbfreak

Excuse me if this has been posted elsewhere... 

 Has the _preferred_ power switch(es) configuration/method with STEPS and PPA been optimized since the two units have been out on the street for a fair amount of time? 

 Aforementioned, taking into consideration the parts listed on Tangent's Part List sheets and each housed in their _own _enclosure.


----------



## FallenAngel

Quote:


  Originally Posted by *dbfreak* /img/forum/go_quote.gif 
_Excuse me if this has been posted elsewhere... 

 Has the preferred power switch(es) configuration/method with STEPS and PPA been optimized since the two units have been out on the street for a fair amount of time? 

 Aforementioned, taking into consideration the parts listed on Tangent's Part List sheets and each housed in their own enclosure._

 

Sure, 2 boxes, 2 switches.


----------



## LawnGnome

Quote:


  Originally Posted by *dbfreak* /img/forum/go_quote.gif 
_Excuse me if this has been posted elsewhere... 

 Has the preferred power switch(es) configuration/method with STEPS and PPA been optimized since the two units have been out on the street for a fair amount of time? 

 Aforementioned, taking into consideration the parts listed on Tangent's Part List sheets and each housed in their own enclosure._

 

I'm going one box. One switch. The switch will be for the amp, if I want to turn off the psu, I will unplug it.

 I chose this because Tangent says if you power off the psu, while the load is active, you can fry the regulator.


----------



## dbfreak

What is it exactly that I jumper? Do I jumper S1+ to S1- or S1+ to S1+ or S1- to S1-? Please help, everything is done but putting power to the board.

 A simple diagram would be good becuase I'm poor with words.


----------



## MisterX

S1+ holes are for the PSU positive side. 
 S1- holes are for the PSU ground. 


 Jumper both S1+ and S1- if you do not want to connect the power switch to the circuit board. 
 If you wish to use a SPST or SPDT power switch connect the switch to the S1+ pads and jumper the S1-pads. 
 If you wish to use a DPST or DPDT power switch connect one half of the switch to the S1+ pads and the other half of the switch to the S1- pads


----------



## dbfreak

Thanks for the clarification


----------



## dbfreak

Initial power-up of PPA was successful (LED lights up and nothing gets hot). Left channel adjusted to 44mv across output resistors, Ground channel also adjusted to 44mv across output resistor. A problem lies with the right channel. I can only adjust it to 36mv and when I continue turning the trimmer in the positive direction the voltage begins to drop. Any suggestions would be appreciated.


----------



## TzeYang

something's wrong with the trimpot. Perhaps you should try replacing it?


----------



## dbfreak

Will try that.


----------



## MisterX

I seriously doubt the trimmer is at fault. 

 Check the transistors and make sure you have the right ones in the right spots (you may have to bend them over to read the numbers)


----------



## dbfreak

Correct about the trimmer. I have 8 other BB627's so I removed the one in the right channel for another and viola, was able to set the R channel like the others. Wierd, guess one of my OPAMPS arrived defective. Now, to case the beast and hear how it sounds...


----------



## MisterX

That is weird, hope the seller offers a refund for that op-amp because those are not cheap (especially now that they are difficult to find).


----------



## dbfreak

I'm not even going to bother seeing if he'll refund it. I've learned to swallow my losses and carry on. Got a decent deal on them anyway although they are not the BP's.


----------



## dbfreak

Whip me with a wet noodle if this is a dumb question. Is S2R also supposed to be jumpered in PPA's preliminary setup? I found the instructions vague in some areas (and yes, I know there is a silk screened diagram for jumpering 
 S2R on the board). I know it's not me, I did score in the top 1% in reading comprehension (nation-wide) on several of the standardized tests (before they were dumbed down).


----------



## n_maher

Yes, jumper S2R assuming that you don't have bass boost installed. 

 Here's a picture of a completed PPA for your use.


----------



## tangent

Step 2 is "Jumper S2". Are you asking whether this means both S2 positions, or is there some other confusion here?


----------



## dbfreak

Thanks for the pic, it does explain everything now! Yes, there was a bit of confusion but now it's straightened out. I guess, it's my having to deal in facts and specifics everyday that gets me wound up even in my electronics hobby. Again, thanks for the replies.
	

	
	
		
		

		
		
	


	




 Edit: I'm going to switch to unleaded solder now...


----------



## dbfreak

Wow and thank you very much! Flipped the switch and she sounds like heaven. Love that STEPS power supply. She compliments the PPA quite well. Now on to going into class A and adding the bass boost.


----------



## Xyrax

What affect does C2 have on the PPA if they aren't exactly what's specified in the parts selection guide? I realized after I finished building my PPA that I got my C2's backwards. It's specified in the parts selection guide that the ideal set up is 2x .01uf-.022uf and 3x .1uf-.22uf. I must have gotten my part numbers mixed up and used 2x .1uf-.22uf and 3x .01uf-.022uf caps in the C2 positions. Will this cause any problems?


----------



## TzeYang

nah, they're going to work like how it was suppose to be at the first place.

 The thing is to sandwich the lowest capacitance values in between three other higher capacitance values.

 You get better bypassing results this way.


----------



## dbfreak

PPA completed (all voltages within spec and sounds very nice).

 Now on to my question...

 I would like to bias into class A and I understand that each voltage drop across R10 (at 1K) means 1mA. So, I measure across R10G and get 21V, 16V on R10R and 22V R10L. What do I dial the trim pots at? All three channels have BB627's, STEPS power supply at 24V and will be using Grado SR225 headphones. Any help appreciated!

 Added: Is the voltage drop based on the output of the power supply at 24V?


----------



## MisterX

Quote:


 Added: Is the voltage drop based on the output of the power supply at 24V? 
 

The JFET cascode is a constant current source, how effective would it be if it's ouptut depended on a specific PSU voltage? 
	

	
	
		
		

		
		
	


	





  Quote:


 So, I measure across R10G and get 21V, 16V on R10R and 22V R10L. What do I dial the trim pots at? 
 

Adjust the appropriate trimmer until the voltage across the appropriate R10 = 1 volt, this = 1mA of current. 
	

	
	
		
		

		
		
	


	




 (1mA is just a good place to start, feel free to experiment with the "settings" and see how much difference it makes)


----------



## dbfreak

Thanks again MisterX!


----------



## d-cee

I just received a PPAv2 + STEPS stack.

 Here are the essential measurements:
 Gain: ~9
 Output buffer bias: ~45mV (measured across all buffer output resistors)
 Opamp bias: ~1mV (measured across R10)
 Output transistors: BD139 and JE253

 STEPS is putting out 24v.

 However I experienced some strange things.

 Only when using my DT880s I got some wierd funky as distortion/white noise when I turned up the volume knob and it got to a loud part of the a song it would go out of control and then even if I turned down the knob the crazy noise stayed. Is this oscillation?

 It happened in a couple of opamp combinations:
 2 x OPA637 + 1 x OPA627
 and
 3 x AD843

 It only happened with the above opamps and with the 250 ohm DT880, does anyone know what's happening?

 Other headphones/opamps used without issue were K501, K701, DT531, 3 x AD8610, 3 x OPA627, 2 x AD744 (using comp pin hack) + AD829.

 I've ruled out oscillation due to low gain, unless I'm reading/measuring the gain resistors wrong (possibly) here's a picture of the left channel gain resistors, right is identical:





 I plugged the values of R3, R4, R5 and R6 into tangent's gain calculator Electronics Calculators and got ~8.9 if anyone would like to confirm... (I can't figure out how to read resistors, I just measured across their leads with my multimetre)

 What else might cause oscillation or whatever's happening?


----------



## FallenAngel

Uhm... I think I see a few little problems.

 First off, you're mixing MJE253 and BD139, I don't think that's a good idea, even those they are PNP / NPN accordingly, I don't think they work together well, they're opposites - one is much lower output current than the other, you're asking for trouble mixing them.

 Reading 45mV across the output resistors, even with 2R2 resistors is only 20mA of current, which is pretty low and you're likely to want to raise it to decrease the chance of oscillation. Even using 2R2 isn't advised because it might be unstable, I upped mine to 4R7 to stabilize the buffer.

 The AD843 is also a little cranky in the PPAv2 for some reason, I read Tangent had problems with this chip, especially in ground (as well as on Pimeta) not sure why, but I didn't chance it using this chip.


----------



## d-cee

Thanks. 

 I didn't actually build the amp and I'm not too up with the technical things. I don't have any other transistors to swap in, so for the mean time I'll try to tweak the bias.

 I somehow mistook mV for mA and I read on tangen't site that 30-40mA was the max before no more improvements kicked in. I read 45mV and thought that must be ok and considering the amp stayed fairly cool I thought it ok.

 I've now adjusted it so that I'm reading ~85mV across the 2R2 resistors (these resistors were easy to read 
	

	
	
		
		

		
			





)

 One thing I'm a little confused about is if it's lack of output current why it's happening to the DT880. It's quite high impedance so shouldn't something like my 62ohm K701s heard the problem first?


----------



## FallenAngel

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_Thanks. 

 I didn't actually build the amp and I'm not too up with the technical things. I don't have any other transistors to swap in, so for the mean time I'll try to tweak the bias.

 I somehow mistook mV for mA and I read on tangen't site that 30-40mA was the max before no more improvements kicked in. I read 45mV and thought that must be ok and considering the amp stayed fairly cool I thought it ok.

 I've now adjusted it so that I'm reading ~85mV across the 2R2 resistors (these resistors were easy to read 
	

	
	
		
		

		
		
	


	




)

 One thing I'm a little confused about is if it's lack of output current why it's happening to the DT880. It's quite high impedance so shouldn't something like my 62ohm K701s heard the problem first?_

 

Wait! 85mV is WAY over what's safe! That's almost 50mA, you're about to burn your output stage! Get it to about 66mV! That'll be 30mA. I had mine running at 35mA and the top of the case gets pretty warm within an hour, after a few it gets VERY warm.


----------



## d-cee

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Wait! 85mV is WAY over what's safe! That's almost 50mA, you're about to burn your output stage! Get it to about 66mV! That'll be 30mA. I had mine running at 35mA and the top of the case gets pretty warm within an hour, after a few it gets VERY warm._

 

i see. i thought under 40mA (85 / 2.2 = ~38) was ok... thank goodness it's only been on for about 6 minutes (1 test song)

 i touched the top of the output transistors and they seemed warm but not too hot, i will drop it as per your recommendation

 i have been listening to it just now with 2 x OPA637 and 1 x OPA627 and it's working fine no more funky crazy distortion/white noise.


----------



## FallenAngel

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_i see. i thought under 40mA (85 / 2.2 = ~38) was ok... thank goodness it's only been on for about 6 minutes (1 test song)

 i touched the top of the output transistors and they seemed warm but not too hot, i will drop it as per your recommendation

 i have been listening to it just now with 2 x OPA637 and 1 x OPA627 and it's working fine no more funky crazy distortion/white noise._

 

Nice, I had some trouble with those opamps with 2R2 and a low bias as well, upped the bias and got stability everywhere except IEMs, then switched to 4R7 and everything worked perfectly at 25-30mA.

 Edit: My mistake on the bias setting, it's very late here, I'm going to sleep


----------



## d-cee

ok i'm measuring about 65mV across the output resistors which works out to be about 29.5mA working stably with the 2 x OPA637 + OPA627

 still no luck with the AD843 though. oh well.

 so what's the general concensus about opamp biasing? i've got a 1k resistor there and reading 1v so that's 1mA what are the limits?

 thanks =)

 edit: one more thing, when measuring DC offset at the jack between L + G and R + G, i get <10mV up until about 80% on the pot, at which point is very rapidly increases until it reaches about 45mV @ 100% pot.

 in fear of deafness I never see myself going past 50% on the pot but is this kind of behaviour normal?


----------



## FallenAngel

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_ok i'm measuring about 65mV across the output resistors which works out to be about 29.5mA working stably with the 2 x OPA637 + OPA627

 still no luck with the AD843 though. oh well.

 so what's the general concensus about opamp biasing? i've got a 1k resistor there and reading 1v so that's 1mA what are the limits?

 thanks =)

 edit: one more thing, when measuring DC offset at the jack between L + G and R + G, i get <10mV up until about 80% on the pot, at which point is very rapidly increases until it reaches about 45mV @ 100% pot.

 in fear of deafness I never see myself going past 50% on the pot but is this kind of behaviour normal?_

 

I bias my opamps into Class-A to about 3mA, no harm in it, but probably minimal performance increase as well, but for an extra 2mA of current draw, why not 
	

	
	
		
		

		
		
	


	




 This amp generally should not see ANY DC offset (as long as the transistors are matched - but in your case with MJE253 + BD139, they are definitely not). <10mV is OK, 45mV is pretty bad.

 Personally, I would recommend replacing the BD139 with MJE243 which should definitely help stabilize your amp, MJE253 and MJE243 are complimentary pairs and I think you're only supposed to use complimentary pairs in this situation.


----------



## d-cee

Well, maybe it was just waiting to happen and this sped it up but as I increased the opamp bias one of my AD744 kicked the bucket.

 As I did my routine checks after each change, I noticed that the DC offset in one of my channels was 2.5v ! yikes, so I swapped the AD744 between left and right and sure enough the offset moved to the other channel.

 Thankfully I got a spare AD744, popped it in and it's all good.

 I have it biased to 2mA at the moment and nothing else has happened, is this a safe value or should I drop it further?

 I'm using the comp pin of my AD744 if that makes a difference.


----------



## n_maher

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_Thanks. 

 I didn't actually build the amp and I'm not too up with the technical things. I don't have any other transistors to swap in, so for the mean time I'll try to tweak the bias._

 

I'll check my parts box and see if I have what you need. I agree that mixed output transistors at least sounds like a bad idea to me, not sure if it would actually cause any problems.

  Quote:


 One thing I'm a little confused about is if it's lack of output current why it's happening to the DT880. It's quite high impedance so shouldn't something like my 62ohm K701s heard the problem first? 
 

Impedance doesn't tell the whole story, you should look at it in concert with the phones relative sensitivity. Those two put together are a much better measure (from what I understand) of how hard they are to drive. 

 DT880 = 96 dB /mW
 K701 = 105 dB / mW


----------



## d-cee

thanks nate

 i'm currently researching my options re: output transistors

 if anyone has an opinion i'd love to hear it


----------



## tsaavik

Hello all, have a ppaV2 ad8610 running 30ma bias with 1ma class A. Power is 24v from steps running around .16ma 

 dc offset is (gnd probe to input gnd):
 -0.4mv right
 0.1mv gnd
 -1.0mv left

 I'm seeing large (1.5v) dc output between input ground and output upon poweroff. My meter goes to 0, then jumps up to 1.5v or so, then slowly drains down to 0. I also have turn on thumb, but i only see about .5v during poweron.

 Is this normal/okay? Should i consider adding a ε12 type circuit? I'm double checking this amp because i had a mysterious headphone failure that I'm hoping not to repeat.


----------



## FallenAngel

Quote:


  Originally Posted by *tsaavik* /img/forum/go_quote.gif 
_Hello all, have a ppaV2 ad8610 running 30ma bias with 1ma class A. Power is 24v from steps running around .16ma 

 dc offset is (gnd probe to input gnd):
 -0.4mv right
 0.1mv gnd
 -1.0mv left

 I'm seeing large (1.5v) dc output between input ground and output upon poweroff. My meter goes to 0, then jumps up to 1.5v or so, then slowly drains down to 0. I also have turn on thumb, but i only see about .5v during poweron.

 Is this normal/okay? Should i consider adding a ε12 type circuit? I'm double checking this amp because i had a mysterious headphone failure that I'm hoping not to repeat._

 

DC offset is measured from output ground


----------



## tsaavik

Whoops, here is the numbers measuring output ground to left/right channel.

  Code:


```
[left]ACTION LEFT RIGHT ------------+-----------+------------ Min Vol | -1.1mv | -1.2mv Max Vol | -1.1mv | -1.3mv MinVol+bass | -4.1mv | -3.9mv MaxVol+bass | -4.2mv | -3.8mv Turn off | +1.2v peak| +1.2v peak Turn on | +.367 peak| +.5v peak[/left]
```

I have an ancient fluke that doesn't have a min/max button so the peaks are kinda guesses. I turned it on and off a bunch and just grabbed the highest number i saw. All tests were run with a really crappy pair of Walkman style headphones plugged in.


----------



## FallenAngel

Quote:


  Originally Posted by *tsaavik* /img/forum/go_quote.gif 
_Whoops, here is the numbers measuring output ground to left/right channel.

  Code:



		Code:
	

[left]ACTION LEFT RIGHT ------------+-----------+------------ Min Vol | -1.1mv | -1.2mv Max Vol | -1.1mv | -1.3mv MinVol+bass | -4.1mv | -3.9mv MaxVol+bass | -4.2mv | -3.8mv Turn off | +1.2v peak| +1.2v peak Turn on | +.367 peak| +5v peak[/left]


I have an ancient fluke that doesn't have a min/max button so the peaks are kinda guesses. I turned it on and off a bunch and just grabbed the highest number i saw. All tests were run with a really crappy pair of Walkman style headphones plugged in._

 

That looks fine, the turn on/off thump isn't great, but I think I get something similar and haven't had any problems.


----------



## tangent

Quote:


  Originally Posted by *tsaavik* /img/forum/go_quote.gif 
_I'm seeing large (1.5v) dc output between input ground and output upon poweroff_

 

Unless you're using super-sensitive headphones, this will just be a loud click.

 How much rail capacitance do you have?


----------



## tsaavik

I have beyerdynamics dt770/pro 80ohm headphones.
 They don't seem to list the sensitivity on their website anywhere. I'll check the box when i get home. It does say the Power handling capacity is 100 mW

 I have 1880uF made up of 4 Cerafine 470uF/25V caps.
 Got them for a great price online, guess where


----------



## tangent

P=V^2/R, so 1.5 V across 80 ohms is 28 mW. You're fine.


----------



## d-cee

I've found the type of opamps make a difference on the startup bump

 AD744 comp pins out w/ AD829 ground makes a barely audible thud

 same goes for the LME49710. AD8610 has loud whack, as does OPA637 w/ OPA627 ground


----------



## Beefy

Hey d-cee......

 Where are you getting all of your different opamps? Did they come with the amp or are you buying them from somewhere?

 I ordered some OPA637 from eBay seller 'Parts and Audio' just yesterday for my upcoming M^3 build, and will probably get some OPA627 as well - but am definitely on the lookout for a few different parts sources......

 Cheers!


----------



## d-cee

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_Hey d-cee......

 Where are you getting all of your different opamps? Did they come with the amp or are you buying them from somewhere?

 I ordered some OPA637 from eBay seller 'Parts and Audio' just yesterday for my upcoming M^3 build, and will probably get some OPA627 as well - but am definitely on the lookout for a few different parts sources......

 Cheers!_

 

http://www.futurelec.com.au/ 

 Good prices, and shipping is only like $4 (for small package of opamps) and most stuff is in stock. Their range is pretty good too.

 I don't trust eBay to be honest, lots of fake stuff =\

 The LME49710 I got as samples straight from national


----------



## Beefy

Thanks for that. The 627's are a good price, but the 637's are really pricey. I'll see what comes through from my eBay order for the 637's, and decide what I want to do.......


----------



## Beefy

To anyone who is interested.......

 My 637's arrived from eBay seller 'Parts and Audio' the other day, and they seem pretty genuine to me. The chips are painted with two colours, and I figure it would take more money effort to fake this than it would to source and sell real ones......

 As such, I also picked up a set of 627BP's. They were only US$2 more than the AP, so why not? My M^3 is finished and running AD8610's A-O-K, and I'll start playing round with these OPAMPs as soon as it is cased up.


----------



## oicdn

Are OPA627's the best opamp for Grado's (SR80 and RS2's) as compared to AD8610's? What are the sonic differences between the two all other things being equal?


----------



## d-cee

Quote:


  Originally Posted by *oicdn* /img/forum/go_quote.gif 
_Are OPA627's the best opamp for Grado's (SR80 and RS2's) as compared to AD8610's? What are the sonic differences between the two all other things being equal?_

 

Don't know about Grados, but the AD8610 imho are a bit dry sounding, with a slightly brittle treble. This may give the impression of being detailed but I find the OPA627/OPA637 to be more detailed while sounding more relaxed in the treble region and smoother in the mids.


----------



## Beefy

Quote:


  Originally Posted by *oicdn* /img/forum/go_quote.gif 
_Are OPA627's the best opamp for Grado's (SR80 and RS2's) as compared to AD8610's? What are the sonic differences between the two all other things being equal?_

 

Perhaps try this link: Notes on Audio Op-Amps

 Theoretically, any of the OPA models should be good for Grado cans because they tend to be smoother and more laid back. The AD models tend to be more detailed and sharp.

 But keep in mind that the tests are done on a modified Cmoy, where the OPAMP is directly driving the headphones. In any amplifier where the OPAMP has low output impedance due to a discrete driver stage, and a higher voltage supply, the relative strengths and weaknesses between individual chips will become less and less obvious.


----------



## d-cee

Well I finally replaced the output transistors on my PPA

 While I was there I replaced the 1W 2.2R resistors with 2W 4.7R ones.

 For the transistors I bought a whole bunch of a 2SA1930 and 2SC5171 by Toshiba. I found 3 pairs that were all quite closely matched.

 These are complementary PNP and NPN transistors however you must turn them 180 degrees as their orientation is reversed. They are physically larger than the BD/MJE but fit quite easily on the board.

 Well I'm very pleased with the sound now. Not only does the DC offset never go above 5mV the sound is also much smoother cleaner sounding than with the BD139/MJE253.

 I've got the transistors biased to about 25mA and everything seems stable at the moment. It's also staying pretty cool too.


----------



## tomb

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_Well I finally replaced the output transistors on my PPA

 While I was there I replaced the 1W 2.2R resistors with 2W 4.7R ones.

 For the transistors I bought a whole bunch of a 2SA1930 and 2SC5171 by Toshiba. I found 3 pairs that were all quite closely matched.

 These are complementary PNP and NPN transistors however you must turn them 180 degrees as their orientation is reversed. They are physically larger than the BD/MJE but fit quite easily on the board.

 Well I'm very pleased with the sound now. Not only does the DC offset never go above 5mV the sound is also much smoother cleaner sounding than with the BD139/MJE253.

 I've got the transistors biased to about 25mA and everything seems stable at the moment. It's also staying pretty cool too._

 

I'd like to hear more of your comments on the 2SC5171/2SA1930 transistor pair. Those are not often used, but they have an unbeatable ft and Ic rating, at 200MHz and 180A, respectively. Steinchen describes them as "warm to dark sound, yet detailed, slightly pronounced bass, smooth highs" in his Millett DB and JISBOS transistor reviews. I've had a bunch that I've been meaning to try for awhile in a MAX, but in other posts from him, I've gathered that the emphasis is on "dark." That's probably not an issue with the PPA, especially if the reulting bass is "pronounced." I've also wondered if higher biases might let the 2SC5171/2SA1930 run at a better operating point and open them up more. Anyway, your experience and listening impressions would be most welcome.

 Glad to hear you got it fixed.


----------



## d-cee

Compared to the BD139/MJE253 combo the sound is at least as detailed if not moreso.

 The treble sizzle that was there previously is now gone. Personally I don't mind a bit of hot treble, but I do notice it. Not enough to get on my nerves though. Obviously sibilance I can't stand.

 The 2SC5171/2SA1930 are really nice though, no harshness whatsoever yet very resolving and smooth sounding. Comparatively it is warmer sounding, the PPAv2 is a pretty crisp sounding amp (IMHO) so these transistors aren't too out of place in balancing the sound. But these are only the second set of transistors I've used. I have some matched BD139/BD140 that I might experiment with later, but atm very happy with these.

 If heatsinks are board mounted it may pose a problem since you must rotate them.

 Give me a few more days to get more thorough impressions as these are just freshly installed. But for the time being it's all pretty positive, nothing obviously offensive to speak of anyway.


----------



## d-cee

It's been a couple of days, and my impression remain unchanged.

 The detail on the 2SC5171/2SA1930 does not give the impression of being detailed, ie. shouty treble, but instead is back in the mix.

 I don't know how it sounds with tubes in front of but with opamps/transistors (AD744/AD829) in the gain stage these transistors sound flat on neutral.

 This is with the DT880 and K701, which some consider bright sounding phones. So it may be that they are the equalising component among bright-ish parts.


----------



## tomb

Quote:


  Originally Posted by *d-cee* /img/forum/go_quote.gif 
_It's been a couple of days, and my impression remain unchanged.

 The detail on the 2SC5171/2SA1930 does not give the impression of being detailed, ie. shouty treble, but instead is back in the mix.

 I don't know how it sounds with tubes in front of but with opamps/transistors (AD744/AD829) in the gain stage these transistors sound flat on neutral.

 This is with the DT880 and K701, which some consider bright sounding phones. So it may be that they are the equalising component among bright-ish parts._

 

Thanks for the additional comments! I will have to give these BJT's a try.


----------



## Jelle Schrijver

coming from this thread, but seems to have died there and this thread could be a good home 
	

	
	
		
		

		
			





  Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_For the more techy's among us, have a read over at altmann SPLIF. This could be a way to decouple the amp from the headphone. Am not sure if/or it will work, but the chip TLE2426, mounted between + and - of the battery and the mass connection of the headphone ONLY connected to the chips 0V connection. Sound much simpler then the 3rd ampchannel and would propebly do the same thing. 

 and talking serious modding here, that tube-o-later stuff on the op-apamp sounds like a good idea. I think, reading all his websited and absorbing his knowledge, it is a carbon (dutch:grafiet) subspended in a natural resin (dutch: natuurlijke hars zoals dennehars). To apply mix all ingredients and use alcohol so make the resin liquid. Apply, let alchol dry and you're set. 

 Anyhow, just kicking some idea's around and putting in my 2 cents worth. (now everything is 2 cents off 
	

	
	
		
		

		
		
	


	




)_

 

 Quote:


  Originally Posted by *Ferrari* /img/forum/go_quote.gif 
_NO, it doesn't ! By using the TLE2426 rail splitter chip, you can create a "virtual signal ground", nothing more or less.
 But still, this "virtual signal ground" is passive... as all other *"passive ground"* in conventional 2-channel amplifiers.

 Conventional 2-channel *"passive ground"* amplifier differs from 3-channel *"active ground"* amplifier in the way how the return current from the drivers (from the speakers in the headphone) is handled. A conventional 2-channel "passive ground" amplifier just dumped the return current from the drivers into the "virtual signal ground" (= "passive ground") created by the TLE2426 rail splitter chip (the "ground" wire of the headphone is connected to chips 0V point, according to you).

 As opposed to 2-channel "passive ground" amplifiers, in a 3-channel "active ground" amplifier, the "ground" wire of the headphone is driven by a third channel of the same topology as the left and right channels (thus 3 amplifiers of the same design). The "active ground" (ground channel amplifier) sinks or sources the return current from the drivers, and this is fundamentally different from what the "virtual signal ground" (= "passive ground") does in a conventional way. 
	

	
	
		
		

		
		
	


	


_

 

 Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_@ ferrari

 but........

 the whole idea is to keep the reference ground for the voltage amplifying opamp clean from those return currents. 

 3ch topology does this by adding a 3rd amplifier tied to ground, so the opamp sends the returning current back to the PSU to maintain 0V at its output and also input.

 The way i understand the TLE2426 works, is that it takes the + (Top leg) and the - (bottom leg) PSU and creates a voltage out right between these too. So this becomes a reference 0V (middle leg). 

 In the case the TLE does not sense its output, then the current from the headphone mass can not flow anymore (because the TLE is ONLY connected to + and - PSU and is in no way connected to our precious reference ground the opamps use (the use there own TLE like PPA). In that case something is gone blow or there is no sound by lack of flowing current. 

 In the case the TLE does sense its output (middle leg), which i think is how it works, then any current (and thus voltage) wil upset the 0V reference and it will bleed away the acces to get back to 0V. In doing so differting the current back to the PSU and keeping it clear from our opamp reference 0V. My only concern is when there is an offset between opamp reference 0V and the 0V created by the TLE headphone side. This could introduce a offset and so burn a headphone by DC current. 

 My scanner/printer is currently down, so i can not chalk a schematic too clear this out. Also i have to find a place on the internet to store the photo to be referenced here. If it is still not clear and there is interest in this topology, please let me know, then i will try to post a schematic of what i am meaning.

 In any case, i believe that a complete amp channel to differt the returning current is a bit over the top and a more simpler solution could be invented here to do the trick. (making the whole schematic smaller and more energie efficient, which are great bonuses for a portable amp).

 And what do you think of using the SPLIF in the PPA design? The buffer makes it very easy to insert such a topology. My only concern is how it will effect the offset. (DC servo perhaps?) And what resistor value to use for baising the reference feedback loop and how this will influence the gain._

 

Love to hear everybody's input over the suggested items.


----------



## amb

Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_In the case the TLE does sense its output (middle leg), which i think is how it works, then any current (and thus voltage) wil upset the 0V reference and it will bleed away the acces to get back to 0V. In doing so differting the current back to the PSU and keeping it clear from our opamp reference 0V. My only concern is when there is an offset between opamp reference 0V and the 0V created by the TLE headphone side. This could introduce a offset and so burn a headphone by DC current._

 

The 3-channel active ground design has been around for quite a long time now and is employed in several popular headphone amp designs around here with great results. You are should search for relevant discussions already in these forums (and at headwize.com).

 The headphone's return current doesn't "stop". It has to go somewhere to complete the current loop. In a conventional passive ground amp it goes back to the PSU via the passive ground. High currents flowing through a passive ground that has finite impedance will induce small voltage fluctuations in the ground (simple Ohm's Law). This gives rise to signal ground pollution.

 In a TLE2426-only virtual ground amp (i.e., cmoy with TLE2426), the load return current goes to virtual ground, and is then diverted to the supply rails by the TLE2426. Since the virtual ground is also the small signal ground reference, it has the same drawback as passive ground (i.e., signal ground pollution). Moreover, TLE2426's maximum current rating is only 20mA. Considering that this virtual ground must source and sink the return current from both stereo channels, it is quite inadequate for a high performance headphone system, particularly with low-impedance headphones.

 In a 3-channel active-ground amp, the load return current is diverted directly to the supply rails by the ground channel amp. The active-ground's current capability is limited only by the robustness of its output stage design. The load return current does not go to ground at all (whether passive or virtual), and thus signal ground pollution cannot occur.

 As far as your "concern" cited above, I can assure you it's completely unfounded.


----------



## Jelle Schrijver

Quote:


  Originally Posted by *Ferrari* /img/forum/go_quote.gif 
_Why should you want to add that into a well performing 3-channel active ground amplifier like the PPAV2 ?
 What is the benefit then? Adding some more parts? more cumbersom wirings? creating some trouble which you not sure how to fix? increasing the cost?

 About your described concern, there is no foundation for that from electronics engineering viewpoint!
 If you think that there is a foundation for that, I would love to hear._

 

 Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_@ ferrari,

 it's about ditching the third channel all together, so making it
 1) smaller, for portable applications.
 2) cheaper, less parts easier schematic
 3) bringing 3ch topology to other 2 channel amps.

 if moved this topic to here_

 

So the TLE 2426 is not up for the job, is there a replacement which handles more current??

 Also i feel the suposed schematic is unclear so i took the liberty to make the schematic as subscribed above. Including the SPLIF and complete isolated headphone ground. May be this schematic makes it clear why i suspect offset (spliff and NO connection between opamp ground and headphone ground). Hope it is more clear what i am supossing here. The third (ground) channel is completly dropped all together and replaced with the TLE2426. May be there needs to be a DC servo kinda thing on headphone ground and/or headphone buffer to prevent offset frying your expansive headphone/iem.


----------



## tangent

Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_So the TLE 2426 is not up for the job, is there a replacement which handles more current??_

 

There is no monolithic replacement for the TLE2426, period. You can make one out of separate parts, but to get the same benefit as a three-channel amp, you basically end up reinventing it. Read my article on virtual grounds to see the progression from a lone TLE to this third channel. If you don't like the complete third channel idea, maybe there is a stopping point somewhere along the progression that you will like.

 As for your schematic, there are two problems. 

 First, those JFETs are likely to choke down on the TLE's low current limit even further, as JFETs with Idss guaranteed over 20mA aren't the most common. We can get away with this in the PPA because the TLE's aren't being asked to source much current; this is one of the benefits we get from the "complicated" third channel. 

 Second, your buffer scheme doesn't make sense to me. It seems to make the amp into a mono amp with dual outputs, one of which isn't under feedback control. What are you trying to accomplish with those dual buffers?


----------



## Jelle Schrijver

@ tangent

 Thanks for your input. Seems like there's no cheating on the 3rd ampchannel. pitty.
 edit: When i saw the schematic of the PPA, i first pounderd for a while what the benefits where of the 3rd channel. And after figuring that one out, it feelt like overkill to use a complete ampchannel to sink the returning currents and started thinking about a more simple solution. So the above is what i came up with. 

 About the 2nd buffer. It's the SPLIF topology explained over here. The general idea is to prevent influence of the headphone/speaker getting into the feedbackloop, creating a sort of (very)shortdelay. The results altmann got was a more natural, relaxed sound more like the single ended non feedback kind of amps. So taking both the advantages of a feedback loop and non-feedback kinda amps. But on his page there's a very clear explenation of the SPLIF topology. 

 The 32 ohm resistor is a stable reference to make the opamps work. To get the same signal you use the buffer 2x. (with 2 different buffers you're propably gone make wrong corrections to the buffer connected to the headphone/speaker).


----------



## amb

Jelle Schrijver, so on the one hand you say that the third, ground channel is "too complicated" and "overkill", and then you proceed to add a whole new output buffer _per stereo channel_ (in effect making the amp 4-channels) to implement SPLIF?

 Second, I am not convinced that driving the headphone load separately (with another ouput stage that isn't under feedback control) is really beneficial. The primary purpose of negative feedback is output error correction, and by including the load in the loop, the amp corrects for errors (and therefore reduces distortion) that are caused by the load. SPLIF seems to deliberately lose that benefit.


----------



## Jelle Schrijver

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Jelle Schrijver, so on the one hand you say that the third, ground channel is "too complicated" and "overkill", and then you proceed to add a whole new output buffer per stereo channel (in effect making the amp 4-channels) to implement SPLIF?

 Second, I am not convinced that driving the headphone load separately (with another ouput stage that isn't under feedback control) is really beneficial. The primary purpose of negative feedback is output error correction, and by including the load in the loop, the amp corrects for errors (and therefore reduces distortion) that are caused by the load. SPLIF seems to deliberately lose that benefit._

 

First off; i am not saying, just wondering. Keeping in mind for a simple mod for 2 ch amps to convert to a 3ch amp and also for a ultra portable ppa... (lisa 3 still looks a little big to me)

 About SPLIF, yes it seems strange to add a whole buffer, but it is possible to only use the output pair of the buffer driving the reference load. That is, if the input pair of transistors in the buffer kan handle 2 pair of output transistors. (That's more simple 
	

	
	
		
		

		
		
	


	




 ). But for my ease (read lazyness) of drawing the schematic, i used the complete buffer picture. 

 Good point of using the feedback to also correct the headphone influence, but the whole idea of SPLIF is to isolate the driver from the feedback loop. I urge you the have a read over at altmann's website, where he makes a good and funny explanetion about the SPLIF topology. Ever noticed how SET amps without feedback sound different? Agian, the idea behind SPLIF is too combine the control and low distortion of feedback, with the joy the vivre (or music in our case) of feedback less amps. 

 Though i am not an experienced amp designer/builder (which you would have geussed by now 
	

	
	
		
		

		
		
	


	




 ), i DO have a lot of experience of how amps sound. Using also my bass as a reference. Of the several basses i have owned, there where a lot of active basses, meaning that there was a battery operated preamp at work. Most of the time opamps. I have noticed, and with the explaination of altmann's website, found out, that musical texture was lost when using the preamp. Active basses sound less musical in my ears. This is why several bassplayers only play passive basses, dispite the disadvantages of playing passive.


----------



## amb

Quote:


  Originally Posted by *Jelle Schrijver* /img/forum/go_quote.gif 
_Keeping in mind for a simple mod for 2 ch amps to convert to a 3ch amp and also for a ultra portable ppa... (lisa 3 still looks a little big to me)_

 

LISA III is too big to be called a portable, but the Mini³ is also a 3-channel active ground amp, and it's tiny (the footprint of a credit card, and about 0.9" thick). There was a DIY project called PPAS which is an adaptation of the PPA topology with some modifications and all SMD parts, and it also fits in the same size case as the Mini³.

  Quote:


 Good point of using the feedback to also correct the headphone influence, but the whole idea of SPLIF is to isolate the driver from the feedback loop. I urge you the have a read over at altmann's website, where he makes a good and funny explanetion about the SPLIF topology. Ever noticed how SET amps without feedback sound different? Agian, the idea behind SPLIF is too combine the control and low distortion of feedback, with the joy the vivre (or music in our case) of feedback less amps. 
 

Yes, I did read it. I am not convinced. By the way, SET amps have feedback, just not in a global loop. There is really no such thing as a "feedback-less" amp. Trust me. Only where, how, and how much.

 If the goal of an amp is to faithfully pass/amplify the input signal without adding coloration, then let's not get into a discussion about how an amp "sounds". That's a rat hole all its own.


----------



## Steve The Egg

What is the price for these amps? I'd want some one to build it for me btw. 
	

	
	
		
		

		
		
	


	




 I have Grado SR-80's with M-AUDIO 5.1 Revo. I figured I'd get this amp first and then get the Keces 131. Are all those a good match and good for upgrading to better headphones in the future? I figure I'll get the amp first since I can use that and if I get the DAC then it'll just be useless sitting on my desk. What do you guys think? Also is there anyone willing to build me one


----------



## rds

these aren't cheap


----------



## d-cee

I've seen a few go through on the FS/FT boards

 Maybe do a WTB and commission someone to build it.


----------



## Steve The Egg

Are they worth it? And does this amp work well with almost everything? I was this to be something I'll own for a loooooong time.


----------



## FallenAngel

Quote:


  Originally Posted by *Steve The Egg* /img/forum/go_quote.gif 
_Are they worth it? And does this amp work well with almost everything? I was this to be something I'll own for a loooooong time._

 

I consider this my best amp and I've had MANY. It beat my all of my other creations for detail, clarity and basically enjoyment of listening (that would include the CKK-III, SOHA, Millet MAX).


----------



## rds

If you want to buy one amp and call it quits, I think this is the one


----------



## Jelle Schrijver

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_... By the way, SET amps have feedback, just not in a global loop. There is really no such thing as a "feedback-less" amp. Trust me. Only where, how, and how much._

 

Hi Amb, thought of your input when watching the picture here below. Would you be kind enough the tell me where the feedback loop is? Not being a brad here, but just trying to learn a little more. Thanks


----------



## amb

Jelle Schrijver, the Szekeres is a simple MOSFET source follower (aka common-drain amplifier). It has no voltage gain and therefore there isn't the classic "feedback" that we speak of. Feedback is usually applied to reduce the voltage gain (at the same time achieve a lowered output impedance, cancel distortion and extend the bandwidth).

 If the amp had been a common-source amp, where the output is taken from the drain pin, then there has to be a resistor from the positive rail to the drain pin, and the ratio of resistance between the drain resistor and the source resistor would determine (roughtly) the voltage gain of the amp. This is called "local feedback", and even though it doesn't look like a loop, it has the same effect.

 The same thing applies to a BJT-based common-emitter amp. In fact, it is a basic building block of more complex topologies, where there is local feedback at each stage, and often also a global feedback loop spanning multiple stages, from the output back to the input.


----------



## Steve The Egg

What are STEPS and OPA627?

 Will they help my performance? Are they worth it?


----------



## d-cee

STEPS = single-voltage tangeant easy power supply - Tangent Easy Power Supply

 OPA627 = a single channel opamp that can be used in the PPA and other amps. made by texas instruments under the burr brown name - Precision High-Speed Difet(R) Operational Amplifiers - OPA627 - TI Product Folder

 your question is a little ambiguous, do you currently have a PPA? what performance improvements do you seek?


----------



## Steve The Egg

No, I don't already have one. I'm looking to get one and I don't know whether I should get it with these. I'll be using it with a Keces 131 DAC, SR-80, and soon some D2000's. I'm basically looking for an amp that I'll never have to upgrade again. I want it to be as transparent as possible.


----------



## Beefy

Quote:


  Originally Posted by *Steve The Egg* /img/forum/go_quote.gif 
_I'm basically looking for an amp that I'll never have to upgrade again._

 

You don't understand this hobby very well, do you? 
	

	
	
		
		

		
			





 In all seriousness, I don't know much about the PPAv2..... but I do know that a STEPS is a very good power supply option. The σ11 over at AMB is a newer design that is arguably 'better', but more expensive. The OPA627 is definitely a premium OPAMP, but there are counterfeits going around - so make sure you get them from a reliable source such as Digikey.


----------



## luvdunhill

hey guys, I'm a problem with my battery pack. It has been left unused for easily more that the 30 days mentioned in the docs and the cells are depressed. I am using a 24v supply, LM317, R1=1k, R2=4.7R, R4=100k, R5=10k, R6=closed, R7=closed, R8=open. I'm getting 2.05v from the R4/R5 node to V-. I'm assuming something is wrong with my battery pack? This exact configuration has worked in the past, nothing has changed. I'm using a 24VAC @ .45A AC wall wart into a TREAD and am getting exactly 24v DC output into the TREAD. 

 Thanks!


----------



## tangent

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I'm getting 2.05v from the R4/R5 node to V_

 

That symptom suggests the opposite of a depressed battery pack: the charge controller would be in trickle-only mode because Vsen was under 1 V.

 Check the pack's health by measuring across it with the charging supply disconnected. If you get approximately 1.2-1.6 * cells, go back and measure across each one to see if any are exceptionally low, like under 0.1 V. If the pack is fine, I'd recheck your R4 and R5 values. I haven't run the numbers, but in my experience, you rarely get such common values out of the calculator without going way down the list of possibles.


----------



## luvdunhill

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_That symptom suggests the opposite of a depressed battery pack: the charge controller would be in trickle-only mode because Vsen was under 1 V.

 Check the pack's health by measuring across it with the charging supply disconnected. If you get approximately 1.2-1.6 * cells, go back and measure across each one to see if any are exceptionally low, like under 0.1 V. If the pack is fine, I'd recheck your R4 and R5 values. I haven't run the numbers, but in my experience, you rarely get such common values out of the calculator without going way down the list of possibles._

 

ok, will do. As for the values I choose, I picked them directly off the bottom of the part selection guide, here, under "12× AAA, 2.8 hour fast charge":

Part Selection Guide

 Now, putting 12 cells @ 650mAH, charge time 2.8 hours into the calc, I get:

 Supply >= 23.75V

 U1 = LM317
 Add U2 and U4
 Add U3

 R1 = 390 Ohms or higher
 R2 = 5.6 Ohms (174.72 min. fast charging, 0.28W, 0.22A)

 R4 = 75K, R5 = 8.2K(Vsen: 1.06 - 1.83V)
 R4 = 82K, R5 = 9.1K(Vsen: 1.08 - 1.86V)
 R4 = 91K, R5 = 10K(Vsen: 1.07 - 1.84V)
 R4 = 82K, R5 = 8.2K(Vsen: 0.98 - 1.69V)
 R4 = 91K, R5 = 9.1K(Vsen: 0.98 - 1.69V)
 R4 = 100K, R5 = 10K(Vsen: 0.98 - 1.69V)

 R6 short, R7 short, R8 open (177 mins)

 The discrepancy is in R2 and 100K/10K is the last option in the table. What would you recommend doing? The LED is indeed always on (it doesn't blink).

 I'll measure the cells when I get home tonite.


----------



## tangent

So yeah, 100K and 10K aren't great because they're not giving you as wide a Vsen range as you could get with the first choice on that list. But that calls into question why such a divider is letting 2.05 V through to Vsen. 2.05 V * 11 (the reduction factor) is 22.55 V, almost your full supply voltage. Maybe the regulator's shorted?


----------



## luvdunhill

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_So yeah, 100K and 10K aren't great because they're not giving you as wide a Vsen range as you could get with the first choice on that list. But that calls into question why such a divider is letting 2.05 V through to Vsen. 2.05 V * 11 (the reduction factor) is 22.55 V, almost your full supply voltage. Maybe the regulator's shorted?_

 

yes. So, total voltage across the pack is 0 volts. There are 2 cells that measure zero volts on the 200mV range of my meter. The rest measure:

 .025
 .059
 .918
 .032
 .050
 .031
 .092
 .047
 .031
 .043

 Also, looks like my regulator is a LDO. I'm using LM1086CT-ADJ. All the resistor values measure fine and the diodes check out using the diode check. Perhaps U2/U4 is bad, or is definitely due to the 0v cells...

 Thanks so much!


----------



## luvdunhill

Nah, I think the cells are find and so are the TLEs. I'll sit down with the schematic tomorrow and see what I can find


----------



## Beefy

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_There are 2 cells that measure zero volts on the 200mV range of my meter. The rest measure:_

 

Wow, they are _really_ dead. Regardless of how the rest of it works out, I would definitely beg/borrow/steal a proper battery conditioner in order to bring those cells back to life.

 Or perhaps invest in some newer, higher capacity, low self discharge NiMH batteries like Sanyo Eneloop or Powerex Imedion. These batteries really are the best you can buy IMHO.


----------



## luvdunhill

problem was a faulty cell carrier. I have worked a fix for it and have raised R2 to 5.6 ohms, as I had one on hand. Seems that you are recommending to change R4 = 75K, R5 = 8.2K, which are the first items in the calculator output and will give Vsen: 1.06 - 1.83V. Off to the store to pick up some resistors then.

 Do you recommend using another charger to bring up the cells, or just fix the voltage divider let the battery board do its thing? I'm getting less than 1v across the entire pack.


----------



## Beefy

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_Do you recommend using another charger to bring up the cells, or just fix the voltage divider let the battery board do its thing? I'm getting less than 1v across the entire pack._

 

As I said in my previous post, beg/borrow/steal a battery conditioner. These cells will need to be very carefully charged.

 At an absolute minimum you should charge them at a very slow rate in a trickel charger, do a partial discharge, then pop them back in the PPA charger.


----------



## luvdunhill

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_As I said in my previous post, beg/borrow/steal a battery conditioner. These cells will need to be very carefully charged.

 At an absolute minimum you should charge them at a very slow rate in a trickel charger, do a partial discharge, then pop them back in the PPA charger._

 

I had some credit at Amazon, so I just "bought" / "got for free" a LA CROSSE BC-900 Battery Charger as I need one around the house anyways 
	

	
	
		
		

		
		
	


	




 Looks like this will recondition the cells for me...


----------



## Beefy

Yeah, that is exactly the sort of thing I had in mind!


----------



## steinba

Never mind. :-/


----------



## JamesL

I've had no formal education in electronic design, so I've done a lot of reading, and I'm still dragging my feet a little.

 I'm building a tread to feed 30v into the ppav2, and I'm not certain what I'm looking for in a power source. The unloaded output voltage should be slightly over 30, correct? 
 Unless I'm looking for all the wrong things, the most promising one I found was this one from jameco. Would this work? Are there alternatives that would be more suitable? 

 The 2n5486 for Q3's 8mA is the minimum possible Idss it could be, right? With the opa627 drawing 7mA, and if I wanted leeway for class A biasing, would it be safe to use the 2n5486? 
 I'm also kind of confused. Tangent says the most you'd likely need is 15mA, but his parts list has a recommendation for min 25mA and min 50mA transistors. 

 About the biasing cascodes; tangent's article on biasing opamps into class A is too complex for me, and out of my reach.. Would it be unwise to just blindly follow the directions on his tweaks page?

 And sorry to have clobbered this thread with so many questions, but it seems that the longer I search, the more information that falls out of my head over time..
 Buncha thanks.


----------



## FallenAngel

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I've had no formal education in electronic design, so I've done a lot of reading, and I'm still dragging my feet a little.

 I'm building a tread to feed 30v into the ppav2, and I'm not certain what I'm looking for in a power source. The unloaded output voltage should be slightly over 30, correct? 
 Unless I'm looking for all the wrong things, the most promising one I found was this one from jameco. Would this work? Are there alternatives that would be more suitable? 

 The 2n5486 for Q3's 8mA is the minimum possible Idss it could be, right? With the opa627 drawing 7mA, and if I wanted leeway for class A biasing, would it be safe to use the 2n5486? 
 I'm also kind of confused. Tangent says the most you'd likely need is 15mA, but his parts list has a recommendation for min 25mA and min 50mA transistors. 

 About the biasing cascodes; tangent's article on biasing opamps into class A is too complex for me, and out of my reach.. Would it be unwise to just blindly follow the directions on his tweaks page?

 And sorry to have clobbered this thread with so many questions, but it seems that the longer I search, the more information that falls out of my head over time..
 Buncha thanks._

 

1) PSU: You likely want to use a proper regulated PSU, not just a wallwart. Consider Tangent's TREAD for the low-end, Tangent's STEPS for high-end and Amb's Sigma11 for overkill.

 2) Opamp Class-A: You really don't need any more than 1 or 2 mA of Class-A on the opamp because they are not driving the headphones directly, they are driving the buffers which don't need that much current. The buffers you'll want to bias to 25 or 30 mA and that's more than enough for any heapdhone.

 Feel free to follow directions on the tweaks page, but first build the amp without biasing opamps into Class-A and get it up and running. I would also highly recommend matching transistors.


----------



## JamesL

Cool, thanks fallenAngel.
 I'm actually planning on building a TREAD, but it only regulates the power, right? I wanted to know if that wallwart would be appropriate if I wanted to output 30vdc from the TREAD. 

 I'm sorry.. I'm not even quite sure what buffers do in a audio circuit, and how transistors work/do. jfet, pnp, H_fe_, I_dss_ are all foreign terms to me. Most buffers I know work only with digital data, to regulate the flow of information... could anyone explain how one would work in a amplifier?

 I know that I need 1-2mA for the class-A bias, but the selection guide states that I need to pick Q3, so it has an Idss that will support the opamp current draw + cascode jfets + extra...
 With the opa627 drawing ~7mA, and cascode jfets at ~1mA, would the 2n5486, with min Idss of 8mA, work for this position(Q3)? Sorry if I wasn't clear.

 Yup. I'm planning on biasing to class-a after I make sure the amp is working fine

 Oh, also, about the matching transistors. A previous post recommended that the transistors worth matching are the isolation JFETS, buffer driver transistors, and output transistors. I need to measure the Hfe of the buffer and output transistors, and the Idss of the jfets, right? I can get approximate Hfe measurements, but I don't know how to go about measuring the Idss. Tangent suggests that I need a accurate milliammeter, and a 9v powersupply. Would the measurements from a standard/budget dmm and a 9v battery give any significant measurements(or work at all?)

 Thanks again


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_The unloaded output voltage should be slightly over 30, correct?_

 

Yes, if "3V" is "slightly"? 
	

	
	
		
		

		
		
	


	




  Quote:


 ...from jameco. Would this work? 
 

They don't give enough information to say. If its output is under 33V when loaded by the amp, you can adjust the TREAD downward to give the ~3V drop you need for it to work well. There's nothing magic about "30V", it's just a de facto standard. When DIYing, you have the freedom to ignore such things.

 Actually, if you want 30V at the op-amp supply pins, you want slightly over 30V going into the PPA, due to voltage drops across the regulation JFETs on the op-amp supply pins. One PPA I have uses a 32V regulated supply, for instance. And before you ask if it's always 2V drop across those JFETs, the answer is "no". The amount of drop depends on the JFETs' Idss and the load current. It just happens to be 2V in the amp I'm talking about.

  Quote:


 I'm also kind of confused. Tangent says the most you'd likely need is 15mA, but his parts list has a recommendation for min 25mA and min 50mA transistors. 
 

The trim pots we added in PPAv2 let you dial the actual bias current way down from the maximum. So, using higher Idss values than you would have used in PPAv1 gives you room to move.

  Quote:


 it seems that the longer I search, the more information that falls out of my head over time.. 
 

Maybe you should build something simpler first, to cement related knowledge. Build up to the PPA in stages.

  Quote:


 'm not even quite sure what buffers do in a audio circuit...Most buffers I know work only with digital data, to regulate the flow of information... 
 

Actually, digital buffers do the same thing as analog buffers. They're so classified only because they're suited better to one type of application than the other. There's a thread on Headwize about an audio amp made from digital buffers.

 Buffers put out the same voltage as they get on their input pin. One of the things that makes a buffer "digital" is that the input and output voltages might not exactly match. As long as a logic 1 on the input becomes logic 1 on the output, it's still useful for digital. Analog buffers have to be more precise. Digital buffers, on the other hand, generally have to be capable of higher frequency than analog buffers.

 So, why have a device that just puts out the same voltage as it gets in? Because it can supply more current than the downstream device can. It "buffers" the signal source from the signal sink. This is important in op-amp audio because a headphone cable and its driver represent a much higher load than most op-amps are designed to drive. This is the main limiting factor to the CMoy pocket amp's sound quality. The higher the load on the op-amp, the higher the distortion and the lower the voltage where it will exhibit clipping. A buffer fixes this: the op-amp puts out as distortion-free a signal as it is capable of.

 The tricky bit is to design the buffer so it doesn't exhibit the same distortion and clipping into this load as the op-amp would have. This is why you read about very complex buffer designs with very large output transistors and high bias currents; or equivalently, buffer stacking. Both practices are an attempt to make studly output stages that don't flinch into a headphone load.

  Quote:


 Would the measurements from a standard/budget dmm and a 9v battery give any significant measurements(or work at all?) 
 

Maybe. 

 The battery quality doesn't matter at all. It just needs to remain at roughly the same voltage across the whole series of tests. So, a nearly dead alkaline or a rechargeable that is near either end of its charge cycle is a bad choice.

 The DMM needs to be able to measure down to 1 mA. A lot of older DMMs can't do this. For a newer cheapie, look in its manual to see if it claims this. Just because its display is willing to show, say, 0.1mA, doesn't mean it's showing you anything but internal circuit noise. You don't require an extraordinarily precise meter for this, as with, say, resistor matching. It just has to be decent.


----------



## JamesL

Thanks for going through that for me tangent. That really explained a lot. 

 I chose 30v, because the opa627 spec sheet suggested +/-15v as the optimal operating voltage for this chip. Most wall warts are rated for 24v, and while some unregulated ones say they go up to 32v unloaded, I wanted to go a safer route by going for a 30v unregulated. From what I've read, unregulated psu's almost always outputs voltages a couple digits higher than what it's rated for. The next highest was a 48v, which I assumed would result in too much of a voltage drop.

 It seems as you've stopped selling STEPS boards.. are you planning on releasing YJPS boards to replace them? On a related note... The tread will be built in the same chassis as ppav2 - If I build a steps or yjps later on, would it be degrading to plug it into the tread(as opposed to bypassing the tread entirely).

 I have already built simpler circuits, including the mini3, and simple diy-type non-audio-related circuits.
 The bad thing about this, was that most of the projects I did were merely pcb-stuffing, or blindly following instructions. 
 I don't want to do this with the ppav2 though. My main goal for this project is to go through each part, understand their operating conditions and their purposes, and get a vague understanding of how each aspect of the design contributes to the amplifier.

 The dmm spec sheet claims to have a resolution of 1μA in the 2mA range with +/-1% accuracy, which seems suspiciously high for a $15 dmm. I suppose(hope) this'll work.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I chose 30v, because the opa627 spec sheet suggested +/-15v as the optimal operating voltage for this chip._

 

Welll...put it this way: if you give it 15V instead, performance doesn't halve. Aside from clipping behavior, performance might drop by 1%.

  Quote:


 From what I've read, unregulated psu's almost always outputs voltages a couple digits higher than what it's rated for. 
 

Yes, but how much, and how big a drop under load? You can't know that without a real datasheet, or measurements.

  Quote:


 It seems as you've stopped selling STEPS boards.. are you planning on releasing YJPS boards to replace them? 
 

I made a small prototype run of YJPSes for early adopters, and am waiting to hear reports about how those are working. In the meantime, I'm working on an improved version. This will probably take a few months to result in boards en masse.

 The STEPS is indeed obsolete...too little benefit over the TREAD to justify the cost.

  Quote:


 If I build a steps or yjps later on, would it be degrading to plug it into the tread 
 

The TREAD will add a little noise and drop some volts, but it shouldn't wreck performance. It's just wasteful.


----------



## StanRex

Hello,

 I had asked questions about building a ppa and sourcing parts on another thread and tangent had kindly replied, but since I've found this topic I'll use it for my next questions.

 Anyway, I've read that for Senns HD650, the OPA627 might not be the best choice (too dark if I understood properly)

 so it seems I have other choices : AD825ARZ, AD8610, etc...

 now, what I'd like to know is, if mount DIP8 sockets on the board, and grab a few SOIP to DIP8 adapters from tangent's site (and maybe also adjust power supply for each opamp), will I be able to switch between all the best opamps (DIP8 or SOIP) choices for the PPA till I find the one that I like the best?

 And concerning rail capacitance (C1s) : is it better to stay under 2000µF or rail cap, or would going slightly over the 2000µF rail cap yield better results in some cases?

 Thanks in advance for your answers

 edit : concerning rail capacitance, looks like the good idea would be to use 9*220µF caps= 1980µF. I'll probably go with this


----------



## FallenAngel

Of course you can swap opamps, that's the idea. 
	

	
	
		
		

		
		
	


	




 AD825 should be nice with HD650. Also the OPA627 isn't very bad with HD650 in the PPAv2. It's just that the HD650 really need a good amp to lose the slow/dark feel and the PPAv2 IS a good amp. I've used the OPA627 with it, sounds nice, but AD825 will be faster, more punchy.

 2000uF is plenty, a little more/less isn't going to matter, quality capacitors will.


----------



## StanRex

Ok good, thanks for your answer FallenAngel. I'll probably try a few different opamps to see how it affects sound

 However I have a new question, regarding C4 this time

 the only "boutique parts" I can find in 10mm diameter are the elna RFS Silmic II in 100µF, 35V. 220µF are at least 12.5mm diameter it seems

 In his parts list, tangent selects 220µF 35V Nichicon UPW caps

 My question would be : would I get better results using the higher capacitance nichicon caps or the "boutique" elna rfs that are "only" 100µF ?

 thanks in advance!


----------



## FallenAngel

C4 is recommended to be no larger than 220uF, I'd go with the 100uF Elna Silmic II, that's what I used in my build, sounds wonderful.


----------



## StanRex

Ok. I'll go with the 100µF then. Thanks for your reply

 Concerning op-amps, I'm going to order :
 opa627 and 637
 ad8065
 ad825
 ad8610

 I hope having that many choices will allow me to find one that I really like ^^

 that said, I'm having doubts on Q3

 Tangent's primary choice for this part is 2N5486 (which has an Idss between 8 and 20mA)

 However, he states in the parts selection guide that Q3's Idss need to be at least as high as the op-amp's current draw. And that when switching opamps, the most hungry can draw up to 15mA.

 This leads me to believe that I should use one of the alternate type transistors for Q3, like the PN4392 which has an Idss between 25 and 75mA. That would allow me to switch opamps without having to worry about transistors. So I was wondering, is there any drawback to using PN4392 for Q3 ?

 Thanks once more for your help!

 edit : quick question concerning the power supply. I plan to build a TREAD. Since wall adapters are quite pricey (at least in Europe), I'll probably buy a toroidal transformer. Would it be ok to put in the same case the toroidal transformer, the TREAD and the PPA, or would it be better to put the PPA in another case, to avoid emi?

 wait a minute, I just realized something. Input voltage is AC. The TREAD supplies supplies the amp with DC. So a 24V AC wallwart would allow the TREAD to output more than 24V DC without too many issues, right? I ask cause if that's the case, I'll use that solution cause 24V AC wallwart are cheap! great!


----------



## tangent

Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_This leads me to believe that I should use one of the alternate type transistors for Q3_

 

The higher the transistor Idss, the less well it works as a regulator, however. Two things to consider: First, none of the op-amps you've selected are anywhere near 15 mA idle current; see their datasheets. Second, instead of getting something vastly overspec'd, you can just get a small bag of several JFETs and test them to find some that are in the higher end of the rating range. All you need to do the test is a basic milliammeter.

  Quote:


 would it be better to put the PPA in another case, to avoid emi? 
 

It's always better to put the transformer in a separate case, for that reason, regardless of the details. Whether you _wish_ to do this is a separate matter. If it's a large case, you can get most of the benefit by just putting the transformer on the opposite side of the case from the amp board, with the regulator between. I've done it both ways.

  Quote:


 a 24V AC wallwart would allow the TREAD to output more than 24V DC without too many issues, right? 
 

It's possible, but not guaranteed. It depends on its load regulation spec and how much current it can put out. Give the power supply parameter estimator numbers from the specific unit you want to try. Don't guess.


----------



## StanRex

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The higher the transistor Idss, the less well it works as a regulator, however. Two things to consider: First, none of the op-amps you've selected are anywhere near 15 mA idle current; see their datasheets. Second, instead of getting something vastly overspec'd, you can just get a small bag of several JFETs and test them to find some that are in the higher end of the rating range. All you need to do the test is a basic milliammeter.

 It's always better to put the transformer in a separate case, for that reason, regardless of the details. Whether you wish to do this is a separate matter. If it's a large case, you can get most of the benefit by just putting the transformer on the opposite side of the case from the amp board, with the regulator between. I've done it both ways.

 It's possible, but not guaranteed. It depends on its load regulation spec and how much current it can put out. Give the power supply parameter estimator numbers from the specific unit you want to try. Don't guess._

 

Ok, understood. Thanks a lot for the advices! I've used the power supply parameter estimator and it seems stable enough ^^


----------



## StanRex

I've just realized that I didn't know how much current a ppav2 draws.

 I checked other amp sites and found the mosfet max needed a supply capable of delivering at least 1A. I hope a PPA doesn' t draw as much because I'm unable to find any wallwart exceeding 750mA output at 24V AC (in fact I've only found two 24AC wallwarts, one outputting 750mA max, the other 500mA).

 So I'm just wondering if one of you know if those would be enough for all kind of ppas, or only those using less current consuming opamps, or even if they wouldn't be enough for any kind of ppa

 thanks in advance

 ps : I've already checked tangent's site multiple times but have been unable to find indications of the ppa current draw


----------



## MisterX

Assuming the 500mA adapter is regulated, it has plenty of output current capacity for a PPA2.

 Edit: Remember the Elpac WM080 suggested in the parts list only outputs .33 amps.


----------



## FallenAngel

You can (and SHOULD) measure it to make sure your build works properly. 
	

	
	
		
		

		
		
	


	




 The current draw of the amp will be the sum of the current draws of the opamps (check datasheet of the opamps of what they should use - *Iq*), plus whatever you set your opamp Class-A bias at and how much you bias your buffers at.

STEP 8 - setting buffer bias.

 So if you're using OPA627 which draws 6mA, you bias it into Class-A with 1mA, and set your buffers to 25mA each, you're looking at ((6 + 1) x 3) + (25 x 3) + a few mA for LED and such (device mismatch tollerence) so it should be a total of about 100mA.


----------



## StanRex

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_You can (and SHOULD) measure it to make sure your build works properly. 
	

	
	
		
		

		
		
	


	




 The current draw of the amp will be the sum of the current draws of the opamps (check datasheet of the opamps of what they should use - *Iq*), plus whatever you set your opamp Class-A bias at and how much you bias your buffers at.

STEP 8 - setting buffer bias.

 So if you're using OPA627 which draws 6mA, you bias it into Class-A with 1mA, and set your buffers to 25mA each, you're looking at ((6 + 1) x 3) + (25 x 3) + a few mA for LED and such (device mismatch tollerence) so it should be a total of about 100mA._

 

Ok, so I'd be good with both wallwarts. Great to know. Thanks to both of you for your answers.

 Just wondering though, why does the Mosfet Max draws so much current compared to the PPA? is it because of the fact it uses tubes?

 edit : oh and the whole idea is to fit the PPA and a TREAD in the same box and use an external unregulated 24VAC wallwart

 if I understood properly there shouldn t be emi issues since the transformer is out of the box and the tread should take care of the regulation


----------



## FallenAngel

Like I said, add the current draw of each.

 MOSFETs are biased to 110mA per channel (as in Mosfet MAX or M^3)! The BJT (as in regular MAX or PPAv2) are usually set at 25-30mA, see the difference.

 Tubes draw 150mA I think in the MAX, most opamps draw under 10mA.


----------



## StanRex

Mmmm, just a quick question concerning CRD, because I'm not totally sure I understood

 it's useless if the amp is not battery powered right? I can just use rled and be done with it?

 thanks in advance

 btw, living in France, I'm going to get *$^f^ù* on shipping costs ^^ (ordered yesterday from tangent, and the digikey, mouser and farnell orders are ready to go)

 I expect to end up @ +- 300 €, everything included


----------



## tangent

"Useless" is a little strong. A CRD does its job quite well no matter what the supply. It just doesn't justify its cost when the supply voltage doesn't change.


----------



## StanRex

Ok, thank you Tangent


----------



## StanRex

Mmm I have a quick question regarding power

 I'd like to have the TREAD (fed by an AC wallwart) + PPA in a single hammond 1455T1601 case to avoid having X thousand boxes of components near my pc

 I was thinking of using a single switch to power on/off both the PPA and the TREAD.

 I recall reading in this thread that there was a risk to fry the regulator and damage the TREAD when powering off either the PPA or the TREAD first (cant remember exactly which one) so you had to do it in a precise order

 I was wondering if there was also a risk to damage components when using a single switch to power on/off both the TREAD and the PPA at the same time.

 If yes, I'll modify my order to use two boxes, one for the TREAD and one for the PPA

 thanks in advance


----------



## tangent

There's less risk of problems here with the TREAD than the STEPS, due to the smaller filtering cap. But if you don't mind burning ~10 mA to keep the TREAD running, the simplest and most reliable is to put the power switch between the TREAD and the PPA. The power supply stays running all the time, but draws very little power, and it's always up and ready to go.

 The only other thing is to avoid excessive rail capacitance in the PPA. See the docs.


----------



## StanRex

Ok, I'm going to go with that solution. 

 And maybe add an additionnal switch for the power supply at the back of the case if I ever feel the need to switch it off separately

 thanks for your answer Tangent


----------



## tangent

Rather than a switch on the incoming line, I'd just use a connector for the wall supply, so you can unplug the cable. Say, for going on vacation. Anything more convenient is just going to cause confusion about which switch to use when, later on when you forget why the amp has two switches.


----------



## StanRex

That's indeed a better though solution ^^ I must be really tired for imagining such an impractical solution ^^

 I'll go with only one switch, thank you once more tangent for your advices!


----------



## steinba

Does anyone have an up to date BOM for the PPAv2 from mouser, digikey or maybe even Elfa?

 (BTW: I have the opamps and C1's as well as the Alps pots)


----------



## StanRex

damnit, I ve just checked the availability of opa627 and 637 at mouser and they re out of stock. I'll still have other opamps to play with, but still... missing those sucks!

 I ve checked farnell and digikey and they dont have them. Do you know where I might be able to find a few 627 and 637 (in a store that ships internationnaly if possible ^^) ?

 PS : i have a bom, but it s not totally up to date, as I ve just found, and it sources parts from digikey,mouser and farnell


----------



## steinba

627's are available at Elfa (ELFA -- Elektronikdistributör i norra Europa) at least.


----------



## StanRex

Thanks for the tip but the pricing is... huh... impressive to say the least. 

 I think I'll just wait for them to be in stock at mouser

 btw, I've found opa627apg5 at farnell, at a similar price (30 euros)

 do you know what the g4 stands for?

 anyway, 30 euros for an opamp (90 for 3 of them...) is just too much. I ll build the amp with ad opamps first


----------



## mwofsi

Don't know about shipping but this seems like it might be a good deal:
https://www.cimarrontechnology.com/i...PROD&ProdID=37


----------



## StanRex

thanks a lot for the link! I m sending them an email asking about shipping immediately!


----------



## funch

Digikey has them in SOIC:
Digi-Key - OPA627AU-ND (Texas Instruments - OPA627AU)


----------



## tangent

Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_do you know what the g4 stands for?_

 

It's probably a RoHS code. The datasheet will have a section explaining the part number.


----------



## steinba

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_Does anyone have an up to date BOM for the PPAv2 from mouser, digikey or maybe even Elfa?

 (BTW: I have the opamps and C1's as well as the Alps pots)_

 

Gaaah! I wish someone was selling a PPAv2 kit!

 (Are you hearing this, tangent? 
	

	
	
		
		

		
			





 )


----------



## tangent

What would such a kit contain? 

 Black Gate, Cerafine, Muse or Panasonic PW caps? AD825, AD8610, AD8065, OPA627, or OPA637 op-amps? Gain resistors for 1, 2, 5 or 10? Output stage biasing for 10, 20, 30 or 40 mA per channel? Q3s matched to the op-amps I send, or oversized to allow op-amp rolling at the expense of regulation? MJE243/253, BD139/140, 2SA1358/2SC3421, or KSA1220/KSC2690 output transistors? C6 big enough to control any op-amp or only as big as necessary to control the op-amp sent, giving wider bandwidth? Which of the rainbow of possible LED colors should I use? Should I ship RLED or RLED+FET+ZNR, and how bright should I make it? Include bass boost, and if so, where to set it? Include op-amp biasing JFETs, and if so, what value? Optimize for wall power or battery, or try to split the difference?

 No doubt you have answers for all of those questions. But do you imagine that your answers will match up with everyone else's? 

 If I ever did offer a kit, there could be only one, for a bunch of reasons. And, the questions above tell us that one kit will not satisfy.

 DIY makes it possible to build something that fits your taste and situation perfectly, which is one of the best reasons to DIY.


----------



## steinba

I know and understand, of course. I wasn't (that) serious, really. Just got a little tired of all my old BOMs at "My mouser" being scattered with "obsolete" parts.

 I'm really grateful that you make the parts you do have available, btw. So thanks!


----------



## steinba

...Ignore.


----------



## StanRex

Well, I ve just sent the last order for all the parts. Unless I've forgotten some components or burn a few and have to reorder, this is what building the ppa + TREAD costs me :

 order from tangent (board, pot, browndog adapters, TREAD kit) : 61 €

 order from digikey (caps, opamps (ad843 and ad8065), case and a few others) : 77 €

 order from mouser (resistors, transistors and a few others) : 86 €

 order from farnell (the french version of newark) (opamps (ad8610, ad825 and opa627/637), transistors, R9 and R12) : 203 €

 total : 427 €

 a tad higher than I had expected ^^ but I took quite a bit of spare parts, 5 different opamp sets to test and well, ordering from 4 different suppliers kinda adds to the shipping costs (mouser asked 30$ for shipping via priority mail... ugh....)

 I learned one thing in the process though. Digikey is incredibly fast (ordered yesterday, package is already in France). And they charged 0 for shipping, since my order was > 75 euros. Pretty cool policy if you ask me, I'd wish farnell and mouser did the same.


----------



## StanRex

I have a quick question, it's not about the PPA but it's related to it : it's about the regulator that is used on the TREAD.

 That thing has, well, BIG pins, that I wouldn't really call leads, and if I put it in the TREAD board, the pins stick out a lot. I'm just wondering if those can't be cut without risk of damaging the regulator. I suppose so, since after all, they re just pins, and it seems it has been done on the pic here : 







 but I'd like to be sure before cutting them, since I've never met that kind of pins before

 thanks in advance


----------



## FallenAngel

What pins?

 If you're talking about the regulator heatsink, you can skip it altogether depending on voltage drop and current requirements.

 If you're talking about the bottom of the board, yes, you're supposed to trim the excess leads.


----------



## StanRex

No, I really mean the pins of the regulator, those that are on that document :

http://www.fairchildsemi.com/product.../to220_dim.pdf

 and that will end up at the bottom of the board, like the leads of the other components, but aren't really leads


----------



## MisterX

feel free to cut them as needed


----------



## StanRex

Good, thank you for your answers guys!


----------



## StanRex

ok, I ve almost everything soldered, just about to try testing the power supply

 but i d like to solder the led first, and I cant seem to find any sort of polarity on the schematic. Where should the longer lead (+) go?

 thanks in advance

 stan


----------



## MisterX

The triange part of the symbol on the schematic = the anode. 
 The flat part of the symbol on the schematic = the cathode. 

 In most cases the anode is the long lead. 
 There is usually a flat spot on the LED for the cathode but there are exceptions (check the datasheet before soldering).


----------



## StanRex

ok, thank you mr X

 well, I ve tested the ps, it seems ok, led is lighting up. I havent tested anything though

 however : 

 epic fail...

 I ran into an issue. It seems I simply cant solder soic opamps to browndog adapters. I ve already destroyed 2 adapters, and probably an ad8610 trying to do so

 so I m going to have to try with the only dip8 opamp I have, the ad843...

 and from what I read, it isnt going to be a particularly pleasant experience getting that beast to work in the ppa 
	

	
	
		
		

		
			





 I m just going to stop working on the ppa for today. I ll try resoldering opamps to browndog adapters this week


----------



## StanRex

well, I m going to re try getting the ppa to work with ad843, since they re the only ones I ve got in dip8

 so I ve read most of the TREAD and found a few tips about using these in a ppa

 right now my ppa is using default configuration

 I plan to :

 replace Q3 with PN4392 so the Idss is high enough (I dont have the equipment to measure idss, so I cant use the 2N5486 with the AD843, since I m not sure they ll have enough idss)

 replace the output resistors (R24/34) with 4.7 ohms

 I hope that will be enough

 If you ve got another suggestion, please feel free to add it ^^


----------



## StanRex

I just realized that I didnt need much equipment to do some Idss measuring : lowering the TREAD a bit and using a dip socket as a "fortune" perfboard for the transistor should do the trick

 however, I was wondering : Tangent speaks about using a 9V powersupply to test the JFET's Idss. And I doubt that I can get my TREAD to go that low. I m pretty sure that I have a ****ty regulated 9V walwart at home that I could use, but I m not 100% sure. 

 If I cant find a 9V powersupply, can I maybe lower my TREAD to something like 18V to test the Idss or will it kill me and the JFET in the process ^^ 

 edit : nvm I checked the 2N5486 datasheet and apparently they can take up to 25 V in the face. I ll lower the tread a bit if I cant find my 9V regulated wallwart


----------



## tangent

Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_It seems I simply cant solder soic opamps to browndog adapters._

 

Have you watched this? What iron are you using? If it's adjustable, what temperature is it set to? What solder are you using?

  Quote:


 so I m going to have to try with the only dip8 opamp I have, the ad843... 
 

I would try a lot of other things before I resorted to that.

  Quote:


 If I cant find a 9V powersupply 
 

Even a 9V alkaline battery will do.

 But again, I think you're asking for trouble going down this path to begin with. 

 If you're giving up on soldering the AD8610s to the adapters, you can buy them pre-mounted directly from BrownDog.


----------



## StanRex

Well, I had watched your tutorial video some time ago yes

 What really surprises me with the soic soldering is that I had had no trouble soldering the REG101s of the AlienDAC, which are roughly the same size, by using flood and suck with my soldering braid

 however, with the ad8610 and the browndog adapters, I simply failed :

 way too much solder gets into the pins of the 8610, and when I try sucking it with the braid, it doesnt get the bridges that the solder made between the pins of the ad8610, yet the chip get really hot

 plus, when removing the ad8610 that I hadnt properly placed, one of the pads of the browndogs moved a bit. So I guess its dead.

 anyway, my issue probably comes from the iron and solder I'm using :

 a cheap (8€) 40W iron, not adjustable and 1mm solder 60/40

 I m probably going to try ordering this : MET@SHOP 

 the tip is 0.6*0.8mm and I think it s a hakko clone, so should be good stuff. Or I ll get a 15W weller

 and if I still cant solder properly with this thing, well I ll resort to buying the ad8610 premounted

 once more, thanks a lot for your help and your advices tangent


----------



## MisterX

Quote:


 flood and suck with my soldering braid 
 

That explains why you failed. 

 I would suggest "drag soldering" them. 
Curious Inventor - Guides : Surface Mount Soldering


----------



## tangent

Also get some thinner 63/37 solder. It will be easier to work with.


----------



## JamesL

I used nothing but this baby for my mini3, and it was easy enough doing the soic-8 pin-by-pin. A little slower, but for me, it was easier than the drag-soldering method(probably cause I didn't use flux).







 If _all_ else fails.. you could pre-tin the pads, and heat up and press down on each of the legs..(this is probably really bad advice though, since there is no flux on the opamp legs. )


----------



## steinba

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_(this is probably really bad advice though, since there is no flux on the opamp legs. )_

 

Get a bottle of flux?


----------



## JamesL

Yup. got one. 
 I don't really use it for anything except for fine-pitched ssop chips though.


----------



## espressogeek

I just completed installing all of the parts on a PPAv2 board. The board looks pretty good to me, no messy joints, etc. I cleaned it up and connected it to my tread that I built a few days ago. When the amp is powered on I get a very hot left channel with the other two are not getting warm at all. It seems to be just the two output transistors and perhaps the resistor that is getting warm. I'll post some pictures tomorrow but does anyone have any ideas on where to start? I have searched quite a bit and read all of the documentation I can find. When I test from OG to OL I see about 500mv and from OG to OR I see 3.5mv.


----------



## espressogeek

I poked around some on the board this morning. With the op amps out I see 20v on each op amp socket which is inline with what I am sending to it. With the op amps in the sockets I see 9.5v at each op amp. I measured the current draw in this scenario and I see about 9.8ma of current at the V+ terminal when the op amps are installed and the left output transistors getting hot. Any ideas of where I should look next?

 BTW please excuse the 100k in positions R6L and R6R. I have some 470Ks on order but they are not here yet.

http://img114.imageshack.us/my.php?i...f001541np8.jpg

http://img114.imageshack.us/my.php?i...f001542iu2.jpg


----------



## tangent

Quote:


  Originally Posted by *espressogeek* /img/forum/go_quote.gif 
_I see 20v on each op amp socket_

 

From where to where? Pin numbers?

  Quote:


 With the op amps in the sockets I see 9.5v at each op amp. 
 

Same pins as before?

 If so, does the supply voltage at the PPA amp board's V+ and V- input pins also sag comparably?

  Quote:


 I measured the current draw in this scenario and I see about 9.8ma of current at the V+ terminal 
 

That doesn't make sense. If the supply voltage is being dragged down so far, it's got to be a much bigger load than that. Like, several hundred mA.

 And if the implied voltage sag above isn't happening, then you should still be seeing more like 100 mA here.

  Quote:


 please excuse the 100k in positions R6L and R6R. 
 

I may see fit to excuse the values, but I can't excuse those long leads. You've gone and created loop antennas in the feedback loop. I won't say this is certainly causing the problem, but it isn't helping.

 You can just take R6 out, and the amp will still work. Gain will go way down, but as long as you're using unity-gain-stable chips, this should be fine.

  Quote:


 ImageShack - Hosting :: cf001541np8.jpg 
 

I don't see much solder up on the top side. It's possible you have some bad joints, since the solder evidently didn't flow very much. You might apply a little liquid flux to anything looking suspect and reflow it. If you don't have flux, just add a little more new solder to the joint.


----------



## espressogeek

Thank you for your help and reply! I have removed the offending R6 resistor on both sides of the amp. I will replace it properly when the new ones arrive. I am using the LME409710's btw.

 I still have the hot'ish left side output transistor issue. I went back and hit up all of the pads on that side with rosin and solder and I now see a good bit more solder up top. I will hit up some other ones later this afternoon when more time is permited.

 I'll try to be very clear on my measurements. The voltage "sag" this morning might have been a bad reading on my part. Here is what I see now.

 Measuring from V- to pin 7 (V+) on each op amp, LME49710 op amps installed.
 Left - 19.05v
 Ground - 19.08v
 Right - 19.08v

 Measuring the input at V+ and V- - 20.01v

 We can ignore the current readings because I did some test and the meter has a problem with this apparently. I have a friend bringing over a known good meter after work so hopefully I can get some current numbers. Any other things I should look at? I really appreciate all of the help.


----------



## espressogeek

Update: I now have a working meter . Ok , so I have connected the meter in line with the power supply and amp and when I hook it up I immediately draw 125mA. This climbs up to around 157mA before I unhook it because the transistors in the left channel get quite hot. 

 I just checked some more and realized that it is not just the left channel but the following.
 Q34L , Q24L, and Q34G. The other three are fine.

 When I look at the voltage across the output resistors I see the following.
 R34L - Begins at 170mv and climbs along with the temp of the transistor to about 203mv before I unplug the amp
 R24L - Begins at 170mv and climbs along with the temp of the transistor to about 203mv before I unplug the amp
 R34G - 25.5mv (I'm sort of miffed about this, I would have thought it would be higher considering the temp)
 R24G - 25.7mv
 R34R - 22.3mv
 R24R - 22.2mv

 UPDATE: I did some checking between the ground and right channels an the afflicted left channel. I noted that the R13 resistor was 200 ohm on the ground and right and 100 ohm in the left. I have now swaped out all three, just to be safe, with 100 ohm parts. My current draw to R24/34 R and R24/34G is around 23mv now. The left side is still screwed. I have also replaced the Q34L and Q4L parts thinking this might resolve the issue. I only have one spare BD139 for Q24. I would replace it if there was a good explanation for doing so. Does anyone think this might be the culprit? How about Q23/33L?

 I swapped the op amps between the ground and left channel. That produced no change in the symptoms.

 I'm going to keep poking around this thing and searching. Any advice is appreciated.
 Thanks


----------



## StanRex

Ok, I ve bought a hakko 937 clone, some 0.5mm solder, flux pen

 and soldering the ad8610 got a lot easier!

 I have 3 mounted on browndogs. I ve tried switching the PPA on. And well, Q24R gets real hot. And there s a bad smell floating in the air. I think something s burnt ^^

 now, I m thinking it s either : 
 _ a bad joint from me
 _ q24 got killed when I had tried doing the power supply test with the AD843
 _ q24 got killed because the browndogs arent too securely attached in the sockets. If I try to put the PPA upside down, the adapters will fall down from the sockets. And maybe the bad contact between the ad8610 and the sockets created some kind of short. That s also kinda problematic because I can't test voltage at the V+ and V- pins of the opamps, since I m pretty sure I ll make them move when touching them

 I'll try to put a few pictures ASAP.

 edit : just checked and I get 21.9 between pins 4 and 7 of the ad8610. Considering I m using a 24V tread as a ps, looks ok to me

 edit 2 : apparently my left channel is working : I can adjust the buffer bias; however, when I try to do the same for the right channel and ground, I just get 0mV at the output resistors pins.

 edit 3 : pics









 ps : there s quite a bit of flux left. I tried cleaning with 99.7 isopropyl but there are some spaces between pins I just cant access

 edit 4 : I ve cleaned up the remaining flux with a toothbrush . It looks better now. Didn't update the pics though

 edit 5 : and yes I m planning to replace C5 with boxed MKP caps


----------



## espressogeek

Seems to be the week for hot output transistors  . Sorry to hear about your issue.


----------



## StanRex

Well, I m thinking it could also be the buffer transistors. Not sure of anything though. But the good thing is I have spares

 edit : I've also realized that apparently my meter sucks a bit too
 I use the default 2.2ohms resistors for output

 and I got something like 60mV and 7.5mA across them

 I think Mr Ohm felt offended ^^

 is there any way to find out if the issue is located at the output transistors or at the buffer transistors without having to desolder them all?

 thanks in advance

 edit : nvm, my voltage readings were ok and I wasn't properly measuring current. I still get 0mV at the output resistors of 2 channels, gonna try switching opamps see if the channels follow, and probably switching output transistors after that.


----------



## espressogeek

Poor Mr Ohm. I had a buddy bring over a Amprobe 37XR-A yesterday and for the cost I am quite impressed. I ordred one like it last night for around 120. I definitly think having a quality meter is worth the beans. 

 Unfortunately my situation went from bad to worse. I replaced Q23/33 and now I just smoked Q24/34L with a whopping 1.7 volts through the associated output resistors . I have no idea what is going on but I suppose a complete rebuild of that side of the amp is in order.


----------



## espressogeek

I have pulled out all of the suspect components on that side of the amp and clean it off. Do you think the board is still serviceable? What can I check to find out what is going wrong? I just dont want to populate this board again and end up in the same position.


----------



## StanRex

oh and btw, there s something I hadnt mentioned earlier. When I plugged in the amp and Q24 got hot, I had a short between IG and IR.

 I suppose it could have done some damage?


----------



## espressogeek

What was causing the short?


----------



## StanRex

My stupidity : when I had soldered the input wires, the unbraided wires that I hadn't cut got pressed against each other

 Yeah, I know, epic fail ^^


----------



## JamesL

I was about to bias my opamps into class A, but I noticed that my current draw was about 16mA over the sum of the draw of the components.
 I have 20mA bias at the buffers, OPA627(should be drawing 7mA each), no class-A, and no LED. = 81mA

 I'm reading the current draw at S1, and it starts off at 81mA, but steadily rises to almost 97mA before it settles down.

 Is that big enough a difference to be worried about?
 I've been running it fine for a few weeks with no problems, and it hasn't been getting excessively hot either.


----------



## espressogeek

Success! I rebuilt the left channel with new parts after posting the pictures and everything seems to be working perfectly! The darn thing plays music and sounds great! 

 The bass coming from this thing is AMAZING! It is super fast and really tight.

 UPDATE: I biased the outputs to 60mv. After listening for a while I checked the right channel and it is somewhere around 16mv. I tried to bias it back up to 60mv and I can only get about 30mv out of it. Everything sounds fine. 

 UPDATE: I just checked resistance across R12. On G and L I am seeing about 360 Ohms resistance. On the right channel with the low bias I see about 140 Ohms. I reckon this is the issue. I suspect that I should just need to replace R12 on that channel and I will be good to go.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I'm reading the current draw at S1, and it starts off at 81mA, but steadily rises to almost 97mA before it settles down._

 

This is normal. The PPA guide text saying you can figure buffer current draw just from voltage across the output resistor is very much an approximation. That's where most of the current goes, to be sure, but it ignores all of the stuff behind the output pair.


----------



## slaikan

Hi

 Finished building the PPA v2, very very happy with it, no problems with the build which I'm thankful for since its only my third DIY project. First was the CMOY (recently destroyed the OPA2132 with reverse polarity... oops), then the Audiosector Premium USB DAC and now the PPA. I struggled more with the casing and getting everything to fit properly than bulding the PPA itself.

 I used all the standard components off the Tangent parts list except for C5's are WIMA MKS4 250V 0.1uF as thats all I could find in a hurry at the time.

 For those who have experience with different caps, should I replace them with WIMA MKS2 63V 1uF or maybe something else and how much do these caps affect sound quality?

 I'm using Panasonic FM throughout, 220uF 35V caps on the input side and 3x 680uF 35V on the power supply side. Is there a significant difference with 'boutique' caps like Blackgates, Nichicon Muse, Elna Silmic etc. cause its quite difficult to get that where I stay, so it all needs to be imported.

 What are you opinions of using CAT5e for hookup wire, thats what I'm using at the moment, I decided not to import fancy hookup wire and my perferred local supplier only sells hookup wire in 20 meter reels, per colour...

 Thanks


----------



## FallenAngel

Quote:


  Originally Posted by *slaikan* /img/forum/go_quote.gif 
_Hi

 Finished building the PPA v2, very very happy with it, no problems with the build which I'm thankful for since its only my third DIY project. First was the CMOY (recently destroyed the OPA2132 with reverse polarity... oops), then the Audiosector Premium USB DAC and now the PPA. I struggled more with the casing and getting everything to fit properly than bulding the PPA itself.

 I used all the standard components off the Tangent parts list except for C5's are WIMA MKS4 250V 0.1uF as thats all I could find in a hurry at the time.

 For those who have experience with different caps, should I replace them with WIMA MKS2 63V 1uF or maybe something else and how much do these caps affect sound quality?

 I'm using Panasonic FM throughout, 220uF 35V caps on the input side and 3x 680uF 35V on the power supply side. Is there a significant difference with 'boutique' caps like Blackgates, Nichicon Muse, Elna Silmic etc. cause its quite difficult to get that where I stay, so it all needs to be imported.

 What are you opinions of using CAT5e for hookup wire, thats what I'm using at the moment, I decided not to import fancy hookup wire and my perferred local supplier only sells hookup wire in 20 meter reels, per colour...

 Thanks_

 

Congrats, it's a very nice amp.

 For the PSU caps, using electrolytic caps made for signal coupling is not recommended (BlackGate N, Muse ES, etc). Going with Elna Silmic II is definitely an option, but I personally wouldn't bother with going above Panasonic FM, they're very good PSU caps.

 Cat5e is also OK, but not the best. I would recommend using a nicer wire like surplus SPC from eBay (Silver Plated Copper) - it's cheap and sounds much better.


----------



## luvdunhill

hey, is there an easy way to verify that Tangent's crossfeed board is working as designed? I'm using a rotary switch in the "simple" configuration.


----------



## StanRex

Mmm, I'm getting confused.

 I've removed all the unnecessary input and output wiring, and have done some tests.

 Voltage at the power supply pins of the opamps is ok. I get 11.5 between V+and ground and the same between V- and ground when no opamp is in the socket. With an opamp, I get lower values (I think 11.1) but I think it's normal

 Anyway,

 Yesterday, I had a working ground channel with an AD8610 in it. It gave reasonable voltage readings at the output resistor (30mV or so)

 I swapped the opamps a few times between the supposedly working right channel and ground. 

 And somehow, I ended up with 0 channels working.
 I believe my AD8610 all fried 
	

	
	
		
		

		
			





 I don't understand how it happened. I'm thinking it could be because the browndog adapters dont have a good fit in the sockets, so it could have caused some of the opamps pins not to connect properly with the socket. But not sure such a thing could fry the opamps

 anyway

 Since I've lost a faire share of useful opamps, I ve decided to do the rest of the "risky" (risky as in "can blow the opamps") testing with my DIP8 AD843.

 I ve put an AD843 in the ground socket. Works ok. Get 30mV at the output resistor. Then I ve tried putting in the right channel socket. Ok once more. I'm going to replace Q24 and 34 before doing the same with the left channel (I'm pretty sure one of them burnt during a previous experiment)

 So far, I haven't dared try with two AD843, one in the right channel and one in the ground (the two channels that work at the moment), because when I had tried doing so with the AD8610, they had died. Was it just bad luck/bad contacts between the opamp pins, or is it possible that these channel work OK when used seperately, but will somehow fry the opamps when used at the same time?

 Thanks in advance for your answer

 ps : I also have some DIP8 OPA627, but I d rather do the risky testing with the AD843 before taking chances with the 627, considering their price tag...


----------



## slaikan

Thanks FallenAngel, it is a very nice amp, HD595's haven't sounded as good they sound now, I only have the CMOY and the output of a Zune and Sony NW-HD5 to compare with though. I guess I'll be shopping for better hookup wire, I'll be keeping the PSU caps as you've recommended.

 What about the Panasonic FM 220uF caps in C4 and the 0.1uF WIMA's in C5, should I toy with them or just leave them as is?

 Thanks


----------



## StanRex

I've replaced the output transistors of the left channel, found there was a bit of solder (causing a short) between two legs of one of them, could be what had caused me trouble

 anyway, I replaced those. Put my "official tester" (AD834) in the socket, switched the amp on and checked voltages at the output resistor. Woohoo! 30mV! Got it to 44mV, like the others.

 Now, I'm going to start with one OPA627 in the ground channel, see if voltage at the output resistor is ok.

 If it is, I'll take the leap of faith and put all my 3 DIP OPA627 in the sockets. I really hope I wont fry them though ^^

 edit : tried. Nothing fried. Adjusted the bias. Then checked DC offset. 1 and 4 mV for ground and right channel, but left channel exhibits 17mV between OL and IG. I'm going to try cleaning things up a bit

 edit 2 : I've tried cleaning and reflowing a few joints, but it didn't lower the offset. could the dc offset be caused by unmatched output transistors? I tried matching the buffer transistors, but not the output ones. Anyway, I think I read that something under 20mV isn't perfect but is acceptable . So I guess I'll just move on.


----------



## StanRex

just a quick question: how exactly do you get the ground strap to stick to the alps pot? I ve tried solder, solder with flux, but nothing gets solder to stick to the damn vise of the pot...


----------



## slaikan

For mine, I just unscrewed the corner screw a little, filed it a bit to make it a little rough, soldering was a little easier after that.


----------



## MisterX

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_hey, is there an easy way to verify that Tangent's crossfeed board is working as designed? I'm using a rotary switch in the "simple" configuration._

 

Mute or disconnect one of the channels.


----------



## StanRex

I'm too tired so I'll stop working on the PPA for today. Anyway, progress report since last weekend :

 ppa doesnt kill opamps anymore
 I have 40mV or so at each output resistor (so technically, I think each channel is working)

 on the todo list :

 fix the output :

 no source connected, ****ty earbuds (connected through a 6.35 to 3.5 adapter) on the output
 The ppa outputs noise. Lots of noise. I think it should be dead silent instead. Groundstrapping the pot didn't help. Anyway what's surprising is that at the lowest pot setting, noise level is very high. I haven't tried increasing the volume, but it s already more than audible at the lowest position of the pot

 (I'm using 3 opa627)


----------



## espressogeek

StanRex,
 I am very sorry to hear of your PPAv2 woes. What type of noise are you hearing? I only had noise on mine , ground hum type noise, when touching the unstrapped pot. Once I strapped it everything was OK. 

 What type of power supply are you using?


----------



## StanRex

I m using a TREAD for PS. For the noise, I ve put the ground strap, but it doesn't change anything. And I dont need to touch the pot. In fact, wether I touch it or not, it doesn't change anything. 

 There s just a lot of noise, that can be heard even though no source is connected. And the noise level goes up to a unlistenable (too loud) level if I increase the volume using the pot


----------



## FallenAngel

Quote:


  Originally Posted by *slaikan* /img/forum/go_quote.gif 
_Thanks FallenAngel, it is a very nice amp, HD595's haven't sounded as good they sound now, I only have the CMOY and the output of a Zune and Sony NW-HD5 to compare with though. I guess I'll be shopping for better hookup wire, I'll be keeping the PSU caps as you've recommended.

 What about the Panasonic FM 220uF caps in C4 and the 0.1uF WIMA's in C5, should I toy with them or just leave them as is?

 Thanks_

 

I wouldn't touch them, the caps are very nice and unless you want "audiophile" parts, you won't find better. Just not worth the trouble to replace them.

  Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_edit : tried. Nothing fried. Adjusted the bias. Then checked DC offset. 1 and 4 mV for ground and right channel, but left channel exhibits 17mV between OL and IG. I'm going to try cleaning things up a bit

 edit 2 : I've tried cleaning and reflowing a few joints, but it didn't lower the offset. could the dc offset be caused by unmatched output transistors? I tried matching the buffer transistors, but not the output ones. Anyway, I think I read that something under 20mV isn't perfect but is acceptable . So I guess I'll just move on._

 

You're suppose to measure offset between OR/OL and OG (not IG).

 Can you measure AC on the output of your TREAD to make sure it's non-existent?

 What's the current draw on the amp?


----------



## slaikan

StanRex, hang in there, it seems like its coming right. Now I'm far from being qualified compared to other posters here, I had some hissing and buzzing with my build, but grounding the pot, moving the PPA away from exposed transformers (which is probably a possibility during assemly) and adjusting the right bias all helped. I found that during testing, I heard hiss on my cheap IEM's at all levels, once I was confident enough to plug in the more expensive headphones, the hiss decreased drastically, once everything is in the right place, adjusted correctly, etc. the hiss completely went away, except at close to max volume.

 Oh, I accidently swopped the ground and left channel, lots of hiss, and had loads of echo which was interesting, but once I found my mistake, everything just came right.

 Good luck, hope it comes right soon.


----------



## slaikan

FallenAngel, thanks again. I guess I'll sit back and simply enjoy the music.... until the DIY and upgrade bug bites again in a few months, or weeks 
	

	
	
		
		

		
		
	


	




 Just just some final things, screw down the tread, close up the cases, sort out the knobs, and we're done... for now


----------



## espressogeek

Quick question for all of you experienced DIY'ers, What size and type standoffs do you use to mount your PPAv2 in a non Hammond case. Also, what case options are considered the best? I am thinking of mounting this in a case with a toroid and tread.

 Thanks in advance


----------



## StanRex

Ok, I've tried to do some debugging tonight. It's limited since I can't use my soldering iron, but heres what I've found

 DC Offsets

 3.5mv dc offset between OG and OL
 18mv dc offset between OR and OG
 1mV offset between OG and IG

 then I've set my meter to VAC and checked between OL and OG, and then between OR and OG. I thought that if noise could be heard, there must be some kind of electric signal. Since DC offset wasnt that high, I thought "it must be AC voltage". 

 Well, apparently I was wrong since my meter measured 0VAC between those points. (I'd like to say that it's not very precise in AC mode apparently, can only set it on 600VAC or 200VAC)

 Then

 AC Output of the TREAD: 

 once again, 0 according to the meter

 Then something struck me.

 Step 13

 Add the op-amp biasing cascodes

 *looks at his board*

 opamps biasing cascodes. Q1 and Q2. Erm... they re already in there... so I guess the amp is already biased in class A, even though it's not working properly.

 I checked the voltage at the three R10 and found it was 1V or so. lowered it to 0.5V. It didn't change much though, I still get a very high amount of noise.


 To give you an idea, I ve tried plugging an ipod playing some music in it and listen to the end result, and well, it's quite similar to what you get when trying to listen to a radio station you re not receiving correctly. I think that kind of noise is called white noise, not 100% sure though

 Oh and last but not least, the regulator of the TREAD gets pretty hot. I definitely need to install the heatsink on it

 I guess I should really remove the opamp biasing cascodes before debugging any further... argh... well, I'll probably do it this week, but not right now

 just a little question : should I remove R9, R10 and Q1, Q2 or only Q1, Q2 ?

 thanks in advance

 Stan

 edit : btw, I dont think the noise can be created by the transformer in my case because I m using a 24VAC wallwart, that is like 1-2m away from the TREAD+PPA block


----------



## FallenAngel

What's the current draw on the amp?
 That TREAD regulator shouldn't get hot, PPAv2 barely pulls 120mA of current, how much are you dropping through that regulator?


----------



## luvdunhill

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_Mute or disconnect one of the channels._

 

right.. so, I did that. And the off position works, but the 2 other positions sound the same to me. I'll verify everyone once I get a chance, but if there is another troubleshooting recommendation, please feel free to speak up


----------



## luvdunhill

well, the switch is definitely hooked up right. The three positions are disabled+low, enabled+low and enabled+high. When switching from high to low, I get a change from around 1.266k to 1.605k in resistance, measured from input to output on one channel (in disabled, I get 1.284k)... I suppose this looks good... interestingly enough, even though I'm using the simple configuration, I don't get any clicks in between positions... thanks!


----------



## JamesL

For those of you that have used the bass boost feature, what do you think is a good value for R7? 

 I have 10k, 15k, and 30k resistors on hand, but it'll be a major pain switching them out with the polypropylenes already soldered on.

 Tangent's guide suggests I start with a 10k, and although I want something subtle, I don't want to have to second-guess if the bass boost is working or not.

 thanks in advance


----------



## StanRex

Mmmm I officially don't understand what's going on.


 First, I've added the heatsink to the TREAD, and I've changed the output resistors to 4.7r (from 2.2)

 then

 I've tried measuring the current flowing to the PPA. However my meter is ****ty : caliber is either 10A, or 200mA and lower

 so I set it to 10A. And get 0.07. So I thought, that's ok, 70mA.

 edit : wait a second, I m just wondering. Wouldn't it be : 10A * 0.07 = 0.7A. Would definitely explain why the TREAD gets hot. I'd need to find why there's so much current flowing though

 I decided to get a more precise value, by switching to 200mA. And the meter doesn't display anything, + the LED of the PPA doesn't light up. Looks like the meter is somehow blocking the current. Which I suppose it does because it's too high (higher than 200mA?)

 anyway, what I've also found very weird, is that, like I said, I changed the output resistors from 2.2R to 4.7R. And it didn't change the DC offset. I thought it would be roughly divided by 2. But no, I still get 18 mV and 3 or 4 mV. Weiiirdddd!

 The TREAD still gets hot even though I use the heatsink

 I'm kinda lost here... I'm wondering if it could be oscillation. But the opas don't appear to get hot

 ps : here's my "config"

 OPA627BP for all opamps
 10pF at C6G (I've got a spare 100pF if you think I should try it)
 MJE243/253 for output transistors
 4.7R for the output resistors
 Wima MKT 2.2µF, 50V in C5s
 I haven't matched transistors, except for the buffer transistors


 ps2 : could someone please tell me if removing Q1 and Q2 would be enough to turn off class A bias or should I also remove R9 and maybe R10?

 thanks in advance

 Stan


----------



## tangent

Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_Wouldn't it be : 10A * 0.07 = 0.7A._

 

Only if the meter was designed by a sadist. I'd go with your lower value, 70 mA, which is a little on the low side, but perhaps sane.

  Quote:


 Would definitely explain why the TREAD gets hot. 
 

A better explanation is making it drop too much voltage. Can you send us all the values necessary to fill out the power supply parameter estimator?

  Quote:


 Looks like the meter is somehow blocking the current. Which I suppose it does because it's too high (higher than 200mA?) 
 

No. When the current is too high, something gets fried: either a fuse, or the ammeter itself. Which one happens depends on whether there's a fuse there to save the ammeter. If there is no fuse, there's a small chance you can fix the part inside the meter that died. If there is a fuse, replace it and try again.

 This is why meters often have two current ranges. You're supposed to measure on the high range first, which is set up to take almost any sane current value. Then if it measures less than 0.2 A, you can switch to your lower range to get better resolution. It's not uncommon for only the low range to be fused.

  Quote:


 I changed the output resistors from 2.2R to 4.7R. And it didn't change the DC offset. I thought it would be roughly divided by 2. 
 

The buffers are inside their corresponding op-amp's feedback loop, so changes in part values within the buffer will be greatly attenuated. Any remaining DC offset usually comes from mismatches within the op-amp itself.

  Quote:


 10pF at C6G (I've got a spare 100pF if you think I should try it) 
 

That would help if the problem is oscillation, which doesn't sound likely from what I see so far.

  Quote:


 I haven't matched transistors, except for the buffer transistors 
 

That wouldn't cause a real problem. It's just a tweak, not a necessity.

  Quote:


 could someone please tell me if removing Q1 and Q2 would be enough to turn off class A bias or should I also remove R9 and maybe R10? 
 

The simplest way to disable it is to lift R10. Pulling the transistors is much harder.


----------



## StanRex

Well, I had already used the power supply parameter estimator

 anyway, I'm using a TREAD kit, so the cap is 680uF

 the power supply is rated for 24VAC, with 35% reg, which brings us to 32.4V unloaded. Rated current is 0.5

 I live in France, line frequency = 50Hz.

 I'm using a standard aavid thermalloy heatsink from the parts list, so values should be standard or close to

 with these values and a power consumption of 0.07A, the ps parameter estimator tells me configuration is sane and that it would be 13°C higher than ambient temp

 I'll try removing R10 when I'm back home

 thanks for your help tangent


----------



## tangent

Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_I'm using a standard aavid thermalloy heatsink from the parts list_

 

The only heat sink in the TREAD part list is Aavid part number 577202B00000G, which has a thermal resistance of 24.4. The estimator's default heat sink resistance is 4, which is the default for the STEPS. Your numbers appear to be using this latter number.

  Quote:


 parameter estimator tells me configuration is sane 
 

"Sane" doesn't mean "recommended". It just means "it can be made to work". The estimator also tells you you're dropping between 13 and 23 V across the regulator, when you only need to drop 2-3 V.

 Is there a reason you can't raise the regulator's output voltage? Now that you're using OPA627s, you can go to perhaps 32 V by taking advantage of the 1-2 V drop between the PPA's power input and the op-amps. Certainly you can go to 30 V, which will help.


----------



## StanRex

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The only heat sink in the TREAD part list is Aavid part number 577202B00000G, which has a thermal resistance of 24.4. The estimator's default heat sink resistance is 4, which is the default for the STEPS. Your numbers appear to be using this latter number.

 "Sane" doesn't mean "recommended". It just means "it can be made to work". The estimator also tells you you're dropping between 13 and 23 V across the regulator, when you only need to drop 2-3 V.

 Is there a reason you can't raise the regulator's output voltage? Now that you're using OPA627s, you can go to perhaps 32 V by taking advantage of the 1-2 V drop between the PPA's power input and the op-amps. Certainly you can go to 30 V, which will help._

 

I'm not 100% sure of my numbers though. I took them from this page : http://www.farnell.com/datasheets/92411.pdf

 where I'm using the AC-2450. So output voltage, 24. The regulation % for AC/DC unreg is said to be 35% so 24*1.35 = 32.4. But I'll try measuring what I get at the jack of the transformer without anything except the meter connected to it, just to be sure

 and I'm indeed using the heatsink that has the 24.4 thermal resistance. Maybe I should try finding a better one


----------



## JamesL

I need some help troubleshooting.


 I was moving my ppa around after having added the bassboost, and there was a component-lead on my desk, that shorted something near the left side of the board(closer to the back)

 About 5 minutes later, the left side goes out. (not completely)
 I have ~44mV through the 2.2ohm output resistors, for about a 20mA bias. 
 It reads fine with no load, but when I plug headphones in, the readings start varying wildly, and at least one of the transistors get instantly hot(very)

 The voltage readings through the output resistors read as following, from front to back.
 20mV, 45mV, 150mV, ~1mV, ~1mV, 120mV

 I took brief measurements, as I'm sure those aren't safe operating conditions for the transistors(which I assume are dead), nor any surrounding component. 

 The left side is now significantly quieter than right side.

 All measurements were excellent, all transistors were closely matched, and I've been running it great for several weeks prior. I'm sure it was the short that caused the amp to fail.

 My first intuition is to replace the output transistors, but I think something else caused the transistors to run at such high currents, which in turn died from excessive heat.

 If anyone can come up with a theory.. suggestion.. conclusion.. etc , I'll be very grateful.


----------



## StanRex

I ve measured the ouput, unloaded voltage of my AC adapter and get 26VAC. According to the ps parameter estimator, that means the reg will get pretty hot. 

 I've raised the output voltage of the TREAD to 27V for future tests. If it still gets too hot, I'll consider changing the heatsink for a better one


----------



## JamesL

Some more measurements

 I'm reading +/-14v supply voltage to the right channel opamp. (I'm using a 28v supply)
 The ground and left channel are only getting around 0.5-2v at the supply pins. 

 With the opamps removed, the left channel shows around +/-9v. 

 Again, the output resistors have varying voltage drop across them when a load is connected.
 20mV, 45mV, 150mV, ~1mV, ~1mV, 120mV(front to back)

 I'm glad to say that looking at the circuit now, I have a much better understanding of the circuitry than when I started. However, I'm at loss at where a single short could leave damage at pretty much all aspects of the circuit. 
 I'm under the impression that each channel is pretty isolated from each other, except at the main power rail. 

 And to think.. I was soo close to casing it up for good. 

 It's such a shame to see such a good amp fall apart.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I'm reading +/-14v supply voltage to the right channel opamp....With the opamps removed, the left channel shows around +/-9v._

 

I'm not certain what this means. I think either the rail isolation JFETs are dead, or you have a short circuit within the low-current area. 

 Removing the op-amp should have resulted in a complete restoration of normal voltages. If it had, you'd know there was nothing wrong in the op-amp area; while it's plugged in, problems in the buffer become problems in the op-amp area, because the buffer's in the op-amp's feedback loop.

  Quote:


 I'm at loss at where a single short could leave damage at pretty much all aspects of the circuit. 
 

An individual transistor is not protected from overcurrent. If any one of them gets to pulling so much current that it melts internally to form a simple closed circuit, it will then start pulling as close to infinite current as the surrounding circuitry can manage. The surrounding circuitry contains more transistors, which in turn start failing rapidly, so the problem can cascade through the entire buffer. It happened to me once, and it's happened to a few others over the years.

 The solution is usually to replace all of the transistors in the buffer. The resistors should be fine, though if you see any that are discolored, replace them, too.

 When this happened to me, just replacing the hot transistors did nothing, because they'd get immediately killed again after applying power.

 The only thing that looks different about your situation is that removing the op-amp doesn't restore the voltage at the op-amp pins. That suggests that something south of the rail isolation JFETs is also having trouble.

 EDIT: I'm not happy with the idea that two unrelated things got killed at once, so proceed with caution. Re-transistoring the buffer may fix everything, or it may not. I'd do some more tests, with a dummy load instead of headphones. I'm sure DC offset in that left channel is very high now.

  Quote:


 I'm under the impression that each channel is pretty isolated from each other, except at the main power rail. 
 

Yes.


----------



## n_maher

Why do I see a resurrection of my smoking resistors thread in the near future...

 Best of luck fixing the PPA, I managed it so it's doable by just about anyone with opposable thumbs. Just buy plenty of spare transistors and be careful when desoldering. I think I had to replace an entire buffer at least twice and the board survived and is still in service today.


----------



## tvkalvas

Hi!

 I have some experience in DIY electronics, but not in amplifiers. I'm interested in building a headphone amplifier for my AKG K601's. I'm aiming for a PPAv2 with some modifications (no virtual ground, but a real one).

 So far I have built one channel of the PPAv2 on a solderless breadboard for testing purposes. I'm using OPA604 (just happened to have one on the shelf), BD140/139 and 1N3906/3906 transistors and BF245A for biasing. The problem I have is that there is some quite large ringing (700mV, around 1 MHz) on output pulse waveforms (pulse +/-5V). The ringing goes away when I connect a 10 Mohm scope probe on the + input of the op amp.

 Is this ringing because of the breadboard/long leads of components or could it be something real? Any idea/suggestions?

 Thanks.


----------



## tangent

Solderless breadboards are no good for fast circuits. The PPA buffer should be good up into the low MHz range, so it certainly qualifies as fast.


----------



## espressogeek

Thanks so much for Tangent and everyones effort who designed and continue to support the PPAv2 and the PIMETA. This morning I have a perfectly working example of each. I managed to fix my low bias on the left channel of the PPAv2 by changing out the 2k trimpot. There must have been a short underneath it. Before I finish this project by boxing it up I wanted to know how much I should bias the op amps? I am running LME49710's right now but I will probably try some AD744's and perhaps 637/627 combo, and maybe even a discrete op amp set such as the OPA Moon. I am running 3ma of bias right now but I don't know how much is to much? I am using wall power so I don't care about battery life, etc.
 Thanks!


----------



## StanRex

I've worked a bit on my PPA today, to try fixing it, here's what I've done :

 1/ I've realized I had forgotten to jumper S2R! doh! fixed it!

 2/ I realized that last week, I had changed the output resistors (from 2.2R to 4.7R) but hadnt touched the output buffer trim pots. So voltage was a tad low at the output resistors. I turned the trim pot to get it to 94mV (20mA)

 3/ I removed the R10s to remove class A bias, as explained by tangent.

 4/ I replaced C6G (10pF) with a 100pF. Tangent had said it could help if it was oscillating, which was unlikely. I decided to try it.

 I ve also reflown a couple joints

 What all these changed :

 DC offset of my right channel, which was near 18mV, fell down to 1mV

 However, I still get my hiss issue in all the channels

 I also decided to check how the amp sounded, even though it hissed. So I plugged an ipod as input, and listened to some tracks. Hiss wasn't the only issue. The sound felt terribly hollow, felt like there was almost no bass

 Oh, and I dunno if I had stated it earlier but i can definitely hear a change in sound when i touch something metallic on the circuit. 

 If I've understood properly, all these suggest a grounding problem. The basic troubleshooting for headphone amps page suggest looking at the amps doc for that kind of problem

 However, I can't find many suggestions for grounding issues on the ppa pages, apart from strapping the pot to the input ground if one gets noise when touching the pot. My issue is that I always get noise, even when I'm not touching the pot. Plus the pot is already grounded!

 I feel kinda lost. What would you suggest doing next? tracing a signal through the amp? or are there some tips specific to grounding issues for this amp?

 Thanks in advance for your help

 ps : my amp isn't cased atm.

 ps2 : I took some new shots.


----------



## tangent

Quote:


  Originally Posted by *espressogeek* /img/forum/go_quote.gif 
_how much I should bias the op amps?...I am running 3ma of bias right now but I don't know how much is to much?_

 

Too much is...

 1. ...when you begin engaging the op-amp's output current limit circuitry. This is much lower than the chip's rated output current limit! I'd set a hard limit of 10 mA due to this concern.

 2. ...when you can't hear a difference relative to a lower value.

 The op-amp bias on the PPA is adjustable. Since you're going to go to the trouble of rolling op-amps, why not take the same time to try different settings to see where the limit is on what you can hear? Keep in mind, you achieve class A with buffered op-amps way down below 1 mA. 3 mA is deep, deep into class A already.

  Quote:


  Originally Posted by *StanRex* /img/forum/go_quote.gif 
_I had forgotten to jumper S2R!_

 

That explains the offset: the op-amp feedback loop was open!

 If you'd had R7 installed, the problem would have been lessened, but you'd have still seen relatively high DC offset: you'd have bass boost permanently engaged, which also magnifies DC.

  Quote:


 all these suggest a grounding problem 
 

Yes.

  Quote:


 I still get my hiss issue in all the channels 
 

What's plugged into the inputs when you do the test? Ideally, the inputs should be shorted to ground.

 The alternatives are to have either nothing plugged in, in which case you could just be picking up interference, or have a source plugged in, which could be the noise source itself.

 Speaking of the inputs, I usually don't run the input jacks' ground wires to the board separately like that. I run a very short wire from one input jack to the other, then one from the joined jacks to the board.

 All of your hookup wires look excessively long. If the hiss is due to interference, this is probably how it's getting in.

 EDIT: You can mitigate some of the downside of the long input and output wires by braiding them together. This is easier to do with 3 wires than 4, another reason to wire the input jacks' grounds together and run only one ground wire to the board.

  Quote:


 my amp isn't cased atm. 
 

Putting it in a metal case could fix an interference problem, though case ground does complicate things.


----------



## espressogeek

Tangent, thanks for the reply about the bias of the op amps. I will try some more comparing when I have time to do some critical listening!


----------



## StanRex

It's alive! I tried it with my Senn hd650, after double checking a few things and it delivers!!!

 now, to bias it into class A 
	

	
	
		
		

		
			





; try different opamps ^^ and case it

 thanks a lot for your help guys, Tangent for all his advices, info and espressogeek for keeping me motivated ^^


----------



## espressogeek

StanRex, What was the exact issue? I'm very glad to hear it is alive!


----------



## StanRex

I was using neutrik nys rca jacks for input, and hadnt taken the time to properly screw the ring that connected ground. It didn't made contact most of the time with the jack, so my input ground wasnt ok ^^


 yup, I feel a bit ashamed ^^

 I'm definitely going to try opamps other than the 627 though. They're really impressive when it comes to detail, but I feel the sound lacks "life". Maybe because of my source, I ve only tested it from the output jack of an Ipod, I'll soon try with my alienDAC. 

 I'll also try with the 637.I ve heard the AD825 were great for the senns hd650. Also going to throw in some ad8610.

 oh and I must say that removing the opamps from their socket is quite hard with all the other components in the way ^^

 it's a really fine sounding amp. Can't wait to bias it in class A


----------



## espressogeek

I'm so glad to hear it StanRex. The ipod out does sound a little lame. I have a cheap used sony cd player over here and the line out clobbers the ipod. 

 Congrats again!

 Oh, I have not used the 627 but I am running LME49710's in the PPA and LME49710 and LME49720 in the PIMETA and they sound great on the HD-580s on my ears. Let me know what you end up with!


----------



## rds

I'm using opa827s with my PPA, and wondering if it would be better to solder them this way:




 Rather than using browndog adapters. It seems those adapters would add more inductance than is healthy.
 On the other hand this method adds extra solder points.
 What do you guys think? ...yeah, I'm probably over thinking this.
 (btw, opa827s are SOIC only)


----------



## Beefy

I'd keep them on Browndog adapters, personally. If only so that they can be switched in and out easier.

 I wonder if anybody has tried these OPAMPs in an MMM yet?


----------



## StanRex

Hopefully last update :

 I've biased the amp in class A, swapped opamps around a bit.

 Impressions :

 Full opa627 : good
 ad 825 : unimpressed
 opa627 on G, 637 on L/R : WOW!!!

 After trying the 627/637 combo, I was sold. Sound is detailed and has enough "punch" to satisfy me.

 I still have to case the beast though. will post pics when it's done

 thanks to everyone who helped me through this build! tangent, espressogeek, fallenangel and all the others


----------



## JamesL

Thanks a bunch bunch for all your help tangent.
 I have been busy a bit and haven't yet touched the ppa for the past week, but I do have some 'corrected' measurements now.


  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_EDIT: I'm not happy with the idea that two unrelated things got killed at once, so proceed with caution. Re-transistoring the buffer may fix everything, or it may not. I'd do some more tests, with a dummy load instead of headphones. I'm sure DC offset in that left channel is very high now.
_

 

I've tested the output transistors again, and I think I made a mis-read one of the buffer bias readings. The right channel reads about a 18mA on both sides, which seems fairly close to the expected value. 

 Right now.. as far as measurements go (with load)

 Right channel
 - Buffer - ok
 - Opamps - bad (~0v)

 Left Channel
 - Buffer - bad (1mA & 55mA)
 - opamps - ok

 Ground channel
 - Buffer - bad (1mA & 55mA)
 - opamps - bad (~0v)


 Do you think the op amps, TLE, and cascode JFETS may be in need for replacement as well?
 Do you think it's possible that a bad/fried opamp can re-do the damage to the buffer once I replace the transistors?

 Thanks once again.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_The right channel reads about a 18mA_

 

Are you interpreting a voltage reading, or did you actually measure current? Please report only what you actually measured.

 (I sincerely hope you're not trying to measure current at the buffer's output.)

  Quote:


 Opamps - bad (~0v) 
 

I don't know what this means. Between what two points are you making this reading? 

 You indicate that this is an approximation...to what precision? 0.0 mV is greatly different from 0.01 V.

 "0 V" does not equal "bad" without context. There are cases where it is exactly correct. I would expect 0 V between op-amp output and OR, for example, or nearly 0 V between op-amp +IN and -IN.

  Quote:


 Do you think the op amps, TLE, and cascode JFETS may be in need for replacement as well? 
 

In the entire history of the PPA, no one has ever been so unlucky. I think it's far more likely that you're misinterpreting what you're seeing or mismeasuring something than half the amp managing to destroy itself all at once.


----------



## JamesL

Quote:


 Are you interpreting a voltage reading, or did you actually measure current? Please report only what you actually measured. 
 

I'm sorry about being unclear. I believe I measured about 40mV across 2.2R after the output of both the right channel's transistors. 
 2mV and 120mV after each of the transistors on the ground and left channels.

 My TREAD supply outputs a steady 29v. 

  Quote:


 I don't know what this means. Between what two points are you making this reading? 

 You indicate that this is an approximation...to what precision? 0.0 mV is greatly different from 0.01 V.

 "0 V" does not equal "bad" without context. There are cases where it is exactly correct. I would expect 0 V between op-amp output and OR, for example, or nearly 0 V between op-amp +IN and -IN. 
 

I am measuring about + 0.1v at the positive supply pin, and about -0.5v at the negative supply pin.. or vice versa. 

 The output transistors were heating up rapidly to extremely high temperatures, so I did not want to keep the amp on for long.
 Thus, the measurements were rather hasty. However, I did measure it several times, and it consistently read something close to 0, but not exactly 0. 



  Quote:


 In the entire history of the PPA, no one has ever been so unlucky. I think it's far more likely that you're misinterpreting what you're seeing or mismeasuring something than half the amp managing to destroy itself all at once. 
 

I could only hope so, but there is no doubt that something got messed up when I shorted 'something' on the board. 
 I had taken careful measurements before when it worked properly, and it had measured very well then.


 edit - one important thing I forgot to mention.
 I mentioned that the left channel(I think) failed(got quiet) while I was listening to it about 1 minute after the accident. 
 Soon after, I shorted the ground and right channel by pulling out my TRS plug.


----------



## tangent

Pull the op-amps and re-measure with no load.

 Also, to be clear, you are measuring these voltages against...what? IG? OG? V-?

 Compare voltage measurements of the power supply unplugged from the amp, and plugged in with the amp's idle current. Then you may also briefly test with a dummy load on. No headphones from this point forward, until we're sure it's not going to fry them.


----------



## JamesL

Quote:


 Pull the op-amps and re-measure with no load. 
 

Opamp supply voltage with no opamps in place(Vs-/Vs+)
 Ground -2.23/+0.53
 Right -14.47/+14.41
 Left -2.09/-0.47


  Quote:


 Also, to be clear, you are measuring these voltages against...what? IG? OG? V-? 
 

The opamp supply voltages are measured against input ground.
 The voltage going through the output resistors are measured before and after the output resistor.

  Quote:


 Compare voltage measurements of the power supply unplugged from the amp, and plugged in with the amp's idle current. 
 

Power supply voltage
 29.57v with no load
 29.56v with amplifier drawing idle current






_Measurement overview_
 **All buffer measurements are across 2.2R output resistor in mV
 **All opamp measurements are measured against IG, in VDC
 **The order of measurements are as follows - Left, Ground, Right (bottom to top of board)
 **PSU measurements are made before the schotty diode. The diode drops approximately 0.9V. 
 **No source is connected



 Without opamp - 
 Buffer -> +41.1/-40.9, +40.1/-40.2, +2.7/0
 Opamp -> -2.09/-0.47, -2.23/+0.53, -14.47/+14.41
 PSU -> 29.57VDC

 With opamp -
 Buffer -> +41.1/-40.9, +41.8/-42.0, +43.6/-43.2
 Opamp -> -2.1/-0.45, -2.1/-0.6, -13.74/+13.8
 PSU -> 29.56VDC

 With opamp & load - 
 Buffer -> +45/-42, +120/-4, +2/-124
 Opamp -> -2.1/-0.5, -2.1/-0.3, -13.7/+13.8
 PSU -> 29.54VDC



 **Measurements are exactly as seen; The "+2.7/0" measurement for the buffer w/o opamps was triple-checked; The voltage after the NPN transistor shows exactly 0 volts; some opamps are seeing negative voltage at the positive supply pin.
 **I wasn't sure of polarity, but the positive lead was connected to OG while measuring the buffer. Actual polarity may be reverse.


----------



## tangent

If it were me trying to fix this, I'd retransistor both the left and ground channels. I mean both bipolars and JFETs. I might even consider starting with a fresh board, to avoid the risk of further problems due to weakened traces, moving across only the parts known to be good and easy to move.

 It's quite possible for either ground to kill one other channel (right, typically, through the TRS plug) or for one of the stereo channels to kill the ground by trying to make it sink more current than it's capable of. I would be more suspicious if all three channels appeared dead, or only left and right. Ground and one other isn't diagnostically interesting.


----------



## tvkalvas

I got convinced in building the real PPAv2 instead of a modification, but before proceeding I would like to ask one question about the design. Why id there three TLEs driving the ground?

 As no component is perfect and the rail isolation JFETs have large manufacturing spreads the TLEs will disagree on what the ground should be and therefore they will fight over control. This contest is going to cause extra current draw, which will then cause extra voltage drop on the rail isolation JFETs. The ground will be balanced somewhere about in the middle of V+ and V- for sure, but I think this is a weird way to do this.

 There was some talk in this thread about this extra current draw caused by the three TLEs (around page 20 or so). I didn't find an answer if the rail isolation JFETs should be matched to minimize this effect?

 And another idea: What if there was only one TLE? The three op-amp could still have separate rails but only one set of them would be used to make the input ground. Does this sound weird? 

 And then another question:
 Have you grounded the case of PPA to the ground produced by the TLEs or to V-? What would be the recommended grounding point if single-point grounding is done? At the input RCA plugs?


----------



## tangent

Quote:


  Originally Posted by *tvkalvas* /img/forum/go_quote.gif 
_Why id there three TLEs driving the ground?_

 

To provide a short path to virtual ground for each channel. If you use just one TLE to drive IG on such a large 2-sided board, you risk problems due to the relatively high resistance across the whole span of the ground traces. It is possible that having just one would be sufficient with a 4-layer board, where one layer is almost completely filled and tied to virtual ground.

  Quote:


 the TLEs will...fight over control 
 

I raised the same objection early on in the PPAv1 design effort. ppl told me to just try it. I did, it worked, and it has continued to work for every PPA since.

  Quote:


 This contest is going to cause extra current draw 
 

As a result of my early misgivings, the first PPAv1 prototype had jumpers on the output of the TLEs for disconnecting them from the local section of IG and for inserting an ammeter there. I didn't find excessive currents flowing here.

  Quote:


 I didn't find an answer if the rail isolation JFETs should be matched to minimize this effect? 
 

If you are of a temperament to match transistors, I'd match them simply because it will make the op-amp supply voltages and the isolation levels consistent.

  Quote:


 Have you grounded the case of PPA to the ground produced by the TLEs or to V-? What would be the recommended grounding point if single-point grounding is done? At the input RCA plugs? 
 

Various people have done it both ways. I think there are fewer difficulties with tying a metal chassis to IG rather than V-, but depending on the circumstances, you could make a good argument for using V- instead.


----------



## Uncle Bob

I've just completed a PPA v2 build but I'm having some basic issues which I'm hoping someone can help me out with.

 I'm using a 24V Tread based power supply which is gives out 24.1V unloaded and has been powering another hp amp without problems.

 The opamps are not installed and I'm getting some very low voltages at the power pins, in fact voltage readings seem off everywhere.

 S1- & S1+ / S2L & S2R are shorted. D1 is installed.
 RLED is installed but the LED is not connected.
 BASS boost is not installed. BBR is open

_measured from vgnd pads_
 V+ on Opamp R = 0.91V
 V+ on Opamp G = 0.91V
 V+ on Opamp L = 0.87V
 V- on Opamp R = -0.68V
 V- on Opamp G = -0.67V
 V- on Opamp L = -0.69V
 +pad of C1 = 0.92V

_measured from dc input pad V-_
 +pad of C1 = 1.65V

 also the voltage measured across the DC input pads (V+/V-) is 2.3V

 Resistance measured
 V+ to V- = open
 V+ to C1+ = 180R (via D1)
 V- to C1- = short

 edit: nothing appears to get hot
 Any ideas anyone?


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_I'm using a 24V Tread based power supply which is gives out 24.1V unloaded and has been powering another hp amp without problems._

 

I don't suppose it's using an LDO regulator? If so, that's the problem. An LDO can't cope with the 1000-2000 uF of rail capacitance in the PPA.

  Quote:


 _measured from dc input pad V-_
 +pad of C1 = 1.65V

 also the voltage measured across the DC input pads (V+/V-) is 2.3V 
 

What's the supply's voltage when disconnected from the PPA? If it shoots back up, and it's an LDO, that confirms the above guess. If it shoots back up and it's a standard regulator, there may be another problem with the supply.


----------



## Uncle Bob

Tangent, I think you're right...
 It is indeed an LDO regulator, the humble LM317T to be precise. I failed to spot the caveat on your website, specifically referring to the PPA/Tread problem -damn!

 Is there an easy way to make the tread work with a PPA?

 edit: reading a bit more.. it seems as far as I can understand it that the LM317 is not an LDO regulator? I have just under 2000uF of rail capacitance installed (5 x 390uF) - so do I just need a beefier regulator - e.g LM338T or something else?
 just incase it's relevant to the problem, the tread is powered by a 15V+15V 15VA torroid with the secondaries wired in series to give 30V


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_it seems as far as I can understand it that the LM317 is not an LDO regulator?_

 

Yes, the 317 is a standard regulator. It shouldn't have any problem working with the PPA. The fact that its output voltage collapses suggests a deeper problem.

  Quote:


 do I just need a beefier regulator - e.g LM338T or something else? 
 

Only if the load is actually killing the 317. See the system design section of the TREAD docs. Also pay attention to the matters of switching.

  Quote:


 the tread is powered by a 15V+15V 15VA torroid with the secondaries wired in series to give 30V 
 

That's fine.

 Can you post pictures of the setup, and/or a schematic diagram of how it's all connected?

 Are you sure the supply still works with the other circuit? Let's make sure it's not been killed.


----------



## Uncle Bob

OK, a little further info.

 The tread is still functional - still powers the other amp ok.

 S1- & S1+ are shorted so there is no switching on the PPA side
 The tread is not switched, so the only on off switch is on the AC side.

 With the tread disconnected from the PPA, with TP2 as common I get roughly +/- 24V at TP1 and TP3 on the tread pcb.

 Connected to the PPA, TP3 reads -2.2V and TP1 reads roughly 40V, also the 317 gets very hot, very quickly.

 Sorry about pics, having problems with my camera atm - I might have to see if I can borrow one.

 thanks for your help so far


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_S1- & S1+ are shorted so there is no switching on the PPA side_

 

You can simulate every configuration you need, assuming there is a power connector between the two circuits. I guess you've been leaving the TREAD plugged into the PPA, and powering the two circuits up together. If so, try powering the TREAD up separately, then plugging it into the PPA.

  Quote:


 with TP2 as common I get roughly +/- 24V at TP1 and TP3 on the tread pcb. 
 







 Either the TREAD isn't properly configured, the regulator is shorted, or you aren't measuring correctly.

 First, the TREAD provides only a single output voltage. "+/-" has no place in TREAD measurements. Do you mean just 24V, or are you reading 48V and splitting it for our benefit?

 Second, are you truly saying you read the same voltage for the unregulated and regulated sides of the TREAD? If so, it's not regulating at all, so no surprise that it's not behaving properly. You need at least 2 Vdc drop across the regulator for it to be able to regulate. If the input side is 24 Vdc, you need to dial the output voltage down to give the LM317 enough voltage to play with, so it can do its job.

  Quote:


 TP3 reads -2.2V and TP1 reads roughly 40V 
 

This also makes no sense.

 First, the LM317 can't drive its output below TP2. Are you measuring backwards, and really getting 2.2V? The black probe goes on TP2.

 Second, the 40V reading on the unregulated side makes me wonder if you weren't reading 48V unregulated above under no load. (Your +/-24V number.) If so, that's an awful lot of voltage for the LM317 to drop, especially at the fairly high current load presented by a PPA. I wonder if it's possible the TREAD is doing more or less what it's supposed to, and you're just running it into thermal shutdown.

 What do you get out of the Power Supply Parameter Estimator ?


----------



## Uncle Bob

Sorry, I really should read your docs before starting to measure things and you're absolutely right, there's no such thing as -V in a tread, I was just measuring backwards between TP1 and 2.

 some pics of the PPA















 and one, not very good shot of the tread






 I'll re-do the measurements, and I will try installing a switch to the PPA and I'll get back to you.

 thanks for your helpful comments so far.


----------



## tangent

No heat sink on the TREAD and a 24 V drop across it strongly suggests thermal shutdown.


----------



## Uncle Bob

I'm still having no luck with this 
	

	
	
		
		

		
		
	


	




 Having tried switching the PPA after the tread and I've installed a heatsink on the regulator with no change to the problem, the voltage output on the tread still sags when connected to the PPA but instantly returns to full output when the PPA is disconnected - even though the regulator is burning hot at that point.

 Some measurements on the tread

 ac in from the transformer is 36.6V
 tp1 to tp3 reads 48V dc ???
 tp2 to tp3 reads 24.1 dc

 the moment the ppa is switched on, tp1 to tp3 reads 8V and tp2 to tp3 reads 5.2V. voltage measured at the PPA power pads reads 4.6V

 where do I go from here?


----------



## tangent

What's the thermal resistance of the heat sink? I took a wild guess and put it at 10 ohms, and get some pretty high heat numbers, still, from the estimator. If your heat sink is smaller, thermal shutdown can still explain the problem. If you don't have another heat sink to try, you can try dialing the output voltage of the TREAD up to 30 or so. If that fixes it, it's a heat problem.

 You can also try testing the power supply in isolation. To simulate the 0.1 A or so a PPA will draw, put a big 220 ohm or so power resistor across it. (No less than 3W, or it'll burn up!) If you can't get such a high-valued power resistor, you can build a Smarty Load from an LM317 and an easier-to-find low-value power resistor. A 10 ohm resistor here will give 0.125 A, close enough, and such resistors are easy to find.


----------



## rogerlike

.


----------



## Uncle Bob

Tangent, thanks once again for your insight and suggestions.

 The tread was originally built to power a Creek HP amp and for that it works very well. The Heatsink I used was rated at 21°C/W which the estimator warns will allow the regulator to get too hot but in practice with the Creek amp it works fine.

 I have a spare tread board which I plan to use as a dedicated PPA power unit and I've got some higher rated heatsinks to use if required. 

 Playing with the numbers in your estimator program, it's seems the main route to happiness is to reduce the voltage drop by reducing the AC input voltage or allowing the output voltage to be closer to the input voltage, correct?

 The difficulty is that common transformer ratings seem to be either 12+12, which would be too low to make a 24Vdc ps or 15+15 which is too high. 

 I will be using AD825 op-amps (at least to start with) so I suppose these should be ok with a 30V supply (assuming this produces +/- 15V in the PPA)

 It doesn't seem possible for the estimator to show any possible benefits of using a higher rated regulator like the LM337 or LM338? Would there be any benefit? as I've not yet built the 2nd tread, I'm open to suggestions.


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_the estimator warns will allow the regulator to get too hot_

 

And so, I expect, it does.

  Quote:


 in practice with the Creek amp it works fine. 
 

You're not comparing apples to apples. The Creek probably draws a lot less current than the PPA. Halve the current, halve the temperature rise.

  Quote:


 Playing with the numbers in your estimator program, it's seems the main route to happiness is to reduce the voltage drop by reducing the AC input voltage or allowing the output voltage to be closer to the input voltage, correct? 
 

Yes.

  Quote:


 common transformer ratings seem to be either 12+12, which would be too low to make a 24Vdc 
 

Not true. Try it in the estimator, and you'll see that after the voltage rise from not fully loading the transformer and rectification, you can often get 24 VDC (or even a little more) from a 24 VAC transformer. You're not creating voltage here, it's just that transformers behave a little weirder than you might initially expect.

  Quote:


 I will be using AD825 op-amps (at least to start with) so I suppose these should be ok with a 30V supply (assuming this produces +/- 15V in the PPA) 
 

There are voltage drops in the PPA that will usually soak up 1-2V, so your supply voltage can actually be a smidge higher than 30V, saving you even more heat.

  Quote:


 It doesn't seem possible for the estimator to show any possible benefits of using a higher rated regulator like the LM337 or LM338? 
 

It's true, the estimator ignores output impedance. Its main purpose is to calculate heat and voltage drops. The regulator type doesn't affect that at all.

 By the way the 337 is just the negative version of the 317. It has no place in this discussion.

  Quote:


 Would there be any benefit? 
 

Electrically, yes. Whether you can hear it or not, or whether you require the electrical benefit is something you'll have to figure out for yourself.


----------



## Uncle Bob

Further update but it's not good news unfortunately 
	

	
	
		
		

		
			





 I've replaced R1 in the Tread and adjusted the output trimmer to give 30V dc. But I still see the same problem when the Tread is attached to the PPA.

 The only differences are that the voltage sags to about 4.5V now (was around 2.3V before) and that the regulator heatsink now takes several seconds before it gets too hot to touch.

 Does this indicate that the problem is likely to be somewhere in the PPA?

 I should mention that for Q21/22 and Q31/32 I'm using 2N3904/2N3906 as these were the only readily obtainable types that didn't have a reversed pinout.

 edit: Q21,22,23 are 2N3904 and Q31,32,33 are 2N3906


----------



## scytheavatar

I am planning on building a STEPS for my new PPAV2. The problem is that I bloody hate ordering from that Digikey due to my bad experiences in the past, and I can't find a Amveco transformer from Mouser or Farnell. Does anyone know of an alternative I can look at?


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_The only differences are that the voltage sags to about 4.5V now (was around 2.3V before) and that the regulator heatsink now takes several seconds before it gets too hot to touch.

 Does this indicate that the problem is likely to be somewhere in the PPA?_

 

No, it means you haven't gone far enough yet. The best bet is to swap out the transformer/wall wart for one with a more appropriate voltage to your target. Ideally, you want no more voltage drop across the regulator than absolutely needed to keep it in regulation in the worst case. A less effective step is to use a bigger heat sink; this isn't recommended as a first step because it's attacking the symptom instead of the case.

  Quote:


 I should mention that for Q21/22 and Q31/32 I'm using 2N3904/2N3906 as these were the only readily obtainable types that didn't have a reversed pinout. 
 

Those are perfectly reasonable transistors.

  Quote:


  Originally Posted by *scytheavatar* 
_I can't find a Amveco transformer from Mouser or Farnell. Does anyone know of an alternative I can look at?_

 

Any dual-primary/dual-secondary toroid will work. There's a bolt hole in the board to mount it. You can find a few reports in the archives here from people who have done this. The hardest part is figuring out which wire goes into which hole. Between the pinout diagrams for both the Amvecos and the transformer you choose, you should be able to figure it out fairly easily.


----------



## Uncle Bob

I had hoped that reconfiguring the Tread output to be closer to the rated voltage of the transformer would have been enough. 
	

	
	
		
		

		
		
	


	





 Playing with the power supply estimator doesn't give many sane scenarios in the desired voltage range when using raw AC input but a regulated DC input seems to offer more hope. 

 However, most of the available commercial power supplies are now switch mode types. Would using a switch mode PSU into the Tread for PPA power be a sensible option?

 Otherwise, what would be my best option to power the PPA?


----------



## tangent

Quote:


  Originally Posted by *Uncle Bob* /img/forum/go_quote.gif 
_Playing with the power supply estimator doesn't give many sane scenarios in the desired voltage range when using raw AC input_

 

Nonsense. There are literally infinite possibilities.

 One, for example, if you have a dual secondary transformer, is to put the secondaries in parallel instead of in series. This will get you twice the current at half the voltage compared to your current situation. Based on what we're seeing in your results above, you might even manage 24 VDC out of the whole thing. 18 V would certainly be achievable, and is still enough.

  Quote:


 a regulated DC input seems to offer more hope. 
 

It does make things easier, yes.

  Quote:


 most of the available commercial power supplies are now switch mode types. Would using a switch mode PSU into the Tread for PPA power be a sensible option? 
 

No.

 The first problem with switch-mode wall warts is that they're almost always not isolated.

 The second is, if you manage to find one that is isolated, you'd be paying for an extra regulator you don't need.

 Third, the regulator you do have isn't going to do well at removing the HF noise put out by the switcher.

 I'd go with a cheap unregulated supply. This still avoids a lot of the voltage drop issues you're seeing, while still putting a lot of problems safely away in another box.

  Quote:


 what would be my best option to power the PPA? 
 

You rejected a +/-12VAC transformer above, and then I told you why you shouldn't reject it. Have you revisited the option?


----------



## linuxworks

quick question: anyone have strong feelings about the ad797 on the ppa? ppav1 but not sure it matters.

 I had a pair of them (old eval pair) and I'm liking them a lot. but they're bipolar and that's supposed to be 'wrong' for the ppa, right (?)

 I'm also not using any special pin6,8 caps (as the data sheet says to). I don't *hear* any problems but have not tried putting it on a scope yet. should I add the 50pf cap just to be safe?


----------



## tangent

Have you checked DC offset, then?

 I'm not wild about using chips made for high gain applications in headphone amps. There's just too much risk of oscillation; the design is counting on the extra gain, and you're not giving it to it. I'm not saying you're doomed, just that if you're going to do it, put it on a scope after you get done with the offset test. Scope it with headhones plugged in.


----------



## linuxworks

that would be checking dc offset from virtual ground or the ground channel and the L and R outs?

 I'm assuming the TLE's ground (electrical ground) and not the ground *channel*'s output is where I should measure from (with the other point being the L or R out).


----------



## tangent

OG to OL and OG to OR are the most important, but it's also useful to check IG to OG. All should be under 20 mV. If they're not, it's oscillating or the bipolar inputs are causing too much offset.


----------



## linuxworks

I need a new scope! ;(

 darnit.

 I have a cheapie velleman lcd digital (that I bought years ago) as a handheld. it has no 'zero' function to short input probe to ground (line flat display) and when I switch from ac to dc coupling on the scope the line is not at zero so my meter is not even usable for this ;(

 if I could trust it, it showed something less than 10mv of dc offset from the ground channel output to L or R. interestingly it varies with volume control and the inputs left floating (maybe I should have shorted ppa's inputs?).

 at any rate, I'll get a new scope somehow and be more careful about dc offsets since that seems to be the hot issue to worry about with bipolars. 
	

	
	
		
		

		
		
	


	




 the sound DID seem quite nice, so there was no oscillating I could detect. if I wanted to try to zero out the dc, assuming I was in love with this kind of op-amp, what is the best way to do it? or is this circuit just not cut out for this kind of OA?


----------



## Uncle Bob

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Nonsense. There are literally infinite possibilities.

 One, for example, if you have a dual secondary transformer, is to put the secondaries in parallel instead of in series. This will get you twice the current at half the voltage compared to your current situation. Based on what we're seeing in your results above, you might even manage 24 VDC out of the whole thing. 18 V would certainly be achievable, and is still enough._

 

OK, I will try parallelling the secondaries over the weekend to see if I can get 15~18V into the PPA.

  Quote:


 You rejected a +/-12VAC transformer above, and then I told you why you shouldn't reject it. Have you revisited the option? 
 

It wasn't a rejection as such, I was simply trying to work with what I already had. If a transfomer with dual 12VAC secondaries was definately going to work then I'd buy one.


----------



## tangent

Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_I need a new scope! ;(_

 

Maybe, but you shouldn't use a scope for DC offset measurements. Even a cheap DMM will give more accurate results. Scopes are for looking at fast signals, DMMs for slow ones.

  Quote:


 it varies with volume control and the inputs left floating 
 

Naturally. From the op-amp input pins' point of view, the resistance to ground is changing. A pot is only constant resistance from the amp's source view.

  Quote:


 maybe I should have shorted ppa's inputs? 
 

Regardless of the above, this is still a good idea. It eliminates the possibility that you're looking at induced noise as well as offset. Alternately, you can just plug in a source, which means you measure both offsets together, which from one perspective adds confusion, but is still useful because you do care about total offset.

  Quote:


 if I wanted to try to zero out the dc, assuming I was in love with this kind of op-amp, what is the best way to do it? 
 

Balance the input offset currents. Working with Cranky Op-Amps

  Quote:


  Originally Posted by *Uncle Bob* 
_I will try parallelling the secondaries over the weekend to see if I can get 15~18V into the PPA._

 

Aim high. I think 24 V may be doable. The higher you can go, the less power lost as heat.

  Quote:


 I was simply trying to work with what I already had. 
 

Good plan. Get it working with this trafo first. Once that's done, you can think about getting a higher voltage unit which is sized more appropriately.

  Quote:


 If a transfomer with dual 12VAC secondaries was definately going to work then I'd buy one. 
 

It definitely _can_ work, but as you've found out, it takes planning and careful design to find the correct transformer.


----------



## Uncle Bob

Some further tests on my ongoing PPA/Tread problem.

 I've tried parallelling the outputs on my transformer as suggested with pretty much the same results;

 Tread configured for 17V to 22V output (there was almost no adjustment of output on a higher setting)

 15+15V, 15VA transformer, secondaries parallelled
 - 18.6VAC unloaded output
 - 21.6VDC output max
 - 16.7VDC output min
 connected to the PPA, gives 4.9VDC at PPA terminals, regulator gets hot quickly, transformer is cool.

 12V+12V 3.2VA Transformer, secondaries parallelled
 - 15.8VAC output unloaded.
 - 16.7VDC tread output (min)
 - 17.9VDC tread output (max)
 connected to the PPA gives 3.4VDC, regulator does not get hot (barely warm) even after several minutes but transformer does get fairly warm.


----------



## tangent

Okay, try the amp with a different supply. We don't need to get fancy...a spare unregulated wall wart with any reasonable voltage and enough current will do.


----------



## Uncle Bob

I thought I might try with a 9V battery - useful test or waste of time?


----------



## tangent

Waste of time unless it's rechargeable. Alkaline and zinc chemistries don't like to put out more than about 30 mA continuously. A PPA wants something like 100 mA. NiCd, NiMH, lithium...they'll all deliver enough current continuously for the test.

 Rather than go buy batteries, though, look around your house. I just repurposed a wall wart made for a Netgear switch I had that died, for instance. If the measured voltage when unloaded is significantly higher than the labelled voltage, it's unregulated, so it's fine for testing. (Then, later, you can add a regulator to get an audio quality supply.)


----------



## Uncle Bob

I have just tested my PPA with the Creek OBH-1 power supply from my OBH-11. This is rated at 24vdc unregulated, 150mA.

 The OBH-1 gives out 33vdc unloaded, but connected to the PPA I measure 4.2vdc at the power input pads.


----------



## tangent

Can you measure current draw when this is happening, with the OBH-1? If your meter offers a choice between a high and low-current scale, use the high-current one first. It could easily be pulling more than the 200 mA that's a common limit for the low-current scale.


----------



## Uncle Bob

Current draw measured just over an amp! After several minutes, Q23 and Q33 on left and ground channels were very hot. all other components cool. 

 It's also fried the OBH-1 
	

	
	
		
		

		
			





 but it's probably repairable.


----------



## tangent

Something's clearly shorted. Either there are parts damaged, or you've got a solder bridge. You're going to have to poke around to figure this out.

 By the way, all the work on the power supply was not for naught. The efficiency improvements will pay off when you get the PPA working.


----------



## applegd

Anyone used OPA827 in PPAv2?

 From one of the emails sent from TI weeks ago, I got the impression that OPA827 is somewhat the successor of OPA627. From slew rate alone, OPA827's is 28V/us, comparing OPA627's 55V/us, I was not impressed at all. It is just better than OPA134's 20V/us.


----------



## rds

Quote:


 Anyone used OPA827 in PPAv2? 
 

I do - it's a very nice op-amp.
 I used to have 627s in it.


----------



## applegd

Quote:


  Originally Posted by *rds* /img/forum/go_quote.gif 
_I do - it's a very nice op-amp.
 I used to have 627s in it._

 

Thanks very much!

 As of now, I am using 637 for LR,627 for G. I will change them to 827 soon.


----------



## dlosborne

I have been toying (i.e., thinkiness guessing) at a decent gain for a 32 Ohm load. Yeah, Grados.

 Would there be any stability issues with a gain of 5, assuming AD8610s all around? Or, any considerations I may be missing?

 My goal is to be able to use more than 30degrees of the volume pot.

 (I do realize I will need to be careful if/when adding bass boost to avoid an ultra-sensitive setup.)


----------



## FallenAngel

There should not be any stability issues with any gain when using AD8610, only a few opamps are unstable at low gains (OPA637, OPA228).

 For Grados, I would actually use AD8065 in all channels but I also really like AD825, perhaps AD8065 on Left/Right and AD825 (I have heard that AD8065 sometimes doesn't like to be in unity gain).

 I used a PPAv2 with a gain of 4.5 with Grados, it was not pretty good. You might want to raise it to a gain of 8 just to make sure you can toss in OPA637 at a later time. The easiest and best way to do this is to simply socket R4 and plug in whatever resistors you want to change the gain.


----------



## dlosborne

Good point on the socket bit. (I should have picked that up after reading Tangent's breadboard suggestion.) 
 The only other thought I had was building a gain switch; say 5, 8, and 10.
 However, I tend to be a little zen with my equipment and doubt I will be using anything else other than my current headphones. ... but the possibility is always there. So, sockets it is!

 Any issues biasing AD8065/825 to class A?

 (Edit: This won't be a portable job. The data sheet doesn't seem to raise any red flags, but I feel only one step away from approaching these like Helan Keller at an art festival.)


----------



## tangent

I recently switched one of my PPAs over to AD825's. I don't remember the gain...built it years ago...but it's certainly lower than 5, and it's a fully-loaded PPA, so it's biased into class A for certain. Seems to be working fine.


----------



## dlosborne

Good to know; the AD825s have good reviews and seem to live happily in a some well respected commercial equipment as well as being a choice upgrade option.
 One of the better things is their price. These things are shockingly cheap; lower cost does not always mean lower performance. (The reverse assumption is a trap I try to be conscious of.)

 I am also encouraged by the review notes indicating midrange emphasis; that is exactly where I need a bit more. (My previous career has left me with a severely sagging mid-range in my audiometry exams. Even my GS1000s sound flat (and senns are down right depressed) in the 4k to 10k region. Bright can/amp combinations certainly help.)

 I will keep the sockets high enough to get them off easily once I get an R4 value that works well.

 Thanks for the advice and enough of my diatribe!


----------



## grenert

I like AD825 all around as well. I preferred it to OPA637/OPA627 and AD843 all around. It produces a very clean, balanced sound, without any "coloring." The AD843 is beefier in the low end, but otherwise lacking. One nice thing about the PPA is the bass boost, which I think is a better way to add bass than choosing a "bassy" opamp. I found the OPA setup simply muddy.


----------



## Vaughn

I am officially climbing aboard the PPAv2 train...

 I've just ordered my boards and pots. I plan on implementing the bass boost 
 feature as well as the battery board for portability. I will be using it to power my current favorites, a Fostex T20v2 and a T50rp(both orthodynamic; 55 and 50 ohms, respectively).
 I will, of course, be relying heavily on the knowledge collected here to successfully complete it!


----------



## Vaughn

I will be ordering parts soon for my PPAv2 with battery board and I'm wondering if any of you have built this and which Hammond enclosure is the best fit. 

 I suppose I could build everything up and then order the enclosure but I would like to order everything at once to save on shipping costs.


----------



## funch

It's designed for the Hammond 1455N1601 enclosure, which will fit both 
 the amp and the battery board quite nicely. The two that I built used
 C1's (220uF/25V) that were 20mm tall. Any taller and you may run into
 part of the case. My setup used 12 AAA cells and a 24V power supply
 which worked quite well.

 Here's a link to my ad with pix. Hope they help:
http://www.head-fi.org/forums/f42/so...-board-375873/
http://i183.photobucket.com/albums/x...d/100_1522.jpg


----------



## Vaughn

Thanks Funch, the photos help enormously. 

 That is a beautiful amp, I wish I had been in the market when it was for sale!


----------



## funch

Thanks. Building it will be more fun. Be sure to scour Tangent's tutorials,
 and don't hesistate to PM me if you have any questions.


----------



## Vaughn

Thanks funch, I will definitely be taking you up on that offer...

 I have printed out loads of info from the Tangent website for my night time
 reading and am trying to absorb all of it before I start ordering parts.


----------



## Vaughn

I've got several windows up trying to order all of the parts for the PPAv2 and 
 I've got a question regarding the output transistors...

 The parts lists recommends the MJE243os and MJE253os transistors for outputs, apparently only available from Digikey. Unfortunately when I try to order them from there it keeps on stating I have met the minimum order. Is there a way around this or, alternately, are these available elsewhere?


----------



## MisterX

Quote:


 MJE243os and MJE253os 
 

Those part numbers are obsolete. 
 Try: 
 MJE253G
 MJE243G


----------



## Vaughn

Thanks Misterx, I don't know why their website doesn't redirect me to the current part number!


----------



## rogerlike

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Thanks. Building it will be more fun._

 

Maybe not so much fun, but I can attest to the enjoyment of buying funch's PPAv2. It _is_ beautiful. BTW The 637s sound great with it. Thanks again funch, especially for the support!


----------



## dlosborne

I know this question has been approached to death from nearly every angle and I apologize for any pain this subject may again surface; I have pondered the various posts and related net search hits to no clear answer. So, here I goes…

 As suggested (though clearly not imperative), when matching output transistors (e.g., MJE243/MJE253), are we matching?:

 1)DC current gain between like parts in all three channels (i.e., hFE (MJE243) L=R=G & hFE (MJE253) L=R=G), or

 2)DC current gain between the complementary pairs in each channel (i.e., hFE(MJE243)/ hFE(MJE253) as close to unity as possible), or

 3)1 & 2 together

 I have built a simple collector voltage test block as suggested by this site: Transistor matching. (It’s more entertaining than eBay-ing another meter.)

 I am not really concerned about the exact hFE values, the relative Vc values are good enough, but what value relationship to match has been confusing.


----------



## tangent

Definitely not #2, because there's really no such thing as "complementary". NPNs and PNPs are inherently different beasts. You can still try, and getting it close is nice, but don't go insane buying bags of transistors just to find an NPN with an uncommonly low hFE to go with a PNP with an uncommonly high hFE.

 The idea is to match the same part among the channels, so the channels all have the same distortion profile.

 The story's a little different with the small-signal transistors behind the output pair. You might guess from a quick glance at their respective datasheets that the 2N5086 goes with the 5088, and the 5087 with the 5089, but if you look at the hFE ranges, you'll see why we paired the 5087 with the 5088 instead: it gives you at least some hope of matching pairs within a channel in addition to across channels. Besides, these transistors are cheaper, and you had to buy a lot of them anyway, so finer matching is more sensible. You just measure them all, arranging them on a sheet of paper or in a fishing tackle box, say, and use pairs that are closest to each other.


----------



## dlosborne

Now that does clear up the issue; thank you! 

 Truly, I am really only doing this for the sport of it and not because I believe it is crucial for my listening pleasure (or headphone's safety).

 The choice of 2N5087/2N5088 did make sense after reviewing the data sheets. 

 The way I had my test block set up was so that I could measure collector voltages on any pair independently as well as the difference in potential between any two...just in case #2 was the goal. (Yes, the resistors were matched beyond my fluke 87s range; I have access to literally pounds of resistors, caps, and most active components.)

 I don't plan on going nuts on the matching. The range of close is determined by the volume of coffee in the morning's pot. The only active components I even intended to put effort into are the output buffer transistors (2N5087/2N5088 & the MJE's) and Q3. Or?

 For Q3, though, I was going to sort by Idss and pick those that would have slightly (10-15% ?) higher saturation currents than the estimated downstream full load current. 

 Waste of time?


----------



## NelsonVandal

Quote:


  Originally Posted by *dlosborne* /img/forum/go_quote.gif 
_I know this question has been approached to death from nearly every angle and I apologize for any pain this subject may again surface; I have pondered the various posts and related net search hits to no clear answer. So, here I goes…

 As suggested (though clearly not imperative), when matching output transistors (e.g., MJE243/MJE253), are we matching?:

 1)DC current gain between like parts in all three channels (i.e., hFE (MJE243) L=R=G & hFE (MJE253) L=R=G), or

 2)DC current gain between the complementary pairs in each channel (i.e., hFE(MJE243)/ hFE(MJE253) as close to unity as possible), or

 3)1 & 2 together

 I have built a simple collector voltage test block as suggested by this site: Transistor matching. (It’s more entertaining than eBay-ing another meter.)

 I am not really concerned about the exact hFE values, the relative Vc values are good enough, but what value relationship to match has been confusing._

 

If you're using the buffers inside the loop of an opamp like in the PPA, matching is not of the essence. If you were to match the transistors, the "input" small signal transistors seem to be more important to match. Not between channels, just the complementary pair in one channel at a time. It's really a pain to try to find matching complementary pairs, and will probably be expensive as well.

 IMO transistors do sound different. At diamondstar.de you can find some words on how different output transistors sound. The small signal transistors are equally influential. I don't know how the 508x's sound, but there are some good transistors from Sanyo and Toshiba.


----------



## tomb

Actually ... you'll find that the output transistors are so consistent in HFE that matching is unnecessary anyway. I've gone through _a lot_ of the output transistors listed on Steinchen's site and they rarely vary by much more than about 5 HFE - many vary less than 1 or 2 HFE - and this is measured over a quantity of 100-300 (MJE243/253 is around 180).

 It's the TO-92 transistors - 2N5087/2N5088's - that can vary widely - anywhere from a low of 250 HFE to over 600 (generally speaking).

 It's correct that the transistors can sound very different, but these differences are supposed to be cancelled out in a design with global feedback.


 EDIT: I'm not that familiar with the PPA, so you'll have to cut me some slack. However, the Q3 transistors are used to isolate the power rails to the opamps, apparently - something with which I'm not familiar. Instead, I believe you may mean Q4 when you're referring to "Q3." Q4 is the current setting JFET for the diamond buffers. These JFETs (one per channel) are in series with the R12 trimmers. So current matching of these JFETs is not really necessary, since you can directly adjust their current with the trimmers.


----------



## NelsonVandal

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_It's correct that the transistors can sound very different, but these differences are supposed to be cancelled out in a design with global feedback._

 

But they're not. Didn't you notice any differeces when you rolled output transistors?

 Regarding matching of transistors. Last time I bought BD137/137, the PNP's was in the region 240 - 250 and the NPN's 80 - 140.


----------



## tomb

Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_But they're not. Didn't you notice any differeces when you rolled output transistors?_

 

Not what? The PPA uses global feedback. Differences in sound quality between transistors will be much, much less than an amp without feedback such as a CKKIII or a Millett MAX/MiniMAX.

  Quote:


 Regarding matching of transistors. Last time I bought BD137/137, the PNP's was in the region 240 - 250 and the NPN's 80 - 140. 
 

For PNP's that would be sufficient for a matching group, anyway. For the NPN's, I'd be interested in how many you found that were really distant from 140. I haven't found either to be that far off. 2SC3422/2SA1359, 2SC3421/2SA1358, 2SC2238/2SA968 - none of these hardly vary more than 1-2 from HFE from the data sheet, which is listed as 240. Toshiba doesn't even list a range as the BD's and MJE's do. Sanyo does for the 2SC2344/2SA1011, but I haven't found them that far off, either.

 Still, there is not nearly the benefit to matching the outputs as with the smaller transistors, especially Q23 and Q33 - and it costs major $$ to do this with output transistors. Some of these output transistors are well over $1-$2 each. Whereas, you can purchase 2N5087's and 2N5088's for $3-$5 per hundred.


----------



## dlosborne

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Actually ... you'll find that the output transistors are so consistent in HFE that matching is unnecessary anyway. I've gone through a lot of the output transistors listed on Steinchen's site and they rarely vary by much more than about 5 HFE - many vary less than 1 or 2 HFE - and this is measured over a quantity of 100-300 (MJE243/253 is around 180)._

 

Over the last couple of hours, I have found that as well. It seems to help if they are all from the same batch run. Oh, well, it was a fun learning process.

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_It's the TO-92 transistors - 2N5087/2N5088's - that can vary widely - anywhere from a low of 250 HFE to over 600 (generally speaking)._

 

True, and these seem to work fine regardless of matching. It is my understanding the design of the diamond buffer helps mitigate this and close is better than good enough. I suspect this is the case since there hundreds of great sounding PPAs out there that have been assembled without any matching at all. I will do a little sorting here since I already built the danged test block and have a couple ten thousand of them in my office’s back bay.

 In tomb’s response to NelsonVandal:
  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_It's correct that the transistors can sound very different, but these differences are supposed to be cancelled out in a design with global feedback._

 

I don’t contest transistor sound variations and certainly don’t know enough about audio electronic circuits to even start speculating on how solid state components can intrinsically alter sound profiles. For me though; as I can tell the difference between different transistor circuits (e.g., opamps and some buffers) with concentrated effort, I strongly doubt my hearing can determine variations in specific transistor models within those circuits.

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_EDIT: I'm not that familiar with the PPA, so you'll have to cut me some slack._

 

No worries; until six-months ago, my range of electrical experience was limited to 480V through 765kV. That stuff is simple in comparison to this new hobby.

  Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_However, the Q3 transistors are used to isolate the power rails to the opamps, apparently - something with which I'm not familiar. Instead, I believe you may mean Q4 when you're referring to "Q3." Q4 is the current setting JFET for the diamond buffers. These JFETs (one per channel) are in series with the R12 trimmers. So current matching of these JFETs is not really necessary, since you can directly adjust their current with the trimmers._

 

My understanding of Q3 is that, when downstream load-currents are near the upper limits of the JFET’s Idss, these transistors are more efficient at ‘cleaning’ AC contamination from the supply current. (That is assuming anything appreciable is left from the power supply and the primary rail capacitors.) This provides a very clean DC supply to the opamps. Just be sure that the load current does not exceed the saturation current; we don’t want to starve the heart of the system.

 You are right that Q4 functions as a stable current source for biasing the buffer and is adjusted by a trimpot. Matching the Idss between the three just puts the trimpot positions closer together; not really that interesting at all.


----------



## tomb

Yep - I agree with all your statements.
	

	
	
		
		

		
		
	


	




 As I've mentioned many times in the MAX/MiniMAX threads, the primary reason for "matching" the TO-92's is to weed out the real oddballs. Generally speaking (very generally), you can easily get groupings at some number between 300 to 450, but then there are those odd ones that are all the way out to 600.

 As you say, the buffer will perform just fine without any matching. However, loosely matched, you can find differences in bias from the PNP output to the NPN output in each channel. A reasonable "sorting" of the TO-92's will help to minimize this.


----------



## tangent

One more comment about Q4: it's possible if their Idsses are too far apart that you'll get into a situation where two channels adjust to a given desired value, but the third can't stretch that far. If they're matched, all three will have similar adjustment limits. I think that's a good thing, since there's no point in one channel having a much different range from the other two. You might wish for a different range for all three, but never for just one.


----------



## dlosborne

*Slaps forehead*
 That's something, (once explained, mind you), that I feel silly having missed.
 I wonder how often that happens (in either the buffer or opamp bias circuit), and it just lives on as an unknown bug?

 That is what tomb was getting at; testing transistor parameters isn't always focused on finding perfect matches, but is also very useful in sorting _out_ the odd balls. (Repetition helps my aging brain, eh? Thanks, TomB)

 Okay, now that I have all the good bits and pieces after my 'sorting day', time to warm the iron...it's been waiting a long time for this.


----------



## applegd

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Actually ... you'll find that the output transistors are so consistent in HFE that matching is unnecessary anyway. I've gone through a lot of the output transistors listed on Steinchen's site and they rarely vary by much more than about 5 HFE - many vary less than 1 or 2 HFE - and this is measured over a quantity of 100-300 (MJE243/253 is around 180)._

 

For my case(years ago), this point is true for MJE243(20 pieces from same batch) but not for MJE253(20 pieces from the same batch) which I bought from mouser. Maybe I was just not lucky enough....


----------



## Dan55

Hi all,

 I've been assembling a ppav2 and unsurprisingly have failed the very first test. When I plug in the power supply, the LED does not light up, and I am not getting any power to the op-amp sockets. I am getting about .8v between v+ and v- but almost nothing between s1+ and s1-, which I did jumper across. Does this indicate that I have reversed the power supply polarity or are there other possible explanations (I'm still working on schematic and layout reading)?

 Thanks in advance for any assistance. Sorry for the lack of photos, but I don't have a camera with me. I'll try to post some pics if this is not a quick fix.

 edit: I idiotically jumpered s1 incorrectly. Things are okay for the moment. I guess I really needed that nap. One more question though, I wanted to make sure that I could get the amp working before I purchased more expensive opamps. I have three OPA134PAs that I was planning to use for testing; can these opamps do any damage to the amp?


----------



## tangent

The OPA134s will work fine. Buffered, they should even sound pretty good. Not awesome, but not bad for sure.


----------



## Dan55

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The OPA134s will work fine. Buffered, they should even sound pretty good. Not awesome, but not bad for sure._

 

Tangent,

 Thanks very much for the reply and for the assembly instructions and also for the parts shop 
	

	
	
		
		

		
		
	


	




. I have a little troubleshooting to do as I am getting some significant hiss (I have yet to ground the pot), but otherwise things are working well. Hopefully I'll be able to order some chip adaptors soon...


----------



## Dan55

In an interesting reversal of correct procedure I fired up the amplifier with source/cheap phones connected before measuring DC offset. I ended up frying my left phone before noticing the problem (bad joints on the op-amp socket in the left channel). I am now getting much more volume out of the right channel than the left, which was not remedied by switching the op-amps. I’m wondering if it’s likely that I damaged components in the left channel or if I should be looking for other explanations. 

 I am also getting a lot of hiss from the amp; I’m not sure if this is related to the above problem. I have not yet enclosed the amp, which I read could lead to some background noise. 

 On the bright side, I think I might soon be able to start a helpful thread for newbies entitled "things not to do when building amps."


----------



## tangent

If you had one bad joint, you might have two.

 Post high res pictures (600-800 px wide on longest edge, closely cropped) of both sides of the board. That frequently yields a solution, as someone experienced -- or just with fresh eyes -- will see something you didn't.


----------



## Dan55

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_If you had one bad joint, you might have two.

 Post high res pictures (600-800 px wide on longest edge, closely cropped) of both sides of the board. That frequently yields a solution, as someone experienced -- or just with fresh eyes -- will see something you didn't._

 

Okay. I'll try to get my hands on a digital camera in the near future. In the meantime, I'll reflow some joints. Thanks!


----------



## TubeStack

Which came first - this or the PA2V2?


----------



## tangent

The first public showing of the PPAv2 was in March 2003. Ideas in the design go back a lot longer than that.

 Why do you ask?


----------



## dhp

If you think the PA2v2 is anything like the PPAv2...


----------



## TubeStack

I don't know anything about the PPAv2.

 Very similar names, curious about a relationship, if any?


----------



## MisterX

None. 
 Good point about the names though. 
 Maybe they should change the name from PA2V2 to POSv2?


----------



## Dan55

I got the amp working after fixing a few more stupid mistakes. I'm really impressed with the sound even with the OPA134s. I look forward to adding better opamps and the tweaks, at which point I'm sure I'll make some more mistakes. Thanks for the help, especially Tangent's Troubleshooting article!


----------



## tangent

For the benefit of future troubleshooters, care to say what was causing the problem?


----------



## Dan55

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_For the benefit of future troubleshooters, care to say what was causing the problem?_

 

Well I was hoping to avoid the specifics but after spending most of the day in Barnes and Noble reading about electronics and staring at the schematic for a few hours, I realized that I had neglected to jumper S2R. It was not my proudest moment.


----------



## DKJones96

When using the bass boost pot you have to manually wire from the pot to the right channel don't you?

 I've been going nuts trying to figure out why the right channel gets full bass no matter what and the left channel works perfectly...


----------



## MisterX

Quote:


 When using the bass boost pot you have to manually wire from the pot to the right channel don't you? 
 

Yep. 

  Quote:


 Finally, you need to run two wires from the pads marked BBR to the R7R pads. The left channel is already wired like this on the board. Layout constraints prevented us from pre-wiring the right channel the same way.


----------



## poweld

So first things first: I'm very new to all of this, and I'm looking for a bit of help 

 So I'm the new guy on the block. I've built a couple of CMoys, and decided to take the plunge into PPAv2. I've got it assembled up to the point of biasing the three channels. Unfortunately I'm a bit bummed out, cause I'm measuring from virtual ground across the final (2.2 Ohm) output resistors, and I'm seeing the voltage is not stable.

 Does anybody have any idea why this might be happening?


----------



## linuxworks

are your inputs shorted to ground when you check outputs?


----------



## linuxworks

also, you have a jumper on s2l but not the matching one to the right. is that correct??


----------



## poweld

Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_are your inputs shorted to ground when you check outputs?_

 

No, I'm not shorting the inputs to ground. Should I?

  Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_also, you have a jumper on s2l but not the matching one to the right. is that correct??_

 

Yes, that's correct, and I suppose I feel kind of silly not noticing that.. I suppose I was just looking for S2 to jumper, not noticing BBR. I suppose that should be jumpered as well before taking the readings?

 Thanks!

 edit: are you sure I should have a jumper on BBR? Looking at earlier pics they seems to be unjumpered...


----------



## MisterX

Yes, you should jumper the "BBR" pads. 

 Also... what output transistors are you using? 
 (why are they all installed backwards?)


----------



## poweld

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_Yes, you should jumper the "BBR" pads. 

 Also... what output transistors are you using? 
 (why are they all installed backwards?)_

 

OK, I will jumper the BBR pad.

 Are they backwards? Really, I'm a fool when it comes to this stuff, but I'm trying. Positive is BD139 negative BD140.


----------



## linuxworks

you should short the inputs to ground otherwise your amp will 'pick up noise' and you'll see THAT in your output measurements.

 if you are trying to bias (etc) you want stable inputs and shorting each input to ground is the standard way about that.


----------



## MisterX

Quote:


  Originally Posted by *poweld* /img/forum/go_quote.gif 
_OK, I will jumper the BBR pad.

 Are they backwards? Really, I'm a fool when it comes to this stuff, but I'm trying. Positive is BD139 negative BD140._

 

From Step-by-Step Assembly Guide







 Notice what way the exposed "thermal" pads are facing in tangent's picture?


----------



## poweld

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_From Step-by-Step Assembly Guide






 Notice what way the exposed "thermal" pads are facing in tangent's picture?_

 

Yes, I noticed that in looking at the picture, but must have gotten them flipped (clearly). I suppose this is a pretty egregious error that would be causing weird voltages in the buffer?

 edit: would these two errors (this and the BBR not being jumpered) cause any damage? I wasn't noticing any excessive heat or anything, but I'm worried..


----------



## MisterX

Good question. 
 Can't say that I have ever made the mistake of installing the output transistors backwards.
 Knock on wood. 
 They may just be OK but it might be a good idea to replace them since you have to remove them anyhow?


----------



## poweld

Unfortunately I don't have any extras on hand, and will have to put in an order to Mouser to get replacements. I'm going to try after work just flipping them, jumpering BBR, and hope for the best. It'd be a real shame if I did serious damage to the output buffers...

 I'll let you guys know how it turns out tonight. Thank you so much.


----------



## linuxworks

if you do order, get a few extra sets. they are not THAT much and I've learned to get extras for situations just like this 
	

	
	
		
		

		
		
	


	




 I was about to power up a minimax and found I put the transistors in the 'mating' holes instead of the proper ones. luckily I found it *before* power-up. visual checking before power-up can not be over-stated! so, you learn this once and won't have to learn it again 
	

	
	
		
		

		
		
	


	




 at any rate, order a set and a spare set. in case


----------



## poweld

Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_if you do order, get a few extra sets. they are not THAT much and I've learned to get extras for situations just like this 
	

	
	
		
		

		
		
	


	




 I was about to power up a minimax and found I put the transistors in the 'mating' holes instead of the proper ones. luckily I found it *before* power-up. visual checking before power-up can not be over-stated! so, you learn this once and won't have to learn it again 
	

	
	
		
		

		
		
	


	




 at any rate, order a set and a spare set. in case 
	

	
	
		
		

		
		
	


	


_

 

Perfectly reasonable logic, and I will do just that (if this doesn't seem to fix anything). I do have another question though: is there any possibility that (if there is damage) the wreckage could reach beyond the buffers? Say, into the opamps?


----------



## MisterX

I doubt that would damage the op-amps.


----------



## linuxworks

see, the neat thing about op-amps is that if its blown, you replace the socketed chip. no need to worry about 'missing' the middle part when you blew a whole set or might have blown a whole set. and when you replace the op-amp, it all 'matches' internally (lol).

 people hate on op-amps but I do like the real-world convenience they give you.

 as long as you installed them ok, I would agree that its not likely their magic blue smoke escaped


----------



## poweld

So! Good news and bad news. I managed to get the transistors out, flip them, and bias the trim pots. Tested it out and I have sound!

 But...

 My left channel is significantly quiter sounding than my right channel. I traced back to the opamp, where both left and right are receiving about 11.5 V +/-, and the signal in is fairly similar, but the output on the good right channel is 23mV and on the bad left channel 6.7mv.

 Since I'm still new at this, I won't immediately jump to conclusions, but I have a feeling that...

 What do you guys think?


----------



## MisterX

Switch the op-amps around (put the op-amp from the right channel in the left channel and the op-amp from the left channel in the right channel)

 If the low output problem moves with the op-amp.....


----------



## poweld

Interesting. Well, I'm happy to say that after switching the opamps the problem still lies in the right channel... however now I'm confused. I'm going to go back to the office tomorrow to use their tools, but before I get there do you guys have any guesses where the problem might lie?

 Oh I should also mention that there's a significant amount of hiss with or without input right now. I can only hear it in the left channel right now (since that one is getting way more power) but I assume it's in both. This may be irrelevant since I haven't grounded the pot yet, and the board is just lying on my desk.

 edit: Nix the hiss issue for the most part. I just got my DAC in the mail (would have been impeccable timing had I gotten this thing working tonight 
	

	
	
		
		

		
		
	


	




). There's still some hissing, but I'm going to chalk that up to the pot not being grounded and the board laying out like it is.

 Oh and in the spirit of honesty, I did not jumper BBR. I looked at the schematic and the PCB diagram, and it looks perfectly harmless as is.

 Could this be due to a busted TLE in the faulty channel? Just doing as much thinking as I can before I get in there tomorrow..


----------



## tangent

Quote:


  Originally Posted by *poweld* /img/forum/go_quote.gif 
_Interesting. Well, I'm happy to say that after switching the opamps the problem still lies in the right channel... however now I'm confused. I'm going to go back to the office tomorrow to use their tools, but before I get there do you guys have any guesses where the problem might lie?_

 

It's possible the output transistors were damaged, either when installed backwards or when transplanted.

 If you have a transistor tester you can take them out and check them. If they're fried, hFE will be compromised.

 You can also check them with a diode meter: bipolars have a diode junction from base to emitter and base to collector, the polarity flipping for NPN vs PNP.

  Quote:


 edit: Nix the hiss issue for the most part. I just got my DAC in the mail (would have been impeccable timing had I gotten this thing working tonight 
	

	
	
		
		

		
		
	


	




). There's still some hissing, but I'm going to chalk that up to the pot not being grounded and the board laying out like it is. 
 

I haven't found PPAs to be greatly susceptible to RFI. Shielding them can help, but usually hiss portends something else. Could indeed be a noisy source, but can also be too-high gain, oscillation, or a roached circuit element.

  Quote:


 I did not jumper BBR. I looked at the schematic and the PCB diagram, and it looks perfectly harmless as is. 
 

That's right, there's no point in shorting BBR.

  Quote:


 Could this be due to a busted TLE in the faulty channel? 
 

Sure, but I don't see a reason to blame it in particular. It's easy to check that it's dividing the voltage correctly. If so, move on to other suspects.

  Quote:


 will have to put in an order to Mouser to get replacements 
 

Just for perspective, I priced comparable transistors at places you're likely to find them locally, and it'll cost you more and you'll get lower quality, even accounting for shipping from Mouser. Unless you must get it up and running _today_, it makes sense to get some more output transistors.

 If you find that the problem is something else, well, good transistors are useful to have around anyway.


----------



## poweld

Well it sounds like my best bet is to get a new set of output transistors to replace the ones I may have broken.

 One more thing that may or may not be telling: I'm doing a little more testing listening to them. Listening to Paul Simon's "Under African Skies" I hear the good channel very (probably overly loud), but it also sounds like it's got a ton of reverb on the midrange, and the midrange is also very removed. Kinda spooky, like Paul's ghost is singing.

 Anyway, I'm not certain if that is at all telling. I'm putting in the order now, and will hope that replacing those transistors solves the problem. Next update on Thursday


----------



## tangent

Reverb means some kind of ground channel issue, or grounding in general. What's the voltage between IG and OG?


----------



## poweld

Dummy post, just letting you know I packed up my gear, so I'll unpack it now and check, then post my results here. Gimme a few, and thanks for helping me out tangent 
	

	
	
		
		

		
		
	


	




 update: Between input and output ground I have a reading of -0.3 mV, or rather 0 mV more likely, since my meter reads 0.3 mV when disconnected.

 Also, my left channel has 2.1 mV to out, and my right shows 32.6 mV

 I switched up some of the cabling since I believe I read the output jack data sheet wrong. The loudness and reverb is coming from the right channel, and the quiet but (seemingly) accurate is coming from the left channel.


----------



## Joannha98

Thanks, for sharing the links.


----------



## poweld

Oh wow. OK, after tracing around to find where the problem might be, I've found a major culprit. So, I'm thinking that you guys were on the right track earlier when you were telling me to jumper *BBR*, but you just weren't using the right words. You clearly meant *S2R*. Because man, that thing is not jumpered, and I feel like a total fool.

 I can't wait till 5 to go jumper that bad boy and try the amp out again


----------



## poweld

Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_also, you have a jumper on s2l but not the matching one to the right. is that correct??_

 

I'd like to also apologize to you, since you were dead on. I just thought you meant BBR. *sigh*

 I guess it's all a part of the learning process. Anyway, 5PM can't come soon enough.


----------



## poweld

Sorry for dominating this thread. After fixing my mistake things cleared right up. Biasing into class A and adding bass boost seems fine as well, and I'm really enjoying the sound!

 Unfortunately, I've run into one (I presume) last issue. I don't have the casing fully drilled out yet, but I've temporarily mounted the board in the aluminum case without caps on the ends.

 Outside of the casing the amp sounds fine, and I can turn the pots to full with almost no audible hum or hiss. Inside the case I get humming. My friend suggested that I try connecting virtual ground to the case, but of course that would make my board either irremovable or at least just a pain to work with.

 Is there any other solution or thoughts you guys might have? I'm using the Elpac 24V .33A power supply, and all of my components are insulated (though they're not attached to the case ends right now anyway).

 Thanks!

 edit: some more findings: when I touch the casing, the humming increases, and when I touch the volume pot it decreases (stops). I've already grounded the pot though by unscrewing the corner screw and securing a grounding wire underneath it. Confuuuused.


----------



## tangent

Take an overhead pic and post it here. It needs to show all the ground and case connections.


----------



## poweld

Been quite busy between work, but I really pushed really hard to finish the amp. I fixed the buzzing- I believe one of my grounding cables was not as secure as I'd hoped. 
 The device is all boxed up now (as of an hour ago) and I'm thoroughly satisfied both with the end product and the amount I learned from creating it.

 My heartfelt thanks go out to Morsel, Tangent, and PPL for creating this DIY. Also, thanks to those that offered their help and experience here on the forum; 
 your advice was invaluable (still so embarrassed about the backwards transistors 
	

	
	
		
		

		
		
	


	




)

 Let the 
	

	
	
		
		

		
		
	


	




 begin!


----------



## scytheavatar

So I am about to finish my PPAv2 but on Basic Troubleshooting for Headphone Amplifiers it is mentioned about the DC offset between input and output ground "This number should be exceedingly low. I’d be bothered by 1 mV here, and would be sure of problems with 5 mV." As it turns out, I have a voltage of 1.04 mV between the input and output ground, which means that I should be "bothered". Then for my right channel I have an offset of 7mV, which kinds of bother me too. So what should I check to see if I could reduce the DC offsets? This is with 3 X AD843 , output resistor of 3.3 ohm, output bias current of 30mA, C6 of 100pF, bass boast jumped off and no class A transistors installed, the rest following the default configuration.


----------



## tangent

The AD843 is notoriously difficult to get stable in the PPA. I see that you've done some of the recommended tweaks, but I'd still scope the outputs to be sure it isn't oscillating. If it is, that explains the offset.


----------



## applegd

Just play around. Couple months ago, I did some PSpice simulation for the standalone diamond buffer.........

 Red line: Input
 Green Line: Output

 Load:330 Ohm





 Load:64 Ohm


----------



## dlosborne

After weeks of great service and an addition of a gamma1 lite configured by MisterX to slide in the top of a 1455N case, my PPAv2 has developed a nasty issue:
 Evil-Loud-Hiss enters the scene (about the same volume as B.B. King's strings) with an associated high DC offset (15mV-25mV) in one side or the other, seemingly random, and sometimes in both channels. I popped everything out of the case to investigate and can easily cause this by changing source, applying a probe to one channel (in reference to output ground), or cranking up the volume rapidly.

 AD825 in all channels
 2R2 output resistors
 Gain of 5
 All standard (as per Tangent's site) transistors, resistors, and caps
 10pF C6
 No Class A bias
 Output bias set at 20mA (as measured at 44mV across the R24/34)
 No Bass Boost (S2s are jumpered)
 This happens with either the DAC in or RCA in from my CD player.

 I first noticed this in a pair of Grado's and promptly swapped them with my sacrificial 32Ohm test bunnies (old apple ipod buds). 

 I didn't think (or read) that the AD825s were prone to oscillation at low gains, but I could be wrong. After dialing down the output bias to 15mA the problem went away... for a couple hours. I adjusted the bias up to 30mA; again, all quite until I turned up the volume and the right channel started hissing. I unplugged the amp and plugged it back in; problem gone. I attached my gator clips to my output ground and the left channel (test points near the output jack) and was promptly rewarded with Evil-Loud-Hiss' presence in that channel only. I can do the same thing on either channel with about a 50% success rate.

 Before I start swapping the R24/34s to 3.3 or 4.7 jobs, adding teeny bypass caps to the power pads on the opamps, playing with the gain (losing half my volume pots range), replacing R8, I thought I might post the issue for advice/humor.

 Thoughts? (Thanks, by the way)


----------



## tangent

Sounds like oscillation due to capacitive load. The fact that it follows the probe is a dead giveaway.

 While the 825s should be fine with G=5, remember that the ground channel is G=1. Raising the gain of L&R might just be missing the point. A more likely fix is to increase C6, which damps the ground channel's tendency to take off into oscillation.

 Bypass caps could also help.


----------



## dlosborne

That sounds like a much easier job than replacing R24/34.
 Is there any drawback to ramping C6 right up to 100pF?

 Also, I have a hand full of 22pF ceramics; I assume these would be adequate bypass caps if necessary. They would be very easy to solder the disk dang near to right on the brown dog adapters. The leg to ground can be as long as needed from my reading; I have extra single post sockets and would drop these in the ground holes just east of the chips if I ever did want to swap opamps.


----------



## dlosborne

UPDATE: 

 I don't know how I missed it in my finger-numbing search fest yesterday, but this could be the prime Evil-Loud-Hiss thread for all those in need of exorcising him from this particular amp/headphone combination:
http://www.head-fi.org/forums/f6/ppa...bility-415863/
 The boiled down solution I am perusing is to drop the value of R11 to 100-200 Ohms for ultra sensitive headphones such as the gs-1000i jobs. This thread was particularly on target for me since these are the same headphones as I am using. I can reproduce the same hiss with an old ipod ear bud (32 ohm) sacrificial/test victim. Adding the Grado extension cable also 'fixed' the problem (to the ear buds as well). Once I get a chance to spot solder a couple of 100 ohm resistors to the R11s, I will drop a post here for record.
 If this doesn't work, I may consider a small cap (22pF? - since I have a ton of them) in parallel with R6. From my interpretation of the rather technical discussion this would create a very high pass filter in the feedback loop. I read this as similar to the bass boost idea of feeding back higher frequencies and not the low ones we want to ‘boost’: block the normal range and then some by putting the knee FAR above anything we, or even dogs, can hear to remove the frequencies responsible for kicking the opamps into oscillation.

 EDIT: title added for searchers


----------



## dlosborne

Problem solved:

 R11 was dropped to 100 Ohms. 

 There is no hiss, distortion, or any noise for that matter. Using a gamma1 lite as source, no music playing, Tread at 24V, there is only silence.

 The only way to get noise in right now is to max the volume pot...then I hear a faint whoosh when I close my eyes and hold my breath.


 foobar/flac -> γ1 -> PPAv2 ->


----------



## MisterX

Do we get to see some pics now?


----------



## dlosborne

I certainly will!

 Unfortunately I will be out of the country for the next 6 days. (-Sitting in JFK right now)

 I will get them in there, though; (especially the bit with the gamma lite slid in a 1455N with the PPAv2).


----------



## dlosborne

I had my co-worker snap a shot. (Who happened to be playing with it in my absence - another issue since I thought I had the only key to my office).

 I ordered new end panels since the old ones were jacked up so bad and, as you can see, I have been playing around with the guts. I still have to replace the source selector switch and its molex connectors (as the DAC is the only thing in there now), the power switch, and add source LEDs to the front.


----------



## tangent

Ah...headphones _and_ fountain pens...a man after my own heart. Noodler's not Diamine, but it suffices.


----------



## dlosborne

(And we haven't even started on my HP calculator collection - and repair business- , but that would be far too OT. Noodler works better in both my Pelikan and Vanishing Point and doesn't bleed too much on cheap paper but the colors are not nearly as good, true.)

 The gamma1 fit so dang perfectly in the case. I had to slide it forward to give room for the line-in conductors; it hovers right above the pots with a bit less than a 1/4" gap. The PPA board is still on the second slot up. MisterX did a damned fine job with the DAC boards. I will, however mount a mini-USB(B) in the back plate and splice in a 3/5" cable to make disconnection easier.
 It is amazing what kind of plans you can come up with when a couple thousand miles away separates you from the project. (And a proper cup of coffee.)
 Also, I have been wondering if I will need to switch source ground (RCA inputs or DAC/USB) as well (i.e., three-pole switch and isolate the DAC board & panel-mounted input sockets. I think I will hold off to see if it is a problem but leave room for a three-pole body in the back.


----------



## dlosborne

MisterX, attached are the promised photos.

 I still have to fix the rear panel; but, just to show how well the y1 fit in there, these will suffice.

 So, my first DIY is that much closer to being done.

 (Sadly, now that this ‘works’ and I am really digging the sound, I am afraid I may just put off finishing this thing up unit Tangent publishes the new power supply boards.)


----------



## Magic77

I am the starting to build the PPAv2 and have a question about S2. I see S2R and S2L. I assume I will be putting a jumper across both of these? I will not be using Bass Boost. If anyone can just answer Yes or No. Thanks.


----------



## FallenAngel

Yes


----------



## Magic77

I have some OPA604's on hand and would like to use these in the PPAv2 before I spend the big bucks on the OPA627's. Would the OPA604's be OK to try out first? Thanks.


----------



## Magic77

I need some help with adjusting the Buffer Bias. I have tested my power supply and Tested the amp,Part 1. Everything is OK so far. In the step-by-step assembly guide it says; The default bias for the PPA's output stage is 20ma. If you are using the default 2.2 ohm resistors,this will force 44mV across each output resistor.

 I am using the default 2.2 ohm resistors. Do I still need to make the adjustments and check the voltages across the default resistors? If I'm Ok with the 20ma bias; should I just leave it alone and not try to adjust the R12's? Thanks for any help or advice.


----------



## MisterX

Quote:


 Do I still need to make the adjustments and check the voltages across the default resistors? 
 

Yes


----------



## FallenAngel

Definitely try OPA604, I like them.


----------



## Magic77

I adjusted the R12's and got the voltages up to around 44mV on each channel. When I powered up the amp and took the readings again, the voltage started at around 40mV and took a few seconds to reach 44mV. Is that normal for the voltage to take a few seconds to reach the correct reading when first powering up? Thanks.


----------



## FallenAngel

Transistors have a negative temperature coefficient - as they transistors heat up, they will conduct more current, that is how they work and normal (as opposed to MOSFET which have a positive temperature coefficient and they conduct less current the hotter they get).

 Start the amp, keep it running for 20 minutes, and adjust again.


----------



## rds

Quote:


  Originally Posted by *Magic77* /img/forum/go_quote.gif 
_I adjusted the R12's and got the voltages up to around 44mV on each channel. When I powered up the amp and took the readings again, the voltage started at around 40mV and took a few seconds to reach 44mV. Is that normal for the voltage to take a few seconds to reach the correct reading when first powering up? Thanks._

 

yes, it takes some time for the buffers to stabilize


----------



## MisterX

Yes, that behavior is normal for a device that has a negative temperature coefficient.


----------



## Magic77

Thank you very much to everyone for the helpful responses. I'll let you know how everything is working after I do the panels and wiring. Thanks again.


----------



## Magic77

I have completed my PPAv2. It is working, I have Music and it sounds great so far.
	

	
	
		
		

		
			





 It took me 6 days from start to finish to complete, but it took 2 weeks to prepare prior to the start of my building, ordering the parts and studying everything on Tangent's website. It was definitely worth it. I had built a PIMETA a couple of years ago, but it can't touch the PPA in terms of Sound Quality. Right now I'm using the OPA604's, but plan to get the AD8610's or the OPA627's. It sounds great with the 604's now, so I'll probably leave them in for a while. I can't post any pics right now, I don't have a digital camera. 

 But, anyway; So far so good.


----------



## applegd

I just found a discrepency between Tangent's PPAv2 schematic(http://tangentsoft.com/audio/ppa/amp...schematic8.pdf) and its PCB(http://tangentsoft.com/audio/ppa/amp...-2.0-hires.png).

 Per the schematic below, the R9 (PIN3) 
	

	
	
		
		

		
		
	


	




 should be connected to VL-.










 From the picture of the PCB below, it shows (OpAmp PIN6)-->(R10R)-->(Q2R)-->(Q1R PIN1&2)-->(R9R PIN1&2)--->(R9R PIN3,Q1R PIN3)-->(Q3R- PIN1,TLER PIN2,C4R-N,R8R-)-->(C5R-,OpAmp PIN4), this shows R9 PIN3 actually connects to VL-ALT as marked in schematic above.





 Maybe the schematic is not the latest version?


----------



## toneman

OK, I'm stumped... I completed by PPA v2, to test it I used an ipod hooked via its dock to line level inputs. Works great, sounds great.

 When I went to place the PPA in its final resting place connected to my Sunfire TG II... no audio at all.

 After some troubleshooting, I isolated the issue. When I connect to my audio gear (various devices) via my Audioquest Quartz cables, I notice that the op amp supplies are @ very low voltage (less than 1 V) and one of the Q3s is getting VERY hot. V+ and V- are fine so my PS (elpac) is doing OK.

 When I go back to my ipod input (no ac power connection), all is well and the amp sounds great with normal voltages everywhere.


 I think I must have the preamp ground at the other end of the cable fighting with my PPA signal virtual ground. I have the chassis grounded to signal ground via the pot. RCAs are wired with signal LR and signal ground coming in to the board via wires (RCAs are electrically isolated from the chassis but shouldn't be an issue?).

 The question: how should I hook-up signal ground? It appears I can't connect signal ground via the cables or I get a fight going on. When I built a class T tripath amp long ago, I left the signal ground unconnected to the BNCs. Is that the trick? Will that work?

 So close, and yet so far....

 Any help is appreciated


----------



## TzeYang

applegd, good catch. 
	

	
	
		
		

		
		
	


	




 It's better to use V-Alt instead of V-. But they should not have a huge difference anyway since the current draw is constant and it's already regulated by the CCS.


----------



## toneman

Problem solved! And as usual it was something stupid. For documentation to save someone else some headache, here's what I discovered.

 The recommended Elpac PS is discontinued, so I ordered a newer version (very similar) from Mouser. I never thought about it, but this power supply has a 3-pin ac plug with ground. And the earth ground IS tied to the - output. Break off the ground pin on the ac plug, and life is good 
	

	
	
		
		

		
		
	


	




.

 For sanity sake, I did some voltage measuring against earth ground as reference. Sure enough, the PPA virtual ground was at 12.5V against earth. And my preamp was at earth. The poor PPA was trying to fight a large preamp to source enough current to maintain the 12.5V delta. V+ in was at 24V relative to earth with V- at 0V.

 After breaking off the ground pin, virtual ground was at 0V relative to earth, V+ at 12.5V and V- at -12.5V.

 Hooked up and sounding FANTASTIC. I have the AD8610s. After a few weeks of listening with the new Grado 325is on order, I'll try the LME49710s and the OPA637/627 combos.

 Thanks Tangent for great info and instructions. Other than my minor opps, everything went smooth and easy.


----------



## tangent

Quote:


  Originally Posted by *applegd* /img/forum/go_quote.gif 
_I just found a discrepency between Tangent's PPAv2 schematic_

 

Hm, okay. I'll fix that...someday. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *toneman* /img/forum/go_quote.gif 
_The recommended Elpac PS is discontinued, so I ordered a newer version (very similar) from Mouser._

 

WM-1024? MW-1224? Something else?

  Quote:


 And the earth ground IS tied to the - output. 
 

Then it's not isolated. (Last paragraph.)

 Not that a PPA powered via a DC wall wart needs any connection to earth ground. You'd only do that if you had wall AC to low-voltage DC conversion inside the same case as the amp, and that case was metal.

  Quote:


 Thanks Tangent for great info and instructions. Other than my minor opps, everything went smooth and easy. 
 

I'm glad to hear that you apparently didn't kill anything in the circuit, making it pick a fight with Planet Earth like that.


----------



## toneman

Power supply is ordered was FWC1824. Datasheet here: http://www.iccus.com/datasheets/fwc18.pdf


----------



## toneman

My Grado 325is just arrived 
	

	
	
		
		

		
		
	


	




. They sound great, but with my PPA the background 'hiss' is significant. With the Senheiser HD420s I was using before, it was non-existent.

 I believe Senheisers are on the high end of impedance and Grado's are on the low side. 

 Update: I found all the discussions on gain. My amp has the default gain of 11 (thats 1 louder 
	

	
	
		
		

		
		
	


	




). Sorry... just watched Spinal Tap.

 I'm back to Mouser to get replacement R4 resistors to lower the gain. For those who have lower gain and have Grado's, does a gain of 6 eliminate the hiss? I want to try both LME49710s and the OP627/637 combos. But I REALLY want to get the noise floor to something I can barely hear. 

 Is there a min stable gain with the LME49710s like the 637s?

 Anything else significantly affect noise w/ Grados besides adjusting gain via R4? I read about changing output resistor values from 2R2 to 3R3.



 My PPA v2: AD8610s, driver bias 28mA, class A bias 1.2mA

 Thanks,

 Toneman


----------



## applegd

Quote:


  Originally Posted by *TzeYang* /img/forum/go_quote.gif 
_applegd, good catch. 
	

	
	
		
		

		
		
	


	




 It's better to use V-Alt instead of V-. But they should not have a huge difference anyway since the current draw is constant and it's already regulated by the CCS._

 

Thanks! I knew the answer to my question after I checked Morsel's PPA webpage this Monday night...


----------



## funch

I've been reading here about the folks that have had hiss problems with

 low impededence cans. I also had hiss in my first PPAv2, and found 

 that replacing the output resistors with Mouser P/N 594-5083NW2R200J,

 the problem was solved. They're Vishay/BC 2W metal film resistors. I'm now

 on my third PPA and these have always worked.

 Link:http://www.mouser.com/Search/Refine....4-5083nw2r200j


----------



## rds

That hiss is most likely not the gain. There might be some noise with grados and gain 11 but it should be very minor in this amp.
 Look back one page and you'll see delosborne had the same problem and found the solution.


----------



## toneman

thanks for the pointers. I am going to try the metal film output resistors. Mostly because I already ordered those from Mouser before getting to the R11 thread.

 as FYI, I tried adding the 15' extension cable and found it made a moderate difference in the volume of background hiss, didn't eliminate it.

 I'll post results when i get them.

 Thanks!


----------



## toneman

Update: Changed my 2.2 ohm resistors for the metal film ones recommended. The noise floor did drop... subjectively 50%. Background hiss is now tolerable (sounds like tape hiss), but still above what i would like (and way beyond the dead silence of high impedance headphones).

 I'm going to try reducing R11 from 1K to 200 ohms as extensively covered in another noise thread.

 Almost there! Noise floor is good enough to start doing some serious listening and compare Op Amps.


----------



## rds

I ended up dropping my r11 to 100 ohm as there was still a tiny bit of noise with gs-1000is (very sensitive phones).
 R11 at 100 ohms has worked great for me.


----------



## toneman

Op Amp experimentation:

 AD8610: Sounded good, but the upper midrange always sounded 'congested'. High end was fatiguing after awhile. Great bass. 

 LME49710: Sounded very clean, very 'accurate'. Congestion is gone, and detail is higher than the AD8610. But the sound is somewhat lifeless. Boring. Bass is a little thin sounding. This op amp sounds great in my Taylor T5 koa guitar (did a mod replacing the cheapo op amps that come with it), but not great here.

 OPA627 (ground)/637 (L&R): One word.... WOW. To my ear and with my Grado cans, this combo sounded amazing. Great clarity and detail, much more than the AD8610. I can still distinguish every individual instrument in the upper midrange. Bass is full. Sound is forward, but not too forward. Some have said these op amps sound a bit 'relaxed' like a good tube amp. I don't hear that. They sound very much like my class- T amp/Vandersteen speaker combo. I can listed to these op amps for hours and hours w/out getting fatigued.

 It always fascinates me how very different a variety of op amps sound. As I learned awhile back, there is lots of electrical engineering involved, but also a bit of 'magic' to get a great sounding amp. I'm in love...


----------



## tangent

Glad to hear it. Thanks for sharing your experiences.


----------



## grenert

I had a well-functioning PPAv2 which was using AD825 opamps and ran at 24V. I then changed to OPA656 opamps, which needed to run at a lower voltage, 12V. So, the PPA was used with a lower-voltage supply, and the new opamps supplied with 12V and biased at 1.6mA. I also replaced the TO-92 TLE2426 with the SMD versions on an AdapTLE. The buffer bias was set at 30mA.

 The setup now had some weak hiss in one channel, present at minimum volume, perhaps slightly decreasing with higher volume.

 I do not know what the buffer bias was in the original setup. When the hiss developed, I thought to reduce the buffer bias, since I know that 30mA is on the high end for the amp. When I checked the bias, it was about 42mA on one channel! Playing around with the three channels, I realized that the bias could be set stably to up to about 13mA. Beyond that, the current would unpredictably jump to a max of 42mA. Sometimes, I could force the jump by increasing bias with the trimmer, and at some threshold (often around 30mA) it would suddenly jump to 42mA. Interestingly, then backing off the trimmer had very little effect (maybe reducing current by 5mA) until at some point it would drop all the way down to about 4mA. 

 Can anyone diagnose the phenomenon here? My guess is oscillation, given that the high bias became independent of the trimmer setting. A friend had suggested thermal problems, but the transistors are barely warm. More importantly, is there a way to get this stable?

 EDIT: More background info: I am using 2.2R output resistors. There is no hiss at 13mA setting.

 Thanks for your help!


----------



## Beefy

Quick guess...... thermal runaway?


----------



## TzeYang

It's BJT.

 You will get insane thermal runaway if they are not matched properly.

 Since the PPA V2 does not have thermal bonding/tracking between transistors, it's best you try not to overdo it.


----------



## grenert

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_Quick guess...... thermal runaway?_

 

Yeah, that's what my friend thought. But, like I said, the transistors didn't get hot. I used a good thermocouple thermometer to test, and they only got to about 43C max. Shouldn't thermal runaway cause hotter temps?

  Quote:


  Originally Posted by *TzeYang* /img/forum/go_quote.gif 
_It's BJT.

 You will get insane thermal runaway if they are not matched properly.

 Since the PPA V2 does not have thermal bonding/tracking between transistors, it's best you try not to overdo it._

 

How many transistors do you typically need to achieve a good match, and how close is a good match for this application?

 I agree that I don't want to run too much bias current, but the standard bias on the PPA is 20mA. So, I feel like something is wrong that it can't even get to that point stably.

 I appreciate your help!


----------



## tomb

Quote:


  Originally Posted by *grenert* /img/forum/go_quote.gif 
_Yeah, that's what my friend thought. But, like I said, the transistors didn't get hot. I used a good thermocouple thermometer to test, and they only got to about 43C max. Shouldn't thermal runaway cause hotter temps?


 How many transistors do you typically need to achieve a good match, and how close is a good match for this application?

 I agree that I don't want to run too much bias current, but the standard bias on the PPA is 20mA. So, I feel like something is wrong that it can't even get to that point stably.

 I appreciate your help!_

 

Not my amp, but I have biased a few discrete buffers in my time.
	

	
	
		
		

		
			





 I agree that thermal runaway is probably not the issue. You should be able to get to 30ma without issue even on plastic-bodied TO-126-type transistors without heat sinks. Also, while lack of transistor matching can cause some issues, I haven't found that to be that much of an issue in total overall bias.

 The problem with matching is that you may bias one side of the complementary output (BD139), but then find that the other complement's bias doesn't match (BD140). Chances are that they'll be slightly off in a matched situation anyway, but unmatched might be way off. Either way, it's the sound/performance that will be affected, not whether you can set a bias.

 Matching the smaller transistors is usually the best time/benefit ratio. The larger output transistors usually don't vary that much.

 Instead, I'm guessing you may have issues in the bias adjustment itself. I've seen this happen if the trimmer is sized incorrectly - larger than it should be, or the accompanying resistor is sized incorrectly, too. You can only adjust a bit down low, then the final setting ramps up almost uncontrollably, with very little to no adjustment capability in-between. Check the values of R12 and R13 in your circuit - see if they're what Tangent recommends - a 2K trimmer and a 100R resistor, respectively.

 Just a guess.


----------



## TzeYang

Quote:


  Originally Posted by *grenert* /img/forum/go_quote.gif 
_How many transistors do you typically need to achieve a good match, and how close is a good match for this application?

 I agree that I don't want to run too much bias current, but the standard bias on the PPA is 20mA. So, I feel like something is wrong that it can't even get to that point stably.

 I appreciate your help!_

 

Mismatch errors is when the HFE difference is too large so when the temp increases they drift even higher. This usually happens rarely and the good way to fix it is to increase some of the resistor values so you make the current less dependent on the HFE. I'm only assuming all parts are well tested before hand and you're competent enough not to mess up resistor values.


 I do think tomb's explanation is more feasible till this point. Check your trimmers and resistor values.


----------



## grenert

Well, I haven't specifically checked yet, but I was told by the individual who sold me the amp that Tangent himself built it! So, the trimmer and resistor are probably fine 
	

	
	
		
		

		
		
	


	




 I'll check just to be sure.

 The amp was originally set up with OPA627/637 opamps and 24V supply. Would a change to a lower voltage supply (12V) necessitate different parts in the biasing system?


----------



## tangent

Tangent is not infallible.

 Some have found stability improvements by lowering R11. Try 100R.


----------



## funch

NVM


----------



## toneman

I changed R11 to 200 ohm. This brought the noise floor WAY down to where I just get small hiss that varies with the volume control that can't be heard unless volume is 3/4 up (and can barely be heard at that).

 After the R11 change and changing my output resistors to metal film, my amp is done and sounds fantastic. 

 Now to decide on my next project... hmmmmmm.


----------



## grenert

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Some have found stability improvements by lowering R11. Try 100R._

 

That did the trick! Stable 30 mA bias through the buffers. I just enjoyed "Sand in the Vaseline" with the new setup. Sounds fantastic. Thanks for the suggestion, and most importantly, thanks for the design! 
	

	
	
		
		

		
			





  Quote:


  Originally Posted by *toneman* /img/forum/go_quote.gif 
_I changed R11 to 200 ohm. This brought the noise floor WAY down to where I just get small hiss that varies with the volume control that can't be heard unless volume is 3/4 up (and can barely be heard at that)._

 

Glad that worked for you. With R11 at 100R, I hear only complete silence with K701s. Looks like it's time for you to put together a Beta22


----------



## dlosborne

Alrighty: after too many weeks away from an internet connection, I am back with the remaining pictures I promised. Rather than fill this post, you can just hit the source.

HERE

 I have to say, the γ1 lite and PPAv2 work wonderfully together.

 Now I just have to get the YJPS put together for a pretty little desk stack.


----------



## funch

Great job! I just now installed the Toslink input on my board and hooked
 up my SlimX 550, listening through my PPA. Fabulous. Can't wait to 
 install the y-2 onto my full++.


----------



## FallenAngel

Hmm... why are there 2 caps per channel bass boost?


----------



## dlosborne

I dropped the gain down to 2-ish (edit: from 5.4) so I could use a bit more of the pot's range. (I use SE530s and GS1000s). But when I rapid cranked the bass boost to dig on Bud Powell I nearly soiled myself: that bass boost had a crazy huge gain (duh) and cut out in the mid range, (again, duh)! I really wanted to slap my forehead as soon as I turned the volume down. 

 *visits Tangent's bass boost calculator*
 (edit: previous configuation after R4 was changed to 1K: fc=376Hz, fs=14Hz, BGain = 26)

 So, I needed to seriously cut R7 down and beef up the capacitance. I didn't want to run another order and wait... 

 *roots through part box*

 I put a 50K in R7 (edit: but these are verticle mounted at the S2R/L points... don't ask) but only had a small hand full of the 0.22uF drops. I didn't have any poly-anything films; only electrolytics left. 
 What the hell, I stuffed another 0.22uF in parallel on each leg.

 (edit: new configuration with amp gain of 2, R7max = 25k ohm, C7 = 0.44uF:
 fc=194Hz, fs=15Hz, BGain = 10.4)

 I still don't even near max it because as it stands, it turns my 1mV dc offset in the left channel up to a 10-11mV offset. I use SE530s and GS1000s in this thing and don't like the idea of running that much voltage over these drivers. Had I AKGs, sure no worries.

 That is the 'War and Peace' version at any rate.

 (edit: once I do run another parts run, I will most likely bump the amp gain to 3, R7' to 33k for a R7max of 20k, C7 will stay at 0.44 but I will drop a smaller/single cap to replace the torpedoes that are in there now. They do look cool though.)


----------



## tangent

Ah, I too was wondering about those doubled Orange Drops. I wouldn't worry about the 10 mV offset, though. It should be fine, even with those sensitive cans.

 Another thing I was curious about: does a USB cable fit solidly in the DAC input? I can't quite tell whether the panel prevents it from inserting as far as it could.

 Nice build.


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## dlosborne

Yup, the usb fits perfect. I blackened the plug with a dry erase marker, popped it in and out of the case, and measured the wipe. Then I did the same with my cell phone: exact same distance. However, I can only barely slide a piece of paper between the case and plug. If the back plate was any thicker I would have to resolder to bump the socket forward and/or machine a groove into the panel.

 The build? Thanks! You did help a ton, this thread was crucial (and should be required reading...all of it), and MisterX configured and build the DAC. But, for my first amp, it went great. 

 I have few 0.68uF film/foils I raided from a 4.16kV variable frequency drive controller that should fit. Then I won't have to parallel to get the cutoff frequency low enough. (And I can shove the orange drops back into the guitars I am fixing.)


----------



## salmagundi

I just finished my PPA v2 yesterday, and I couldn't be more pleased as this is my first high-end project. I used Elna Silmic II electrolytics and AD843 op-amps in all three channels. I found two RK27 pots @ 100Kohm and utilized those for volume and bass boost.

 I biased the output to 30mA, measuring 66mV across the 2W 2.2 resistors, easy.

 Now, with R9 installed as a trimpot, I measured across R10 to find that the Voltage drop is 9.11—a 9.11mA bias! Is this a concern? Everything operates normally and sounds excellent, but does the above measurement indicate that something else is wrong? 

 The only transistor parts where I deviated from Tangent's guide were the 2N5246, 2N5247, and BF245C for Q1, Q2, and Q4, respectively.

 Datasheets:
 Q1 
http://www.fairchildsemi.com/ds/2N%2F2N5246.pdf
FAIRCHILD SEMICONDUCTOR|2N5246|JFET | Newark.com

 Q2 
FAIRCHILD SEMICONDUCTOR|2N5247|JFET | Newark.com

 Q4 
http://www.fairchildsemi.com/ds/BF/BF245C.pdf
FAIRCHILD SEMICONDUCTOR|BF245C|RF JFET | Newark.com


----------



## funch

Guess this is a question for Tangent.

 Is the battery board discontinued, or just out of stock?


----------



## tangent

Discontinued, to be replaced much the same way that the TREAD replaced the STEPS: smaller board, lower cost, very similar functionality, but DIY mounting required. The new board also adds a low-voltage cut-off circuit, so the load can't kill a battery pack by driving it into the ground. (You can still kill the cells by letting them self-discharge in a pack for a year, of course.)

 I'll get that going when the pain of these recent PIMETA v2 and YJPS board runs wears off a bit.


----------



## wuerzig

Hi forum, hi diyers,

 I finished my PPAv2 today and so far everything is beautiful, DC-offset is about a millivolt even with maximum bass-boost, and after grounding the pots I dont have any issues that i can hear. I am a bit concerned about the idle power consumption tho, i'm measuring 140mA at 24VDC. Following tangents notes on iq-calculation, it should be about 110mA. Buffer bias is at 25mA, OPA bias is at 1mA, led is taking 'bout 2mA. The outputs are warm, tolerable, not the burning kind. I'm using OPA627 all around and BD139/BD140. I cleaned the board, all trannies except the outputs are matched nicely.

 From reading this thread I suspect there might be some oscillation going on. I have access to a scope and signal generator. What am i looking for? I figured i could throw a square wave to the inputs and look for anything unusual at the outputs, is that right?

 Oh and thanks to tangent for your fantastic website, I spent something like 20 hours reading it over and over before I started my build.

 On a side note, matching my BD's was kinda difficult, the best I could do was hfE 110 vs. 150.

 I'll post pics of my build as soon as I can get my hands on my cam again, my gf stole it weeks ago ^^

 Edits: More details, grammar mistakes


----------



## tangent

Quote:


  Originally Posted by *wuerzig* /img/forum/go_quote.gif 
_i'm measuring 140mA at 24VDC. Following tangents notes on iq-calculation, it should be about 110mA._

 

That calculation might be missing something. I'm not entirely confident in it. No one has pointed out what that "something" might be, though.

  Quote:


 From reading this thread I suspect there might be some oscillation going on. I have access to a scope 
 

Easy, then: just scope the output. If you can't get anything but a flat line out of it with the inputs shorted, it's not oscillating. Oscillation will usually show up as a clear sinusoidal waveform, often dirty, sometimes very clean. Only occasionally will you see just a blur.

  Quote:


 and signal generator 
 

You can also try running square waves through the amp. Try 1 MHz or so. If the scope shows a lot of ringing, the amp is marginally stable and might oscillate with some loads. Look earlier in this thread for R11.

  Quote:


 Oh and thanks to tangent for your fantastic website, I spent something like 20 hours reading it over and over before I started my build. 
 

You're welcome!


----------



## vixr

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Discontinued, to be replaced much the same way that the TREAD replaced the STEPS: smaller board, lower cost, very similar functionality, but DIY mounting required._

 

its awesome...I highly recommend it. You can see it in my sig (PIMETA) its the last two pics


----------



## dbfreak

Quote:


  Originally Posted by *vixr* /img/forum/go_quote.gif 
_its awesome...I highly recommend it. You can see it in my sig (PIMETA) its the last two pics_

 

What software did you use to create the flash presentation of your Pimeta?


----------



## vixr

Quote:


  Originally Posted by *dbfreak* /img/forum/go_quote.gif 
_What software did you use to create the flash presentation of your Pimeta?_

 

its a slideshow from photobucket...


----------



## tangent

Quote:


  Originally Posted by *vixr* /img/forum/go_quote.gif 
_its awesome...I highly recommend it._

 

The TANC-F is officially on the schedule now. I'd press the button on it now if it weren't for the recent YJPS and PIMETA v2 board runs, plus a need for a PPA v2 board run.


----------



## wuerzig

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_scope the output. _

 






 I think this might be due to the case not being grounded yet. Also, I remember this looked different in analog mode (didnt take a pic sorry).


  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_try running square waves through the amp._

 





 Input vs. output. Is that good enough?






 The power-on "thump", left and right. Its interesting that the channels differ, but then I only scoped that once.

 I also measured the frequency where the signal drops 3dB to be at about 2 Mhz (darn my english vocabulary is missing a word here, whats that called, the upper frequency threshold?), but with much degredation due to what you see in the second image.

 Sorry for the crappy pics, I took them with my cellphone.


----------



## tangent

I'd bet on that first one being low-level oscillation rather than induced noise. Uncased PPAs are generally pretty quiet. Are you using the schematic value for R11, or a lower one you saw recommended above in this thread?

 Your other oscillograms look fine. The square waves aren't ringing badly, and the turn-on thump voltage is acceptably low.


----------



## rds

What load were you driving when you scoped the amp?

 Even with R11 at 100 ohms I get some hiss in my Shure se530s (IEMs), so I'm thinking there is some oscillation going on there. I'll try to scope it this week and see what's happening.


----------



## tangent

With IEMs, I would use a gain of 2, no more. That rules out OPA637s and other uncompensated chips, but it sounds like a good trade for noise floor to me.


----------



## wuerzig

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I'd bet on that first one being low-level oscillation_

 

I didnt expect the amp oscillating at 100Mhz. I will investigate further.

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Are you using the schematic value for R11?_

 

Yes.

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Your other oscillograms look fine. The square waves aren't ringing badly, and the turn-on thump voltage is acceptably low._

 

I thought so, thanks for your input 
	

	
	
		
		

		
		
	


	






  Quote:


  Originally Posted by *rds* 
_What load were you driving when you scoped the amp?_

 

Some random sennheiser headset, I think the PC150.


----------



## tangent

Lower R11 to 100 or 220 ohms, and let's see if that helps. If it does, that might be enough to push me to change the schematic.


----------



## wuerzig

In my effort to identify the signal from the first oscillogram, I connected the probe to nothing but a short piece of wire (~3cm). The same thing happens, so my guess is that this is noise after all.

 I wont have access to the scope for a couple of weeks, so trying to lower R11 will have to wait until I get my hands on it again.


----------



## rds

I did some measurements of my PPA v2 (with r11 = 100 ohms, MJE243/MJE253, OPA827) driving 40 ohm Ultrasone Pro 900s. I had to keep the voltage low so as to not blow the drivers. Unfortunately the equipment I used is not the best, so there is some noise but I thought the measurements look very good.









 520Hz square wave




 3.2kHz square wave




 12.1kHz sqaure wave

 I couldn't find any high frequency oscillation


----------



## tangent

It'll look even better if you turn on the 20 MHz bandwidth limit to get rid of some of that HF noise. I take it from the use of photos instead of screen grabs that you don't have the TDS2MEM or similar?


----------



## rds

Ah, I didn't realize that it had a bandwidth limit ...and it's right on the screen too 
	

	
	
		
		

		
		
	


	



 I know it can be connected to a computer ...by a serial cable iirc. But I didn't have a cable with me, and even if I did I'd probably be too lazy.
 I realized I should have taken a shot in the MHz range too. I'll probably bring the PPA in again with my YJPS (once it's done) and take some more measurements.


----------



## FallenAngel

Interesting thing I found out today with my PPAv2 - AD744 (comp output) doesn't like class-A bias in the amp (anything above 2mA and it starts to output DC like crazy) and AD829 (comp output) REALLY doesn't like class-a bias and goes haywire with even 0.5mA.

 Oh well, live and learn; now 3x AD744 compensation pin output at 1.5mA class-A sounds damn good and without any DC offset. 
	

	
	
		
		

		
		
	


	




 YJPS is one damn great PSU by the way, very impressed with it compared to how I remember STEPS and Simga11 with the PPAv2.


----------



## NelsonVandal

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Interesting thing I found out today with my PPAv2 - AD744 (comp output) doesn't like class-A bias in the amp (anything above 2mA and it starts to output DC like crazy) and AD829 (comp output) REALLY doesn't like class-a bias and goes haywire with even 0.5mA.

 Oh well, live and learn; now 3x AD744 compensation pin output at 1.5mA class-A sounds damn good and without any DC offset. 
	

	
	
		
		

		
		
	


	


_

 

When used "comp pin out" (output buffer is bypassed and the signal is taken from the voltage amp stage), both AD744 and AD829 are single end class A and external biasing isn't beneficial in any way.


----------



## MisterX

Yep, check the the simplified schematic in each of the respective datasheets and you should see why you had a problem when you tried to apply "class-A bias"


----------



## FallenAngel

Thanks guys, now I have to find a way to bypass it. 
	

	
	
		
		

		
		
	


	




 Probably just going to cut R10.


----------



## tangent

Yes, that's the easiest way.


----------



## spendorspain

Hi all

 I’m going to build a PPA v2 powered with a YJPS psu and I’d be grateful if you could help me regarding several doubts.

 1) I have two unused Black Gate series N non-polar capacitors. I had installed them at the output of a headphone amp but now, with a FET-input opamp in it and very low dc offset, I’ve desoldered them. I think their value (1000uF/25v) and size (D 16mm x H 23mm, LS 7.5mm) are appropriate for the main cap C1 in PPA v2. I know they are too expensive, but I have no better use for them. They are very good caps for music signal and I’ve seen used in power supplies too. Mi plan is to use both in two C1 positions, in parallel, to obtain the recommended C1=2000uF capacitance in the PPA. Is their dc rating (25v) high enough for a 24v YJPS psu? Is it a problem their non-polar (bipolar) design, when used in the power section?

 2) Is it possible to mount the YJPS pcb vertically to save space or perhaps will the heatsinks reach too high a temperature this way, as their fins are more effective if not horizontal? (the recommended heatsinks are from 25 to 50 mm, so perhaps the shorter one is still suitable for the expected heat)

 3) I currently use a headphone amplifier with a gain of 4.3x, that is a little high for my Grado HP2 cans (I have to use a loss L-pad before the 10k stepped attenuator). Is it recommended a gain of 2x or 3x in PPA v2? I’m going to test with PPA the AD8610, AD8065, AD744 (pin 5 out) and LM49710 opamps, that I believe can be used at such low gain without problem.

 Thanks in advance for your comments

 Jose


----------



## tangent

Quote:


  Originally Posted by *spendorspain* /img/forum/go_quote.gif 
_I think their value (1000uF/25v) and size (D 16mm x H 23mm, LS 7.5mm) are appropriate for the main cap C1 in PPA v2_

 

When the docs say you can make 16 and 18 mm diameter caps work, it's not recommending that. The way you make them work is having them span two cap positions, positive on one to negative on the other. This makes the cap hang over the board edge, so it's no good if you're using the recommended Hammond case or anything else that fits the board outline tightly. It's also less mechanically secure, so probably not a good idea for an amp that gets moved around a lot, unless you hot-glue them in place after soldering them down.

  Quote:


 I’ve seen used in power supplies too. 
 

They're no good in a YJPS. 25 V main reservoir caps means you'd be configuring it for 12 Vdc out or less.

 Even if they were a more appropriate voltage, I doubt they'd perform better than some nice, big, low ESR caps.

 If you have to use these caps, much better to use them on the amp board, not the power supply.

  Quote:


 Is their dc rating (25v) high enough for a 24v YJPS psu? 
 

Yes. D1 cuts the supply voltage down a bit, so you have about 1.7 V of margin to play with.

  Quote:


 Is it a problem their non-polar (bipolar) design, when used in the power section? 
 

I don't know, but at least it seems wasteful. Why not save these caps for what they were meant for, AC signal coupling?

  Quote:


 Is it possible to mount the YJPS pcb vertically to save space or perhaps will the heatsinks reach too high a temperature this way, as their fins are more effective if not horizontal? 
 

I've not tried it, and I wouldn't unless I'd configured the power supply to have lots of heat margin.

  Quote:


 the recommended heatsinks are from 25 to 50 mm, so perhaps the shorter one is still suitable for the expected heat 
 

Don't guess, find out.

  Quote:


 Is it recommended a gain of 2x or 3x in PPA v2? I’m going to test with PPA the AD8610, AD8065, AD744 (pin 5 out) and LM49710 opamps 
 

It should be fine. Be sure to use the lower R11 value recommended earlier in this thread. That's more important at lower gains.


----------



## whitelabrat

I've begun stuffing my PPA2 board. I'm on a very tight DIY budget these days so I have to use what I've already got, before buying parts. I've got some decent parts, but it's a bit of a hodgepodge. For example I have a combo of Panisonic FM and Nichicon KZ's on C1. I don't have any small film caps so I used ceramics. 
	

	
	
		
		

		
			





 Super cheap Nichicon PM's in C4 bypassed by 0.1uF ceramics again. I did find a pair of 1uF film box caps, but I figured I try this out before unsoldering anything. I'd post a picture but it's pretty sick.

 I've got a pair of OPA637's DIP8 and three OPA827's SOIC's. No adapters for 827's so I'll be using the 637's with a OPA602 for the ground channel.

 I've got a Blue Velvet 100k volume pot, and I'll probably just on/off switch the bass boost for now.

 I'll use a TREAD for the power supply, perhaps 24v. I need to reform some old stock 2200uF 100v caps for that.

 My only pinch is R12. Can I just fake the trimmer with a resistor until I get the proper part?


----------



## tangent

Yes, you can use a plain resistor in place of R12. The thing is, though, you won't know what the right resistor value is here at first: we made this a trimmer because there is no fixed resistance-to-bias-level function. It depends on the specific transistors. 

 You'll end up putting in something plausible, powering the amp up, measuring the effect, powering off, desoldering the R12, trying something else that moves you in the direction you want, powering up....

 How's your stock of random resistor values?


----------



## whitelabrat

I rarely buy just one of anything, so I've gotten a fairly broad variety of values now. A fellow was closing up his electronics shop and sent me a large box of resistors. Thousands! Mostly carbon film along with a mess of capacitors. It pays not to be picky. 
	

	
	
		
		

		
		
	


	




 So in a pinch I can parallel or serial resistors for just about any value.

 I was planning to "plug in" various resistors without soldering until I get the ideal value. Power on, test, change value, repeat.

 What would be a good value to start with? I would guess something around 1k.


----------



## whitelabrat

I'm stuck. I didn't order any 2N5484's. I'd like to get all my parts from Allied Electronics, so I'm thinking that an NTE457 may serve as an alternate. Idss=1-5ma, Crss about 1.5pf, Ciss about 4.5-7.0pf. Looks good enough. Looks like I'll be getting the trim pots after all.


----------



## uvacom

I've just ordered parts for my PPAV2 and for the most part everything seems clear, but I have one nagging question - what is the black RCA signal ground input used for? I don't have any sources which have a discrete signal ground output. Why is the sleeve on the RCA jacks not sufficient for signal ground?


----------



## n_maher

Quote:


  Originally Posted by *uvacom* /img/forum/go_quote.gif 
_I've just ordered parts for my PPAV2 and for the most part everything seems clear, but I have one nagging question - what is the black RCA signal ground input used for? I don't have any sources which have a discrete signal ground output. Why is the sleeve on the RCA jacks not sufficient for signal ground?_

 

I think you're going to have to clarify what exactly you're not clear about. The RCA sleeve needs to connect to the PCB at any of the IG pads. You can tie the sleeves together if you like, most do, and just run a single wire to the PPA PCB. Your statement, "black RCA signal ground input" is what is confusing me since I have no reference for whatever color coding scheme you're referring to.


----------



## uvacom

Ah, I'll take a step back. Let me ask this instead: why does the parts list at tangentsoft specify 3 rca jacks - one red, one white, and one black?


----------



## MisterX

Notice how the "QTY" colom says you only need 2? 
 Maybe part numbers for red, white and black jacks are 
 provided so people can pick the colors they prefer? 
 Or maybe it's because RS only stocks red and black ones.

 Either way I would suggest finding better jacks then those....


----------



## uvacom

Ah! That does make *much* more sense. Silly oversight on my part.


----------



## tangent

Quote:


  Originally Posted by *whitelabrat* /img/forum/go_quote.gif 
_I'd like to get all my parts from Allied Electronics_

 

A quick look suggests you can probably save enough on parts to cover shipping from Mouser. Allied's prices and selection for semiconductors is poor.

 If there were just one distributor that had it all, we'd all be using them. You see people recommending so many distributors more because no one has all the best stuff, rather than primarily because of different preferences.

  Quote:


 I'm thinking that an NTE457 may serve as an alternate. 
 

There are a few valid reasons to buy NTE parts, none of which apply here:

 - you have more money than sense

 - you need a specific part and the original manufacturer no longer makes it, but NTE carries a replacement

 - you have a local NTE dealer and can't wait for a mail order

 The 2N5458 and 5459 look like better bets to me. But again, I think you'd still be better off getting some cheap Fairchilds from Mouser and letting the price difference cover the extra shipping charge.

  Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_Maybe part numbers for red, white and black jacks are provided so people can pick the colors they prefer?_

 

What he said. Some like white and red, others prefer black and red. I've collected all three color options so you can select the pair you like.


----------



## whitelabrat

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_A quick look suggests you can probably save enough on parts to cover shipping from Mouser. Allied's prices and selection for semiconductors is poor.

 If there were just one distributor that had it all, we'd all be using them. You see people recommending so many distributors more because no one has all the best stuff, rather than primarily because of different preferences.

 There are a few valid reasons to buy NTE parts, none of which apply here:

 - you have more money than sense

 - you need a specific part and the original manufacturer no longer makes it, but NTE carries a replacement

 - you have a local NTE dealer and can't wait for a mail order

 The 2N5458 and 5459 look like better bets to me. But again, I think you'd still be better off getting some cheap Fairchilds from Mouser and letting the price difference cover the extra shipping charge._

 

I agree their selection is less impressive and I wouldn't recommend them for PPA2 parts. It's all the other parts that I buy from their overstock selection that make it cheaper than Mouser by a long shot. The $0.94 cent 2k trimmers (not perfect fit) are a nice thing. The NTE parts are more expensive but my order is much cheaper overall. 
	

	
	
		
		

		
		
	


	




 I took a long hard look at the 2N5458, but it didn't fit the bill where Idss is 2-9ma and I need 1-5ma for Q1. I've got 2N5486 in for Q2.


----------



## tsaavik

Just wanted to add this comment after proof reading the below, I really have no idea what I am talking about, I'm still a beginner in the world of electronics, so i may be missing something totally obvious or misstating facts as I see them from the schematics. It does seem like I'm actually learning some stuff though!! 
	

	
	
		
		

		
		
	


	




 I built a wonderful ppaV2 with 3 ad8610 running 30ma bias with 1ma class A. Power is normally 24v provided from a steps running around .16amps. It has been running pretty well the last 3 years, except for a minor probe slip during biasing tweaking that resulted in me replacing the *Ground *TLE a few years back.

 A few months ago i was playing around with my e12 trying to get it to function reliably while at work and managed to short something out on my PPAv2 
	

	
	
		
		

		
		
	


	




 I finally had a chance to look at my PPA tonight. My Left/Right opamps show ~23v between their VH/VL pins but my *Ground *opamp was only showing 5.5v

 I assumed I blew my TLE (again), so i quickly soldered in a replacement. Unfortunately this had no effect.

 I pulled the opamp (smd on browndogs) and the voltage measured ~23v. I swapped opamps with another channel and the problem stayed with *Ground* (still 5.5v). *Assumption: 2 opamps are not failing to run in unity mode*

 I plugged 2 wires into the VH/VL pins and ran them over to my otherwise unplugged *Ground* opamp. When i attach them to the opamp the voltage on VH/VL falls from 22v to 5.5v. *Big Assumption: You can power an opamp this way as a test and oscillation won't be an issue*

 A rising or falling voltage seems to take about 8seconds to complete (fast at first then ramps off) so I'm guessing this is some cap charging/discharging somewhere. I don't think its the large bulk C1s, and am guessing its the C4 + and - 100UFs. *Assumption: There is current limiting going on (Q3?) that causes the 100UF C4s to charge slowly* (maybe not see below)

 During all of this the consumed current from the amp's (bench) power supply never changes.

 This leads me to suspect Q3G + and/or Q3G-. I measured between audio source input *ground* and pin 1 on the *Ground* channel and got the expected ~11v + and - respectively. However when i measured between audio source input *ground* and pin3 I got 2.8 + and -. I disconnected the opamp and measured again, I got the expected +-11volts. I checked Left and Right channels Q3s and they read the expected +-11volts on pins 1 and 3. 

 It seems like I have a large current draw, which is odd since my bench supply didn't show a current increase. I decided to monitor the Bulk C1 capacitors and sure enough voltage drops from from 11.53 to 11.38 when i connect the *ground* channel opamp.

 Should my next step be swapping out both Q3 parts? Or is running the opamp without the other pins causing some sort of oscillation that is invalidating this type of test. I'm guessing i shorted the *Ground* output to something, so maybe i should be focusing on the output buffers instead, or perhaps that push/pull circuit between them and the opamp? Can i "jumper" over either as a test? Btw, my *ground* channel transistors feel about the same temperature as my Left/Right channel ones.

 I do have access to an old scope (analog 60mhz circa 1982) as well so if there is any testing that would be useful with that let me know, I'm still trying to learn how to use it AND trust my measured results.

 Here are some old pics of it during construction, since people like pictures
DIY Audio Projects

 Thanks for reading this!!


----------



## tangent

Quote:


  Originally Posted by *tsaavik* /img/forum/go_quote.gif 
_I assumed I blew my TLE (again), so i quickly soldered in a replacement. Unfortunately this had no effect._

 

The other likely possibility is a damaged buffer section, but given that no transistors are getting hot, I don't buy this.

  Quote:


 A rising or falling voltage seems to take about 8seconds to complete (fast at first then ramps off) 
 

Could you graph that? Got a DMM with a data logging function, perhaps? The shape of the curve might be educational.

  Quote:


 I'm guessing this is some cap charging/discharging somewhere. I don't think its the large bulk C1s, and am guessing its the C4 + and - 100UFs. *Assumption: There is current limiting going on (Q3?) that causes the 100UF C4s to charge slowly* (maybe not see below) 
 

Nothing I can think of to explain this makes sense.

 First take charging of C4 through a CCS, which you propose. t=CV/I, so if we assume your rail isolation JFETs are 10 mA, the caps around the op-amp should charge in just about a quarter second. Way too fast to explain what you see.

 If instead we assume it's the C1 bank getting charged through a CCS, we can get an 8 second charge time to 24 V if the bank is 2000 uF and C is 6 mA. 6 mA seems really low to me. It could possibly be your Q3s, but why would they be charging C1? Besides, charging a cap through a CCS gives a linear charge curve, not the variable one you claim. (This is one reason I want to see a graph -- to be sure.)

 A nonlinear voltage vs. time curve suggests RC charging. To get ~8 seconds to full charge, R would have to be somewhere around 10-20K if we assume it's C4 getting charged, based on the 5 TC rule. None of the ground channel amp section Rs in that resistance range make sense as charge paths, and there aren't any such large resistors in the high-current section. Well, there's RLED, but how does that make sense? RLED and C4 are nowhere near each other.

 You could get such weirdness if you'd mistakenly put 10K in R8, not 10R, but then how does your amp make you happy for 3 years?

 That leaves RC charging of C1. By my figurin', it takes about a 1K resistor to cause an 8 second charge time for a 2000 uF C1 bank. It's much easier to find such R values in the PPA circuit, but which one?

 All of this is just babbling speculation, but maybe it gives you something to think about when planning your next test.

  Quote:


 Should my next step be swapping out both Q3 parts? 
 

It solves the mystery above if we assume that one of them somehow started choking off current far more than it should. Like, it got turned into a near-open condition. You can get that quarter second charge time up to 8 with a 32-fold reduction in current. Although this gives a linear voltage curve, not variable, we have to take into account that the op-amp isn't going to be running properly on such a trickle of current.

 Before you start replacing parts, you might put a current meter from V+ to V- on the op-amp socket, and see what the circuit is capable of delivering. Or safer, put a big 1 ohm power R across here and measure the voltage.

  Quote:


 During all of this the consumed current from the amp's (bench) power supply never changes. 
 

That seems to rule out RC charging, since that gives a high current at first, dropping rapidly to the circuit's steady-state current. It might be hard to see this happening, since most of the RC charging is going to happen in that first second or two. Again, data logging and graphs are wanted.


----------



## tsaavik

Quote:


 A rising or falling voltage seems to take about 8seconds to complete (fast at first then ramps off)
  Quote:


 Could you graph that? Got a DMM with a data logging function, perhaps? The shape of the curve might be educational. 
 


 

No fancy DMM, but i do have a fancy cellphone, I took videos and uploaded them to Youtube, then went through them frame by frame!

 I made the following table and graph (Sorry I suck at Excel):






 from the following movies i made last night:
Opamp removed, voltage ramping up (chart above)

Opamp powered, voltage drops (didn't chart this one, will on request!)

 Since i was plotting a voltage over time I kicked myself and went back into the garage and hooked up my oscilloscope:
 I believe it provided similar data for ramp up and down here is the video:

Oscilloscope Video

 I suspect that trying to rely on my DMM's refresh rate lead me down a false path before, this is a mostly linear function.

  Quote:


 You could get such weirdness if you'd mistakenly put 10K in R8, not 10R... 
 

Confirmed, both are 10R

  Quote:


 Before you start replacing parts, you might put a current meter from V+ to V- on the op-amp socket, and see 
 what the circuit is capable of delivering. Or safer, put a big 1 ohm power R across here and measure the voltage. 
 

I didn't have any BIG 1R resistors (tore apart a ton of busted PC power supplies but no luck) but i did have some
 leftover 1watt 2R2 resistors from the output section, here is what i got:

 Resistor remains cool to the touch during entire (several minutes) length of testing.
 I read .010 VDC across the resistor

 voltage .010
 ------------ = .0045454 (or ~ .005amps or 5mA)
 resistance 2.2 

 That seems awfully....low

 The current shunt resistor when attached caused the amp to draw an additional ~.04amps of power from the bench power supply (went from .14amp to .18amp). I felt both Q3 and they didn't seem any warmer.

 Based on this I believe I should continue to focus on the components that supply the split rail supply for the ground channel. The Q3G parts are especially guilty looking in my mind. Although i may try to figure out a way to test the C4s and C5s in circuit, perhaps comparing values i read off the other channels with an LCR.


----------



## tangent

Quote:


  Originally Posted by *tsaavik* /img/forum/go_quote.gif 
_this is a mostly linear function._

 

Actually, it looks like an RC charge curve to me, but the C1 bank will do that, and it could be masking the test results. Ideally you'd power up the amp and ground channel separately. 

 You could do this while you play with Q3G: desolder them, jumper Q3G- (big loop so it's easy to remove), and put a switch across Q3G+. Then you'll get one of two results when you power up the ground channel: either the amp will function again, or you will get the same result, which rules out the Q3Gs being a problem.

  Quote:


 I didn't have any BIG 1R resistors (tore apart a ton of busted PC power supplies but no luck) 
 

Radio Shack sells them. Get some 10Rs while you're there, for use as high-power shunts.

  Quote:


 5mA 
 

It's barely high enough that it could work with your AD8610s + 2 mA bias current. You could try dialing R9G down to zero bias, just as a test, before you remove the Q3s. If that fixes it, what probably happened is that the trim pot got vibrated into a new resistance that just barely pushes the circuit over the Q3's ability to provide current.

 If that doesn't fix it and you move on to removing the Q3s, I'd test them for Idss while they're out, to see if one is ~5 mA. If so, there's your culprit. I'd do this no matter what the above test told me...I'd just want to know regardless. But that's me. If I found that I was that close to the margin, I'd replace it with one with a higher Idss.


----------



## steinba

I'm sure this has been covered somewhere in this mammoth thread, but I can't find it. I'm getting ready to assemble a PPAv2 with a modified Linkwitz crossfeed. (Both PCBs from Tangent) It'll primarily be driving a 300 Ohm Sennheiser HD650.

 I'm wondering what'll be a good starting point for the value of R4L/R4R (gain). (I've ordered the default values from tangent's part list, and the current R4 is 10K if I'm not mistaken,) What range of resistor values should I buy for experimenting with R4L/R's values? (ie. gain)

 It seems like a good idea to use a socket for R4L & R4R. What kind of socket would be good?

 Thank you very much in advance. Please bear with the noob.


----------



## steinba

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_I'm sure this has been covered somewhere in this mammoth thread, but I can't find it. I'm getting ready to assemble a PPAv2 with a modified Linkwitz crossfeed. (Both PCBs from Tangent) It'll primarily be driving a 300 Ohm Sennheiser HD650.

 I'm wondering what'll be a good starting point for the value of R4L/R4R (gain). (I've ordered the default values from tangent's part list, and the current R4 is 10K if I'm not mistaken,) What range of resistor values should I buy for experimenting with R4L/R's values? (ie. gain)

 It seems like a good idea to use a socket for R4L & R4R. What kind of socket would be good?

 Thank you very much in advance. Please bear with the noob. 
	

	
	
		
		

		
		
	


	


_

 

I guess it was too late at night for my brain yesterday. 
	

	
	
		
		

		
		
	


	




 I found this:

Electronics Calculators

 ...And have ordered resistors for R4 in 5.23K, 6.49K, 7.5K, 8.8K, 10K, 11K, 12.4K, 13.7K and 15K for gain=6, 7, 8, 9, 10, 11, 12, 13 and 14. I hope that should cover it.


----------



## steinba

I just keep on nagging, don't I? 
	

	
	
		
		

		
		
	


	




 Will this work as a power connector for a PPAv2 driven by a 24V STEPS. More specifically: Is the 2A rating enough?


----------



## tangent

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_I'm sure this has been covered somewhere in this mammoth thread_

 

More like "somewhere in this mammoth forum". The "what gain should I use" question is covered in conjunction with every amp design you can think of, and the answer doesn't change with amp design. Things like crossfeed do modify it, but I thought my crossfeed documentation page answered that part of it.

  Quote:


 It'll primarily be driving a 300 Ohm Sennheiser HD650. 
 

Somewhere between 5 or 6 and the default of 11 would be my guess. (Including compensation for crossfeed.) Depends on your source.

  Quote:


 What kind of socket would be good? 
 

Answered at the top of this page in the PPA docs.

  Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_Is the 2A rating enough?_

 

Yes. The STEPS is current-limited to 1.5 A, if you used the recommended LM317. Even if not, you could get over 2 A while the PPA's C1 bank charges, but that doesn't take long enough to melt the jack.


----------



## steinba

Excellent. Thank you! I've read the "2-3x more gain" in the crossfeed docs, now that you mention it. I've ordered R4's for gain levels from 6 to 14, so I've got everything covered. Now I know where to start. 
	

	
	
		
		

		
		
	


	




 And, i've RTFM-ed, and will "Use SIP socket strips" for R4.

 Great about the DC connector as well.

 Thanks again. 

 Now I hope mouser moves quickly.


----------



## slowpogo

I did a search in this thread but can't find the info I'm looking for. Has anyone built the PPAv2 in balanced configuration?

 If I had to guess I would say this would involve populating two boards, but with the ground channel parts eliminated (the actual input "ground" signal would just be grounded to the case). Then it just comes down to correctly wiring the inputs/outputs and using a quad pot...am I basically in the ballpark here?

 Also, would one YPJS be able to drive the balanced configuration, or would two be needed?

 I really would like to build a balanced SS amp and am looking at options. I do have a balanced source (modded 1212m) and would mod my K701s to balanced. I'm also wondering about the Pimeta V2 as a balanced amp; it's cheaper and I know the Pimeta V1 sounded great....


----------



## tangent

Quote:


  Originally Posted by *slowpogo* /img/forum/go_quote.gif 
_Has anyone built the PPAv2 in balanced configuration?_

 

Not that I recall.

  Quote:


 If I had to guess I would say this would involve populating two boards, but with the ground channel parts eliminated (the actual input "ground" signal would just be grounded to the case). Then it just comes down to correctly wiring the inputs/outputs and using a quad pot...am I basically in the ballpark here? 
 

Sounds plausible to me.

  Quote:


 would one YPJS be able to drive the balanced configuration, or would two be needed? 
 

I don't see why you'd need two power supplies, but then, I have yet to build a balanced amp. Maybe someone else will chime in who has actual experience in this.

  Quote:


 I'm also wondering about the Pimeta V2 as a balanced amp; it's cheaper and I know the Pimeta V1 sounded great.... 
 

One advantage is that you might be able to get away with a single board, by hacking the ground channel to be more like the L&R channels and using the scratchpad area to build your fourth channel. Again, no one's done this to my knowledge.


----------



## Volkum

Hey guys, I think I'm experiencing an issue with my ground channel buffer--read on, please.

 I'm not the most experienced with electronics (built CMOY prior to this so I guess I kind of dove into the deep end of the pool) so I'm also assuming, for the sockets, I'm to measure OG to -Vs/+Vs (pins 4 and 7 on the datasheet here) in step 6 of the step-by-step assembly guide?

 PSU: STEPS @ 30V 

 Sockets empty:
 L, +14.64/-14.54
 G, +14.65/-14.54
 R, +14.64/-14.54
 PSU, 30.02V

 Sockets populated with OPA627:
 L, +13.50/-13.39
 G, +13.51/-13.41
 R, +13.48/-13.38
 PSU, 30.01V

 LED lights up

 Looks alright, right? Then I got to part 8 of the guide, adjusting the buffer bias and here are my measurements:

 R34L, 44.1 mV
 R24L, 43.7 mV
 R34G, 0.0 mV
 R24G, 0.0 mV
 R34R, 44.4 mV
 R24R, 43.6 mV

 I get absolutely nothing across R24G/R34G. Nothing appears to be overheating, I don't see any obvious bad joints, and I'm not sure how to start troubleshooting. Any suggestions? I'm hoping I just overlooked something silly. Thanks in advance!


----------



## diditmyself

Have you measured across R21/22/23/31/32/33? Does it pass any current here?

 What about the rails to the buffer? What's the voltage reading from collector to collector on the output transistors?

 Are you sure your measuring probes have metal connection? If you measure on the topside there could be some isolation on the resistor leads.


----------



## Volkum

First, thanks for the suggestions. Here is what I have:

  Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_Have you measured across R21/22/23/31/32/33? Does it pass any current here?_

 

L:
 R21, 0.679 V
 R22, 0.691 V
 R23, 31.2 mV
 R31, 0.681 V
 R32, 0.694 V
 R33, 31.7 mV

 G:
 R21, 0.860 V
 R22, 0.771 V
 R23, 0.0 (still measures 10 ohm resistance)
 R31, 1.622 V
 R32, 1.639 V
 R33, 74.2 mV

 R:
 R21, 0.773 mv
 R22, 0.793 mV
 R23, 34.4 mV
 R31, 0.774 V
 R32, 0.784 V
 R33, 34.5 mV

  Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_What about the rails to the buffer? What's the voltage reading from collector to collector on the output transistors?_

 

Would this be referring to C-C of Q24 to Q34 within the same channel?

  Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_Are you sure your measuring probes have metal connection? If you measure on the topside there could be some isolation on the resistor leads._

 

There is a good amount of pad that I can use to measure on the top, but to be certain I just measured from the bottom, giving me the same results.


----------



## diditmyself

I don't get it. Maybe there's something wrong with Q22. I hope Amb or Tangent chimes in. I guess you've already checked to see that you haven't mixed up PNP and NPN transistors, and that all solder joints are OK.


----------



## Volkum

Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_I don't get it. Maybe there's something wrong with Q22. I hope Amb or Tangent chimes in. I guess you've already checked to see that you haven't mixed up PNP and NPN transistors, and that all solder joints are OK._

 

You bet; I've rechecked all the transistors a few times now to ensure I didn't mix them up. I didn't see any bad joints upon inspection, but I reflowed (or reflew, rather?) a large amount of them just in case, but it didn't help.


----------



## tangent

Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_I hope Amb or Tangent chimes in._

 

I don't have much constructive to offer here. Only two thoughts occur:

 1. The board version number makes me wonder if this is a new build with a board you bought a long time ago, or if it once worked and now it doesn't and aren't telling the full story. The 'C' run comes from a year or two ago.

 If you just didn't get around to building the board for a long time, some of the joints might be iffy. PCBs do have a shelf life, especially with the new lead-free plating used for the PPA v2.0C. You can cope with this by using extra flux or taking extra care with the joints.

 Which brings me to my next not-very-helpful thought:

 2. The build is a little messy. That in turn calls into question the quality of the joints, which coupled with an oxidized board could spell trouble.

 One knee-jerk thing to try would be to reflux and reflow all the joints in the ground channel, or at least those that look at all suspect. Clean the board, too, if you haven't already.


----------



## Volkum

Yes, I have had the board for quite some time. I had started and stopped a couple times for various reasons in the past 1.5 years or so. If it's my best bet, I'll order up a new board and move everything over (hopefully doing a less sloppy job in the process).


----------



## tangent

I'd still try reflowing everything first.

 The main reason to expect a better build the second time would be more to experience, both in soldering and parts selection -- you'd heed the 12mm diameter recommendation for the C1s, f'rinstance -- rather than because you got a fresher board. As I said, I don't put a huge amount of stock in the "stale board" theory. It's possible, but not the first thing I'd look at.


----------



## diditmyself

If it was my amp, I'd probably change Q22.


----------



## Volkum

I got some new transistors (and correctly sized C1s) from Digi-key today. I replaced Q23/33G and that fixed the ground channel. After that, I had the same prior ground channel issue on the left channel (odd?), so I swapped Q23/33L and now everything appears to be in order. On to finishing the build!


----------



## Volkum

All wired up and working, however I'm getting some hiss/white noise at high volumes with my HD-595s. Any chance this is just because I'm using the default config resulting in 11 gain with 50 ohm phones? My DC offset is quite low (1.0mv on left and 0.2mv on right) and I don't have any higher impedance headphones lying around to test with unfortunately.

 I'll tinker with the R4 value tomorrow to drop the gain and see what happens. I also read a few pages back that a lower R11 value may help with hiss when using lower impedance/sensitive headsets so I may give that a shot as well.


----------



## tangent

Yes, the gain's probably too high. The default is a for a good stable build. Once it's stable, a setup like that should them be dropped much lower. Since you've used 627s all around, I'd first try dropping it to 2.


----------



## Volkum

All done (sorta). Thanks for confirming the gain was too high, Tangent; I lowered the gain to 3 which is working out much better with my HD-595s.





 The R4 situation is temporary as I'm going to swap in SIP sockets so I'll be able to more easily accommodate different headphones in the future.

 Last inquiry/concern:

 While measuring the R10 voltage drops the measurements seemed odd to me:

 R: 15.1 mV / 1.152 V
 G: 3.3 mV / 1.032 V
 L: 1.7 mV / 1.017 V

 Is it normal to have values of these sorts where one channel varies so much from the other two (and all being so low?)? Maybe I'm measuring incorrectly?


----------



## steinba

It's alive!







 Just need a case now! :-D

 (Sorry, just had to brag a little.)


----------



## FallenAngel

Nice, but I hope that the 1/4" isn't soldered or you won't get it through the case.


----------



## steinba

Thanks. Yes, it actually is but not very thoroughly, and only with cat5 single conductors. The cables will be simple to swap to do the casework nicely. There's a crossfeed filter going in there as well. Just had to test the amp, you see.


----------



## FallenAngel

well... what opamps - and how come you only have 4 caps in there?


----------



## tangent

So...the dark bits at the bottom edge of the table there are residuals of the lighting strikes?


----------



## steinba

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_well... what opamps - and how come you only have 4 caps in there?_

 

OPA637 left and right, and a 627 for ground. The C1's are Elna Cerafine 470uF's, and I stopped at four because I read something Tangent said about it being smart not to exceed 2000uF rail capacitance. Could I have misunderstood that? I have more lying around.

 Maybe he'll chime in.


----------



## steinba

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_So...the dark bits at the bottom edge of the table there are residuals of the lighting strikes? 
	

	
	
		
		

		
		
	


	


_

 

Yeah. It actually is quite difficult aiming those things. Especially when it's your first time trying throwing lightning bolts. 
	

	
	
		
		

		
		
	


	




 When I get the hang of it, I'm going out to smite people.


----------



## tangent

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_I read something Tangent said about it being smart not to exceed 2000uF rail capacitance._

 

Yes. I doubt you can hear a difference with more capacitance, and if not, then adding more just makes your power supply work harder in startup _and_ shutdown. You might even give it karōshi.


----------



## steinba

Great! I'll leave it as it is, then. Thank you.

 (Great word, btw. I'm gonna use it some time.)


----------



## steinba

I couldn't wait for the case, so I soldered the PPAv2, STEPS and crossfeed boards together on the table, hooked up my CD Player and HD-650s and got out a few CD's. 

 I first played Tarja Turunen's solo album, which has a passage I really like where the soundstage is really full of loud details, so I can't get my speaker setup to resolve it good enough. At least that's what I thought. Initially, it sounded good (not great) on the headphones, but the "reference passage" sounded even more muddy than on my loudspeakers. Bummer. Maybe the PPA needs more headroom. The gain is set at a moderate 8x. I'll try raising it to 11x and try again. Could be that the CD just is a victim of the Loudness War though,

 Then, I got out Roger Waters' "Amused To Death" and pressed play...

 HOLY SWEET MOTHER OF.... :-O THIS IS ABSOLUTELY, GOBSMACKINGLY AMAZING! (Just had to get that out.) 
	

	
	
		
		

		
		
	


	




 I carried on with a few classical Telarc recordings, some Dream Theater and some reference CD's from hifi magazines. This all confirmed the impression I got from the Roger Waters CD. I must say I'm well and truly stoked about this.

 There was a noticable hum when I touched the bare metal potmeter shaft, but I hope this will be gone when I get the pot mechanically attached to the metal case. (Confirmation, anyone?)

 I hope more gain (and headroom) will improve things further.

 I already biased the buffers to 30 mA, and the opamps into class A with 1 mA. Can I hope to improve sound quality even further if I raise the opamp bias?

 Any tips om improvement options will be greatly appreciated.


----------



## tangent

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_Could be that the CD just is a victim of the Loudness War though_

 

That, or they just multi-tracked it to death.

  Quote:


 HOLY SWEET MOTHER OF.... :-O THIS IS ABSOLUTELY, GOBSMACKINGLY AMAZING! (Just had to get that out.) 
	

	
	
		
		

		
		
	


	



 

I'm glad you like it. 
	

	
	
		
		

		
		
	


	




 Since you like Roger Waters, you may also have some Pink Floyd, much of which is also reference worthy. They recorded some of the best bass testing material available, particularly if you're not interested in electronica type bass. Delicate Sound of Thunder....yummy.

 The only acoustic bass I like better for testing is disc 2 of Talking Heads' Sand in the Vaseline. _Life During Wartime_ from that disc is simply amazing.

  Quote:


 There was a noticable hum when I touched the bare metal potmeter shaft, but I hope this will be gone when I get the pot mechanically attached to the metal case. (Confirmation, anyone?) 
 

A naked amp board should still be quiet if you added a ground strap to the pot. If you did and it isn't, it could indicate a ground loop. Confirm by testing with a battery-powered portable player. If that cures the hum, the problem is systemic, not something with the PPA in specific.

 You might be able to cure it with a ground loop breaker in the PPA. I show one such in this thread.

  Quote:


 I hope more gain (and headroom) will improve things further. 
 

The only way that would happen is if you have some uncommonly high dynamic range recordings, on high bit depth media. For instance, an SACD where most of the music is at like -40 dB below full scale. Virtually no real-world recordings do this, quite aside from the Loudness War issue.

 Clipping isn't one of those squishy matters of audiophile opinion. If you think your amp is clipping, it's east to find out for certain. Set the volume to the correct listening level for the recording in question, then play a full-scale test tone from a test disc on the same player. (Don't have cans plugged in for this.) Measure the volts, multiply by 2.828, and see if that fits within the op-amp's output voltage limits. If it does, it can't be clipping, at least not due to insufficient voltage gain.

 For instance, an OPA637 wants approximately +/-3 V between the rails and the output signal. Call it +/-3.5 V to be safe. With a 24 V supply, that leaves 17 Vp-p to play with, or almost exactly 6 Vrms. 6 Vrms into almost _any_ dynamic headphone is destructively loud, to your eardrums for certain and probably to the drivers, too. And at G=8, you can get a 6 V signal with a 0.75 V input signal, which isn't all that many dB off full CD line level.

 I'm ignoring things like passive crossfeed filter loss here, of course.


----------



## steinba

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Since you like Roger Waters, you may also have some Pink Floyd, much of which is also reference worthy. They recorded some of the best bass testing material available, particularly if you're not interested in electronica type bass. Delicate Sound of Thunder....yummy._

 

I'll get to that for sure. 
	

	
	
		
		

		
		
	


	




 Thanks for the tip.

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The only acoustic bass I like better for testing is disc 2 of Talking Heads' Sand in the Vaseline. Life During Wartime from that disc is simply amazing._

 

I haven't heard that, but I'll check it out.



  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_A naked amp board should still be quiet if you added a ground strap to the pot. If you did and it isn't, it could indicate a ground loop. Confirm by testing with a battery-powered portable player. If that cures the hum, the problem is systemic, not something with the PPA in specific._

 

Ah, but I didn't. That's just a small cable from a screw on the pot to the ground plane, right?


  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_You might be able to cure it with a ground loop breaker in the PPA. I show one such in this thread._

 

Thanks. I'll check it out. I'm sure it'll be fine once I add the ground strap, though.


  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The only way that would happen is if you have some uncommonly high dynamic range recordings, on high bit depth media. For instance, an SACD where most of the music is at like -40 dB below full scale. Virtually no real-world recordings do this, quite aside from the Loudness War issue.

 Clipping isn't one of those squishy matters of audiophile opinion. If you think your amp is clipping, it's east to find out for certain. Set the volume to the correct listening level for the recording in question, then play a full-scale test tone from a test disc on the same player. (Don't have cans plugged in for this.) Measure the volts, multiply by 2.828, and see if that fits within the op-amp's output voltage limits. If it does, it can't be clipping, at least not due to insufficient voltage gain.

 For instance, an OPA637 wants approximately +/-3 V between the rails and the output signal. Call it +/-3.5 V to be safe. With a 24 V supply, that leaves 17 Vp-p to play with, or almost exactly 6 Vrms. 6 Vrms into almost any dynamic headphone is destructively loud, to your eardrums for certain and probably to the drivers, too. And at G=8, you can get a 6 V signal with a 0.75 V input signal, which isn't all that many dB off full CD line level.

 I'm ignoring things like passive crossfeed filter loss here, of course._

 


 I appreciate your input. Since the muddiness ONLY occurs with that one CD, I'm gonna declare the CD the culprit. With gain=8, I am at maybe 80% volume at loud (but not crazy loud) "normal" listening volume. With the crossfeed, that is. I'm gonna try a gain of 10x and see what happens.

 Thanks again!


----------



## steinba

The ground strap worked like a charm. Dead quiet now. Thanks. I guess I should have RTFM first. 
	

	
	
		
		

		
		
	


	




 I've tried the Tarja Turunen CD again too, and I have determined that everything but electric bass sounds fine from it, but the bass is bloated and distorted on every track. The producer's choice and not a fault in the amp, then.

 I still think I'm going to boost the gain a little. I'm gonna drive the amp from an iPod dock as well as my Marantz CD6000 KI Signature that I'm testing with now, and the outputs on the iDock might be less powerful than the CDP as well.

 Thanks again!

 Edit: So, I've set gain to 10x. Cant say it got very much louder, but it's just a bit more than "loud enough", so I'm happy with it, and gonna leave it like that for now.

 Am I right in assuming that changing the gain doesn't affect opamp or buffer bias in any way, so I don't need to recheck those?


----------



## jezz

I wired up my PPAv2 to a Sigma11 and it sounds absolutely great. I followed the directions on the website and everything worked flawlessly the first time. I can truly attest to the quality of the PPA design and documentation, so thank you Tangent for a phenomenal amplifier. With the parts listed on Tangent's site (gain = 11, OPAMPG = OPA627, OPAMPLR = OPA637), it drives my K340's with ease.

 An aside about panels: I'm thrilled to report that blanks can be ordered fairly cheaply in packs of 10 from Mouser, so if for those of you as "skilled" with a drill as I am there's plenty of "room to learn." If you think you will ever attempt to create your own end panels in the future, I would highly recommend the purchase of the appropriate chassis punches. Otherwise, like me, your handshake may become fierce after the abuse of a nibbler, and you too may convert to the exclusive use of Front Panel Express.


----------



## steinba

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_The ground strap worked like a charm. Dead quiet now. Thanks. I guess I should have RTFM first. 
	

	
	
		
		

		
		
	


	


_

 

But alas, all is not well. 
	

	
	
		
		

		
		
	


	




 Everything's fine with the HD-650, but with my Denon AH-D1000, there's a barely noticable hiss (I only hear it when no music is playing) that disappears when I touch the neutrik jack.

 Could this be a bad connection to ground on the jack? Will it be OK when the jack's bolted to the metal front plate? 
 Could it just be that the hiss is oscillating due to too high gain (11x/R4=11K) with the AH-D100's? Should I just drop the gain down to 10 again, or is there another trick to getting the amp to drive the Denons while keeping the high gain?

 The "lower R11 to 100-200R-trick; could that solve my problem, or would thar cause otther issues? (When using higher impedance headphones like the HD-650 for example?)

 Thanks.


----------



## steinba

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_But alas, all is not well. 
	

	
	
		
		

		
		
	


	




 Everything's fine with the HD-650, but with my Denon AH-D1000, there's a barely noticable hiss (I only hear it when no music is playing) that disappears when I touch the neutrik jack.

 Could this be a bad connection to ground on the jack? Will it be OK when the jack's bolted to the metal front plate? 
 Could it just be that the hiss is oscillating due to too high gain (11x/R4=11K) with the AH-D100's? Should I just drop the gain down to 10 again, or is there another trick to getting the amp to drive the Denons while keeping the high gain?

 The "lower R11 to 100-200R-trick; could that solve my problem, or would thar cause otther issues? (When using higher impedance headphones like the HD-650 for example?)

 Thanks._

 

This drives me crazy. 
	

	
	
		
		

		
		
	


	




 I'm not entirely sure it's not a grounding problem, since now the hiss is stronger when (or only audible when) i touch the pot. It sure sounds like the oscillation problem, though, since it's only present with the 32Ohm (?) Denons.

 The hiss is less intense when I touch the male jack on the headphone cable. (Not the female Neutrik as I said before.) 

 Could I safely swap R11 with 200 Ohm resistors without risking other issues? Would I have to do the bias adjustments over again?

 I tried 10x gain instead of 11x, but with no noticable difference. I'd like to keep the high gain because of the attentuation that the crossfeed causes. I also tried 8x, and the hiss is reduced, but I need more gain than that if I want to keep the crossfeed.

 That being said, I built this for the Sennheisers, and they sound SO good driven by it that I could easily ignore the hiss with my Denons, but it _would_ be nice to get rid of it.

 Thanks.


----------



## tangent

Quote:


  Originally Posted by *steinba* /img/forum/go_quote.gif 
_The "lower R11 to 100-200R-trick; could that solve my problem, or would thar cause otther issues?_

 

I don't know anyone who's tried it and had it fail. But then, not many have tried it, which is why I haven't yet made the change in the docs.


----------



## steinba

Thanks. I'll be sure to let you know what happens if I try it.


----------



## wuerzig

Quote:


  Originally Posted by *wuerzig* /img/forum/go_quote.gif 
_




 I think this might be due to the case not being grounded yet. Also, I remember this looked different in analog mode (didnt take a pic sorry)._

 


 Just a quick follow-up on the possible oscillation problem. I scoped it again and did an FFT on the scopes memory contents. Its several FM radio stations. I get it even with the probe shorted.

 The amp sounds fantastic. I cant wait to build the YJPS.

 Cheers, and ein gesundes neues jahr ("a healthy new year") from germany!


----------



## whitelabrat

Almost done with my PPA2. I've used whatever I already had where possible, and a lot of surplus parts. There are even a few SMT chip resistors in there.


----------



## whitelabrat

Up and running. My first solid state amp... that works. First try too!

 *pat self on back*

 I haven't set the opamp bias for class A yet. Running at 17.5v with OPA602's. Driving Beyerdynamic DT880's.

 All is safe so I'm going to break out the OPA637's.


----------



## whitelabrat

Biased the OPA637's a bit over 1ma.

 I'm in the happy place.


----------



## tangent

I'm glad to hear it's working well. I was a bit worried after seeing that pic above.


----------



## noveltone

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I don't know anyone who's tried it and had it fail. But then, not many have tried it, which is why I haven't yet made the change in the docs._

 

For what it's worth, I changed out that resistor, to no ill effect. I didn't have an oscillation problem to solve, but I didn't want to find one later. 

 Thanks again for great documentation.


----------



## whitelabrat

For what it's worth, despite the scary look of it, I did use high quality parts overall. The weakest links are the capacitors used near the opamp. The C1 layer of capacitance is from Nichicon KZ's and Panasonic FM's with a lone Elna that I had nothing else to do with. The C2 set are ceramics along with an old 0.47uf film cap that wasn't doing anything. I figure those are better than nothing, especially when their purpose is to smooth power supply ripple and to react to audio frequencies.

 I didn't think that C4 would be as important as long as you have a good C5. Unfortunately I didn't have anything good for C5 except for ceramics. Nothing small at least. I was worried that they wouldn't be fast enough in case RF became an issue with the OPA637's. Apparently they are, but just barely. I think that it would be good to replace these with fast 1uF's.

 Most of the resistors are nice PRP or Vishay/Dale. A lot are 1/2w which is super overkill, but I made 'em fit anyway.

 I'm currently using a 100k stepped attenuator for volume. Good for sound quality, but poor for adjustment.

 The power supply is a big old 15v 3A brick I had laying about. I'd like to replace it with a TREAD and set for about 20-24vdc. I think I've got a big old EI core transformer perfect for the job.

 Excellent design and well done manual! Thanks!


----------



## whitelabrat

I found a SMPS I had laying about that puts out what appears to be 28v regulated. I wired it up to and set off to adjust the buffer bias. I'm doubting my measurement now. Do I measure vdc or vac? Measure at the output or before the output?


----------



## tangent

Quote:


  Originally Posted by *whitelabrat* /img/forum/go_quote.gif 
_I found a SMPS I had laying about that puts out what appears to be 28v regulated._

 

Is it isolated?

  Quote:


 Do I measure vdc or vac? 
 

Whenever you see someone talk about a voltage _drop_, it means DC. The AC case would be described differently...attenuation, perhaps.

  Quote:


 Measure at the output or before the output? 
 

From the docs: "across each output resistor". (R24 and R34) You only have to measure the drop across R24 _or_ R34, not both. The current through one will be the current through the other, and since they're the same value, so will the voltage drop.


----------



## whitelabrat

I've not tried to open the case on the SMPS to determine if it is isolated. In any case it appears to cause the amp to go crazy so it goes back to where it came from.

 My bad. Wasn't thinking. Ohms law.


----------



## tangent

You don't have to open it. Unplug it from the wall, and measure resistance (or continuity if your meter has that feature) between all combinations of input and output terminals. If any reads near-0, it isn't isolated.


----------



## whitelabrat

Just measured the SMPS. All the outputs read in the kiliohms. Seems isolated to me. I'm tempted to swipe some nice Elna Certifines and film caps from other projects to see if that will stablize the OPA637's at higher voltages. Stay tuned...


----------



## tangent

I'm confused.

 First, you measured the outputs against _what_? You should have made at least 4 resistance measurements, for a 2-blade AC plug on one end and a plain DC barrel plug on the other. If the power supply has a safety ground as well, you should have 6 measurements instead.

 Second, if it's isolated, why did it make the amp misbehave when another power supply is powering the amp successfully?


----------



## whitelabrat

You're right. I didn't measure the input. Resistance is below 1ohm from the input ground to output. That would be a problem as you suggest.


----------



## noveltone

Hello! I am using a PPAv2, powered with a STEPS in separate cases. The PPA is actually not cased at the moment, but I have a piece of metal mocking up the case. The audio input grounds and volume pot are tied to the case. The power input and headphone output are isolated from it.

 The real issue is that I had a lot of hash-sounding noise. It's only present with shorted inputs and with an ipod connected, not with a pcomponent CDP. I don't think the amp is oscillating. I am using AD8610 opamps all around. Regarding possible oscillation, I have lowered the value of R11 as recommended here, have upped the value of C6 to 75 pF, and reduced the gain to about 2.2. I moved the STEPS around in the room. Since I don't have a scope, I can't be sure. None of these things had any effect on the noise.

 Here's why I don't think it's oscillation: When I ran a wire from my mocked-up PPA case to the safety ground (earth/grounded/third house wire) bolt on the STEPS case, the noise immediately vanished. Now, I measured about 46V AC between the two. That seemed really weird. The STEPS output is isolated from line voltage and its case, however, so I suppose it doesn't really use earth as a reference. As a test I measured about 100V between audio output ground and safety ground on my component CDP. So they're not always connected. Fine.

 Then I measured that the ipod's audio output ground is about 1.0V AC above safety ground. Signal operates above that voltage. Weird. I suppose earthing this ground voltage will drain the ipod's charge pretty fast. Still, the noise is gone, and the amp sounds great again. If I were using a component CDP this isn't an issue, so I wouldn't use the grounding wire. The CDP designers probably have a reason to have audio ground at 100V AC above safety ground. 

 I can't think of a reason that it would be bad to tie audio input ground to earth this way. Can any of you? Are there other solutions? Thank you all very much!!


----------



## tangent

My iPod touch puts out high-frequency digital hash sometimes, depending on how I connect it to the dock. Removing it and plugging it back in carefully fixes it.

 It seems to happen more often when the audio selector switch (preamp without the "amp") is set to the speakers when I drop the iPod into the dock, then flip the switch to the PPA. This could be another ground negotiation issue like you're seeing.

 I suspect that if you add the input caps, these problems will go away. I built the PPA discussed above so long ago that I cannot be sure that it is DC-coupled, but it would be my normal practice, so I assume it is. Because I have a tolerable solution to my problem, I don't think I'll open it up and add the caps, but you might do this to yours.


----------



## M3NTAL

is there any benefit to using a "discrete op-amp" in the circuit? (ÐÂ½¨ÍøÒ³ 1)


----------



## M3NTAL

Using the calculator - the lowest gain I can get is 1.1x with 10K at R3 and 1K at R4... is this correct? Will there be any issues with certain OP-AMPs with the gain this low?

 Cheers


----------



## tangent

You can get to g=1.0 by leaving R3 out. R4 can be left in place at any value, or shorted.

 Obviously doing this rules out some op-amps. The higher the gain, the higher the stability, generally speaking, because it reduces the bandwidth of the circuit. Some op-amps tell you right in their datasheet that they need a certain minimum gain. Others are technically unity-gain stable but really shouldn't be operated below some minimum. e.g. AD8397, which really should be considered to have a g=2 minimum.

 If you can't glean this from the datasheet yourself, do searches for it and "stability" and other such terms here and on Google. If there are problems with that chip, you'll probably find them.


----------



## M3NTAL

Tangent - Thank you very much!

 Would I be risking any stability by removing the R3? I could possibly do a gain of 3 and be fine also.


----------



## tangent

Again, it depends on whether your op-amps are unity gain stable in a PPA v2. A lot of op-amps have been tried over the years, and many have posted their results publicly somewhere.


----------



## M3NTAL

Thank you.. and sorry for the re-hash of info.


----------



## askforwhy

Something is wrong with my ppav2 left channel.
 It is using OPA627X3, gain=5.
 The opamp and buffers are a little warm but not hot.
 I adjusted buffer bias to 30ma in all three channels.
 But there is no voltage drop across R10 in my left channel and the dc offset is ~330ma(OL to OG). My right channel is fine, dc offset is 0.7ma.
 I guess Q1 and Q2 are fired? I am really sick of soldering and desoldering recently so I just want to make sure.
	

	
	
		
		

		
			




 Thanks.


----------



## askforwhy

Problem solved.
 Stupid mistake, I installed two TLE2426 in the PPA. Removed one, Okay.
 Now work on the chasis.


----------



## qusp

hi, I know this is probably a bit OT so I apologize, but I would like to use the battery board for the PPA for a portable balanced dac/amp (+/-12vdc). I would be right in assuming that there will not be an issue using the supply as speced for a balanced build? I will further regulate the DC with some super regulators down to +/-9vdc


----------



## tangent

Quote:


  Originally Posted by *askforwhy* /img/forum/go_quote.gif 
_Stupid mistake, I installed two TLE2426 in the PPA._

 

One may work, but it was designed and tested with three. Two is definitely not right.

  Quote:


  Originally Posted by *qusp* /img/forum/go_quote.gif 
_I would like to use the battery board for the PPA for a portable balanced dac/amp (+/-12vdc)._

 

I don't quite understand what you're doing with your split supply. If you mean to use dual battery banks and dual chargers, I don't think that will work well. If you're splitting a single battery pack with some kind of virtual ground, it comes down to the standard details of proper grounding and such.

  Quote:


 I would be right in assuming that there will not be an issue using the supply as speced for a balanced build? 
 

Best to post a power system design diagram. What are all the rails, what are they connected to, is there a metal case, what's connected to that, what are all your grounds...? Etc.


----------



## qusp

yes, its to split a single supply to create a V-ground for the star ground , with the bonus of also including a battery charger for the device. yes there is a metal case. i'll try to put together a block diagram a bit later tonight as I havent gotten as far as a schematic yet, IU still havent totaly decided on the output stage, whether I use the buffer or a fet follower, I need +5V (dac), +5v(digital volume) , +5V (toslink spdif receiver or ASRC unit), +/-9V (10 preferred, for opamp supplies) +/-9-10v (peranders discrete SMD diamond buffers). so the rails should be at least +/-12vdc, shooting for 14vdc so that can be regulated down to 9-10v with the voltage drop covered nicely.


----------



## askforwhy

I hope this time isn't some stupid mistakes again.
 My PPA is completely fine working on the bench. But when I place them in my case(tie the rca jacks to the case I think), the Q3 isolation jfets just blow away as I power up. I checked the PSU and it wasn't shorted to any ground.
 Desoldering six small transistors is not really a easy job for a person like me.


----------



## tangent

You're likely doing something like tying both IG and V- to the case by using metal-bodied jacks for both the input and DC jacks. It could be OG instead, through the output jack, or IG through the pot body.

 The PPA v2 docs do mention this, but don't discuss it very deeply. I wrote up a much more exhaustive treatment of the topic for the PIMETA v2 docs, on this page.


----------



## askforwhy

Thanks Tangent, your website is always a pleasure to read.
	

	
	
		
		

		
		
	


	



 I put the trafo, psu and the PPA in the same case, so there will only be a IEC receptacle. I did ground the OG to the case because I didn't have a isoloated jack(isolated jacks arrive tomorrow) at hand, but the case is only grounded to the OG, neither IG nor V-.
 I will install sockets in the Q3s so it won't be so much pain if I mess up again.


----------



## tangent

Quote:


  Originally Posted by *askforwhy* /img/forum/go_quote.gif 
_Thanks Tangent, your website is always a pleasure to read.
	

	
	
		
		

		
		
	


	


_

 

Thanks, it's good to know that there are people who think that. 
	

	
	
		
		

		
		
	


	




 As I read a page I wrote for the 20th time, I lose track of whether it's still good or not. At some point, I have to rely on reader reports.

  Quote:


 there will only be a IEC receptacle 
 

Plastic body? No safety ground connection?

  Quote:


 the case is only grounded to the OG, neither IG nor V-. 
 

I'd check it anyway; maybe there are connections present you didn't intend. 
	

	
	
		
		

		
		
	


	




 With the amp off, but everything hooked up as normal, use a continuity meter to check IG to OG, OG to V-, and V- to IG.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_If it were me trying to fix this, I'd retransistor both the left and ground channels. I mean both bipolars and JFETs._

 

Its been a year now and i finally got back to this. I re-transistored the left, right, and ground channels. There was a lot of flux and isopropyl involved 
	

	
	
		
		

		
		
	


	




 I'm listening to music right now, and the amp exhibits no audible problems, but I'm unsure about some of the measurements.



 Without the opamps installed, I get +/-14.4v at the opamp pins and +15/-14.4v at v+/v- with respect to IG. 

 With the opamps installed, I get +/-2.5v at ground channel's Vs, and +/-3.5v at L and R channels Vs. at v+/v- pads next to the power input, I'm getting +24.5/-4.7...
 Output transistor at Q24 runs a LOT hotter than the one at Q34, which makes sense given the relative VH.

http://img.photobucket.com/albums/v404/reihn/ppav2.jpg

 I don't think theres anything wrong with the soldering... My bet is somethings still broken from when I first shorted out the amp.


----------



## Spacehead

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_Its been a year now and i finally got back to this. I re-transistored the left, right, and ground channels. There was a lot of flux and isopropyl involved 
	

	
	
		
		

		
		
	


	




 I'm listening to music right now, and the amp exhibits no audible problems, but I'm unsure about some of the measurements.

 Without the opamps installed, I get +/-14.4v at the opamp pins and +15/-14.4v at v+/v- with respect to IG. 

 With the opamps installed, I get +/-2.5v at ground channel's Vs, and +/-3.5v at L and R channels Vs. at v+/v- pads next to the power input, I'm getting +24.5/-4.7...
 Output transistor at Q24 runs a LOT hotter than the one at Q34, which makes sense given the relative VH.

http://img.photobucket.com/albums/v404/reihn/ppav2.jpg

 I don't think theres anything wrong with the soldering... My bet is somethings still broken from when I first shorted out the amp._

 


 Did you replace TLE2426 too? Where was the short located? I guess it would pop only nearby components.


----------



## JamesL

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_Did you replace TLE2426 too? Where was the short located? I guess it would pop only nearby components._

 

Yes, I replaced all three TLEs. Replaced all active components except the opamp and power supply.

 I'm not sure where the short occurred. I think it was near the rail caps.
 I was happily listening to it on my bench, procrastinating on the casing..
 One day, I moved it while it was turned on, and a clipped lead came in contact with the bottom of the pcb.. there was a *crack*, and the music disappeared.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I'm unsure about some of the measurements....+15/-14.4v at v+/v- with respect to IG._

 

You're measuring in front of the protection diode. The even +/-14.4 V split occurs after that diode. Nothing to worry about.

  Quote:


 With the opamps installed, I get +/-2.5v at ground channel's Vs, and +/-3.5v at L and R channels Vs. at v+/v- pads next to the power input, I'm getting +24.5/-4.7... 
 

What if you install just one op-amp? Try the ground channel one first, then R, then L. If the symptom appears immediately with just G, start with R instead, then go L then G. The goal here is to find some combination of two channels that work fine together but fail when the third is added. If that exists, your problem is in that third channel.

 It may be that the problem channel is R, the one still using the original parts.

 If you still can't chase it down further, what is the amp's current draw?


----------



## Spacehead

COOL I got most of the parts ordered. I hope I didn't forget anything super important. I don't yet have a case or ALPS pots. Next week I will join this thread with construction pics, if you don't mind. I ordered only 15 pcs 2N5087 transistors, they were 0.20 € each (and 25 pcs 2N5088)!! But matching shouldn't be so important as they are in op amp feedback loop, right?


----------



## FallenAngel

Matching is still a very good idea.


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Matching is still a very good idea._

 

OK 

 I couldn't find PN4392 or MPF4392
 so
 I ordered J310 instead, it has min IDSS of 24 mA and same pinout

 parts cost me 60€ with shipping , there was some extras


----------



## tangent

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_matching shouldn't be so important as they are in op amp feedback loop, right?_

 

The fewer distortions the op-amp has to correct for, the better the amp will sound.

 I would take your set of transistors and sort them by hFE. Then take 3 neighbors at a time for the same transistor in each of the channels. They won't be as tightly matched as if you were able to take arbitrary transistors from, say, a bag of 100, but they'll be as close as you can get them.


----------



## Spacehead

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_The fewer distortions the op-amp has to correct for, the better the amp will sound.

 I would take your set of transistors and sort them by hFE. Then take 3 neighbors at a time for the same transistor in each of the channels. They won't be as tightly matched as if you were able to take arbitrary transistors from, say, a bag of 100, but they'll be as close as you can get them._

 

that will I do. 

 When my 2N5486 (100pcs) arrive, I need to create a device for matching Idss. I have never done that before.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_You're measuring in front of the protection diode. The even +/-14.4 V split occurs after that diode. Nothing to worry about._

 

Ah, that makes sense.. Silly me
 However- I tested it again, this time measuring the voltage after the diode, and I got +14.7/-14.4(from 15/14.4) Acceptable? or still something wrong?
  Quote:


 
 What if you install just one op-amp? Try the ground channel one first, then R, then L. If the symptom appears immediately with just G, start with R instead, then go L then G. The goal here is to find some combination of two channels that work fine together but fail when the third is added. If that exists, your problem is in that third channel. 
 

I actually did replace the right channel as well. 
 These are my measurements

 With ground opamp installed
 +/-14v on Left and Right supply pins, +-2.5v at ground

 With right channel opamp installed
 +/-14.4v at left and ground supply pins, 12.9/-12.8 on left

 With left channel installed
 +/-14 at right and ground supply pins, -3/+3 on right.

 To me, it doesn't seem like the problem is isolated to just one channel so I'll probably end up starting with a fresh board which will save me the pain of desoldering any more transistors. I appreciate all the help&support you've given all this time.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_I got +14.7/-14.4(from 15/14.4) Acceptable? or still something wrong?_

 

Yes, it's probably fine. At 28V, the TLE's split tolerance is 2%, so you can see a bit over half a volt of mismatch between the split halves. A third of a volt is more than I remember seeing, but still in-spec.

  Quote:


 I'll probably end up starting with a fresh board which will save me the pain of desoldering any more transistors. 
 

That's what I'd do. The most rework I've done on a single board is retransistoring a single channel.


----------



## Spacehead

thanks tangent, I got my PPA v2 PCB today in mail! 






 I have almost all the parts now, I am missing 2N5088 and 2N5087 transistors and jfets.

 I don't yet know how to measure Idss of a JFET. I want to have everything matched in my PPA , it must be pure HIFI. My output transistors will be BD139 and BD140. 
 I have only TIP41 and TIP42 too, but they don't sound good? Do you think BDs will color the sound?


----------



## FallenAngel

I recommend reading these: discrete diamond buffer - parts list
 Measuring IDSS : Transistor matching


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_I recommend reading these: discrete diamond buffer - parts list
 Measuring IDSS : Transistor matching_

 

Oh it is pretty easy to measure JFETs. I absolutely must make my power supply current limited (will I put a resistor in series with the battery, like 100 ohm?)

 I don't like BD139 and BD140 sound. It sounds very solid state hard and dry. I must look better alternatives from somewhere.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_That's what I'd do. The most rework I've done on a single board is retransistoring a single channel._

 

how do you feel about reusing parts?
 10 minutes with some flux, and I desoldered the electrolytes, trimpots, potentiometer, and dip8 socket.

 The trimpots tested good, at least resistance-wise, and a simple 9v battery and volt reading suggested the capacitors held their charge.
 Should I be more weary about taking parts from a broken amp?


----------



## tangent

I almost suggested you do harvest the most expensive of the old parts. Basically, anything over $1, I'd save. I wouldn't have bothered with the sockets, but then I bought a few tubes of them years ago, so they're like dust to me now.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I almost suggested you do harvest the most expensive of the old parts. Basically, anything over $1, I'd save. I wouldn't have bothered with the sockets, but then I bought a few tubes of them years ago, so they're like dust to me now._

 

Hehe. I have a bit of chip-quik I have left over from when I had to desolder some resistor networks, and taking things out have been a piece of cake since.

 I thought i might as well take out the sockets since its really impossible to damage those things. 

 Not sure what to do with my set of opa627's though. I'm paranoid that plugging it into the new board is going to blow it up 

 board ordered =)


----------



## tangent

I'd test the opamps in another known-working circuit. Maybe build my op-amp tester. That will only tell you if the chips are still plausibly op-amps; valuable, but it doesn't rule out all forms of damage.

 By the way, I've been rethinking my harvesting rule: I like 50 cents a pin better. It accounts for the difficulty of removing parts. The new rule makes you replace your TLEs, which I would do anyway, since there's some question about your voltage split.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I'd test the opamps in another known-working circuit. Maybe build my op-amp tester. That will only tell you if the chips are still plausibly op-amps; valuable, but it doesn't rule out all forms of damage._

 

sweet deal. I wonder if I can scrap pieces from the old board for your little circuit. 

 For r1-r4, do the absolute values matter much, as opposed to the relative values? 
 (eg. can I use 4.32k & 3.32k at r1/r2 for a x0.56 divider, and do a similar thing at r3/r4 long as it provides appropriate gain.. or is that stupid)


----------



## tangent

I cover all that in the docs.


----------



## Spacehead

I have DC offset on my source. I need to add input capacitors. I have two 2.2 uF Wimas. Any suggestions where to put them? 

 I have not yet received 2N5088 and 2N5087. I wonder how long Futurlec shipments take to arrive here. 
 I have been thinking if I absolutely cannot wait to start building, how bad it would be to use BC337 and BC327 or 2SC1815 and 2SA1015 (except japanese transistor won't fit at all?)


----------



## tangent

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_Any suggestions where to put them?_

 

See the PIMETA v2 schematic. Essentially, the cap and R1 go in series using the existing two R1 pads on the PPA.

  Quote:


 how bad it would be to use BC337 and BC327 
 

Probably not a big difference. I don't know that it's been tried, though.


----------



## Spacehead

I have now matched pretty closely most of the transistors. 
 2N5486 by 1 mA from 12 to -15 mA 
 J310 40 mA , 25 mA , 30 mA
 2N5087 of 5 hFe 
 2N5088 of 5 hFe
 output transistor don't need matching and I cannot do that because I have only 6
 still need to check BF246 
 I have all the resistors, there is some carbon resistors, most of them are metal. I have socket strips , sockets, most of the misc parts, 
 polyester capacitors and Panasonic FM and FC for power supply 







 I have OPA1611 op amps too, I wonder If Should balance the inputs right away so that I could use all op amps. 

 What I am missing is A PROPER SOLDERING STATION!

 I ordered a very cheap electronically power controlled soldering station, VTSS4 and some solder wick. 
 I bought a 2 euro soldering iron and tried to do some proper joints with that: 





 I think I am ready to start soldering the resistors tomorrow, it should be easy if my head is clear. 

 I will use strips on gain resistors, input resistor (1M), gain to ground resistor maybe, so I can balance the input bias currents. 
 This is pretty easy to comprehend, but many many things must be taken care of for successful build.


----------



## Spacehead

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_See the PIMETA v2 schematic. Essentially, the cap and R1 go in series using the existing two R1 pads on the PPA._

 

there is only R1 L , G , R
 on my PPA v.2.0E version

 I can of course solder the cap into input rca jacks. I'll start now adding socket strips. 
 Are the + and - inputs now balanced? 1M down and 470K + 1K + 10K on input -


----------



## FallenAngel

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_there is only R1 L , G , R
 on my PPA v.2.0E version

 I can of course solder the cap into input rca jacks. I'll start now adding socket strips. 
 Are the + and - inputs now balanced? 1M down and 470K + 1K + 10K on input -_

 

You shouldn't need to solder the caps on the RCAs. If they are small, you can make them "stand", have R1L/R1R "stand" as well and solder them together at the top. This way you can actually use considerably smaller caps. 
	

	
	
		
		

		
		
	


	




 With an R2 of 470K (should be approximately 10x higher than POT and I'm assuming you're using a 50K pot), you can use a 0.1uF capacitor. 
	

	
	
		
		

		
		
	


	




 There are no balanced inputs on the PPAv2 overall, though opamps have both + and - inputs. This does not change.


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_You shouldn't need to solder the caps on the RCAs. If they are small, you can make them "stand", have R1L/R1R "stand" as well and solder them together at the top. This way you can actually use considerably smaller caps. 
	

	
	
		
		

		
		
	


	




 With an R2 of 470K (should be approximately 10x higher than POT and I'm assuming you're using a 50K pot), you can use a 0.1uF capacitor. 
	

	
	
		
		

		
		
	


	




 There are no balanced inputs on the PPAv2 overall, though opamps have both + and - inputs. This does not change._

 

I maybe understand what you mean.

 And about + - inputs, I have read the article about Working with cranky op amps and section Balancing the Input Bias Currents
Working with Cranky Op-Amps

 Both inputs should equal if I would like to use bipolar op amps like OPA1611 which is very good op amp. With 470K R2 I would need very large feedback loop resistors to make it "balanced" / equal. 

 How this would work on this multiloop setup? I am now building this amp and first I have been adding buffers resistors because they don't need tweaking, or could changing output resistors make a difference?

 I noticed that if I solder a part down to the PCB, it will be very hard to desolder it. It sticks very hard to PCB. 

 PCB is GREAT quality! It is pleasure to handle it anyways!


 Edit: I read the part selection guide:
 "R1

 The main purpose of R1 is to help balance the op-amp’s input impedances. You want it to be equal to R3 + R5.

 R1 interacts with R2 to form a voltage divider. If R1 is much smaller than R2, this effect is negligible, which is the way you’ll almost certainly want it. I imagine someone might choose to configure this to divide the voltage down by a significant amount on purpose, but that’s not the intent of this layout.

 Optional? Technically yes, you can jumper it, but you should put a resistor here."

 So input impedances are balanced with default resistor values?


----------



## FallenAngel

Oh no, R2 is just a resistor to ground in case the pot tracking lifts, it's not a problem.

 Overall, PPAv2 wasn't designed to work with bipolar opamps and I'm not sure if anybody has ever set it up to.

 R1's value isn't really critical, but it's good to keep it = R3+R5. 1K-4K is what I see being quite common.


----------



## Spacehead

Do I need to jumper empty place near R1G Or does the ground channel op amp get its signal from TLEG?


----------



## FallenAngel

Do not jumper the empty position beside R1G, leave it empty.


----------



## Spacehead

I have added most of the resistors, click for larger pics








 I use cheap soldering iron with power control pot





 When testing this amplifier, I won't use volume pot, so my + and - op amp inputs are more closely equal, maybe OPA1611 will work, maybe not, but it doesn't matter, I have AD8597 x 2 , ADA4898-1 x 2 , ADA4627-1 x 2, OPA552 x 4 so I can get started. 

 I will add next buffer transistors

 I match them in one channel at a time.


----------



## Spacehead

I added buffer small BJTs
 Next JFETS 

 click for larger image








 I will use 2N5486 15 mA for Q2 and 2N5486 12 mA for Q1

 J310 30 mA Idss for Q4

 Could I use higher Idss Q4 for higher bias point?


----------



## Spacehead

I didn't yet add Class A biasing parts as suggested. 

 I used 50 mA IDss J310 for Q4 , same pinout as PN4392

 Q3 is rail isolation jfets, I used 2N5486 matched to 14 mA Idss 

 I bought 2SA1011/2SC2344 transistors 2.8€ per pair, very expensive

 I installed them correctly, they are base collector emitter

 Next I'll add buffer CCS trimmer and capacitors, then I can try the amplifier. Parts are closely matched, so it should sound pretty good. I will clean the flux before and check things with multimeter (feedback loop, voltages) visual inspection for solder bridges, I am pretty sure there ain't one because I always correct my mistakes right away. 

 Pics (click for larger image)


----------



## Spacehead

I am ready to fire up the PPA v2:

 Click for larger images: 














 Voltages are right in every op amp

 -11.9V

 and 12V

 referenced to input ground

 I am going to put op amps in sockets after I have added input RCAs with input caps and output 6.3mm neutrik jack 
 I won't use volume pot yet, I have only cheap crap that would ruin the sound.


----------



## Spacehead

Output transistors oscillate... I can hear loud buzzing that varies with bias setting

 2SA1011/2SC2344 are 100 Mhz

 Should I increase emitter resistors to 4.7 ohm? 

 What about 10 ohm output resistor?

 I still have 600 mV DC offset , I am testing with output capacitors. The offset comes probably from oscillation , it (buzzing) is there with and without source connected.


----------



## FallenAngel

Need some info:
 1) Opamps
 2) Value of emitter resistors

 As the buffer is within the feedback loop of the opamp, you don't need output caps.


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Need some info:
 1) Opamps
 2) Value of emitter resistors

 As the buffer is within the feedback loop of the opamp, you don't need output caps._

 

ADA4898-1 on left and right
 AD8597 on ground

 2SA1011/2SC2344 output transistors

 Emitter resistors 2.2 ohm

 Q4 J310 50 mA IDSS 

 R4 4.32K
 R3 1K
 R2 1M
 R1 4.32K
 R6 470K
 R5 3.32K

 C2 0.1 uF + 0.01 uF 
 C1 5x470 uF
 C6 10 pF + 2 nF 

 other parts default

 high res pics:
http://i39.tinypic.com/2gtx4js.jpg
http://i42.tinypic.com/10nazkk.jpg


----------



## tangent

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_I bought 2SA1011/2SC2344 transistors...
 I installed them correctly, they are base collector emitter_

 

As far as I can tell, it looks exactly opposite the pin ordering of the recommended transistors.

 If I'm right, you can try flipping them around. Maybe they weren't damaged by this mistreatment.

 Are they getting hot?


----------



## Spacehead

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_As far as I can tell, it looks exactly opposite the pin ordering of the recommended transistors.

 If I'm right, you can try flipping them around. Maybe they weren't damaged by this mistreatment.

 Are they getting hot?_

 

I think they are right way, I installed them checking that emitter resistor goes with emitter 
 sometimes it is pretty hard to understand datasheet markings, but I found the dots on 2SA1011 













 They didn't get hot, only warm, 
 adjusting pot so that there was 44 mV voltage drop across R24 made the buzzing go away intermittently 

 I have read this thread and learned that what I could try is R11 to 100 ohm

 And probably I didn't understand C2 right, I have 0.1 uF and 0.01 uF parallel as you can see, they were supposed to be like
 first 0.01 uF , then 0.1 uF, then again 0.01 uF and so on? 
 So that between channels is 0.1 uF and between buffers in each channel is 0.01 uF?


----------



## FallenAngel

Transistors look to be installed correctly and if you get adjustment across output emitter resistors, they are "working" properly. 44mV is really not that much, that's only 20mA. I'd feel safe with those up to 30mA and more current should make them a little more stable.

 Personally, I would go with 3R3 or 4R7 resistors (and have before) if you have any instability in the buffer.

 Reducing R11 may help, but I wouldn't really expect it to. I'd try other things first.

 Your implementation of C2 should not cause any problems.


----------



## Spacehead

R11 -> 100 ohm 
 3.3 ohm R24 and R34 didn't change DC offset at all. 

 It is 610 mV on right and 480 mV on left

 I measure this against output ground. 

 How do I short the inputs exactly?


----------



## FallenAngel

Uhm... isn't ADA4898-1 bipolar? You need to use a FET-input opamp in the PPAv2.

 You said there is only DC offset on left/right, not ground? Is ground using a bipolar or fet input opamp?

 Measure DC offset against input ground to make things easier.


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Uhm... isn't ADA4898-1 bipolar? You need to use a FET-input opamp in the PPAv2.

 You said there is only DC offset on left/right, not ground? Is ground using a bipolar or fet input opamp?

 Measure DC offset against input ground to make things easier._

 

there is not mentioned in the datasheet that ADA4898-1 would be indeed a bipolar op amp
 but it's 
 input bias current: −0.1 μA 
 is high

 There is AD8597 on ground which I think is JFET input because it's
 input bias current: 40 nA
 which would be normal for a JFET input op amp


 Out of curiousity I installed OPA552 to left and right
 it's input bias current: 20 pA

 ok and it works. headphones connected dc offset is -2.5 mV and -1.5 mV

 I now have 60 mV across 3.3 ohm R24 and R34

 I need to solder ADA4627-1 to dip8 socket. I hope I don't fail it because I don't like OPA552 sound at all. 

 I could now restore R11 to 1K , would it reduce distortion? 
 I also could remove external 10 ohm resistors 
 And I will add the class a biasing circuit 

 thanks for help


----------



## Spacehead

ADA4898-1 works now when I changed R2 from 1M -> 50K 
 I don't have volume pot so I need to think only if RC filter goes too high , but 2.2 uF caps make it possible to lower R2 to 20K before losing any bass. 
 DC Offset is 20 mV and 25 mV 
 I could make it lower but I want to listen a little before tweaking any more

 Ohms law tells me that 3.3 ohm and 60 mV would generate only 18 mA bias, is that right?


 I am pretty proud of my skills
 just a while ago (1-2 months) I built my first cmoy 

 But since then this has been all tweaking and building


----------



## FallenAngel

Keep R2 at 470K and install a 50K volume pot. In parallel, these would be around 50K anyway. For the input cap, keep it at 0.1uF.


----------



## Spacehead

I added the class a biasing circuit. I immediately set high bias, 3.7 mA for all op amps. Got DC offset to 15 mV and 19 mV , which is low enough for now.

 Biasing op amps to class A really makes a difference in sound quality. It clears and opens up the sound, everything is more defined and detailed. 

 My PPA v2 runs now hot but its performance is very excellent. It was stable for RMAA test. Here is the testing setup:




 And the results. Next to it are loopbacks with -6 dB and -1 dB , line in adjusted accordingly, Sound Blaster X-FI with OPA1642 out and LM4562 in




 0.0015% THD 
	

	
	
		
		

		
		
	


	




 I guess that test should be run at -1 dB level from Sound Blaster X-FI output , so that amplifier would be driven into full volume
 and the line in recording should be reduced accordingly?


 Here are the pictures of completed amplifier, except volume pot and bass boost








 Gain is 5 , 4.3K R4 and R3 1K

 Ask if you need to know about any specific part. They are pretty generic but accurate. Matching has been done with care.


----------



## jezz

I've noticed that my PPAv2 has some hissing with some of my lower impedance (60-70ohm) headphones. I've got it configured with 3 OPA627's, a gain of 3, and 3.3ohm resistors in R24 and R34 at a bias of 20mA. Other than that, it's basically stock.

 I've run through the some of the things to try when debugging hissing, however haven't found anything that works. The switch from 2.2ohm to 3.3ohm resistors on the output buffers didn't change the hissing, nor particularly did changing the gain from 11 to 6 to 3. Interestingly, the hissing does change with volume; the hissing at zero volume did not change when I changed the gain. I have installed C5. As of now, DC offset is very low at 5mV per channel.

 Is there anything else I can do to try to reduce the hissing? It's not audible when I use my higher impedance headphones :-/.


----------



## TzeYang

lower the resistor between the buffer and the output of the opamp to about 100 ohms.


----------



## jezz

Quote:


  Originally Posted by *TzeYang* /img/forum/go_quote.gif 
_lower the resistor between the buffer and the output of the opamp to about 100 ohms._

 

Thanks TzeYang! I don't have any 100ohm resistors on me. I tried 110ohm however the hum is still present. Given that I'm at least within the correct order of magnitude, I'm assuming that R11 isn't my issue.

 Edit: As I had the case open, I pushed my buffer biases up to 100mV (~33mA per channel) just to match the bias I had before I changed R24/34. No change in hissing or DC offset.


----------



## tangent

Have you ruled out the source as the culprit? Noise from the source is "detail" that a better amp can reveal, which may be inaudible without the amp.


----------



## jezz

It's not the source; the hiss is present when I tie the inputs to ground. The source is a γ2 which is dead silent in my EHHA with a closed loop gain of 9 incidentally. Even then, the hiss is still present when the volume is turned to zero. Thanks though :-/

 Given that the hiss is present equally in both channels, should I start assuming it's the ground channel? I was very careful with ESD-sensitive components when building it, but could I have blown the TLE2426?


----------



## Spacehead

Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
_It's not the source; the hiss is present when I tie the inputs to ground. The source is a γ2 which is dead silent in my EHHA with a closed loop gain of 9 incidentally. Even then, the hiss is still present when the volume is turned to zero. Thanks though :-/

 Given that the hiss is present equally in both channels, should I start assuming it's the ground channel? I was very careful with ESD-sensitive components when building it, but could I have blown the TLE2426?_

 

At gain of 3 and ADA4627-1 op amps on left and right
 and AD8599 on ground I have no hiss if my source is quiet. 

 I have 10 pF compensation capacitor (C6G), multilayer ceramic on ground channel 

 What kind of C6G you have?

 I think if you get non distorted sound from your PPAV2 you haven't blown anything. 

 It is easy to check if TLE is working correctly, measure +V and -V to input ground
 If they are about the same tle is working. 

 Ground channel can easily give out hiss if configured differently. PPAv2 should be peacefully quiet if it is built with correct parts.


----------



## jezz

The C6G I used is this one, Mouser part 5982-15-500V10 from the BOM. It's a mica cap instead of a ceramic cap. I'll check later to see if I can replace it with a film cap, but I don't know if I have a 10pF lying around.

 I don't get any distortion besides the hiss, and V+ and V- are just about perfect referenced to ground. However, I'm measuring with just a multimeter so I can't measure if there's any AC there. My understanding of the TLE is not so great, so I didn't know if they failed by arbitrarily oscillating or something.

 Thanks all so far; hopefully it's an easy issue and I don't have to start going through the transistors.

 Edit: In my bin, I've got one of these 33pF ceramic caps and one of these 100pF film caps. I'm fairly tired now, but if anyone has any input into which of these I should try first, let me know.


----------



## Spacehead

Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
_The C6G I used is this one, Mouser part 5982-15-500V10 from the BOM. It's a mica cap instead of a ceramic cap. I'll check later to see if I can replace it with a film cap, but I don't know if I have a 10pF lying around.

 I don't get any distortion besides the hiss, and V+ and V- are just about perfect referenced to ground. However, I'm measuring with just a multimeter so I can't measure if there's any AC there. My understanding of the TLE is not so great, so I didn't know if they failed by arbitrarily oscillating or something.

 Thanks all so far; hopefully it's an easy issue and I don't have to start going through the transistors.

 Edit: In my bin, I've got one of these 33pF ceramic caps and one of these 100pF film caps. I'm fairly tired now, but if anyone has any input into which of these I should try first, let me know._

 

Your C6G is fine I guess. Could you get a good picture of your PPAs upside and bottom?
 Are your solder joints all shiny?


----------



## jezz

I'll check and reflow all the joints when I get the opportunity. This probably won't be the week for it though. I'll report back if I find anything. When I put it together I seem to recall checking everything fairly well.

 I did notice something though; with no source connected, if I quickly turn the volume up, this hissing turns into a very distinct buzzing. I suspect that's real oscillation and only happens because I'm leaving the inputs floating, but maybe that's meaningful?

 Also, is it worth reducing the bandwidth of the opamp by increasing my C6G to 100pF? Should I prioritize reflowing the joints or swapping out C6G?

 Thanks everyone.


----------



## Spacehead

Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
_I'll check and reflow all the joints when I get the opportunity. This probably won't be the week for it though. I'll report back if I find anything. When I put it together I seem to recall checking everything fairly well.

 I did notice something though; with no source connected, if I quickly turn the volume up, this hissing turns into a very distinct buzzing. I suspect that's real oscillation and only happens because I'm leaving the inputs floating, but maybe that's meaningful?

 Also, is it worth reducing the bandwidth of the opamp by increasing my C6G to 100pF? Should I prioritize reflowing the joints or swapping out C6G?

 Thanks everyone._

 

You could try increasing C6G to 100 pF. 

 In my experience soldering job is usually good enough if there is no solder bridges. Solder joint needs to be pretty ugly so that it would cause whole amplifier wide hissing. 

 The hissing comes from both channels, doesn't it?

 I would try different op amps. Some op amps hiss more , again in my own experience. 

 AD8610/AD8620 is very quiet op amp.


----------



## jezz

I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here (those links will die probably within the next 2 months).

 I tried reflowing all of the joints but the hissing is still present. However, the right channel now has more hissing than the left. The left also has a very high pitched whining noise when I turn the volume up to maximum with the input pins tied together. I also tried changing out C6G for the 100pF cap I had but that didn't change anything.

 I'm using OPA627's on all channels right now. Do you really think they could be the cause of the hissing? It was my understanding that they were up there in terms of opamp quality. While I'd be up for trying the AD8610, I don't have any lying around and would rather not spend $30 debugging this. I've been meaning to try some AD744's; would those be worth trying to reduce the hissing?

 Because the hissing isn't present when I drive high impedance/low sensitivity headphones, would it be a logical assertion that the issue is isolated to the gain stage? I'm trying to figure out where to look while debugging. I don't hear any hissing (or anything, for that matter) when the opamps aren't in their sockets. It looks like that's a valid test because the input to the buffer is pulled to ground via the feedback loop, though it might not be because the output is also pulled to ground?

 Edit: Has anyone tried the Audio-gd discrete opamps in the PPAv2? They have the requisite FET input stage and, while much larger, are cheaper than OPA627's.


----------



## Spacehead

Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
_I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here (those links will die probably within the next 2 months).
_

 

You need to jumper S2L and S2R! That is pretty common mistake


----------



## jezz

All times AM.
 1:30, Email about subscribed thread.
 1:31, Done reading, soldering iron heating up
 1:32, Random resistor found, leads trimmed
 1:33, Resistor in place, accidentally broke Molex
 1:43, Fixed stupid mistakes from 1:33 to 1:43 while fixing Molex
 1:44, Fixed Molex
 1:45, Started searching for how to send beer to Finland
 1:58, Found out I can't ship alcohol from Massachusetts
 1:59, Failed at being witty instead
 2:08, Gave up on figuring out how to ship alcohol to Finland
 2:22, Had a few OCD issues

 If you're ever in Boston, drop me a line and I'll buy you a beer.

 That totally fixed it, which is unsurprising because running it without those jumpers basically leaves the buffers uncompensated. I'm humbled by your eyes sir.

 For future reference to any folks who have been debugging hiss, gain of 3, 3x OPA627's, 3.3ohm output resistors, 110ohm R11's, and no bass boost when built properly has none of it to my ears with AKG K271's.

 Things to try when debugging hiss:
 - Double check your solder joints
 - Check against the schematic
 - Swap out R11 for a ~100ohm value
 - Swap out the output resistors R24 and R34 for 3.3ohm or 4.7ohm equivalents
 - Really check against the schematic

 Thanks again. Smart people in these parts


----------



## Spacehead

Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
_Thanks again. Smart people in these parts 
	

	
	
		
		

		
		
	


	


_

 

I am glad that you got your amplifier working! 

 BTW Pretty soon I got my PPA v2 working my ears fatigued pretty badly. Don't listen too long periods now, or you might get that pain too


----------



## joe_cool

jezz;6555925 said:
			
		

> I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here.
> 
> Nice work. I have two suggestions (this is DIY so that's part of the fun).
> 1) Clean the flux off your board with isopropyl alcohol or a commercial flux remover. It may not sound better but will look better.
> ...


----------



## jezz

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_I am glad that you got your amplifier working! 

 BTW Pretty soon I got my PPA v2 working my ears fatigued pretty badly. Don't listen too long periods now, or you might get that pain too 
	

	
	
		
		

		
		
	


	


_

 

Thanks! I've never found the sound from the PPAv2 fatiguing; only a nice neutral frequency response, a lack of distortion, and a marked propensity towards revealing the sound signatures of the opamps used. I fervently avoid any headphones or configurations with sibilance though, which probably has something to do with it (OPA627's, AKG headphones, γ2 at the source). 

  Quote:


  Originally Posted by *joe_cool* /img/forum/go_quote.gif 
_ Quote:


  Originally Posted by *jezz* /img/forum/go_quote.gif 
I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here.

 

Nice work. I have two suggestions (this is DIY so that's part of the fun). 
 1) Clean the flux off your board with isopropyl alcohol or a commercial flux remover. It may not sound better but will look better.
 2) A neat way to ground the potentiometer shaft is to install a ring lug between the front bushing and the front panel, and use this to attach the ground wire. Of course this only works if you attach the pot to the front panel using a nut. I generally use an internal-tooth lockwasher as well, it helps to prevent pot rotation when tightening the nut. 

 Let us know if the sound changes after training (burn-in)._

 

Thanks for the tips! I do tend to clean the flux off using my trusty liter of 91% isopropyl (lasted me for over a year now, still 3/4 full). Those photos are from when I was still actively debugging the board so they're a bit messy. I think I personally like the look of the ground strap; I don't plan on removing the RK27 any time soon anyway.

 I've actually run my amp for ~300 hours listening to my AKG K340's which have a low enough sensitivity that I didn't hear the hissing. Curiously I don't find there to be a difference in sound signature between PPAv2: the uncompensated buffered CMoy and PPAv2: the proper Jung multiloop. I'm sure there is one, but I don't hear it? Or I'm very odd; it's hard to say. The gain did seem a bit high though... Actually, looking at the schematic and how I had it configured, what the heck? I was running it at a gain of >100? 

 Well, for what it's worth, I didn't hear much difference in regard to burn in after about an hour anyway. I should say that I wasn't looking for the sound to change with burn in either, so it may have been the placebo effect.


----------



## Spacehead

I got tired of using input capacitors on my PPA v2 and to the fact that bipolar input op amps put out DC offset of their own. 

 I added my small DC servo to the circuit. It takes input from the amplifier output and injects DC corrected signal to other end of R4 (op amp feedback loop). 
 When the amplifier idles without phones the offset with AD8620 on the servo is 0.1 mV





 When I connect the headphones, DC offset gets to 5-6 mV on both channels. I am using LME49860 on the ground channel, so that might be reason for slight shifting (should have JFET on ground too)

 I have still so long cables that there is slight hiss when there is no signal. It doesn't bother me now, maybe later.


----------



## nini_knoxville

hi,
 i found the PPAv2 diy headphoneamp project through google and i don't know if it is a good amp? i currently have the sennheiser hd590... but its getting kinda old.. maybe soon the hd650 or if i have enough money dhe hd800 (dreaming). i wanted to try a diy amp before i will buy (if needed) a mid/high end amp (lehmann linear or grace m902) just to really know.. how good my headphones can be/get. so... my question is.. is the ppav2 a good starting point? i have soldering skills, but i'm not a audio electronic freak, but a computer programmer and have some microcontroller experience (maybe i could add an display and controll the amp digitally or so)


----------



## Spacehead

Quote:


  Originally Posted by *nini_knoxville* /img/forum/go_quote.gif 
_hi,
 i found the PPAv2 diy headphoneamp project through google and i don't know if it is a good amp? i currently have the sennheiser hd590... but its getting kinda old.. maybe soon the hd650 or if i have enough money dhe hd800 (dreaming). i wanted to try a diy amp before i will buy (if needed) a mid/high end amp (lehmann linear or grace m902) just to really know.. how good my headphones can be/get. so... my question is.. is the ppav2 a good starting point? i have soldering skills, but i'm not a audio electronic freak, but a computer programmer and have some microcontroller experience (maybe i could add an display and controll the amp digitally or so)_

 

I think PPA v2 is a high end amplifier, it is very transparent, you shouldn't need any better amplifier if you build this. 
 It should be good for any headphone out there.


----------



## Hifihedgehog

I have a question. I am having a heck of a time obtaining a trim pot so if I'm going with the default parts (including resistors) in my PPA V2, what regular resistors values could I substitute in for the trim pots in R9 and R12? Also, is there a way I could solve for this with a formula, because I'd prefer a bias current of 30-40 mA. Thanks!


----------



## tangent

The purpose of R12 is only partly to let you vary the bias current. It's also because there's a second variable in the equation you're looking for, due to the random variation in bipolar transistor hFE.

 The best you can do is just try some plausible resistor value, measure the voltage drop across it, calculate current from that, then work out the actual resistor value you want to change it to. I suggest starting with 1K, since that will make the calculations easiest.

 As for your difficulty in finding trim pots...I hope you aren't making the mistake of believing you can source all the parts you need without any mail orders. Even people living in Silicon Valley have to mail order parts occasionally.


----------



## JamesL

Hey, I forgot to post this last week, but I got my ppav2 working again on the new pcb! I can't thank you enough 
	

	
	
		
		

		
			




 Only thing left to finish this up is find a missing screw, find a reverse-bipolar LED to mount to the panel, and maybe add a preamp output.

 thought I might post some pictures












 



 Right now, I have a DPDT switch selecting between the y1 dac and whatever's connected to the rca sockets.
 Is there some way I can rewire the socket/switch so it can function as a ppa input and y1 output?
 I thought about using one throw of the switch and wiring the socket directly the ppa inputs, but that would present two loads in parallel... that would affect the output of the dac, right?.. even if the ppa is turned off. 

 btw, I also built one of your opamp testers. works fantastically


----------



## tangent

Quote: 





> I got my ppav2 working again on the new pcb! I can't thank you enough


 
   
  Yay!
   
  Quote: 





> thought I might post some pictures


 
   
  A truly beautiful build, James!
   
  Who made the panel?  It looks like an FPE job, except that the edges aren't shiny.  Has FPE figured out how to do post-machining anodizing since I used them last?  Or, did you send a pre-made anodized plate to them for machining?
   
  Quote: 





> Is there some way I can rewire the socket/switch so it can function as a ppa input and y1 output?


 
   
  I'm not sure what you're asking.  Maybe you should post a quick hand-drawn schematic showing what you'd like.
   
  If you're asking whether you can connect one throw of your DPDT to the y1 outputs and the other to a pair of RCAs for direct analog input, yes, that might work.
   
  It might be necessary to use a 3PDT instead, so you switch the grounds, too.  This isn't needed if IG in the PPA is tied to the chassis and the y1 is ground-referenced to that, too.  I don't know the y1 design, but digital being what it is, I suspect it needs a different ground.
   
  Quote: 





> I also built one of your opamp testers. works fantastically


 
   
  Yes, for the price, it's good test equipment.  One could conceive of a better tester but that starts getting more costly than the price of a mail order for more op-amps.


----------



## JamesL

Quote:


> Yay!
> A truly beautiful build, James!


 
  Thanks! and it sounds amazing as well 
	

	
	
		
		

		
		
	


	



   
   
  Quote: 





> Who made the panel? It looks like an FPE job, except that the edges aren't shiny. Has FPE figured out how to do post-machining anodizing since I used them last? Or, did you send a pre-made anodized plate to them for machining?


 
  It is indeed a FPE panel.  The edges were shiny when I first sanded it down but over time, it somehow developed a slightly matte/anodized appearance.
   
   
  Quote: 





> I'm not sure what you're asking. Maybe you should post a quick hand-drawn schematic showing what you'd like.
> If you're asking whether you can connect one throw of your DPDT to the y1 outputs and the other to a pair of RCAs for direct analog input, yes, that might work.
> It might be necessary to use a 3PDT instead, so you switch the grounds, too. This isn't needed if IG in the PPA is tied to the chassis and the y1 is ground-referenced to that, too. I don't know the y1 design, but digital being what it is, I suspect it needs a different ground.


 
  That is exactly how it is currently wired up - the ground is tied together and the switch selects between the y1 and RCAs to feed the ppa.  
  This is what I had in mind earlier- 
  http://img.photobucket.com/albums/v404/reihn/switch.gif
  with the switch open, I can take a analog input from the RCA pair.
  With the switch closed, I could use the RCA sockets to hook up the output of the y1 dac to a external device or amplifier .. (effectively the same as using a y-splitter cable).  should there be any problems with this wiring?
   
   
  Quote: 





> Yes, for the price, it's good test equipment. One could conceive of a better tester but that starts getting more costly than the price of a mail order for more op-amps.


 
  Definitely.  The opa627's are pretty pricey - $75 for the three.  The opamp tester cost me 44 cents and a few spare parts


----------



## Lil' Knight

That's an amazing build, James! The PCBs fit like gloves with the case.
   
  What case is that?


----------



## JamesL

Thanks lil-knight.
  The case is a common hammond extruded enclosure
   
  Instead of the 160x100mm enclosure that actually fits the pcb itself perfectly, I used the 160x160mm enclosure to allow space for the regulator, dac, and extra panel space.
  I printed out the pcb layout before picking out a case and to my surprise, I measured/calculated the potentiometer to sit at the dead-center of this particular case.
  (i'm actually now curious if tangent planned for it to work out this way)


----------



## tangent

Quote: 





> (effectively the same as using a y-splitter cable).  should there be any problems with this wiring?


 
   
  At least two:
   
  - The y1 might get annoyed if you flip the switch its direction while there's a source plugged into the RCA inputs.
   
  - If you're able to avoid such screwups, it still does bad things because it puts the 50K input impedance of the PPA in parallel with the input section of the other amp, which probably has an input impedance on the same order; the interaction between the two isn't likely to be inconsequential.  At minimum, the volume level of the other "sink" is likely to change as you rotate the PPA's volume knob.
   
  You can avoid both problems by adding a second set of RCA jacks, connected to the y1's outputs, keeping the current switch arrangement.  They're thus live only when the switch is in the y1 position.
   
  If this doesn't work because the RCAs are floating when the switch is in the other position, you can fix it by putting some high-value resistors to ground from those RCAs' center pins.  1M, say, just to act as weak pull-downs.
   
  Quote: 





> i'm actually now curious if tangent planned for it to work out this way


 
   
  Nope.  That version of the 1455 didn't even exist when we designed PPA v1.  They've added several new sizes since those days.


----------



## Koen

OK everybody, time to make my contribution to this thread.
   
  Last Friday, I received the board for the PPA from Tangent, including ALPS pots + TREAD board.
   
  This was actually my first serious DIY electronics build ever, and I succeeded! Thanks to everyone contributing knowledge, instructions etc. etc. Special mention for Tangent's excellent webpage with part selection guide, build instructions etc. etc. Actual build time was around 3 hrs. Was succesful on first power up, thanks to excellent step-by-step build guide.
   
  The amp is running @ 21.5V, using 3xAD8610. Output buffer bias is set to 20mA, but will up that to 30mA tonight just for the fun of it. Will be adding a battery board somewhere this week (16*AAA), running off 24V from wall wart.
   
  Also, I have biased into class A, but I migth have overdone it: from reading this thread, going above 1 V drop across R10 (=1k) really shouldn't be necessary. Thing is: I have trouble hearing any difference; I'll try reducing voltage drop across R10 to close to 0, see if that gives audible change.
   
Question, though: the max voltage drop across R10G I can create using R9 pot is about 1.8. R10L/R10R max out at only 3.3V. Is this difference in adjustability normal/by design?
   
  Another question: I have added a fixed bass boost, R7=10k, C7=0.1uF (6dB boost). I can not say that I find the functionality of the bass boost very pronounced. I even wonder if it is working at all, considering I have difficulty telling whether it is on our off. Any pointers for obvious places to look?
   
  The build has been very much fun. Somebody I can build a PPA for?


----------



## tangent

Quote: 





> Special mention for Tangent's excellent webpage with part selection guide, build instructions etc. etc. Actual build time was around 3 hrs. Was succesful on first power up, thanks to excellent step-by-step build guide.


 
   
  Thanks!
   
  Quote: 





> I have trouble hearing any difference; I'll try reducing voltage drop across R10 to close to 0, see if that gives audible change.


 
   
  Consider adding a 3PST switch across R10 instead.  When "on", it switches the resistors into the circuit, enabling the biasing.  When "off", R10 is open, so you get no bias.
   
   
  Quote: 





> the max voltage drop across R10G I can create using R9 pot is about 1.8. R10L/R10R max out at only 3.3V. Is this difference in adjustability normal/by design?


 
   
  Yes.
   
  If JFETs weren't so variable in their Idss, we could have done without the R9 trim pot in the PPA.
   
  PIMETA v1 dealt with this a different way, by requiring hand-matched JFETs, which in turn meant a fixed bias level.  The PPA scheme is superior, being adjustable, but is more costly both in terms of parts (3x trim pot) and board space.
   
  PIMETA v2 deals with this same problem an entirely different way by using a different CCS design which lets all three channels be adjusted from a single pot.  The downside there is that applying that to the PPA would pretty much require moving to a 4-layer design, doubling the board cost.
   
  It's all tradeoffs.  There is no single perfect solution.
   
  Quote: 





> I have added a fixed bass boost, R7=10k, C7=0.1uF (6dB boost). I can not say that I find the functionality of the bass boost very pronounced. I even wonder if it is working at all, considering I have difficulty telling whether it is on our off. Any pointers for obvious places to look?


 
   
  That gives only 3-6 dB of boost down in the true bass regions.  To hear the difference, you need headphones with strong bass response -- not "bassy", just not weak -- and music with actual bass.  I don't see any music preferences in your profile, so I don't know which artists or tracks to suggest.


----------



## Koen

Quote: 





tangent said:


> That gives only 3-6 dB of boost down in the true bass regions.  To hear the difference, you need headphones with strong bass response -- not "bassy", just not weak -- and music with actual bass.  I don't see any music preferences in your profile, so I don't know which artists or tracks to suggest.


 

 I have added my music preferences (mostly Pink Floyd, Radiohead, U2 of mid-90s). I have tried Massive Attack - Mezzanine - Angel. Will the last song do? I *think* I heard a change when turning on the boost. BTW, headphones are Sennheiser HD 555.


----------



## tangent

I don't see the music prefs in your profile, but Pink Floyd gives me all the material I need.  I found three tracks for you to try:
   

 San Tropez (studio) from Meddle - nothing jaw-dropping, just a good bass line to work with
 Run Like Hell (live) from The Delicate Sound of Thunder, about 1:20 where the drums kick in
 The Dogs of War, either live off DST or studio from A Momentary Lapse of Reason - the real cello that starts up after the growling at the beginning is better than the electronic one on the studio cut, but both were noticeably different when toggling the bass boost
   
  I used my main PPA with K1000s and a decent outboard DAC for this test, so it's not exactly a fair comparison with your system, but there should be _some_ difference to be had on these tracks.
   
  Mind, this feature is only meant to fill in the bottom end on weak bass recordings, not make you believe someone secretly installed a sub under your listening chair.
   
  If you added input caps, that counteracts the bass boost feature unless you set the corner frequency very low.  Output caps in your PC's sound card can do the same thing.
   
   
  By the way, if you don't have DST, get it.  It's the best live album, ever.  Disclaimer: I hate Radiohead, so let that guide your interpretation of my opinion.


----------



## Koen

I did get a copy of DST, but couldn't tell bass were on or off with Run Like Hell. However, I think it is best to wait until I have constructed my DAC board before any further testing. Maybe my setup is a bit too low-end to be judging bass-boost 
   
  I surely will return here in about a month or so.


----------



## vgjako

Hi
   
  I was wondering if somebody has tried the Burson Audio Single & Dual Op-amps in their PPA? It would be interesting to hear how they compare to lets say a AD8610, or a OPA627/37. I am planning to build a PPA V2, so it would be nice to know if they will function in the PPA V2 design. I guess they will, but I am just asking so that I don't do something stupid, after all the single op-amp costs 48,50 £, and the dual op-amp costs 78,50 £ at http://www.hificollective.co.uk/components/bursonaudioopamps.html
   
  Thanks
  vgjako


----------



## Koen

Hi vgjako,
   
  Congratulations on your decision to build a PPA! You will not regret that decision.
   
  I have no experience with the opamps you are asking question about. However, I do have experience with deciding on an opamp when I built my PPA.
   
  Which specification(s) of the opamps you mention make you believe they are THE choice for your PPA?
   
  If you can't answer that question for yourself, I'd say go with an AD8610 or OPA627/37 set. Maybe save the money (if relevant at all) for your source, power options.
   
  Just my $0.02.
   
  (btw, I have AD8610 in my PPA, based on Tangent's opamp reviews on his website).


----------



## Spacehead

I can provide you pair of OPA637 at a nice price, if you are interested , PM me. I have 8 left.
   
  OPA637 doesn't work in ground channel. So only two OPA637 needed for left and right, because it needs gain of 5 to be stable. With my headphones and PPAv2 there isn't much background hiss at gain of 5 and OPA637 works fine. Usually I use OPA827 or ADA4627-1 on ground channel, those are unity gain stable.


----------



## tangent

I know nothing about those op-amps, but can tell you you'll need to use three of the singles for a PPA.


----------



## vgjako

I haven't been able to find a datasheet of the Burson Audio op-amp, so I haven't any good reason to choose this op-amp. The specs I have found on this op-amp is:
   
  Working voltage: +/-12-25v DC
 Current Draw: 19mA (each module)
  THD: Less than 0.0007%
 Dimensions: 39mm × 10mm × 29mm, (single) 39mm × 23mm × 29mm (double)
 Weight: 19g
   
  But according to the people who have reviewed this op-amp, they where very pleased with the results, follow this link: http://bursonaudioblog.blogspot.com/search/label/HD%20Audio%20Opamp%20(Review)


----------



## vgjako

Hi again
   
  I have a few questions listed below:
  1. What is the highest voltage I can use on OPA637/27 op-amps? The datasheet says plus-minus 18 V, can I use lets say 24 V? If not, what would you suggest as an appropriate voltage level?
  2. Is the resistor R4G supposed to be the same value as R1G if you tune the gain? I have chosen to go for a gain at 7, just changing R4L/R. To put the question in another way: Do I have to change the value of R4G to tune the gain, I guess not.
  3. The input called B+ on the high-current power section is there if you are going for battery power, right? Or am I wrong?
   
  Thanks 
  vgjako


----------



## FallenAngel

1) Well, if you can use +/- 18V, that's 36V rail-rail, you can use anything below that, including 24V.
  2) Ground channel is running with gain of 1x, R4G stays = R1G.
  3) Yes, B+ is battery contact.


----------



## Koen

Quote: 





koen said:


> (..)
> I surely will return here in about a month or so.


 

 Hi, I'm back!
   
  Built my DAC, see this post for details.
   
  I am convinced that with my DAC, the 'issue' of not noticing bass boost effect is not at the source (still can't hear a difference when flipping bass boost switch). Will have to open up my PPA to put in the 3PST switch across R10 tangent suggested a few posts ago. This is probably an error on my side: this amp is still incredible!


----------



## tangent

While in there, you might just want to increase the boost's strength.  No point in having an audio filter that's too subtle to hear.


----------



## phishhead92

I accidentally got 6 BD139's insead of 3 of those and 3 of the 140, can i use the 139s in place of the 140s? or should i try and find the 140s (currently out of stock on mouser and i dont want to order just 3 little chips and pay like 3$ for shipping)


----------



## FallenAngel

I'd send you some, but it would take some time to arrive.


----------



## phishhead92

slow and having some is better than paying more for shipping than what the 3 parts cost 
	

	
	
		
		

		
			




   
  im down, PM me if you actually want to do this
    
   
  Quote:


fallenangel said:


> I'd send you some, but it would take some time to arrive.


----------



## FallenAngel

PM address, I'll drop them in the mail for you.


----------



## phishhead92

Also, i want to use a RLED, but i cannot figure out which resistor i need, i will be using a 12V supply, and i want somewhere around 10mA or less going through the led, can someone help me out in figuring out the "Vf"?


----------



## tangent

As I said in my PM reply to you, you will find the Vf figure in your chosen LED's datasheet.


----------



## phishhead92

OH, for a sec i thought you ment something else, like on the site. sorry i was really tired when i first read it (got back from a long bike rid
  so here is what i have so far, not completely done but pretty close, just waiting for some parts from mouser

   


 that  PCM2707 is crooked, oops! oh well, its all on the right pads it looks like
   
   

   
  the upsampling chip was being difficult, and so was desoldering the bridges, looks messy now


----------



## vgjako

Hi again,
   
  I once again have a question, the standard configuration of C5 on the PPA V2 uses a 1 uF capacitor, this gives a corner frequency of 16 kHz. I've would guess that a lower corner frequency is better, say I use a 2,2 uF capacitor instead of 1 uF, this will give me a corner frequency lower than 16 kHz.
   
  I know that I could instead raise the value of R8, but as tangents guide says: "Theoretically you could instead raise the value of R8, but as its value rises, so also does the current-modulated rail ripple due to the op-amp’s varying current draw. We decided during development that 10 Ω was the best trade-off here."
   
  Is there a formula for calculating the corner frequency?
   
  Regards
  vgjako


----------



## vgjako

bump


----------



## tcpoint




----------



## FallenAngel

I don't get it, C5 is a filtering cap for the opamp, there is no "corner frequency" in relation to sound as you're dealing with the power supply, not audio input.


----------



## mugdecoffee

While R8 and C5 do form a low pass filter, the idea of corner frequency and that formula don't really apply since there's current being drawn out of the resistor in effect making the resistor and capacitor not a simple RC filter.  However, the basic trend still applies in that the larger the cap, the less higher frequencies (which are in this case noise) are passed.


----------



## vgjako

Quote:


mugdecoffee said:


> While R8 and C5 do form a low pass filter, the idea of corner frequency and that formula don't really apply since there's current being drawn out of the resistor in effect making the resistor and capacitor not a simple RC filter.  However, the basic trend still applies in that the larger the cap, the less higher frequencies (which are in this case noise) are passed.


   
   
  Thanks mudgecoffe, that really cleared a lot of things up for me.
  So the higher the cap value, the less noise you get.
   
   
  What gain do you think I should be running on, 3, 4, 5...? I will use the Burson Audio HD Op-amp (single) which is unity gain stable. I would guess that a gain between 4 and 6 would be best, what do you think


----------



## whitelabrat

So I've had some issues with one of my channels with an OPA637 getting cranky. If you look at post #748 you'll see that I used cheap electrolytics and ceramic caps for power smoothing near the opamps.  So I reclaimed four Elna Certifines and some 4uf film capacitors and replaced the cheap stuff for the left and right channels hoping that would get the oscillation under control.  In the process I appear to have hosed up something.  I replaced the stepped attenuator with a ALPS blue velvet pot and that made no difference.  I pulled out the 637's and replaced them with a pair of OPA37's for testing.  No luck.
   
  So things sound OK, until I turn up the volume.  Then the right channel gets very distorted and ugly.  I also measured about 10ma of dc offset on the right channel.  Something must be blown.  Any guess where i should start pulling parts?
   
  I should also mention that I'm using a TREAD power supply and a doorbell ringer transformer that I got for $3.  Gives me a solid 24v.


----------



## ShinyFalcon

What gain is your PPA set to? OPA637 are not stable at gains of 5x and below. Same with the OPA37.


----------



## FallenAngel

That is one funky looking amp.  Put a finger on all the transistors and see if anything gets hot.  Check output stage current to make sure it's reasonable.


----------



## whitelabrat

I have a 10k resistor for R4.  My guess is gain would be 10k/1k = 10?  Or is my math wrong?  Left channel is a happy camper.  I could drop in OPA27's for testing.
   
  A few parts are barely warm.  Nothing hot.  The capacitors all check out so nothing weird there.  The silicon parts are suspect.  I'll need to probe for shorts.
   
  Yes.  It's even funkier looking now.  I tried to use only parts that I had already.  I think the build of this only cost me $50 including the PCB.


----------



## tangent

Did you jumper S2?


----------



## vgjako

Is there a formula for calculating the buffer bias? I am going to use a 3,3 ohm resistor for R24 and R34, I want 30 mA of buffering. What will R12 be?
   
  Thanks


----------



## whitelabrat

Quote: 





tangent said:


> Did you jumper S2?


 

 Absolutely.  I don't care for bass boost.


----------



## tangent

Then the only things I can suggest are the standard ones: post larger, clearer pics (both sides!), and the results from going through the troubleshooting guide.


----------



## whitelabrat

I didn't find any shorts, so I figure I'll put a 1k sine in and test the signal path with an oscilloscope.


----------



## vgjako

I have a dual-power supply which I am going to use to power my PPA V2. The power supply has three connections, +, - and G (Ground). So my question is: Can I use the + and - connections on my power supply to power the PPA V2, this gives me +/- 15 V. Or would I have to use + and G?
   
  Thanks


----------



## FallenAngel

If you don't figure out the answer to this question, I would not recommend doing it.
   
  It's certainly possible to run the PPAv2 off a split supply, and there may even be potential benefits to doing so.  Just don't install the TLE and wire ground there.  V+ and V- are left self-explanatory.


----------



## vgjako

So, can I connect the + connector on my PSU to V+ on the PPA, and the - connector to V- on the PPA and just ignore the G connector on my PSU?


----------



## FallenAngel

Uhm... no, that would be bad.  Don't install TLE, wire PSU ground to where the TLE is supposed to create ground.


----------



## vgjako

In Tangent's guide it says: "If you have a dual-voltage power supply, it's probably better to run the amp from the outer terminals and ignore the ground lead than to try and hook up the ground lead"
   
  Doesen't this mean that i can do what I asked about above
	

	
	
		
		

		
			





?
   
  If I understand you correct, I should run the ground lead from the PSU to the ground plane of the PPA V2, and just jumper across all the TLE positions and wire + and - from the PSU to V+ and V- on the PPA V2?
   
  What voltage would the op-amps get then, I am using the DACT CT-102 PSU, which is selectable between +/- 15 V, and +/- 20 V.


----------



## FallenAngel

Some supplies don't like working without the ground tap, I figure, why ask the TLE to make a split supply when there's one already there.
   
  Voltage choice depends on opamp choice.  +/- 15V is... well 30V.  That's more than enough for any opamp.  40V will likely be too much.


----------



## vgjako

Ok, I get you.
	

	
	
		
		

		
		
	


	



  Thanks for taking the time to explain it to me.


----------



## vgjako

One last question: Am I supposed to leave the TLE positions open or jumper them? I would guess I should leave them open, because if I jumper them it would mean that VH+ and VH- will be connected to ground, am I correct?


----------



## FallenAngel

Uhm... your questions worry me.  You can simply install the TLE and wire the PSU while leaving the ground alone, or something might burn up.


----------



## vgjako

Hi,
   
  I have drawn a schematic which shows how I think it should be done:
   

   
  As you can see, I am running the ground lead to the ground plane. I am measuring 30 V from + to ground, everything seams to be working well. Wouldn't this configuration be correct, isn't this what you meant? In other words I am leaving the TLE's open and running the ground lead to the ground plane.


----------



## MisterX

Omit the TLEs (do not jumper them!), jumper D1, I would also jumper the switch positions and omit the LED on the PPA board, connect the + output from the power supply to the V+ input on the amplifier, connect the - output from the power supply to the V- input on the amplifier and connect the ground from the power supply to one of the IG pads on the amplifier.


----------



## vgjako

I have trouble sourcing parts, so I was wondering if anyone had some PN4392's laying around, I will need at least nine of them, more would be better. I also need the output transistors, MJE243 and MJE253, I need at least 3 of each. I can pay via PayPal.


----------



## MisterX

Did you try Farnell?
   
http://no.farnell.com/fairchild-semiconductor/pn4392/transistor-jfet-n-to-92/dp/1471025?Ntt=PN4392
   
   
  Kunder som kjøpte dette produktet, har også kjøpt:
   
  MJE243G
  MJE253G


----------



## funch

Quote: 





vgjako said:


> I have trouble sourcing parts, so I was wondering if anyone had some PN4392's laying around, I will need at least nine of them, more would be better. I also need the output transistors, MJE243 and MJE253, I need at least 3 of each. I can pay via PayPal.


 


      I have 3 of each of the 243/253.  PM me if you still need them.


----------



## vgjako

Quote: 





misterx said:


> Did you try Farnell?
> 
> http://no.farnell.com/fairchild-semiconductor/pn4392/transistor-jfet-n-to-92/dp/1471025?Ntt=PN4392
> 
> ...


 

 Farnell only do business with companie's, they don't take credit card's. The only thing I could do is to order the parts through my school.


  
  Quote: 





funch said:


> I have 3 of each of the 243/253.  PM me if you still need them.


 


 You don't have any PN4392's?


----------



## funch

Quote: 





vgjako said:


> Farnell only do business with companie's, they don't take credit card's. The only thing I could do is to order the parts through my school.
> 
> 
> 
> ...


 


      No, sorry, just the 243/53.


----------



## vgjako

I managed to find both transistors on ebay, so now I am almost ready to start assembling my PPA V2.


----------



## phishhead92

how do i ground this in a wooden box? i do not have a drillpress (and i dont want to buy one just for this) for a metal case.
   
  plus i have the perfect box for this project.
   
  also do you guys just use standoffs and glue the standoffs to the base of the box? i never understood how you mount the finished project in there
   
  EDIT: also i am a noob DIY'er, could anyone give me some tips on how to bias the opamps?


----------



## tangent

Quote: 





phishhead92 said:


> how do i ground this in a wooden box?


 
   
  You don't.
   
  The panel components with ground connections get tied to something on the PPA amp board.  That's all.
   
  The only potential problem with this is that it means you don't have an RF shield, but PPAs don't seem especially troubled by RF, so I wouldn't worry about it.
   



> i do not have a drillpress (and i dont want to buy one just for this) for a metal case.


 
   
  You don't need one.  I use a vise and a hand drill.  For very large holes, I use either a Greenlee panel punch or a step drill bit.  Everything else I shoot straight through.
   
  I pad the panel from the vise jaws with a rectangle of denim cut from some old jeans.  One pair of jeans makes a lot of shop rags. 
   
  Quote: 





> also do you guys just use standoffs and glue the standoffs to the base of the box? i never understood how you mount the finished project in there


 
   
   
  If the project won't be bounced around, you might get away with mounting the board only to the front panel by the pot shaft.
   
  If the rear edge needs some support, yes, you can just glue some standoffs in there, but personally I'd use the kind that are threaded straight-thru and use screws from both sides: one affixes the PCB to the top end of the standoff, the other comes from the bottom outside the case to hold the standoff to the bottom of the case.  Use flat-head screws for the bottom-side ones so you can countersink them into the enclosure.
   
  You can go ghetto here, too, if you'd like.  A couple balls of Blu-Tak would would give some of the benefit of a standoff with virtually no work.
   
  It's DIY.  Work something out.
   
  Quote: 





> EDIT: also i am a noob DIY'er, could anyone give me some tips on how to bias the opamps?


 
   
  What's wrong with the instructions? (URL fixed; previously pointed to buffer biasing instructions.)


----------



## phishhead92

^^ wow thanks for all the info, i am not sure about the metal box tho, and i have the perfect wooden box atm (fits the TREAD board and the transformer in there perfectly)
   
  and i think i will do the holes in the bottom and the double ended standoff, that sounds good and sturdy.
   
  man i need to read closer i think i missed the article that went into detail.
   
  anyways i hope to be getting said box ready soon, thanks for the help!


----------



## vgjako

I just finished building this amp yesterday, and I knew from various reviews that the amp would be good, but not this GOOD! 
 
*Listening Impressions:*
The first thing I noticed was the separation of the instruments, I was listening to Telegraph Road by Dire Straits and heard many “_new_” sounds which I never had heard. The top and bottom is _silky smooth_, I have never heard such a good separation between bass and tremble. The sound is _crystal clear _and is a pleasure to listen to. 
  
Here are the parts used:
- DACT CT-102 Audio Power supply (+/- 15 V)
- Burson Audio Single op-amp
- Elna Silmic II C1 and C4
- Wima MKP10 C2
- Wima MKS2 C5
- 10 pF Silver Mica C6
- Vishay 64W pots
- DACT CT2 50K
- Vishay Dale RN55 resistors
- Takman REY resistors
- 2N5484 Q1
- 2N5486 Q2
- PN4392 Q3, Q4
- 2N5087_J18Z Q-21-23
- 2N5088_J61Z Q31-33
- MJE243G Q24
- MJE253G Q34
- No TLE 
 
Im running 20 mA through the output buffers, I have tried to ramp it up to 30 mA, but stangely the DC offset increased. At 20 mA the offset is under ten in all channels. However when I ramp it up to 30 mA the offset is 50 mV in the left channel, 39 in the rigth and 20 in the ground. 
What could be causing this sudden increase of DC offset? 
 
Link to Pictures (Photobucket):
http://s789.photobucket.com/albums/yy179/vgjako/PPA%20V2/


----------



## tangent

Thanks for the review!
   
   
  Quote: 





> What could be causing this sudden increase of DC offset?


 
   
  Your amp may be marginally stable.  I'd try two things:
   
  First, measure supply current to the whole amp while you're adjusting the bias.  If current draw goes up nonlinearly with respect to current setting, it's likely oscillating, which you could verify with an oscilloscope.
   
  Second, try a "normal" op-amp, one known to work well in the PPA.


----------



## vgjako

Quote: 





tangent said:


> Thanks for the review!
> 
> 
> 
> ...


 

  
  OK, I'll try measuring the current through the amp.


----------



## vgjako

OK, so I have a problem. I turned on the amp today, and I measured 15 V at the left- and ground channel, luckily I didn't plug my headphones in
	

	
	
		
		

		
			





. I suspected that the Q3's were fried, and so it turned out. I simply replaced them and everything was ok. I measured under 10 mV at each channel.
   
  A few hours later the Q3's (PN 4392) fried again, and I don't have any more left. Is there a substitute for Q3 which I can easily get here in Europe/Norway. I use to order parts from https://www.elfa.se/elfa3~no_no/elfa/init.do?init=1&shop=ELFA_NO-NO
   
  The PN 4392's have a minimun Idss of 25 mA, the burson op-amps draws 19 mA, and I have a class-A bias of 1,5 mA. This would add up to 20,5 mA which should work just fine. I don't have a clue why this happens, any here who does?
   
  Thanks
  vgjako


----------



## Avro_Arrow

A devices full power rating is only available with proper heat sinking.
  Maybe you just exceeded the temperature rating.
   
  Maybe a TO-92 heat sink will help the issue.
   
   
  Quote: 





vgjako said:


> OK, so I have a problem. I turned on the amp today, and I measured 15 V at the left- and ground channel, luckily I didn't plug my headphones in
> 
> 
> 
> ...


----------



## vgjako

Well, they didn't get hot, just sligthly warm.


----------



## Koen

Hi, back again but now with some not-so-good news.
   
  It seems I have fried my PPA while trying to power it off of an SLA (battery). Turned out the wires in the DC connector to the PPA were shorted inside. I did not yet have a fuse in the battery wiring to the PPA, nor any kind of current limiting (if that would have helped...).
   
  This resulted in
  1) A lot of smoke and smell from the plastic burning from the - connection (so - terminal on the battery to V- in the PPA).
  2) A PPA which has bad sound in the left channel and no sound in the right channel at all. 'Bad' in the left channel as in quieter than normal and when turning up the volume distorted sound.
   
  So somehow the battery short damaged my PPA  And I have really fallen in love with it over the last few months...
   
  So, basically, I have just one question:

 Would somebody be so nice to help me troubleshoot and fix this? I have taken the following measurements, all with respect to V- (unless noted otherwise)
 
 V+/V- = 13.4 (low, I know, but as designed; has been working fine on this voltage until now)
 Q3R+ = Q3G+ = Q3L+ = 13.4
 *Q3R- = 11.7 || Q3G- = 12.3 || Q3L- = 2,6*
 DC Vout left channel (respect to out ground): -0,3 V
 DC Vout right channel (respect to out ground): 0,09 V
 VopampLv+v- = 10.8V
 VopampGv+v- = 1.1V
 VopampRv+v- = 1.6V
 I stopped measuring after this because I don't know yet what exaclty I am looking for...
   
  Possibly the following bits of information help:
   

 Opamps are AD8610
 There's no visbile damage to the PCB nor any of the components.
 If it helps, I do have access to a scope.
 (Academic-type-question) how/why did the 'infinite' current @ ~ 13 V between the battery terminals (and thus the V- and V+ pads?) damage the PPA?


----------



## tangent

Quote:   





> how/why did the 'infinite' current @ ~ 13 V between the battery terminals (and thus the V- and V+ pads?) damage the PPA?


 

 I don't see how it did.  The fact that your + and - rail measurements don't add up to the + to - rail value is also suspect.
   
  I'd look farther up the chain.  I'd replace the DC input jack for one thing.  If it melted, even a little bit, it could now be permanently shorted, or near-shorted.  That can cause all sorts of havoc.


----------



## Koen

Quote: 





tangent said:


> I'd look farther up the chain.  I'd replace the DC input jack for one thing.  If it melted, even a little bit, it could now be permanently shorted, or near-shorted.  That can cause all sorts of havoc.


 


 Removed the jack (and switch) completely and took the board out of the case to make sure there's no ground loops there. Power supply is OK, nice flat 13.4 as indicated before. I did some additional measurements:
   
  (these are the output resistor pairs, 2.2Ohms, there used to be 44mV across each single resistor, + probe always closest to output pad)
  R24R -23,1mV
  R34R 42,1mV
  R24G -25.9mV
  R34G 11,1mV
  R24L -13.9mV
  R23R 8.9mV
   
  ??? So there's not a single 'normal' channel, as these should all be at ~44mV..? Considering also there is no single pair showing the same drop across both resistors, would the Q24/Q34s be the next parts to check? If so, how do I check them??..
   
   
  Also checked in/output of the L/R opamps:
  * Both get the correct input-waveform (verified with scope)
  * The R-opamp is outputting nothing (that's why I am hearing nothing in that channel, I guess)
  * The L-opamp is outputting correct waveform, but is clipping (that's why I am hearing distorted sound in that channel). Clipping is on the top-side of the waveform, bottom side seems not to clip. Clipping occurs at around +140mV
   
  I will be adding more troubleshoot data as I investigate further.


----------



## Koen

OK, some additonal troubleshooting info:

 Removed the TLE for the (dead) right channel from the circuit to verify it's working: nicely splits 14V in half. So I guess that rules out the TLE as the source of the problem.
 Also removed the opamp for the right channel from the socket to rule this part out as the culprit. Still seeing the same odd voltages at the pads for V+ and V-:
     measuring 1.56V from the opamp V- pad to opamp V+ (I expect this to be around DC nput V+/V-, so around 14V in my case)
     0.93V from V+ pad to signal ground (no source connected)
     -0.6V from V- pad to signal ground
     these nicely add up to ~1.56V difference...., but I guess not what I should be seeing here.
 Q3 transistors nicely pass the V+/V- from the input, so I don't think these are the issues either.
   
  Does anybody know what voltages I should be seeing here (feeding 14V from TREAD supply)?
   
  Reading this on vritual grounds I should be seeing ~7 V between signal ground and input V-, but I am seeing ~12.4V??
   
  Also swapped opamps, symptoms stay the same. I definately think there's something wrong with the part of the amp powering the opamps. Amp is drawing only 50mA (inluding a dimly lit green LED). I'll continue studying Tangent's troubleshooting guide.
   
  In the mean time, any advice on where to look next much appreciated.


----------



## Soymilk

come to think of it, i never really did any empirical test to see that my ppa was working properly after i finished building it. i just plugged stuff into it and sound came out so i assumed it works. what would be the best way to go about testing it so i know for sure? it's been sort of nagging me at the back of my mind for a while now. function generator -> ppa -> oscilloscope should do the trick, but what if i don't have access to any of those at the moment? are there any simpler tests i can do?


----------



## Koen

Quote: 





koen said:


> OK, some additonal troubleshooting info:
> 
> Removed the TLE for the (dead) right channel from the circuit to verify it's working: nicely splits 14V in half. So I guess that rules out the TLE as the source of the problem.
> Also removed the opamp for the right channel from the socket to rule this part out as the culprit. Still seeing the same odd voltages at the pads for V+ and V-:
> ...


 

 OK, figured it out: I had already ordered 6 new rail isolation jfets (the Q3s), because was seeing strange voltages on the opamp power supply pins.
   
  While reading the tweaks section of Tangent's website I found this sentence: "You may have noticed that you can jumper across all of the Q3 positions to get a single set of power rails for everything." Well, I had wondered what if..., but didn't actually know it was 100% safe to do so... So after reading this, I went ahead and jumpered the Q3 positions (first remove the Q3s!!):
   
  AMP is WORKING again!!
   
  So shorting the +- DC input pads across a 12V SLA blew all but one Q3.
   
  Also checked why my bass boost didn't seem to work. It turns out I had a 47k resistor as R7. I have replaced those with 10k resistors (same as R4) and will do some listening tests later today!
   
  For now, I am  a happy camper and rest assured once the Q3s come in the mail I will put them back in the amp!


----------



## tangent

Quote: 





soymilk said:


> what would be the best way to go about testing it so i know for sure?


 

 An easy first test is to measure the amp's quiescent current.  If it's around 100 mA (say, +/-20 mA), it's probably fine.  If it's over about 120 mA, it could be fine, but you'd have to be able to justify it with component or biasing choices.
  
  Quote: 





koen said:


> So shorting the +- DC input pads across a 12V SLA blew all but one Q3.


 

 I still don't see how that happened, but I'm glad you figured it out.


----------



## qusp

i'm making some upgrades to my lisa III when I replace with new batteries, thought this would be a good place to ask for info since apart from some tweaks its the same amp. I want to buy a few spare output transistors from BDENT in case of mishap and possibly an entirely new set more suitable for low impedance headphones (higher current). I already have hundreds of BC550/60C. so before I pull the BD139/140 out to check for IDSS/hfe, i'm wondering if anyone knows what they might be? being that there is no bias pot in the lisa I have to get this matched pretty right I would imagine. I saw earlier in the thread that these should be matched +/-10% at 180-190ma, do you think this still holds for lisa? 
   
  so the parts are BD140-16 and 139-6, this still gives a range that is too wide to be assumed matched. any clues? i'm also going to replace the EROs with some small auricap polyprops bypassed with vishay MKP and either amtrans polyprop 220pf or the unfortunately not so easy to source and not given enough daylight here; EVOX/RIFA 5mm spaced box polypropelene  film and alfoil. I really wish these were available more places and in larger values, as you just dont see fully fledged film and foil caps in such small convenient sizes and for such reasonable prices. all are metalized PP normally.
   
  so any advise on other devices to try here in the output positions and with fairly low bias due to battery power? any insight into degree of matching and IDSS values, or confirmation that I should just pull a pair to find out would be appreciated.
   
  thanks for reading


----------



## tarking

I have built three Pimetas (two v1s and one v2) and decided to take the next step for fun 
	

	
	
		
		

		
			








. I am sourcing components right now. I have about all covered but I have some trouble finding Q4s (buffer bias CCS JFETs). PN4392 is not available now and wait time for more stock is veeery long. I could get PN4391 or J310 right away. The question is which one should I get. J310 is specified from 24mA to 60mA and PN4391 is specified from 50mA to 150mA. J310 is closer to PN4392 but PN4391 is cheaper .
   
  Thanks for any advice!
   
  EDIT: I bought three J310s from local electronics component shop (0.80€/ea. not cheap but only type available locally right away!) and measured their Idss. I got 26 mA, 31 mA and 32 mA. Are these values a) close enough each other (there is 2K Burns) and b) is this enough for 30 mA buffer bias. Sorry for asking "dumb" questions but I have not enough knowledge in electronics to understand how this works i.e. is maximum bias current same as Idss of JFET or is it amplified.


----------



## tangent

Quote: 





tarking said:


> Are these values a) close enough each other


 

 Yes, and that's probably because they are from the same batch.  This is why we don't bother to talk about "close enough" in the docs: three transistors bought from the same vendor at the same time should always be close enough.
   
   
  Quote: 





> is this enough for 30 mA buffer bias....is it amplified.


 
   
   
  No, it's not amplified.  The Q21/Q22 and Q31/Q32 structures are called current mirrors.  It means the current through Q4 gets mirrored to go through the output transistors.
   
  There's nothing magical about the 30 mA output stage bias point.  It's a common number, but in your case, I'd just go with 20 to 25 mA and be happy.  It'll still sound good.


----------



## vgjako

Quote: 





tangent said:


> Thanks for the review!
> 
> 
> 
> ...


 

 Hi again,
   
  I finally found out the source of my problem, it turned out that I pulled too much current from the PSU (DACT CT-102). The power supply is rated at max +/- 200 mA, but when I measured the current going through my PPA V2 using my bench PSU I only measured 150 mA when biased to 30 mA. The power loss over the darlington transistors in the PSU is at 4,4 W, the heatsinks for the darlington transistors are in other words too small, this results in an extremely high temperature. So in other words the DACT CT-102 is not capable of delivering +/- 200 mA, but maybe under ideal conditions.
   
  This explains why I was seeing such a rapid increase of DC offeset when I adjusted the bias point, and maybe why the Q3's fried.


----------



## tarking

Quote: 





tangent said:


> There's nothing magical about the 30 mA output stage bias point.  It's a common number, but in your case, I'd just go with 20 to 25 mA and be happy.  It'll still sound good.


 
   
  Ok. Thanks a lot! I bought one J310 more because 26 mA was uncomfortably close to 25 mA if I decided to need a bit more than recommended 20 mA of bias current. Now I have all three a bit above 30 mA (31 mA to 32 mA).
   
  You probably saw this coming... I have another question for you... I did not get this (yes, my daughter calls me stupid nearly every day 
	

	
	
		
		

		
		
	


	




):
   

   Quote: 





tangent said:


> I would take your set of transistors and sort them by hFE. Then take 3 neighbors at a time for the same transistor in each of the channels. They won't be as tightly matched as if you were able to take arbitrary transistors from, say, a bag of 100, but they'll be as close as you can get them.






 Do you mean by this that I should take three at a time and use these three within one channel for same part type or distribute them one for each channel for same part position? I wasn't smart enough to order more than what is needed and can't get more of them without huge cost overhead (shipping costs from the US to Europe).
   
  I measured hFE for the parts and got 347 - 312 for 2N5088 part and 295 - 248 for 2N5087 part.
   
  This is really strange. Maybe something wrong with my meter? Edit: I used another meter and got the same result with that one too:
   
  I got hFE values 130 - 133 for MJE253G (PNP) but only 67 - 90 for MJE243G (NPN). Shouldn't NPN hFE values be bigger than for PNP part?
   
  Trying to learn something at the same time here! Thanks.


----------



## Soymilk

Quote: 





> distribute them one for each channel for same part position?


 
  this one


----------



## tarking

I though so but wanted to verify. Thanks! Can anyone comment about the big hFE difference between MJE243 and MJE253. If I use these parts what kind of effect does it have on the performance of the amp? I really cannot match these pairs. Oh, well, should have bought more of these too I suppose.


----------



## tangent

They're different polarities, which means they must behave differently.  There's really no such thing as matched complementary pairs, never mind what the marketing copy on the first page of the datasheet says.  Look at the curves and other data on subsequent pages, and observe the wild differences.  Be sure not to be fooled by differing axes; the top two charts on page 5 of the On Semi MJE243/253 datasheet are this way, for instance.  (hFE vs Ic)
   
  Match the NPNs to the NPNs, and the PNPs to the PNPs.  It's the best you can do without buying huge amounts of extras and hoping to find uncommonly strong PNPs to pair with uncommonly weak NPNs.  Even if you did that, they won't stay matched over temperature.  Again, study the datasheet...see how the curves change shape differently over temp for NPN vs PNP.


----------



## tarking

tangent said:


> Match the NPNs to the NPNs, and the PNPs to the PNPs.  It's the best you can do without buying huge amounts of extras and hoping to find uncommonly strong PNPs to pair with uncommonly weak NPNs.  Even if you did that, they won't stay matched over temperature.  Again, study the datasheet...see how the curves change shape differently over temp for NPN vs PNP.





 You missed my point. Isn't it strange that PNP part i.e. MJE253 has much higher hFE than NPN part. Almost twice as high. I checked ON semi's datasheet and that's what prompted me to ask about this. According to datasheet hFE values should be another way i.e. MJE243 hFE values should be over 100 and MJE253 hFE values under 100. I checked meter manual but it didn't help at all. I thought that maybe because pinout is different ECB vs. EBC displayed values should be interpreted differently.


----------



## Soymilk

well if the pinout's different you should be measuring across the pins you're supposed to if you arent *shrug*


----------



## tarking

Quote:


soymilk said:


> well if the pinout's different you should be measuring across the pins you're supposed to if you arent *shrug*


 
   
  I didn't say that I measured across the wrong pins (I am pretty sure that I wasn't but I'll check again). I was just wondering how the meter is implemented i.e. could that be an explanation to this. I am planning to borrow a better meter from work to measure hFEs (Fluke).


----------



## tangent

Some datasheets aren't clear about the pinout.  It's easy to get the pinout backwards when they only give you a 2D drawing.  The On Semi one gives a nice 3D drawing, with the metal tab showing clearly, so it's much easier to get it right.
   
  As for borrowing the Fluke, beware that it won't have a dedicated hFE feature.  You'll have to build up a measurement circuit of some sort.


----------



## tarking

Quote:


> Originally Posted by *tangent* /img/forum/go_quote.gif
> 
> 
> 
> ...










 Yes. I noticed that. So I am not going to measure with the Fluke. I am pretty sure that I measured them correctly. I naturally checked pinout from datasheet before measurements and noticed that in ON semi's datasheet the pinout was not shall we say easily obtainable (on the last page they give 1 = E, 2 = C, 3 = B and then you have to go back to page one to see clearly which way you should look at the part to get 1, 2 and 3 right). Anyway I'll measure them again about sixth time. Can you elaborate (if I measured correctly) why I get these results?


 EDIT: I did measurements again and got the same results. I tried to measure PNPs as NPNs and other way around and using different slots as to go through all possible lead order. I either got nothing or values around 1000 for other combinations but the one I used originally.


----------



## tangent

Your results might mean nothing at all.  Such a reversal is unusual, but the values are within specified limits.


----------



## MathNO

HI everyone,
   
  I have a problem with the construction of my PPA from Tangent website.  I don't know if you can help me. 
   
  Here some information of my set up.
   
  Power Supply : Young-Jung power supply that I build.  Work perfectly and give me 24vdc.
  PPA board : PPA v2.0E
  Chip : AD843 (gain) BUF634(ground)
   
  I am at the stage of testing my board with my amps. I notice problems on my board and I'm quite lost. 
   
  Before explaining my problem, I would like to say that none of my part come hot during my testing.  I think none of my part are burn.
   
Amp voltage problem
   
  I test my board without any amps in my board.  I test the voltage V+ and V- on each socket.  I have a nice 11.6v and -11.6 everywhere.  Everything look fine.
   
  When I had the amps and began my test, I note that the supply voltage for each of my AD843 drop to a 3.21V.  For the BUF634, the voltage is 11.49V.  I swap my amp and the 3.21v seems to follow the AD843.  
   
  I must said that I had to find an equivalent for Q3s.  My local store give me K117 (TO-92).  The supply voltage for the AD843 should be at maximum 13ma.  The Idss for K117 is 14ma max.  Is that limit?
   
  Could that cause the problem?
   
Adjustment of the Buffer Bias
   
  I see another problem.  I couldn't read any voltage difference across output resistance on 2 of my channel ( left (AD843) and ground(BUF634)).  However, I was able to read a voltage difference on my right channel(AD843) but I wasn't able to reach 44mV.  I reach the limit of my 2kohm pot.  I use 2.2ohm output resistance.  
   
  Here against,  I had to go to my local store to tried to find an alternative for Q24 and Q34.  I use a C3422 for the Q24 and an A496 for the Q34.
   
  I'm really not sure that is a good thing.  
   
  In conclusion, I will probably change my Q24s and Q34s for the ones recommend by Tangent.  I will buy them at Digi-Key.  However, before I make an order, I just want to figure out my problem with my voltage at my amps.  Is that could come from my Q3s part?  If I need to change them, which part should I order?
   
  Which test I should do?
   
  Thanks in advance for your help!
   
  P.S.  Forgive me for my English.  I come from the french part of Canada!


----------



## tangent

Quote: 





mathno said:


> Power Supply : Young-Jung power supply that I build.  Work perfectly and give me 24vdc.
> PPA board : PPA v2.0E
> Chip : AD843 (gain) BUF634(ground)


 
   
  The BUF634 is not an op-amp.  It will not work in OPAG.
   
  That alone will explain a lot.
   
  Quote: 





> I must said that I had to find an equivalent for Q3s.  My local store give me K117 (TO-92).


 
   
  I can't find a K117 JFET datasheet.  The closest thing I can find is a 2SK117, which is a MOSFET.  If it's a MOSFET, same thing as before: not the right part, won't work.  If it's a JFET, please point me to a datasheet.
   
  As for your other problems, I'm ignoring those because I want to get these two out of the way first.


----------



## MathNO

Ohh,
   
  That could explain a lot of thing.
   
  I will change the BUF634. 
   
  I will also change all Q3s.
   
  Thanks for the help.  I let you know when I install those new component!


----------



## MathNO

I have a question about Q3 JFET.
   
  When I look to the spec of JFET, I see a minimum and a maximum Idss.  How I should select which JFET to use.  If I understand well, my minimum Idss should be higher than my amps quiescent current and the current for other parts.
   
  If I understand well, if I use an AD843 with a quiescent current maximum 13ma.  So, I should at least use JFET with a minimum Idss of 15ma is I plan to use the Class A.
   
  Am I right?
   
  Also, I see that DigiKey have a J111FS-ND JFET.  The minimum Idss is 20ma.  Is that be good?
   
   
  Another question,
   
  I need to order new amps to replace my mistake with the BUF634.  The AD843 is not available on digikey right now.  I will probably go for the AD845.  However, I see an AD845JN (not in stock) and AD845JNZ (in stock).  What is the difference?
   
  Thanks!


----------



## tangent

Quote: 





mathno said:


> If I understand well, if I use an AD843 with a quiescent current maximum 13ma.  So, I should at least use JFET with a minimum Idss of 15ma is I plan to use the Class A.


 
   
  Yes.
   
  Beware however that the AD843 is one of the most troublesome op-amps in PPAs.  No doubt it can be made to work, but there have been more problems with that chip than any other popular chip I can think of.  Search this thread.
   
  Also, the 843 doesn't especially need biasing.
   
   
  Quote: 





> I see that DigiKey have a J111FS-ND JFET.  The minimum Idss is 20ma.  Is that be good?


 
   
  I don't remember seeing any reports saying it works, but it looks okay.  The PN4392 is more tried-and-true in this application.
   
   
  Quote: 





> AD845JN (not in stock) and AD845JNZ (in stock).  What is the difference?


 
   
  RoHS.


----------



## MathNO

Thanks!


----------



## MathNO

Hi,
   
  I have done some work on my PPA.  Now, I could say that all my 3 channel are working well.  
   
  I change Q3s for J111 and I found an unweld resistor in my right channel
   
  I'm currently using 3x AD845 and I adjust each buffer to 44mv, so 20ma.  
   
  However, I have an "Hiss" sound issue that I suspect to come from the ground channel.  The sound seems to be the same on my left and right channel.  The "Hiss" sound is the same for every volume setting and the sound is present if the source is plug or not.  .  I should say that my PPA isn't in the enclosure yet.  Should I place it in the enclosure first?.
   
  Also,  I have a question for the buffer adjustment.  Should I adjust the buffer value with or without the headphone plug?
   
  I read most of the 63 pages of this forum.  I see that some people change the output resistor from 2.2ohms to 4.7ohms.  Is there a special quality resistor I should use?.  Also, they changed the value of C6 from 10pf to 100pf.  It looks like this solve the "hiss" sound problem for some peoples?
   
  With which modification should I start?  Did some have any other idea?  Is there some test I could do to pin point the problem?
   
  A lot of people talks about oscillation problem in their PPA.  Could someone explain me this problem?  In the Tangent website troubleshooting part, I see that the oscillation problem cause noise in the headphone,  My problem is more like a steady "Hiss" sound.  Is could be related to oscillation problem?
   
  Except for the steady "Hiss" sound, the PPA look to work well. 
   
  Thanks!


----------



## FallenAngel

1) adjust buffer bias without headphones.
  2) check current draw, make sure nothing is weird
  3) put it in a case and check for background noise, with the input floating, it's an antenna


----------



## tangent

What gain value is your amp set for?
   
  A very low hiss level can just mean "too much gain".


----------



## MathNO

Hi,
   
  Quote: 





fallenangel said:


> 1) adjust buffer bias without headphones.
> 2) check current draw, make sure nothing is weird
> 3) put it in a case and check for background noise, with the input floating, it's an antenna


 

 1 )  Thanks for the information.
   
  2) How could I check the current draw and what is a typical value of this current?
   
  3) I will put it on my Hammond case... However, I doubt that I have background noise.  I make several precaution to avoid the noise.  
   

 Quote:


tangent said:


> What gain value is your amp set for?
> 
> A very low hiss level can just mean "too much gain".


 
   
  How I can measure the gain value.  I use value for R3,R4,R5,R6 from Tangent web site 
   
  R3: 1K
  R4: 10K
  R5: 3.32K
 R6: 470K

 It said that for changing the gain, I should change R4.  How I could calculate which gain I need.  Should I decrease or increase the R4 value to lower the gain.
   
  Thanks


----------



## FallenAngel

Quote: 





mathno said:


> Hi,
> 
> 1 )  Thanks for the information.
> 
> ...


 

  
  2) Measure current draw using the amperes meter setting on your DMM, value should be the sum of all parts in the circuit (3 channels of opamps - Iq from opamp datasheet, 3 channels of buffers at whatever bias you set).
  3) Putting the amp in a chassis will create a huge ground plane, making the amp a lot less likely to catch noise.
   
  Gain : That's 11x gain, quite high for almost every headphone, and yes, it's very likely to hiss with no input.


----------



## tangent

Quote: 





mathno said:


> How I could calculate which gain I need.


 

 There are ways to do it numerically, but it's simpler to just try a few different values of R4.  Try 2K or so.
   
   
  Quote: 





> Should I decrease or increase the R4 value to lower the gain.


 
   
  Gain in the PPA is approximately (R4/R3)+1.  So, lowering R4 or raising R3 lowers gain.  R3 has a better reason for staying as-is, so change R4.


----------



## zenon

It is mentioned here that "The PPA board will accept one to four buffers per output channel", is this referring to Q24/Q34 on the PPA v2.0e?
  How is this accomplished??? 
  I bought a bag full of BD139/BD140 transistors and am thinking about using perf-board to make break-out panels.
   
  Thanks!


----------



## FallenAngel

PPAv1 used monolithic buffers, PPAv2 uses a discrete buffer, they are really not the same amp.


----------



## tangent

You're reading a reference to PPA v1. The buffers on v2 are an entirely different design.


----------



## moro

hi there
  i need a portable amp (for home use) with the best sound possible so i'm thinkin' of assembling a PPAv2
  so could anyone tell me, are recommendations on http://elvencraft.com/ and http://tangentsoft.net true for a portable version of the PPAv2 ?
  i'm asking cause on these sites they mention only non-portable power supply option. so my question is are those caps (uF, V and so on) recomended for portable version too
  sorry if these are some stupid questions
  thx


----------



## FallenAngel

moro : The PPAv2 may be used for portable use, but it's quite a power hungry amp, you'll be pulling around 90mA of current constantly... you'll have quite poor battery life unless you go with a AA battery pack.
   
http://elvencraft.com/ppav2/ is the version of the site you want to go with, but I think all the information you can possibly need on this project is on Tangent's page http://tangentsoft.net/audio/ppa/amp2/
   
  You do have to consider that this is not a small amp in terms of physical size.  Along with a battery pack, it'll be quite large and heavy.
   
  Just a question - how come you want a portable version of the amp for home use?


----------



## tangent

Large and heavy is relative.
   
  I remember seeing a hillarious scene in a Hawaii 5-0 episode where this guy is wearing a set of bright red headphones with a radio and battery built in, boppin' down the street to his 60's hippy tunes.  They were bigger even than Koss PRO4AAs:
   

   
  Whether you can sanely use a PPA portably depends on where on the tradeoff curve between portability and sound quality you want to be.  Personally, I've not used a PPA very often that way.  I did use a transportable PPA config while camping once, though.


----------



## Avro_Arrow

Those were my first set of cans when I was a teenager 30 years or so ago...
  
  Quote: 





tangent said:


> Large and heavy is relative.
> 
> I remember seeing a hillarious scene in a Hawaii 5-0 episode where this guy is wearing a set of bright red headphones with a radio and battery built in, boppin' down the street to his 60's hippy tunes.  They were bigger even than Koss PRO4AAs:
> 
> ...


----------



## moro

ok, thank you *FallenAngel* for the reply
  glad to hear all the parts will do for portable version
  i know that the amp is quite big but i just like carrying the music around hate sitting in front of pc to listen to music also i could carry it in a bag to the country and so on i just wanted good quality amp that i lack.
  AA pack is ok, but is it possible to use 18650 batteries? they are twice as powerful as AAs with the same "mah"
	

	
	
		
		

		
			




  buy the way, what are the dimensions of PPAv2 (battery version) ? 
	

	
	
		
		

		
		
	


	



  thx
   
  P.S. *tangent* what can you say about the SQ of the portable version? is it too bad if compared with the other version? 
  and what's the typical play time with a 2600mah-batteries board?


----------



## Avro_Arrow

You can use any kind of batteries you wish as long as they fit into your
  space/current/voltage requirements. I use 18650s with my amps but
  you will need to come up with your own way to protect them and charge them.
  
  Quote: 





moro said:


> ok, thank you *FallenAngel* for the reply
> glad to hear all the parts will do for portable version
> i know that the amp is quite big but i just like carrying the music around hate sitting in front of pc to listen to music also i could carry it in a bag to the country and so on i just wanted good quality amp that i lack.
> AA pack is ok, but is it possible to use 18650 batteries? they are twice as powerful as AAs with the same "mah"
> ...


----------



## tangent

Quote: 





moro said:


> what can you say about the SQ of the portable version? is it too bad if compared with the other version?


 

 You're talking like there are two static configurations only.  In fact, there is a universe of possibilities.  (That's why the PPA Part Selection Guide is so long.)  I'd say that what makes one PPA portable and another not has more to do with the case — is it as small as it reasonably can be? — and whether it's battery powered than anything in the amp circuit itself.
   
  Naturally, you probably want to do things like use more efficient op-amps and use a lower buffer bias point for a portable amp, and these things will change the sound over using different op-amps and a higher buffer bias point.  There's no requirement that you do these things.  It's DIY.  If the configuration makes you happy and it works, go for it.
   
  Quote: 





> what's the typical play time with a 2600mah-batteries board?


 
   
  It depends on things like which op-amps you choose, what your buffer bias point is, how many cells are in the pack, and other things, too.
   
  You can build a PPA that will sip as little as about 50 mA from its battery pack, which means you could get 52 hours of run time, ideally.
   
  On the other end of the scale, 130 mA isn't out of reach, which would give only 20 hours of run time.
   
  Again, it's DIY.  How you configure your particular PPA is up to you.


----------



## moro

i understand the DIY philosophy well: do whatever you want)
  20 hours with 130mah - it's more than enough i think  considering the powers it delivers


----------



## FallenAngel

Yeah... it won't really deliver much more "power", just different opamps and deeper Class-A...


----------



## zenon

What needs to be altered in the circuit to accommodate a set of Beyerdynamic DT 880 - 600 Ohm cans.
  I'm sure the gain will need to be on the high side (how high?) but, is there anything else?
  Thanks.


----------



## tangent

A gain of 6 will probably be fine.


----------



## tarking

Just finished my PPA V2 a few days ago. I built amb sigma11 first . Boxed and was working great with a pair of AKG K601s (120 ohm impedance phones). With AKG K701s (62 ohms impedance phones and my favorite) there was intermittent hissing and pops... funny thing was that hisses and pops would change just waving my hand near the amp (I felt a bit like a magician . With Alessandro Music Series One (32 ohms impedance phones) there was a constant moderate loud hiss but no pops. Recommended parts except R2L/R is 499 kohms and R4L/R is 4.75 kohms, opamps are LME49710s on all channels for now as my OPA637AUs are waiting to be installed on Brown Dogs .
   
  Anyway, I changed R11L/R/G from 1 kohm to 100 ohm as suggested in the "ppa instability thread" mentioned earlier and all the symptoms above are now gone. Thought this might be of help to somebody.
   
  Great amp BTW .
   
  EDIT: It was R11 that was changed from 1 kohms to 100 ohms.


----------



## FallenAngel

How is the grounding on your amp?  The hand waving is a dead giveaway of improper ground.
   
  I never saw a big difference with R10 - that's simply the Class-A bias on the opamp, but it's good that it worked for you.
   
  I would still take a look at grounding and before deciding on the OPA637 (only for Left/Right - you can't use 637 in ground, 627 can be used), I would highly recommend trying the AD825. 
   
  Photos would also be great.


----------



## tarking

Quote: 





fallenangel said:


> How is the grounding on your amp?  The hand waving is a dead giveaway of improper ground.
> 
> I never saw a big difference with R10 - that's simply the Class-A bias on the opamp, but it's good that it worked for you.
> 
> ...


 

 Oops... I meant I changed R11L/R/G from 1 kohm to 100 ohm, sorry & 
	

	
	
		
		

		
			





. Grounding is OK, input ground and potentiometer connected via aluminum case, output jack and DC input jack isolated. This has worked great for me in the past with Pimetas. I'll post some photos when I'll get them resized.
   
  I have OPA627AUs on BrownDogs already, didn't have time to solder OPA637AUs yet . Well, I got OPA637AUs for free (well, almost  and I happen to like them. I admit I have not listened to AD825. The problem is that this part is not available in Finland.


----------



## FallenAngel

R11 separates the buffer from the opamp, definitely something that should be OK with a lower value than 1K.
   
  The amp picking up radio interference (your hand close to the chassis) certainly suggest that your input is floating and it's picking up anything around.
   
  Photos are easily hosted on imageshack.us and they resize automatically.
   
  Good luck


----------



## tarking

Photos added per request..


----------



## FallenAngel

Looks great!
   
  I would also suggest grounding your POT (screw on back of pot to IG of board).  I'm not sure where you have the input ground connected to chassis either...


----------



## tarking

Quote: 





fallenangel said:


> Looks great!
> 
> I would also suggest grounding your POT (screw on back of pot to IG of board).  I'm not sure where you have the input ground connected to chassis either...


 
   
  Thanks, I am pretty satisfied with the end result myself too.

 There's no need to ground pot separately because input ground and pot body are connected via aluminum enclosure. Input ground is connected to chassis because input jack body goes through back panel and the hole in the back panel is precision machined i.e. tight . The plastic washers on the inside were there just to make connecting cables easier for me... they do not isolate body from the chassis. All verified with my meter's continuity mode of course.


----------



## bikeboy24

When setting the buffer bias, does it matter whether the source and/or the headphones are plugged in? It may be my imagination, but the reading across the output resistors change.


----------



## tangent

You can have the headphones plugged in while you do this, but you don't want to do that if you're also measuring at the same time.  Leave them plugged in if you're trying to play with bias by ear, rather than by meter.


----------



## bikeboy24

What about the source? It seems like the readings across the output resistors go down when the source is plugged in.


----------



## tangent

That's DC offset from the source.  It's just confusing things.  Unplug it.


----------



## bikeboy24

The weird thing is that if I unplug everything, all the measurements seem way off. The amp is working and everything. I get sound (sounds pretty good!).
   
  Wouldn't plugging in a load (headphones) affect the readings across the output resistors though?


----------



## tangent

Yes, which is why I say leave them unplugged if you want accurate _readings_. Plug them in if you want accurate _hearings_.


----------



## bikeboy24

After playing around with the amp some more, I noticed a couple things. I'm using BD139/BD140
   
  -The 100ohm R11 fixed my hiss issue with lower impedance / high sensitivity headphones (I'm using Grados)
  -I'm still having issues with the buffer bias, but I figured out what is causing the strange readings. When the amp is not grounded to the case, all the readings seem normal. As soon as I connect input ground to the case (such as RCAs, grounding strap), the buffer bias voltage will drop. Anyone know why that is? Is this normal? Output ground is isolated from the case. I don't have any shorts.


----------



## tangent

I think you're just measuring the buffer bias voltage plus the source's output DC offset times the amp gain.


----------



## NixNada

Hey my first post here 
	

	
	
		
		

		
		
	


	



   
  I'm having issues with amp. It's a v1.1 from 2004 i think.
   
  It has worked wonderfully the last 6 years. But last year the solderpoints on the input wires started to fail. Perhaps due to my inexperience.
   
  I tried to resolder, but now there is something wrong. I got a very loud static hiss in earphone. So i started to investigate.
   
  I found that it draws a lot of current about 500 mA from a 9 V battery. Also there is a large voltage drop about 3 volts, so something is drawing a lot of power.
   
  The buffer chips (those are the intersil ha3-5033-5) are getting hot all 3 of them. After about 10 seconds too hot to touch.
   
  Also i'm reading a 50 mV from the output to ground, which might explain the unpleasing sound i got in my earphones
	

	
	
		
		

		
		
	


	



   
  What could be the problem? And what should i do next?
   
  I really have no clue. Is it possibly an easy fix or is there somthing serious wrong with my beloved ppa


----------



## NixNada

Ok something is wrong. I tried tangents guide for tracing a 1khz input signal. 
And it fails when i+ should equal i- on the opamp (both channels)
The i+ equals that of the input (source).

 According to guide something is wrong with the feedback loop? 

I suspect oscillation because the IN (leg 4) on the buffer transistor is building up voltage as it gets hotter and hotter.

I wonder what could be the problem here?


----------



## tangent

Quote: 





nixnada said:


> It has worked wonderfully the last 6 years. But last year the solderpoints on the input wires started to fail


 

  Input wiring can't explain hot buffer chips. Something else is wrong.
   
  For what it's worth, though, if you've destroyed the rear input pads, you can just run longer wires to the front set. I'd braid them together to try and get some shielding benefit from the ground wire.
   
   
  Quote: 





> I found that it draws a lot of current about 500 mA from a 9 V battery. Also there is a large voltage drop about 3 volts, so something is drawing a lot of power.
> 
> The buffer chips (those are the intersil ha3-5033-5) are getting hot all 3 of them. After about 10 seconds too hot to touch.


 
   
  It sounds like the buffers are destroyed. I see that you've left out D1, which could mean you connected power backwards once, which will kill chips very quickly. If that happened, the op-amps might be dead, too, though perhaps the isolation JFETs saved them.
   
   
  Quote: 





nixnada said:


> I suspect oscillation because the IN (leg 4) on the buffer transistor is building up voltage as it gets hotter and hotter.


 
   
  You also left out all the bypass caps, which could explain oscillation and heat. But, the fact that it worked for 6 years argues against that.
   
  Try removing the buffers and replacing them with jumpers. If they're the only part that died, you've just created a glorified CMoy. If it sounds okay, it confirms the death of only the buffers.


----------



## NixNada

Quote: 





> It sounds like the buffers are destroyed. I see that you've left out D1, which could mean you connected power backwards once, which will kill chips very quickly. If that happened, the op-amps might be dead, too, though perhaps the isolation JFETs saved them


 
  You're right! And what a stupid mistake that was. I just realized that i had the D1 in my inventory, but somehow have missed putting it to good use. Come to think of it i'm pretty sure that i have reverse voltaged the d... thing fiddling with the powersupply.
   
  Quote: 





> You also left out all the bypass caps, which could explain oscillation and heat. But, the fact that it worked for 6 years argues against that.


 
  I will try installing the bypass caps and see if it helps
   
  Quote: 





> Try removing the buffers and replacing them with jumpers. If they're the only part that died, you've just created a glorified CMoy. If it sounds okay, it confirms the death of only the buffers.


 
  I tried jumpering the buffers and although i did hear the testtone, it was horribly distorted. So my guess is that pretty much all the chips are fried 
	

	
	
		
		

		
			




   
   
  Seems i must place some orders for new IC's. 
   
  I'm unsure of how many transistor buffers i need for each channel, and if they need to go in the order of the numbering on the board? ie. could i place a transistor in 1 and 4 position?
   
  I'm using it with HD600. Thank You very much for input.


----------



## tangent

Quote: 





nixnada said:


> I'm unsure of how many transistor buffers i need for each channel


 

 It's covered in the docs, here.
   
   
  Quote: 





> [Do] they need to go in the order of the numbering on the board?


 
   
  All four spots are equivalent in each channel. You could put one buffer in position #1 in the left channel, one in #2 in the ground channel, and one in #3 in the right channel, if that made you happy.


----------



## NixNada

Update on my problem:
   
  I have now installed bypass caps (1uF), fresh transistors, new wiring, reverse voltage protection and new opamps (opa627).
   
  Although it did solve the problem with hot chips and an insane amount of curent draw it still don't sound right.
   
  A fresh round of measurements reveals that the quiescent current draw is now abt. 70 mA compared to over 500 mA before, i recon this is acceptable. However when i measure the oR, oG and oL against iG i get a voltage of 500 mV 
	

	
	
		
		

		
		
	


	



   
  The curious thing is that it is constantly 500mV even with no signal input.
   
  So could it be that something else is broken because of the reverse voltage stunt?
   
  Once again thank you very much for input.


----------



## tangent

You say "fresh transistors", but from your previous posts, I think you mean "fresh buffers."  All transistors on the PPA board are named with a Q prefix. You didn't replace any of them, right?  I don't immediately see why you should have, just trying to add some clarity.
   
  Also left untouched, which could also affect this, are the TLE2426es.  In fact, these are just as likely as the op-amps to have been damaged, because they _contain_ op-amps.


----------



## NixNada

Update:
I am happy to report the PPA is working now 
I changed the rail splitters and buffer transistors. 

However i now have issues with the powersupply. There is noise with no input connected which gets worse when touching the volume knob and turning up the volume . I am sure it has to do with my new power supply. With batteries there is no noise.
I might have made a poor choice here http://docs-europe.electrocomponents.com/webdocs/0d52/0900766b80d523c7.pdf
Bought the 24V version.
Is it because it is switched?
Can this be remedied?


Anyways thanks for help.


----------



## tangent

That sounds like the pot ground strap isn't installed, or has caused a conflict with another connection, like V-, through the case.


----------



## NixNada

Last update:
ok now everything works 
Amazing how much effect a toothbrush and some alcohol can have. Absolutely no noise now whatsoever not even when volume turned to max. So i was wrong thinking it was the powersource. I think the alcohol had some isolating stuff in it.
Yes im a happy camper now 
Next project bass boost and maybe a y1. But for now i will enjoy a fully working PPA 

Thanks Tangent. Your detailed files got me through this once again


----------



## Spacehead

Hi! I have three boards which I am building. I have first bent most of the resistors to the circuit. Next I solder them.

   
  I need to build these pretty fast. Any suggestions for quick completion techniques?


----------



## FallenAngel

Yeah... don't rush or you may spend tons of time debugging.   Just take your time, populate each part and double check schematic/parts list before you solder.  Personally, I like to populate all matching parts at the same time (eg all BC550, then all BC560, etc).


----------



## Spacehead

Hmm I need a switchable gain. How should I do it? I have no experience on it. I guess I will use dtdp and two R4s. But how to implement it on the PPA v2 board?


----------



## Avro_Arrow

I would install the higher gain value resistor for R4 and then calculate a resistor
  in parallel to create the lower gain value you need. Switch in the parallel resistor
  when you want the lower gain. That way there is no chance for an
  accidental open loop.


----------



## Spacehead

Quote: 





avro_arrow said:


> I would install the higher gain value resistor for R4 and then calculate a resistor
> in parallel to create the lower gain value you need. Switch in the parallel resistor
> when you want the lower gain. That way there is no chance for an
> accidental open loop.


 

 I have hard time figuring out the correct way to use the switch. Could you draw a schematic for it? It would help a lot. I know, if there is open loop, DC offset gets very high and headphones can burn.


----------



## Avro_Arrow

Lets say the two values of resistor you want are 6k04 for the higher gain and
  4k02 for the lower gain. 12k1 in parallel with 6k04 is about 4k...close enough.
  Solder in the 6k04 resistor for R4 as normal. Now, make a wire to go from one
  side of R4 to your switch with the 12k1 resistor in it. The return wire from the
  switch goes to the other side of the R4. Repeat for the other channel.
  The switch needs to be a double pole, on/off (single throw).
   
  I can draw you a schematic if you need but I am short on time at the moment...


----------



## MisterX

If you're not adding bass boost a high / low selectable gain switch is as easy populating the "R7" positions and connecting a switch to the "S2" pads.


----------



## Spacehead

Quote: 





misterx said:


> If you're not adding bass boost a high / low selectable gain switch is as easy populating the "R7" positions and connecting a switch to the "S2" pads.


 


  I will need bass boost too so this doesn't work  Good advice though!


----------



## Spacehead

Quote: 





avro_arrow said:


> Lets say the two values of resistor you want are 6k04 for the higher gain and
> 4k02 for the lower gain. 12k1 in parallel with 6k04 is about 4k...close enough.
> Solder in the 6k04 resistor for R4 as normal. Now, make a wire to go from one
> side of R4 to your switch with the 12k1 resistor in it. The return wire from the
> ...


 


  I try to implement it, thanks! I will put a strip socket in place of R4, so that changing gain is easy. I think 6k is fine but the lower gain needs to be 2k. The headphones are Denon AH-D2000, and sometimes high impedance devices.


----------



## MisterX

Apply a similar (series) switching arrangement to the R3 positions when the amplifier is equipped with bass boost. 
  (the "return path" is much shorter, the effect on the bass boost is not as dramatic and there is no point where the feedback loop becomes "broken" by the switch)


----------



## Avro_Arrow

The values I used were meant to be examples only.
  MisterX's idea is a good one too. You might want to
  use his if you are going to use the bass boost. In
  that case, you would just use the switch to "short
  out" one of the resistors in a series pair to change
  the value.


----------



## Spacehead

I managed finally to implement that gain switch. I used R3  2.2K + 4.3K  and R4 10K , then I have switchable gain from 5.5 to 2.5.
  But I just cannot seem to figure out what causes constant hissing. I have it in default metal case and input grounds are tied to it. Output ground is isolated.
   
  Is it normal that when amp is powered, the resistance between input ground and outputs (all of them) is zero? Does that indicate some kind of ground loop? How can I cut it?


----------



## MisterX

Quote: 





> Is it normal that when amp is powered, the resistance between input ground and outputs (all of them) is zero?


 
  No, most people realize trying to measure resistance when then power is on is not going to work.


----------



## Spacehead

OK now I see the logic. But what about that hissing?


----------



## MisterX

See up there where it sez "Search This Thread"?
  Click it, type in hiss and then click the search button.
  You'll find a few different ways to solve it.


----------



## Spacehead

Thanks for your help MisterX. It seems that I am so frustrated that I cannot think , when I noticed the hissing I had thought that I had finished the amp.


----------



## Dan55

Hi all,
   
  I'm looking for a 2.1mm jack to use with a TREAD (I believe Tangent has a 2.5mm jack on the parts list), and I'm having difficulty locating an isolated jack. Digikey and Mouser don't seem to have a filter for isolation, and the data sheets I've looked over don't specify whether the jack is isolated either. Is there some other was to identify whether the jack is isolated?
   
  Thanks!
  Dan


----------



## tangent

The easiest way is to look for plastic-bodied jacks.


----------



## Dan55

Will do. Thanks!


----------



## H22

Hi all, finally getting around to putting My PPA v2 together, I have the resistors mounted (RN55's) and the Q21-23&Q31-33 (5087's and 5088's). Still need to order Q1,2,3&4, I forgot to get them from Mouser so I will need to make another order
	

	
	
		
		

		
			





 . I jumped the gun a little it installing Q21-23&31-33, I am second guessing my decision not to match them, is it a good idea to match these? The only meter I have that can do this (I think) is a very cheep unit that came with a Millett mini-max kit I bought a few years back. If it is a good idea I don't mind pulling them, Part of My job involves making repairs to PCB's so I have gotten quite good at removing components.
   
  I am also planning on using high end caps in this amp, Silmic II's for C1 and C4 as these seem to be generally considered good(open for suggestions though  ), as for the bypass caps I was thinking some whima's, but as I am putting in an order for the silmics at handmade, are there other "botique" film caps that anyone would recommend? 
   
  Power supply is going to be a sigma 11 (thanks AMB) I just finished set to 24v (actual output is 24.34v on My fluke)
   
  Trying to build this amp as high end as is reasonable, Its my first desktop SS amp and I am hoping to be as pleased with it as i was with the milletts I built (mini and mosfet max)
   
  Thanks


----------



## tangent

Quote: 





h22 said:


> I jumped the gun a little it installing Q21-23&31-33, I am second guessing my decision not to match them, is it a good idea to match these?


 

 It is not important to match transistors in the PPA v2 buffer. The design makes it unnecessary.
   
  It doesn't hurt to try (!) and match them, and if you're the OCD sort, go ahead and obsess over it.
   
  Personally, I wouldn't bother now that they're soldered down. The potential benefit is too small for the risk to the board.


----------



## H22

Spoiler: Warning%3A%20Spoiler!



 

 It is not important to match transistors in the PPA v2 buffer. The design makes it unnecessary.
   
  It doesn't hurt to try (!) and match them, and if you're the OCD sort, go ahead and obsess over it.
   
  Personally, I wouldn't bother now that they're soldered down. The potential benefit is too small for the risk to the board.
   


  Thanks.
  I will probly leave them alone, It just came to me after I had put them on that (if memory serves me) the buffer in the PPAv2 is pretty much the same as the buffer in the millett max that i built, and the instructions for it recommended matching them.


----------



## H22

Well, I did it anyway  

Took a few pics while I was at it, solder wick and chip-quick work wonders, had them off and the board ready in about 15 min.

Cause I didn't trust myself, and I was ordering a few things from him any way, I had Tomb over at beezar send me some matched units.


So, I finished up most of it tonight, I still need a few minor parts, but got it powered up (sigma 11
at 24v), set the buffer bias at 20ma,


The opamp bias at 1.5ma (opa637 L&R,627G) and everything tested out awesome, dc offset was to small to measure. 

I used elna silmic II's for the caps, c5 is right off the BOM, C2 is just a pair of .18uf vitamin Q's for now, need to order the "odd"caps as I seemed to have missed them on my last order.

Initial impression was using a clip+ and M50's,HOLLY FREAKING COW, this thing sounds amazing right out of the gate, massive power, dead quiet background, crystal clear highs with great detail, and the low end has everything I want with authority.

Very nice amp and I am kicking myself for not finishing it sooner. One thing I did note, it does not seem to pair well with my pro-900's. Highs are just way to simblant, tinny, and forward and the 900's don't seem to like the BB at all, low end just falls apart, like they can't handle the power. 

But that's ok with me, the 900's are that way to me with all my gear, just more so with the PPA. But the M50's sound great!

Can't wait to get this little gem burned in, thanks a ton Tangent.


----------



## H22

Ok, update, The 900s work just fine with this amp, it was the massive EQing I had in the clip they didn't like. This is my first "real" SS amp, I also have a mini3and a pimeta, and I must say that this is one of those rare occasions where the outcome far surpassed my expectations. This isn't just better, it's a whole new level. Not that the afore mentioned amps are bad, they are very good, but this thing is just amazing, and it convinced me to start playing with my MOSFET ax a little, love the max, but it is lacking somewhat in the bass department compared to the PPA. Not a slam on the max, I used silmic caps rather than the recomended Muze, so fault may be on me, not sure, but I intend to find out.

This is an awesome amp, granted I do not have another SS amp to compare to, but wow. Can't recommend it enough.


----------



## tangent

Thanks for the report!
   
  Yes, EQ appropriate for low-end amps and headphones is often overpowering once you upgrade. Dialing it back or even turning it off at this level is usually a good idea.


----------



## H22

Quote: 





tangent said:


> Thanks for the report!
> 
> Yes, EQ appropriate for low-end amps and headphones is often overpowering once you upgrade. Dialing it back or even turning it off at this level is usually a good idea.


 


  bit of an under statement, yea the 900's have a lot of good points, but they do have a few draw backs as well. a healthy dose of EQ through this amp seems to bring all the bad stuff foreward, however, going with no EQ sounds very very good.


----------



## BionicBadger

I'm building a PPAv2 amp, and have most of the parts soldered, following Tangent's guide.  I made it to the stage where the buffer bias is being set.  Channels left and right were easily configured to 20mA (measured 44mV); however, the ground channel had a problem where for some range of the trim pot it would be extremely low, around 6-8mV, and then after some threshold, it would jump to about 60-70mV.  In both ranges, adjusting the pot further would affect the mV range, so I don't believe the pot itself is defective.
   
  On a suggestion and after reading some posts, I changed R11G to a 100ohm resistor.  Now it only changes the measured mV across R34G/R24G within the lower range.
   
  I've gone and replaced transistors, thinking it might be a problem, but to no avail.  When comparing the like-settings for R9G compared to R9L and R9R set for about 60mV instead of 44), the resistor voltage measurements seem within range of each other, with exception to the output resistors R34 and R24, and R11:
   
   

```
R13 ( R21 R31 ) ( R22 R32 ) ( R23 R33 ) ( R24 ) R11 R10 ----------------------------------------------------------------------------------------------------- L 0.488 1.071 1.072 1.084 1.079 46.5m 47.2m 58.2m 0.1m 0.572 R 0.477 1.054 1.046 1.066 1.052 45.7m 46.1m 58.7m 0.1m 0.737 G 0.480 1.059 1.057 1.071 1.066 48.5m 47.5m 5.1m 0.0m 0.530
```
   
  Things I've tried:
   
  - Swapping Op-amps - Swapping op amps didn't affect the circuits, and the swapped op-amps functioned in other channels (all OPA627APs)
  - Checking for overheating - Nothing is overheating or remotely hot
  - Changed R11G to a 100ohm resistor after reading some suggestions
  - Replaced practically all the transistors in the buffer
  - Tested and compared outputs of the TLEs for all channels
  - Cleaned, and inspected all solder points.  Did some resoldering just to clean up a bit just in case. Did continuity tests as far as possible.  Here is a photo of the back (little "hairs" are just from the Q-tips' cotton from cleaning; they don't conduct).

  Symptoms and conditions:
  - Voltages are correct and constant for the op amps, TLE, ground planes, and other points in the circuit as per the testing in the guide.
  - Adjusting R9G scales the offset for the ground channel as it does in the other channels, but off by an order of magnitude.
  - Measured output voltage bias is (ground to other channels) greater 0.5V for no signal.  This makes it dangerous for headphones at this point, and may indicate some reason why something is broken.
   
 How should I proceed to troubleshoot this?  I've replaced many of the transistors, and the ones that are there seem to function consistent with the other channels. I've replaced the two output Q24G and Q34G transistors and the buffer didn't operate any differently.
   
  Any insights would be appreciated.  Thank you for your help!


----------



## i_djoel2000

is tangent not selling ppa board anymore? i can't find them in the tangent shop, it was there the last time i visited them


----------



## Avro_Arrow

From Tangents site...
   
  "NOTICE: The PPA v2 amp board is no longer available"
   
  He has the ExpressPCB files available for download if you want to do your own board.


----------



## BionicBadger

Quote: 





avro_arrow said:


> From Tangents site...
> 
> "NOTICE: The PPA v2 amp board is no longer available"
> 
> He has the ExpressPCB files available for download if you want to do your own board.


 

 I probably bought the last one.  Too bad the proprietary ExpressPCB format requires the user to fab the designs with ExpressPCB's service (though it isn't a terrible price actually).  Standard Gerber files would allow the design to be fabbed by other PCB fabs as well.


----------



## Spacehead

Quote: 





avro_arrow said:


> From Tangents site...
> 
> "NOTICE: The PPA v2 amp board is no longer available"
> 
> He has the ExpressPCB files available for download if you want to do your own board.


 


  Avro, are you skilled enough to show that it is possible to etch the board at home?


----------



## Avro_Arrow

I can etch down to SSOP in size (thats the smallest I've tried), so size isn't a problem.
  Accounting for the components that rely on a plate-through
  hole for a connection under a component is the hard part.
   
  When I design a board I'm going to etch myself, I take that into account
  in the layout.
  
  Quote: 





spacehead said:


> Avro, are you skilled enough to show that it is possible to etch the board at home?


----------



## BionicBadger

Well, I found out what the problem was, and it was all my doing:  I had ordered 4.32 Ohm resistors instead of 4.32 kOhm resistors.  As you can expect, it caused all kinds of problems, not least of all requiring two extra orders of parts from Mouser, replacing innocent transistors, and wasting time.  ::facepalm::
   
  Oh well, it sounds incredible and is a great replacement for the TPA61220A2 evaluation board I was using as a $50 headphone amp (though it was decent).


----------



## tangent

Quote: 





spacehead said:


> possible to etch the board at home?


 
   
  Personally, I hate hand-etching 2-sided boards for anything with traces smaller than about 50 mil.
   
  If you're willing to venture down into the ~25 mil territory of most of the PPA amp board, I'd say it's probably the easiest layout on my site to hand-etch, short of the near-trivial crossfeed board. The PPA has no SMDs, no vias, and few layer changes at component legs. At 25 mil tolerances, you still have to be quite careful about aligning the copper masks, and again very careful when drilling the holes.

 I wouldn't attempt it unless I needed a board in a hurry, I'd rather just send off for a prototype run somewhere. Quality from even a really bad board house is better than you can do by hand at home. Yes, it's more expensive than hand-etching, but my time and aggravation aren't free, either. 
   
  If I considered my time free and absolutely couldn't spend the money on a professional PCB prototyping service, I'd rather try to come up with a single-layer layout than hand-etch a 2-layer layout this dense. Time spent on the puzzle of minimizing jumpers would be more rewarding than time spent with a magnifying glass trying to align layer masks.
   
  Quote: 





bionicbadger said:


> I had ordered 4.32 Ohm resistors instead of 4.32 kOhm resistors.


 

 Thanks for the report. This is one reason we always want pics. 
   
   
  Quote: 





> Oh well, it sounds incredible and is a great replacement for the TPA61220A2 evaluation board I was using as a $50 headphone amp (though it was decent).


 
   
  Glad to hear it!


----------



## Mach3

Anyone know where I can purchase the PPAv2 PCB? Can't seem to find anyone who sell it no more.


----------



## tomb

Quote: 





mach3 said:


> Anyone know where I can purchase the PPAv2 PCB? Can't seem to find anyone who sell it no more.


 

 Send Tangent a PM or e-mail.  He's probably just out of stock temporarily.


----------



## Mach3

How does this amp compare to like say HeadAMP GS-1, B22 (I know I'm being unreasonable as these amps are way beyond the cost of the PPAv2) But I'm curious


----------



## tangent

Quote: 





tomb said:


> He's probably just out of stock temporarily.


 

 No, he's out of stock permanently. 
   
  Demand had dropped to the point that it was not worth making another batch. I could have ordered a smaller batch, but that would increase the board cost greatly, which would brake demand even more. There comes a point when you have to say that most everyone who wanted one has one now, and it's time to move on.


----------



## Avro_Arrow

Deleted


----------



## Mach3

I was on his site yesterday and it still had a section to email him for an expression of interest. It stated that if enough people contacted him in regards to the board he might make more and notice you by email. Check again today and it seem it's been deleted!


----------



## tangent

Are you sure? The only solicitation for interest I recall putting on my site is for the LNMP, and that I removed when the current board run came in.
   
  I certainly didn't publicly ask for opinions when discontinuing the PPA v2 amp board.


----------



## tomb

Quote: 





tangent said:


> No, he's out of stock permanently.
> 
> Demand had dropped to the point that it was not worth making another batch. I could have ordered a smaller batch, but that would increase the board cost greatly, which would brake demand even more. There comes a point when you have to say that most everyone who wanted one has one now, and it's time to move on.


 

 I can't speak for your business, Tangent, but there are new people that come to Head-Fi and the hobby every day.  In fact, there's a new crop almost with every class change because a great number of headphone/DIY fans are high-school/college age.  In other words, the customer base renews itself every year.  It won't approach the initial interest in a design, but it's enough to support long-term sales, IMHO.
   
  For instance, if there were some more 19J6 tubes somewhere, we could've sold the Starving Student PCB forever.
   
  No question - it's your choice - but it's sad to see the community lose another one of your products ...


----------



## Mach3

Quote: 





tangent said:


> Are you sure? The only solicitation for interest I recall putting on my site is for the LNMP, and that I removed when the current board run came in.
> 
> I certainly didn't publicly ask for opinions when discontinuing the PPA v2 amp board.


 


  I'm serious, I some how got the link from google, might be cached? not sure, anyway manage to get my hand on one from a fellow head fier. All good.
  Also, any chance I can grab some pic and diagram of the tread power supply? I wanna make one for the PPA v2


----------



## tangent

Read the LM317 datasheet


----------



## t0ttie2

Posted in the wrong location. Deleted.


----------



## H22

Well, it is sad that demand dropped off, I have only tried a few other DIY kits, mainly the millet hybrids, have about 1/2 the parts I need to start a b22, but that will take awhile.

I can say that I really enjoy the PPAv2 I built, it definatly showcases the difference between a portable and a desktop amp. 

With so many good kits out there i can understand demand for a particular amp dropping off, especially when everyone wants the newest latest amp, an older design would tend to get overlooked, ireguardless of how good it might be.

Tangent, it would be cool if you could keep the schemes and BOM Available, so those of us die hards could still build the amp.


----------



## FallenAngel

Design age notwithstanding, the PPAv2 is a king among amps, I love this amp and have enjoyed it for years!  Matched with a pair of headphones that aren't bloomed in the mids and highs, it's a perfect match.  HD650 are detailed to a beautiful level, K240 Sextett show great detail level, DT880 are driven to a wonderful level.  Above this amp, you have to really get into the personal preference level.


----------



## rawrster

Quote: 





fallenangel said:


> Design age notwithstanding, the PPAv2 is a king among amps, I love this amp and have enjoyed it for years!  Matched with a pair of headphones that aren't bloomed in the mids and highs, it's a perfect match.  HD650 are detailed to a beautiful level, K240 Sextett show great detail level, DT880 are driven to a wonderful level.  Above this amp, you have to really get into the personal preference level.


 

 That's good to hear about that. I still have my PPAv2 amp but I got a V200 amp which is a bit more colored but in a nice way but also much more expensive than the PPAv2. I never compared the two but I always wondered how the PPAv2 fares against the more recent amps and DIY usually has good value.


----------



## Mach3

My PPAv2 with Bass Knob sound so similar to my LISA III.


----------



## tangent

Quote: 





h22 said:


> Tangent, it would be cool if you could keep the schemes and BOM Available, so those of us die hards could still build the amp.


 

 I have no plans to remove those pages from my site.
   
  Since discontinuing it, I've put up the ExpressPCB design files, too, as was also always the plan. If one were interested in trying to revive the board availability, one would be welcome to as far as I'm concerned. One attempting that should ask ppl and Morsel, too, however.


----------



## Mach3

Quote: 





fallenangel said:


> Design age notwithstanding, the PPAv2 is a king among amps, I love this amp and have enjoyed it for years!  Matched with a pair of headphones that aren't bloomed in the mids and highs, it's a perfect match.  HD650 are detailed to a beautiful level, K240 Sextett show great detail level, DT880 are driven to a wonderful level.  Above this amp, you have to really get into the personal preference level.


 


  Hi FallenAngel, nice to here these comments coming from you, as I've heard from other head fier's that you've built a B22 before. How does the PPAv2 stack up against the B22 amp? Just curious as I'm planning on building one.


----------



## H22

Quote: 





fallenangel said:


> Design age notwithstanding, the PPAv2 is a king among amps, I love this amp and have enjoyed it for years!  Matched with a pair of headphones that aren't bloomed in the mids and highs, it's a perfect match.  HD650 are detailed to a beautiful level, K240 Sextett show great detail level, DT880 are driven to a wonderful level.  Above this amp, you have to really get into the personal preference level.


 

 King indeed! I just finished moving and now have the PPA v2 beside my bed, where I now use it several times a week before falling asleep. The more i listen to it the more it shines.
   
  My headphone selection is only so-so, a pair of M50's and a pair of pro-900's. I personally like the M50's signature better with this amp, the 900's are a bit harsh on the high end for me. The detail and staging even with the "entry level" M50's is just awesome to me. I love this little amp and doubt i will ever get rid of it. 
   
  I did use a few nice components in it, Silmic II caps in the C1 and C4 spots, C2 got a couple of vitamin Q's. I bypassed the C4 with some polyester caps, going to upgrade these to MKP type, also the "odd" positions for C2 are polyester too, thinking of swapping those for polypropylene as well. I used matched parts for the buffer, as well as 637/627 for the op amps. I built a sigma 11 to power  it.
  I'm not sure where this would stack up in terms of "maxed" builds, but I sure like it  .


----------



## christsay

Looks like a 2-layer board?
   
  -chris
   
  Quote: 





tangent said:


> I have no plans to remove those pages from my site.
> 
> Since discontinuing it, I've put up the ExpressPCB design files, too, as was also always the plan. If one were interested in trying to revive the board availability, one would be welcome to as far as I'm concerned. One attempting that should ask ppl and Morsel, too, however.


----------



## tangent

Yes.
   
  Definitely no good for hand-etching in its current state. We knew we were going to make professionally-etched PCBs from the start, so we took full advantage of the tighter margins that affords.


----------



## christsay

yeah, looked a bit tight for that.  The expressPCB 'standard' process isn't completely cost prohibitive but I'd loose the silkscreen and the solder mask... if I did it I'll let you know so I can send something  your way.
   
  -chris


----------



## tangent

The first several rounds of PPA prototype PCBs were made on that process. Of the three of us involved in the PPA development, I'm pretty sure I assembled and tested more prototype boards than the others, so I feel comfortable assuring you that that silk and mask are very much optional with the PPA. Nice, but not actually necessary for a design with this component density.


----------



## BionicBadger

Way back when I built my PPAv2, I had bought 8x 220uF 35V Panasonic FM caps for C1, figuring that more smaller caps was better than a few bigger caps.
   
  I've purchased some 480uF 50V and 680uF 35V FM caps, for some other purpose, and have enough extra that I can replace the old caps too.  I was wondering if it worth the effort to swap out the old C1 caps for a set of the new ones.
   
  With the 8x 220uF caps, the total capacitance is about 1760uF.  With 3x 680uF, that would be 2040uF; with the 4x 480uF caps, about 1920uF.  I was thinking of using the 4x 480uF caps, but their rating is 50V vs 35V of the others.  Does the voltage rating affect things much besides being above my 24V supply?
   
  As a secondary benefit, the old caps are 8mm in diameter versus 12.5mm of the newer ones (a mistake I made).  I'm not really _that_ concerned about the diameter though, as the amp is essentially immobile its whole existence.
   
  Thanks!


----------



## tangent

I think you should leave it alone.


----------



## tsaavik

tangent said:


>





> Actually, it looks like an RC charge curve to me, but the C1 bank will do that, and it could be masking the test results. Ideally you'd power up the amp and ground channel separately.
> 
> You could do this while you play with Q3G: desolder them, jumper Q3G- (big loop so it's easy to remove), and put a switch across Q3G+. Then you'll get one of two results when you power up the ground channel: either the amp will function again, or you will get the same result, which rules out the Q3Gs being a problem.


 
   
  Just wanted to let you know it turned out to be Q3G-. I shorted across the pins with a screwdriver and amp came back to life. I've since replaced the part.
   
  Unfortunately I have a new problem, the computer at my new job is causing an issue with I plug my usb-powered AlienDAC into the PPAv2. 
  I run the PPAV2 off a STEPS that i'm pretty sure is constructed properly. Everything works fine if I plug a diffrent source (like a cellphone) into the PPAV2 (but goes to hell again if I put the cell phone on a usb charger hooked to same PC)
   
  Seems like a ground problem, But i'm at a loss how to solve it. Anyone have any tips?
   
  p.s. anyone have a link to a tutorial/video on how to trace a signal though a ground amplifier like the PPAv2 uses? I've been able to use the math function on my scope to do L/R without differential probes, but no luck on Ground


----------



## tangent

Radio Shack sells an audio ground loop isolator. If it fixes the problem, then you know you do have a ground loop. It effectively turns the PPA into a transformer-coupled amplifier.


----------



## nini_knoxville

Hi everyone,
  
 i finally have my PPAv2 running, after sitting in the basement for almost 2 years waiting for its enclosure 
  
 So far so good, everything is fine, the sound is awesome! I'm using OPA627s and running 30mA buffer bias and 2mA op-amp bias (2V drop).
  
 The only "problem" i have is that if i turn up the volume from nothing, the right channel gets louder first... if i have the volume set to my listening volume, i am not a 100% sure, but it seems to be still out of balance, meaning that the right channel seams to be louder.
  
 All biases are exactly the same and i don't know what could cause that problem...
  
 Anyone knows whats going on?


----------



## Avro_Arrow

It sounds like the volume pot is dirty
 Try rotating it back and forth many times
 and see it the problem goes away.


----------



## nini_knoxville

avro_arrow said:


> It sounds like the volume pot is dirty
> Try rotating it back and forth many times
> and see it the problem goes away.


 
 Thanks for the fast anweser, i already did that trick a couple of hundred times with no difference.
  
*EDIT*
 I just switched my input channels to cancel out the source when i noticed, that if i only have one channel input attached, i still hear it on both channels, but only quiter on the missing channel. is that normal?!?!
  
*EDIT2*
 I just tested it with test sound files, even if only the right channel is playing, i hear it on the left channel too, but much much quieter... i do not have a crossfeed or anything installed. i play back the files using foobar+asio and my asus xonar st...


----------



## tangent

Do you have a fairly sensitive meter? If so, give the AC voltage measurements of the input signal -- both before and after the pot -- and both output signals. Also give the R3 and R4 values. Do this with a simple sine wave.
  
 High crosstalk is usually a grounding problem, which often comes down to the power supply. What power supply are you using?


----------



## nini_knoxville

tangent said:


> Do you have a fairly sensitive meter? If so, give the AC voltage measurements of the input signal -- both before and after the pot -- and both output signals. Also give the R3 and R4 values. Do this with a simple sine wave.
> 
> High crosstalk is usually a grounding problem, which often comes down to the power supply. What power supply are you using?


 
 R3: 1k
 R4: 10k
  
 How should i measure this? If i measure from ground to either input r/l before the pot, i get exactly 0.7V AC on both channels. After the pot, from ground to R1, i get nothing realy? Just tipping it with one lead, i get 1.49 on left and 1.44 on right. i don't know if this is a valid measurment. same if for the output.. from ground to l/r nothing, just tapping r or l 1.39 V AC. But that cannot be a correct measurment. All done with a 400hz sine wave.
  
 for the psu i use your yjps at 16.7V output. i could not find a problem within the psu, but U1 gets pretty damn hot.
  
*EDIT*
 I just checked some of the voltages.. from ground to the op amps v+/v-, each rised by 0.1v per chip. left: 6.11V each, ground: 6.21V each, right: 6.31V each. Also.. from ground to the left output i get 1.7mV, right: 1.6mV and ground... 180mV.. something is wrong with that but what? I also swapped the op-amps... still the same issue.
  
  
*EDIT*
*I found an error!* I'm feeling kinda stupid now, but i forgot to add C6. I don't know why, populated the board 2-3 years ago. Now each channel is about 1.6mV. The crosstalk is gone and so is a grounding problem (touching the headphone metal 3.5 to 6.3mm adapter). Whats left is that left/right problem. I mean that the right channel is "louder"/starts earlier.
  
 Some pictures of my build:


----------



## tangent

Pots are imperfect, increasingly so at low settings. If you decrease the gain to something more appropriate, you will get past the bulk of these imperfections.
  
 All I can see in your pics is that you're using some BB chip, but not which.  If it's the OPA637 or OPA228, you can't go below g=5. Most other BB op-amps popular for audio will let you go down further. A lot of people use g=2 happily.


----------



## nini_knoxville

tangent said:


> Pots are imperfect, increasingly so at low settings. If you decrease the gain to something more appropriate, you will get past the bulk of these imperfections.
> 
> All I can see in your pics is that you're using some BB chip, but not which.  If it's the OPA637 or OPA228, you can't go below g=5. Most other BB op-amps popular for audio will let you go down further. A lot of people use g=2 happily.


 
 I'm using the OPA627. I guess with g you mean the op-amp biasing voltage?


----------



## vixr

Tangent supporting this amp after all these years is effin awesome...I love him.


----------



## tangent

nini_knoxville said:


> I'm using the OPA627. I guess with g you mean the op-amp biasing voltage?


 
  
 It's shorthand for "gain".
  


vixr said:


> Tangent supporting this amp after all these years is effin awesome...I love him.


 
  
 I, um, love you, too?


----------



## proid

Did anyone try the Dyno-bias Buffer in PPAv2? I have read something good about it and want to try it. In the schematic, 1n4935 is used to provide a voltage drop for working condition so can i change it to something like 1n4148?


----------



## tsaavik

I thought I had resolved my 'ground' issues at my new location  (my Aliendac failed chip gets REALLY hot, but no audio output). Ha no ground problem at all!
  
 I got feed up with no PPA at work, so I brought it back in and plugged it into the built in sound on my MB.
 I didn't have my STEPS with me so I used a 16V laptop power supply (sucky, but better than nothing, SOO MUCH BETTER).
  
 The next day I brought the 24V Steps in and hooked it up. I got horrible white noise and muffled-weird-phased music.
 When I touched the (grounded) case of the STEPS the white noise changed! I made sure the steps and ppa were not touching chassis or anything.
  
 I'm happily back on the laptop power, but any ideas what is wrong? Could my work have a poor ground? The power DOES run through a cubicle tray system.
 I checked the STEPS, I get continuity between chassis and AC ground pin, and no continuity between +- DC or either phase of AC.
  
 ** Update **
 Update, after an hour of bliss I walked away and came back to some hiss (not like before though, the audio was not muffled or out-of-phase sounding). The hiss does not increase/decrease in volume in relation to input volume (pc volume) or analog volume on the amp. For kicks I pulled the gnd opamp and hiss went away. I swapped chips (no change), then I got crazy and shorted pins 3 to 5 of the gnd opamp together (+ in to output), NO HISS! I've since pulled the ground opamp out and shorted from pin 3 to pin 5 (R1G to R10G), the socket holds the wire well.
  
 No parts were too hot to touch and opamps were cold as ice. Maybe I have some instability? Can that sound like constant hiss? Or maybe it is just an artifact of running the PPA without an (presumply) isolated power supply.
  
 AD8610 in all 3 locations. Should I buy/try a different model GND opamp, or add some resistance/capacitance between pins 3/5?


----------



## tangent

> Maybe I have some instability? Can that sound like constant hiss?


 
  
 Yes.
  
 What have you got in C6?


----------



## tsaavik

First off, YOU ROCK for replying to me (AGAIN) with an issue, so sorry!
 Please trust that I've had many years (8 now) of enjoyment between the problems, and its why I don't give up on this great little amp 
  
 C6G is:
     CAP 10PF 500V MICA RADIAL
     standard dipped silvered mica capacitor
     CUST REF #: C6G
     Digikey 338-1061  $1.14 x2 $2.28 (I bought 2, so I should still have a spare at home)
     http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=338-1061
     datasheet: http://www.cde.com/catalogs/STD-DIPPED.pdf
   
 So I could quickly replace/add the 2nd cap if you think it might help (or order something else and wait).
  
  
 P.S. I tried the steps again with no gnd opamp and pins 3-5 shorted. I got no audio on left channel and the same weird muffled/staticy/badness on right channel I had initially.


----------



## tangent

I doubt the STEPS has any part in your problem. I believe the only reason the symptom changes is that the voltage changes. If you were to run this amp from a bench supply, I believe you'd find that it behaves up to a certain point, then stops working well.
  
 Any chance of trying that? You'd also learn whether the amp is oscillating, since current draw would spike at the same time.
  
 What are the results from trying the standard troubleshooting steps? Measurements at PPA-specific nodes could also help.
  
 There's a lot of knowledge in this thread, too.


----------



## jboehle

I made a PPA v1 a long time ago (2003 or 2004?), and I absolutely loved it with the Sennheiser HD650.  I sold all my audio & headphone equipment in 2004/2005 and got out of the hobby.  I am getting back into headphones now (have Beyer DT-880 600ohm on the way, and already catching the Head-Fi bug again) and was thinking about building another PPA, but I see the boards are no longer for sale.
  
 ExpressPCB is prohibitively expensive for a small board run.  It looks like Futurlec will accept ExpressPCB files.  I have a question, were the PPA v2 boards made with 1 oz copper?
  
 Also, I haven't gone looking for parts availability yet.  Are any of the PPA v2 parts out of production or otherwise hard to source?


----------



## MisterX

~~


> Are any of the PPA v2 parts out of production or otherwise hard to source?


 
 The PN4392s are no longer available at Mouser or Digi-key but a couple of DIY sites offer them.


----------



## stixx

> ExpressPCB is prohibitively expensive for a small board run.  It looks like Futurlec will accept ExpressPCB files.  I have a question, were the PPA v2 boards made with 1 oz copper?


 
 Just a modest remark... before going into the trouble of having boards made in very small numbers... wouldn't it be a better choice building something readily available, like an M3?
 I know it's the PPA2 thread, but ...


----------



## muskyhuntr

Hi;
  
 Although I have not listened to the PPA-V2, I still have to agree with stixx.  I built my M3 a little over a year ago and could not be happier with it.  Easy to build, allows op amp rolling, parts are easy to find and it has an excellent support base.


----------



## tangent

jboehle said:


> were the PPA v2 boards made with 1 oz copper?


 
  
 ExpressPCB uses 1-¼ copper.
  
 The difference shouldn't matter much.  It's not like the PPA v2 was so close to the resistance margin that we need that extra quarter ounce.


----------



## EdibleStereos

A question for anyone who may know.

 I built a PPA V2 several years ago with the STEPs power supply. I fell out of the hobby for a few years and lost all my documentation I had saved and Tangents site doesn't seem to be accessible.

 I'm trying to  tune my PPA V2 as after a few years being moved around in boxes I think some of the Trim pots may need to be readjusted.

 First issue is, I tried tuning the buffer bias points. I was looking for somewhere around 30ma bias. So I was looking to set around 65mv on R24/34 on all three channels. However I found my meter would read 63mv, and then slowly travel up to 65mv on before settling on the right rail. Also, as I adjusted one rail, and went back to check the others, I found they fell out of balance and needed to be readjusted. Is this normal operation for the PPA V2 or indicative that something may need to be repaired/changed?

 Also, my 2nd issues I came across is biasing the op amps into Class A. On R10 I balanced all three channels to 1.7v, though I only did this for balance's sake, as I have forgotten how to properly bias the PPA into Class A. What sort of readings should I be looking to get across R10 for a properly biased setting?

 The op-amps used are 8610A if that makes any differences.


----------



## tangent

As for the web site itself, it's back now. (Some file permissions accidentally got reset.)
  
 As for your PPA v2 buffer biasing symptom, that sounds like a tempco issue. I'm not sure I ever learned how a simple JFET CCS is supposed to behave as a function of temperature, but I'm pretty sure it isn't inherently tempco-stabilized. One of the whole points of this sort of biasing, though, is to force a constant current through a part specifically in order to keep temperature stable, assuming the rest of the environment has reached equilibrium. In order to get to that equilibrium point, though, you have to case it up and stop wafting strange breezes across the board. 
  
 As for the op-amp biasing, it's simple Ohm's Law. V=IR, so given the fixed R and the desired I, you know what V should be. Or, given that V=1.7 and R=1000, we know that I must be I=V/R, or 1.7 mA.


----------



## EdibleStereos

Excellent! It seems everything is working as it should then. Good to see you still supporting your projects. Even after its been 7 years since I built it.

 Great work all around Tangent.


----------



## EdibleStereos

Anybody know why the buffer bias reading would drop across one channel when hooked up to headphones without sound. The right and ground channel only vary from no load readings by 3mv. while the left channel drops about 20mv.

 With another set of headphones it is the opposite. Left and ground stay stay around 63mv, while the left channel drops about 40mv to 24mv. Also, DC offset shoot up on the Right channel, to 2.2mv. While the Left channel stays at under 1mv.


----------



## fc911c

Hi all

I just built a PPA v2 that I had for years with my spares. I cleaned the board off it had some oxidation. I am having a problem with the ground channel no voltage when trying to adjust buffer bias. Both the left and right channels are fine and voltages to the ground op amp are correct. I checked all the obvious things bad joints re flowed the ground circuit, wrong parts, all are correct, nothing gets hot either. The only thing I did wrong was to have a 10K resistor in (R4G gain ) in stead of a 3.32K. Any ideas what could be wrong could you give me some test points to try to track down the problem. I tried changing a few of the transistors still no voltage.

I have a few Pimeta that I love that both sound great.

Thanks for the help


----------



## tangent

There are a whole bunch of tests given in the docs, here. What are the test results?
  
 What do you mean by "no voltage"?  No voltage across _what,_ and at what setting on the meter? I can give a wild guess that you mean DC voltage across R10G, but you aren't actually saying that.


----------



## fc911c

Hi sorry for being so vaig . I was measuring dc volts at R24. Anyway it turns out I had a 1M resistor in R13 instead of 100R not sure how that happened. I changed all the transistors just to be sure and all is working fine.

I noticed that there is an additional .01uf cap on c2 why was this added?

Thanks for the quick reply


----------



## MisterX

The C2 positions are bypass caps for the output stage.
 IIRC there is detailed explanation in the parts guide page.


----------



## fc911c

Thanks I missed that. I am waiting for the 50k pot to come I have a 100k pot on hand is there any harm in using it till the right one comes?


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## tangent

If you're going to use the 50k anyway, and your 100k pot sits down on the board's existing pads, don't bother installing the 100k; wait for the 50k to arrive. Swapipng a 6-pin DIL board-mount device without exposed pins is a royal pain. You stand a good chance of destroying your board.
  
 If the 100k pot would be connected via wires, that changes everything. Now your replacement problem is six independent wires, which is a much simpler task.


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## fc911c

Yes I am hooking it up with wires it's not a board mount. I agree it wouldn't be wise to install it on the board only to remove it in a few days. So my question remains is it ok?


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## tangent

It's already explained in the docs.


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## MisterX

And in the section about R2.....


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## fc911c

Hi Back again not having much luck with this build. The amp stopped working I am getting a loud hum. I think the problem is in the ground channel my supply voltage to opamps is 13.6v which checks out on pins 2,4 and 7 except for pin 2 on ground which is high at around 19v, pin 3 and 7 is 13.6 on ground. Pin 2 is 13.6.
 I changed the tele on the ground channel no change. Voltage across R 24 is 46mv on all three Chanel's. Any ideas?

Thanks


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## fc911c

Never mind sorted it out bad power supply ground.


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## fc911c

Hi I just completed basing to class A. I am having a few issues one is not being able to get down to 1 mv across R10, the lowest is around 2mv with 627/637 and around 4 mv with ad 8610. Amp does not sound right. Here are some measurements and parts used. I am also using bass boost alps 50k pot. The heat sink on the steps supply is hot.

637 l&R 627 gnd I also tried Ad8610 
Q1 2N5484 Q2 2N5486
R9 2K pot
R24/34 2.2K buffer bias 46mv

Power supply voltage 29v
Left opamp pin 4 to pin 7= 23v
Pin 4 to in gnd 11.6
Pin 7 to in gnd 11.7

Right
Pin 4 to 7 23.5v
Pin 4 to gnd 11.6v
Pin 7 to gnd 11.87v

GND
Pin 4 to 7 24.2v
Pin 4 to gnd 12v
Pin 7 to gnd 12.1v

S1 to v+ L&R 26v gnd 26.5v
S1- to V- L&R 26v gnd 26.5v



Thanks


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## tangent

fc911c said:


> not being able to get down to 1 mv across R10


 
  
 The documentation doesn't tell you to expect that you can do that. It says, "If R10 is 1 kΩ, then each volt of drop across R10 equals one milliamp through the cascode." 1 mV across a 1 kΩ R10 would mean one _micro_amp of current through R10.
  
 This is a simple application of Ohm's Law: I=V/R, in this case.
  


> Amp does not sound right.


 
  
 So go through the troubleshooting guide, as directed by the docs.
  


> The heat sink on the steps supply is hot.


 
  
 What are the measurements on its test points? Specifically:
  

AC voltage between TP1 and TP2
DC and AC between TP3 and TP5
DC between TP4 and TP5
  


> S1 to v+ L&R 26v gnd 26.5v
> S1- to V- L&R 26v gnd 26.5v


 
  
 That makes no sense on its face, and is inconsistent with your earlier test results. The DC voltage drop between S1+ and V+ should only be one diode drop, and there should be nearly zero drop between S1- and V-.
  
 More useful is DC voltage between either V+ and V- or S1+ and S1-. The two pairs should differ, again, by only one diode drop.
  
 The drop between VH+ and VL- and between VH- and VL- is expected, and is why you are getting 26-ish volts at VH+/- and 24-ish volts down at the op-amp power supply pins. The minor difference in supply voltages to each op-amp is also expected, owing to process variations in the JFETs.


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## fc911c

Hi thanks for the reply.

I should have some time this weekend to go through trouble shooting guide. I will report back with my findings.

Thanks


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## tangent

In case it isn't clear from the above, you should be measuring 1V across R10 if it's 1k to achieve 1mA through the resistor, not 1mV.


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## fc911c

Thanks for clearing that up. I was running the amp at around 250mv that's why it didn't sound right. Every thing else checks out in the troubleshooting guide. Also I had the power supply set at 24v not 29v.

Supply 23.88v
S1+ to S1- 23.08v
DC offset input to output gnd .02v
V+ to V- = 21.8v on L R and gnd
V+ to input gnd = 10.8v
V- to input gnd = 10.9v
Amp is drawing 100 - 125ma depending on opamp 8610, 637 627
Dc offset R output to out gnd .2 mv Left .9mv.


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## tsaavik (Mar 5, 2018)

tsaavik said:


> I thought I had resolved my 'ground' issues at my new location  (my Aliendac failed chip gets REALLY hot, but no audio output). Ha no ground problem at all!
> 
> I got feed up with no PPA at work, so I brought it back in and plugged it into the built in sound on my MB.
> I didn't have my STEPS with me so I used a 16V laptop power supply (sucky, but better than nothing, SOO MUCH BETTER).
> ...



4 years later, here is an update! 

After 4 years of running off a 16v switch-mode power supply and bypassing the ground channel, I finally decided to fix my amp, darnit!
I recently got a smart load, so hooked my STEPS (at 24v) up and confirmed everything was good with a 120ma draw. I lowered voltage to 16v to match my SMPS at work and rule out the 24v causing the issue.

I confidently brought it into work, swapped out my SMPS with the STEPS and powered it on. Everything seemed normal until I touched the STEPS and PPA at the same time, massive white-noise! WHAAA?!
I took a page from 1950s style troubleshooting and thumped the STEPS a good one and BAM no more right channel!

Upon closer examination of the case, it appears my heatsink was making contact with the side when the lid was installed AND the back screwed on, but not when the screws were removed!
I've now insulated this area with a long piece of hot glued lego axle (don't judge, it fit perfect in the hammond case's rails).

The PPA suffered 3 dead 2n5486 power rail isolation jfets. 1 in the right channel and 2 in the ground. I'm assuming I blew the ground channel ones 4 years ago 
I still had spares, so I swapped them out and will be bringing the amp back into work on monday, wish me luck!!

** UPDATE ** I'm at work, listening to Orbital's 'The Box' and it sounds so beautiful...I can't even **


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