# the Pimeta-V2 thread



## linuxworks

since 'the other forum' seems still to be down, lets talk about the pimeta-v2 here.

 I just built my prototype last nite. some pics:

















 I opted to go with a 'mostly SMD' build ... all the fun stuff is underneath 
	

	
	
		
		

		
		
	


	




 one thing that I wasn't 100% sure of and needed to check the spec sheets on; I used tantalum smd caps and they mark the band with the PLUS side of the cap not the minus! I did recall that they were the opposite of eletrolytics but its probably worth mentioning in the instructions just for safety sake.

 I wasn't sure if I had a solder bridge on the pads that hold the tant caps but it appears the resist did its job. still, I would have liked a bit more void around the copper pads on parts like that. once a tant or diode is soldered down, its hard to tell if there is excess solder that could short or not.

 also, I'd suggest adding or moving the index dots (plus signs or dots for chips or other indexing silkscreen) so that even when the parts is installed, the legend isn't covered. this helps desk-checking or magnifier checking without having to have a board layout printout handy. example would be the smd buffers - once they are installed, the silkscreening is completely covered and you can't see where the index dot is anymore. minor detail, though - but if there is going to be another rev before its final, I'd like to suggest this slight silkscreen change.

 I have not used the proto area yet. still thinking what my first hack will be for that section of the board 
	

	
	
		
		

		
		
	


	




 I used the default gain as spec'd in the schematic. on my sony mdr-v6 phones (my junk ones that are 'ok' to blow up on testing) I noticed more hiss than I'd want, on pause. however on my senn hd650 it sounds fine so it was probably a gain issue. on my next build I might lower the gain a bit or just provide switchable gain via relay-paralleling R's at the R4 spot.

 the pimeta is being fed 24v from a TREAD that also supplies voltage to my volume control chip (burr brown PGA chip thing that I'm also working on). when I tested it at 9v, it sounded 'just fine' also, so I guess it passes the portables voltage test, too.


----------



## Heady

Beautiful pics and the soldering's great too. Good job.


----------



## Nemo de Monet

Looks nifty... but haven't you always insisted 470uf per rail is "too little", in a Pimeta? 

  Quote:


 once a tant or diode is soldered down, its hard to tell if there is excess solder that could short or not. 
 

That's what multimeters are for.


----------



## Forte

Very nice.

 Apart from the addition of all the smd solder pads what has changed from V1?


----------



## linuxworks

its a 4 layer board, for one. so I think more 'planing' is there and that's supposed to be a Good Thing(tm) 
	

	
	
		
		

		
		
	


	




 no more need to cut traces on the input cap pads. now you either elect to install a cap OR you install a jumper (I went with the jumper, for now). but no more taking a knife to the pretty pcb to pick cap or capless 
	

	
	
		
		

		
		
	


	




 there are more spots that are designed-in for molex headers. I made use of quite of few of them. one of them is a power switch and I elected to install headers AND put in a jumper shunt, just to remind me and also provide a real easy manual 'stop button' if I was under the cover and troubleshooting a system that had this pimeta 'module' installed. or if you really do want a power switch, this is the place to connect it.

 there is a whole proto area (scratch pad) that has power rails and room for a large DIP there (or perhaps 2 smaller dip8's). or more rail cap. or other things. I left mine alone. for now 
	

	
	
		
		

		
		
	


	




 the buffers now mount SMD style and they benefit from having solder pads or 'pillows' under them. these buffer chips have metal heat pads built into the chips and so having those 2 touch makes good heat dissipation sense. there is no DIP way to do the buffers anymore so SMD is a must, now. the 2 opamps are still DIPable if you want and they also have SMD pads undeneath if you wanted to go all SMD for the chips.

 the transistors for biasing are not SMD (sniff) and I didn't install mine yet. I plan to but not on the first pass. there is a pot, now, that adjusts the bias for both and one of the 2 LEDs is 'part' of the biasing, now.

 there is formal support for battery and trickle charging with a lm317 onboard.

 (that's just off the top of my head)


----------



## linuxworks

Quote:


  Originally Posted by *Nemo de Monet* /img/forum/go_quote.gif 
_Looks nifty... but haven't you always insisted 470uf per rail is "too little", in a Pimeta? _

 

me? I never insist. do I? 
	

	
	
		
		

		
		
	


	




 I picked what I had that had a high voltage on it. I planned to use a dual 12 or dual 15 and didn't want to skimp on getting too low a safety margin on the cap. plus, these fit the holes well 
	

	
	
		
		

		
		
	


	




  Quote:


 That's what multimeters are for. 
 

I disagree. ideally, it is preferable to know from just looking (even with naked eye and no magnifier) if its 'good' or not. that's one of my litmus' for a perfect design.


----------



## joneeboi

Excellent photos as usual, linux.

 I'm going for an SMD PIMETA v2 as well, but I'll probably populate more of it than you did such as the volume pot and class A. I really like the through-hole/SMD duality because it makes troubleshooting easy when going the SMD route. I actually asked tangent if it were possible to configure the board to allow a DC regulator. Of course, there would have to be some tweaking on the user end. I was thinking of using the LM317 as a regulator instead of as a CCS for the battery, and it could easily be done with the prototype board. Simply omit the diodes, solder pins ADJ and Vout to the board while leaving the Vin in the air, bridge Vout with the Vin/B+ trace, and air-wire resistors, diodes and capacitors accordingly as per the datasheet. An even easier regulator would be to use the LM78xx series of regulators, and that would do away with the air-wiring and parts count. There is a small line up of Xicon linear unregulated wall AC/DC supplies available at Mouser, so that will be part of my PIMETA v2 prototype plans. Any ballpark figures for current draw, linux? I may go with 3x OPA627 off the bat, and that should send my max current draw somewhere around the 100mA area. Mind you, those are from the max readings when operating at +/-15V. Would it make sense to use an LM7824 with an unregulated 24V wall wart? I know the unloaded voltage will be a bit higher than 24VDC, but I wonder if the LM78 would stay in regulation as it has a 2.0V dropout. I could easily go with the LM7818, but I just want to know if I could pull off 24V. I likely wouldn't be able to hear the difference anyway. I only need a gain around 2-3, so I likely won't need all that much extra voltage swing on my low-ohm headphones.

 Edit: Also, wouldn't you rather just jumper from the inputs to R1? It may not be as clean, but you shorten the signal path and blah blah blah. Just a thought.


----------



## nsx_23

I need a kit for this, like now. My old pimeta sounds fantastic, so this is very interesting.


----------



## joneeboi

You *need* a kit? The old PIMETA didn't even have one.

 Looking at the board and LM78xx datasheet a little harder, you can insert all three TO-220 terminals right in there with a few sleights of hand. Omit the diodes from the board again, throw in the LM78xx, and omit RCCS and the Molex connectors for the battery and the wall input. Then wire in the wall power into the WALL input holes; just bridge the diodes' anodes (non-striped ends) and jumper the wall V- to the hole for RCCS that's nearest the R in RCCS. Then you get to use the remaining battery Molex holes for the input capacitor for the LM78xx with more creative wiring.

Schematic
Board layout
LM317 datasheet
LM78xx datasheet

 Surely, this is a deviation from the original powering options for PIMETA v2, and I can see this kind of thing mucking up a beginner's understanding of the amp with the different power supply choices. Approach this option with caution unless you're sure of what you're doing. We still don't know what the final board will look like, so don't throw all your eggs in this basket just yet. I'm merely exploring the possibilities as the board stands.


----------



## nsx_23

I need a kit as in I need all the parts now 
	

	
	
		
		

		
		
	


	




 Just a shame ordering stuff from the US is so expensive....


----------



## Earwax

This looks great. I hope it will be possible to use the scratch pad area for a bass boost?


----------



## joneeboi

If you check the schematic and board layout, there's room for a bass boost incorporated into the amp already. That's why there's an extra set of holes for R4LR. Hm, maybe I'll try bass boost with my amp too.


----------



## linuxworks

if you notice, I lifted the red input connector off the pc board a bit. if you install it flush, it covers the silkscreen lettering/legend and I wanted to be able to see that ground wasn't in the middle (as I normally make plugs like this) but on one side. if I covered up the lettering I would probably make a cable incorrectly for this module; if not now, then later. I know myself too well 
	

	
	
		
		

		
		
	


	




 so I allow the lettering to be seen by this 'cue'.

 same issue with the battery molex - except that there are some more holes to one side and that shows the left/right plus/minus labelling which applies to the smaller 'wall' connector as well. still, I do prefer all *important* labelling to be visible even when a component is installed. I guess this is an eagle library issue (?)


----------



## linuxworks

I'm planning on having some relay switchable bass-boost in a few levels. not sure how to mount the relays yet (in air or on the scratchpad) but switchable levels of BB is one of the things I like about this design. I made an early hack here:

http://www.head-fi.org/forums/f6/bas...ke-ppa-393311/






 and I might try something similar again on the v2. maybe even more relays, for more finer grained levels (selectable) of boost. a binary code to 'address' the r/2r resistors would give 2^n levels of selection


----------



## cobaltmute

Quote:


  Originally Posted by *Earwax* /img/forum/go_quote.gif 
_This looks great. I hope it will be possible to use the scratch pad area for a bass boost?_

 

From Tangent's docs:

  Quote:


 One of the most popular features of the PPA is its bass boost circuit. The cool thing about it is that it uses the op-amp circuit that already had to be there and it’s completely bypassable. As audio filters go, it’s about as problem-free as you could hope for.

 There are a couple of ways to get bass boost with the PIMETA v2.

 The first way is hinted at on the schematic. There are two extra pads off the ends of the thru-hole footprint for R4, plus the SMT pads on the bottom side. This allows for up to 3 components here, a resistor, a cap, and a switch. This is enough to give us a weaker form of bass boost than in the PPA, which I call “unity boost.” The difference is, the resulting amp is effectively just a unity-gain headphone driver with bass boost. This is fine for many situations. Most sources these days have enough voltage to drive headphones; they’re just current starved and have too high an output impedance to drive high-quality headphones to their full potential. A PIMETA in unity gain solves that problem. If you do this, I recommend using the outer pair of holes for the caps, the inner pair for the switch, and the 1206 SMT pads on the bottom side for the R4 resistor.

 If you really do need voltage gain, you can still get a PPA-style bass boost. The thing you need, which we didn’t have room for on the PIMETA v2 board, is what the PPA calls R7: a resistor in series between the buffer output and R4. You can do this by running two pairs of hookup wires from the ends of R4R and R4L to the scratchpad area, then build out the bass boost circuit there. The needed changes will be obvious with a little study of the PPA schematic. Alternately, you can build this R7+R4+cap+switch circuit on a small chunk of perfboard and mount it vertically, like an add-on card in a PC, in the R4 thru-hole pads.


----------



## linuxworks

if you only want to switch BB in or out or even have a pot like PPAv2 does, then why even waste scratchpad for that? the pot has enough room to mount an R and C in parallel and then run THOSE 2 wires back to the r4 l/r holes.

 r/c at the pot or at the board - its all the same in the end


----------



## rds

Looks like the other forum is still down. Is there any word on when pcbs will be available?


----------



## tangent

The latest thing holding the production run up is that the AD8620/10 combo was oscillating. I think I found the fix last night, but need to verify it before proceeding.

 For anyone who has a prototype and wants to test it, here's the scenario: With a BrownDogged AD8620 in OPALR and a BrownDogged AD8610 in OPAG, and everything else set to stock values, you should see oscillation of 0.5 or 1 MHz -- these seem to be the two stable states of the system, with the choice seeming to depend on the C3-5 values. Sometimes the oscillation only appears at some volume settings, or at some supply voltages.

 Known and suspected fixes, some of which are impractical but interesting, are:

 - Change OPALR to something else that's always stable. Changing OPAG does not help.

 - When scoping OR/L, connect the scope probe's ground clip to IG instead of OG.

 - Solder the chips to the board; no BrownDogs, no sockets. I haven't tested this, because I built my prototype mostly thru-hole. I'd have to cut the sockets off the board to properly test this, as some of the stray capacitance would remain otherwise.

 - Lower R7. I've tried 1K and 100R, both of which seem to work just as well, despite the instructions in the LMH6321 datasheet to use 10K. Now that my test amp is stable, I need to return to 10K to see if this is a real fix, or if something else I tried fixed it.

 - Add a few puff of capacitance across R6L/R. This damps out some severe ringing when testing with square waves. 10 pF overdamps it, but probably doesn't hurt the AF performance audibly. Still, something smaller would probably be better.

 Until I've nailed this down more precisely, it will continue to block the production run. Can't allow such a popular chip to be excluded.


----------



## TzeYang

I'm pretty sure regardless, the compensation capacitor is needed. Unless you go super tight SMD but even so I doubt it's still going to output perfect square waves.


----------



## NelsonVandal

Tangent, since you're not using the 1 nF cap bypassing the 10 k input resistor suggested by National I don't think 10 k is an appropriate value. Besides, the LMH6321 is inside the loop of an opamp in PIMETA and is run open loop in the data sheet. I think PIMETA is deemed to be unstable with a 10 k resistor in this position. I've found all my similar amps to be stable without any isolating resistor, but I've read about instablity issues that's been cured by a 100R resistor. I don't think you'll need anything larger than that.


----------



## grenert

These SOIC-DIP adapters
SOCKET ADPTR SOIC/8PIN .300 DIP - 08-350000-10
 have traces that take a far less circuitous route than Browndogs. Maybe they'll fix the oscillations. Just don't look at the price


----------



## NelsonVandal

Just to illustrate what happens in this circuit (I have no generic buffer symbol, so I use a discrete diamond buffer instead, but it should make no difference):





 with no PIMETA resistor R7, R14 in the schematic above (it looks exactly the same with a 100R resistor)





 with a 10k resistor





 with an added 1nF cap in parallel, but I can't see why one would want capacitor coupling





 with no or a 100R resistor and a 3pF cap in parallel with R6





 So you see, even in a perfect simulator-world the amp oscillates with a 10k resistor. Just lower it to 100R. I think it would be wise to have pads for compensating capacitors. You could have SMD 0805 pads on the bottom, under the R6 resistors.


----------



## tangent

Quote:


  Originally Posted by *Horse* /img/forum/go_quote.gif 
_How can there be such a problem with such a stable opamp as the AD8620?_

 

Even slow, docile chips can be made to oscillate, and 25 MHz isn't slow.

 It appears from further study of the datasheet that the bandwidth of this particular op-amp is probably what's to blame here, not some special thing about the chip itself. Another 25 MHz chip might behave the same way.

  Quote:


 what if one wants to use a better (and bipolar) opamp such as the LT1028? Or one of the LME duals? Or an LT1358? This could be easily done if that jung multiloop thingy was left out, one and for all 
	

	
	
		
		

		
		
	


	



 

It's easy to convert the PIMETA v2 to the standard feedback configuration: leave R6 out, and short R5. Balance the input offset currents, and there you are, bipolar-input based amp.

  Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_Tangent, since you're not using the 1 nF cap bypassing the 10 k input resistor suggested by National I don't think 10 k is an appropriate value._

 

Ah, I clearly misunderstood what they were doing there. And page 15 is suddenly so clear now. It all but told me this would happen. 

 Luckily the current board design doesn't have to change to fix it. Not that that would be a blocker. There are already changes coming in the next version. I just don't want to try to make room for more parts if I don't have to.

  Quote:


 I've read about instablity issues that's been cured by a 100R resistor. 
 

Yes, page 15 of the datasheet covers this, in the Bandwidth and Stability section.

 Some buffers, like the BUF634, have this input resistor already. If you go back to the META42, it had this resistor, because the sadly departed EL2001 and 2002 don't have internal input resistors.

  Quote:


  Originally Posted by *grenert* /img/forum/go_quote.gif 
_These SOIC-DIP adapters
SOCKET ADPTR SOIC/8PIN .300 DIP - 08-350000-10
 have traces that take a far less circuitous route than Browndogs._

 

Aries' real strength is in the breadth of their offerings. BrownDog doesn't have nearly as many adapter types.

  Quote:


  Originally Posted by *Horse* /img/forum/go_quote.gif 
_BTW maybe one could have chosen the LME49600 for the buffers._

 

Or maybe one could not tolerate a footprint 50% bigger than a DIP-8 on a board that wasn't allowed to get bigger just to make room for it. 
	

	
	
		
		

		
		
	


	




 If they made it in a DIP-8 or SO-8, I'd definitely have tried it. Then again, if it were in that package with the same pinout as the BUF634, maybe PIMETA v2 wouldn't exist. Constructive destruction.

  Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_Just to illustrate what happens in this circuit_

 

Awesome, thanks for that. The 10K goes. 
	

	
	
		
		

		
		
	


	




 The schematic won't change for a while yet, as my web host seems to be having network problems. (Ain't my server, really!)

  Quote:


 with an added 1nF cap in parallel, but I can't see why one would want capacitor coupling 
 

You might be forced into it with some chip combinations. Page 15 again.

  Quote:


 with no or a 100R resistor and a 3pF cap in parallel with R6 
 

Beautiful, that's almost exactly what I see in the real world with 10pF across R6, only with somewhat rounder corners, as you'd expect.

 I have some 1s, 2.2s and 4.7s coming, so we'll see how little capacitance we can get away with here.

 So the next question is, do I shove parts out of the way to make room for the new C6L/R, or do I just have people use SMT caps with leaded R6es, and leaded caps with SMT R6es? It's fine with me, but maybe there are good reasons not to do it?

  Quote:


 You could have SMD 0805 pads on the bottom, under the R6 resistors. 
 

Almost every thru-hole part on the PIMETA v2 board has SMT pads on the bottom side of the board already. They're mostly 1206es, though. Nothing smaller than that.

 The only place this isn't done, where it might have made some sense, are the transistors, which could probably accept SOT-23s on the bottom side. Not that explicit pads are really necessary.


----------



## MisterX

Actual 100kHz square wave responce with a 10K R7 and a *slow* OPA2107 op-amp. 






 Change R7 to 100 and things look a lot better. 






 (the strange twisty shape is because of the camera)


----------



## Voodoochile

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I think I found the fix last night, but need to verify it before proceeding._

 

It's good... it's good! 
 Wish I'd seen this thread 15 hours ago. 
	

	
	
		
		

		
		
	


	




 I Browndogged an old AMD Duron processor and stuffed it in there; even that doesn't oscillate.


----------



## odigg

Any ideas when the PIMETA board will be for sale again?


----------



## tangent

From the FAQ: "summer".


----------



## odigg

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_From the FAQ: "summer"._

 

Ahhh..sorry for not checking there!


----------



## cobaltmute

After too long of having the parts on my bench, another Pimeta 2 is born:





 Would take more pictures but the battery in the camera is dead so all I got was one.
	

	
	
		
		

		
		
	


	




 Running it currently at ~14V as that is what I plan to put together for a battery pack. Biased by a single resistor to 10ma Class A if I figured the math right.

 First pass test was running OPA2107/OPA602 which sounded almost the same as my Pimeta 1 running OPA2107/OPA227 with discrete buffer. Maybe a bit fuller in the sound and a touch more bass.

 Currently it is running LME49720/LME49710. Seems a bit more of a natural and full sound than the OPA combo. Have to listen a bit more but this may become my preferred combo.

 My main deviations from Tangent's parts list:
 - set for gain of 3 (iirc correctly)
 - no current limiting on the buffers
 - bypass caps on the opamps are 1uF
 - currently no C4 caps
 - R7 is 221 Ohms - missed the discussion here and had 10K resistors to put in. Then saw the discussion and pulled the 221 out of a box on the shelf.
 - My C2's are 560uF Panasonic FCs
 - Biasing NPN transistors are BC337s

 Have one little issue that if I try to increase the input voltage to 20v, I lose the left channel (just goes to quiet noise) but it comes back if I reduce the voltage. But that will be tomorrow's problem.

 Other than that, thanks to Tangent for letting me have one of the first boards. It was a good build. Now I've just got to build my battery pack and case the thing.


----------



## tangent

Thanks for the report!

 Do you have the ability to scope square waves thru it?


----------



## cobaltmute

I've got an old signal generator (not sure how well it works), but no scope.

 I really need one, am cheap, but something that could monitor the signal lines in a DAC.


----------



## cobaltmute

Figured out that it is something in the Class A bias circuit that is running away when the supply voltage passes 18V. I rotated op-amps (in both OPALR and OPAG) to see if it was the opamp and experienced the issue in all combo's I could do. On further testing as I increased the supply voltage, the current draw wouldn't change and then it would start slowly increasing. Snipping the RLIM resistor (removing the biasing) results in stability at 20V supply.

 I'm going to replace the BC337s with 2n3904s and see what happens.

 The LME49720/LME49710 combo does sound very good. I'd recommend giving it a try - especially for the price of the chips.

 I'm going to look around at a couple of the local stores and see if I can rent a scope for a day or two. Can't justify buying one yet.


----------



## tangent

That's odd. I would expect that if the biasing circuit were the problem, the symptom wouldn't go away until you got rid of the Q3s, as they're the only parts to "touch" the feedback circuits. The CCS side of things should be quite decoupled from the op-amps.

 Before you swap the transistors, try putting a switch in for RBLIM and see if you can correlate class A bias current with stability. Without RBLIM, you'll be able to dial up bias current way beyond practical levels, which may be educational. It would be useful to know if you can get it stable somewhere in the RBIAS range without having to break the CCS path with the switch.


----------



## cobaltmute

As a note, you may have missed - I don't have RBIAS in line right now. I put RLIM across RBIAS + RLIM. I was set for doing fairly deep biasing (10ma), but well within spec for the chips (the LME49720 can output 25ma). Cutting RLIM took out all the Class A bias.

 Part of the reason for this was that I was going to do something different and not use the bias at all, but at build time I changed my mind and threw in what was in my parts bin.

 I'll check to see if I can get a pot at the local shop and get some adjustability.


----------



## cobaltmute

Tests made wiith a 340Ω RLIM resistor and a 5KΩ RBIAS pot

 12.5V supply, Highest setting on pot - stable (50mA draw for amp)
 15V supply - stable (52mA)
 17.5V supply - stable (53mA)
 20V supply - stable (54.5mA)

 Starting at 12.5V supply with a 60mA draw:
 15V - stable (61.5mA)
 17.5V - stable (64mA)
 20V - stable (67mA)

 Starting at 12.5V supply with a 65mA draw:
 15V - stable (69mA)
 17.5V - possible very slow runaway
 20V - slow runaway

 Starting at 12.5v supply with a 76mA draw (maximum)
 15V - stable (83mA)
 17.5V - runaway

 What I don't understand right now is why the CCS is not stable for a particular setting - by looking at the schematics, I would figure that it would be independent of the rails for the large part. I can see a small current increase with the increase in supply voltage, but it seems to be a bit dramatic. Playing with this in simulation shows small increase in current for change in rails, but nothing like what I see in real life.

 Any thoughts as to what might be messed up are appreciated.


----------



## tangent

Many chips vary in current draw as the supply voltage varies. I, too, have observed that the LMH6321s are in this class. Perhaps your op-amps are, too.

 What value do you have in R7? Do you have any small caps across R6, as discussed above? Both changes (relative to the original docs) aren't necessary in my experience, but then, I have never used the chips you're playing with.


----------



## nullstring

I am thinking about making a pimeta sometime next year as my first PCB amp

 I am curious, should the pimeta v2 be better, worse, or about the same performance wise vs the pimeta v1.

 the pimeta v1 certainly looks more impressive than the pimeta v2 from an outsider and amateur perspective. more large capacitors, etc.


 I want to make one like tomb's
http://www.head-fi.org/forums/f6/diy...7/#post3991061

 I think those look really really nice. I plan on using 4 to 6 CR123A's instead of the 9V batteries and adding li-ion charger inside as well if possible.
 I'd also like to change it so that the LED is multicolor and will change color and maybe flash based on charging status.
 Of course, this is gonna require space.. and so anything the saves space is nice, but I just hope that the original performance of the pimeta is unhampered =)

 This is all completely in the planning stage, however. I don't plan on building it till maybe next summer.


----------



## JamesL

A quick look at the schematic looks like there's no considerable changes in the design. 
 The most evident changes are the addition of some very nice features. It looks like a trickle charger and bass boost was introduced in v2, as well as a scratchpad for additional features or experimentation. some changes regarding the class-a bias.
 SMD pads to allow for almost a all-smd build, layout changed to accommodate the lmh6321 without modification, a mounting hole in the front to replace the evj-c20 support.
 That's all I can see so far... Performance-wise, I'd expect it to be similar, but I'd like to hear it from tangent as well.


----------



## JamesL

Quote:


  Originally Posted by *nullstring* /img/forum/go_quote.gif 
_the pimeta v1 certainly looks more impressive than the pimeta v2 from an outsider and amateur perspective. more large capacitors, etc._

 

What does "etc" pertain to? The 2 rail capacitors lost in v2 can easily be soldered onto the scratchpad. I wasn't particularly interested in building a v2 before but after looking into it, I'm definitely looking forward to it's release =)


----------



## cobaltmute

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Many chips vary in current draw as the supply voltage varies. I, too, have observed that the LMH6321s are in this class. Perhaps your op-amps are, too.

 What value do you have in R7? Do you have any small caps across R6, as discussed above? Both changes (relative to the original docs) aren't necessary in my experience, but then, I have never used the chips you're playing with._

 

R7=221Ω R6=499kΩ. I don't have any caps across R6.

 IIRC, the OPA2107/OPA602 were in the amp for testing.


----------



## cobaltmute

Quote:


  Originally Posted by *nullstring* /img/forum/go_quote.gif 
_the pimeta v1 certainly looks more impressive than the pimeta v2 from an outsider and amateur perspective. more large capacitors, etc.

 I want to make one like tomb's
http://www.head-fi.org/forums/f6/diy...7/#post3991061
_

 

My Pimeta 1 is like tomb's using 12xAAA's instead of 2x9V's. This allows for lots of run time (800mAh vs 250-300mAh). My Pimeta 2 will be cased the same way.

 As for the number of caps etc between Pimeta1 and Pimeta2, there are a lot of things to take into consideration. IIRC, my Pimeta1 uses 4x330uF caps for a total of 1320uF. For my Pimeta2 which is the same kind of tomb like build, I'm using 2x560uF caps for a total of 1120uF. The area of those two caps is a little larger in the Pimeta 2 so you can get away with a larger (not taller) cap. Yes, I did lose a little capacitance, but you can always add one in the scratchpad area if you really feel like more.


----------



## cobaltmute

As another note, after some longer sessions, I'm starting to not like the LME49720/LME49710. It may be "fuller" and "warmer", but they are not without their flaws that I find annoying.


----------



## hopeless

Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_As another note, after some longer sessions, I'm starting to not like the LME49720/LME49710. It may be "fuller" and "warmer", but they are not without their flaws that I find annoying._

 

What exactly? I'm curious... To me they're overly smooth in the upper mids, making them appear very detailed (and a bit spiky) in the treble while they aren't necessarily. 
	

	
	
		
		

		
			





 Plus they're blue-sounding like the rest of the series.


 Try the LT1355 and LT1354? Or LT1358 and LT1357?

 Or LT1469 and LT1468?


----------



## hopeless

Ouch, wait, I guess the LT's are worth nothing to you.


----------



## tangent

Quote:


  Originally Posted by *JamesL* /img/forum/go_quote.gif 
_A quick look at the schematic looks like there's no considerable changes in the design._

 

- The new class A biasing scheme removes previous requirement for hand-matched transistors
 - The new biasing scheme is adjustable, with a single pot adjusting both channels' bias
 - 4-layer board, allowing full ground plane and heat-sinking for the buffers
 - better bypassing

  Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_R7=221Ω R6=499kΩ. I don't have any caps across R6._

 

Try dropping R7 to 100R.

  Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_my Pimeta1 uses 4x330uF caps for a total of 1320uF_

 

The rail caps in the v1 are from the rails to virtual ground, so you can only count half the capacitance.

 Actually, I can make an argument that you only get a single cap's worth of overall capacitance in PIMETA v1: two equal caps in series have half the capacitance of the single unit (but twice the voltage tolerance) and two in parallel add: (330 / 2) + (330 / 2) = 330.

 In PIMETA v2, the caps span the rails, so total capacitance is either equal to that of a PIMETA v1 using the same caps, or twice as much if you buy my shaky analysis.


----------



## JamesL

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_- The new class A biasing scheme removes previous requirement for hand-matched transistors
 - The new biasing scheme is adjustable, with a single pot adjusting both channels' bias
 - 4-layer board, allowing full ground plane and heat-sinking for the buffers
 - better bypassing_

 

Thanks for the additional notes =)
 I mentioned the changes in biasing scheme but I wasn't completely sure what it did.
 Does the bypassing refer to the addition of c3/c5? The first time I looked at them, I thought those were the electrolytes, but I realize they were moved prior to the rail splitter.

 And lastly, do you think the ad8610/lmh6321 will perform well on a 9.6v supply? The datasheets specify min Vs of +/- 5v for both, but it seems theres quite a bit of leeway before the opamp completely craps out.
 If it's a bad idea, any alternatives that you can recommend in particular?
 Thanks


----------



## diditmyself

LMH6321 is specified from 5V so the use of a single 6F22 battery will cause no problems at all. Since the output transistors are common collector you'll loose about 2V swing but since it's the same for most of the good sounding opamps it doesn't matter. It might bother some half-deaf loudheads with high impedance phones.

 Regarding the cap discussion: don't worry about the cap size, you wont hear any difference anyway. If you're not convinced do a blind listening test with normal and "oversized" caps in any 3-channel amp.


----------



## diditmyself

... and i forgot the AD8620. As far as I remember it's one of the better performers at low voltage supply, but I don't really like the sound of it and it's far too expensive to recommend.


----------



## hopeless

Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_... and i forgot the AD8620. As far as I remember it's one of the better performers at low voltage supply, but I don't really like the sound of it and it's far too expensive to recommend._

 

The LT1469 and LT1468 sound better than the AD8620 and AD8610.

 Also it can work great with the LMH6321 in terms of tonal transparency. Try to believe.


----------



## joneeboi

After much delay, I have cased up my PIMETAv2. I haven't implemented Class A biasing yet (where are my transistors?), but it's good so far. DC offset used to run wild (think ~100mV), but after throwing in my bass boost, it seems to have calmed down. More info will come after work.


----------



## Voodoochile

That's great man. I still haven't cased mine, but I did make the PSU for it, and I have a small case on the way.

 Looking forward to seeing your cased up.


----------



## joneeboi

Ehh, it's nothing to write home about. I'm actually just lucky that everything fits inside. As for a power supply, I just have the AC-DC wallwart putting 24V through an LM7818. 
	

	
	
		
		

		
		
	


	




 Just a note about bass boost. In the schematic, there's a switch to turn BB on and off, but there really isn't a need for it if you just turn the bass boost pot all the way down. Saves money, panel space, so on and so forth. I don't know if this has been covered in other BB discussions, but this is the first time I'm using it.

 Also, does anyone have any explanation for why my DC offset was running wild like that? For just one channel, it would go from 38mV to 120mV and just bounce back and forth when the music was on. I'm just connecting my iPhone as source. It's fine now that my BB is wired up. I'm BrownDogging AD8620 and AD8610 into a mostly SMD build.

 When I get the chance, I'll go into more depth about my LM7818 config.


----------



## tangent

Measuring DC offset while music is playing means nothing. Your meter is just being confused by the AC.


----------



## joneeboi

Fair enough. Now what if it varies with the pot and no music is playing? A fully open volume pot meant no DC offset, but as I decreased the volume, the DC rose.


----------



## tangent

It could indicate a problem. Are you using the new values on the schematic, particularly R7 = 100R instead of 1K?


----------



## joneeboi

My R7 is indeed 100R. I used 3.32K for R1G and R4G, but I figured it would be okay since it's just a voltage follower anyway.


----------



## tangent

You should have the inputs grounded when doing this test. If the inputs were floating or connected to a source, your results are again questionable.


----------



## joneeboi

Hm, I can't remember if I did ground the inputs for those tests. I think I did, but it doesn't matter now that my DC is pretty much zero.

 Anyways, on to the main event. I finished building my PIMETAv2 last night in preparation for the Calgary meet this Saturday. I installed Class A just yesterday night, and biased my RBLIM of 287R to have ~0.56V across it, about 2mA of bias. I tweaked my BB to only have the pot and caps in parallel (no R4, so it's in unity boost), so it's plenty deep right now through my normally airy SR60s. I must say, I may be a bass junkie. 
	

	
	
		
		

		
		
	


	




 My pot is 50K, and I have 0.22uF K42Ys from my Millett Max build paralleled with an additional 0.1uF of Wimas I grabbed from Mouser. Wow, I can get used to this much bass. All these values weren't really calculated. Class A could be biased deeper, but I don't know if I really need to; I could stand to with the additional PS headroom. The bass sounds great to me, so I have little impetus to get it "just right."

 Here is my configuration:

 - SMD build. All resistors are SMD, and so are C3, C4 and C5. It was good experience, but I much prefer having through hole. It's easier to see what you installed because it's all on top of the board.
 - AD8620 and AD8610. I used to have OPA627s with my PIMETAv1.1, but i think I might have blown them up
 - R7s are 101R
 - R4 is absent. I have the amp set up in unity boost.
 - C4 is 1.5uF
 - Class A 2mA. Trimpot 5K and RBLIM 287R. Both my LEDs have Vf 3.5V.
 - I went with the 1.1mA CRD for RLED
 - Volume pot is Alps Blue
 - BB pot is 50K Alps RK097
 - Jacks are nothing special
 - No switches for PWR and BB. If I'm not using the amp, I don't really care to shut it off. If I don't want BB, I just turn down the pot. It turns on when I plug it in.
 - Case is 1455K1201.
 - PSU is a 24V AC/DC wallwart into an LM7818. Here's the different part for me. No particular reason I did it besides proof of concept. You install it the same way you'd solder in the LM317, but you don't connect any diodes. Instead, you bridge their anodes (non=striped ends), and connect pin 2 with V-. You can use the other end of RCCS to do this if you don't want to solder directly to the LM78xx. If you just compare the two pinouts with the schematic, you'll see what I'm talking about. I've linked them for your convenience. Plus, you have to make sure you include the proper stability capacitors. I don't know if tangent plans on incorporating this into the next design, but it can be done with this revision of board if you so desire. I also got a huge heatsink for the VREG, which I don't think helped with the casework. Nevertheless, huge heatsinks are always cool. 
	

	
	
		
		

		
		
	


	




 If any of you are familiar with my workmanship, it's not as it should be. I usually only use one type of hookup wire and I don't have any heatshrink. Just lazy to invest in the proper tools, but I'm getting there. I'm a little hesitant to show the internals, but since I'm a prototyper and not just doing my own thing, I'll share. You'll understand when you see it.

 Anyway, just wanted to report a successful build with no major complications. If anyone wants my BOM, I can share that too. Thanks, tangent, for including me in the proto group. I really liked the card. Classy.

 #0006, done.


----------



## linuxworks

I had to fix my pm2. I had a power supply failure on my 20-24v rail. oh my.

 I think the 2 op-amps survived but the 3 buffers were on their last legs 
	

	
	
		
		

		
		
	


	




 ground channel was 'gurgly', like under water sounding. bypassing ground channel (taking ground from input ground) was mostly ok.

 8620 had problems at various voltages, yet 2134 was ok almost all voltages.

 at lower listening levels, things were passable but as you turned the volume up, things distorted a lot.

 I replaced all 3 soic buffers. that fixed it.

 while I was in there, I put in the tangent fixes from v2.00 to 2.01. I think I got most of them:

 r7 goes from old of 10k to new of 100
 r4g goes from old of 4.7k to new of 4.32k
 c6g goes from old of 10pf to new of 4.7pf (I have not done this one yet)

 for now, I've left out r11 (l.r,g) entirely.

 I had extra buffers so I just clipped the old ones off the board (ouch!) and then soldered new ones in. first did l/r and verified that fixed the main channels. then did the ground buffer and that fixed it all.

 lesson: don't get power supply problems and you won't have to fix circuits downstream of them!


----------



## joneeboi

Where was R4G mentioned? Why was it changed?


----------



## linuxworks

obligatory update pics 
	

	
	
		
		

		
			




















 yes, its funny looking.

 you got a problem with that??









 it sounds quite nice. I like it a lot. even on a single 9v battery (which is what its running on now, inside the lower box) its great.


----------



## tangent

Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_Wow, I can get used to this much bass._

 

Yeah, there's something very clean about this style of bass boost, as compared to other implementations. (A typical graphic EQ or tone knob, for instance.) These new buffers help a lot, too, I think.

  Quote:


 The bass sounds great to me, so I have little impetus to get it "just right." 
 

What cap value did you use || R4?

  Quote:


 R4 is absent. I have the amp set up in unity boost. 
 

You certainly should have an R4. Unity boost needs it. If you're misspeaking and what you've left out is the equivalent of the PPA's R7, that's fine, but R4 isn't optional. If you really did leave it out, that would explain the DC offset, because you would then have no DC feedback path when bass boost is engaged.

  Quote:


 LM7818. Here's the different part for me....I don't know if tangent plans on incorporating this into the next design, but it can be done with this revision of board if you so desire. 
 

It's not clear to me what you're doing with this.

 The LM317 in the PIMETA v2 is officially only for charging a NiMH battery, as it's configured as a constant current source. Since I've not heard of using an LM78xx as a CCS, I'm guessing you're using it for its intended purpose, a voltage regulator. I don't immediately see how you're doing that, so if you could post a hacked copy of the PIMETA v2 schematic showing your connection changes and any trace breaks...?

 One of the things I have tried to work out is a way to change the LM317 from a CCS into a voltage regulator with the same board design. I haven't figured that out yet, but may revisit it before the final design push.

  Quote:


 Thanks, tangent, for including me in the proto group. I really liked the card. Classy. 
 

You're welcome, and thank you, too.

  Quote:


  Originally Posted by *linuxworks* /img/forum/go_quote.gif 
_r7 goes from old of 10k to new of 100
 r4g goes from old of 4.7k to new of 4.32k
 c6g goes from old of 10pf to new of 4.7pf (I have not done this one yet)_

 

Yes, those are the important ones.

 The R11 calculation changed since the 2.00 days, though the schematic doesn't show it.

 RBIAS changed from an unrealistic 3K to 5K. 2.5K can work, but doesn't give you as much adjustment range as you might want. RBLIM changed at the same time for related reasons, though there's no reason to change yours if your class A is adjusted the way you want now.

  Quote:


 lesson: don't get power supply problems and you won't have to fix circuits downstream of them! 
 

Yes. A berserk power supply can ruin your whole day.

  Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_Where was R4G mentioned? Why was it changed?_

 

Don't worry about it. The new value is just slightly more correct. It won't really affect anything.

  Quote:


  Originally Posted by *linuxworks* 
_yes, its funny looking._

 

I made a double-decker amp once, not entirely unlike that. Two mint tins glued back-to-back so I could have a spacious amp circuit in one and 2 x 9V in theother.


----------



## joneeboi

I have 0.1uF and 0.22uF paralleled with 50K for my bass boost. I _was _misspeaking earlier: you can't call my implementation unity boost. I left out R4, but I still don't see any DC. There was DC before I installed BB, so I will have to run some more tests later.

 For the power supply, I did use the LM7818 as a voltage regulator. I had to add two jumpers, but for the most part, it's a simple change. I hope the schematic is clear.


----------



## tangent

Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_I left out R4_

 

I still don't see how you can get away with that. That opens the op-amp feedback loop at DC. You still have feedback for music, since the caps are kicking in. Also, R4 is a fundamental part of the bass boost filter equation: no R in parallel with the C == no boost.

 Or am I still just misunderstanding what it is you're doing?

  Quote:


 For the power supply, I did use the LM7818 as a voltage regulator. I had to add two jumpers, but for the most part, it's a simple change. I hope the schematic is clear. 
 

Yes. It tells me that this really isn't something we can just offer via a jumper or something on the existing board. I may document something like this in the tweaks section, but what I was hoping for is that someone could solder an LM317 in the IC1 position, and with just a jumper or two on the board, reconfigure it as a voltage regulator instead of a current regulator.


 By the way, I finally got the benchmark pages up:

RMAA tests
square wave tests

 Whew! Lot of work in those pages.

 This puts us very near the end of the development process. This was the last major thing left to-do, along with deciding about the vreg issue. Is my TODO list missing something, or am I pressing the button on Monday, after spending the weekend staring at Gerbers?


----------



## joneeboi

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_I still don't see how you can get away with that. That opens the op-amp feedback loop at DC. You still have feedback for music, since the caps are kicking in. Also, R4 is a fundamental part of the bass boost filter equation: no R in parallel with the C == no boost.

 Or am I still just misunderstanding what it is you're doing?_

 

The caps are paralleled with the potentiometer.

 edit: I'm so sorry, I was talking about the PPAv2's R4. I don't have that R4, but I do have the PIMETAv2 R4 as the potentiometer.


----------



## cobaltmute

Ok after many weeks, I've finally been able to spend some time working on the Pimeta2 and my biasing issue.

 Replaced all the CCS transisitors and replaced R7 as 100Ohms as tangent suggested. Significantly improved the situtation. I am now able to run at 20V supply and have the bias up into the fairly deep rang (~11mA) with no issues. I can still reach a runaway point if I keep biasing, but I think I should be fine where I am 
	

	
	
		
		

		
		
	


	




 Now on to building the battery pack and casing.


----------



## sandbasser

joneeboi -

 Is there any chance you could post a photo or two of your board??? I like the idea of the LM78xx; but I couldn't figure out how to implement it.

 Many thanks,


----------



## tangent

v2.01 final?






 Changes since the v2.00 prototypes:

 - Changed RBIAS part to one with centered pins instead of offset

 - Inserted a pair of wire pads in series with RBLIM to make switching bias on and off easy. The pads are inline so you can just jump over this with the resistor leads if you don't want this feature.

 - Labelled B+ pad between C2 caps

 - Several minor value changes on the schematic, described above

 I expect to send this off for manufacturing tomorrow, barring any last-minute changes. This will take about a month, barely letting me slide under my "summer" deadline.

 Thanks to everyone for participating in this development process. The PIMETA v2 is better for it!


----------



## cobaltmute

Pimeta1 on the left and Pimeta2 on the right. They are variations on a theme - 12x AAA in the case with the power for the trickle chargers coming out of the right side of the case.

 v1 is running OPA2107/OPA227 with Monofied Sijosae buffers in LR and Buf634 in G. Bias is 3-4 mA if I remember correctly.
 V2 is running OPA2107/OPA602 with spec buffers. Bias is 11mA.

 Both sound very good. When switching back and forth between the two, I notice that the v2 is slightly brighter in the mid to high end. It is not fatiguing, and I have been listening to it for a while now.

 Took me a while, but I got there in the end. Thanks Tangent.


----------



## tangent

Still about two weeks of summer left!


----------



## funch

Slightly off-topic, but why does Internet Explorer abort my attempt 

 to go to his store page?


----------



## Reima

Quote:


  Originally Posted by *funch* /img/forum/go_quote.gif 
_Slightly off-topic, but why does Internet Explorer abort my attempt 

 to go to his store page?_

 

It does the same thing to me.
 RC


----------



## tangent

*EDIT*: It turned out to be an IE6/7 bug. IE8 and all other non-IE browsers coped with the new image popup feature on the shop page just fine. I've changed it to work on all browsers. But y'all might want to upgrade, too.


----------



## cobaltmute

Ctrl+Shift+F5 will force the browser to reload the page skipping the cache.

 Congrats on finally getting the boards into the shop.


----------



## Juaquin

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_*EDIT*: It turned out to be an IE6/7 bug. IE8 and all other non-IE browsers coped with the new image popup feature on the shop page just fine. I've changed it to work on all browsers. But y'all might want to upgrade, too. 
	

	
	
		
		

		
		
	


	


_

 

Might I suggest the Kill IE6 information bar? 
	

	
	
		
		

		
		
	


	




 I'm only half kidding. While that's a bit extreme (I use it on my site, but that might drive some people away...) there are _serious_ security risks when using IE6 and IE7, people. Especially when using those browsers to process transactions and credit card info. Upgrade to IE8, or better yet, Firefox or Chrome.

 Back on topic, the new board looks awesome and I'm doing one as soon as I finish the other couple projects I'm working on.


----------



## linuxworks

geeze, both amb and you (tangent) are using that popup graphic window thingie.

 what's up wid dat? 
	

	
	
		
		

		
			





 is this a new cult of sorts?

 seriously, I'm curious - why are websites going with MORE popups?

 javascript. brrrr. me no likey.


----------



## tangent

The shop page has been JS powered since its inception, and has absolutely required JS since January of 2007, when spammers began randomly submitting crap to every form on the Internet they could find, just in case it might do something interesting. (Try loading the shop page with JS disabled.) They don't yet usually bother to run pages through a JS interpreter to see if it generates a form they can spam.

 Regarding popups, the previous mechanism used an actual popup window, which most browsers now block or redirect to a separate page. The new mechanism at least pops up inline where you can see it, and goes away at a click.

 So no, I'm not changing it.


----------



## MrMajestic2

Would it work ok to run the Pimeta from a computer PSU? I had wild idea to put one in a drive bay.


----------



## Voodoochile

It would work, but it would probably be pretty noisy.
 Might be better to at least power a seperate linear PSU from the 12v rails of the computer's PSU.


----------



## nightanole

Id just filter the 12v. Just pretend the 12v is regulated and apply some fast caps and some large caps. Just make a make shift tread or YJPS without the regulator. just pop in c5,c6, and c8 of the tread in your 12v wiring to the amp. That gets your fast and large caps right there, and the amp itself will filter some of the noise too.

 Hell just get a tread for 5 bucks when you order the audio board, both will fit in any slot. Just feed the 12v pc in after the rectifier.


----------



## tangent

You also have an isolation problem. Search this forum for "USB power". It's the same problem, only you have the option of using either the +5 or +12V rail, instead of just +5. Working around the isolation issue is harder than dealing with low voltages.


----------



## acvtre

Hi everybody, I've got a couple of questions. I was wondering If I can use only a 9V battery to power the pimeta and if the answer is positive, if I can solder the cable of the battery clip in the holes labeled wall.
 Another thing, I can't realize how and where I can solder the I/O jacks. 

 Sorry, I'm a biiiiiiiiiig noob.
 Already read about 5 times the tangentsoft guide.


----------



## nightanole

The unit can use 5v-30v depending on your parts you picked out. If you had 600 ohm beirs then 9v isnt good enough and you would have made a 30v unit. On the other hand if you had 16-32 cans then 9v is enough for you to go deaf 
	

	
	
		
		

		
		
	


	




 So no you are not limited to a 9v battery

 Wall on the board refers to a external unregulated power source that is higher in voltage then your battery. Wall runs thru a diode and UC1 regulator to both power the unit and charge the battery.

 If your going to make one without abattery, then soldering your power supply to wall is a good idea. 

 However soldering a battery to wall is a bad idea. It will go dead pretty quickly.

 Solder your outs to OL,OR,OG. Output left, output right, and output groud. Dont let output ground touch chassis ground.

 Solder your inputs to InputsiL,InputsiR,InputsiG. They are in one spot in the middle labeled IL,IR,IG.


----------



## acvtre

Quote:


  Originally Posted by *nightanole* /img/forum/go_quote.gif 
_The unit can use 5v-30v depending on your parts you picked out. If you had 600 ohm beirs then 9v isnt good enough and you would have made a 30v unit. On the other hand if you had 16-32 cans then 9v is enough for you to go deaf 
	

	
	
		
		

		
		
	


	




 So no you are not limited to a 9v battery

 Wall on the board refers to a external unregulated power source that is higher in voltage then your battery. Wall runs thru a diode and UC1 regulator to both power the unit and charge the battery.

 If your going to make one without abattery, then soldering your power supply to wall is a good idea. 

 However soldering a battery to wall is a bad idea. It will go dead pretty quickly.

 Solder your outs to OL,OR,OG. Output left, output right, and output groud. Dont let output ground touch chassis ground.

 Solder your inputs to InputsiL,InputsiR,InputsiG. They are in one spot in the middle labeled IL,IR,IG._

 

Ok great, for now I've got only a 9V battery and a battery clip with only the red and the black cable, where do I have to solder these two cables?
 The ground should be the wood table because I don't want to build the enclosure. Is it good enough?


----------



## nightanole

You dont have to ground anything. However if you have a metal case, you dont want the input ground to be touching the outputground.

 Your battery clip with a red and black cable is called a "pigtail" if you want to call it by its real name.

9V Battery Pigtail - Autocom America

 Solder your pigtail to your battery in on the unit "-bat+" next to wall. Red goes to + and black to -.


----------



## acvtre

Ok, now the problem is: where do I have to solder the toogle switch and the big problem are the jacks.
 I bought two kind of jacks, this kind 35RAPC4BH3 Switchcraft Audio/Video Connectors is strange because it has more than 3 pins so I don't know how to solder it.
 The second type is this one N112BPCX Switchcraft Audio/Video Connectors
 do I have to solder the pins soldering any order or it makes no difference?


----------



## nightanole

Ok install the toggle switch on the red wire. So it should go red wire, toggle switch, then to the unit.

 Your 35rap style connector is a switched type, thats why it has more then 3 connectors. Odds are it has 5. Its used when you have a internal and external music source. When there isnt a jack in the plug, 2 sets of pins are shorted together so the sound is coming from inside the unit. When you plug in your external source, then the switch is broken and the internal sound is cut off and the plug will feed the sound from your external source.

 I would go with your N112 connector for both your in and out if you can. Its real easy to solder to and only as 3 prongs.

 Now for soldering the thing. You have 3 terminals, tip, ring, and sleeve. Tip is left, ring is right, and sleeve is ground. If you dont have a multimeter then this is gonna be kind of tough to figure out. You have to get sleeve right, worse case if you get ring and tip mixed up is that you have to put your head phone on backwards
	

	
	
		
		

		
		
	


	




HeadWize - Headphone FAQs


----------



## acvtre

I've got 2 N112 but the pins have got little holes and I can't understand which one is right or left.
 Another thing: the toogle switch has got two pins with holes, if the red wire is only one, how can I solder with one wire the switch and the pcb?

 EDIT: 
 Ok maybe I've understood which one is the right and which the left. As soon as I plug in the headphone plug in the jack I can see a little "draft" the touches the ring and another that touchs the tip.
 Now the problem is the toogle switch, then I can start soldering.


----------



## nightanole

I cant help you understand. You have 3 pins with holes, they are left right and ground, but i cant tell you which is which because i dont have that plug in front of me. From the looks of things, looking at the back of the plug, the shaved off corner pin is sleeve, the one clock wise of the shaved corner is ring, and the one counter clockwise of the shaved corner is tip.

 As for the switch. You solder the red wire to one pin, then another wire to other pin. You then run the other wire to the "+" of the batt in.


----------



## acvtre

OK great, thank u so much. As soon as I finish to solder and it works I'll tell you.

 Cheers!


----------



## acvtre

In the part list there aren't the resistors. Which kind of resistors do I have to use?


----------



## tangent

Resistors are generic. There are many kinds you can use, they're available everywhere, and there's no big reason for me to recommend a particular kind. There are only two important rules for most of the resistors: use metal film types, and make sure they'll fit the 300 mil pin spacing. Other than that, use whatever is convenient for you, or which makes you happy.

 Personally, I use Vishay-Dale RN55Ds, from Mouser.

 EDIT: Some of the resistors have different pin spacing and some have wattage requirements, covered in the parts guide.


----------



## acvtre

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Resistors are generic. There are many kinds you can use, they're available everywhere, and there's no big reason for me to recommend a particular kind. There are only two important rules for most of the resistors: use metal film types, and make sure they'll fit the 300 mil pin spacing. Other than that, use whatever is convenient for you, or which makes you happy.

 Personally, I use Vishay-Dale RN55Ds, from Mouser.

 EDIT: Some of the resistors have different pin spacing and some have wattage requirements, covered in the parts guide._

 

Ok, thank you so much, sorry but I'm the biggest noob ever. I would like to have a balanced amp so, as you suggest in your guide, I'm going to use the scratchpad as fourth channel. How can I do that?


----------



## diditmyself

Quote:


  Originally Posted by *acvtre* /img/forum/go_quote.gif 
_Ok, thank you so much, sorry but I'm the biggest noob ever. I would like to have a balanced amp so, as you suggest in your guide, I'm going to use the scratchpad as fourth channel. How can I do that?_

 

You'd better use two boards without ground channels.


----------



## acvtre

Quote:


  Originally Posted by *diditmyself* /img/forum/go_quote.gif 
_You'd better use two boards without ground channels._

 

What does it mean? So, how would you use the scratchpad?


----------



## cobaltmute

The issue with trying to just add a fourth channel to the board is that the ground channel is not the same as the other two channels. You need four identical channels to do balanced. Using two boards would give you the four identical channels + two grounds.


----------



## acvtre

Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_The issue with trying to just add a fourth channel to the board is that the ground channel is not the same as the other two channels. You need four identical channels to do balanced. Using two boards would give you the four identical channels + two grounds._

 

So how can i link two pimeta boards? How have you used the scratchpad?


----------



## diditmyself

Quote:


  Originally Posted by *acvtre* /img/forum/go_quote.gif 
_What does it mean? So, how would you use the scratchpad?_

 

I'm not suggesting you should use the scratch pad at all. I mean, I don't think you can build a portable balanced pimeta because you need a 4 ch pot and some kind of "balanced" connectors, so size shouldn't be an issue. To my knowledge there are no portable balanced sources either. You need 4 channels. It must be easier to use the L/R channels of one board as L pos/neg and the other board as R pos/neg, than to cram in one more channel with all parts needed on the sctrachpad. I think there are some balanced old PIMETAs out there. Do some searching to see how they're made.


----------



## cobaltmute

If you are looking for ideas on what to do with the scratchpad, check the PimetaV2 thread at Headwize. IIRC there were some ideas floating around in the design discussions.


----------



## tangent

Quote:


  Originally Posted by *acvtre* /img/forum/go_quote.gif 
_Ok, thank you so much, sorry but I'm the biggest noob ever. I would like to have a balanced amp so, as you suggest in your guide, I'm going to use the scratchpad as fourth channel. How can I do that?_

 

No one's worked out the details and posted it yet. Noobs don't make good pioneers. 
	

	
	
		
		

		
			





 My advice is to build it with 3 channels now, enjoy it while the pioneers do their work, and then evaluate later whether to convert to four channels.

  Quote:


  Originally Posted by *cobaltmute* 
_the ground channel is not the same as the other two channels_

 

True, but off the top of my head, the biggest problem is just the lack of gain in the ground channel. This means either you configure all channels for G=1 -- getting G=2 due to the balanced action -- or just solder-tack an R3G into the ground channel if you really must have G > 1.

 This from someone who has never built a balanced amp. Find salt grains. Apply appropriately.


----------



## acvtre

Hi guys, since I'm a noob do you have a set of resistors do suggest? I mean something that surely works good, how much bias, gain etc etc. I need only them in order to put the word end to the work.


----------



## acvtre

Ok, I've built the pimeta V2 but nothing works maybe because I can't solder the switch.
 How should I solder the switch?


----------



## MisterX

There are lots of different kinds of switches available. It helps if you narrow it down a little. 
	

	
	
		
		

		
		
	


	




How to Wire Panel Components


----------



## acvtre

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_There are lots of different kinds of switches available. It helps if you narrow it down a little. 
	

	
	
		
		

		
		
	


	




How to Wire Panel Components_

 

I've got this one 10TA805 Mountain Switch Toggle Switches
 How do I have to solder it? I mean there are two pins on the pcb and the toggle has other two pins.


----------



## MisterX

If you are using a RK27 pot simply connect a wire from one of the terminals on the switch to one of the "S1" pads on the circuit board. 
 Then connect another wire from the other switch terminal to the other "S1" pad on the circuit board (It doesn't matter which switch terminal is wired to which pad with a SPST switch (nobody is going to call a wambulance if you install your switch upside down)).
 If you are using a RK097 pot you won't need to wire in a switch...


----------



## acvtre

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_If you are using a RK27 pot simply connect a wire from one of the terminals on the switch to one of the "S1" pads on the circuit board. 
 Then connect another wire from the other switch terminal to the other "S1" pad on the circuit board (It doesn't matter which switch terminal is wired to which pad with a SPST switch (nobody is going to call a wambulance if you install your switch upside down)).
 If you are using a RK097 pot you won't need to wire in a switch..._

 

Ok so everything is right, since I've got a RK27 pot but.....nothing works. Not even the led lights up. What do I have to check?


----------



## MisterX

What pads on the circuit board do you have the power supply connected to? 
 May be more direct to post a couple of pictures so we can double check the wiring....


----------



## acvtre

Quote:


  Originally Posted by *MisterX* /img/forum/go_quote.gif 
_What pads on the circuit board do you have the power supply connected to? 
 May be more direct to post a couple of pictures so we can double check the wiring...._

 

The pictures will arrive in the afternoon. I've got a battery pigtail, red in the V+ pin black in the V- pin.


----------



## MisterX

Do you have the diodes in the right way around?


----------



## acvtre

I've just senn that I haven't soldered the buffer chips, cn it be a problem?
 However the diodes are okay.


----------



## tangent

The power LED should still light up with no buffers soldered in.

 Post pics and voltage measurements between IG and all the power pins in the circuit.


----------



## sgtroyer

Hi folks, I'm working on planning an amp / dac to sit on my desk at work. I don't intend to include battery power since it's not going to be portable. With that in mind, would the canonical AD8620/8610 op-amps still be the sensible choice, or should I "upgrade" to something like the AD843? From my understanding of tangent's op-amp reviews, the big advantage of the 8620 is that it works well with batteries. Low voltage requirements, low current draw. Since neither of those are really a consideration with a wall supply, I'm inclined to try out the 843, if it might sound a little better. The price difference is pretty small.

 On the other hand, has anybody even tried the 843 in the pimeta v2? I'm not sure how much pathclearing I want to do on my first attempt. After all:

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Noobs don't make good pioneers._

 

Any thoughts?


----------



## tangent

Quote:


  Originally Posted by *sgtroyer* /img/forum/go_quote.gif 
_has anybody even tried the 843 in the pimeta v2?_

 

I'll get around to it someday. 
	

	
	
		
		

		
			





  Quote:


 I'm not sure how much pathclearing I want to do on my first attempt. 
 

Well, this question is a little different from the post you quoted me replying to. You can't break the amp by using the wrong op-amp. You just have to be prepared to do tests and have a fall-back plan if it doesn't work. Do a current measurement test before plugging headphones in, start with cheap phones you can afford to fry, and only then step up to the good ones.

 It might be nice if you had a current-limited power supply, but lots of people roll op-amps without one.

 If you're not prepared to buy multiple sets of op-amps or are unwilling to do careful testing, best wait for someone else to be the pioneer.


----------



## sgtroyer

Hmmm, might be fun. I don't have a current limited supply, just the el-cheapo variable supply built into my breadboard. I mean, it's definitely current limited, just not in the way that you want. But I can bring it up gradually and keep an eye on the current draw as I do so. I've got a scope, not much of a scope, but probably enough for audio debugging. I assume the failure mode here is oscillation? Drive a square wave and look for ringing on the output?

 Other than the fun of messing around and forging ahead, is this worth it? Is the AD843 "better"?

 The fact that no one has done this yet makes me wonder if anyone really sees any value in it.


----------



## cobaltmute

Quote:


  Originally Posted by *sgtroyer* /img/forum/go_quote.gif 
_Other than the fun of messing around and forging ahead, is this worth it? Is the AD843 "better"?

 The fact that no one has done this yet makes me wonder if anyone really sees any value in it._

 

Just because no one else has used it doesn't make it a bad chip. Yes you'll burn a few dollars in chips, but then you'll know if the chip works for you.

 You can check the Op-amp thread for what some people will do for different opamps.


----------



## tangent

Quote:


  Originally Posted by *sgtroyer* /img/forum/go_quote.gif 
_I assume the failure mode here is oscillation?_

 

Yes. My comments about frying headphones are because rail-to-rail oscillation looks like really really loud obnoxious music to the cans. Beware that an amp that doesn't oscillate without phones plugged in could still take off into oscillation once you do plug something in, due to capacitive loading and such. Cans are a complex network of Rs, Cs and Ls.

  Quote:


 Drive a square wave and look for ringing on the output? 
 

That would be good. You want to do that anyway, if you have the tools for it, since that helps you pick optimal C6es. And that in turn is an option for making these chips work if they don't, initially: increasing C6 can rescue an amp that won't work with C6 left out or using its low default value.

  Quote:


 The fact that no one has done this yet makes me wonder if anyone really sees any value in it. 
 

*Shrug*. You've read my review....I like 'em. They're not my absolute favoritest chips in the whole wide world, but they're certainly worth trying if you've got the cash and time.

  Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_Just because no one else has used it doesn't make it a bad chip. Yes you'll burn a few dollars in chips, but then you'll know if the chip works for you._

 

True, though a trio of AD843s is a significant chunk of change. Pizza dinner tonight or rollin' chips? Tough choice.


----------



## sgtroyer

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Beware that an amp that doesn't oscillate without phones plugged in could still take off into oscillation once you do plug something in, due to capacitive loading and such. Cans are a complex network of Rs, Cs and Ls._

 

Wouldn't the buffers mostly isolate the op-amp from the complexities of the load, though? It still feeds back, I guess, so something ugly could happen.

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_True, though a trio of AD843s is a significant chunk of change. Pizza dinner tonight or rollin' chips? Tough choice._

 

They aren't cheap, but neither are the AD8620/8610. By my math, once I've bought the necessary brown dog adaptors, the 8620/8610 solution is $26.65 from digikey (and out of stock), while 843 is $32.98 for three op amps and an adaptor. So the price difference is all of $6.33. The AD843 is actually cheaper for OPAG than AD8610 because, being dip, it doesn't need an adaptor. 

 Of course, that math all hinges on them *working*. If I fry them, or have to get a replacement because I can't make them work, it looks more expensive.

 Speaking of expensive, I didn't realize how fast those square wave tests you're using are. I figured they were well within the audio band and I could just use a soundcard or my spiffy new, yet to be built, DAC to drive the amp, and watch it on my 5MHz heathkit scope. To drive the kind of square waves you're using, I would need an actual signal generator. And a better scope wouldn't hurt either. 

 Both of which I want, so having an excuse is okay, but it makes the cost of op amps the least of my problems. 

 Any advise for signal generator shopping? 20MHz or so? I know Tektronix is a favorite brand for scopes, is there a corresponding popular choice for sources?


----------



## Beefy

Quote:


  Originally Posted by *sgtroyer* /img/forum/go_quote.gif 
_The AD843 is actually cheaper for OPAG than AD8610 because, being dip, it doesn't need an adaptor._

 

Why not just solder the SOIC-8 OPAMPs to the bottom of the board on the SMD pads?


----------



## tangent

Quote:


  Originally Posted by *sgtroyer* /img/forum/go_quote.gif 
_is there a corresponding popular choice for sources?_

 

Agilent makes me happy, but I can well understand if they make you very unhappy after you see the prices.

 My previous sig-gen, a B+K 4017A, was flaky as a box of Wheaties. 1.8% THD on the "sine wave" output, square waves that ring pretty badly, low build quality... It's back in the box now. Anyone want it?


----------



## sgtroyer

Quote:


  Originally Posted by *Beefy* /img/forum/go_quote.gif 
_Why not just solder the SOIC-8 OPAMPs to the bottom of the board on the SMD pads?_

 

Fair enough, I guess I could. I just like the idea of sockets in case something goes wrong, or I change my mind. 

  Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Agilent makes me happy, but I can well understand if they make you very unhappy after you see the prices._

 

Agilent makes me happy, too. I used to work there, so I've got a soft spot in my heart for anything Agilent or HP. But $1200 for a signal generator? Little bit out of my price range. I think I'll watch ebay for an old HP. Maybe I'll look for an old HP bench supply to keep it company. Then get a Tek scope so they can fight.


----------



## cobaltmute

I think you should get something like this:





 To be honest I've got the check if it actually outputs a signal. It powers up, but it has been in the basement for a *long* time.

 Pre-post edit - I just Googled this thing - it apparently runs on tubes.


----------



## Skoalman

I'm not getting the correct values when testing the power supply in step 11 of the step by step assembly guide. It appears the voltage isn't being split. Here are the voltages I'm getting with a slightly used 9v battery:
 OPALR V- -8.77 V+ -.56
 OPAG V- -8.77 V+ -.56
 TLE2426 COM -8.77 OUT -4.66 IN -.56
 I also measured the + and - pins of the power caps and got -8.77 on the negative pins and -.56 on the positive pins. Any ideas on what would cause this? I have no idea where to go from here other than maybe replacing the tle2426.


----------



## linuxworks

anyone want any signal generator chips? 
	

	
	
		
		

		
			





 I found some old (very old) 8038 chips. anyone remember those? those used to be good (sort of) way back when.

 new chips are MAX038 (from what I've read). but I have some IC8038's in DIP form in case anyone wants any


----------



## Skoalman

I just remeasured the voltages and on OPALR and OPAG and got
 4.09 for V+ and -4.09 for V-. I used a different spot the board to
 measure the input ground IG. This time I used the area in the
 scratchpad marked IG. Previously I was measuring from where the
 input ground IG is right by IL and IR. I also measured this time by
 using the top of the board so I could just stick one probe in a DIP
 socket and the other probe in the hole marked IG in the scratchpad
 area. When I use the bottom of the board I have a harder time
 with the measurements because the probes want to move around
 the soldered connections causing the voltage measurements to jump
 around. I think my original issue with the voltages was just with me
 not being able to hold the probes still enough.


----------



## HD-5000

Alright, I think I'm going to build one of these babies. 

 If I am, I would build it in the standard Serpac case with the 9V battery cover. Could someone give me tips on picking parts to strike a nice balance between SQ and battery life? I imagine that I would use this amp maybe 50% home, 50% on the go. Good battery life would be a plus.

 Thanks.

 edit: actually, good battery life isn't THAT important because I would use rechargeable batteries. Maybe if it could last 15-20 hours, I would be happy.


----------



## MisterX

Quote:


 Maybe if it could last 15-20 hours 
 

You are going to have to leave the buffers out to get anywhere close to that .. otherwise you are looking at closer to 4 hours with a single 9 volt NiMH battery.


----------



## tangent

With a 500 mAh LiIon "9V" rechargeable, you might get close to 10 hours. That runs the cost up due to the special battery and equally special charger, though.

 As for parts advice, I've said pretty much all I have to say in the docs. Hint.


----------



## Skoalman

Just finished my pimeta. I only have a couple of hours of listening time
 on it but i'm loving it. I've only heard this amp and a cmoy I built and
 i'm really impressed with how good music sounds at low volumes with
 this amp. I can't believe there is so much impact at low volume levels.

 I didn't class A bias so I'll have add that later. I'm really curious to see
 if there any sonic differences with the class A biasing. Just ordered a
 tread today to hookup to the pimeta. It will fun to see how it sounds
 with a tread vs 9v battery.

 Thanks for a great amp Tangent. I wish I didn't have to work tonight so I could stay home and play with my new toy.


----------



## tangent

Quote:


  Originally Posted by *Skoalman* /img/forum/go_quote.gif 
_i'm really impressed with how good music sounds at low volumes with this amp. I can't believe there is so much impact at low volume levels._

 

Yeah, the LMH6321 is a studly little thing. Much better than the BUF634.

  Quote:


 Thanks for a great amp Tangent. 
 

You're welcome! Thanks for the review.

  Quote:


 I wish I didn't have to work tonight so I could stay home and play with my new toy. 
 

Listen at work?


----------



## HD-5000

Just finished the main stuff on the amp. Parts selection and assembly was straightforward with tangentsoft's guides, and soldering took just a few hours. When it came time to test out the amp with headphones, I was greeted with glorious music, no troubleshooting required. It surprised me considering how much of a klutz I am with this kind of stuff. 

 Right now I'm just powering it with a 9V battery, but I do have a tread I need to finish.

 I think I will stick it in a case after a round of tests coming up.


----------



## HD-5000

Oh I forgot, I used an OPA2132 and an OPA132 for the ground channel. Gain of 3. I think I may bump it up to 5 to ensure that I can achieve earsplitting levels with any headphone.


----------



## tangent

Nice!

 On the gain, what cans were you testing with, and where was the knob in clock terms?


----------



## HD-5000

Monster beats Solo - These headphones are very sensitive, so I keep it around 11 o'clock for massive sound.

 Klipsch S4 - Even more sensitive, 9-10 o'clock.

 Grado SR-80 - Much less sensitive than either of the above, so I crank it to around 12.

 Sennheiser HD580 - Also around 12.

 The amp is more than loud enough right now, but I could see myself using quieter sources in the future (and I've been listening to mostly hip hop lately. Classical/jazz music is quieter and I could use some more knob travel to be comfortable).


----------



## tangent

Okay, just realize that the higher the gain, the higher the noise floor. Raise it too much and you can get audible levels of hiss, especially with the more sensitive headphones.


----------



## HD-5000

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_Okay, just realize that the higher the gain, the higher the noise floor. Raise it too much and you can get audible levels of hiss, especially with the more sensitive headphones._


----------



## Judge Buff

Can anyone tell me the maximum height of C2 for the Serpac H-65? Is it 15 or 16mm?

 This BOM is getting a little pricey... I may need to do a little sweet-talking to the Mrs.


----------



## tangent

Quote:


  Originally Posted by *Judge Buff* /img/forum/go_quote.gif 
_Can anyone tell me the maximum height of C2 for the Serpac H-65? Is it 15 or 16mm?_

 

More like 10 mm or 12.5 mm, depending on the cap diameter and whether you're willing to bevel the board edges so it sits lower in the case.

 I like to bevel the edges regardless so I can run the pot shaft straight out of the exact center of the front panel.


----------



## Judge Buff

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_More like 10 mm or 12.5 mm, depending on the cap diameter and whether you're willing to bevel the board edges so it sits lower in the case.

 I like to bevel the edges regardless so I can run the pot shaft straight out of the exact center of the front panel._

 

Thanks, tangent. Since I will only be using a 9V NIMH, can I get away with 10V caps at C2 or do I need to go with 16V or higher?

 Sorry for the noob questions...


----------



## tangent

Quote:


  Originally Posted by *Judge Buff* /img/forum/go_quote.gif 
_can I get away with 10V caps at C2_

 

"9 V NiMH" is a misnomer.

 There are three varieties, with 6, 7 and 8 cells, at 1.2 V each nominal, for 7.2, 8.4 and 9.6 V nominal for the battery. Charging NiMHs requires about 1.5 V per cell, so only the 7.2 V variety will let you get away with 10 V rail caps.


----------



## pulsar08

I have a +/-12v dual regulated supply that is lying around. I checked to see if it's isolated and I think it is. Is it possible to use a dual supply with a pimeta that also has nimh batteries? Do I just keep TLE2426 as designed and connect the V+ and V- and leave ground unconnected or would there be a way to leave TLE2426 out and still charge the batteries (15xAA nimh)

 I also have a +/-15v dual regulated but Power Supply Matters says:  Quote:


 The PIMETA can run on anything from about 5 to 30 V. The extremes pose some problems 
 

 What are the issues involved with this much voltage? From the data sheets I think ad86xx are only useable with below 26v so this might be what you're refering to but I'm not sure I'm even reading that right.


----------



## pulsar08

Oh yeah. Sorry. I forgot about the second issue I have.

 Which caps would be best for power supply rails. Assuming I can use the +/-12v supply/15xAA nimh. The tallest caps my enclosure can hold are 34mm. 

 I'm considering these which are available on mouser:

 3x 647-UHD1H681MHD 680uf 50v Nichicon HD 12.5x31.5mm total impedance .007ohms

 3x 647-UPM1V681MHD 680uf 35v Nichicon PM 12.5x25mm total impedance .012ohms

 3x 647-UPM1E681MPD 680uf 25v Nichicon PM 10x31.5mm total impedance .0153ohms

 I'm not sure if impedance was the main thing to look at or if being near to the max voltage was more important.


----------



## tangent

Quote:


  Originally Posted by *pulsar08* /img/forum/go_quote.gif 
_Is it possible to use a dual supply with a pimeta that also has nimh batteries?_

 

I don't see why not.

 The ground channel isn't pulling much weight when you use a dual supply. Consider converting your PIMETA to a 2-channel amp if you use this supply.

  Quote:


 What are the issues involved with this much voltage? 
 

Aside from limiting your chip selection, it pushes you to 35 V rail caps, which means you sacrifice quality or capacity relative to equivalent 25 V ones if you can get away with a 24 V or lower supply. It also means the amp gets warmer.

  Quote:


  Originally Posted by *pulsar08* /img/forum/go_quote.gif 
_Which caps would be best for power supply rails._

 

There's vast advice on this topic in the archives, and a fair bit in the PIMETA docs, too.


----------



## pulsar08

Quote:


  Originally Posted by *tangent* /img/forum/go_quote.gif 
_it pushes you to 35 V rail caps, which means you sacrifice quality or capacity relative to equivalent 25 V_

 

I don't understand this relationship you claim between voltage and quality. Looking at previous discussions to me has been inconclusive because some claim that the voltage rating doesn't influence quality at all and some claim it does. 

 This list I posted for instance seems to indicate the complete opposite because the 50v capacitors have a lower impedance. 

  Quote:


  Originally Posted by *pulsar08* /img/forum/go_quote.gif 
_I'm considering these which are available on mouser:

 3x 647-UHD1H681MHD 680uf 50v Nichicon HD 12.5x31.5mm total impedance .007ohms

 3x 647-UPM1V681MHD 680uf 35v Nichicon PM 12.5x25mm total impedance .012ohms

 3x 647-UPM1E681MPD 680uf 25v Nichicon PM 10x31.5mm total impedance .0153ohms_

 

Could you please just look at this list to help me understand which is the best choice.


----------



## tangent

You're not comparing apples to apples. You'd have to compare caps varying only in voltage ratings. The ones you're comparing vary in can size, too, at the least.

 As to your plea that I give specific part advice, sorry, won't do it. Maybe someone else will. I much prefer to give more general advice that will help you pick your own parts. This is DIY, not letmeDIYthatforyou.


----------



## jcaps

Quote: 





misterx said:


> If you are using a RK27 pot simply connect a wire from one of the terminals on the switch to one of the "S1" pads on the circuit board.
> Then connect another wire from the other switch terminal to the other "S1" pad on the circuit board (It doesn't matter which switch terminal is wired to which pad with a SPST switch (nobody is going to call a wambulance if you install your switch upside down)).
> If you are using a RK097 pot you won't need to wire in a switch...


 

 First off, I'm super new to this stuff as well. Just completed two CMoys, so decided to move onto the Pimeta v2.
   
  I'm using the RK097 with built in switch. Therefore, I don't need an additional switch at S1 (right?). So can I just jumper S1 - I figure I still need to complete the circuit? I don't see any reason to use a molex here either (as tangent uses) with the RK097.
   
  Am I correct here.
   
  Cheers.


----------



## MisterX

Quote: 





jcaps said:


> First off, I'm super new to this stuff as well. Just completed two CMoys, so decided to move onto the Pimeta v2.
> 
> I'm using the RK097 with built in switch. Therefore, I don't need an additional switch at S1 (right?). So can I just jumper S1 - I figure I still need to complete the circuit? I don't see any reason to use a molex here either (as tangent uses) with the RK097.
> 
> ...


 


 Depends.
  Jumpering the S1 pads would defeat the switch in the RK097 (you would not be able to turn the amp off) so you might want to re-think that one


----------



## tangent

I've updated the new schematic to show that the RK097's built-in switch connects V+ and B+, just as S1 does.


----------



## GregVDS

Hello,
   
  Long time no see!
   
  I'm interested by the Pimeta V2 with Linkwitz. But I would mainly use it with a Nagra VI. Source would come from the balanced XLR 4.4V, and power from the Hirose 12V of the Nagra.
  I'm wondering if someone knows how I can convert balanced to unbalanced input, so I can feed it to the Pimeta?
  I was also fearing to have ground loops and hum and buzz from mixing ground from the Hirose and balanced cold?
   
  What do you think?
   
  And some more in fact:
  If I want to replicate balanced input signal towards balanced output XLR, what should I do, simply hardwire it? What will be the sonic effect of having a headphone amp in parallel on the output of the Nagra with other fed equipments?
   
  Gedupaaaaa


----------



## tangent

Quote: 





gregvds said:


> I'm wondering if someone knows how I can convert balanced to unbalanced input, so I can feed it to the Pimeta?


 

 http://pinouts.ru/Home/xlr3_pinout.shtml
   
   
  Quote: 





> I was also fearing to have ground loops and hum and buzz from mixing ground from the Hirose and balanced cold?


 
   
  Unlikely.  I can't say I've ever heard of someone getting a new ground loop after adding a headphone amp to a previously quiet system.
   
   
   
  Quote: 





> What will be the sonic effect of having a headphone amp in parallel on the output of the Nagra with other fed equipments?


 
   
  Not a good idea.  That parallels the input sections, which means they'll likely interact audibly.
   
  Preamps exist for a reason, and almost all of them are active for the same reason.


----------



## GregVDS

mmh,
   
  the pinout of an XLR is one of my knowledge. At least I can find docs explaining without too much problem.
   
  I was more thinking of something like this:
   
  http://www.jensen-transformers.com/an/an003.pdf
   
  in which one can find active circuits to pass a balanced signal into an unbalanced one, and vice-versa.
   
  So I was thinking of using such schematic in front of the input of the pim, maybe with a selector switch to select a second unbalanced input.
   
  Now I would like to keep balanced line through the pimeta, so I should pick up the signal, and have it re-balanced to an output.
   
  So, Anyone with suggestions for this is welcome.
   
  Thanks,
   
  Greg


----------



## tangent

Quote: 





> in which one can find active circuits to pass a balanced signal into an unbalanced one, and vice-versa.


 
   
  Why add yet another active stage when it's not necessary?
   
   
   
  Quote: 





> Now I would like to keep balanced line through the pimeta, so I should pick up the signal, and have it re-balanced to an output.


 
   
  Look into 4-channel amps.  You could probably use the PIMETA v2 scratchpad to build a fourth channel and hack the ground channel to be its mate.


----------



## GregVDS

Maybe so, the more I think about it, the more I think it will be easier to use an unbalanced input into a balanced amp rather than the contrary.
   
  Thanks,
   
  Greg


----------



## caughtthought

I've been working the last couple of days on a Pimeta v2. I've gotten it mostly put together, successfully tested the power supply, and gone on to the buffers. I soldered pin 1 of the first buffer to its pad, and then gently nudged one of the other pins with my iron. The chip simply fell off the board, pad and all.
   
  I think the work that I have put into the amp has instantly been trashed. These are the only components that absolutely have to be surface mounted, and with no pad, there is no way to attach it. Correct?
   
  I am going to get a drink.


----------



## sandbasser

check the schematic... that pin is probably not used if it fell off that easily...  (Something similar happened to me on a Mini^3.)


----------



## caughtthought

Yes, thanks, I figured out what to do after I stopped freaking out about it and looked at the schematic. Pin 1 goes to V-, I will jerry rig that pin and hopefully it will work fine.


----------



## yaaayoldthings

If I want 3 milliamps from biasing by using the stock values and don't want adjustability, do I solder RBLIM so that it "spans the switchable bias jumper pads" as shown in the step by step assembly guide, or do I solder it so that it spans all the way into the RBIAS slot too?


----------



## tangent

Your question is answered at the bottom of the parts selection guide section on RBLIM: http://tangentsoft.net/audio/pimeta2/pguide.html#RBLIM  There's even a picture.


----------



## yaaayoldthings

Well I mean, that's what confuses me. So the assembly guide assumes that you'll be wanting to use an adjustable trim pot and the selection guide doesn't. I was just making sure is all.
   
  Oh also, the schematic values for C3 says that it should be 470 uF but the part selection guide/list says and gives parts for .1uF. This also confuses me and I'm kind of wary of soldering any on since the values are so different.
   
  I didn't want to bump the thread so edit: Thanks for fixing things! I appreciate the clarifications.


----------



## tangent

All fixed now.


----------



## funch

Aw nuts!!  Just checked my DC offset. OG about 1mV; OR about 25mV; OL about..... 233mV!?*#%
  Solder joints look good, nothing gets hot, everything else checks out. Using AD8066/8065. Battery
  power (1 - 8.4V NiMH). Any ideas?
   
  Oops! Just realized I don't have anything in C6G 'cuz I only ordered two cap's instead of three.
  Maybe that' the problem with the ground channel.


----------



## tangent

Yes, C6 is most definitely not optional.


----------



## funch

Well, um, er, it appears that all I did wrong was install the L channel buffer BACKWARDS!!!!
   
       Jeez! Now I know why my name and the word 'smart' never appear in the same paragraph.


----------



## funch

All is well. I replaced the L channel buffer, installed a 33pF C6G that I had and it's up and it's sounding great. Now I need to
  order some 25V C2's as I'm measuring a little over 17V to the (16V) C2's I've got in there now when I connect
  the 18V PS to charge the battery. The 25V cap's are 16mm tall, so I hope they'll fit.


----------



## tangent

Good to hear it.
   
  A cheaper way to fix the C2 problem would be to put another diode or two inline with the power supply's V+ line.
   
  Also, be sure you're measuring at the caps, not at the power inlet pads on the board.  The existing on-board diode OR bridge will buy you a half a volt or so already.


----------



## funch

Yep, measured at the cap's; 17.1V. I'll try new C2's since I have to put in an order anyway. I'll report back if the 16mm tall cap's fit in the Serpac. Or should
  I say, how I got them to fit.


----------



## Takaji

I finally got around to getting the plates printed for my pimeta, and here's the results:
   


 


   
  I only wish I had gone with some larger knobs, as the alignment pins on the crossfeed and volume shafts are visible. But I'm fine with that!


----------



## tcpoint

Nice build.  Where / how did you get the plates printed?


----------



## Takaji

Quote: 





tcpoint said:


> Nice build.  Where / how did you get the plates printed?


 

 I sent them to a metal etch company in my city. Just provided him with a pdf of the design, as well as dimensions of the plate... the case is a Hammond case.


----------



## funch

My build is finished. Pix:
































   
  Opamps are AD8066/65. C2's are 470uF/25V FM's; 16mm tall and they fit. Barely.
  Signal wiring is SPC.
   
  iPod is 5G diyMod w/Blackgate cap's in the LOD. Now I'm on the hunt for a pair
  of sealed cans. Maybe the Phiaton MS400's to match.


----------



## Takaji

Very nice! The red case matches your red iPod


----------



## tangent

Quote: 





> C2's are 470uF/25V FM's; 16mm tall and they fit. Barely.


 

 Sweet.  I guess you didn't bevel the board edges to help with this?


----------



## funch

Quote: 





tangent said:


> Sweet.  I guess you didn't bevel the board edges to help with this?


 


 Nah. Didn't need to.


----------



## H22

Wow, truly nice stuff. I am kicking myself for not getting mine done already......I've had the PCB for about 4 months now.
  Just now getting a digikey order made up. I should tell you that the one 3.5mm jack listed from digikey on the BOM (the high quality one) is no longer available.
   
  My plan is to try to make the best sounding portable I can, using the standard case (of possibly one without the 9v compartment) and use the biggest li-po battery pack I can get to fit. 4 cells should give ~16.8v fully charged, and ~12v at the low voltage cut-off. I am wondering if the OPA627 will work ok with those figures? (I'm thinking they will).
  Opamp recomendations and biasing options for the *best* sound are greatly apriciated!
   
  I know a 14.8v 500ma pack will fit, as i have those cells and thay are almost exactly the same size as a 9v battery, but looking at the case, i may be able to go with a bit wide cell and bumo it up to 800-1000ma.
   
  I have a mini3, and love it, can a pimeta be built to sound even better?
   
  now to deside on resistors......


----------



## H22

Hmmm, I am wondering what the best way to byass the opamps is.
   
  with the options available, is there a prefered method? is there any detriment to using CRD's instead of resistor's/trim pot?
   
  I am trying to keep the bulk down, so using the smallest components possible on the bottom, or mounting them in the scratch pad area, is what i want to do.
   
  My idea here is that if I can leave a large portion of the top of the board free of components, I can use this area for a stack of lipo cells.
   
  Honestly, I'm starting to consider buying a couple extra boards and build a couple of versions......
   
  Love this sesign, as far as tweek-ability anyway. can't wait to hear it!


----------



## H22

"The maximum safe output current for this buffer is 300 mA, and the output current limit increases as the resistor value increases, so the smallest safe value for R11 is 667 times your power supply voltage. These formulas are based on single-voltage power supplies, so if your power supply is 24 V, use 24 for V+, not 12, as you would if it were referring to the ±12 split supply. This is why the formulas above differ from the ones in the datasheet, by the way; National’s formulas assume a split supply"
   
  sorry for all the questions. not quite a nood to DIY, but new enough that i know its better to ask then make an assumption.
  I'm trying to understand this, as the way i read it it sounds kinda contradictory to itself.
   
  So if I undersand correctly, to keep the output current limmited to the "save 300ma" level, I need to choose a value that is 667xV+, a higher value resistor will allow the buffer to exceed 300ma?
   
  So, with a 16.8v battery, i need to select a value for R11 of ~ 11.3k-11.4k?  a larger value will allow more than 300ma from the opamp if output is shorted, and a lower value will limmit the amount of current available to drive headphones?
   
  Hope I have this right. thanks


----------



## funch

Quote: 





h22 said:


> I should tell you that the one 3.5mm jack listed from digikey on the BOM (the high quality one) is no longer available.


 


      Slightly new number: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=cp5-43502pm-nd&x=23&y=22


----------



## MisterX

Quote: 





> My idea here is that if I can leave a large portion of the top of the board free of components, I can use this area for a stack of lipo cells.


 
   
  You could just leave the "Class A" suffs out.
  I built one a while back with a "stealthy on off switch" for that and the difference was very subtle.


----------



## tangent

Quote: 





> Slightly new number


 
   
   
  Thanks, funch, fixed.
  
  Quote: 





h22 said:


> should give ~16.8v fully charged, and ~12v at the low voltage cut-off. I am wondering if the OPA627 will work ok with those figures?


 
   
  Yes.
   
  Quote: 





h22 said:


> Hmmm, I am wondering what the best way to byass the opamps is.
> 
> with the options available, is there a prefered method? is there any detriment to using CRD's instead of resistor's/trim pot?


 

 What, pray tell, are you talking about?
   
  The only "bypass" on the op-amps is the bypass caps, C3 and C5.
   
  It sounds like you're talking about class A biasing instead, but the docs don't talk about CRDs for this, so I don't see why you describe it as an option, as if you're being made to choose.  There's only one standard bias circuit: Q1-4, RBIAS, RBLIM and friends.
  
  Quote: 





h22 said:


> a higher value resistor will allow the buffer to exceed 300ma?


 

 No, the greater the resistor value, the greater the current limiting.  You may want to look at page 16 in the LMH6321 datasheet.
   Quote: 





funch said:


> Slightly new number: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=cp5-43502pm-nd&x=23&y=22





   

   Quote: 





funch said:


> Slightly new number: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=cp5-43502pm-nd&x=23&y=22





   

   Quote: 





funch said:


> Slightly new number: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=cp5-43502pm-nd&x=23&y=22





   

   Quote: 





funch said:


> Slightly new number: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=cp5-43502pm-nd&x=23&y=22


----------



## H22

Quote: 





> What, pray tell, are you talking about?
> The only "bypass" on the op-amps is the bypass caps, C3 and C5.
> 
> It sounds like you're talking about class A biasing instead, but the docs don't talk about CRDs for this, so I don't see why you describe it as an option, as if you're being made to choose.  There's only one standard bias circuit: Q1-4, RBIAS, RBLIM and friends.


 
   Um..... wow, thats what i get for trying to post while im at work doing 3 other things!
  Yes, I was asking about biasing. I re-read the assembly notes and think I have a little beter understanding, I *thought *the CRDs could be part of the circuit, as in some other amps (B22, Lisa3). but as i understand it now, one would just use a CRD in place of a resistor to assure no LED dimming?
   
   
  Quote: 





> You could just leave the "Class A" suffs out.
> I built one a while back with a "stealthy on off switch" for that and the difference was very subtle.


 
   Yes, but I did a little experiment with express PCB last nite, and a SOT 23 (2n3904) could be mounted on the bottom of the board using the TO-92 through holes as pads. The SOT 23 would be mounted, but oriented at a right angle to what would look "normal"
   
   
  Any sugestions on good 1206 sized resistors? thick film or thin film or other? _*metal film*_ in  1206 are very pricey, and i would use them in the audio path, but they are very limmited in what values are offered.


----------



## tangent

Yes, that's one use for CRDs.
   
  There are lots of other ways you can mod the standard PIMETA v2 circuit to make use of CRDs.  If you want feedback on circuit mods, best to post new schematics instead of just proposing ideas in prose, since there are no standard options here to refer to to make sure everyone's on the same page.


----------



## cobaltmute

Quote: 





h22 said:


> Yes, I was asking about biasing. I re-read the assembly notes and think I have a little beter understanding, I *thought *the CRDs could be part of the circuit, as in some other amps (B22, Lisa3). but as i understand it now, one would just use a CRD in place of a resistor to assure no LED dimming?


 
  A CRD is a constant current source. If you check the documentation, there is already a discrete constant current source on board.  
  Quote: 





> Any sugestions on good 1206 sized resistors? thick film or thin film or other? _*metal film*_ in  1206 are very pricey, and i would use them in the audio path, but they are very limmited in what values are offered.


 
   
  1206 versus through hole?  You'll same some height, but not a lot compared to some of the other taller components.


----------



## H22

Quote: 





cobaltmute said:


> A CRD is a constant current source. If you check the documentation, there is already a discrete constant current source on board.
> 
> 1206 versus through hole?  You'll same some height, but not a lot compared to some of the other taller components.


 

 Yes, But i like SMD, also, finding resistors that match the schem is proving to be difficult. Vishay has a metal film MELF, but some of the values are out of stock (digikey &mouser). Thin film 1206s are plentifull and have the right values. wanted to use the RN55 stuff, but again i was hit by a couple "out of stock 12 week lead time" issues.


----------



## H22

Quote: 





> No, the greater the resistor value, the greater the current limiting.  You may want to look at page 16 in the LMH6321 datasheet.


 
   Ok, Got it.  I will check out the datasheet.
   
  So I am wondering, as this will be powered from a battery, would it be to dangerous to calculate it from the low batt voltage, in this case 12v? or play it safe and base it on the fully charged voltage ~16.8v? 8000k and 11.4k respectivly


----------



## tangent

I guess you're asking about the C2 cap voltage ratings and such?  Rate those for the highest voltage they will ever see.  If you're hacking some kind of external charging circuit into this, beware that this will have to put a higher voltage across the battery than their highest off-charger voltage.


----------



## H22

Quote: 





tangent said:


> I guess you're asking about the C2 cap voltage ratings and such?  Rate those for the highest voltage they will ever see.  If you're hacking some kind of external charging circuit into this, beware that this will have to put a higher voltage across the battery than their highest off-charger voltage.


 

 Tangent, thanks for all you help and designing a much loved amp. I was not concerned about C2 voltage, I plan to use 25v caps here. And the charge circuit I have for the lipo pack ensures that the voltage never exceeds the max volt per cell for li-pos (4.2v), so 16.8 is max, and the circuit also cuts the current flow round 12v (3v per cell) to avoid cell damage. 
  What I was asking about was a safe yet unrestrictive (buffer current/audio quality wise) resistor velue to use for R11, as the V+ is dynamic, using your simple formula of 667xV+ will provide a range of resistor values. safest bet is to use a larger resistance to limmit current to 300ma at full voltage, but, if i understand it correctly, this will limmit the current at nominal voltages. I realise this is splitting hiars, as 300ma is WAY more current than will likelly ever be needed. But in e an effort not to hamper the performance, im wondering if the buffer can take momentary current surges of over 300ma (within reason). So, pick a R11 resistance that allows a full 300ma at 12v, and should the output be shorted (witch it most likely will at some point) the momentary >300ma surge wont hurt anything. You stated somewhere that the chip can handle higher momentary currents, so I am thinking it is not a huge deal....
   
  Again I am splitting hairs here i think. As for the resistor dilemma I was facing (out of stock on some of the good resistors in the proper schem values), I found your wonderfull resistor calculator! so I can substitute more common and "in stock" values, and it only changes the gain by a tiny bit. But with that in mind, i have made up my mind to build 2 Pimetas, 1 lower gain for portable use (thinking a gain of 3-4) and a higher gain for home use with full sized cans.


----------



## tangent

Quote: 





> safest bet is to use a larger resistance to limmit current to 300ma at full voltage, but, if i understand it correctly, this will limmit the current at nominal voltages.


 
   
  Yes, to about 212 mA, by my calculation.  That still sounds like enough to me.


----------



## evolo

Hey guys I'm just starting out.  This is my first pimeta build and I have a question.  The input power (v+ v-) for OPAG is still pin 4 and 8 right?  I'm getting correct v- from pin 4 but v+ from pin 7 and not pin 8 for OPAG.


----------



## MisterX

I was going to ask if there was a reason why you couldn't just check the schematic but it's easy to see how you could be confused after checking it.


----------



## evolo

Mister X you are right.  I do look at the schematic but at this point I'm pretty confused.  My v+ and v- readings are different from OPALR to OPAG so I'm a little concern.


----------



## Spacehead

Quote: 





evolo said:


> Hey guys I'm just starting out.  This is my first pimeta build and I have a question.  The input power (v+ v-) for OPAG is still pin 4 and 8 right?  I'm getting correct v- from pin 4 but v+ from pin 7 and not pin 8 for OPAG.


 

 OPAG is a single channel op amp and OPALR dual channel. They have different pin outs as the way you described.


----------



## evolo

Spacehead thanks for you answer.


----------



## gurusan

Hi all. For my next project I wanted to build a pimeta v2 and grubDAC in the same enclosure.  I have a 24VAC wallwart transformer I planned to use with a TREAD for an 18VDC supply to the Pimetav2. However Tangent's shop no longer contains the TREAD kit? 
	

	
	
		
		

		
			





  
   
  Otherwise I will just use amb's sigma25.


----------



## evolo

Alright the amp is done.  Wow this is one sweet sounding amp.  I love it.
   
  Any one using Lipo for power source?


----------



## MisterX

Is a 2 cell LiFePO[size=x-small]4[/size] pack close enough?


----------



## evolo

Yeah, LiFe are suppose to have really high discharge rate.  I just used 5000 4s lipo pretty crazy.
   
  MisterX what opag and opalr are you using this that one?


----------



## MisterX

http://focus.ti.com/docs/prod/folders/print/opa1641.html
   
  OPA1641/OPA1642.


----------



## gurusan

hmm that looks like a nice little opamp for the price


----------



## Reima

I am in the process of building my second Pimeta V2 (the first was built for a friend). During the power supply testing (using an 8V battery) I got 3.9V on Pin 8 and -3.9V on pin 4 of the OPR\L (as expected). I also found that I was getting -3.9V on pins 1 and 7, is this normal?
  RC


----------



## tangent

Pin 1 on OPAG isn't connected to anything.  That may not be strictly true, I haven't checked the PCB layout.  Point is, it doesn't matter what the voltage is.
   
  Pin 7's value is backwards.  It should be V+, not V-.
   
  If you were using the pin numbers on the schematic, redownload the schematic.  The previous version's numbers were arbitrarily numbered 1-5.  Now they correspond to the actual package pin numbers.


----------



## Reima

Hello Tangent,
   
  I am referring to OPALR not OPAG.
  RC


----------



## tangent

Oh, I see.  In that case, it makes sense only if you haven't installed BUFL, BUFR, or the R7s yet.  If you have, these pins should be 0 V relative to IG.


----------



## Reima

Quote: 





tangent said:


> Oh, I see.  In that case, it makes sense only if you haven't installed BUFL, BUFR, or the R7s yet.  If you have, these pins should be 0 V relative to IG.


 
  I haven't installed the buffers as yet, I am at the stage where I am checking that the supply voltages are correct. My next set is to install the buffers and opamps.
  BTW I am going to be using 2 x 8.4V Lipo batteries. In the Pimeta V2 that I have already built I get 16.03V at C2 (when batteries are hot off the charger). With this voltage would it be safe to use 16V capacitors at C2?
  RC


----------



## tangent

It's not a good idea to exceed the C2s' rated value, but they won't suddenly explode with 0.03 V over their rated voltage.  I'd be tempted to put a second diode in series with D2 to remove any possibility of risk here.


----------



## evolo

Here are a couple of pictures.  Finally got it done.  This is my second amp.


----------



## tangent

It's a beautiful enclosure, evolo!
   
  Are you going to leave it open on top?


----------



## evolo

Thanks tangent.  I will put a cover on it.  I might do magnetic attach cover or latch style.  Haven't decide yet.  I should have wooden knobs done soon also.  I have a second pimeta and ppa on the way also.  Can't wait to finish those.  This head phone amp stuff is really fun.


----------



## Spacehead

Why my Pimeta v2 burns both leds when I connect wall wart to it. I have it regulated. I have most as in schematic, I used SMD resistors. I currently have RLED 16K.
   
http://dl.dropbox.com/u/7337908/IMG_6830.JPG
  I have cleaned the board but maybe the denatured ethanol leaves some residue. Amplifier works fine though. I run out of blue leds and soon those led pads will be destroyed if I don't soon find out what is causing that.
   
  Leds work when wall wart isn't connected, with battery that is. Wall wart voltage regulated 22V.


----------



## cobaltmute

Have you checked the wattage on your RLED?  You're dropping about 18V across it when your are on line, something funky could be happening with it.


----------



## Spacehead

I guess it is 1/8W like rest of the 1206 SMD resistors
  
  Quote: 





cobaltmute said:


> Have you checked the wattage on your RLED?  You're dropping about 18V across it when your are on line, something funky could be happening with it.


----------



## tangent

Quote: 





spacehead said:


> my Pimeta v2 burns both leds when I connect wall wart to it


 

 May we see a top-side pic showing D1 and D2?
   
   
  Quote: 





> I have cleaned the board but maybe the denatured ethanol leaves some residue.


 
   
  Clearly so.  As messy as it's left your board, I wonder if you wouldn't have been better off not cleaning it at all as use that stuff.  Instead of flux around the solder points, you have junk evenly spread over the board now.
   
  I think you have little choice but to make another cleaning pass at it.  Try to find something purer: tape head cleaner, high-purity isopropyl from a drug store, etc.  
   
  Heet gas additives are high-purity alcohol (yellow bottle = methanol, red = isopropyl), but I don't know how the 1% of "proprietary additive" affects its suitability as a PCB cleaner.
   
  I also see the potential for several shorts:
   

 BATT wires, extra exposed length and solder splatter on the blue one
 several places around BUFG
 extra unclipped lead lengths and unshielded jumpers in the scratchpad area
   
  Is that a scratch or wire strand near forward LED?


----------



## Spacehead

Here are better pics:
   
http://dl.dropbox.com/u/7337908/IMG_6844.JPG
  
http://dl.dropbox.com/u/7337908/IMG_6845.JPG
   
  It burned the led when there was only one, in LED1
   
  In scratchpad I have diode bridge and LM317T configured to 24V. The wall wart outputs 26VAC.
   
  I added 0.1uF caps to BUFG pins because all the buffers ran hot at one point. I need to measure the current draw...
   
  I will get back to it...
   
  There can be scratches.
   
  I need to get some clean isopropyl alcohol soon.
   
   
  Quote: 





tangent said:


> May we see a top-side pic showing D1 and D2?
> 
> 
> 
> ...


----------



## tangent

The diode bridge...your wall supply is AC output?
   
  If so, try an isolated DC power supply.  If it works, there's something wrong with your rectification or you're connecting something to the amp's power input incorrectly.  (Grounding, etc.)


----------



## Spacehead

There is -6V in the LED2 pins when both leds are burned and after rectification and regulation 22VDC supply is used.


----------



## Spacehead

I chose that 24VAC supply because it allows me to get higher voltage supply rails. I have lower voltage DC supplys, like 17 VDC in no load. They could be regulated to 13-14VDC. Do you think that is enough voltage?


----------



## tangent

It sounds like there's something wrong with your AC-DC circuit in the scratchpad area, then, or in the way it's connected to the PIMETA proper.
   
  As for your unregulated DC supply question, yes, that should be enough for most purposes.


----------



## pulsar08

I had 11.6v on the V+ and V- of both opamp sockets prior to installing any opamps or buffers.  Once I install the opamps and buffers I check and the rail voltage was like 19 on the V+ and 1.9 on the V- of both opamps. The buffers were hot too.  I went back and cleaned up my soldering around the buffers and cleaned the flux off and now the voltages are normal again but BufL is hot still.  I've googled this problem but couldn't find more info so I'm looking for advice what to do now.


----------



## tangent

There are lots of things that could be wrong.
   
  What supply type are you using?  Model numbers and part values, where applicable, please.
   
  Have you gone through the troubleshooting guide?
   
  Post pics.


----------



## pulsar08

There is an external power supply (an acopian 24v linear regulated) being fed into the pimeta.  The battery pack has not been constructed yet (planning to use 10-14 2500mah AA nimh depending how they fit in the case).  I was going to do that when it came time to case it.  C1 is jumpered.  It's using 3x 680uf 50v nichicon HE series for c2.  There is a lm317 to-220 package with rccs of 5ohms 1/2watt to charge the 2500mah nimh at 250ma.  Opamps are biased at 1ma atm  (3000 ohms).  rblim is 301ohm and rbias is 10k or something large.  Gain is set at 3.  That's about the extend of the customizations.  Everything else is following the docs I think.  I've look over the board pretty well and can't see any shorts.  I'm afraid that the 19v I measured earlier toasted my buffers.  I had r11 unpopulated.  I tried to see if populating them would help but it had no effect.  BufL still gets too hot to keep my finger on it and I shut it off immediately.


----------



## pulsar08

Whoops I see the mistake! BufL is reversed...lol.  I guess was paying more attention to putting on the right amount of thermal paste than the direction.  Now to try desoldering it and see if it's salvageable


----------



## Hrimthursum

I FINALLY built mine and I am very happy with the results!

  In case you are wondering, yes it is a laptop li-ion cell battery. giving me 12 volts of endless power!!!
   
  This is the semi-final boxed project:

  Excuse my crappy cell pics.


----------



## tangent

Cool!
   
  How do you charge the battery after modding it like that?  I guess the charge controller is inside the battery pack, so it doesn't have to be in the computer to charge?


----------



## Avro_Arrow

The battery pack usually only contains a protection circuit that shuts down the battery if
  the voltage is too high or too low. The charging circuit is usually in the laptop.
  You can charge a Li + batteries with a constant current then constant voltage profile.
  Charging rate can be 1/C with charge termination at .1/C. The main thing is to never
  exceed 4.1 or 4.2 volts per cell depending on the exact chemistry.
  
  Quote: 





tangent said:


> Cool!
> 
> How do you charge the battery after modding it like that?  I guess the charge controller is inside the battery pack, so it doesn't have to be in the computer to charge?


----------



## Hrimthursum

I do not want to risk overcharging so I just plug it into the laptop every week or so charge and it is good. Any suggestions on a trickle charger?


----------



## Avro_Arrow

Darn double posts...
  
  Quote: 





hrimthursum said:


> I do not want to risk overcharging so I just plug it into the laptop every week or so charge and it is good. Any suggestions on a trickle charger?


----------



## Avro_Arrow

"Trickle charging" a Li + is not a good idea.
  What you are doing now is a better idea.
  Building a dedicated Li+ charger would be the best idea.
  The Texas Instruments BQ2000 series is a good place to start.
  Maxim also makes some good chips.
  I use two, three and four series cells for my amps.
  I'm just using an adjustable constant current, constant voltage
  charger I made based on a LM317 but my next project is
  a dedicated charger.
   
  We will now return you to the original thread topic...


----------



## wew01

Edited. Thanks, Reima, for pointing out.


----------



## Reima

^ That's a V1.
  RC


----------



## H22

Well, I finally got one board finished
	

	
	
		
		

		
			





 . 
   
  Didn't take too long, and went fairly smoothly. Tangent, that is a very high qualty board, much better than the ones i get from express PCB.
   
  I did have to substitute the C3 & C5 with some kemmet gold, these were X7R rate rather than those specified. Had them left over from a mini3 build. ( do have the right type on the way)
   
  I ordered a set of 637 opamps to use as L&R (on a brown dog) and a 627 for opaG. however I could not get them to work. when testing I got 1.17ish volt DC offset between IG and OR, the OL test was fine.  SO I swapped the 637's on the brown dog to see if it would follow the opamp, but instead it made both channels read 1.17v on the DC offset 
	

	
	
		
		

		
		
	


	




 .
   
  So I put some 843's in all the chanells and got no DC offset at all. 
   
  So I  listened to it for awhile, sounds very good, looking forward to analizing it more as the built progresses ( case etc. )
   
  I am curious why the ($$$) 637's did not work though, are they a finiky op amp? Would love to test them, not only did i spend a small fortune on them, but i really want to kno how they sound. 
   
  Also, Tangent, you just sent me a couple of SOIC to DIP adapters with the brown dogs, but they do not apear to be pin for pin.  I soldiered couple 8610's t the 2 you sent and tested the DC offset, over 2 volts! once i took a closer look, it apears they are not pin to pin?  So i will be needing to order a couple more 8610's and the proper adapters.
   
  Will post pics and more impressions later.
   
  so far sound like an awesome amp so far.
   
   
  hope i can get the 637's to work.......
   
   
  Joe


----------



## H22




----------



## H22




----------



## MisterX

Quote: 





> I am curious why the ($$$) 637's did not work though, are they a finiky op amp?


 
   The default gain is a little low for those op-amps but your DC offset numbers suggest another problem.
  Try soldering both sides of your R7 resistors and see if it helps.


----------



## tangent

Quote: 





h22 said:


> Tangent, that is a very high qualty board, much better than the ones i get from express PCB.


 

 Thanks!  The PIMTEA v2 boards are indeed made by another board house. 
   
   
  Quote: 





> I soldiered couple 8610's t the 2 you sent and tested the DC offset, over 2 volts! once i took a closer look, it apears they are not pin to pin?


 
   
  Check the bottom side of the adapter: if there's a second SO-8 footprint down there, it's the dual op-amp adapter, not the SO-8 to DIP-8 adapter. That's what you want for AD8610s in OPALR.  You want the other SO-8 adapter -- the straight one -- for OPAG.  Better to use an AD8620 in OPALR, though.
   
  If you got the wrong parts, email me.
   
  Quote: 





misterx said:


> Try soldering both sides of your R7 resistors and see if it helps.


 

 A plan so crazy it might just work.


----------



## H22

Quote: 





> The default gain is a little low for those op-amps but your DC offset numbers suggest another problem.  Try soldering both sides of your R7 resistors and see if it helps.


 
  Good Eye MisterX ! lol
   
  yea, I took that pick before I was done soldering everything . that was all done two days ago, ( and i did get R7 tacked down on both sides, just dawned on me i should take a pick of the assembly )
   
   
  Quote: 





> Check the bottom side of the adapter: if there's a second SO-8 footprint down there, it's the dual op-amp adapter, not the SO-8 to DIP-8 adapter. That's what you want for AD8610s in OPALR.  You want the other SO-8 adapter -- the straight one -- for OPAG.  Better to use an AD8620 in OPALR, though.


 
  Yea, I saw the bottom side (after I installed the opamp's on the top and it tested out bad.......) and indeed there is another SOIC8 pad there, so I asummed that was the case ( that i got a dual adapter...) I was running out of time to mess with it today, but if I understand you correctly, the adapters you sent me allow 2 single SOIC8 to be installed and mimic a DIP8 dual opamp ( ie, use 2 8610's to create an 8620?) . If so i will try to remove one of the 8610.s and install it on the bottom of the adapter. Only reason I ordered 3 8610's instead of an 8620&8610  is I wanted to play with op amps to decide what i liked the best. 
   
   
   
  Still not sure why the 637's were giving me trouble, I can asure you it was not the R7  . But I will keep working with it.
   
  Thanks for the help guys.
   
  Joe


----------



## H22

Quote: 





> A plan so crazy it might just work.


 
  ..........I knew i should'nt have posted that pic..., that just happened to be the one that came out the best......
   
   
  In any case, The only divergence I have taken from the specs is the use of X7R rated "kemet-goldenmax" caps in C3&5, Could that cause an instabillity issue? My instincts tell me not, but I am no expert.
   
  just turned it on again, and now it has distortion and clipping, ??. might be the batteries going dead, but i doubt it. they were just charged (for testing using two 300ma 9v batteries in series) and only been on for an hour or so, tested the current draw back at the shop while running LOUD on my M50's and it waqs averaging 75ma, so i doubt it is low voltage. If I touch the board right between R1/2lL and R1/2R the distortion and clipping goes away. not sure what is going on here, it was just sounding great.
   
  I have re-flowed everything at least once, most likelly twice ( usualy standard procedure for me when doind SMT, makes it look much nicer ) so I highly doubt it is a cold joint.
   
  OH well, sure it will pan out!
   
  HAPPY NEW YEAR !!!!!
   
  Thanks Tangent for all you work!
   
  I have a hang over to look forwad to!!!!!!!


----------



## H22

Quote: 





> just turned it on again, and now it has distortion and clipping, ??just turned it on again, and now it has distortion and clipping, ??


 
  OK, well no volt meter handy, but the tounge test tells me the batteries are running low. guess I will have to test the current draw again.
   
  What is the "idle" (on with no headphone load) current for a "schem" PIMETA with an 8620+8610 and three buffes, even with the max ~3ma opamp biasing?
   
  without the 2-3ma bias, and 643'sin L&R, and an 8610 for opaG, MY M50's ( granted not a hungry can at all ) up to the pain level i saw ~75ma. So a little suspicious why mt spanking new 300ma batteries are dead after less that a couple hours of moderate listening with the same cans...
   
  more testing!


----------



## tangent

Quote: 





h22 said:


> The only divergence I have taken from the specs is the use of X7R rated "kemet-goldenmax" caps in C3&5, Could that cause an instabillity issue?


 

 No.
   
  Quote: 





> tested the current draw...averaging 75ma


 
   
   
  That's a bit high, but not unreachable. Minimum likely current draw is about 50 mA, but you'd have to change several things about your configuration to achieve it:
   

 two AD8610s draw about 8 mA less than two OPA637s (OPALR)
 3 mA bias is probably too high. I doubt you can hear a difference relative to a much lower level, 1 mA or less.
 Your ~18 V supply voltage causes the buffer current draw to go up. You can probably get away with a single 9 V battery, which will reduce current draw.
   
  Quote: 





> Originally Posted by *H22* /img/forum/go_quote.gif
> 
> 637's did not work...i spent a small fortune on them...no volt meter handy


 

 I think your sense of priorities needs adjustment.


----------



## H22

Quote: 





> I think your sense of priorities needs adjustment.


 
  Just meant i did not have the multimeter with me, I am an electronic tech by trade, so my bag of tools is fairly well stocked 
   
   
  Quote: 





> That's a bit high, but not unreachable. Minimum likely current draw is about 50 mA, but you'd have to change several things about your configuration to achieve it:


 
  The ~75ma reading i obtained when it was far from idle, had a set of M50's blairing away. 
	

	
	
		
		

		
		
	


	




.


----------



## H22

Ok, now for the good news.
   
  I removed one of the 8610's from the top side of the DIP adapter it was soldered to and put it on the bottom of the other DIP adapter, works great now, DC offset is neglagible, and idle current draw is ~40ma  Sounds very good.
   
  As for the 637's, I suspected the issues i was having were due to the DIP socket > brown dog adapter > two more DIP sockets > opamps.......
   
  So I removed the DIP sockets from the brown dog and soldered the 637's right to the brown dog. Resulted in an idle current of just over 60ma, and DC offsets of ~3.5mv R and ~5mv L . Sound is aslo very good.
   
  For now both combo's are using an 8610 on the ground as I put it on the board.
   
  Also wired up the 4 cell Li-PO pack and controll board, its 16.8+v fully charged, and should cut out at about 12v, and using 500mah cells should give 10+ hours on the 8610's, and hopefully 7-8 hours with the 637's. So so far so good.
   
  Still have to get it mounted in the case, but trial fit looks like there should be no issues. I did play around with the opamp biasing with both set-ups, and if there is a benifit to the biasing it will take some real in depth listening. sometines it seemed like i could tell a very, very subtle differance with the biasing in, but hard to tell for sure.
   
  Thanks Tangent


----------



## tangent

Yes, many contacts make for many parasitic Cs and Ls, which can cause a problem with a fast chip like the OPA637, particularly when you're running it so close to its minimum stable gain.
   
  Glad you got it worked out.


----------



## H22

Quote: 





tangent said:


> Yes, many contacts make for many parasitic Cs and Ls, which can cause a problem with a fast chip like the OPA637, particularly when you're running it so close to its minimum stable gain.
> 
> Glad you got it worked out.


 

 Well. sorta....... just realized last night that i grabbed the two 843's and hard soldiered them to the brown dog, not the 637's. my eye sight is not what it used to be. So I ordered a couple more brown dogs from you, as well as a PPA board to start playing with  . 
   
  So, for now i will listen with the 3 8610's in place, and play with op-amps as time permits. Here are c few shots of me getting it cased up :

   
  side shot showing the big MUSE caps, 2x470uf, I may change these out at some point to make more room.
   
  also shows how tall the 4 cell Li-PO pack is, the 14.8v cell protection PCB is on end in front of the cells, wrapped in white electrical tape to protect from shorts.
   

   
  one from the top, charging the batteries from a benchtop power supply. Full charge is ~17volts, I need to build a small regulator for my charger to keep the voltage to ~17.5-18volts, and under 500ma charging current, but with those figures it should charge in about an hour.
   
  The battery pack is a tight fit, had to cut the  9v holder out of the case, but it does fit. with the current op-amps and no biasing, should be able to get well over 10 hours of playback.
  I am going to try and implement a PPA style bass boost, but it will be a serious effort to make room for it.
   
  Joe


----------



## paul3

Amazing - Just finished my build, and it worked first time.
   
  I was very worried about the SMs but I guess I pulled it off.
   
  A few minor glitches - I ordered/ fitted incorrect R6s so the gain off.
   
  I set the gain too high, as I expected iPhone LOD to give a lower signal than phones out, and am planning to fit a crossfeed later.
   
  Not sure what bias current to set - guess in the 1-3 ma range - still to experiment with.
   
  SQ is amazing, even on IEMs, iGrados, didn't expect much difference with such small drivers, and HD650s sound great.
   
  Thanks all for a great design, and tangent for your tutorials. I've learned so much.
   
  Paul


----------



## tangent

Thanks for the report, Paul!
   
  I'd definitely wait to drop the gain until after you insert the crossfeed. It will change things considerably.


----------



## mfueger

With the default RBLIM of 1k and 24V PS, is is correct to only be able to dial in about 2.8mA maximum for the Bias?


----------



## tangent

Yes, you can "only" push the op-am into class A by about two orders of magnitude.
   
  How much deeper into class A do you believe you need to go?


----------



## mfueger

I am not sure. I read through some articles which mentioned higher values based on volume and load. Driving higher impedance headphones, or so I understood, require a higher bias level. I am still studying this, so please excuse my ignorance.


----------



## tangent

I think you're confusing the PIMETA biasing with that for different amps where the adjustable bias is in the output stage. That changes everything.
   
  For the bias on an intermediate stage op-amp as in the PIMETA, 3 mA is "lots".


----------



## TheLaw

Very nice soldering. Look's almost like a machine.


----------



## mfueger

Could you point me in the right direction on how to determine optimal bias current for a given opamp?


----------



## tangent

Use your ears.  If it sounds right, it _is_ right.


----------



## i_djoel2000

what do you guys think about listing all opamps (LR & G) that has been known work well in pimeta v2 in the first post? some sound characteristic explanation would be nice too..
   
  what do you think? not a bad idea, right?


----------



## mashuga

Hello
   
  I have a pair of newly acquired Pimeta v2 boards and some of the parts from Tangent's shop, but I still need to pull the trigger on a Mouser and Digikey order.
   
  I guess my dilemma is that I want to pick all the components at once and not have to place multiple orders to the same shop because I picked something incorrectly.
   
  After studying this thread as well as Tangent's site, (and anything else that Google would pull down) I seem to keep coming up against the same brickwall questions.  Hopefully my newbishness will be forgiven, 'cause I really feel that the specific answers aren't out there ( at least not without being an EE! ):
   
  First thing is the bass boost.  I am comparing the PPA schematic to the Pv2 and I just don't get it.  In the Pv2, the switch seems to bypass the cap and R4...  Wouldn't that break the Jung multiloop topology? ( I say that like I understand it...!)  So is the bass boost active when the switch is closed or open? It's gotta be when it's open, right?  I'm thinking that I should just use the PPA style boost because it makes more "sense" to me, but I'm still not sure how the values for R4 compare between the two designs..  Is it really just a case of picking whatever works for the desired amount of gain?  Also, a .1uF polypro cap of "acceptable" quality that will fit on the board seems hard to find.  Is the quality of this cap that important?  If I do the PPA I will likely use Tangents suggestion to have a small piece of perf board like a daughter card.  Maybe I should just leave the boost out for now....
   
  Next thing is power...  The recommended Elpac PS is no longer out there so I'm inclined to use a cheap(er) 24v wall wart and a LM7818 to get linear, regulated, isolated power.  Is it really as simple as having a .33uF cap on the input side and a .1uF on the output to get a decent quality PS for the Pimeta?  I'm not interested in battery power or charging at this point.  An 18v PS works out to a 12k R11 as best I can figure..  Just hoping for confirmation on my math..
   
  I'll also just mention that availability of the recommended quality of caps seems to be a major stumbling block.. I'm really surprised at the huge gaps in inventory that Digikey and Mouser seem to have.  Not much demand out there I guess?  
   
  Those are the holes in my shopping list so any help from those who have dealt with these questions would be much appreciated..TIA


----------



## tangent

Quote: 





mashuga said:


> In the Pv2, the switch seems to bypass the cap and R4...


 

 Yes, that's why I call it "unity boost". It works fine if -- and only if -- you need current gain without voltage gain.
   
  If you need both voltage gain and current gain, do what the docs tell you: build a PPA-style bass boost in the scratchpad area.
   
   
  Quote: 





> is the bass boost active when the switch is closed or open? It's gotta be when it's open, right?


 
   
  Yes.
   
   
  Quote: 





> I'm still not sure how the values for R4 compare between the two designs..


 
   
  If you build out a PPA-style bass boost, the equations you find in the PPA docs work for the PIMETA v2.
   
  The default PIMETA v2 gain is lower than for the PPA, but you had that choice with the PPA already. They're just defaults, not commandments.


----------



## i_djoel2000

tangent, i'm now building my pimeta and i decided to use resistor values which are not the same as per your suggestion.
   
  i read your assembly guide and i think i have followed the rules correctly. but can you confirm that this circuit is ok? just to double check. i'm going to use 9.6V "9V" battery for this project, if that matters..
   
  nb: forgot to mention, *the value of R6 is 390k ohm*
   


   
  what do you think? thanks


----------



## tangent

Your 9.6 V battery could be as high as about 11 V when fresh off the charger. If you charge the battery in the amp using the built-in trickle charging circuit, the V+ voltage can be even higher, so R11 should be higher, too. I'd recommend at least 7.5 K.
   
  The other changes should be fine.


----------



## i_djoel2000

Quote: 





tangent said:


> Your 9.6 V battery could be as high as about 11 V when fresh off the charger. If you charge the battery in the amp using the built-in trickle charging circuit, the V+ voltage can be even higher, so R11 should be higher, too. I'd recommend at least 7.5 K.
> 
> The other changes should be fine.


 

 how to predict, or calculate the voltage of the battery after charging using the built in trickle charging circuit?
   
  also, i want to add extra LED instead of populating LED2. i want this LED to give indicator when the wall adapter is plugged in and the battery charging is running

   
  is my LED implementation correct?


----------



## i_djoel2000

double post. see previous post


----------



## tangent

Quote: 





i_djoel2000 said:


> how to predict, or calculate the voltage of the battery after charging using the built in trickle charging circuit?


 
   
It's in the docs.
   
   
  Quote: 





> is my LED implementation correct?


 
   
  No. It will stay on after you unplug the charger, until the batteries die.
   
  To do what you ask, you'd have to put the + end of the LED and current limiting resistor subcircuit between WALL and D1. The other end still runs to V-.


----------



## i_djoel2000

tangent, is it still recommended to use 22-33pF in C6 when i set the gain to 6? bigger capacitance makes the opamp more stable, right?
  
  Quote: 





tangent said:


> It's in the docs.
> 
> 
> 
> ...


 

 i see..
   
  so i guess it will be like this

   
  tangent, i'm still confused why the opamps choice in pimeta are able to run perfectly fine with 8.4V battery
   
  after the supply passes through TLE2426 (voltage divider), the voltage on each rail would be roughly 4.2V/channel (correct me if i'm wrong), while the minimum supply voltage of your opamps and buffers choice (ad8620, ad8610, LMH6321) are all 5v. how could they still run perfectly fine with 4.2V voltage supply?


----------



## tangent

Quote: 





i_djoel2000 said:


> is it still recommended to use 22-33pF in C6 when i set the gain to 6?


 
   
  What does gain have to do with it?
   
The docs are clear, I thought: 4.7 to 10 pF if you don't want to test (or can't), 1 to 100 pF if you do a square wave test.
   
   
  Quote: 





> bigger capacitance makes the opamp more stable, right?


 
   
  It isn't that simple. If the highest possible value gave the best performance, I'd just say "use X". The higher the cap value, the greater the impact on the amp's bandwidth, and thus its overall performance. That is why there is an upper 100 pF limit in the range given in the docs.
   
   
  Quote: 





> how could they still run perfectly fine with 4.2V voltage supply?


 
   
  You're confusing split supply voltages with rail-to-rail voltages. When the datasheet says a buffer works down to 5V, it means the same thing as if it says it works down to +/2.5V.


----------



## i_djoel2000

Quote: 





tangent said:


> You're confusing split supply voltages with rail-to-rail voltages. When the datasheet says a buffer works down to 5V, it means the same thing as if it says it works down to +/2.5V.


 

 in that case, using 4x AA batteries (1.7V each) we can get a total of 6.8V. so using ad8620/8610 configuration with those 4 AA batteries should be more than enough right? because i'm still under the impression that using nearly 5V power supply is not really recommended. i was referring to your comment in the doc here:
   
_*'*Bottom line: you can design a good-sounding PIMETA v2 that *runs on 5 V*, but you’d best have a good reason to push things this hard. If not,* you’re needlessly closing off options for better sound'*_
   
  because i'm really concerned with the battery life of portable pimeta. based on rough calculation, using 9V 230mAh battery, you only can get 3.8 hours, 4 hours top! i cannot even consider that kind of battery life as portable


----------



## tangent

Where do you get 1.7 V per cell?
   
  Even if you're looking at the still-on-the-charger voltage, it's going to drop quickly from that after you unplug the power supply.


----------



## i_djoel2000

Quote: 





tangent said:


> Where do you get 1.7 V per cell?
> 
> Even if you're looking at the still-on-the-charger voltage, it's going to drop quickly from that after you unplug the power supply.


 

  
  oh sorry, it's 1.2V (got wrong info!). let say i'm able to stick 6 AAA batteries into my casing, i can get a total of 6.6-6.8V. is it more than enough for ad8620/8610 or opa627 configuration?


----------



## tangent

I'd characterize that as "barely enough". It's equivalent in voltage to a 7.2 V type of "9V" NiMH battery. It differs only in being able to provide more current, or run for longer on the same current.


----------



## i_djoel2000

Quote: 





tangent said:


> I'd characterize that as "barely enough". It's equivalent in voltage to a 7.2 V type of "9V" NiMH battery. It differs only in being able to provide more current, or run for longer on the same current.


 


  i guess i will have to work really hard to stick those 4 AAA batteries to my small aluminium case then. haish...
   
  report will follow, the board is not even arrived yet


----------



## i_djoel2000

i found this in other thread:
  Quote: 





tangent said:


> Quote:
> 
> 
> Originally Posted by *headfone* /img/forum/go_quote.gif
> ...


 


 why can't i use the built in charger for charging paralleled 9v batteries?
   
  i'm planning to use 2 x 8.4V batteries in my pimeta..i changed my plan of using 6 x AAA batteries after i saw this post:
  Quote: 





amb said:


> 9V = +/-4.5V rails, and this is when the battery is not near depletion. This is too low for AD8620. The recommended minimum supply voltage is +/-5V, and add the fact it is not a rail-to-rail opamp (it clips at 1V below each rail), results in a rather sub-optimal combination.


 
   
  this is what i was trying to say earlier..amb put it together into the right sentence. i read your comment (tangent) regarding the above post as well, but i did not quite understand it (something about rail to rail supply)


----------



## tangent

Quote: 





i_djoel2000 said:


> why can't i use the built in charger for charging paralleled 9v batteries?


 
   
  It's not so much a "never do this" as a "not a good idea" matter. Batteries are very strange beasts when you start to really look into how they behave; they are far from ideal energy storage devices. When you put two in parallel, they interact, multiplying the number of strange behaviors.
   
  In any case, I don't think you actually want to parallel them. I think you want a series connection and are confusing the terms.
   
  Quote: 





> Originally Posted by *amb* /img/forum/go_quote.gif
> 
> 9V = +/-4.5V rails, and this is when the battery is not near depletion. This is too low for AD8620. The recommended minimum supply voltage is +/-5V, and add the fact it is not a rail-to-rail opamp (it clips at 1V below each rail), results in a rather sub-optimal combination.


 
   
  AMB is quoting the datasheet here, which isn't really on-point on this matter. The fact that the datasheet recommends a given running voltage and gives its test result graphs at that voltage doesn't actually tell you where the lower limit is. This test does, and in fact it's overly harsh for a PIMETA, since it will have buffers easing the load on the op-amps. Even if for some reason the buffers don't help at all, my worst-case 7.6 V number is close to the minimum useful voltage from an 8.4 V battery anyway.
   
  Bottom line, I think you probably could effectively drain a single 8.4 V NiMH battery with an AD8620/10 combo before you made the amp clip.
   
  That's not to say that the op-amps will perform their best at these low voltages. It is quite possible that they will sound better when run closer to the datasheet recommended voltage, or higher. To do that, you would need to put the two 8.4 V batteries in series, not parallel, to create a 16.8 V battery. The third paragraph here tells how to connect them.


----------



## i_djoel2000

Quote: 





tangent said:


> It's not so much a "never do this" as a "not a good idea" matter. Batteries are very strange beasts when you start to really look into how they behave; they are far from ideal energy storage devices. When you put two in parallel, they interact, multiplying the number of strange behaviors.
> 
> In any case, I don't think you actually want to parallel them. I think you want a series connection and are confusing the terms.


 

 woww, so 7.2V really is barely enough..i think using 9v battery would be the best choice for portable, but i cannot get a long battery life with it
   
  so just this afternoon, i came across this thing 
	

	
	
		
		

		
		
	


	




:

  it's an ON-ON switch. implementation:

  i'll use 2 x 9v battery in parallel, then put a switch between them. this way, i can get double battery life, by using single supply only. when the first battery runs out (after around 4 hours), just toggle the switch, then you get another 4 hours 
	

	
	
		
		

		
		
	


	



   
  charging would be easier too since the supply is actually single supply, not paralleled, i can use pimeta's built in charger


----------



## tangent

There are 3-position switches of that sort.  An on-off-on switch would let you center the switch to turn the amp off entirely, or you could use an on-on-on switch to have the "off" position be one of the two end positions.


----------



## i_djoel2000

Quote: 





tangent said:


> There are 3-position switches of that sort.  An on-off-on switch would let you center the switch to turn the amp off entirely, or you could use an on-on-on switch to have the "off" position be one of the two end positions.


 


  i bought ALPS RK097 pot with built in switch from your shop. so i think an on-off-on switch should be unnecessary


----------



## i_djoel2000

i just finished my pimeta amp. now it is up and running 
   
  i got almost 0V dc offset using LM4562/LME49710 configuration. but i don't know why, the LED1 is not turned on when i turn on the amp, the amp itself is working and no problem whatsoever. any idea what's the problem?
   
  and i want to ask about the trimmer pot. i used bourns 10k 25 steps. isn't the rotating knob should rotate in steps? because my trimmer rotates just like analog potentiometer, and i can't really hear any sound difference when i play with the trimmer pot except a little bit distorted bass when i set the knob to minimum. also the knob does not have maximum and minimum limit, i tried to turn it up to maximum impedance, but there is no maximum, the knob keeps rotating when i rotate them. is this normal?
   
  nb: i did not install RLIM, i bypassed them with wire


----------



## tangent

Quote: 





> LED1 is not turned on when i turn on the amp


 
   
  Are you certain you didn't put it in backwards?
   
   
  Quote: 





> isn't the rotating knob should rotate in steps?


 
   
  Probably not. I've never heard of a "stepped" trim pot. Without the part number, it's impossible to say more. (Bourns makes a _lot_ of trim pot types.)
   
   
  Quote: 





> the knob keeps rotating when i rotate them


 
   
  If you listen very carefully, you should be able to hear a faint click when you are trying to push the pot adjustment past its limit point. I've broken cheaper trim pots by doing that too often. I don't think I've ever broken a Bourns that way, but best not to do it.


----------



## vodkex

Beautiful amps guys! I've made a CMOY following your schemes tangent (etched my own PCB) and I have to say that it sounds wonderful. I'm using some modded HD202's (opened them up among other things), plus quite a modded xtrememusic. Nice combo! Anyway, I'd like to build something more powerful which will give me some room to upgrade, since I'll probably upgrade to some HD650s in the future 

I live in Argentina so it's difficult for me to find quality components, the only way to get decent opamps, rail splitters, buffers is through TI's free samples program. Right now some TLE2426s and BUF634s are on their way home, takes them three days to get from the USA to down here. I also ordered some OPA827s to try the "FET magic" I keep on reading around here... I already have some OPA1612s, which I've used in my CMOY and my x-fi. Beautiful opamp!

I've been reading your PIMETA schematics and I think it's just complicated enough that I, following the schematics, can turn them into a single layer PCB on my own. (The PPA is too complex for me to design and debug, I won't go that far right now...) This would be my second amp. I think I'll build the v2; but I see that you're using other buffers (the LMH6321, not the BUF634). Can I adapt BUF634s on the opamp outputs instead of the LMH6321, without ill effects on the circuit? If it's not possible, I see the v1 already has them on the schematics, and that'd be the way to go.

I've also read your notes on the V2, and it seems you've tailored it to use FET opamps like the OPA827 instead of bipolar opamps like the OPA1612. Would it be a safe bet to just use the 827s and not even bother with the 1612/pair of 1611s? What do you think? Thanks in advance.


----------



## i_djoel2000

Quote: 





tangent said:


> Are you certain you didn't put it in backwards?
> 
> you're right! i thought the longer leg was the cathode. silly me..lol
> 
> Probably not. I've never heard of a "stepped" trim pot. Without the part number, it's impossible to say more. (Bourns makes a _lot_ of trim pot types.)


   
  this one: http://my.element14.com/jsp/search/productdetail.jsp?SKU=9353186

    
  i just checked it with my multimeter, the pot is still working. but there is no mark indicator to inform us on which impedance we are now. i have to change it manually using multimeter everytime i change them to know the exact value i have at the moment.
   
  it's pretty annoying when you can't just play with them on the go, or without using multimeter. because you want the opamp to get to the maximum performance, yet you don't want to go to deep biasing them.
   
   
  Quote:


tangent said:


> i just checked it with my multimeter, the pot is still working. but there is no mark indicator to inform us on which impedance we are now. i have to change it manually using multimeter everytime i change them to know the exact value i have at the moment.


 

 it's pretty annoying when you can't just play with them on the go, or without using multimeter. because you want the opamp to get to the maximum performance, yet you don't want to go to deep biasing them.


----------



## Avro_Arrow

Maybe you put the LED in backwards..?
  The Trim Pot is 25 turns, not 25 steps.
  That means you have to turn the adjustment
  25 turns to go from the highest to lowest setting
  and visa versa. The is a clutch in the pot so if
  you turn it past the end it will not be damaged.
   
  Follow Tangent guide on how to properly
  set the trim pot.


----------



## tangent

Quote: 





vodkex said:


> I live in Argentina so it's difficult for me to find quality components


 

 You'll have to do the same thing we do here in the US: mail-order them.
   
   
  Quote: 





> the only way to get decent opamps, rail splitters, buffers is through TI's free samples program.


 
   
  That is simply not true:
   
DigiKey Argentina
RS International
Farnell Argentina
   
   
  Quote: 





> Can I adapt BUF634s on the opamp outputs instead of the LMH6321, without ill effects on the circuit?


 
   
  As you've noted, we used to use that in PIMETA v1. There are no changes in PIMETA v2 that prevent you from using this other buffer. The main reason to use the LMH6321 instead is that it sounds better.
   
   
  Quote: 





> Would it be a safe bet to just use the 827s and not even bother with the 1612/pair of 1611s?


 
   
  Yes.


----------



## vodkex

Thank you tangent! I'll keep those in mind next time I'm in the need of parts. On the other hand, I've got some more questions, if you don't mind. I've already designed the entire amp, one PCB for the PSU and another for the amp itself and its 3 channels.

What's up with RBIAS in the v2 schematic? I don't understand how should I wire it up in the PCB. I mean, it's a trimpot, one pin goes to ground, the other's the input and the middle one is the wiper. Am I right?





What should I do here? As I understand it, both the wiper (middle) and either left or right pins are connected (and shorted, maybe?) to v+, while the other remaining pin goes to RBLIM and then it connects to Q1's emitter pin. I think I don't have a use for the SBIAS switch in the schematics, so I left it out. What's the correct way to wire this trimpot into the PCB? Is it as I have described? I have a feeling it's not like that, so that's why I'm asking. If you can shed some light on this one, I'll be really grateful.


----------



## tangent

Quote: 





> both the wiper (middle) and either left or right pins are connected (and shorted, maybe?) to v+, while the other remaining pin goes to RBLIM and then it connects to Q1's emitter pin


 
   
  That is indeed what the schematic says.


----------



## fylde

Hello,
   
   
  First post here.
   
  I have just received the board and parts for the PIMETA V2 and have completed the build. To my total amazement it worked first time with no problems and the DC offset seems well with the acceptable limits per the guidance notes. The amp sounds great and I have never attempted anything like this before.
   
  One question, if anyone would be so kind, is regarding the class A biasing. I have followed the notes to activate this and have installed the relevant parts. If I adjust the trim pot I can't detect any difference when adjusting either way. I did have trouble with my soldering iron when soldering the Q1, Q2 and Q3 parts and I wondered, if I have killed any of these parts would the amp still work, allbeit without the class A biasing, or would I not be getting any sound at all?
   
   
  Many thanks in advance.


----------



## MisterX

Did you install a jumper between the two through hole pads located below the RBLIM resistor?
   
http://tangentsoft.net/audio/pimeta2/bitmaps/brd-2.01.png


----------



## fylde

Thank you for the reply.
   
   
  Yes I installed that jumper and also the resistor RBLIM. I realised the jumper could have been left out an I could have used RBLIM to span the gap but I have left the jumper and RBLIM as they are.


----------



## tangent

When you say you cannot "detect" a difference, do you mean you cannot hear it or you cannot measure it with a DMM?
   
  If you just can't hear the difference, beware that class A biasing isn't a night-and-day kind of thing.  Some op-amps are so designed that you might get no benefit from additional biasing at all.


----------



## fylde

Hello Tangent,
   
   
  Thank you for your reply.
   
   
  My multimeter has now gone on the blink so I haven't measured the bias. I couldn't detect the difference when listening and from reading the notes I thought that I should detect a slight difference in volume and possibly quality / character of sound.
   
  My main question is whether the amp would still operate at all even if I had killed any of the Q1, Q2 and Q3 parts? Or would it work as if the bias was disabled? Apologies if this is a question that cannot be answered given the limited information I have given.
   
  The OP amp I am using for OPALR is AD823ANZ per the parts list and OPA134PA for OPAG. Further listening has shown me that this chip does sound a tad edgy with my Grados so I may try the other recommended DIP 8 OPALR OPA2132PA or even AD8620ARZ with an adapter socket.
   
  I would like to add the unity bass boost also, but am unsure what type of capacitor should be used and what sort of range of capacitance I should be looking for?
   
   
   
  Many thanks again.


----------



## i_djoel2000

Quote: 





tangent said:


> When you say you cannot "detect" a difference, do you mean you cannot hear it or you cannot measure it with a DMM?
> 
> If you just can't hear the difference, beware that class A biasing isn't a night-and-day kind of thing.  Some op-amps are so designed that you might get no benefit from additional biasing at all.


 

 hi tangent, can you mention some opamps that benefit greatly from class A biasing? i'm now using between OPA827, LT1364, or LM4562 (depending on mood), and i couldn't really notice any difference when i play with the trimpot


----------



## tangent

Quote: 





fylde said:


> My main question is whether the amp would still operate at all even if I had killed any of the Q1, Q2 and Q3 parts?


 

 You can kill a transistor in probably half a dozen different major ways.  If I remember my combinatorics correctly, that makes for 6 * 5 * 4 = 120 unique failure mode combinations.
   
  So no, you haven't given enough information.
   
   
  Quote: 





> I would like to add the unity bass boost also, but am unsure what type of capacitor should be used and what sort of range of capacitance I should be looking for?


 
   
  See the bass boost docs for the PPA.  The same principles apply.
   
  Quote: 





i_djoel2000 said:


> can you mention some opamps that benefit greatly from class A biasing?


 

 I've never bothered to sit down and compare op-amps purely in terms of "biasability".
   
  Generally speaking, the lower the device's idle current, the more likely it is to benefit from a little extra bias on the output stage.  This is why the 13 mA Iq AD843 is famously among those chips not really helped by extra biasing.  It already has plenty designed into it.


----------



## fylde

Thank you for the reply.
   
   
   
  I borrowed a multimeter and have measured the voltage going through RBLIM and this does change as RBIAS is adjusted. At the maximum I get 0.964 V. I do not have the knowledge to do any further tests on my PIMETA V2 build and the class A biasing so any further pointers would be gratefully received.
   
   
  Many thanks.


----------



## fylde

Hello,
   
   
   
  I have just built my Linkwitz Crossfeed circuit as supplied by Tangentsoft and I am a little unsure if I have installed the jumpers correctly. I wanted to use the board in a set configuration of low crossfeed so have not installed switches. I have soldered one jumper from S1L1 to S1L2 and a second jumper from S2E1 to S2E2. I have tested the circuit and the bass just disappears and the presentation is a little harsh.
   
  I have re-read the article on the Tangentsoft website and in particular the bit that says _"If you only want one crossfeed setting, you can leave out the R1As and jumper from each S1C to the corresponding S1L"_ which I think suggests that my jumpers are incorrect.
   
   
  Any help is appreciated.
   
  Many thanks


----------



## tangent

Yes, you've wired it incorrectly all right. To get the effect you want, the correct jumper configuration is:
   
  S1C1 -> S1L1
  S2C1 -> S2E1
  S1C2 -> S1L2
  S2C2 -> S2E2


----------



## fylde

Thank you for clearing that up for me!
   
   
  The crossfeed circuit has really transformed the sound, it sounds so much more spacious and even, for some reason, tamed some of the hard edge to the upper frequencies I was experiencing.
   
   
  I would still like to try the unity gain bass boost and have read the information on the PPA page, but when I use the bass boost calculator and enter my resistor values it seems as though I would have to use a different R7 with much higher resistance than the one I have used per the schematic (100 Ω). All my resistor values are as per the schematic exept R3 and R4 (2K and 10K). Is there anywhere I can find out what R7 values I can go up to safely?
   
  Many thanks.


----------



## tangent

The PPA bass boost calculator doesn't work for the PIMETA circuit. I pointed people to the PPA docs only for advice on cap types.
   
  If you want to use the calculator, you'll have to build up the PPA circuit atop the PIMETA circuit, as described in the PIMETA docs.


----------



## fylde

Thank you for your reply.
   
   
  Do the notes on the capacitor values recommended (0.01UF to 0.1UF) still apply to the Pimeta?
   
  I am just trying to find out what sort of range of capacitance I need so I can try a few different values and see what works for me.
   
   
  Many thanks


----------



## ShadowKntSDS

I've built a CMOY, and am planning building a PIMETA next.   I also have an E9 for comparison.   Can anyone speculate on what sonic differences these circuit level changes make:
   
  What does the 3ch topology do for the sound?
  What does biasing into class A do sonically?
  Does the buffer matter as much if I am driving high impedance (600ohm) head phones? .
   
  I know what all of these changes do electrically, but have no idea what they might do for the sound.


----------



## tangent

Quote: 





fylde said:


> Do the notes on the capacitor values recommended (0.01UF to 0.1UF) still apply to the Pimeta?


 
   
  What's important the ratios of the cap and the resistor paralleling it.  If you use the same resistor value as recommended for the PPA, then yes, the cap value range is the same.  By default, we recommend a lower R4 value about half that in the PPA, however, so you might need to use a cap value twice what you'd use in a PPA. Quarter the resistor value, quadruple the cap value, etc.


----------



## fylde

Many thanks again for your help, I understand now.
   
   
  I just changed my R3 and R4 to increase the gain to compensate for the crossfeed board I have installed, R3 was as per the schematic 1K and R3 was not as per the schematic at 2K for a gain of 3.
   
  I used the calculator to go for a gain of 6 and it gave me an R3 vlaue of 2K and R4 10K so I have installed these. I may be imagining it but it possibly doesn't sound as good as before but I can't put my finger on it, I looked back through the notes in the part selection guide for these resistors and it does mention keeping R3, R5 and R6 the same and just adjusting R4 for the gain.
   
  Have I made an error in keeping R5 and R6 as per the schematic and changing R3 & R4 instead of just R4 as suggested?
   
  Many thanks


----------



## tangent

I think it's more likely that you just don't like the sound of the crossfeed circuit.


----------



## fylde

Thak you for the reply.
   
   
   
  I did think that the crossfeed sounded great, then I installed different R3 & R4 to compensate for the loss in gain and further listening was wondering if I had lost something. If changing R3 as well as R4 doesn't throw anything out in relation to R5 & R6 then thats all I was concerned about.
   
  I have just taken delivery of a couple of switches that I shall wire up to the crossfeed circuit so I can get a better idea when comparing.
   
   
   
  Many thanks.


----------



## fylde

Quote: 





shadowkntsds said:


> I've built a CMOY, and am planning building a PIMETA next.   I also have an E9 for comparison.   Can anyone speculate on what sonic differences these circuit level changes make:
> 
> What does the 3ch topology do for the sound?
> What does biasing into class A do sonically?
> ...


 


  I have a basic CMOY I got off ebay which then prompted me to build the PIMETA V2. The PIMETA sounds much cleaner and drives my Grado SR80s much better than the basic CMOY. Sorry i am not much good at going into detail here but I am glad I bulit the PIMETA.


----------



## alphaman

[size=10.0pt]I haven't fully explored this thread (much less this forum on the following topics) so please forgive any waste-of-bandwidth. Anyway ...[/size]

  [size=10.0pt] [/size]

_[size=10.0pt]WRT tweaking v2 ...[/size]_[size=10.0pt][/size]

  [size=10.0pt] [/size]

  [size=10.0pt](1) How much extra benefit can be obtained further bypassing (beyond Tangent's topology/schema) various opamps (either buffers or main)? E.g., for the main L/R opamp, I am using 10uF BlackGate electros + AVX 0.1uF PPS smd's. Not a whole lot of room, but the electros have improved SQ.[/size]

  [size=10.0pt] [/size]

  [size=10.0pt](2) C6 (NP0 or C0G) seem to be located – PCB footprintwise -- quite far from opamp pins (esp. C6 R/L). Has anyone experimented with moving R6/C6 closer -- make a diff.? Also, given the signal-path route of this cap, I wonder how much benefit can be obtained using Styroflex (shown below) – anyone experiment with this type?[/size]



   

  BTW ... for you fellow op-amp rollers ... I've just installed LT1364, which is (shudder!) a bi-polar device. Haven't 'scoped the output yet but, even simply 'dropped in' into Tangent's default topology, they seem to work and work well! Prev. running AD825 (best IMO!), but also tried AD8620 and OPA2132.

  [size=10.0pt][/size]


----------



## i_djoel2000

@alphaman: have you tried ad827 on both signal and ground opamp? i like them better than the ad8620/8610 combo


----------



## alphaman

Quote: 





i_djoel2000 said:


> @alphaman: have you tried ad827 on both signal and ground opamp? i like them better than the ad8620/8610 combo


 
  Thx for reminding me of this OPA ... no I haven't, tho' I have it in my parts bin. (Feedback on this soon ...)

 About the AD8610/20 ... 
  GOOD: Pace, rhythm, acceleration and timing (aka PRaT) is among the best (like AD825).
  OK: Detail, image focus
  BAD: Graininess, unrefined, "loud" (as opposed to fwd or lively) sounding.
  I'm not sure there is any way to tame these BAD qualities. Certainly, my added bypassing, noted above, didn't help. There is also op-amp snubbing, which I've tried in other projects, but not in Pimeta due to limited space.
   
  I have some voltage limits, too, so I've gotta be somewhat selective with OPAs. FWIW, I use two parallel 9.6V Imedion NiMH batts. (Parallel for longer-duration pwr).
   
  BTW: (Mostly a query for Tangent, I guess, tho' anyone's reply is welcome) ... how _important_ is it to have "matching" OPAs for BOTH gnd _and_ main L/R? E.g. AD8610/8620; OPA132, 2132; etc.?
   
_Notes on tweaking op-amp performance via non-std. bypassing and snubbing:_
  47-100 uF high-quality electro cap from each rail to gnd (hard to do in Pimeta). Add a very small cap _across the rails_ (1nF MKT). Snubbers: from each rail to ground (0.22R+3.3nF).


----------



## i_djoel2000

Quote: 





alphaman said:


> Thx for reminding me of this OPA ... no I haven't, tho' I have it in my parts bin. (Feedback on this soon ...)
> 
> About the AD8610/20 ...
> GOOD: Pace, rhythm, acceleration and timing (aka PRaT) is among the best (like AD825).
> ...


 

 have you tried to upgrade your resistor? i use full takman metal film resistors 1/4W on the signal and ground path and i did not find those problems with the ad8620/8610 combo, not grainy at all and very transparent sounding. i know tangent will deny this statement, but, why don't you just give it a try? there must be good reason why gaincard uses premium quality resistors in their signal path 
	

	
	
		
		

		
			





 i know it's like 8 times more expensive than RN55 (which is only around 0.1 cent a piece), but i did not regret buying those resistors at all 
	

	
	
		
		

		
		
	


	



   
  as for the ad8620, i just found it too bright for my current setup, that's why i switched to opa827


----------



## tangent

Quote: 





alphaman said:


> BTW: (Mostly a query for Tangent, I guess, tho' anyone's reply is welcome) ... how _important_ is it to have "matching" OPAs for BOTH gnd _and_ main L/R? E.g. AD8610/8620; OPA132, 2132; etc.?


 

 Tangent already answered that, in the docs. Quoting:
   
   
  Quote: 





> Some argue that you should use the single-channel version of the chip you used for OPALR in OPAG; the theory goes that because the ground channel must counteract the currents created by the left and right channels, using the same type of chip in all three channels is likely to give the lowest distortion since they all react to the signal in the same way. What we find in practice is that because both contribute to the sound of the amp, using dissimilar chips in OPAG and OPALR lets us fine tune the amp’s sonic signature more finely than if we always use the same chips for all channels. There is no practical limit on how widely different your OPALR and OPAG chips can be, as long as each is compatible with the PIMETA v2 circuit as a whole.


----------



## Avro_Arrow

While not a PIMETA, here is a good example.
  My amp uses 3 LT1363 with OPA633 buffers on the channels
  and BUF634 on the ground.


----------



## alphaman

Quote: 





i_djoel2000 said:


> have you tried to upgrade your resistor?
> as for the ad8620, i just found it too bright for my current setup, that's why i switched to opa827


 
  It has been a while since I built the unit, but I'm pretty sure I chose HQ metal film Rs ... mostly Panasonic and Vishay. But, since you brought it up, I may experiment with other brands.I agree that signal-path Rs must be of v. HQ.
  Did you mean the *AD*827 (and not *OPA*827)?


----------



## i_djoel2000

Quote: 





alphaman said:


> It has been a while since I built the unit, but I'm pretty sure I chose HQ metal film Rs ... mostly Panasonic and Vishay. But, since you brought it up, I may experiment with other brands.I agree that signal-path Rs must be of v. HQ.
> Did you mean the *AD*827 (and not *OPA*827)?


 

 no, i really meant opa827: http://my.element14.com/texas-instruments/opa827aid/ic-op-amp-jfet-30mhz-ln-8soic/dp/1684749?Ntt=opa827


----------



## alphaman

What are you folks using for C6 (which Tangent suggests as NP0 or C0G)? I'm using CAP CERAMIC 10PF 50V NP0 1206 (Digikey 399-1192-1-ND; Kemet C1206C100J5GACTU), which is a $0.14 part. 
   
  Not sure whether upgrading this to something better will make much of a diff. I noted Styroflex above, but I have none that go this low in capacitance value, e.g., 10pF. Any thoughts?
  Thanks!


----------



## jcx

I would suggest discussion of gnd channel op amp/buffer choice fine tuning the sound are evidence of conceptual failure of the whole "3-channel" idea


----------



## MisterX

My nonsense to English translator must be broken again.


----------



## jcx

you must have broke it, it had to have worked at one time if you build, sell, advocate for  "3-Channel" headphone amps as having technical justification and measureable superiority to good dual supply amps with layout by people who actually understand grounding


----------



## Spacehead

Now testing Ready-to-use NiMH batteries and I must say that Pimeta v2 excels so well in producing purest sound for a battery powered device!


----------



## i_djoel2000

just thought i should share my recently cased and perfected pimeta. it's not the most beautiful looking one, though


   

   
  i use 4x aaa batteries and dc-dc step up converter (stepped up to 12V). i already anticipated that the sound will not be as good as i would like it to be, but i was wrong! there is no noise at all even though i cranked up the volume to maximum (no music playing)
   
  this configuration gives me almost 20 hours of run time. much better than using 9v battery 
	

	
	
		
		

		
			




   
  next plan: install dc socket to make the battery rechargeable without taking it out of the case. then buy this: http://store.curiousinventor.com/tenergy-universal-smart-charger-for-nimh-battery-packs-2-4v-7-2v.html


----------



## tangent

Quote: 





> i use 4x aaa batteries and dc-dc step up converter...no noise at all


 
   
  Cool! Which one did you use?


----------



## i_djoel2000

Quote: 





tangent said:


> Cool! Which one did you use?


 

 this one: http://my.element14.com/jsp/search/productdetail.jsp?SKU=1818377
   
  by the way, i noticed some annoying buzzing sound after the batteries are almost out of juice. i was wondering what is the problem?? i thought it's broken opamp or soldering. but then i measured the dc offset at the ouput jack, it went to 0.5V!
   
  how could this happened, tangent? the dc-dc converter requires a minimum of 4.5V supply voltage, and the battery goes to 3.6V when it is out of juice. do you think the problem is because the battery is running out?


----------



## tangent

Quite possibly. I don't see a reason to expect a DC-DC converter's performance to degrade gracefully when not given enough voltage to operate.
   
  If you search the archives, you can find low-battery voltage indicator circuits that will warn you to turn the amp off before you get to that point.


----------



## i_djoel2000

Quote: 





tangent said:


> Quite possibly. I don't see a reason to expect a DC-DC converter's performance to degrade gracefully when not given enough voltage to operate.
> 
> If you search the archives, you can find low-battery voltage indicator circuits that will warn you to turn the amp off before you get to that point.


 
   
  is it in here? http://tangentsoft.net/audio/pimeta2/tweaks.html
   
  i couldn't find it


----------



## Avro_Arrow

It's here.
  
  Quote: 





i_djoel2000 said:


> is it in here? http://tangentsoft.net/audio/pimeta2/tweaks.html
> 
> i couldn't find it


----------



## i_djoel2000

Quote: 





avro_arrow said:


> It's here.


 

 thanks for the link. i checked the circuit, it is too big for portable use. my pimeta case barely have the space for something like that
   
  @tangent: how do i check the opamp functionality? i'm afraid there is some problem with the opamp or the buffers. it all started after the opa827 left channel suddenly died, then i switched to ad8610, then the buzzing sound and run out of battery happened


----------



## Avro_Arrow

There is a simpler one in Tangents site that just turns off the LED
  which should fit. I don't remember off hand which amp it is
  associated with.


----------



## tangent

Quote: 





i_djoel2000 said:


> i checked the circuit, it is too big for portable use





   
  There are at least two mentioned in that thread. The one I posted above the one Avro's link takes you to requires a dual op-amp, a handful of resistors, and a reference. Even with thru-hole, you could probably pack that into a corner somewhere. Do it with SMT, and it should be easy.
  
  Quote: 





> how do i check the opamp functionality?


 
   
  The best way is to plug them into a separate, known-working circuit.
   
  Lacking that, you can build this or something like it.
   
  I doubt your low-battery problem killed the op-amps, by the way. I think it's more likely that your initial successes with the DC-DC conversion circuit were a matter of insufficient testing, and that you're now finding the downsides.
   
  Try temporarily bypassing the conversion circuit and powering from a good linear power supply.
   

  Quote: 





avro_arrow said:


> There is a simpler one in Tangents site that just turns off the LED
> which should fit. I don't remember off hand which amp it is
> associated with.


 

 You're thinking of the zener/CRD cut-off circuit in the META42.
   
  You don't have to have a CRD. You can replace it with any constant current source. There are many in my op-amp biasing article, but easiest would be to use the one the PIMETA v2 already gives you, in _its_ class A biasing circuit.
   
  If you put a zener in series with LED2, you get the META42 circuit. The downside of that is that when the LED cuts off, it also cuts off class A biasing, though that's a small matter. You could even spin it as a positive thing, since it's a way to save on battery power.
   
  If you don't like that, you could just add another transistor to the current mirror and run your zener-limited cut-off LED from that.


----------



## i_djoel2000

tangent, thank you for your respond. i think voltage indicator would not be necessary for my pimeta. the dc-dc converter simply won't turn on when voltage supply is below 4v
   
  now i'm running the amp on another set of 4 aaa batteries, still no problem so far. i'll turn it on for 5 hours and see what happens, i hope the previous problem was only a small glitch and nothing goes wrong this time. what is the capacitance of normal aaa batteries? i'm trying to predict the hours of the run-time


----------



## i_djoel2000

i think i just found the problem..
   
  well, it is not really a concerning problem but it is the downside. it turns out that the dc-dc converter consumes some heavy current as well as the pimeta. i measured the current draw on the battery socket and i got reading of around 150mA (more than twice of normal pimeta!!), the volume pot was set to 9AM, hence you pretty much get the idea of how power-consuming this converter in normal usage. i checked the murata datasheet but i couldn't find any current consumption of this converter, then i thought it only consumes very little current if does not consume them at all
   
  when the voltage across battery drops below 4V, the converter produces really low voltage (below 1V), then the buzzing noise comes out of the headphone jack, i guess this explains everything.
   
  now i'm out of idea on how to utilize this pimeta, 4 hours of run time with 300mA 9v battery is pretty much useless for portable use. someone please enlighten me! 
	

	
	
		
		

		
			








 anybody knows a good dc-dc step up converter that does not consume much current?


----------



## tangent

There's no such thing as a free lunch, dJoeL.
   
  5 V divided into 12 V is 2.4, which is how much output current must be multiplied to get input current, if the converter is 100% efficient.  The actual efficiency is closer to 80%, so the multiplier is closer to 3.
   
  If it were otherwise, power in would be less than power out. In other words, you would be creating power.
   
  The actual situation: P=IV, so if current out is 50 mA and voltage out is 12 V, then P_out = 0.6 W. Likewise, P_in is approximately 0.75 W, or 125% more than P_out, as expected. The law of conservation of energy is preserved.


----------



## i_djoel2000

Quote: 





tangent said:


> There's no such thing as a free lunch, dJoeL.
> 
> 5 V divided into 12 V is 2.4, which is how much output current must be multiplied to get input current, if the converter is 100% efficient.  The actual efficiency is closer to 80%, so the multiplier is closer to 3.
> 
> ...


 

 i know there is efficiency takes place in the equation. but still, almost 100mA current consumption for the converter alone is way beyond my expectation!
   
  i thought about the dc-dc converter after local member made a cmoy with cheap dc-dc converter. with ad8397 opamp, it gets the amp to run around 10 hours, meaning the converter does not consume current that much. the converter simply looks like a miniature transformer, unlike mine. based on that experience, i figured using more expensive dc-dc converter will get you the same result plus better efficiency. i guess i was wrong..
   
  now i'm thinking to use buf634 (min. 2.25V supply voltage) as buffer, LM4562 (min. 2.5V supply voltage) in signal, and lt1364 (min. 2.5V supply voltage) in ground without the converter. i tested the same configuration but with the LMH6321 buffer, works great, got reading of 0.5mV dc offset.but the music is still distorted when bass impact is involved, otherwise fine. i thought the problem was the insufficient buffer, LMH6321 (requires 5V supply voltage, while the battery only gives around 3V after rail splitter). what do you think, tangent? do you think the distortion was caused by the opamp, or buffer?
   
  note: my power supply is 3x aaa rechargeable batteries (around 4.8V max)


----------



## cobaltmute

Quote: 





i_djoel2000 said:


> now i'm thinking to use buf634 (min. 2.25V supply voltage) as buffer, LM4562 (min. 2.5V supply voltage) in signal, and lt1364 (min. 2.5V supply voltage)


 

 You need to check those voltages again as they are incorrect without some signs in front of them (which changes things significantly).


----------



## cobaltmute

Quote: 





i_djoel2000 said:


> I know there is efficiency takes place in the equation. but still, almost 100mA current consumption for the converter alone is way beyond my expectation!


 
   
  This is not about efficiency.  It is about power and the convertor is not consuming 100mA.
   
  Let say you amp is drawing 50mA @ 12V
   
  12V x 50mA = 0.6W.
   
  So we need 0.6W of power.
   
  0.6W / 4.8V = 125mA.
   
  So 4.8V @ 125mA is the **same power** as 12V @ 50mA.
   
  And a DC-DC convertor uses the same *power*, but converts the voltage.  Now a DC convertor is not 100% efficient.  Let's say it is only 80% efficient, so 20% or 25mA is wasted in the conversion, make the total draw 150mA
   
  Don't forget that the situation gets worse as the batteries discharge, as 4.8V is fully charged.  As the the voltage drops in the cells, the current demand goes up, hasten the death of the battery.


----------



## i_djoel2000

Quote: 





cobaltmute said:


> You need to check those voltages again as they are incorrect without some signs in front of them (which changes things significantly).


 

 it has plus minus sign in front of them, i just don't know how to type them with the keyboard. if i'm not mistaken, 2.5V supply voltage needs at least 5V in single supply operation
   


  Quote: 





cobaltmute said:


> This is not about efficiency.  It is about power and the convertor is not consuming 100mA.
> 
> Let say you amp is drawing 50mA @ 12V
> 
> ...


 

 thanks for the explanation. but, maybe you got me wrong? my pimeta is drawing 150mA after the conversion, meaning it was already in 12V. if the amp is really drawing 150mA, i wonder why i still need to crank up the volume to the same level as when i used 9V battery, which in fact only gives around 60mA current draw?


----------



## i_djoel2000

btw, can i solder the buf634 SOIC's pins on the LMH6321 pad? i looked at the buf634's data sheet and pin 5 is not connected anywhere, while in pimeta v2 pin 5 is connected to ground.
   
  but i do remember tangent used buf634 on pimeta v1, that is why i'm asking this


----------



## cobaltmute

You could get adapters, but that will make your amp non-portable.
   
  And read my comment about the voltages again.  The minimum supply voltages are the same.
   
  And if you are really concerned, you could consider another case.  Unless I'm reading the dimensions wrong, the Hammond 1455J1202 is the same size as the Serpac H-65 and I have 12xAAA in my Hammond case.  14.4V with 800ma capacity.


----------



## Reima

My solution was to use 3 x 1500mah Iphone 1G batteries that I got off of Ebay. I wired them in series with a protection PCB (see link below). On the second charge I got 17 hours of running time. You will also dedicated Li-poly charger. I have installed a jack so that I can charge the battery witout removing it from the amp.
   
http://www.batteryjunction.com/prcimopcbfor1.html 
   
http://www.tenergybattery.com/index.php?option=com_virtuemart&page=shop.product_details&flypage=shop.flypage&category_id=17&product_id=85&Itemid=1&vmcchk=1 
   
  RC


----------



## i_djoel2000

Quote: 





cobaltmute said:


> You could get adapters, but that will make your amp non-portable.
> 
> And read my comment about the voltages again.  The minimum supply voltages are the same.
> 
> And if you are really concerned, you could consider another case.  Unless I'm reading the dimensions wrong, the Hammond 1455J1202 is the same size as the Serpac H-65 and I have 12xAAA in my Hammond case.  14.4V with 800ma capacity.


 

 wait, i'm still confused..if i want to use buf634 in pimeta v2 pcb, i need to use adapter??


----------



## cobaltmute

Quote: 





i_djoel2000 said:


> wait, i'm still confused..if i want to use buf634 in pimeta v2 pcb, i need to use adapter??


 

 This is my mistake - for some reason I was thinking of the Buf634 in DIP, not SOIC.


----------



## i_djoel2000

Quote: 





cobaltmute said:


> This is my mistake - for some reason I was thinking of the Buf634 in DIP, not SOIC.


 

  
  right, so the soic buf634 is directly compatible in the pimeta v2's buffer pads then?


----------



## tangent

It looks like it.
   
  Why do you want to do that? It won't sound as good. The compensation is that it will draw less power if you leave the bandwidth pin floating. Is that what you're after?


----------



## i_djoel2000

Quote: 





tangent said:


> It looks like it.
> 
> Why do you want to do that? It won't sound as good. The compensation is that it will draw less power if you leave the bandwidth pin floating. Is that what you're after?


 


  aahh..so in the datasheet, BW stands for bandwidth
   
  no, i am after the supply voltage range, because 4x aaa batteries is the maximum allowed space in my serpac h65.
   
  why did you use BUF634 in pimeta v1, then? i saw the schematic in pimeta v1 and the BW pin is not connected anywere, either..*i'm thinking to use the BUF634 SOIC version


----------



## tangent

http://tangentsoft.net/audio/pimeta2/history.html


----------



## i_djoel2000

Quote: 





tangent said:


> http://tangentsoft.net/audio/pimeta2/history.html


 


  got it. thanks


----------



## boris81

Hi,
   
  I just assembled a PIMETA v2 but it doesn't work right. I'm using this 24V wallwart and the LEDS light up.
   
  However all 3 buffers are getting very hot within a few seconds of operation while the opamps stay at normal temperature.
  I hooked up headphones against the documentation advice and found out that one of the channels works while the other doesn't. I jiggled some of the components to look for bad connections and discovered that when pushing down the ALPS RK27 pot the second channel comes in. There are also some crackling sounds when touching the pot.
   
  Is it likely that the buffers overheating can be caused by a defective pot or that i broke a pin on the pot while soldering it?
   
  I have almost no experience with soldering but it looks like I put everything together pretty good. I will take some measurements and pictures later to aid the debugging.


----------



## tangent

The pot may be bad, but I can't see a way it can cause the buffers to get hot.
   
  Yes, pics, definitely.  Both sides.


----------



## Maverickmonk

Alright, IE9 is giving me some crap trying topost this, but I came across the Audio GD PSU09 board today, and was wondering how it would work for the Pimeta? http://www.audio-gd.com/Pro/diy/PSU09/PSU09EN.htm
   
  Could one wire up this board, with 2 torroidal transformers, and then output the V+, GND, and V- lines directly to the Pimeta, eliminating the need for the power-section of the original board schematic? This would require shorting the two output grounds on the Audio GD board, is that possible? This would be for a desktop implimentation of the Pimeta, and I was thinking that a dedicated transformer with board might be more effective and efficient than a wallwart type supply.


----------



## boris81

Yes, it turns out it's 2 separate issues. The pot is good but I had a peculiar problem with it. I can't see very well under it but it seems like there are some metal elements sticking out besides the actual 6 pins. The metal parts from the bottom of the pot are touching the holes on the board for the smaller pot. It was shorting one of the channels.
   
  I don't know how to desolder the pot and I didn't want to cut the pins to investigate so I stuck a piece of plastic underneath and that seems to fix it. Now I have 2 clear channels but all 3 buffers still get very hot.


----------



## boris81

My PIMETA v2 plays music but the buffers get very hot within a few seconds. I have almost no experience with building amps so I'm posting pictures and the components I used hoping that you guys can spot what I'm doing wrong much faster than I can debug it. I visually inspected all solder joints and they look OK to me but I could try to get a close up of some parts if needed.
   

  top
  I didin't realize those red caps are so bulky until they arrived. They fit OK though.
   

  bottom.
  I really wish I used headers for all wiring. I tried soldering twisted copper wires from the power supply wires directly to the board and they eventually ended up touching and throwing sparks. There are burn marks on the board but I think it's OK.
   

  side.
  I wanted to make C6 replacable so I "hacked" the header you see on the left from an old 28pin DIP socket. For the moment I'm using 10pF caps for C6.
   
   
   
   
  I followed the suggested values on the schematic for the most part. The only deviations I chose were 10pF for C6 and .12uF for C1, C3 and C5.
  Here is a list of the components I used:
   
  - power supply 1 24V VDC 1A linear regulated 2.1mm  jameco
  
  - R1L/R  2  4.32 KOhm .4W 1%   digikey PPC4.32KYCT-ND
  - R1G  1  = R1
 - R2  2  499 kOhm 1/4W 1%   digikey 499KXBK-ND
  - R3  2  1 kOhm .1%    have it
 - R4L/R  2  4.75 kOhm 1/4W 1%   digikey RNF14FTD4K75CT-ND
  - R4G  1  = R1
 - R5  2  3.32 kOhm 1/4W .1%   digikey RNF14FTD3K32CT-ND
  - R6  2  = R2
 - R7  3  100 Ohm .5W 1%    digikey PPC100XCT-ND
  - R11  3  = R5
 - RBIAS  1  5K trim pot    digikey 3296W-502LF-ND
  - RBLIM 1  1 kOhm .1%    have it
 - RCCS  not used
 - RLED 1  10 kOhm     have it
 - C1  2  .12 uF 1% 50V    digikey p3874-nd
 - C2  3  470 uF 20% 25V    digikey 493-1553-nd
 - C3,C5  4  = C1
 - C4  2  6.8 uF     webshop
 - C6G-L-R 3  10 pF 5%    digikey 490-3678-ND
 - LED1,2  2  3.7V digikey 404-1175-ND
 - D1,2  1 (D1)  diode     digikey 1N4001FSCT-ND
 - Q1 1  PNP transistor    digikey 2N5087
  - Q2-4 4  NPN transistor    digikey 2N3904BU
 - IC1    - not used
 - IC2  1  TLE2426 rail splitter   digikey 296-1994-ND
 - BUF*  3  LMH6321MR buffer   newark LMH6321MR
  - OPALR  1  AD8620 dual sm    digikey AD8620ARZ
 - OPAG  1  AD8610 single sm   digikey AD8610ARZ
 - vol pot 1  50 K     webshop
 - input  1  3.5mm .125" 3way   digikey CP1-3513-ND
  - output  1  6.35mm .25" 3way   digikey SC1317-ND


----------



## vodkex

Well, my homemade pimeta v2 is up and running! I used the v2's L and R channels plus the v1's ground channel, all with BUF634s in WB mode. Opamps are OPA827s. Nice sound quality, a clear improvement from my OPA1612a powered CMOY. It's a good match to my SR850s.
   
  Anyway, I'm having a little problem, I think it has to do with the PSU I designed. It's a dual voltage one, 220v AC -> 15+15v AC. I'm converting those ±15v AC to DC with a 4 diode bridge, then filtering with 3 1000uF 63v caps and then it gets regulated with a LM7815+LM7915 pair. The regulated output is then filtered with 2 1000uF 50v caps (the rail caps in the schematic), after that comes the v2's class A biasing circuit, and after all that the 6 bypass/high speed caps, as per the v2's PSU schematic. The only thing missing is the TLE2426 since I have a real ground here. The problem is, I think there's a grounding issue...
   
  When the PSU is plugged and feeding the amp, I can hear a faint "scratching" hum in the background. When music is playing nothing gets hot, so everything's working fine. When I unplug the PSU and the amp goes on only with the capacitors' reserve current until they get depleted, that scratching hum is gone, the background is pitch black as it should be. 
   
  It's not a PSU problem since I was using it with the CMOY; ±15v to the opamp's V±, and its ground connected to where the virtual ground point should be (between the caps and the 4.7k resistors, which I removed). Pitch black background with the CMOY, but not with this homemade PIMETA v2. 
   
  What could be the problem? Is there something I'm hooking up the wrong way? Thanks.
   
   
  EDIT: I probably have a bad pot. When it's at maximum volume that scratching sound is almost gone, but if it's not, it gets a lot more noticeable, apart from the fact that one channel sounds louder than the other at anything other than max volume. But as I've just said, when I unplug the PSU that sound is gone for the time the capacitors hold their charge. I'll change the pot and report back..
   
  EDIT2: I'm now using another source to try the amp.. my x-fi (I was using my nokia 5800 before). The pot is still doing its weird stuff but the faint scratching noise is now mixed with hiss. Now when I unplug the PSU, the hiss is still there until the caps run out of juice. Interesting.. That's the noise of my sound card. It's bad :/ but it's badly amplified since I have to use the pot at 100% volume to keep it from producing a stronger scratching noise. I'll change it tomorrow..


----------



## boris81

vodkex said:


> EDIT: I probably have a bad pot.




 Vodkex, are you using the ALPS RK27? I was having a problem with that pot on the pimetav2 board. Check out my earlier post #339


----------



## vodkex

Unfortunately I'm not using that well built pot. Just using parts from the local electronics shop just to get this amp going. Probably in the future I'll get higher quality parts.
   
   
  I've solved my problem!!! I had two 1000 uF 50v caps after the LM7815 and LM7915 outputs in order to filter the regulated voltage. I decided to remove them (due to having read somewhere that having caps after regulators defeats their purpose) and solder some 4.7 pf ceramic caps I had as spares on the regulators' legs, between ground and their outputs. After that I took the CMOY's 10k pot and 100k input resistors and changed the 50k pot and 470k resistors I had on my homemade PIMETA... and almost all of that scratching humming noise is gone! There's still a liiittle bit, but to hear that I have to stop all music and listen to background noise. At least it's listenable now..
   
  I'll see what other changes I can do to my PSU to improve its performance with the PIMETA. Really solid amp! I love it 
   
  EDIT: I think the regulators are shot somehow... I hooked up this PSU to this pimeta when I was half way through building it.. somehow I managed to solder the three TO220 BUF634s backwards :facepalm: when this happened, I remember hearing the regulators! They were doing this very same scratching sound but I could hear it... they got very hot too. After getting new buffers and putting them in the correct orientation, that didn't happen and of course everything's working fine. But when I turn on the PSU I hear the regulators do that sound.. for a second, then they go silent. Probably they're broken (although their outputs are correct, voltage wise) and feeding electronic noise to the pimeta.. which translates into that (now) very quiet noise. I'll get a new pair of 7815+7915 and see if that solves the remaining noise.
   
  EDIT2: Well, I added two 6.8 uF nonpolar electrolytic caps as input bypasses on both regulators, one on each. All that scratching noise is GONE! 
	

	
	
		
		

		
			





 the regulators were fine after all.. okay guys, I'm off to enjoy some music on this excellent amp. I'll post pictures of the mess later, I'll have to get/design a case for this but that'll have to wait since university exams aren't far away.


----------



## boris81

Help,

I can't figure out why the buffers of my PIMETAv2 get really hot. If I plug earphones there is sound playing.
I measured the V+ and V- voltage to the chips, also the AC signal from the input, the chips to the output and it seems consistent with what I am expecting. I can't measure the current because I don't have an ammeter. I put up pictures and the components I used in the previous post.

I'm at a loss and I don't know what else to check. Any ideas?

Here is what I get when I trace the power. Pin1 of the buffers is labeled as V- on the schematic but I'm getting pin4 instead. Is that normal?
DC = 24.42
IG-OPAG4 = -11.77
IG-OPAG7 = 11.84
IG-OPALR8 = 11.83
IG-OPALR4 = -11.77

IG-BUFG1 = 1.1
IG-BUFG4 =- 11.77
IG-BUFG5 = 0
IG-BUFG7 = 11.84

IG-BUFL1 = 1.1
IG-BUFL4 =- 11.77
IG-BUFL5 = 0
IG-BUFL7 = 11.84

IG-BUFR1 = 1.1
IG-BUFR4 =- 11.77
IG-BUFR5 = 0
IG-BUFR7 = 11.84


----------



## tangent

Quote: 





boris81 said:


> I can't figure out why the buffers of my PIMETAv2 get really hot.


 
   
  It would be good if you could define "really hot".
   
  The LMH6321 does run fairly warm. Maybe it's fine, and you're just expecting that the chip should run cool to the touch.
   
  Do you have a cooking thermometer? Even that rough a measurement would help.
   
  Quote: 





> If I plug earphones there is sound playing.


 
   
  What's the DC offset on the output?
   
   
  Quote: 





> I can't measure the current because I don't have an ammeter.


 
   
  Are you sure? Only the cheapest sort of DMM doesn't have at least a coarse 10A measurement feature.
   
   
  Quote: 





> I put up pictures and the components I used in the previous post.


 
   
  The silence means no one has seen a problem with either. That's no guarantee that all is well, but usually simple mistakes get noticed pretty quickly.
   
   
  Quote: 





> Pin1 of the buffers is labeled as V- on the schematic but I'm getting pin4 instead. Is that normal?


 
   
  Yes, the schematic was wrong. I've fixed it.
   
  Your measurements look sane, too.
   
  The fact that the power rails aren't sagging under the load of a burning chip makes me question whether they're having a problem after all. A DC offset check will help decide that.


----------



## pulsar08

I have the same problem where one of my buffers gets hot enough to hurt me if I touched it.  I know I installed one of them in reverse and I think on a different one there was a bridged solder joint and after I corrected it then one gets hot so they're probably fried or something.  I'm using the same pot as boris so I'd also better check that.    I haven't ordered new buffers yet though but probably will soon.


----------



## vodkex

Well, I've been experimenting with the BUF634's bandwidth control pin in my hybrid pimeta. I started with the 220 ohm resistor recommended in the schematic, and it sounded quite good. A bit veiled, I believe... so I added something like a 82 ohm resistor in parallel with the 220 one, taking it down to about 60 ohms. 

 I read that thread where kurtw tested this buffer and found out that distortion goes up when you go lower than 200 ohms.. but it didn't seem to my ears that the buffers were distorting at 60 ohms. In fact, it sounded better! Sound was a bit less veiled, but the TO220 package was getting a bit hotter than what I was comfortable with at this setting.. So I hacked up an old pentium II heatsink into four pieces, resulting in four generous heatsinks for a TO220 chip. After mounting them to the buffers with some MX-2 thermal paste and superglue on the tabs' corners.. I connected the BW pin directly to V-... and it sounds even better!! The heatsinks are keeping those buffers about five degrees over ambient temperature if my fingers don't deceive me. Temperature's alike to overclocked DDR2 memory overvolted to 2v, lukewarm. I'll try stacking those buffers some time soon.. no time right now to do that.
   
  The OPA827/BUF634 WB mode combo sounds really good!! Even better than I expected. This PIMETA amp is completely worth it. Nice project, I'm glad it turned out well. No DC offset! Not even 0.1 mv, that's wonderful. In RMAA my x-fi scores -101.5 dB in dynamic range and noise... this amp's getting a dynamic range/noise over -95.5 dB while adding no THD/IMD compared to my x-fi's lineout on its own. Channel separation is -91 dB, vs -98.8 on the x-fi itself... 
   
   
   
  Here's some pics of the PSU and the amp... I'll build a case for all this in some months when I get some free time from college. About the psu.. yeah, I'll add some more filtering caps there when I get more appropiate ones. (1000 uF 35v instead of 63v, my bad on that one) and that big mess o' caps is just three 2.2 uF caps in parallel to get near the 6.8 uF recommended value there..
   
  http://www.imagebam.com/image/377ea8131325698
  http://www.imagebam.com/image/f9928d131325701
  http://www.imagebam.com/image/4f9f96131325703
  http://www.imagebam.com/image/4e6ec6131325707
  http://www.imagebam.com/image/130498131325710


----------



## tangent

Cool report.
   
  Heh, you overclocked your PIMETA. I'm waiting for the picture where you put it in a case with a window in the side and EL tape everywhere. 
   
  I'm surprised you're not seeing line hum from the EI transformer placed so close to the amp stage.
   
  Care to show your PCB layout, or at least a bottom-side pic?


----------



## vodkex

hehe thank you tangent, I'm even more thankful to you for making such a nice amp design available for everyone to build.
   
  You know, there's no line hum, nothing! The amp's background is pitch black, I can hear a reaaaaaaaaaaaly faint hum at 100% volume, not at something like 95%... Needless to say that 50% provides more than enough amplification for my SR850 no matter what source I'm using, anything more than 55-60% is loud enough to hurt... so that's not a problem. Probably that's a sign of needing more filtering before the 7815/7915 pair in the PSU... 

 Sure, here's my layout. It's not exactly the same as what I've built, there were some minor bugs that were quite easy to correct.. which are taken care of in this schematic. When I build a case for all this, I'll probably desolder everything and make another final PCB. Here are some pictures, and if you use PCB wizard, the PCB file. The components' names are the same as in your schematics. The only thing missing in the PSU schematic are the regulators' bypass caps, both at the input and the output.
   
   


 Look for the improved version of both the amp and the psu on post 351


----------



## tangent

Oh, I clearly didn't look at your pictures closely enough. There are _two_ PCBs. In that case, I'd just advise keeping the transformer as far away from the amp board as your enclosure allows. Put them in opposite corners, if you can.
   
  The other thing you can do to help is lower the gain a bit so that your standard rock-out volume is at the 2 or 3 o'clock position. This gives you a little bit more volume range if you need it, while not raising up too much noise.


----------



## vodkex

That's right, there are two PCBs. One's the amp and the other's the PSU. Yes, that'll be something I'll take care of when I build an enclosure for this. It won't be a problem to have them in opposite corners... as you can already figure out this PIMETA is being used as a desktop amp, so it won't be a problem to have a slightly larger enclosure for that purpose.
   
  Thank you for the tip tangent, I've read your notes on this amp and you recommend to play with R4 to change the gain. That's what I'll do, I have some spare resistors here to lower the gain.
   
  ----------------------------------
   
  EDIT: (31/05/11) Well I've redone the PSU entirely, thicker traces, much cleaner and logical design, more capacitance, bypassed both regulators with tantalum caps, recommended on the datasheet. Same with the amp board... thicker traces... I've added more ground surface around the three channels so I can bypass everything as per the opamps and buffers' datasheets recommendations. 0.1 uF ceramics for the opamps and 10 uF tantalum + 0.1 uF ceramic in parallel for the buffers. I also lowered the gain from about 4.7 to 3.8, that's more than enough for my SR850.
   
   
  All I have to say is WOW! Bass now has a much stronger kick and clarity, while everything else is as clear and sparkling as before, probably even better!! I literally dropped my jaw with some songs. Those buffers are really benefiting from those caps at its power pins... as a result, now my headphones are actually getting all the current they want!  Soundstage grew bigger... it got more 3D! so did instrument separation and clarity. BTW I'm using the amp without input caps because DC offset is below the milivolt range. Much cleaner sound just from removing them. I think this DIY pimeta is at its apex... dunno what else I can do besides stacking the buffers, but they're already running at full WB mode, heatsinked... more than happy with what it's become, an excellent desktop amp. I'm in love with it 
	

	
	
		
		

		
			





  
  Have a look at the new designs if you want

 amp board (7x6.5cm board)
 psu board (10x10cm board)
 PCB wizard file with both the amp and psu


----------



## H22

been awhile since i last visited, just thought i would give a status report. been enjoying my pimeta v2 for months now, it really steps up the fun factor when paired with my M50's. its working great! going to start on another one soon (i already have the board) Going to try for a little larger unit with higher end components and a tad more voltage i think, I also need to play around with more op-amps!


----------



## steinh

I am working on a balanced linestage, and just discovered the class A bias circuit used in Pimeta v2. Could this support 4 channels, by just adding 2 more Q3??


----------



## tangent

Yes, current mirrors do work as you're hoping.


----------



## i_djoel2000

so i have successfully installed 3 cells of 3.7V 1400mAh lipo battery with protection circuit board into my portable case, and my pimeta is up and running now. the problem is now, the battery only last 6.5 hours while i was expecting more like 18 hours in a single charge (based on basic calculation)
   
  i'm using ad8620 on L & R channel, and opa827 on ground. i jumpered rblim and i got 1.43V across rbias-rblim so i set the rbias to 1.6k ohm using the trimpot (i intended to hit around 1mA bias current). can someone answer why i'm getting a short battery life time with my current configuration? any help would be much appreciated


----------



## nikongod

How much idle current do you expect each device to be using? 
   
  Add the class-A current to whatever the spec is for the op amps & dont forget the buffers.


----------



## i_djoel2000

i'm doing a re-run on my pimeta using ad8620 & ad8610 combo now. rbias is set to 5k (no idea why i particularly set it to 5k, to reduce the bias current i guess). will let you guys know the result later
   
  @tangent: is it normal to have 1.43V across rbias-rblim?


----------



## i_djoel2000

just want to inform that my pimeta runs more than 18 hours now, and i think i owe this thread a couple pictures for helping me finish this pimeta 
	

	
	
		
		

		
		
	


	



   

   
  i'm really loving my new setup, diymod>pimeta>im716, it's really portable and sounds *BIG*!!


----------



## tangent

Cool!
   
  How did you do the panel lettering?


----------



## i_djoel2000

Quote: 





tangent said:


> Cool!
> 
> How did you do the panel lettering?


 

 thanks, tangent. i went to the acrylic shop which have laser etching machine and have it done there..


----------



## i_djoel2000

quick question. how do we determine whether the LMH6321 is dying or broken?
   
  my friend lent my pimeta this afternoon and before i was able to tell him how to use it he already switched headphones while the music was still playing, i left out the R11 to reach optimum sound quality (no current limiting). now i noticed there is some harsh/peak around upper mid-lower treble area, i don't know whether my brain is making this up, that's why i need to ask. any respond would be appreciated


----------



## MisterX

Quote: 





> how do we determine whether the LMH6321 is dying or broken?


 
http://tangentsoft.net/audio/trouble.html


----------



## tangent

Check the supply voltage. You may not have fixed the battery problems as well as you thought you had.


----------



## vodkex

Hey tangent, I have a question. You've seen my DIY pimeta v2 with BUF634s in WB mode, being fed with a dual 15v PSU. I don't think I'll be building another amp, so.. Is this amplifier powerful enough for high impedance headphones like the HD650? I'll get a pair in some years.. 
   
  I suppose it's powerful enough with a high enough gain (other than the 3.5 I'm using right now) but you're one of the ones who designed this, so you know better.


----------



## tangent

I don't see what kind of guarantee you can be expecting. Yes, you used my information to build an amp, but in the end, it's DIY. You built it, yourself, so you are responsible for qualifying its behavior.
   
  I will observe that PIMETA v1s were known to drive such headphones, using those buffers.


----------



## vodkex

Now that I review what I've written, I think I should've worded my question in another way. My apologies.
   
  What I meant is; is the pimeta design able to drive more demanding headphones, like 300 ohm models? Particularly the HD650. Yes I understand that this is all DIY and that I'm the one who is assessing what I've built, but putting it that way is more like what I wanted to ask in the beginning. You've said that yes, you've seen v1s driving such headphones, so my question is answered.

 Thank you for your time!


----------



## tangent

Actually, higher impedance headphones are usually _easier_ to drive than low-impedance headphones.
   
  A typical 32 ohm headphone might require 0.5 V to sound "loud", which equates to ~8 mW. A typical 300 ohm headphone might require over twice as much voltage, but because the impedance is so much higher, the power to the headphones is much lower, more like 5 mW.
   
  The only trick for driving high-impedance headphones is having enough voltage. I cover that on my site here.


----------



## hmohammed43

Hi everyone! A quick q on the whole "needed parts" thing
   
  How many DIP-8 sockets and op-amps do you need in total? and also, what would be the best op-amp to use in the pimeta for improving bass response?


----------



## MisterX

Quote: 





> How many DIP-8 sockets


 
  Either 2 or none for a Pimeta 2. .
   (dunno were the"1-5" suggested in the parts list came from)
   
   
   
  Quote: 





> and op-amps


 
  2 or 3.
  3 singles or 1 single and 1 dual.
  Obviously you would need an adapter if you go with 3 singles...
   
   
   
  Quote: 





> what would be the best op-amp to use


 
  Best would depend on how the amplifier is powered.........


----------



## tangent

Quote: 





> what would be the best op-amp to use in the pimeta for improving bass response?


 

Notes on Audio Op-Amps
  Quote: 





misterx said:


> (dunno were the"1-5" suggested in the parts list came from)


 
   
  Sorry about that.  It was a copy-paste holdover from PIMETA v1, where the buffers were socketable.


----------



## alphaman

Tangent notes ... "Most headphones sound best when the amplifier's output impedance is as close to 0 as possible."
   
  Not sure about this ... std. cans like Grado, beyer, and IEMs like ER 4P, IME, sound better at higher-impedance O/P (but _not_ the newer 600-ohm versions of beyer). E.g., my Meier Corda II has both 120-ohm and 0-ohm O/P. I was a bit shocked to find that my 16-ohm Senn. IE-8 IEM -- my go-to can if there ever was one -- also performs better at 120-ohm. This makes more than 1/2 my cans inventory better suited for _above-0-ohm_ O/P impedance.
   
  Back OT ... what's your general experience here with Pimeta 2? I mostly couple the Pi2 with IE-8. So now I'm wondering ... build a  special  high-O/P-impedance jack? ... and how much/little/optimal O/P impedance I really require for _this_ IEM, and IEMs in general.  (i.e., I only have experience with 0 and 120)
   
  [ *Note*: Sorry if this topic is redundant. My lousy excuse: I'm too lazy to do research today. Just point to links as necessary. Thx!!  ]


----------



## tangent

Quote: 





alphaman said:


> Tangent notes ... "Most headphones sound best when the amplifier's output impedance is as close to 0 as possible."
> 
> Not sure about this ... std. cans like Grado, beyer, and IEMs like ER 4P, IME, sound better at higher-impedance O/P (but _not_ the newer 600-ohm versions of beyer).


 

 You're welcome to stick series resistors in between the output pads on my amp boards and the output jack solder lugs.
   
   
  Quote: 





> E.g., my Meier Corda II has both 120-ohm and 0-ohm O/P.


 
   
  As does my original Corda, and I couldn't say I heard a worthwhile difference in 120 ohm mode. I'm not saying _no_ difference, I'm saying none I wanted to keep.
   
  The only two arguments I've heard for why there should be an improvement are:
   

 The German standard that says you should do this, quoted by Jan Meier in defending the high-Z output. This standard also says you should design headphones with the same 120 Ω impedance. That's a double failure, as far as I'm concerned. On one front, we have a bureaucracy trying to set standards for audio equipment; what next, oil-on-canvas brush stroke styles? On another front, we have the reality that the other half of the standard is largely ignored, so even if there is acoustic merit to this idea, shouldn't the output impedance change depending on the headphone?
 The fact that you get optimal power transfer to a load when the impedances are matched. This is probably the reasoning behind the German standard, but I consider it separately because it seems bogus in its own right. I'm not doubting the engineering, I'm doubting its applicability to headphones. The only time I've ever seen serious engineers bother with impedance matching is at RF, to avoid reflections. That's a complete non-issue at audio frequency. (Well, it is to those of us who can't hear green markers anyway.)


----------



## alphaman

Tangent/ALL:
  Not sure about the German std. I could very well get even better performance above or below the "politically-standardized" 120-ohm -- haven't tried. Also -- and as I speculated elsewhere in this forum recently -- better performance at higher O/P imp. may have more to do with operating the volume pot in its more-linear range.
  The improvements I heard were subtle ... but noteworthy.


----------



## mfuerst

Hi,
   
  In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:
  - Serpac H65 enclosure
  - Li-Ion cell pack 14.8V 0.75Ah with protection circuit
  - Integrated modified Linkwitz Crossfeed circuit
  - Integrated Bass Boost and Volume Boost circuit
  - Integrated battery level control circuit with bi-color led
   
  For some of you this may be a bit over-engineered, but to me it was a good exercise.  The amp sounds brilliantly and qualitatively excellent, and the cells last for well over 10 hours.  As a proof, see the following pics.
   

  Lots of cables for the filters and boosters, but eventually it will fit.  On the bottom see the bass/volume booster circuit as a piggi-back board to the R4 pins.
   
   

  The 4 circuits all connected.  The Linkwitz circuit required the big caps to be soldered horizontally, while one of the C4 Wima caps had to be moved to the scratchpad area.
   

  On the bottom of the pic see the battery control circuit, which goes as a vertical piggi-back board onto the sratchpad area.
   

  All fits precisely into the enclosure.  The Li-Ion pack has been R&D'ed for this purpose - newest technology you can build these days.
   

  Finally, the enclosure can be closed and the product is finished... happy listening!
   
  Cheers.


----------



## tangent

Quote: 





mfuerst said:


> For some of you this may be a bit over-engineered


 
   
  Actually, this sort of build was one of the drivers behind the PIMETA v2 design: the scratchpad area, Molexes everywhere...
   
  Thank you for taking the PIMETA v2 in its intended spirit.


----------



## i_djoel2000

Quote: 





mfuerst said:


> Hi,
> 
> In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:
> - Serpac H65 enclosure
> ...


 

 those are full pack of pure awesomeness!!
   
  i wanted to try to plant the the crossfeed before, but it's just too troublesome, plus, i want the amp to sound as pure as possible. now i prefer my pimeta than my previous iqube and balanced RSA Protector


----------



## Skoalman

I've been trying to figure out how to run the pimeta from a dual supply.  I have 2 12v sla batteries
  that I connect in series to run an amp for my speakers.  For some reason I only recently used
  the batteries in series to power my pimeta.  Everything worked fine and I tried to find
  information on using the 2 batteries as a dual supply.  I have 3 pimeta's that I built over a year
  ago to play with seeing how different parts and configurations affected the sound.  Two of the pimeta's
  have buffers and one is bufferless.
   
  Now for the bad news.  I've tried to mod the 2 pimetas with buffers to run with a dual supply and failed.
  Hopefully I haven't ruined them, but if I have it's not the end of the world.  I knew the risks of trying this
  without coming to these forums and making sure what I was doing was correct.  On one pimeta all I
  removed was the tle2426 and on the other I removed everything in the ground channel and the tle2426.
  I connect the V+ from one battery and the V- from the other battery to + and - power connections on the
  pimeta.  This is exactly the same as how I connect them to the pimeta with the batteries in series.  To
  create ground I connect the positive and negative terminals on the batteries and run a wire out from this
  connection to the pimeta.  I connect this ground wire to the IG on the scratchpad.  When I apply power
  to either pimeta the buffers get burning hot very quickly, in fact I worry I've destroyed the buffers.  I've taken
  some quick power measurements from pin 4 and pin 8 on OPALR.  On pin 4 I got -12.33 and pin 8 was 11.61.
   
  Something is not right here and I have no idea what could be wrong.  Any help would be appreciated.
  If I haven't been clear enough with my description then I'll be happy to provide more information.


----------



## Avro_Arrow

The PIMETA is not designed to be run from a dual supply.
  You would be better off using a different amp designed to
  be run from a dual supply.
   
  If you really want to modify one, you will need to remove
  all the ground channel components and jumper IG to OG.
  Then you can use the center tap of your batteries as ground.


----------



## Sublike

Hi,
   
  I've been trying to solve this problem by myself but I can't figure it out.. Could someone help me!
   
  My problem is when I'm trying to run my pimeta from a 18v power supply, the leds won't light on. The op-amps and buffers are still unpopulated.
  There are also a S1 shorting connector and jumper between ol and rblim pads which does not show in those pictures.
   
  Pics:

   

   
   
  EDIT: Problem solved.. LED1 was dead so I replaced it and jumpered LED2. Now everything should work.


----------



## firefish15

Quote: 





mfuerst said:


> Hi,
> 
> In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:
> - Serpac H65 enclosure
> ...


 
   
  Wow,  Great job mfuerst. That's a lot of components to pack in such a small space.
  Is that Lion battery control circuit board a commercial product, or did you design if yourself?


----------



## Bcatarozoli1

Im an electronic engineering student. And for my electrical fab class i wanted to make a pimeta v2 headphone amplifier. one problem i was coming up with was finding the pcbs? does anyone know where i can get the circuit boards for this project. cause tangetsoft has a great parts guide but no link for the boards.


----------



## Avro_Arrow

http://tangentsoft.net/shop/
   
  it's on the top left.


----------



## Skoalman

I have a question about resistor values used in the pimeta.  After I failed to get my pimeta running from a dual supply I decided to go in another direction.  I'm using R1 and R2 as a voltage divider to drop the incoming audio signal around 30 decibels and from there I adjust volume digitally with foobar.  I've been using this setup for about a week and I'm really happy with how this is working out.  The only thing that is bothering me is the values I used for R1 and R2 are really low and I was wondering if R1 right and left can differ from R1 ground and R4 ground.  If I read the documentation correctly  these values are supposed the same.  Here are the values I'm currently using in my unity gain pimeta.
  R1   6.49K
  R2  220R
  R3  empty
  R4  6.49K
  R5  shorted
  R6  empty
  R1G  6.49K
  R4G  6.49K
   
  My source is a gamma 1 which has 3ohm output impedance, so I think my current values are ok.  I have resistors on hand to change R1 right/left and R2 to higher values.  I could change R1 to 49.9K and R2 to 1.6K while leaving R1G/R4G at 6.49K so my source would see a higher input impedance from my amp.  Would I benefit from this change or should  I be ok with the current resistor values?


----------



## tangent

If you're not using a volume pot on the PIMETA board and you're using JFET-input op-amps, you can put aside your input resistance worries. You might improve distortion a tiny bit by balancing the input resistances, but it probably isn't worth bothering about. It's more a thing we do because we can in the standard configuration.


----------



## Skoalman

Thanks tangent.  I'm going to change R1 and R2 to higher values.  Hopefully I'll have the amp all cased up by the end of the weekend.  Its going into a translucent grey serpac H65.


----------



## alphaman

*My PIMETA2 is broke -- please help!*
   
  Not meant to excuse myself of SNAFUs or responsibility -- nor do I claim any great DIY skill  … but …(along with several other “DIY” amps and mods), I’ve successfully built both a PPA2 and this now-“broke” Pimeta2 -- they all have worked pretty much from the get go… up to and including several interim tweaks and op-amp rolls. And, for well over a year, my Pimeta2 has survived near-everyday use (including gazillions of the ever-inconvenient 9v NiMH changes). Again, all w/o incident. Until now … my “indestructible” Pimeta2 has crashed, big time, and I have not been able to troubleshoot it for a week -- literally 20+ hrs of hair-pulling and still no luck.
   
  How it all started (?? best guess!) and where stuff stands …
   
  After rolling in a new op-amp, I turned the Pimeta2 on and heard a loud pop over my IEMs. _Cause_: I did not seat the opamp properly into the 8-DIP plug-in socket -- so  I seated it correctly and turned on the amp. Sounds fine again but now LED2 is not lit (LED2 is one of two the class-A-biasing LEDs from Tangent’s schematic; I’ve always used both LED1 and LED2, and they are mounted on the front panel for easily visibility). Troubleshooting, I found that as I was inserting the opamp, I had broken one of the pins on Q2 (2N3904) [I use a SOIC-to-DIP BrownDog adptr and that’s hard to squeeze in w/o bending some of nearby components, like Q2.] Anyway, I replaced Q2, and the LED was restored …_ but now_, I heard a loud pwr-on thump in the L ch only (which is now also dead); R-ch sounds fine and no pwr-on thump).
   
  After a bit of checking, I noticed that the opamp (AD8620 or 8066) was getting VERY warm after about 5 sec. I moved the opamp to a breadboard and attempted “piecemeal” troubleshooting. The opamp draws 54mA (!!) when the V_out1 (Pin 1 for L-channel on dual-ch opamps) is normally connected to the L-ch ckt in front of it -- this includes the feedback loop, PREBUF, 100-ohm R, and the LMH6321 buffer.
   
  If I disconnect the opamp’s V_out1 pin (L-ch), it draws a mere 8mA .If I swap output pins (dual opamp's pin 7 now feeds the L-ch ckt in front, I get the same 54mA draw -- this will make the opamp v. warm in a few secs). Feeding ONLY the R-ch ckt (L-ch open in front of _opamp_) with either V_out pin results in normal 8mA draw.
   
_Note_: opamp V_out (1 or 7, i.e., whichever is feeding L-ch ckt in front of it) has V = 2.8vdc. The one that feeds R-ch is normal (few mV)
   
  I haven’t checked the LM6321 buffer’s current draw -- FWIW, it runs cool. And they do have built-in "OVERVOLTAGE PROTECTION" per National's datasheet. Just in case, I also replaced it (L-ch only). No diff (for all I know, this buffer could have _blown again_ by whatever else is messing up the L-ch). I also replaced Q3L (2N3904, the L-ch op-amp class-A bias trans).
   
  I checked the output of the buffer (the ‘phones O/P jack) -- and L-ch turns on with (and remains at) a whopping 2.6 volts DC offset (no wonder I heard that pop-thump)!! R-ch is normal (3-4mV). All this with NO audio/music signal at input -- i.e., running idle. Soundwise, R-ch sounds fine, while L-ch is "dead"/broke/whatever.
   
_Shorts_ in the L-ch ckt ahead of the opamp output? None I could find with a decent DMM (Fluke 87). Alas, my o’scope is itself dead so I can’t do detailed troubleshooting.
   
  Power suppl. -- which is TLE2426-based with 9v batt (default) -- _seems_ to be fine -- so, all powered opamps/buffers are getting proper +/- 1/2 the supply volts.
   
_Other notes_:
  - I've almost never use passive "protection" (on any amp  -- for the Pimeta2, that means C1 is bypassed (jumpered). BUT ... I do use output-current-limiting resistors, R11 (3k-ohm), for all buffers.
  - Ground channel seems to be fine (this is a _deduction_ based on the fact that R-ch seems to be good).
   
_Questions_:
  With the L/R-ch opamp(s) REMOVED, but with the buffers connected (in normal circuit), why do I get large DC offset at output for BOTH channels?
  L-ch: 2.6V (as noted above); R-ch: 160mV.
  If there is no input, the buffers should not output any voltage (other than a few mV idle, of course). Or am I missing something here?
   
  My brain is mush and my head is bald from all the hair-pulling! Please help -- thanks!
   
  [BTW: after that initial thump, which my IE-8s survived, I switched to a pair of junk cans -- they seem to be able to handle the 2.5V DC offset. This is how I’m able to test for music/signal and distortion]
   
*EDIT: *Problem solved (or isolated) somewhat ...  but WHY?
   
  Okay, I noted above that I replaced Q3L (the L-ch class-A bias trans.). Honest to dog I replaced it with another 2N3904 -- and I did. Yet when I removed it (just a few mins ago), all returned to behaving "normal" (at least WRT basic metrics: DC o/p offset is normal, quiet pwr-on/off, no pops or crackly volume, etc) ... _except_ that topologically I have a 2N3904 Q3R for R-ch, and the rest of the class-A transistors (and all the related LEDs and resistors) all _in situ_  (i.e., nothing else removed, bypassed or jumpered). *What just happened?* *What is STILL happening*: I installed another NEW 2N3904 and the problem returns again! (dunno if it's same batch as orig 2N3904 -- the one that worked in the Pimeta2 orig. built 2 yrs ago -- the one that I replaced a few days ago). I tried another putatively higher-quality NPN (Toshiba 2SC2240, and accounted for its pin diffs) ... but same problem when installed in the Q3L footprint. *Yes* ... _I checked all trace_s -- with Q3L removed -- for shorts or opens. All's normal. At least as far as I can test. I haven't tweaked the bias trimpot because (I assume) Q3R is functioning normally???


----------



## geofftnz

The last required bits for my PIMETA2 showed up today, so I can finally start building. Here's the plan:
   

 Hammond 1455 enclosure  with custom laser-cut front and back panels from Ponoko NZ
 Integrated Alien USB DAC, powered from the amp.
 AD8620/8610 SMD opamps (soldering direct to board because I forgot to order the browndog adapters)
 10xAAA NiMH cells for a 12V supply. I was going to go with 9.6V, but then realised I needed V+/2 to be at least 5V for the DAC.
 Moving the trickle charger to another board (or prototyping area), so that the battery can be fully isolated from the amp while charging from a switchmode supply. I'm doing this to avoid any potential ground-loop problems via USB.
 Battery level meter using a LM3914 in dot mode with a 3 red / 7 green LED bar graph. (Depends how low I can get the current draw - this might end up having a push-button to check battery level).
 a switched 3.5mm socket between the DAC and amp to act as a line-in for analog sources.
   
  For C1 I have some 470nF WIMA MKS4 polyesters that fit the board perfectly, or some 220nF polyprops that overhang and will need to have a leg bent back under the board to reach the pad. Hopefully I'm not about to spark a religious war here, but is it worth going with the polyprop in this case, or the polyester with the lower corner frequency?


----------



## tangent

Quote: 





> after that initial thump, which my IE-8s survived, I switched to a pair of junk cans -- they seem to be able to handle the 2.5V DC offset. This is how I’m able to test for music/signal and distortion


 
   
  You should have been testing _only_ for DC offset, from the start. It is not a sufficient test, but you would have seen the problem without risking your expensive IEMs _or_ your junk cans. Nothing you've reported about how the problem sounds tells us anything more than a high DC offset measurement would have.
   
  Maybe you're annoyed now, thinking I'm armchair quarterbacking. But, a DC offset test is one of the standard testing steps. When you rolled that op-amp, you should have gone back through that test sequence. Plugging cans in is four paragraphs down the sequence, and it recommends _starting_ with the cheapies.
   
  Quote: 





> With the L/R-ch opamp(s) REMOVED, but with the buffers connected (in normal circuit), why do I get large DC offset at output for BOTH channels?


 
   
  Because you've broken the feedback loop.
   
  The class A biasing circuitry is dragging the input of each buffer to V-, so the output will go as close to V- as it can get, without the op-amp there to fight against the bias.
   
  With Q3L out, you would still expect a high DC offset between OL and OG with the op-amp out because then the input of BUFL is left floating, so it can be pushed about by RFI and electrostatic fields in the room.
   
  Bottom line, there's no point in testing what's happening at OL and OR when there is no op-amp plugged in.
   
  Quote: 





> *What just happened?*


 
   
  It is indeed a mystery why Q3L is behaving differently from Q3R.
   
  Since the two transistors should do the same thing at all times when under the same forces (and they are, in the idle amp tests) and you have exonerated Q3L, that leaves the op-amp.
   
  So: put the original op-amp back in. Does the DC offset symptom go away? If so, the amp probably sounds fine now, too. (As good as it can sound through cheap cans, because you're not going to test with expensive IEMs first again, are you now? Of course not. You've already learned that lesson. 
	

	
	
		
		

		
		
	


	




)
   
  Quote: 





> (I assume) Q3R is functioning normally???


 
   
  It's not hard to test. With the op-amp removed, put your meter on the milliamps scale and stick it between V+ and pin 7 on the op-amp socket. You should get 3 mA or less, and it should change as you adjust the trim pot.
   
  If that gives believable results, you can then try measuring between op-amp pin 1 and V+, while Q3L is installed. There is some risk to the meter here, as we haven't absolutely proven that the left channel bias path actually behaves the same as the right. You might want to start with the meter on the amps scale, if you have one. (Typically 10 A.) Even in the worst case, the meter should survive if there is a dead short down this path. Then once you get a believably small reading, you can switch to the milliamps scale.


----------



## tangent

Quote: 





geofftnz said:


> Integrated Alien USB DAC, powered from the amp....I needed V+/2 to be at least 5V for the DAC.


 
   
  I don't know anything about that DAC, but you'll want to check that its output is AC coupled. It won't work otherwise.
   
   
  Quote: 





> Battery level meter using a LM3914 in dot mode with a 3 red / 7 green LED bar graph. (Depends how low I can get the current draw - this might end up having a push-button to check battery level)


 
   
  If you end up going with the pushbutton method, I think it would be neat to use the chip in bar mode but feed it through an RC filter with a time constant of half a second or so. You would then see it "fill up" the bar over the course of a few seconds, rapidly at first, then leveling off at the true value. It should look cool.
   
   
  Quote: 





> is it worth going with the polyprop in this case, or the polyester with the lower corner frequency?


 
   
  I'd go with the polypropylene cap _if_ it's not a box type. If it is, the legs probably aren't ductile enough to withstand the sharp bend, and are likely break. If not during the assembly attempt, then shortly after due to vibration.
   
  If you don't need the cap to create an AC-coupled situation between the DAC and PIMETA, I'd short C1, because you already effectively have an input cap.


----------



## geofftnz

Quote: 





> I don't know anything about that DAC, but you'll want to check that its output is AC coupled. It won't work otherwise.


 
   
  It's a PCM2702-based design. Site here. It's normally AC-coupled with 47uF electrolytics (for space reasons I think - the board is tiny). The analog section runs on 5V, so the caps are always forward-biased by around 2.5V. I figured that it's probably best to use the coupling caps on the PIMETA, so I'm taking the signal from the capacitor + pads on the DAC. The DAC draws power for its analog section from V+ and GND on the amp (it buffers the ground via a BUF634 so as not to adversely affect the ground level in the amp). Some people have reported problems due to a voltage offset between the input of the buf634 and the output ground of the DAC. (I saw this when testing the DAC using a voltage divider for the ground level). The solution seems to be to reference IL and IR against the amp ground instead of IG coming from the DAC.
   
   
   


> If you end up going with the pushbutton method, I think it would be neat to use the chip in bar mode but feed it through an RC filter with a time constant of half a second or so. You would then see it "fill up" the bar over the course of a few seconds, rapidly at first, then leveling off at the true value. It should look cool.


 
   
  Good idea, will try it out tonight... Another potential mod described on the data sheet is to do a simple PWM on the voltage signal so that the brightness of the last LED indicates the fractional portion of the voltage.
   
   Quote:


> I'd go with the polypropylene cap _if_ it's not a box type. If it is, the legs probably aren't ductile enough to withstand the sharp bend, and are likely break. If not during the assembly attempt, then shortly after due to vibration.
> 
> If you don't need the cap to create an AC-coupled situation between the DAC and PIMETA, I'd short C1, because you already effectively have an input cap.


 
   
  It is a box cap, but the leads do not exit the cap body flush with the board (the bottom is slightly inset). Do you think it'd be OK if the lead had more of a radiused bend? The way the caps overhang the corner notches of the board means that I've got the thickness of the board to work with when bending the pins. (I can take a photo when I get home, but basically one pin would be normal through-hole on one end and the other would bend back under the board to meet the SMT pad. Would this introduce problems via the inductance of the longer lead, or is that irrelevant at audio frequencies?
   
_edit: spelling_


----------



## alphaman

Thx for the response ... I'll get to the rest of the reply later as I'm still troubleshooting ... but I wanted to address a quickie:

 Quote:


tangent said:


> You should have been testing _only_ for DC offset, from the start. It is not a sufficient test, but you would have seen the problem without risking your expensive IEMs _or_ your junk cans. Nothing you've reported about how the problem sounds tells us anything more than a high DC offset measurement would have.
> 
> Maybe you're annoyed now, thinking I'm armchair quarterbacking. But, a DC offset test is one of the standard testing steps. When you rolled that op-amp, you should have gone back through that test sequence. Plugging cans in is four paragraphs down the sequence, and it recommends _starting_ with the cheapies.


 
  In my orig. post, I noted the gazillion times I've cycled thru battery changes and OPA rolls and misc. tweaks. Even batt changes requires I remove the cover, creating some risk for messing something up. My routine was to use my default cans, the Senn IE-8s. Frankly, then, even with $$$ cans, I'll still take the risk since: the Pimeta2 has proven to be v. reliable/durable; the sequence method is mostly (IMO) for initial builds/testing; TIME=$$ (especially in today's economy) and, my 'problems' generates content for HF and more biz and troubleshooting-skill-building for you/readers-of-this-post  [For more enlightened philosophical discussion on these issues, see my HF Profile.   ]
   
This just in ...
   
  I *just discovered* that the orig.-installed Q3R and Q2 are not 2N3904 but 2N5088. Although I trashed the Q3L I removed earlier, i now assume it was 2N5088. I got mixed up because on your schema, you label the defaults as 2N3904 but on your Parts List they are Alternatives.
  To be cont ...


----------



## tangent

I think you're chasing the wrong thing by continuing to swap Q3L. The circuit is not super-specific about the type of transistor it takes here. That's one reason I'm not particular about 2N3904 vs. 2N5088 in the docs. They're both small-signal NPNs, which is all that matters here.
   
  Swap that op-amp again and do the bias current test. Those are far more likely to give interesting results.


----------



## alphaman

Quote: 





tangent said:


> I think you're chasing the wrong thing by continuing to swap Q3L. The circuit is not super-specific about the type of transistor it takes here. That's one reason I'm not particular about 2N3904 vs. 2N5088 in the docs. They're both small-signal NPNs, which is all that matters here.
> 
> Swap that op-amp again and do the bias current test. Those are far more likely to give interesting results.


 
  I'm away from my testbench so it'll be a few hrs before I can re-test.
   
  I did change the opamp. Several X's using several diff models: 2132, AD825, and I now have 5532 plugged in. Same confusing result.
   
  BUT ... (and not sure I made this clear in the orig. post) ... with the opa (or even buffer) REMOVED I continue to get that 2.6V wrt gnd (so, that's what buffer sees, and sends to the jack as a pwr-on pop). IOW, it's coming from an _in situ_ Q3L. Any clues as to how much voltage SHOULD be present (i.e., w/o opa)?
   
_Also this may not have been clear in OP above:_
  When I changed that Q1 with a broken leg, I also CONCURRENTLY changed Q3L because it looked bent and roughed up (not sure it was damaged but since i was in the area anyway, and had a new 2N3904 on-hand, I thought I'd play it safe). But the orig. Q3L was almost surely a 5088, so me now thinks diff model/manuf = diff bias metrics??

 I don't have any 2N5088s in my bin ... just about every other small-signal NPNs, like 3904, etc.
   
*EDIT:*
Issue Resolved (I think...)!!
   
  It was the small-signal NPN  "species" that I'd speculated was suspect, above.
   
  I found a BC639 in my bin , and threw it in [CAUTION: despite the European "BC" prefix, this trans. uses Japanese pin config. Mine is a Fairchild.]. _No need elaborate_: L-ch is behaving normally again -- as is the whole amp AFAICT. Just to re-confirm, I did throw the 3904 and 2SC2240 back in -- in case something else, known to me or not (like cold solder joint, etc), "magically" fixed the issue. But those produced same problem as before -- returning the BC639 into position restored orig. functionality.
   
  Guardian: All is as it was before. Many such journey's are possible.
  Kirk: Let's get the hell out of here.
  from Star Trek -- The Orig. Series, Epi "The City on the Edge of Forever" 1967.
   
  Sorry, Tangent, it was the small signal trans. so nahhh ... nahhh ... na... nahh nahh 
  Seriously, tho ...WOW ... what an epic. I may ditch DIY for a while and give Fiio and others some of my upcoming head $$'s. As  I said above, time=$$ and I'm not sure about the DIY hassle any more. Great sound, good initial learning experience ... but as an ongoing "hobby" ... methinking paradigm shift


----------



## alphaman

Abstract: *R7, and other "signal-path" R's -- using "high-quality" resistors*
   
  That 100-ohm R7 resistor is directly in the signal path. Has anyone experimented with upgrading this to a higher-quality R? I was thinking Vishay's newer (and $$$!!) "PTF":
   
http://www.vishay.com/docs/31019/ptf.pdf
   
   
  SOME FEATURES
  • Extremely low temperature coefficient of resistance
  • Very low noise and voltage coefficient
  • Very good high frequency characteristics 
  • Can replace wirewound bobbins


----------



## i_djoel2000

you can even use this if you want, no one can stop you: http://www.partsconnexion.com/resistors_vishay_var.html


----------



## alphaman

Quote:


i_djoel2000 said:


> you can even use this if you want, no one can stop you: http://www.partsconnexion.com/resistors_vishay_var.html


 
  Cool! Has anyone used this R? If so is there an important improvement in SQ?
  IAC... actually, it's YOU --  *i_djoel2000 *-- who's stopping me ... by not offering to send me FREE samples 
  How about touring them? ... like some others on this forum do for various high-$ (= unaffordable) gear. 
   
  Speaking of samples ... Vishay does have a sample program ... hmm...


----------



## alphaman

Okay ... I'm recanting a bit on my promise to back off a bit on DIY  ... but since my soldering iron is out of basement storage from that pesky troubleshooting job (see above   ...
  ... on the topic of substituting better-quality parts, anyone experiment with trans. from Zetex or Toshiba, etc. for the class-A ckt? In some DIY circles, Zetex get some attn. I couldn't get the Toshiba 2SC2240 to work, but I didn't tweak the bias resistance; 2240 and its PNP "equiv." 2SA970 are popular in some circles.


----------



## geofftnz

Built the amp today... all goes, no magic smoke got out, buffers don't seem to get too warm. Bit of a hum off the pot, so I grounded to PG as suggested.
   
  Where I do have a problem is the interconnection with the DAC. The DAC is powered by the amp: V+, IG and V- are passed, with IG providing the ground reference for the DAC. Unfortunately OG of the DAC sits about 0.5VDC above IG of the amp, with around 80mV of 10kHz tone on it (at a guess - will hook the scope up soon). Coupling the signal grounds with a 47uF electrolytic (left over from the DAC construction) or a spare 6.8uF Wima film cap quiets the noise, so I'll do some experimenting around that. I'm still not sure whether this is oscillation within the amp (unlikely, because it only appears with the DAC hooked up) or DAC, or something to do with the DAC ground connection to USB ground. Needless to say USB is probably not the ideal electrical environment to hook a sensitive audio circuit up to...
   
  Apart from that, it sounds good and I can't wait for my case (and batteries) to arrive so I can finish the build!


----------



## firefish15

*I/O jack question.*
   
  Hi, I'm building my first Pimeta amp. I just realized I ordered just the input jacks (Mouser 502-35RAPC4BH3), but no output jacks from the parts list.
  The 502-35RAPC4BH3 is a switched jack (http://www.switchcraft.com/Drawings/35rapc__h3_cd.pdf) with 5 pins. Pins 4 & 5 are connected to the tip and are shorted when a plug ins not inserted. Similarly pins 2 & 3 are connected to the sleeve. Pin 1 is ground.
  The questions I have are:
  1) The left channel uses the tip, so I would connect pin 4 to IL. What would I connect pin 5 to? Pin 2 would go to IR, what is pin 3 connected to?
  2) Can I use the same jack for the output?
   
  Thanks,
  Paul


----------



## firefish15

Quote: 





firefish15 said:


> *I/O jack question.*
> 
> Hi, I'm building my first Pimeta amp. I just realized I ordered just the input jacks (Mouser 502-35RAPC4BH3), but no output jacks from the parts list.
> The 502-35RAPC4BH3 is a switched jack (http://www.switchcraft.com/Drawings/35rapc__h3_cd.pdf) with 5 pins. Pins 4 & 5 are connected to the tip and are shorted when a plug ins not inserted. Similarly pins 2 & 3 are connected to the sleeve. Pin 1 is ground.
> ...


 

 Correction for my previous post.
  1) The left channel uses the tip, so I would connect pin 5 to IL. What would I connect pin 4 to? Pin 2 would go to IR, what is pin 3 connected to?
  2) Can I use the same jack for the output?


----------



## geofftnz

Quote: 





firefish15 said:


> Correction for my previous post.
> 1) The left channel uses the tip, so I would connect pin 5 to IL. What would I connect pin 4 to? Pin 2 would go to IR, what is pin 3 connected to?
> 2) Can I use the same jack for the output?


 

 Either leave them open, or connect them to IL/IR. If you're using it as a normal socket, then it wont matter. They're there so you can interrupt the signal path when you plug something in. I'm planning on putting one of these as a line-in between the DAC and amp in my build. When another source is plugged in, the internal switch disconnects the DAC.


----------



## MisterX

There is no need to connect pins 3 & 4 to anything. 
   You could just go with # 502-35RAPC2BH3 if you do not need a jack with a switching function.
   
  And... Yes, you can use it as an output jack as well.
  (The parts list ID is listed as IN/OUT and the quantity is listed as 2)


----------



## firefish15

Thanks Goefftnz and MisterX


----------



## SoundOfKhaos

Quote: 





mfuerst said:


> Hi,
> 
> In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:
> - Serpac H65 enclosure
> ...


 

  
  I'm still having trouble keeping my mouth closed. I do not have the skill, or knowledge to accomplish something of this caliber yet but I find this to be very inspirational to keep learning. Amazing work. Can I ask about how long this took? For design, fabrication and troubleshooting and stuff. Just amazing.


----------



## alphaman

Anyone using (_and_ achieving GOOD results with) LM6171? I was thinking something like this:


----------



## geofftnz

Got everything working properly last night - such a great feeling...
   
  BUT THEN... must have slipped removing a scope probe and killed a channel on the DAC.


----------



## tangent

Ouch!
   
  Would you mind drawing up a simple block diagram showing how everything's connected, for the benefit of future builders? I'm thinking of two boxes with labeled lines between them showing the wires and what they connect to on each end. Maybe some caps between them if they are required, as I thought originally.


----------



## geofftnz

Quote: 





tangent said:


> Ouch!
> 
> Would you mind drawing up a simple block diagram showing how everything's connected, for the benefit of future builders? I'm thinking of two boxes with labeled lines between them showing the wires and what they connect to on each end. Maybe some caps between them if they are required, as I thought originally.


 

 Apologies for the ugly visio diagram - I'm still at work and it's all I have...

Fullsize image
   
  So in summary:
   

 The Alien DAC design includes an option for powering from a virtual-ground amp. This uses a BUF634 to pass & isolate the ground level from the amp.
 The Alien DAC's outputs have a DC offset of 2.5V (half-rail)
 Since the coupling capacitors are installed on the PIMETA, there are no coupling caps installed on the DAC. Output from the DAC has been taken from the cap mounting pads.
 With the BUF634 installed on the DAC, the DAC ground is 0.5V above PIMETA ground. DAC OG is not connected to PIMETA IG for that reason.
 With the BUF634 installed, there is a clearly audible 4kHz tone present on the output. This tone is not present if the DAC is not connected to the amp, so it's definitely coming from the DAC.
 Coupling the DAC ground to PIMETA IG with a 47uF capacitor largely (but not completely) quiets the tone. This may suggest that the 4kHz noise is present on both DAC ground and signal, so passing that back to the PIMETA means the difference between output and ground contains less of the noise. (Not sure?)
 Removing the BUF634 (luckily it was a free sample) and passing power to the DAC via a LM317 regulator set to 6.5V above V- works. This means that USB ground is tied to V- on the PIMETA and the signal from the DAC is centred around 2.5V above V-
 I fear I may have shorted a DAC output to ground while removing an oscilloscope probe. Next time the amp+DAC was powered up I didn't have a right channel.
 I have ordered a GrubDAC kit to replace the DAC, seeing as the AlienDAC kits are now showing as backordered on Glass Jar Audio. _(edit: they're not backordered anymore - oops)_


----------



## tangent

The diagram is more than adequate for the purpose. It's more than I expected. Thanks!
   
  I know nothing about the Alien DAC, and only skimmed the 2702 datasheet, but from what I can see, shorting output to ground shouldn't hurt anything. I don't see any warnings in the datasheet about doing that.
   
  I also don't see any mention of output short circuit current protection.
   
  However, I do see that it says you have to ensure the load impedance is > 5 kΩ, but I expect that just means it's allowed to go out-of-spec below that point. It also implies that the output DACs inside the chip aren't capable of pushing a lot of current, which actually argues in favor of them being effectively short-circuit protected, because it means they can't put out enough current to burn transistors or melt bond wires.
   
  Could be wrong, but I'd look elsewhere for the problem.
   
  Do you have a way to test the DAC in isolation? Maybe play a test tone through it and measure it with an AC voltmeter? Or better, a scope?


----------



## geofftnz

Quote: 





tangent said:


> Do you have a way to test the DAC in isolation? Maybe play a test tone through it and measure it with an AC voltmeter? Or better, a scope?


 

 Here's a few pictures: http://imgur.com/a/ZUpw0
   
  The noise on the DAC outputs looks the same when isolated from the amp. I set up a resistive voltage divider on a breadboard to simulate the ground level. When that was noisy I tried a TLE2426, same result.
   
  Noise on DAC outputs, virtual ground buffered through buf634, USB not connected. The lower frequency you can see here is close to 4kHz and the higher frequency is inaudible. I stupidly forgot to take a photo of the voltage and sweep settings on this one, but the tone is audible with music playing over the top and I think it was around 80mV p-p.
   
   

   
  After plugging in USB, it goes to this (4kHz, audible):

   
  This is the last photo I have of the DAC working properly. BUF634 removed, 12V V+ from amp regulated down to 6.5V before passing to DAC as if it was a regular battery supply. Multimeter is showing current draw in mA. Scope is showing the right channel input (bottom) and output (top). Breadboard contains the LM317T regulator along with the battery meter prototype I mentioned a few days ago. The DAC is off the bottom of the photo.


----------



## geofftnz

There have been a few reports of people frying one or both channels on their Alien DACs, eg: here. Possibly if the PCM2702 outputs see an unexpected transient, which I may well have done while disconnecting the scope probe.
   
More pictures
   
  Top pic is a post-build, pre-clean shot of the DAC and PIMETA. Excuse the shocking SMT soldering work, it's been a few years.
  Bottom pic is the DAC with the BUF634 removed (was in IC4 on bottom left) and powered from a regulated +6.5V referenced from V- on the PIMETA. Signal outputs are straight from the PCM2702 outputs, but are AC coupled via the input caps on the amp. The scope probes were hooked up between the DAC and amp, so anything bad I did was fed straight into the PCM2702 without anything in the way.


----------



## tangent

Well, short of swapping the DAC chip, I have no ideas. Given that it's not an interaction with the PIMETA, that seems like a pretty good bet, since the outputs of that chip are directly connected to the output pads on this DAC design. (Ignoring the RC filter.)
   
  You'll probably get more eyes on the problem with a fresh thread. (Or by joining another existing omnibus thread, if one exists for this DAC.)


----------



## geofftnz

Quote: 





tangent said:


> Well, short of swapping the DAC chip, I have no ideas. Given that it's not an interaction with the PIMETA, that seems like a pretty good bet, since the outputs of that chip are directly connected to the output pads on this DAC design. (Ignoring the RC filter.)
> 
> You'll probably get more eyes on the problem with a fresh thread. (Or by joining another existing omnibus thread, if one exists for this DAC.)


 

 Yeah, I think the PIMETA is blameless in this, but thanks heaps for taking the time to check it out... Unfortunately I don't have access to reflow gear (and no spare toaster ovens), so it's easier to just chalk it up to experience and buy a new DAC kit.
   
  The batteries I ordered showed up today, so I can build the trickle charger and battery meter side of things.


----------



## tangent

Quote: 





> I don't have access to reflow gear


 
   
  You only need that if you want to save the chip.
   
  If you're prepared to destroy the chip, you can cut the leads away from the chip with a hobby knife. The leads can then be desoldered individually with a regular soldering iron.
   
  Obviously you need to be careful with the cuts so as to not damage the traces on the PCB.


----------



## geofftnz

Yeah, I suppose I could have done that, but I've already pulled the trigger on a new DAC kit 
	

	
	
		
		

		
			




  In any case, a new PCM2702 from RS is around 60% of the cost of a whole new kit and would be a couple of weeks away if it came from the UK. Next order I make with RS I might get one and try to repair the broken DAC - I've still got a spare PIMETA pcb and all the parts except for the opamps and buffers. The plan was always to build one for work and one for home.


----------



## MisterX

http://uk.farnell.com/chip-quik/smd1/kit-smd-removal/dp/1850214
  (chip quik)
   
  Is another option for removing SMD parts


----------



## firefish15

Quote: 





misterx said:


> http://uk.farnell.com/chip-quik/smd1/kit-smd-removal/dp/1850214
> (chip quik)
> 
> Is another option for removing SMD parts


 


  Chip-quik works great, easy to use. used chip-quick to remove a smd capacitor I soldered to the wrong Pimeta pad. Expensive though, I paid $15.00 for it. Here's a youtube video of how to use it:
  http://www.youtube.com/watch?v=7kyaz4Zrd78


----------



## mfuerst

Quote: 





firefish15 said:


> _"Wow,  Great job mfuerst. That's a lot of components to pack in such a small space._
> _Is that Lion battery control circuit board a commercial product, or did you design if yourself?"_


 
   
  As I mentioned in my first post, the Li-Ion pack has been specifically R&D'ed for this purpose - this includes also the CCB.
  I haven't been able to find a commercially available product, hence I had to design and build it on my own...


----------



## mfuerst

Quote: 





soundofkhaos said:


> I'm still having trouble keeping my mouth closed. I do not have the skill, or knowledge to accomplish something of this caliber yet but I find this to be very inspirational to keep learning. Amazing work. Can I ask about how long this took? For design, fabrication and troubleshooting and stuff. Just amazing.


 

 Hi,
   
  Thanks for the compliments.  It has taken indeed a lot of time, I would say 4-5 month considering that I could spend time only during the weekends and a few evenings.  Most of the time went into design and specification, the build phase was quite quick.  The selection and sourcing of components was the most frustrating phase, until I got all to properly fit and at a standard that was meeting my expectations (only the best - cost was secondary).  No troubleshooting required, all worked perfectly right from the start.
   
  Note that I have an electronic engineering education, but I've never worked in this area.  Only now - 30 years later - I thought I could do something useful.  In a couple of weeks I will be posting the pictures of a desktop version that I built recently - stay tuned!


----------



## firefish15

Quote: 





mfuerst said:


> As I mentioned in my first post, the Li-Ion pack has been specifically R&D'ed for this purpose - this includes also the CCB.
> I haven't been able to find a commercially available product, hence I had to design and build it on my own...


 


  I found 2 sources for a PCB for the Li-IOn batteries, They are huge compared to yours, but will fit in the serpac.
  http://www.batteryspace.com/pcbfor148vli-ionbatterypack5alimitwithfuelguagesocket.aspx
  http://www.all-battery.com/protectioncircuitmodulepcbfor148vli-ionbatterypack4cellswith65alimit-lipcb14v4.aspx
   
  I finished my Pimeta and have been listening for a few days. I went with a smd build using thin film resistors, smd capacitors, with audiophile grade capacitors in a few places. I'm currently using OPA627's.
  Impressions so far:
  Clean, very detailed sound. On well recorded material you can easily pick out  individual voices and instruments.
   
  My only disappointnent is is the battery life using 9v rechargables. I intend to change this to a 15v lion battery pack. I couldn't find a pre-built battery pack that will fit, so I'll have to build the pack myself using four of these 680 mAh cells:
  http://www.all-battery.com/TenergyLi-Polymer3.7V680mAh603040Battery-30191-0.aspx
   
  A question on the Pimeta V2 board. At the bottom of the board there are four holes. Are these for mounting a daughter board?
  Can these be cut off? If so I might be able to squeeze in this 900 mAh cell instead.
   
  http://www.all-battery.com/polymerli-ionbattery37v900mah463455.aspx
   
   
  A few pics of my build:


----------



## tangent

Quote: 





firefish15 said:


> At the bottom of the board there are four holes. Are these for mounting a daughter board?


 
   
  Yes.  They're spaced for the now-discontinued Modified Linkwitz Crossfeed board.
   
   
  Quote: 





> Can these be cut off?


 
   
  Yes, as long as you're careful.
   
  The easiest guide for a safe cut is to just cut off the "tabs" containing the mounting holes.
   
  You can actually cut a little deeper than that, right along the line of the rear-most diode inline with the trace from WALL +, but you risk nicking traces.
   
  Either of these cuts will expose copper, so be careful not to touch anything metal to that raw board edge. You might want to re-insulate it.
   
  Oh, and don't breathe the dust.


----------



## firefish15

Thanks Tangent.
   Any suggestions on what I can use to insulate the board edge?
   
  Quote:


tangent said:


> Either of these cuts will expose copper, so be careful not to touch anything metal to that raw board edge. You might want to re-insulate it.
> 
> Oh, and don't breathe the dust.


----------



## MisterX

Quote: 





> Any suggestions on what I can use to insulate the board edge?


 
   
   
   
   
http://en.wikipedia.org/wiki/Conformal_coating


----------



## firefish15

Thanks MisterX
   
  Quote: 





misterx said:


> http://en.wikipedia.org/wiki/Conformal_coating


----------



## tangent

Hot glue would work, too.


----------



## alphaman

Quote: 





alphaman said:


> I'm away from my testbench so it'll be a few hrs before I can re-test.
> 
> I did change the opamp. Several X's using several diff models: 2132, AD825, and I now have 5532 plugged in. Same confusing result.
> 
> ...


 
  Okay, you Pimetans figure this out ... 
   
  As noted a few weeks ago, Q3L was replaced with Fairchild BC639 (the only one I could get to work as I did not have a Fairchild 2N5088 in my bin; remember, a Fairchild 2N3904 did not work -- see above); Q3R was/is Fairchild 2N5088.
   
  One thing I've noticed with the BC639 is that the L-ch turns on with a relatively loud (but not dangerous) transient  from cold start [I never had this transient -- much less ANY transient -- with the orig. 2N5088]. If the unit has been on for a while and/or I cycle power (on/off) quickly ("warm pwr cycle"), no transients audible. I thought this new phenomenon may have been due to different Beta (or other) parameter diff. *between* Q3L BC639 and Q3R 2N5088. So I ordered new Fairchild 2N5088s. When I installed a new Fairchild 2N5088 Q3L, the L-ch -- as with the 2N3904 -- gave a loud thump (and I once again had that prev.-noted out-jack 2.6V L-ch wrt gnd ... like with 2N3904. And a dead L-ch, of course). I put the BC639 back in and ... voila! ... things are back to normal. What!!!???
   
*The ONLY conclusions I can come to are*: Fairchild has recently changed the parameters of (at least) some of their transistors; _and/or_ the Pimeta's topology, WRT the class-A biasing ckt, is too damned sensitive to sample-to-sample (batch) diffs in small-signal NPN parameters (Beta, etc.)
  
*Notes*: No, I did not remove/replace Q3R 2N5088 to test its parameters. I'm not superstitious but I don't want to jinx this touchy piece of kit any more than I have to! And its a royal pain to remove (de-solder) parts from that crowded-footprint space.


----------



## tangent

Quote: 





> Fairchild has recently changed the parameters of (at least) some of their transistors


 
   
  No.
   
  The whole point of assigning part numbers to transistors is that they are labels for a specific bag of parameters. When manufacturers change the contents of the bag, they change the label, too. This is why there are so many types of bipolar transistors on the market despite the fact that they're all fundamentally the same device.
   
  It is common for parts from different manufacturers that have the same base part number to have slightly different parameters. But, these differences will remain over the long term, because each manufacturer isn't going to change the parameters without at least adding a new variant code to the part number scheme.
   
   
  Quote: 





> Pimeta's topology, WRT the class-A biasing ckt, is too damned sensitive to sample-to-sample diffs in small-signal NPN parameters


 
   
  Also no. I told you that two weeks ago, and it's still true.
   
  Are you ready to consider the possibility that I might just have some idea of how this circuit works, and that when I tell you that there is no magic transistor type, it means the problem lies elsewhere?
   
  It's probably time for you to post high-res pictures of the top and bottom sides of the board.
   
  Measurements of the voltages at the op-amp pins relative to IG would be good, too. Maybe you did that already in the past 2 pages and I don't see it in skimming, but you should re-measure anyway, since you've gone and changed the circuit.
   
  Any chance of scoping the op-amp outputs to check for oscillation?


----------



## alphaman

Quote: 





tangent said:


> Quote:
> 
> 
> > Pimeta's topology, WRT the class-A biasing ckt, is too damned sensitive to sample-to-sample diffs in small-signal NPN parameters
> ...


 
   
_I don't have a 'scope on hand_. I did swap the orig. opa's (two AD825s BrownDog'd) for an AD8620 and NE5532. No difference. Cold pwr-on, for L-ch, causes opa (V_out) AND post-buffer output-jack voltage to v. briefly (transiently) peak 300-400mV with AD825s. About 500mV with the AD8620. And 600mV with NE5532 [The 825's are the most-forgiving opa I know (transient-wise).]
   
_Tangent wrote:_ "Are you ready to consider the possibility that I might just have some idea of how this circuit works, and that when I tell you that there is no magic transistor type, it means the problem lies elsewhere?" 
   
  Not sure what type of omnipotence you are claiming here??? .... the (Pi)Meta (and other projects on your site) are standing on the shoulders of many....Jung, C Moy,  PPL, et. al. So don't flatter yourself too much!! Agreed that PART of the problem lies elsewhere (remember that the majority of the issue was resolved with selecting the BC639; and as I noted in post#393, your advice was counterproductive) ...but that doesn't mean this "novel" class-A scheme isn't, etiologically, a bit whacky or risky -- e.g., earlier, I noted massive DC at o/p if, say, the opa was removed or one of class-A transistors wasn't working (or removed). You may want to write that one up in some project cautionary notes on your site. All that said, I don't expect you to be an oracle on this issue -- the choice to comment is welcome but not compulsory. DIY is a crowdsourced community.
   
  BTW...
   I'm prefectly willing to live with this Pimeta2 in its current cond. The SQ is not affected AFAICT. Only that 400mV L-ch transient, which is not too bad. And I can get around it by plugging in cans AFTER pwr-on.


----------



## tangent

Quote: 





alphaman said:


> _Tangent wrote:_ "Are you ready to consider the possibility that I might just have some idea of how this circuit works, and that when I tell you that there is no magic transistor type, it means the problem lies elsewhere?"
> 
> Not sure what type of omnipotence you are claiming here???


 
   
  I think you mean "omniscience," but regardless, the answer to your question is "none." I am neither all-powerful nor all-knowing. I am merely claiming to have some confidence that I have applied some well-known principles of electronics correctly.
   
  I think I have several reasons to be confident:
   

 The part of the circuit you're blaming is well-known outside this little world of headphone amps. More below.
 The PIMETA v2 is about 3 years old now, and none of the others built so far has shown this same problem. That suggests that the problem is in your particular amp, not in the amp design. If the problem were in the circuit design, why are you the first in three years to have this problem?
 It's been two weeks since your original claim to have diagnosed the problem. Where are the confirmatory reports from those who have also been affected? Absence of evidence isn't evidence of absence, but all my training in how Internet geek communities work tells me to expect some piling on by now if you were right. Silence, on the other hand, means either no one else has a better idea, or that everyone else has gotten bored of the discussion and moved on.
   
  I am well aware that there's a fine line between confidence and arrogance. That's one of the reasons I remained silent for these past two weeks. Instead of piling on, we got crickets.
   
  Quote: 





> the (Pi)Meta (and other projects on your site) are standing on the shoulders of many....Jung, C Moy,  PPL, et. al. So don't flatter yourself too much!!


 
   
  So you want an argument from authority? Okay, I refer you to pages 73 and 90 in The Art of Electronics.
   
  I just re-read these sections, and I see only two quibbles you can bring against the PIMETA v2 class A biasing circuit from what's given:
   

 I don't specify matched transistors in the mirror. This means the per-channel currents aren't necessarily absolutely identical. Since we can be within a factor of 2 or so and still get the behavior we want here, I don't see that this matters. But if you think I'm wrong, go and match your transistors, then see if that fixes things.
 Instead of pinning the voltage drop across the current-setting resistor with an LED, Horowitz and Hill use either a zener or a diode string. I talked about the diode string alternative in the docs and explained why I thought the LED is better. The zener option has the same squishiness problem, and is nosier besides. Besides, I got the LED+bipolar current source idea from Jung, which should satisfy your need for authoritative reference. But if you feel Jung and I are wrong and Horowitz and Hill have the right of it, go ahead and swap in a zener or diode string for LED1. I predict it will perform about the same as it does now. You'll lose one LED, and you'd have to make some careful measurements to show the flaws in the modified circuit, but the main point is that I don't believe it will change your symptoms.
   
  Quote: 





> that doesn't mean this "novel" class-A scheme isn't, etiologically, a bit whacky or risky


 
   
  Apparently you are assuming that when I called this circuit "somewhat novel" that I think it is some grand invention, created from whole cloth, and that I am therefore some kind of electronics super-genius.
   
  All I meant is that I had never seen anyone use this particular arrangement for op-amp class A biasing.
   
  You should be able to show this circuit to any EE graduate and maybe get, at most a "huh, that's interesting" reaction. I imagine many would be somewhat bored by it; it is after all, AoE Chapter 2 material. Not exactly high tech stuff.
   
   
  Quote: 





> I noted massive DC at o/p if, say, the opa was removed


 
   
  I already told you why that happened. You will get massive DC output when removing the op-amp from _any_ buffered op-amp headphone amplifier design. When you break the feedback loop, there is nothing to prevent the biased buffer input from being pushed to one rail or the other.
   
  This is not a flaw of the PIMETA v2 or an indicator of a fault in your particular amp. It is simply the way the circuit works when you do that.
   
   
  Quote: 





> You may want to write that one up in some project cautionary notes on your site.


 
   
  You are asking me to add a cautionary note that if you remove essential parts of the circuit that it will not work correctly? That's not obvious?


----------



## alphaman

Quote:


alphaman said:


> Only that 400mV L-ch transient, which is not too bad. And I can get around it by plugging in cans AFTER pwr-on.


 
  One other mod that I did concurrently with the initial opa roll was putting two 9.6v NiMH in SERIES (to give a total of ~20v) as the new opa that I rolled in was a bit more voltage hungry. With my Pimeta2, I normally have the two 9.6's in PARALLEL for longer run time .
   
  Anyway, to make a long story short, I went back to the two-batts-in-parallel (or even a single 9v) arrangement and the L-ch transient is GONE. All totally normal again.
  Batteries are strange creatures. NiMH 9v especially so IME. So another species (alk, LiPo, etc)  may work better IN-SERIES.
  I've also got some wall-based reg'd DC adapters, which output higher-than-10vdc, so I may experiment sometime with them.
  Say tuned...


----------



## tangent

You risk battery damage by putting rechargeables in parallel. You don't have to believe me on this, either. Check any NiMH manufacturer's application manual.


----------



## mfuerst

Hi,
   
  As mentioned a couple of weeks ago, find herewith the Desktop version of my Pimeta v2 amp with the following features:
  - Integrated power supply with the r1 regulator - 25V DC
  - Selectable 3 line Input and 3 lines Output
  - Integrated modified Linkwitz Crossfeed circuit
  - Integrated Bass Boost (pot) and Volume Boost (switch) circuit
   
   
  Here a few pics:
   

   
  The main boards (Pimeta v2, Linkwitz Crossfeed and r1 regulator) assembled and ready for installation.
   
   

   
  As a support, I've chosen an acrylic plate that I can slide into the Hammond enclosure.  Bottom-left see a little board for the power cabling, while on the top-right side the micro-switches have been mounted on another little board.
   
   

   
  From the bottom, with the I/O connectors and the back panel.
   

   
  These little boards are used as indicators on the front panel for the selected I/O lines - the selectors are on the back panel.
  
   

   
  Here the Bass and Volume Boost board - it has taken me a while to get the components for the best audio experience - that can be mounted as piggy-back directly onto the Pimeta v2 board.
   
   

   
  Lastly, another little board that mounts the Bass Boost pot and an LED supposed to indicate the operation mode (Headphone = green, Preamp = red).
  
   

   
  Here from the bottom, pretty much ready to be put into the enclosure.
  
   

   
  Same from the top, all modules are plugged-in and the amp has undergone all tests.
  
   

   
  Sliding it into the enclosure, there is not much room left for other stuff.  I've tried to isolate the toroid transformer (german manufacturer, high quality) as good as possible, and luckily there is no electric or magnetic interference.
  
   

   
  Here the finished product - front and back view.  Note the holes that I had to drill in the cover to allow some airflow - a bit of an artistic touch with the 4 inside LEDs spreading rays of blue light.
   
   

   
  Here another view of the two units I've built.
   
   
  My objective was to have a modular design with all the features I needed to have.  In order to eliminate the hum, I had however to ground the IG to the case.  Else everything worked as per plan, exception made for the 'Preamp' mode of operation that is miserably poor...
   
  Cheers!


----------



## mfuerst

Originally posted by *firefish15*:
   
   
 Quote:


> I found 2 sources for a PCB for the Li-IOn batteries, They are huge compared to yours, but will fit in the serpac.
> http://www.batteryspace.com/pcbfor148vli-ionbatterypack5alimitwithfuelguagesocket.aspx
> http://www.all-battery.com/protectioncircuitmodulepcbfor148vli-ionbatterypack4cellswith65alimit-lipcb14v4.aspx


 
   
  The second one will do and will fit into the Serpac case, no worries.  You will have to pack it along one of the long sides of the battery pack.
   
   
  Quote: 





> My only disappointnent is is the battery life using 9v rechargables. I intend to change this to a 15v lion battery pack. I couldn't find a pre-built battery pack that will fit, so I'll have to build the pack myself using four of these 680 mAh cells:
> http://www.all-battery.com/TenergyLi-Polymer3.7V680mAh603040Battery-30191-0.aspx


 
   
  I had to go for a 453048 spec, I don't believe the 603040 will fit into the case if you pack 4 cells together with the PCB, the cabling, the insulation, etc.
   
   
  Quote: 





> A question on the Pimeta V2 board. At the bottom of the board there are four holes. Are these for mounting a daughter board?
> Can these be cut off? If so I might be able to squeeze in this 900 mAh cell instead.
> http://www.all-battery.com/polymerli-ionbattery37v900mah463455.aspx


 
   
  You can trim a bit the board as explained by *tangent*.  Note however that 600-700 mAh is plenty of capacity, you don't need 900 mAh.  In my case I can operate the amp for about 10 hours, even though I've biased the amp to class A with 1 mA on RBLIM.


----------



## tangent

That's an exceptionally beautiful build, mfuerst!
   
  As for the "miserably poor" preamp mode, I suspect you have some sort of ground loop problem. Since the PIMETA wasn't designed to do that, I haven't collected much info on how to hack it to behave as you want. My vague recollection is that people have managed to make it work by disabling [part of?] the ground channel, so that IG comes from the outside. This means IG goes floating when you unplug the source cables, but again, the PIMETA (v1 or v2) wasn't designed to do this, so...


----------



## mfuerst

Hi Tangent,
   
  Thanks for commenting on the preamp mode quality issues and potential solutions.
   
  I appreciate that the Pimeta v2 wasn't built as a preamp, but the motivation to build this feature came from the Project FAQ page on your website:
   
  Quote from http://tangentsoft.net/audio/pimeta2/faq.html: 





> Can I use the PIMETA as a preamp?
> 
> (...)
> 
> ...


 
   
   
  What I did is to add a switch on the scratchpad area that would toggle between "headphone" and "preamp".  A picture may be helpful:
   

   
  The molex connector right beneath is meant to power the dual-color LED in the middle of the front panel and switch from green to red respectively.  When in "preamp" mode, I do short the Ground Channel as per schema below:
   

   
   
  With the gound channel shortened for "preamp" mode, the effect is that the sound is deamplified to about half the volume (I believe because of the Linkwitz filter) and the sound characteristics is also very poor, like if the low and high frequencies have been cut.
   
  To be honest I didn't have time to debug and find out the root cause, but I would appreciate any comments from fellows that are using the Pimeta v2 as a preamp.
   
  Thanks!


----------



## tangent

The ground channel is still there, fighting against the external ground (EG). Worse, you've increased the EG impedance by 6.49k because the IG-OG short comes from after R1G. This puts EG at a severe disadvantage to OG, which has a near-zero output impedance.
   
  If you moved the left side of that short to the other side of the resistor, you'd still have the ground channel components there, fighting against the external ground.
   
  It may be possible to hack the board to physically disconnect the entire ground channel from the circuit at the same time that you connect IG to OG, but I think it would require modifying traces. It's probably even tougher than you initially think due to the internal ground plane.
   
  A middle ground that _might_ work is replacing that SPST with a 3PDT. Use the extra two poles to open/close the R4G and R7G paths. This would still leave you with BUFG's output fighting with EG, but it wouldn't have a feedback loop wrapped around it to drive its impedance low. With the IG connection moved to before R1G, that might be enough to let EG win the fight for control of the OG node.
   
*EDIT:* I don't mean to suggest that you go and redo all that wiring to add a switch. You should first try simply desoldering R4G and R7G. This should be easy, since you've used SMT resistors. Open the preamp switch and try it. If it starts working well, you can consider how to proceed.


----------



## mfuerst

Thanks tangent!
   
  Your comments make absolutely sense - I will follow your advices.  I should have invested a bit more time to study the circuit...
   
  Cheers


----------



## Yoga Flame

Some time ago I got myself a Pimeta board thinking I would try going balanced with it. But as I planned and researched, I soon realized that would be above my skill level. Thus far I've mostly just been a paint by numbers DIYer.
   
  Still, I've long been intrigued with the idea of driving my headphones in balanced mode. So here is my attempt at implementing the PIMETA v2 balanced on a perf board. I tried to follow Tangent's schematic, but obviously my layout is different. I've left out the biasing scheme for simplicity (and because I wouldn't know how to do it balanced). I used two sigma25 PSUs to get +/- 15V.
   
  Noble 20K pot
  OPA627 x 4
  (LMH6321 x 4)
  Cthulhu grounding scheme 
	

	
	
		
		

		
			




  Using only a 2 wire power cord for now since that's what came with the "enclosure" I have.
   
   
     
   
   
  As you can see, I removed the LMH6321 buffers. I think they were oscillating badly. Horrible sounds with rhythmic clicking and very hot ICs with them installed. My guess is I either screwed something up or they just aren't suited for mounting on an adapter. Maybe I'll try BUF634 instead?
   
  With the buffer positions jumpered, it sounds fine.
   
  I'll post pics again after the casework is done. But I could use some advice on the buffers in the meantime.
   
   
  ps Never again will I use those SOIC adapters. I thought the holes would aid cooling. But soldering with that layout is a pain.


----------



## tangent

Quote: 





yoga flame said:


> Cthulhu grounding scheme


 
   
  Oh, is _that_ what it's called? 
   
   
  Quote: 





> I either screwed something up or they just aren't suited for mounting on an adapter.


 
   
  It's broader than that. No 110 MHz part is well-suited to such a loose layout.
   
  The more parasitics you introduce, the more problems you will have at such speeds. Yes, the adapters are part of it, but I'd say the wiring and such are a bigger part.
   
   
  Quote: 





> Maybe I'll try BUF634 instead?


 
   
  You'll have a better chance of success, particularly if you don't run them in high-bandwidth mode.
   
   
  Quote: 





> Never again will I use those SOIC adapters. I thought the holes would aid cooling. But soldering with that layout is a pain.


 
   
  Another weakness it has is that they had to use extra-short pads in order to fit between the DIP-8 pads, and even then they've created a few risks of shorts. Yes, it's clearer, but there's a reason both Morsel and Brown Dog decided to go with 90 degree variants instead.
   
  I'd check for shorts between neighboring pins.
   
  I think the clicks you're hearing are due to the the buffer shutdown circuitry. It's heating up for some reason (short or oscillation), hitting its thermal limit, shutting down, cooling down, then starting back up. GOTO 10.


----------



## Yoga Flame

Thanks, Tangent! I swapped in some BUF634s and it works well now. 
	

	
	
		
		

		
		
	


	




 And it was a direct replacement too, with no need for wiring changes especially since I'm not using high-bandwidth mode. That was a pleasant surprise.
   
  Casework is turning out to be lots of work, as usual. Don't know when I'll be able to do a proper paint job, so here are some updated pics of my build in working condition.
   



   
  The board is backwards now due to my lack of foresight regarding the XLR input jacks.


----------



## geofftnz

Here's my completed PIMETAv2+GrubDAC amp:



   
  (Fullsize images also here: amp exterior and interior)
   
  Details:

 PIMETAv2 using AD8620/8610 opamps. Everything's pretty standard.
 Power supply is 10 x NiMH AAA cells, for a nominal supply voltage of 12V.
 Input is a GrubDAC mini-USB version.
 NiMH trickle charger moved to its own board. The battery pack is switched between the charger and the amp, to allow the use of non-isolated switchmode supplies. Rccs on the charger is socketed in case I upgrade the cells to higher capacity.
 Prototyping area on the PIMETA is used for molex plugs for audio output and power to pass to the battery meter.
 Battery meter doubles as a power-on LED. LM3914 bargraph driver in dot mode, with the range set to around 9-14V. The first of the 3 red LEDs on the bargraph lights up when the individual cells hit 1V.
 Added a bunch more rail capacitance on a section of proto-board. If nothing else, this makes the battery meter decay in a cool way on power-off.
 Black anodised Hammond case, with laser-cut acrylic panels from Ponoko. The washers on the case screws are temporary until I can find some non-countersunk screws. It also appears that the top of the case isn't aligned to the panel. The original panels wrapped around the case, hiding this. A lot depends how it's screwed together.
   
  The interior layout leaves a lot to be desired. I didn't plan it too well and ran out of room. The amp and DAC are screwed down, but the rest of the stuff is jammed in and taped into place. I've held it upside down and shaked it and nothing came loose, but it's very much something that will live on a desk rather than being thrown around in a backpack.
   
  I like the sound using the Senn. HD518s in the picture above, but my Audio Technica ATH-M40fs headphones seem to lack punch at the bass end (I find myself upping bass substantially in the EQ). On the whole I'm very happy how it turned out, despite a number of setbacks in the build (blowing up DAC kits mostly).


----------



## tangent

Nicely documented, Geoff!
   
  On the bass, the amp is probably just keeping better control of the headphone drivers in bass, giving the impression of "less" bass, when it's just presenting what's in the audio file more accurately. This is one of the reasons bass boost circuits are fairly common around here.
   
  You might also look into Burr-Brown chips. You might like the sound difference.
   
  Can you explain the bargraph driver circuit a bit? I guess it's something fairly standard out of the datasheet, but I suspect there are some component customizations. A resistor divider selection at least?
   
  On the stability of the thing, I'd only worry about the battery pack. Everything else should survive anything that wouldn't put your panels in danger, too. I've used Velcro to hold battery holders inside the case. The industrial strength stuff is significantly better than the normal kind; I had to reinforce the normal Velcro glue with hot glue, since the normal adhesive was the weak point. The nice thing about Velcro is that it automatically pads out the space you have. If you can arrange it so it's anchored top-and-bottom, it'll be a lot more stable.


----------



## geofftnz

Yeah, the "lack of bass" might be that. Those specific headphones are marketed as flat-response phones for mixing and production work, so it's not surprising they don't have the subwoofer-on-your-head marketing many other headphones have.
   
  I do have a couple of Burr-Brown OPA2132PA opamps around (thanks TI sample programme!), so my next PIMETA (I originally ordered 2 boards and have everything for another one bar the buffers) will use BBs. While I was waiting for the panels to be lasered, I turned one of the OPA2132s into a CMoy, with a TLE2426/BUF634 virtual ground:

   
  I do have a source of industrial velcro and am well familiar with its stickiness (having tried to remove the adhesive in the past - can't be done - you end up tearing the structure of the velcro first), so will repack the battery when I get the chance.
   
  The battery meter circuit is the basic one in the datasheet:

  The circuit I ended up building on the breadboard is written down at home, but the basic principle is that one trimpot is used as a voltage divider to take the ~12V supply voltage down to something usable to feed in as a signal. The other trimpot uses the internal 1.25V reference to set the lower limit of the bargraph. These two settings interact, so it takes a bit of adjusting to get the low-high range you want. Out of the 10 LEDs on the bar, I wanted the top couple to indicate a full battery (1.3-1.4V/cell) and for the 3 red LEDs at the bottom to represent a "charge now" indication at 1.0V/cell.
   
  I'll dig up my bit of paper when I get home and post the circuit. I'd modify it slightly if I did it again because one of the trimpots is only using the last 5% of its travel.
   
  Thanks for the feedback!


----------



## geofftnz

Here is the circuit I drew for the battery meter. Like I said, if I was doing this again I'd add a resistor in series with the scale set trimpot (on the V+ side) in order to make the pot range more useful.

  Both pots are (I think) 50k linear, R2 (LED brightness) is 2.7k, LED power bypass is 4.7uF electro. It draws somewhere around 5-10mA in dot mode (this config). Bargraph mode (pin 9 to V+) will draw more, depending on how many LEDs are lit.


----------



## firefish15

.It fits!! It's a tight squeeze but I managed to fit the 60340, and I didn't have to cut the Pimeta board.
  I got the Serpac model without any battery holder to minimize any cutting. I still needed to remove most of the ledges at the top and bottom of the cover opening:

   
  Instead of mounting the board in this side of the case, I mounted it in the other side so that the board sits lower in the case 
   

  Quote: 





mfuerst said:


> I had to go for a 453048 spec, I don't believe the 603040 will fit into the case if you pack 4 cells together with the PCB, the cabling, the insulation, etc.


----------



## firefish15

My next Build is to try and squeeze the Pimeta in a Hammond 1455B case which looks a lot better than the Serpac case.
  http://www.hammondmfg.com/pdf/1455B1202.pdf
   
  Its about the same size as the Serpac but the height is only 19mm.
  The inside of the Hammond has ridges to support a circuit board but can't be used because the board will sit too high to fit potentiometer ( plus some of the traces on the Pimeta are too close to the edges). Power will be supplied by the same 60340 li-ion cell I used before but using 3 cells instead.

   
   I removed one set of the ridge allowing the Pimeta board to fit.
   

   
  I was going to place a sheet of mylar between the case and the Pimeta board. 
  But since the buffer chips are electrically non-conductive does anyone see a problem with allowing the chips to rest on the bare aluminium case? 
   
  Paul


----------



## H22

Just finished putting together my second Pimeta, this is a gift for my little sister so I used the input caps and current limiting resistors in place. I built this out of spare parts i had laying around. I used an 823 opamp in the LR channel, and a 627 for the ground. She is a bit of a bass head, and I found the 823 to be lively sounding with good low end, so think it will work pretty good. I did have to order caps for the C6 position, as well as another alps POT for the BB. cant wait to get it boxed up and shipped off to her.


----------



## H22

more pics:
   
  Power caps are MUSE, two 330uf and one 470uf. Still need to built a power supply, right now I am running it off of a 12 volt AA battery pack.


----------



## tangent

Quote: 





h22 said:


> I used an 823 opamp in the LR channel


 
   
  It's nice to see that op-amp getting a little publicity. Its one serious weakness — low output current — totally doesn't matter in a PIMETA v2.


----------



## jcx

I wish you would quit making that statement without added qualification - at higher supply V the AD823 has more current capability than many "generic" op amps
   
  the data sheet shows multiple tables of specs for a wide range of supply V - if you only read the 5 V spec you get the wrong impression
   
   
  [size=x-small]Quote:[/size] 





> [size=x-small][size=x-small]At T[/size][/size][size=x-small][size=xx-small]A [/size][size=x-small]= 25°C, V[/size][size=xx-small]S [/size][size=x-small]= ±15 V, R[/size][size=xx-small]L [/size][size=x-small]= 2 kΩ to 0 V, unless otherwise noted. [/size][/size]
> [size=x-small][size=x-small]...[/size][/size]
> 
> 
> ...


 
   
  for driving 300 Ohm cans you could be better off with the bare AD823 from +/-15 V supply without buffers eating V headroom


----------



## H22

Quote: 





tangent said:


> It's nice to see that op-amp getting a little publicity. Its one serious weakness — low output current — totally doesn't matter in a PIMETA v2.


 

 Yes, I have 6 or so various op-amps that I ordered based on your op-amp page. When I started building this amp I sat down with my little Cmoy and did some testing. the Cmoy is easy to roll op-amps in, and its just the op-amps in the circuit so it makes for good A-B comparisons.I really liked the 823, to me it really expanded the "sound stage" and "depth" compared to the others i had (sorry, don't have them in front of me so i cant give the PN's). All the others sounded kind of flat by comparison. Plus the 823 just sounds lively or fun if you will. I actually preferred the lowly little Cmoy with the 823 over my mini3 (the HP build). I did find that it did not have the grunt my mini3 has, but i did prefer the sound. As you say though with the buffers its a non issue. In the Pimeta running 12 volts, even with the standard gain (4.75 R4 if memory serves me, gain of ~5) its plenty loud!.
   
  Tangent, just got the parts I ordered from you last week, so i can finish this one up. Thanks.


----------



## alphaman

Alternative (better, IMO) to AD823 is AD8397. Not too $$, and HIGH current. It seems to have gotten mildly popular in some audio circles. Anyone try it in Pimeta?


----------



## tangent

The 8397 is a bipolar input chip, and so may cause a DC offset at the output of the PIMETA without tweaking the values of the resistors attached to its input pins.


----------



## alphaman

Quote: 





tangent said:


> The 8397 is a bipolar input chip, and so may cause a DC offset at the output of the PIMETA without tweaking the values of the resistors attached to its input pins.


 
  I've found that *modern* bipolar op-amps like the 8397 are okay to use "naked". In fact, that opa is used as an output for the QLS-350 DAP and several other commercial jobs like the Xin SM3 headphone amp.


----------



## elec999

Anyone selling these already built?


----------



## tomb

Quote: 





alphaman said:


> I've found that *modern* bipolar op-amps like the 8397 are okay to use "naked". In fact, that opa is used as an output for the QLS-350 DAP and several other commercial jobs like the Xin SM3 headphone amp.


 
  That doesn't matter.  I think if you look into the history of the AD8397, you'd be a bit more careful in recommending its use.  Tangent himself, along with AMB, both came out with brand new designs when the AD8397 came out (a few years ago).  Tangent went with the PINT - an amp so small, it was intended for use in a mint tin with a couple of 9V batteries.  If I recall correctly, the PINT PCB was 3/4" x 2-1/4" (or same size as the PPAS).  Unfortunately, there were enough problems that Tangent removed the PINT design completely from the market.  He didn't feel that it was stable enough to support as a product from tangentsoft.com.
   
  AMB did the same in working with Head-Fi/Headwize user Morsel - who helped on both the M3 and the PPA.  AMB's version used a larger PCB based on 2 - 9V batteries in a large, PIMETA-styled Serpac case.  It was not stable in all regimes.  After more than a year of on-and-off testing, etc., AMB finally came to the conclusion that the AD8397 would only operate with stability with one 9V battery, not two.  That's how the current Mini3 came about.
   
  Anyway, all that stuff means is that you shouldn't trifle with the AD8397.  It's not something that you can simply "roll-in" as an opamp choice.  Tangent is being kind in his reply - he knows this more than anyone else.


----------



## vixr

wow...that was an awesome post.


----------



## tangent

Quote: 





tomb said:


> Unfortunately, there were enough problems that Tangent removed the PINT design completely from the market.


 
   
  I'm pretty sure the problem with the AD8397 in the PINT was due to the ground channel. If you find the gain vs. frequency chart in the chip's datasheet, you see that the GBW is only flat at gains of 2 and above. The peak you see at ~40 MHz at g=1 causes positive feedback, which in electronics is a Bad Thing if you weren't intending on building an oscillator.
   
  I think if someone takes a PINT and replaces the ground channel with a true dual supply scheme with a passive ground, it'll be quite stable.
   
  (As for why I didn't just start recommending that with the PINT, it's because I didn't want to stop recommending the AD8397 for OPALR, and there's a segment of the community that won't listen when you tell them it's fine — better even, sometimes — to use a different ground channel chip than for the L&R channels. I've toyed with creating a passive-ground version of the PINT, basically a glorified CMoy pocket amp, which if it ever gets off the ground will be called the PINT/2. Yes, the half pint. Laugh, it's funny.)
   
  As for the matter of the AD8397 being "modern," that has nothing to do with anything. Input offset current is all that matters. The physics have no respect for modernity of design.


----------



## alphaman

I have not experimented with Pimeta + 8397. This opa has become a favorite in other apps so I suggest it as a possibility for a DEFAULT Pimeta.
   
  The *DEFAULT* Pimeta has/uses:
   
  - single voltage source (not a separate 9v for each rail)
   
  - multiple "layers" of purpose-built protection. E.g., R11 limits the max. output current on the buffers. 
   
  So given the above, experimenting with the 8397 + DEFAULT Pimeta should, at worst, lead to harmless untweakable distortion. 
   
  As much as I like the Pimeta, I may like the 8397 more. Specifically, when traveling with my portable rig., a Colorfly CK4 DAP (with both LO and HO opa's modded with 8397's) + Pimeta v2 , I no longer feel I'm missing all that much with an external amp. The only thing I REALLY miss is input-based MLC.
   
  Hmmm .... since I like the 8397 so much, maybe I should design a novel/ad hoc amp _around it_, rather than adapt a "generic" pre-existing job like Pimeta.


----------



## MisterX

Quote: 





> I've toyed with creating a passive-ground version of the PINT, basically a glorified CMoy pocket amp, which if it ever gets off the ground will be called the PINT/2.


 
  Since you're toying with ideas...
  How about using a charge pump configured as an inverter to create a - voltage "rail"?
   
http://www.linear.com/product/LT1054
   
  Of course being as there is no such thing as a free lunch,  you would need deal with the switching noise and the uneven "split" from the voltage loss but should be pretty easy.


----------



## tangent

Because if I'm going to create the negative rail with a DC-DC converter, I might as well create both of them so I can run the thing off a single NiMH cell.
   
  And the reason I don't do that is that in order to fix the noise created, you need big Cs and Ls, which eats into that space savings budget.


----------



## alphaman

Quote: 





tangent said:


> Because if I'm going to create the negative rail with a DC-DC converter, I might as well create both of them so I can run the thing off a single NiMH cell.
> 
> And the reason I don't do that is that in order to fix the noise created, you need big Cs and Ls, which eats into that space savings budget.


 
_*No*_, Tangent .... MODERN (I know you love _that_ word) i-[devices], DAPs, etc. effectively use MODERN Buck/DC-DC chips with MODERN Li-ion batts in extremely compact packages. No "big" C or L really needed; for C, high-qual. SM tants should be fine, add a few SM ferrite beads for even better SNR. I've 'scoped some of them and even most stock-jobs are _clean enough_.


----------



## tangent

Okay. Go make that.


----------



## niksh

1) I have question about R11. Tangent says that its 667X power suppy. So if my supply is 24V, the R11 should be 7.3K. But using 7.3K the current limit for 24V is 24/7.3k = 3.3mA. If I want to limit current to 300mA using 24V the appropriate value should be 24/0.3 = 80R. Can someone please help me.
2) I have difficulties sourcing 6.8uF for C4 with the right size. Can I use tantalum here. i have 10uF, 47uF and 150 uF. Which one should I use. Thanks.


----------



## tangent

Quote: 





niksh said:


> But using 7.3K the current limit for 24V is 24/7.3k = 3.3mA.


 
   
  You can't use Ohm's Law that way. The resistor is not simply sitting there across the power supply. It is controlling the amount of current that goes into the buffer's current limiting circuit. We say the current limiter is "programmed" by this tiny controlling current.
   
  Read the LMH6321 datasheet for more info on this.
   
   
  All the rest of your questions are answered by the C4 section in the docs.


----------



## niksh

Tangent, I ordered 2 sets of Pimeta2 PCBs and parts on Aug 15. According to the tracking no LK074729587US, it has been shipped out on Aug 16. However, until today, I have yet to receive the goods. Usually it only takes about 2 weeks for shipment from US to Malaysia. I have contacted the local post office but they are unable to check since it is under ordinary mail and treated as normal letter. I would appreciate if you could trace the transaction at you end. Thank you.


----------



## tangent

Sorry, but I can't trace it from this end, either.
   
  To get international tracking, you would have had to use Express Mail, which is faster, but about twice as expensive as Priority Mail.
   
  From the few reports I get back, two week deliveries are normal, but I have also seen it take longer, even a month.


----------



## niksh

Ok then, I wait another week or two. Then what? I have to place another order. Is it insured? Thank you.


----------



## tangent

Don't worry about the package being lost. That is a very rare thing in my experience. Delays in international mail, however, are not rare at all.


----------



## niksh

Thanks for the reply. I will wait for the board, better late than sorry. 

Btw, back to C4 issue, I have read the doc, but it does not mentioned anywhere about the size ot tant caps. You only mentioned that easiest to use are 7343 surface-mount caps. It is better to use the same size i.e 6.8uF or can I go for 47uF tant or larger, does it make any different.


----------



## tangent

When you asked about the size, I assumed you meant the physical size, not the capacitance.
   
  As to that, the capacitor dielectric doesn't change the advice: 1 to 10 uF is a good range for C4.


----------



## niksh

Thank you for your reply. FYI, I finally received the Pimeta V2 PCB and I am really impress with the quality.
It is the best that I that I have seen so far. Btw, I am still using Pimeta V1 and I really enjoy listening to it.
I hope the V2 will be an upgrage.


----------



## firefish15

LMH6321 product change notice.
   
  I recently receive an email from Mouser that the manufacturer has published a product change notice for the LMH6321 . Can the new chip still be used in the Pimeta without any changes? Attached is the data sheet Mouser sent me.


----------



## jpaul64

Working on my version of the Pimeta...


----------



## tangent

Quote: 





firefish15 said:


> I recently receive an email from Mouser that the manufacturer has published a product change notice for the LMH6321 . Can the new chip still be used in the Pimeta without any changes? Attached is the data sheet Mouser sent me.


 
   
  I had a copy of the original datasheet on hand. According to DiffPDF, that PDF is identical to the original, except for the two TI pages added to bookend the original NatSemi document.
   
  Unless that change notice said anything other than a datasheet change, that may be enough to explain it.
   
  I suppose it's possible there is a process change happening, as chips move from a NatSemi foundry to a TI one, but since the datasheet hasn't changed, it hasn't changed the chip's operating parameters.


----------



## firefish15

Thanks Tangent, paul64. Just want to be sure that the LMH6321 can still be used without any modifications.


----------



## jpaul64

... finished!


----------



## jpaul64

I will try to reduce the dimensions of the board. I will replace the relays with AQW612S to reduce the overall power (µC had brown mode). Perhaps smaller SMD components?


----------



## niksh

Hi Tangent. Thank you for the PCB and Alps Vol which were delivered last week unopened. It takes only 8 days compared to 42 days last time. I have completed my Pimeta V2 and I am so happy that it works the first time. I am using OPA 227/2227PA and I have to get use to the tremendous bass it produces compared to V1 using AD8610/20. I changed to OPA134/2134 but I dont like the sound, too laid-back. Most probably the OPA227/2227 are still new need time to settle down. Here are the photo for both V1 and V2.

Presently I adjust the bias to 1 mA and max it can go only up to 1.3 mA with OPA227/2227. Both the opamp and buffers are warm. Btw what is the optimum bias. I saw in some thread someone mentioned the optimum bias in the range of 3 mA to 5 mA. Thank you.


----------



## tangent

Quote: 





niksh said:


> It takes only 8 days compared to 42 days last time.


 
   
  Yes, international mail delivery time is quite variable. Your previous delivery time is well outside the normal range, but it's not the first I've seen to take that kind of time, either.
   
   


> Most probably the OPA227/2227 are still new need time to settle down.


 
   
  Op-amps don't change in sound over time. Your mind may change over time, though, as your preferences develop.
   


> I have to get use to the tremendous bass it produces compared to V1 using AD8610/20.


 
   
   
  Yes, a lone LMH6321 is a better headphone driver than a lone SO-8 BUF634, as you've done.
   
  It also looks like your PIMETA v2 has a bit more rail capacitance, which would help with the bass, if true.
   
   


> what is the optimum bias. I saw in some thread someone mentioned the optimum bias in the range of 3 mA to 5 mA. Thank you.


 
   
  It depends on the chip.
   
  The only reason to go higher than you currently can is with uncommon chips like the AD843 where you're having to overcome an already-high bias point.
   
  For many chips, even 1 mA is vastly more than needed to achieve a change in operating point.


----------



## niksh

Hi Tangent,
After running my Pimeta for a few days I noticed that the right side sound much lower than the left. Upon checking I discover the following:
1) High current draw from regulated 24 volts supply using LM317.
2) Voltage drop from 24V to about 12V (+/- 6 V on opamp)
3) R1/R2 on LM317 is hot.
3) Changing the opamp does not help.
4) I suspect it must be the buffer coz removing both opamp the voltage drop is the same.
5) How can I check the defective buffer without removing it.
6) Other than the buffer, any where else should I check. Is it possible for something else drawing the current, C3/C5 shorting out?
Thank you.


----------



## tangent

I doubt your buffer diagnosis, because the voltage setting resistors on the LM317 should _never_ be hot, no matter what the load on the power supply is. The output current doesn't go through them, so the heat in these resistors should be constant.
   
  I think your problem is in the power supply.
   
  Easy test: disconnect the power supply from the amp. Does it bounce back up to 24 V, or does it stay sulking down at 12 V? If it bounces back, put a 470 ohm resistor across the power supply. (This gives approximately 50 mA, roughly equal to the draw of a PIMETA v2.) Does the voltage remain at 24 V, or does it fall to 12 V again?


----------



## niksh

Thank you. But why is that the left channel sound louder than the right channel even with opamp change. I don't have 470R and will get some. In the mean time will test using 2 fully charge 9V battery.


----------



## niksh

Using another 24 volts regulated power supply in series with 1R resistor, I measured current draw of 120mA with both opamp and 105mA opamp removed. No wonder using the earlier supply the voltage drop so much coz its only rated 100mA. The opamp is warm while all the buffers are quite hot to touch more than 30 sec. The DC offset tested on all output is almost zero. All measurement done with biasing switch off. 

When I plug the headphone, the sound is ok except the right channel is softer than the left. I am rather worried with the heat generated by the buffers. Any suggestion?


----------



## tangent

http://tangentsoft.net/audio/trouble.html


----------



## acvtre

Hi, I've just built the pimeta v2 but it doesn't work. Some days ago the led didn't even light up, but after a bit of troublshooting I found out that I made some ridicoulus mistakes. Now the led lights up, but there's no sound, so I've checked the voltages at OPAG, OPALR and BUF pins relative to the IG and on a couple of pins for each I have 4V. I use a 9V battery as power supply.
   
  More info: I've built the pimeta avoiding the problem of the bias, for now, so no second led, no RBLIM ecc. and without BUF chips. So I've avoided everything possible.
   
  What's wrong?


----------



## tangent

Post high-res pictures of both sides of the board. Also, go through the rest of the standard troubleshooting steps.


----------



## acvtre

Here are some pics, I know I've built it really bad. 
  EDIT: (troubleshooting referred to the tangentsoft preliminaries)
  1) using a 9V battery I measure 8.77V at V+ and V-.
  4) no more the 15mV ground and the L/R output.


----------



## tangent

You have no op-amps and no buffers. These aren't optional components.
   
  Well, the buffers are optional in a kinda-sorta way, in that you can short them, but you haven't done that, either. And if you do, you basically end up with a glorified CMoy Pocket Amplifier. Not that there's anything wrong with that, but a nerfed PIMETA v2 is a pretty expensive way to achieve that end. 
   
  You could short the op-amps, too, but then you'd just have a really expensive interconnect. Some audiophool companies call these "passive preamps", but you still don't want it.


----------



## acvtre

Ok, I've got the opamp but not the buffers. I'll buy 'em sonner or later. In order to realize if it works, how do I have to short the buffers?


----------



## tangent

Connect each buffer's input pin to its output pin.


----------



## acvtre

Quote: 





tangent said:


> Connect each buffer's input pin to its output pin.


 
  Ok, can you please show me input and output for each buffer chip?
  Thanks.


----------



## MisterX

http://tangentsoft.net/audio/pimeta2/misc/sch-2.01.pdf
   
  Pin 3 is the input, pin 6 is the output.


----------



## Ongar

Hello, I was interested in building one of these amps, but have a couple of questions. I was planning on including it into a casemod on my PC, and possibly powering it through 4 pin molex connectors. I was also thinking of connecting it to the motherboard's headers for the front panel audio, or even joining it to the jacks that already exist on the case. The problem is I am a complete newb, although I am willing to put the time in to learn. Would any of this be feasible? I am most interested in powering it through the PC power supply, but connecting it to the motherboard would be awesome too.
   
  Thanks!


----------



## tangent

Quote: 





ongar said:


> possibly powering it through 4 pin molex connectors.


 
   
  It's not as easy as you think it should be. A PC power supply is not isolated. You can't power it from USB, either, for the same reason. (Or from your car's cigarette lighter, yet another frequently-asked-and-shot-down-proposal.)
   
  You basically have two alternatives:
   
  1. Run power in from an external isolated source
   
  2. Put an isolated DC-DC converter between the PC power and the PIMETA. You can buy these from the same place you get most of the other PIMETA parts. Expect a good one to run you at least $15 or so, and maybe a few times that.
   
   


> I was also thinking of connecting it to the motherboard's headers for the front panel audio


 
   
  Totally doable. You'd just have to find the pins, then build a suitable cable.
   
  There's a tiny chance, these days, that you have a CD-ROM audio connector. If so, then you don't even have to build the cable. Just take the cable that already plugs into that connector, snip one end off, strip to taste, and there's your amp-side.


----------



## tent

Hello,
   does anybody of you try to add to the pimeta v2 a preamp out connector by adding a dual opamp in the scratchpad area? Something like suggested by Warren in the tweaks section. Maybe you are able to show some hint/idea/picture about how it was done? I'm looking into correctly wiring the dual opamp that would be needed for that and also to be able to correctly fit it in that scratchpad area.
   
  Thanks in advance,
   tent:wq


----------



## tent

up? 
   
  I'd also like to add another newbie question: do I need to put single opamp at the OPAG socket or if I have just double opamps is it ok to use a double also in this one?
   
  thanks in advance,
  tent:wq


----------



## tangent

Quote: 





tent said:


> do I need to put single opamp at the OPAG socket


 
   
  Yes. A dual op-amp's pinout is not a superset of a single's.
   
  5 minutes' study of the datasheets would have answered this for you, faster, and you'd probably have learned at least one other thing along the way accidentally.


----------



## tent

yes, I dit that indeed in meantime.. I was lazy and threw in the question while up-ping.. 
  anyway, since I'm still without any single opamp I'll need to search about one (I have only dual opamps ghosh!), now I started firstly in testing the PSU by checking V+ and V- compared to IG with my meter (I'm using a 9V NiMH battery as power source) on OPALR, but I read 4.5V on V+ and -3.4V on V-.. that looks to be quite off, right? The same measurement I can read if measuring the correct pins on OPAG.. so Is there something wrong? in the woltage splitter most probably (could it be defective)? or is there some further checking step that I should do, still without opamps?
   
  thanks in advance,
   tent:wq


----------



## tangent

It's normal to get bogus results for that test without OPAG installed. It's kind of like complaining about low gas mileage on your car with the transmission in neutral.


----------



## tent

uhm.. I see.. so I'll need to figure out how to get a single opamp like opa132 since I have some opa2132s and put it in opag and recheck again. Thanks!
   
  tent:wq
   
  PS: btw. I just noticed that on texas' site the OPA132P is considered obsolete, only U version is available.. so what would be the replacement of OPA132 when all of them will be obsoleted? I mean having same quality and sound?


----------



## tangent

There are many op-amps that will work here. I've reviewed a few of them. OPA134 and OPA227 are still being made in PDIP, for just two examples.


----------



## tent

Thank you Warren. I think I'll use OPA134 then to match it with my OPA2132s...
  but one question still for my understanding: if instead I would like to use OPALR with LM4562NA, what would you suggest better in OPAG? OPA227 or OPA134? I understood that LM4562 has no single version companion...
   
  tent:wq


----------



## tangent

If I had given you four examples, would you now be asking me to rate all four configurations?
   
  There is no objective answer, and I don't have a subjective one, since I haven't listened to all combinations of op-amps. I don't even have a review of the LM4562 up, so I clearly haven't even heard them individually.
   
  You're just going to have to try it.


----------



## MisterX

Quote: 





> I understood that LM4562 has no single version companion...


 
   
   
   
   
http://www.ti.com/product/lme49710


----------



## tent

Wow thanx Misterx! 
  Why do they use such confusing and cumbersome numering system to name their chips??
   
  tent:wq


----------



## tent

Hello, news and updates: I've managed to get around a single opamp for OPAG and still the difference between IG and V+ is 3.00V and IG and V- is -4.71V with my 7.2VNiMH 9V battery.. still do you think it's ok, Warren?
   
  I've also tested further: There is no DC offset between OL or OR and OG, no DC between OG and IG, no other strange DC is seen in other sides.. I've also tested music using some old crappy headphones and music seems to come out even if volume seems to me quite low.. even at full pot turned up (I use my SANSA as source, if I use my iPod with Fiio Line OUT of course I get a lot more power.. but to me PIMETA was a method to get more volume from SANSA).
   
  I've used basically only the values of original schematic for all my resistors...
   
  Another thing I checked and found kind of "wrong" is the ClassA BIAS circuit: the LED2 is not powering on, the LED1 is bright when I turn on BIAS and is very dimmed when I turn off the BIAS. Additionally trying to adjust the bias to 1mA (so looking for 1V across RBLIM, I'm only able to get close to 0.653V, but I can't go further because the trimpot seems to be at one turning end (5k trimpot as per schematic as well).
   
  How do you see it? Is allright? Is something probably going on with the split ground regulator?
   
  tent:wq
  
  EDIT FYI: actually I noticed that now that RBLIM is 0.653V I actually cannot see even LED1 powering on (unless of course I turn off BIAS)


----------



## tent

I've now listened to it anyway with this setup (no BIAS, one OPA2132 in OPALR and one LM6171 in OPAG) with the ipod and the Fiio Line out and I have to say it really sounds amazing there! The bass boost circuit is a bit too much even if impressive itself as well, no particulare difference noticed at the moment when turning on or off this BIAS but probably something is fault.. could it be the LED2 is failed? For the V+/V- IG voltage difference instead it seams at the moment not to be a problem.. chips are not hot after use.. but wondering still if it is normal or if I should attempt to change the virtual ground trans.. and also the gain seems to me to feew like suggested in the schamatics..
   
  tent:wq


----------



## tangent

Quote: 





tent said:


> still the difference between IG and V+ is 3.00V and IG and V- is -4.71V with my 7.2VNiMH 9V battery.. still do you think it's ok, Warren?


 
   
  Nope. You shouldn't measure more than about a tenth of a volt off of ideal.
   
   


> volume seems to me quite low.. even at full pot turned up


 
   
  Also a good problem indicator. The stock PIMETA v2 gain, while lower than that of the CMoy, is still fairly high as headphone amps go.
   
  (Why? So that uncompensated op-amps like the OPA637 will work. If not using uncompensated op-amps, you probably want something lower.)
   
   


> LED1 is bright when I turn on BIAS and is very dimmed when I turn off the BIAS.


 
   
  The brightness of LED1 should only change as a function of supply voltage changes.
   
  This suggests that your problem may be a dead short across the battery, causing its voltage to drop.
   
  So, one test is to be measuring voltage across the battery terminals while you flip the switch. It shouldn't change much, if at all. If it does, your amp is drawing more than the battery is intended to supply, but with NiMH you can pull 1C continuously without problems. That's on the order of 4-5x the expected supply current of a PIMETA v2. One 7.2V NiMH "9V" datasheet I just looked at fully characterizes the battery up to 3C. (900 mA!)
   
  You can try measuring current directly instead, but be sure to use your DMM's high current range first. It's quite possible to get multiple amps out of a NiMH battery for short periods, which will blow the fuse (or the meter, if there is no fuse) on low current ranges.
   
  Another test is to measure resistance from the top of LED1 to V- while the amp's power is switched off, or the battery is removed. I get 56 kΩ here on one of my PIMETA v2s. If you get something much lower, especially near zero, you have a short or you've got something connected across the rails that you shouldn't have.
   
   


> RBLIM is 0.653V I actually cannot see even LED1 powering on (unless of course I turn off BIAS)


 
   
  I can't be sure that's wrong without knowing the Vf of your LEDs.
   
  With a 7.2 V battery, you shouldn't be using 3.7 V LEDs as shown in the schematic. To a first approximation, you can add the two Vf values and get the minimum supply voltage. The transistor behaviors change that a bit. At these low voltages, they may well change it more than 10%, which is why I say it's only a first approximation.
   
  I use two 3.7 V white LEDs in one of my PIMETA v2s (the red one in the docs) but it has never been tried with less than an 8-cell (9.6V) NiMH battery.


----------



## tent

Uhm.. ok then let me check carefully what it could be...
   
  First of all the battery: I just discovered it is a 8.4V 200mAh NiMH and not 7.2V like I belived... not easy to understand which is the matching datasheet tough..
  basically it is this one: http://ecx.images-amazon.com/images/I/61m1PaFM3aL._AA1500_.jpg
   
  But now I have the battery empty since I was letting the board running overnight with the idea of letting it roll out......gh..... question is: should/could I dare to plug in the wall wart to charge it or is it risky at this point since some short is suspected? Maybe if not turning on the pimeta but just recharge the battery?
   
  Anyway what I could do is measure the resistance between LED1 and V- and I read 11.61k and 9.8k (I measured both LED1 pins) so it seems to be compatible with your suspects.. so maybe some not so evident short or contact??
   
  Also the led V value is unknown to me (I was having them lying in my parts bin, were actually new ones, but no idea about voltage etc.. just blue led with 2.5mm diameter I'd say.): is there a method to know V of those with the meter? otherwise I could just attempt to change them with others.. led2 on the other hand does not even light on with both BIAS settings..
   
  Kr,
   tent:wq


----------



## tangent

Quote: 





tent said:


> I just discovered it is a 8.4V 200mAh


 
   
  Okay, so what does its voltage measure unloaded and loaded, and does the loaded voltage change when you toggle the bias switch?
   
   


> now I have the battery empty


 
   
  I hope that's not literally true. You can damage NiMH batteries by draining them too far. 0V is very very bad. You shouldn't go any farther than about 0.8 V per cell, or about 5.6 V for the entire battery in this particular case. (8.4V = 7 cells for a NiMH.)
   
   


> could I dare to plug in the wall wart


 
   
  Do you have a big power resistor on hand? If so, you can put it across the battery contacts, then measure voltage drop across it to infer that the trickle charger is working. V=IR, so if you use a 10 ohm resistor, you'd expect to see 0.2V across it if you set up the trickle charger for 20 mA, as would be appropriate for a 200 mAh battery.
   
  You'll want to use at least a half watt resistor in this case. Power dissipation is 0.4W, so a 1W or bigger resistor would be better.
   
  Or, you could put your ammeter across the battery terminals to measure the thing directly, though if something is very badly wrong, you risk blowing up the meter or its fuse. The resistor test is less risky.
   


> I read 11.61k and 9.8k


 
   
  It's a pretty crude test, so it's hard to say for certain, but that result doesn't jump out at me and scream "FAIL!". The actual values depend on details of your circuit build and, crucially, on how your meter works. Without a result down in the 100 ohms or less range, I think you've ruled out a dead short.
   
  By the way, the 9.8k is your RLED, in all likelihood. (The result I was looking for is the 11.61k.) If so, and you used a 10k resistor, then either:
   
  a) you didn't use a 1% resistor
  b) your resistor is out of spec, or
  c) your meter is el crap
   
   


> just blue led


 
   
  Most blue LEDs are at least 3.7V, and some go as high as 5V.
   
  You can test whether your battery voltage is too low by running from your wall power supply, which should be considerably higher voltage than your battery. If all the problems clear up on wall power, then you know you just don't have enough voltage to do what you're asking of the amp.
   
   


> is there a method to know V of those with the meter?


 
   
  Few meters do a good job of testing Vf of LEDs. Many meters don't test with enough voltage to light the LED at all, and some that will light the LED don't give the right measurement. Diode testers on DMMs are typically intended to test regular diodes only, not LEDs.


----------



## tent

Ok at the moment I measured voltage unloaded and it was 8.05V but if I turn the pimetav2 on the voltage will quickly go down (the battery was almost empty) so not really able to tell the voltage drop difference when turning BIAS on/off.. so definitely need to charge the battery first..
   
  I tried to put an 1ohm 10W resistor (the available one) on the battery and without wall wart plugged it measured something like 0.2V but if I plugg the wall wart (12V linear, isolated) the voltage drops to just 0.02 and decreases.. so I disconnected the resistor... the voltage of the battery goes back up to something like 6.56V and stays there.. if I plug the wall wart like that in the wall it will rise the voltage of the battery but if I disconnect it it will quite obviously go back to 6.56V.. so now I'm not sure if I should/could let it be charging overnight like that or not.. it seems to behave ok.. but...?? (I've also tried a 33ohm resistor, 10w I also had lying around but also that one drops the voltage to 0.02V c.a. while wallwart is powered... should I wait more time?)
   
  About the BIAS and RLED: not sure what you really want to measure, but I confirm my rled is 9.8k (I measured that too).. do you think it is too few and I should change the resistor to one that is more stick to 10k? (testing it before with the meter maybe)
  In addition I'm using another meter and measured also from the other led pin to V- and I read 11.78V (9.79V still on the other led pin). So again, the meter seems ok, maybe my resistor is not precise enough and I should change it?
   
  Finally I change the two leds putting there some "old" leds found in my parts bin, that looked to me being of the ones of the good old day's.. green in color.. now when I turn on the pimetav2 also led2 shines.. ok.. led1 now makes very few difference in brightness when turning BIAS switch on and off.. still does tough.. but the proböem atm is that everything fades quickly since battery is exhausted.. so I think I need to concentrate further on how to charge (or better dare to charge) the battery...
   
  tent:wq


----------



## tangent

Quote: 





tent said:


> I tried to put an 1ohm 10W resistor (the available one) on the battery


 
   
  I meant the _amp's_ battery terminals, not the terminals of the actual battery.
   
   


> do you think it is too few and I should change the resistor to one that is more stick to 10k?


 
   
  The only reason I brought it up is to get you to indicate whether this is a trustworthy meter or not. It affects how much I'm going to second-guess your measurements.
   
  Anyway, forget the test we started off with. As I said, it was a crude test. The only way for it to have incorrectly failed to indicate a short is for it to be actually broken.
   
  I think the real problem is the discharged NiMH.
   
  I don't want to tell you to charge it in the PIMETA until I hear whether you did the 1 ohm resistor test across the battery itself or — as I intended — across the amp with _only_ the wall supply powering it.


----------



## tent

ok, maybe I'm missing then what you mean by testing the battery terminals at the amp... do you mean measuring difference between V- and V+? Or just on the "batt" 4 pins plug? I really think there is no difference between measuring it at the battery terminals o at the pins.. anyway I've now charged the battery using an external charger and I've measured absolutely NO difference in voltage (still at the battery terminals) when switching BIAS on or off... so is this clarifying maybe some doubt? for the rest I'm willing to retry the 1ohm resistor test as soon as I understand how to do it. Anyway looking at the schematic of the charging part it really seems simple and failure proof, so since I do not see any evident error there it should be able to charge the battery imho.. would it help if I post some photos?
   
  tent:wq


----------



## tent

I also wanted to point out again that now that I'm using two green "normal" or low voltage leds the problem of the green led1 to change brightness is not there anymore..
  So now for example I have full battery (giving 9.24V when amp is off, 9.04V when on and going down slowly, like 0.01V each 10seconds), and the led1 is same brighness with both BIAS settings, led2 is clearly on when BIAS on and off when BIAS off.. I also managed to set 1V trough RBLIM (1k) rotating the RBIAS, so seems good news and problem solved on this side..
   
  But problem still is this V- to OG being different than V+ to OG (-5.53V vs 2.55V). I also tryied to change the OPAG to see if something changes.. but nothing..
   
  So could we say it is not a problem of some sort of short but something else instead?
   
  tent:wq
  PS: (I also have 11.05V and 9.78V still between led1 legA and legB and V-, but you confirm no need to change that rled 9.8kohm resistor, right?)


----------



## tent

ok sorry for posting so much but I dared to make some further investigation step: I tried to measure the difference between V-/V+ and OG also with the amp powered with the wall wart (12V) and indeed some further odd result comes out: -11.75V vs 2.55V (curiously enough the 2.55V is same as with battery only).. I really start thinking something is wrong in the virtual ground rail splitter maybe?
   
  tent:wq


----------



## tangent

Quote: 





tent said:


> I really think there is no difference between measuring it at the battery terminals o at the pins..


 
   
  That's right. It's simply easier to alligator-clip a resistor to the amp's battery terminals than to clip it to the header pins.
   
  I just want to make sure you're not connecting the resistor across the battery itself, either outside the amp or in parallel with the battery installed in the amp. We're trying to test the charge circuit separately, without the battery getting in the way, confusing things.
   
   


> I've now charged the battery using an external charger and I've measured absolutely NO difference in voltage (still at the battery terminals) when switching BIAS on or off


 
   
   
  Good.
   
  Quote: 





tent said:


> led1 is same brighness with both BIAS settings, led2 is clearly on when BIAS on and off when BIAS off.


 
   
  Also good news. Now the question is, will the problem return with the blue LEDs reinstalled, indicating it wasn't the battery after all? I think not, but if you're happy with green... 
   
   


> PS: (I also have 11.05V and 9.78V still between led1 legA and legB and V-, but you confirm no need to change that rled 9.8kohm resistor, right?)


 
   
  Yes, and no need to keep repeating this crude test. There's no more juice to be squeezed from that stone.
   
   
  Quote: 





tent said:


> further odd result comes out: -11.75V vs 2.55V (curiously enough the 2.55V is same as with battery only).. I really start thinking something is wrong in the virtual ground rail splitter maybe?


 
   
  That is indeed very odd.
   


> would it help if I post some photos?


 
   
  Probably. High-res pics of the board, both sides, please.


----------



## akselo

Hi
   
  I am having some serious trouble with my Pimta v2 build and was wondering if some of you could give me some hints on how to troubleshoot. The amp worked fine for quite a while and sounded great until suddenly the left channel died. 
   
  I used the following comonent values: 
   
  R1-R7: schematic values
  R11=3.09k
  RLED=10k
  LED1: Vf=1.8 v
   
  C1=0.47 uF
  C2=2*680 uF
  C3 and C5=0.1 uF
  C4=6.8 uF
  C6=10 pF
   
  OPALR: BB OPA2132
  OPAG: BB OPA134PA
   
  Vol.pot.: Alps RK127
   
  Measurements discribed in the troubleshooting guide:
   
  Vg+=11.61 V for all opamps and buffers
  Vg-= 11.51 V for all opamps and buffers
  V+-= 23.12 V for all opamps and buffers
   
  Offset Vlg=4.6mV
  Offset Vrg=3.9mV
   
  Input voltage= 23.8 V
  Supply voltage(no load)= 23.89 V
   
  Quiesent current Iq=117 mA
  Expected Iq= around 50-60 mA
   
  The bias circuit is not active for the moment.
   
  Headphones: AKG K702
   
  I don't know what I was thinking when I selected the value for R11. This is way to low so I'm afraid that I've fried one or more buffers as the current limit is set way to high. Is there any way to check this or do I just have to get new ones? Could this have caused damage to the opamps as well?
   
  I read somwhere on this forum that the volumepot has some metal parts underneath that can cause a shortcircuit so I decided to desolder this. I'm a little bit afraid that I ruined it during the process as it only reads 42.8k and 42.5k on the lowest setting. Isn't this supposed to be 50k? Should I replace this or is it okay?
  I also discovered that I used 35 v caps for C2 and 50 V caps for C1. Is there any disadvantages to this?
   
  Here are links to a few pictures of it:
  https://www.dropbox.com/s/5dn6jonrjdw5aup/_DSC1938.jpg
  https://www.dropbox.com/s/ymvcowat66l2nai/_DSC1936.jpg
  https://www.dropbox.com/s/39ddnk0v6ibd8dc/_DSC1935.jpg
   
  Any help would be greatly appreciated.


----------



## tent

Quote: 





tangent said:


> That's right. It's simply easier to alligator-clip a resistor to the amp's battery terminals than to clip it to the header pins.
> 
> I just want to make sure you're not connecting the resistor across the battery itself, either outside the amp or in parallel with the battery installed in the amp. We're trying to test the charge circuit separately, without the battery getting in the way, confusing things.
> 
> ...


 
   
  I've attached some pics.. but let me know if I should upload them in some separate image hosting, zoom in some specific place or take it out from the cables.
   
   

   

   

   

   
  But still wondering how it could be that just on V+ there is a fixed voltage value whatever I use 8.4V or 12V.....
   
  tent:wq


----------



## tangent

Quote: 





akselo said:


> R11=3.09k
> ...
> I don't know what I was thinking when I selected the value for R11. This is way to low so I'm afraid that I've fried one or more buffers as the current limit is set way to high.


 
   
  Possible.
   
  The best argument against it, though, is that it's typically the _right_ channel that gets damaged due to [un]plugging headphones while music is playing, since the ring contact in a TRS plug is right next to the sleeve (ground) lug, so the right channel is momentarily dead-short connected to ground when you [un]plug normally.
   
  You're certain you didn't swap the channels? I've done that before. If you did, too, that would help me believe this is the explanation.
   
  I didn't figure out the channel swap in my amp until I used the amp with a computer in a FPS game, and realized the sounds were coming from the wrong direction. 
   
   


> Quiesent current Iq=117 mA


 
   
  So is the left channel buffer hotter than the right?
   
  Try a spit test first: lick your finger, tap the top of the chip with your fingertip, and guesstimate how long it takes the spit to evaporate. Repeat a few times. If it evaporates faster on BUFL than BUFR, BUFL is considerably hotter, and you've figured this out without burning your finger or breaking out the thermocouple.
   
   


> Could this have caused damage to the opamps as well?


 
   
  No.
   
  I don't mean the op-amps couldn't be damaged, but they can't be damaged purely because R11 is too high. Something _else_ would have had to happen to them.
   
   


> the volumepot has some metal parts underneath that can cause a shortcircuit


 
   
  MMmmmmayyyybe. I've just tried to reproduce it here, and it's not happening.
   
  In any case, it doesn't explain your high Iq.
   
  When you reinstall it, it wouldn't hurt to be sure you've got a bit of an air gap below it. Or, I suppose you could Dremel off those outer "feet" surrounding each PCB lug.
   
   


> I'm a little bit afraid that I ruined it during the process as it only reads 42.8k and 42.5k on the lowest setting.


 
   
  That's lower than what I get here (more like 47k) but the absolute value of the pot doesn't matter much.
   
  What matters is that it give the proper voltage divisions, and that these be well-matched. So, put a lowish voltage across both gangs of the pot (the outside lugs) and measure the voltage at the center pin relative to one of the outer pins. It doesn't matter which way you measure, as long as it's consistent throughout the test sequence. The voltage source is ideally an adjustable bench supply so you can dial in something easy to work with like 1.0V or 10.0V, but any small battery will suffice. It could also be a test tone generator.
   
  For each measurement, compute the decibel difference: dB = 20*log(V1/V2). If it's consistently under 3dB difference except down near the bottom, the pot's fine.
   
   


> I also discovered that I used 35 v caps for C2 and 50 V caps for C1. Is there any disadvantages to this?


 
   
  Nope.
   
  For audio path caps like C1, you'd ideally want a very low voltage, since they'll never see more than about 5V peak-to-peak, but you can't find film caps that low in voltage tolerance. Even 50's are a bit hard to find. 63V, 100V, and 200V are more common for the low end of a cap line.
   
   


> Here are links to a few pictures of it:


 
   
  I don't have any comments of consequence, but here they are anyway. 
   

 Nice soldering job, clear pics. Thanks for not making it hard on us.
 What are the turret pins you're using for the I/O connectors? Are you using a mating connector, or soldering to them?
 Why did you populate RCCS? IC1 isn't populated, so you must not be using the trickle charger. Also, you've used a 1/4W resistor here, so it's probably too small to be used with a trickle charger anyway.
 Next time you use those Vishay-Dales, you might consider bending the leads so the values are face-up. You don't have to worry about this with stripe-coded resistors, but with these... I also like to make sure resistors oriented the same way have their labels all facing the same way, too.


----------



## tangent

Quote: 





tent said:


> I've attached some pics.. but let me know if I should upload them in some separate image hosting, zoom in some specific place or take it out from the cables.


 
   
  The current pics zoom in far enough. I was a little weirded out when I saw them...there are no IKEA PIMETAs! 
   
  The haphazardness of your build worries me, but I don't see anything specific that could cause your problems. It just makes me wonder how _solid_ it all is. (Bent over caps, LEDs flying around on stilts, melted caps, flux residue...)
   
  Check underneath that white wire that obscures the area between IC2 and C3-. There could be a solder short there, but I can't tell with the wire in the way. It could explain everything.
   
  I assume those green SMT caps across R4 for some kind of bass boost? Are they at least PPS film? If they're ceramics, they're not going to be doing your sound quality any favors.


----------



## akselo

> You're certain you didn't swap the channels? I've done that before. If you did, too, that would help me believe this is the explanation.


 
  I checked and it's connected correctly but it might acctually have been the left channel. I decided to check again earlier this day, and now both channels are dead
   
   
   


> So is the left channel buffer hotter than the right?


 
  I tried the spit test, but didn't see any big difference between the two. All three buffers gets very hot and burns my finger if I keep it on there for more than a few seconds.  
   
   
   


> What are the turret pins you're using for the I/O connectors? Are you using a mating connector, or soldering to them?


 
  Here are links to the pins and connectors I used:
  https://www.elfaelektronikk.no/elfa3~no_en/elfa/init.do?item=48-924-85&toc=0&q=48-924-85
  https://www.elfaelektronikk.no/elfa3~no_en/elfa/init.do?item=48-924-93&toc=0&q=48-924-93
   
  I think i will swap these for molex connectors as I get metal particles on the board everytime i connect/disconnect them from the board. Is it possible to make the molex plugs without a crimping tool?
   
   
   


> Why did you populate RCCS? IC1 isn't populated, so you must not be using the trickle charger. Also, you've used a 1/4W resistor here, so it's probably too small to be used with a trickle charger anyway.


 
  This was one of the first things I noticed as I started the troubleshooting I built this three years ago just as I started my power engineering education so I wasn't very good at reading schematics at the time When the amp failed I put it away and forgot about it until now. Too bad I suck at electronics. We have just had a look at power electronics like frequency converters, rectifiers and inverters.
   
  Should I try to swap the buffers and R11s for new ones or do you have any other suggestions?


----------



## tangent

Quote: 





akselo said:


> Is it possible to make the molex plugs without a crimping tool?


 
   
  Sure.
   
  The advantage of the crimping tool is how it curls the ends of the contacts around so they kind of weave into the stranded wire you're using. If you use needle-nose pliers instead, you still get a decent connection, just it's a flat connection, so the surface area in common between the contact and the wire strands is lower. This means it won't be as strong and might be measurably higher in resistance. You can fix that by flowing a little solder in there, if you're concerned about it.
   
  On the other hand, the tool I use — Molex part # 63811-1000 — is cheap enough that it's cost me about $0.01 per crimp now, and there's no reason to believe it won't work for thousands more crimps.
   
   


> Should I try to swap the buffers and R11s for new ones or do you have any other suggestions?


 
   
  You could try removing the buffers and then shorting them from pin 3 to 6 with a bit of resistor lead clipping. That turns the amp into something halfway in between a CMoy and a MINT. If it starts working beautifully, you know at least one of the buffers isn't a buffer any more. If the problem remains, you can put them back one at a time, measuring the amp's Iq each time to see if just one of them shoots the amp's current draw up unduly.


----------



## MisterX

I like GC/Waldom/Molex # W-HT-1921-P for KK pins but to each their own.
   
  Trying to find the pin 1 indicators for the buffers on the .png image of the PCB is easier said then done and they're covered once the buffers are soldered in place....
   
http://tangentsoft.net/audio/pimeta2/bitmaps/brd-2.01.png
   
  Maybe actual pictures of the top and bottom of the PCB would help?


----------



## tent

Quote: 





tangent said:


> The current pics zoom in far enough. I was a little weirded out when I saw them...there are no IKEA PIMETAs!
> 
> The haphazardness of your build worries me, but I don't see anything specific that could cause your problems. It just makes me wonder how _solid_ it all is. (Bent over caps, LEDs flying around on stilts, melted caps, flux residue...)
> 
> ...


 
   
  I checked carefully and I really do not find any short or similar.. no contact evident between IC2 and C3.. what could I've done wrong?
  (The green caps are very good caps for the C6 positions, Im using 12pf and I suppose it is correct to put them across R6 positions.. the bass boost instead also has good film caps, but are big yellow ones across R4.. my first test hearing tests are impressive tough!)
   
  tent:wq


----------



## saraengelstad

I love molex connectors. I haven't shelled out for Tangent's tool yet, I use an inexpensive crimp tool made for beading and jewelry making. (A lot of beading tools cross over nicely for electronics, especially the wire turning stuff like the round nose pliers.)  It's about $6-$8 and is available at most beading stores, Jo-Ann, Michaels, I think even Wal-Mart.
   
  It's called a Beadalon Bead Crimping tool:
http://www.amazon.com/gp/product/B00114OY06/
  
  It requires practice and some finesse, but I'm sure that's true of the $45 Molex WM9999-ND crimper.
   
  It might not work for you, it does take a few tries, and I do plan to get the Molex crimper soonish. But the beadalon thing has done the job for me for quite a while. I do put a tiny drop of solder in there just to make _sure_, but that's just a weird thing I do and would do no matter what.
   
  Good luck and if anyone picks one up, I'm very curious to know how well it works for others.
   
  Cheers!
  -s


----------



## tangent

Quote: 





misterx said:


> I like GC/Waldom/Molex # W-HT-1921-P for KK pins but to each their own.


 
   
  Yes, that looks like a good choice.
   
  I suppose I skipped over it because I already have more wire strippers than I know what to do with, and as a rule, I tend to prefer the T-stripper sort over that kind, so having everything in one tool doesn't really appeal.
   
  Still, it's hard to argue with $20.
   
  The official Molex tool has more sizing choices, but the two your tool provides probably suffice for most jobs. Worst case, you get a half-crimp and then have to crush it a little with needle-noses.
   


> Maybe actual pictures of the top and bottom of the PCB would help?


 
   
  Heh. I've just been walking over to Tangentsoft Intergalactic Headquarters (a cabinet in my front room) and grabbing a PCB to look at. 
   
  I'll keep it in mind. It takes a bit of time to set up a proper shoot.
   


tent said:


> The green caps are very good caps for the C6 positions, Im using 12pf


 

   
  Never mind, I see what you did now. I was referring to these green "capacitors":
   

   
   
  I see now that they must be your actual R4s, not ceramics paralleled across the thru-holes I assumed were on the other side. I didn't cross-reference both top and bottom pictures against each other before commenting.
   


saraengelstad said:


> It requires practice and some finesse, but I'm sure that's true of the $45 Molex WM9999-ND crimper.


 

   
  On the contrary, the proper crimp tool is very quick to use. You just place the terminal in the slot, line up the stripped wire, squeeze, done. The hardest part is making sure not to tip your hand, thereby dropping the terminal out of the crimper's jaws, and that's no harder than learning how not to tip a hand of cards.
   
  By the way, Mouser only wants $33 for that tool.


----------



## saraengelstad

> On the contrary, the proper crimp tool is very quick to use. You just place the terminal in the slot, line up the stripped wire, squeeze, done. The hardest part is making sure not to tip your hand, thereby dropping the terminal out of the crimper's jaws, and that's no harder than learning how not to tip a hand of cards.
> 
> By the way, Mouser only wants $33 for that tool.


 
   
  
 OK, you might have sold me. Do they work well, anyone have any idea, on FCI terminals?
 I really like the dobox connectors, I think they look a lot sharper.


----------



## tent

No problem.. I also did not understand you were referring to those as per "green caps".. 
  anyway suggestions for next steps? should I dismantle and start over from the beginning? I would maybe try to:
  - susbtitute the split rail ic2
  - swap the PSU caps.. they were some samsung caps I found in some compoents bin.. could be they (or one of them) is somehow "old"?
  - any other idea...
   
  tent:wq


----------



## tangent

Quote: 





tent said:


> - any other idea...


 
   
  I'm out. Need fresh data.


----------



## tent

no success so far.. I keep seeing this "unbalanced" voltages about everywhere on the board.. across C4+ the 2.55V and across C4- 5.65V, etc..  is there some specific measurement I could do to try to isolate the component or area where the issue could be? (for example if some cap or some ic, etc) Did someone else also have ever had such strange "unbalance" ever?
   
  tent:wq


----------



## tangent

At this point, if it were me doing the work, I think I'd remove the buffers and the op-amps, then re-do the power supply tests.
   
  If the power supply is fine with the amplifier ICs removed, clearly one is broken, or the problem is due to the feedback loop.
   
  If the power supply remains imbalanced, I'd replace the TLE2426, then re-test, expecting it to be fixed now,


----------



## tent

Hello,
   I was out of town but finally back.. actually without good news: without ICs the issue was still there, so I ordered and replaced the TLE2426.. bit without success, everything still unbalanced..  what could it be?? 
   
   
  tent:wq


----------



## MisterX

Measuring the resistance between the V+, IG and V-, IG pads may help point you in the right direction.....


----------



## tangent

Quote: 





misterx said:


> Measuring the resistance between the V+, IG and V-, IG pads may help point you in the right direction.....


 
   
  Yes, with the power switch turned off. It's looking like some kind of partial short circuit.


----------



## tent

uhm... interesting.. I read 684ohm between both chip's V- and IG and somehow infinite resistance between V+ and IG (the ohmmeter counts up till out of scale..)
  I can try to make some better high res shots of the board if needed or the short could be in some cap or else (for instance I decided to use some tantalum cap C4+ and C4- but not sure of the origin of those tants.. maybe too old.. )?
   
  tent:wq


----------



## tangent

I was just looking at your pictures again, tent, and I think I see the problem: you've shorted C4, haven't you? If so, time to re-read the docs.
   
  Not only should that jumper _not_ be there, the cap isn't optional when you install C3 and C5, as you have.


----------



## tent

actually I just wrote I've used two black tantalum caps in C+ and C- (22uF, 16V, with black drop ceramic coating) but I'm starting to have some suspect those are some old tants that might somehow have issues? could I test that? or should I simply try to substitute them? But definitely I have not shorted the C4 position, but the picture isn't clear enough indeed.. 
   
  tent:wq


----------



## MisterX

Is C4- installed the correct way around?
  A backwards tantalum capacitor seems like a fitting explanation for the 684 ohm reading between V- and IG...


----------



## tent

uhm.. also this seems to be a good point!
  But first of all let's say I interpreted the writings on the PCB like that: C4- writing means the - leg of the cap should go in the hole nearest to the - sign of the C4- writing, correct? I interpreted the opposite for the other tant: the - leg of the cap needs to go on the opposite/farest hole of the + of the C4+ writing, is this also correct?
   
  tent:wq


----------



## MisterX

Nope, the component labels are not polarity indicators for the C4+ and C4- capacitors.
  And....if C4- is installed as as described it is backwards.


----------



## tent

woa! that was a hint indeed! thanks! I will do the desoldering and resoldering of the cap in correct orientation and let you know asap!
   
  tent:wq


----------



## tangent

No, tent, both C4 caps are oriented the same direction on the PCB: the negative thru-holes are toward the back end of the board, where the power input pads are, and the positive thru-holes are toward the volume control pads.

The C4+ and C4- labels are just the names of the part. You aren't supposed to read anything more into their names than that, such as part orientation. I didn't see a potential for confusion since the top-side footprints are intended for box caps, which are film, hence non-polarized.

If you look on the bottom side of the board, where the SMT footprints are, you find + signs since those footprints are intended for SMT tantalums.

Now, there's still one mystery remaining, which is that the IG to V+ measurement looks correct, yet your misinterpretation of the labeling suggests that the C4+ cap is the one you installed backwards. I would guess that the solution to the riddle is that you're thinking the stripe on a tantalum marks the negative lead, as on an electrolytic cap. On a tantalum, it's the _positive_ lead that's marked with a stripe. On some tants, at least, you should also see a very small + sign near that lead.


----------



## tent

IT WORKED!
  The C4- and C4+ writings I was referencing at were the ones on the top side not on the bottom side (that where as well reversed.. ) but at the end I also used the opportunity to get rid ot those tants and am using now instead some good and huge richmond 4.7uF MKTs unpolarized. But definitely you were right: I should have noticed that in the bottom side there were those "real" + signs indicating polarity.. =)
  But now the voltages are finally perfect and balanced: Great!
  On a side note the bass boost: this is really too much for my headphones.. bass sounds really overdriven at the point it is unbearable.. if I would have, say, half of the db kick, should I change the 0.1 cap or the value of R4?
  A part from that the sound of the device is really astonishing (with bb off).. no big difference to be noticed instead in switching class A on or off, to be honest.. maybe in some rapid passages where bass and trebles alternate themselves.. not sure it is an illusion anyway..
  I also started to change some opamp in the sockets.. not sure if I prefer the bb 2132 or the lm 4562.. will still try others too and let you know..
  Thanks a lot for the great and successfull hunt for the bug.. as always human error/misinterpretation showed up again.. 
   
  tent:wq


----------



## tangent

Quote: 





tent said:


> if I would have, say, half of the db kick, should I change the 0.1 cap or the value of R4?


 
   
  I assume you have a PPA style bass boost?
   
  If so, then you'd want to change the value of its "R7". (Not the "real" R7 on the PIMETA v2 board.) This affects the amount of boost. (As opposed to its associated cap, which the PPA calls C7, which affects the filter's corner frequency.)
   
  0.5 dB is just 1.06x your gain without bass boost. So with the stock 4.7K R4, the bass boost "R7" should be 330 ohms or so, ideally. The PPA bass boost calculator says you get more boost than that. I don't know if it's the equations that are misbehaving because the dB boost is so low or if the circuit just can't achieve such low boost values.
   
  Also note that 0.1 uF is probably way, way too low for the cap. Again, use the calculator. I think R4 = 4.7k, R7 = 470, C7 = 2.2 uF should give a nice mild bass bump.


----------



## tent

actually I was using the "pimeta" style called "unity" boost.. just putting tha cap across r4 and a switch as well to set it off..
  R4 is indeed 4.7k and the cap is 0.1uF from some suggested sentence.. maybe that's the reason about this "huge" bass boost?
   
  tent:wq

 PS: by the way the LM4562 is a lot better sounding than BB2132 indeed.. but still testing some other opamps that seem to be great like LME49860 which seems to me even better.. but this seems always kind of difficult to judge or stay objective imho..


----------



## tangent

In that case, pretty much everything I wrote goes out the window.
   
  Unfortunately, what you ask isn't readily within the grasp of the unity boost circuit. Unity boost means the un-boosted gain is 1x, and you're asking for a bass boost of only 0.5 dB. This means you have to calculate R4 to give 1.06x gain, which means it has to be 60 ohms if R3 is 1K! Not only is this an ugly duckling in its own right, it then means the parallel bass boost cap has to be ~8uF in order to keep the corner frequency where you have it now, ~330 Hz. If you want to lower the fc, as would make sense to reduce the BB's effect, the cap has to be even bigger. You'll find that if you go shopping for such big film caps, they're not terribly practical, and if they're small enough to fit your box, they're probably not very good for audio.
   
  I'd suggest giving up on your 0.5 dB boost wish, set R3=R4 for 2x bass boost (6 dB), and just adjust the fc to taste by changing the cap value.
   
  To keep your current fc=330 Hz with R4=1K, you need a cap value of 0.47uF. Doubling that cap value to 1 uF pushes the fc down by half, to around 160 Hz, more of a true bass region.
   
  Such caps are still a bit on the big side, so you might want to set R3=R4=10K instead. That shouldn't hurt the noise floor _too_ badly, and it lets you drop the cap values by 10x.
   
  There's a middle ground between these approaches, of course. Let's say you end up with R3=10K and fc=150 Hz and decide the boost start point is fine, but the boost level still a bit too high. So, to cut that in half to ~3 dB boost, you'd use R4 = 3.9K and a ~0.22 uF cap.
   
  Bottom line, play with the circuit, and play with the equations. Wolfram Alpha makes the math easy.


----------



## alphaman

Given that one only powers this device with pure DC (i.e batts. only), anyone know the usable lifetime of the electrolytic caps used? The rated lifespan of electros is not that spectacular (a few K hrs). You may have noted some of the better computer motherboards touting use of "Japanese solid caps". These are also electros but not as "leaky"...so longer lasting? 
   
  Refs:
  http://electronics.stackexchange.com/questions/12636/how-do-i-compute-the-lifetime-of-an-electrolytic-capacitor
  http://www.hardwaresecrets.com/article/How-to-Identify-Japanese-Electrolytic-Capacitors/595/2


----------



## tangent

I'm not really sure what you're asking. You appear to have done your homework, and are wanting...what? An acknowledgement that you have, or a refutation that you've done it correctly, or...?
   
  It is true that cap life doubles for each 10℃ step away from the temperature rating for your device. Therefore, a 105℃ cap will last 4× longer than an 85℃ cap, all else being equal. Further, reducing idle current and increasing ventilation may be worthwhile. But a bigger improvement in lifetime than either may simply be to turn the amp off when you're not using it; the PIMETA v2 design supports this by not having a warmup period or a nasty turn-on thump.
   
  It should also be pointed out that in a circuit like the PIMETA v2, rail caps don't hit some magic point and then die, poof. What's going to happen is that at some point, the caps will drop beneath their rated performance limits, but will continue to work. Effective capacitance will drop, but DIYers being DIYers, you've probably put more capacitance in place than you really had to have, so you've bought yourself that much more effective lifetime.
   
  It is also true that not all electrolytic caps are created equal. I don't think it's true that only Japanese caps are worth using, any more than it is true that only Japanese TVs are worth buying. More important is doing that homework, finding out if you can trust the specs in the datasheet, then finding a datasheet that gives you the assurances you want.


----------



## MisterX

I originally had a 2 cell, 800mAh LiFePO4 pack earmarked for this build but decided against waiting the 3 months for a MCP73X23EV-LFP module so went ahead with a 9 volt NiMH battery instead. 
  Worked out pretty nice if I get to say so myself. 
	

	
	
		
		

		
			




   
  Link without the accoutrements:
   
http://i23.photobucket.com/albums/b393/X86inside/Pimeta%202/Again/P1000738_zps80f62f67.jpg


----------



## tangent

Solid build.
   
  I'm not sure I've seen anyone use Phoenix Contact connectors in a PIMETA v2 before. Nice to know they fit.


----------



## mendiola

Can I remove the Class A Biasing from the Pimeta V2 schematic?

I would like to remove Q2, Q3R, Q3L and the RBias resistor?

Is there a problem If a Remove the Class A Biasing from Pimeta V2?

Scehamtic:

http://tangentsoft.net/audio/pimeta2/misc/sch-2.01.pdf

Regards.
Alfredo Mendiola Loyola
Lima, Peru


----------



## tangent

> Can I remove the Class A Biasing from the Pimeta V2 schematic?


 
  
 Yes.


----------



## mendiola

I have designed a Pimeta V1 mod for desktop use.

I don't use a virtual ground.

Does Pimeta work with real ground instead of Virtual Ground?

How can I attach a picture on this forum?

I'm using a 7812 and 7912 regulator to get +/-12v with real ground.

Here is the schematic link:

https://www.dropbox.com/s/o6s2gh3v2qu3yzc/PimetaDesktop.png

Regards.
Alfredo Mendiola Loyola
Lima, Peru


----------



## tangent

mendiola said:


> Does Pimeta work with real ground instead of Virtual Ground?


 
  
 Yes.
  


> How can I attach a picture on this forum?


 
  
 In the "Reply" composition area, the toolbar above the message box has a button for this.
  


> Here is the schematic link:


 
  
 Thanks for posting it.  It looks like it should work.
  
 You might want to give it a different name, though. Virtual ground is pretty essential to the "PIMETA" nature. Also, I've always thought of the PCB as an essential part of each project's identity. You will necessarily have to come up with a different design for this one, so you're getting into something that needs its own name.
  
 You might want to create a new symbol for the BUF634, based on the traditional buffer symbol. My EAGLE videos will show you how. You can use the LMH6321 symbol in my PIMETA v2 schematic as a guide.


----------



## mendiola

I have uploaded the new schematic and the board of the CMD v1.0
  
 CMD: Cmoy Multiloop Desktop.
  
https://www.dropbox.com/s/tsuml8vn4e9aqdy/CMDV1.png
  
  
https://www.dropbox.com/s/z9cjbjtp9n59gw7/CMDV1.rar
  
 Regards.
 Alfredo Mendiola Loyola
 Lima, Peru


----------



## alel

Hi is their anywhere I can get the pcb alone?


----------



## 3l3tric

Question:
 I'm about to start building a PIMETA (I've had the PCB for a while, just haven't gotten around to building the thing yet), and I had one question for people who've already built their's:
 Has anyone used the OPA627 OpAmp for a battery powered PIMETA? I use a tube amp with my desktop setup, and I'm afraid I won't like the sound of the Analog Devices opamp due to its brighter nature (At least, according to tangent).
 Right now, I'm considering building the Pimeta using 2 9V batteries in series for an 18V supply for the OPA627, but before I pulled the trigger, I wanted to know if anyone else has used a similar setup and how successful it was.
 Thanks!


----------



## tangent

3l3tric said:


> Has anyone used the OPA627 OpAmp for a battery powered PIMETA?


 
  
 The PIMETA is primarily designed as a battery-powered headphone amplifier, so when the docs tell you that the OPA627 is known to work, well, what more did you want? 
  


> I use a tube amp with my desktop setup, and I'm afraid I won't like the sound of the Analog Devices opamp due to its brighter nature (At least, according to tangent).


 
  
 You need to listen to at least one of the chips with a lengthy review, then use that to calibrate what I wrote about that chip with what you hear. Only then can you hope to make good buying decisions based solely on my reviews.
  
 It's really important here, because you're talking about ~$26 x 3 = $78 worth of chips. If you don't have any of the reference chips' sounds in your head, I'd think you'd want to start with something a little more reasonable.
  


> I'm considering building the Pimeta using 2 9V batteries in series for an 18V supply for the OPA627


 
  
 The docs already tell you that alkalines aren't powerful enough for this, and it isn't good to stack so many NiMH cells in series. (The more cells in series, the greater the risk of cell reversal if you let the battery voltage drop too far.)
  
 If you're just itching to use the 2-battery input feature on the board, have you considered using two 4xAAA cell holders? That's not a lot bigger than a single "9V" NiMH, but will run a lot longer, and only strings 8 cells in series, which is what you get in the 9.6V flavor of NiMH "9V" battery.
  
 If you're basing the decision to start with 18V on my clipping tests, you're misapplying the results. Those clipping tests were done with the op-amp directly driving headphones, which is not the case in the PIMETA, or in fact in any of the headphone amplifiers on my site other than the CMoy. In all the other cases, it is the buffers that carry the load, and there is no virtual ground shift to contend with. Hence, the op-amps will work to lower voltages in a PIMETA than the values I give for a CMoy Pocket Amplifer.


----------



## 3l3tric

Is the PIMETA V2 site not working for anyone else?
 Everything on Tangent's site seems to be giving a 403: Forbidden error.
 I found the site on the Internet Archive, but I'm curious as to if the site is working for anyone else.


----------



## tangent

Sorry about that...file permission bug. It's fixed now.


----------



## vixr

tangent said:


> Sorry about that...file permission bug. It's fixed now.


 
 yay!!!    thought I had been banned!


----------



## omonoid

tangent, can you help me troubleshoot? 
  
*Notes:*

Omitting buffers (for now)
    - omitted R6's
    - jumped R5's
    - jumped buffer input to R7 (see pic to confirm i did this right)
    - omitted C6g
    - installed C6 R/L (not sure if needed??)
Omitted input caps
Omitted R11G/R/L
Jumpered LED2 
LED1 hole damaged so soldered direct to RLED
Installed diodes (D1, D2)
op amp: OPA2132P
Configured for bias always-on
Used LM317 so i can trickle charge
Q2/3L/3R used 2N5088
Q1 used 2N5087
R1G is currently 4.1k and is two resistors in parallel since i forgot to order the right size
  
*Testing:*
 Used a 9V wall wart connected to the WALL molex 2 pin connector (reads 9.1V before connected)
 When connected but with the ALPs vol toggle OFF the voltage at the WALL molex pins reads 8.3V (why is there a V drop when it is off???)
 When the ALPs is switched ON, the voltage at the WALL molex reads 8.06V and the LED1 turns ON
 In attempting to "check the voltages at all of the DIP-8 chips’ supply pins relative to input ground (IG)...should be about half the PS voltage..." I find that all pads for both opamps (not yet installed) read 0V except pin 5 for one and pin 6 for the other, which read 8.57V
  
 This is where i have stopped because it seems something isn't right. I went through and checked all my solder connections for shorts or discontinuities, but didnt see anything
  
 I'm hoping since you have a much better understanding of the circuit, you could help me resolve this.
  
 I uploaded some pictures as well (see link to google drive since i dont have permission to post them here). Hopefully the pics plus the notes above can give you an idea of where i am and what may be wrong.
  
  
*Pictures:*
 https://drive.google.com/folderview?id=0B_Z_i1f1IePDeVlxTG1VM3F6N28&usp=sharing
  
  
 Thanks,
  
 Jake


----------



## tangent

omonoid said:


> jumped buffer input to R7 (see pic to confirm i did this right)


 
  
 I think it would have been simpler to just jump from pin 3 to 6 on each BUF SO-8 footprint, but buzzing it out on a bare board here says the pins you chose instead do also connect to the same locations.
  
 Your use of bare wires for jumpers is a worry. You have to be very careful that they're not touching anything. Where I have to jump over exposed metal, I prefer to use insulated wire for jumpers, stripping it at the tips only.
  
 A much bigger problem is how messy that soldering job is. Carbonized flux can be conductive, flux can trap conductive debris, and flux can conceal solder bridges. Even if it ends up not helping your immediate symptom, a good cleaning will at least add a touch of pride to the build.
  


> LED1 hole damaged so soldered direct to RLED


 
  
 Have you watched my soldering videos?
  


> Used a 9V wall wart


 
  
 Unless your battery supply is going to be something marginal like 4 x AAA NiMH, that's not enough voltage to charge the battery. The charge controller section of the docs should have made this clear.
  
 That doesn't explain your present problems, but it's a risk of problems down the road. There is a whole section of the docs on choosing a power supply for the amp, which your design choices seem to ignore.
  


> connected to the WALL molex 2 pin connector


 
  
 That's not what your pictures show. The orange/white pair is connected to BATT.
  
 Why are you using Molex connectors but soldering directly to them, anyway? You should be doing it one way or the other: hard-wire it or use connectors. If the orange/white pair is just for testing, I'd still make up a female Molex KK adapter. If you continue doing electronics, you may reuse that adapter later.
  


> why is there a V drop when it is off???


 
  
D1 and IC1.
  


> When the ALPs is switched ON, the voltage at the WALL molex reads 8.06V


 
  
 That means you're either using an unregulated power supply or it's too weak for the job. I highly doubt the latter, unless you've shorted something. The existing troubleshooting guide tells you how to test the board's current draw, which will tell you if your board is drawing too much power for your wall wart.
  


> In attempting to "check the voltages at all of the DIP-8 chips’ supply pins relative to input ground (IG)...should be about half the PS voltage..." I find that all pads for both opamps (not yet installed) read 0V except pin 5 for one and pin 6 for the other, which read 8.57V


 
  
 I'm guessing this is due to your R1G hack. It appears you've misread the board labeling for the scratchpad area, thinking the two long strips are IG. The docs make this clearer: there are only two IG pads in the scratchpad area. Using them for R1G is a bad idea. Just piggyback the two resistors on the existing R1G pads: solder one in place, then solder the other on top.


----------



## omonoid

Thanks for taking the time to give feedback.
  


> I think it would have been simpler to just jump from pin 3 to 6 on each BUF SO-8 footprint,


 
  Ill do that since i want to redo my jumps with insulated wire
  
 Quote:


> I prefer to use insulated wire for jumpers, stripping it at the tips only


 
  will do
  


> Have you watched my soldering videos?


 
 No, 'll check them out. I kinda just whipped this up with tools and parts I had, so I definatley could have done better with more ideal tools and planning
  
 Quote:


> a good cleaning will at least add a touch of pride to the build


 
  good point. isopropyl alcohol should clean it up right?
  
 Quote:


> Why are you using Molex connectors but soldering directly to them, anyway?


 
  
 The orange/white soldering on the BATT was just a quick and dirty way to test with a battery, but it turns out I dont have any fully charged 9V batteries, so I used a molex adapter with the two pin WALL to connect to my wall wart. I should get a 4 pin molex to use with the BATT connector too, but i dont currently have one.
  


> I'm guessing this is due to your R1G hack. It appears you've misread the board labeling for the scratchpad area


 
 Hmmm ill check it out
  


> The existing troubleshooting guide tells you how to test the board's current draw


 
 Wasn't aware of this, i'll go through the steps after I fix everything else addressed above
  
 I haven't put much thought into the trickle charging. I will definitely reread the appropriate sections before i ask more on that topic. My priority is to get it working first. 
  
 About my op amp selection (OPA2132P) I had these already from a previous project that i didnt end up pursuing. After reading your op amp selection guide i determined ( a few months ago) that these would work (can't remember my exact logic). Do you agree that these are an ok selection for my build? If I decide to add the buffers later will they still be ok?
  
 I get that the buffers help take some of the work from the op amps, but i am a bit shaky on what specs of the op amp make it ideal for not needing buffers. I would assume it should be an op amp capable of not saturating at the requested headphone vol, and also be somewhat low power consumption. I'll re-brief myself on op amps in the meantime. 
  
 I bought components and planned this out like 6 months ago (and took minimal notes) so i am still trying to remember why i made certain part selections. 

  

 Ill report back with what I get after I address everything above (probably not til next weekend)
  
 Thanks again for helping me out. I'm learning alot from this project
  
 --Jake


----------



## tangent

omonoid said:


> isopropyl alcohol should clean it up right?


 
  
Tangent Tutorial #05.
  


> About my op amp selection (OPA2132P) I had these already from a previous project


 
  
 Why the plural? ("These")
  
 You should be using _one_ dual-channel op-amp (e.g. OPA2132) and _one _single-channel op-amp (e.g. OPA132). If you were hoping to use two OPA2132s, it's not going to work.
  


> Do you agree that these are an ok selection for my build? If I decide to add the buffers later will they still be ok?


 
  
 They're barely usable without the buffers, at 9V. See my clipping test results.
  
_With_ the buffers, you might be able to drain a 9V battery dry before the op-amps start clipping.
  
 Also keep in mind that a NiMH "9V" will only be at or above 9.0 V briefly, if ever.
  


> i am a bit shaky on what specs of the op amp make it ideal for not needing buffers.


 
  
 You're not going to find such a spec in a datasheet. The best you can hope for is a front-page marketing claim that it's made for driving headphones directly, and you should take that with the same size grain of salt you use prophylactically for dealing with all marketing claims.
  
 This is why I did the clipping tests in my op-amp review article. It provides information you could not get before, short of doing the test yourself.


----------



## omonoid

> You should be using _one_ dual-channel op-amp (e.g. OPA2132) and _one _single-channel op-amp (e.g. OPA132)


 
  
 You are right. They I mistook them as the same when quickly reading off the tiny label on the op amp. Like i said i gathered these components a while ago, so i am re-famliarizing my self the the design.
  
 It sounds like leaving the buffers out is not as good of a long term idea as i originally gathered. I was hoping to optimize it for portable use, but after reviewing the "power supply matters" I'm thinking about ditching batteries for now and just trying to get it working on off a 9 or 12V supply first.
  
  
 Could powering off the usb bus be done effectively if the voltage were boosted?  
  
 The more I think about how i will use this amp, the more i realize having it portable isnt really a priority. Having it powered of my pc could be useful because that is my main music player.
  
 Do you think i should try to get it working as is, then add buffers, or purchase buffers then try to finish assembling the amp? I'd rather stick with the op amps i already have, and it sounds like buffers are optimal for my config.
  
 Thanks,
 Jake


----------



## tangent

omonoid said:


> Could powering off the usb bus be done effectively if the voltage were boosted?


 
  
 http://www.head-fi.org/t/386517/usb-powered-pimeta
  


> Do you think i should try to get it working as is, then add buffers, or purchase buffers then try to finish assembling the amp?


 
  
 A PIMETA without buffers is a glorified CMoy pocket amp. Is that what you were after?


----------



## omonoid

Thanks for all the help. Now that i am on winter break (im an undergrad ee student) I have had time to actually learn about the circuit and have decided to keep the OPA2132/132 and add buffers and modify some values to best suite my 36 ohm impedance headphones. I also have access to campus bench testing gear and multisim, so i might as well make use of it and optimize components. I plan on eventually adding trickle charge and other tweaks, but want basic functionality first. I ended up desoldering the buffer jumpers and some other things i want to change. I am debating whether I should start with a fresh pcb, or use the possibly damaged one that I have. I am still learning about the theory of the amplifier, and for fun have started drafting up a spice (multisim) model to try to visualize how changing certain values affects the signal. I was wondering if you had an already made model that I could compare to. In the meantime i am reading all the content on your site, which is proving to be very useful, so thanks for organizing it.


----------



## tangent

omonoid said:


> I am debating whether I should start with a fresh pcb, or use the possibly damaged one that I have.


 
  
 Are you considering doing your own layout, or were you hoping to get another board from me?
  
 The first option is of course open to you, and may make an interesting project, particularly if you do something a bit different with the circuit design or layout. A simple clone is boring. The main argument against it is the cost, particularly if you make yours a 4-layer board, as the official boards were.
  
 As for the second option, original unpopulated PIMETA v2 boards are no longer available for sale, and haven't been for nearly a year.
  


> I was wondering if you had an already made model that I could compare to.


 
  
 No.
  
 I only use circuit modeling programs as a glorified calculator. I can also see a use for such programs in IC design, where it is simply too expensive to just go try an idea.
  
 Neither situation really applies to the PIMETA v2. Calculations are either basic applications of Ohm's Law or elementary op-amp theory, and it is neither terribly expensive or time consuming to just try things with it.
  
 If you think modeling is fast, it's probably because you aren't doing it right. I'll bet you haven't modeled all the parasitics, or swept the model over input offset voltage, or applied ripple to the power rails, etc.


----------



## 3l3tric

So, I ordered my parts, but I messed up just a tiny bit...
 I went for the 2x 4xAAA holder battery option and the Serpac H65 enclosure (no access, b/c I wanted the translucent grey and didn't see the need for access once the amplifier was built). Unfortunately, without the board test-fitted, there's no way that the battery holders will fit and the enclosure close, and with the board in, the holders cover up the on-board battery and wall power connectors.
 I ordered this holder, for reference.
 What holder should I order so that the batteries fit well in the case? You claimed in an earlier reply that:
  


> If you're just itching to use the 2-battery input feature on the board, have you considered using two 4xAAA cell holders? That's not a lot bigger than a single "9V" NiMH, but will run a lot longer, and only strings 8 cells in series, which is what you get in the 9.6V flavor of NiMH "9V" battery.


 
 But I can't seem to find a way to arrange the batteries, holder or not, that allows me to fit all 8 AAA batteries into the case with the board.
  
 Finally, just as a sanity check: Is it OK to run the board off of wall power without batteries? I got a 12V source to charge the batteries with, and just wanted to make sure that I read the guide right. The estimated voltage of the combined batteries is 9.6V.


----------



## tangent

> I messed up just a tiny bit...


 
  
 I hope by that you mean "I didn't read the datasheet," rather than "I took a vague comment by some guy on the Internet as a physical dimension specification." 
  
 I just measured an actual 9V battery and a 4xAAA holder similar to the one you point to, and a single 4xAAA holder is about 35% larger than a single 9V battery. Two such holders would be 171% larger, but I was responding to your post where you talked about 2x9V, so that's still just 35%. 2x9V won't fit into a Serpac H65, either.
  
 Is 35% "a lot?" It depends on your application. I can think of several good cases that I'd call small, which would fit a PIMETA v2 board and 2x4xAAA.
  


> What holder should I order so that the batteries fit well in the case?


 
  
 If you must use the H65 case, I'd tell you to go with a single 9V NiMH.
  
 If you want 8xAAA, you need a larger case, period.
  
 Incidentally, I see only one other post from you in this thread, and it doesn't even mention the Serpac H65. I don't see how you got from my comment to the thought that 2x4xAAA should work in the Serpac H65. The PIMETA v2 doesn't _only_ work in that enclosure.
  


> Is it OK to run the board off of wall power without batteries?


 
  
 There's a whole section in the docs on this very topic.


----------



## 3l3tric

tangent said:


> I hope by that you mean "I didn't read the datasheet," rather than "I took a vague comment by some guy on the Internet as a physical dimension specification."
> 
> I just measured an actual 9V battery and a 4xAAA holder similar to the one you point to, and a single 4xAAA holder is about 35% larger than a single 9V battery. Two such holders would be 171% larger, but I was responding to your post where you talked about 2x9V, so that's still just 35%. 2x9V won't fit into a Serpac H65, either.
> 
> ...


 
 Alright, sorry for my misreading, haha. For some reason, I assumed that your comment applied for the H65, because that's the standard enclosure. I also thought you were talking about the 2x 4xAAA being the same size as a 9V instead of 2x9V just because I wasn't thinking.
  
 Thanks for your help! I'll keep the AAA for another project and buy a NiMH 9V locally with holder.


----------



## Hifihedgehog

Hat's off to Tangent for releasing the ExpressPCB files for the PPA V1 and Pimeta V1. The ExpressPCB files for these projects are now available, as well as those of the PPA V2 which has been the case for a decade or so.
  
 Visit the project pages below to download the ExpressPCB files.
  
 PPA V1: http://tangentsoft.net/audio/ppa/amp/
  
 PIMETA V1: http://tangentsoft.net/audio/pimeta/
  
 PPA V2: http://tangentsoft.net/audio/ppa/amp2/
  
 It is possible to have these files converted for use with your own PCB mill or a professional service other than ExpressPCB. To do so, follow this guide below to convert them to generic Gerber and NC drill files. In summary, this guide will describe the process of opening the PCB files in ExpressPCB, printing them to a PDF with a virtual PDF printer, and finally converting them to Gerber and NC drill files in Windows via Command Prompt using the Perl-based program pdf2gerb. Before beginning, you _must_ read the following terms and conditions.
  
*OBLIGATORY WARNING: *
  
*Before proceeding, please note that there is absolutely no warranty or guarantee that these steps will work correctly for everyone in all circumstances. None of these steps have been approved, tested or even encouraged**, formally or informally,** by the original creator of these PCB files, Tangent, and any semblance of such is purely coincidental and should be promptly disregarded. *
  
*Even after following these steps to the letter, you may still encounter errors or inaccuracies which are specific to your physical computer build, your operating system and program installations, and/or your PCB fabrication process leading to undesirable or even hazardous results. By choosing to follow these steps, you formally agree that (a) you realize that Tangent has neither endorsed nor condoned the use of any of these steps and that (a) the author of this guide, Hifihedgehog, is not liable for any and all injuries, damages and losses of any and all physical or monetary value you may experience during the course of this procedure. *
  
*If you knowingly and of a sound mind agree to these terms and conditions, read on.*
  
 To begin with, you will need to obtain and install the software which will be used in this guide. The software components which have been tested and have been found to work are below. Please install them using only the default settings during the installation process.
  
 1. BullZip PDF Printer Community Edition
 http://cdn.bullzip.com/download/pdf_free/Setup_BullzipPDFPrinter_10_10_0_2307_FREE.exe
  
 2. ExpressPCB
 http://www.expresspcb.com/ExpressPCBBin/ExpressPCBSetup.exe
  
 3. Strawberry Perl 
_Note: Only use this older build which is linked below. In testing, the latest builds have been found to be incompatible with pdf2gerb._
 http://strawberryperl.com/download/5.12.1.0/strawberry-perl-5.12.1.0.msi
  
 4. pdf2gerb
_Extract the contents of this archive to its own folder, taking note of its location for future reference. _
 http://github.com/swannman/pdf2gerb/zipball/master
  
 After installing each of these programs, first open a PCB file in ExpressPCB. To do this, run the program ExpressPCB and go to _File, Open_. Once in the file management window, navigate to where you have your _PCB_ file located. Select the file and press _Open_. Having opened the _PCB_ file successfully, you should see a populated PCB blueprint in the middle of the main program window.
  
 Now, go to _File, Print_. In the _Print layout_ pop-up window which should appear, you will select two options. Note that we will be repeating these steps in a moment with one slight modification. First, in the _Printer_ drop-down menu, select _Bullzip PDF Printer_. Second, under _Layers to print_, check_ Top copper layer_. Having selected these two options, press OK. In the screen which should soon appear, specify the filename and location of the PDF and save it. Save it in the same folder location as where your pdf2gerb.pl file was extracted. For the purposes of this guide, you will be naming it _top.pdf_.
  
 Now, to repeat the process with the one slight modification mentioned earlier. Perform the same steps just performed to print, only this time, under _Layers to print, _only check _Bottom copper layer_ and name the file _bottom.pdf_ and place it in the same folder as the other PDF.
  
 Finally, for the last round of steps. Open command prompt with administrator privileges (i.e. right click on the program Command Prompt and select _Run as Administrator_). Type the command _cd c:/the/path/to/your/folder_, replacing the generic file path _c:/the/path/to/your/folder _with the actual folder path to gerb2pdf.pl and your two pdf files and press Enter. Next, enter the command _perl pdf2gerb.pl top.pdf bottom.pdf _and press Enter.
  
 Once the process has completed, go to the folder where your PDF files and pdf2gerb.pl are located. If the conversion was successful, you should find five newly created files there--four Gerber _.grb_ files and one NC Drill _.txt_ file. If so, congratulations! Be sure to verify their accuracy and precision with a Gerber viewer such Gerbv (available for download here: http://downloads.sourceforge.net/project/gerbv/gerbv/gerbv-2.6.1/gerbvinst-2.6.1.exe ) before using them for fabrication.


----------



## 3l3tric

Finally finished my PV2!
 I opted to switch the default Serpac enclosure with something a bit more... sturdy, since all my components blatantly refused to fit in the serpac and full pocketable mobility wasn't of prime importance.
 Pics to follow, but here are the basic specs:
 -Default ADZ8620/8610 Opamp pair
 -2 Panasonic 1000uF Electrolytic rail caps
 -1mA Class-A Bias Current
 -Slightly oversized WIMA Film caps for C4 (lol)
 -2x 4xAAA 9.6V Battery Bank (over 2K mAh!)
 -Somewhat eye-catching case
 -Jumpered input caps, as the amp is only used with high-end sources (AMB y2, Fiio X3)
  
 Pics to follow fairly soon. This thing is crazy. It was even able to power my HiFiMan HE-4 at a good, loud volume at about the 12o'clock position with no bass distortion, which was a hugely pleasant surprise. The sound with the AD opamps is a little bit too forward for my taste, but I use a hybrid amp with 12BH7 tube as my primary amp, so my perspective is a bit skewed. Makes me wish that I had thought ahead and bought DIP adapters and sockets, but NBD.
  
 Thanks Tangent!


----------



## tangent

hifihedgehog said:


> *OBLIGATORY WARNING:*


 
  
Do not taunt Happy Fun Ball.
  


> Open command prompt with administrator privileges


 
  
 Seriously??
  
 What possible justification can there be for that?
  
 Sorry, _pdf2gerb, _but no. You will not be getting Admin privs on my box just to translate a file from one format to another.
  


> Be sure to verify their accuracy and precision with a Gerber viewer such Gerbv


 
  
 I've recently been trying to learn KiCad. For the most part, I'm missing Eagle pretty hard, but I think I may be switching from gerbv to KiCad's gerbview, if only because gerbv can be cranky to build on OS X. Building KiCad is a pain, too, but it's at least on a popularity upswing, so there is plenty of help online for pushing past problems.
  


3l3tric said:


> Finally finished my PV2!


 
  
 Yay!
  


> The sound with the AD opamps is a little bit too forward for my taste


 
  
 Plenty more fish in that sea.


----------



## Hifihedgehog

tangent said:


> Do not taunt Happy Fun Ball.


 
 ROFL. I think my ribs will be sore for the next week! XD
  
 Actually, the agreement is more along these lines:
  
 http://youtu.be/W9hkGqH2D8c?t=6m4s
  
  


tangent said:


> Seriously??
> 
> What possible justification can there be for that?
> 
> Sorry, _pdf2gerb, _but no. You will not be getting Admin privs on my box just to translate a file from one format to another.


 
 No, it's even worse than that. The cherry on top of it all is that to run any Perl program with Strawberry, you have to run it as an Administrator. That obligatory warning includes any unforeseen interdealings with the NSA you may have from any carefully hidden payloads.
  
  


tangent said:


> I've recently been trying to learn KiCad. For the most part, I'm missing Eagle pretty hard, but I think I may be switching from gerbv to KiCad's gerbview, if only because gerbv can be cranky to build on OS X. Building KiCad is a pain, too, but it's at least on a popularity upswing, so there is plenty of help online for pushing past problems.


 
 I should try my hand at KiCad on a more permanent basis. I remember trying it and liking it a lot on my older system before switching to my Surface Pro 2. Open source programs with a strong community are always the bee's knees, anyway.


----------



## 3l3tric

As promised, pics:
  
  

 I will attest, the battery connector is a little bit messy, but it was the best solution I have right now (as I don't have a molex connector for that part of the board.)
 The batteries are charging right now on the trickle charger. I ensured that all contact points match up. The upper 9V connector looks wrong just because the orientation got reversed when the connector "jumped over," so to speak. (Black became the V+, Red became common).
 The AAA banks are adhered using double sided tape, while the knob and jacks are all nutted on. The potentiometer is held in place by the board, which is held in by two screws that were melted into the plastic, as to not be visible from the bottom of the case.
 Everything seems to be working fine! I don't have my official charger yet, so I'm currently using a charger rigged up from a barrel adapter of the right size soldered (after checking orientation) to the outputs of an old 12V outputting monitor PSU.


----------



## Hifihedgehog

3l3tric said:


> As promised, pics:


 
 Which case exactly is this? It looks like a water resistant one I haven't seen before. I am actually using a V1 board for my next build because that is the only thing that is cost effective these days. That case there you are using would be about the right size for me if I ever wanted to go the buffer stacking route.


----------



## 3l3tric

It's a Pelican case, I'm not sure of the exact model number. I'd look it up right now, but I'm currently working on a writeup for this, as I'm entering the amp in a contest (not stating that I designed it, but a contest for assembling and writing about an electronics kit design that someone else created, if that makes sense).
 It's in the micro series, I believe. 101 maybe?
 And it is (was) waterproof. However, that rubber rim you see used to be a distinct rubber boot that lined the entire inner bottom half of the enclosure. Everything except what you see was removed to accommodate the board. I also had to drill 4 total holes for external hookups, and the 3.5mm jack holes had to be dremeled out from the inside so that the jacks could sink in and have their threads show through on the other side.
 Where can you get V1 boards? I haven't seen V2s anywhere, and I kinda want to build a desktop-optimized PIMETA now lol.


----------



## Hifihedgehog

3l3tric said:


> It's a Pelican case, I'm not sure of the exact model number. I'd look it up right now, but I'm currently working on a writeup for this, as I'm entering the amp in a contest (not stating that I designed it, but a contest for assembling and writing about an electronics kit design that someone else created, if that makes sense).
> It's in the micro series, I believe. 101 maybe?
> And it is (was) waterproof. However, that rubber rim you see used to be a distinct rubber boot that lined the entire inner bottom half of the enclosure. Everything except what you see was removed to accommodate the board. I also had to drill 4 total holes for external hookups, and the 3.5mm jack holes had to be dremeled out from the inside so that the jacks could sink in and have their threads show through on the other side.
> Where can you get V1 boards? I haven't seen V2s anywhere, and I kinda want to build a desktop-optimized PIMETA now lol.


 
 As I posted earlier, you can now get the board files for all of Tangent's projects, sans the PIMETA V2 due to its cost-prohibitive four-layer design. In other words, last I checked, the cheapest and most reliable service I could find for four-layer boards, ITEAD, required a minimum of 10 boards at $99 plus about $12 shipping and handling. And, from what I have been told, they do throw in two boards or so extra free of charge if you ask real nicely for it.
  
 So at this point, we would have to organize a group buy to pull off getting more PIMETA V2 boards. Due to the Objective2 hype which has swamped the portable amp builder's market, this is a lot harder than it sounds. Then, we would have to figure in the costs of shipping the boards to everyone individually once the group's chosen buyer received the goods. It would probably come out to $12 to $15 a board once we factored in USPS First Class shipping. Alternatively, we could also get 50 made for about $140 plus about $20 shipping and handling. That's a boatload of boards, but probably the better route to go if we were doing a group buy. Personally, I have never organized a group buy before, but I would be willing to head it up since I have about five years of event organization under my belt which is pretty closely related.


----------



## Hifihedgehog

3l3tric said:


> Where can you get V1 boards? I haven't seen V2s anywhere, and I kinda want to build a desktop-optimized PIMETA now lol.


 
  
 About the board I had made: it is only 25 cents a square inch at my university shop, but there isn't any solder mask included with the service and the copper was etched on a bare minimum basis. My board still looks pretty darn cool, but I have one final thing to take care of. A new guy, green around the gills and fresh on-the-job, overcharged me and forgot to finish cutting the board. Like this:
  

  
  
 Guess where I am heading early in the morning to get a few minor PCB and price woes sorted out.


----------



## Hifihedgehog

Here are the Gerber files I just converted for the PPA V2 and the PIMETA V1. I inadvertently found out that the PPA V1 ExpressPCB files Tangent uploaded to his site are ones to the PPA V2. We will have to wait on those before I can convert them into Gerber files. As always, there is zero warranty and you risk life and limb all at your own expense. 
  
 PIMETA V1 Gerber files: http://1drv.ms/1CS4jOj
 PPA V2 Gerber files: http://1drv.ms/1LkwpYG


----------



## tangent

Try the PPA v1 ExpressPCB files now.  I don't have ExpressPCB installed right now, and don't especially want to install it just to check whether this is the right version.


----------



## Hifihedgehog

tangent said:


> Try the PPA v1 ExpressPCB files now.  I don't have ExpressPCB installed right now, and don't especially want to install it just to check whether this is the right version.


 
 Well, I was a bit trigger happy.  They are half-way right where they count. The PCB file, the important one, is right now with the socketed buffers and all but the schematic file isn't.


----------



## Hifihedgehog (Aug 3, 2020)

Here are the latest PIMETA V1, PPA V1 and PPA V2 Gerber files. Note that that PIMETA V1 files do not have an outline file because of a minor incompatibility in PDF2GERB with non-rectangular board shapes. Related to this, the PPA V1 and PPA V2 now have outline files. Let me know how they work. I will probably get some PIMETA V1 boards fabricated in the next few weeks.

See attached:


----------



## 3l3tric

> So at this point, we would have to organize a group buy to pull off getting more PIMETA V2 boards.


 
 I'd be up for this.
 Assuming you are too, 8 to go. Lol.
 But reading the rest of what you stated, the price point is a tad bit meh. 
 I thought about it a bit, and maybe (with tangent's blessing) we could get another DIYer with a storefront to carry the boards?
 Ti Kan (AMB) has a pretty robust storefront already with multiple boards and other products for sale. Although I'm not sure how keen he'd be on selling a second 3-channel board (his M^3 design is also 3 channel).


----------



## Hifihedgehog

3l3tric said:


> I'd be up for this.
> Assuming you are too, 8 to go. Lol.
> But reading the rest of what you stated, the price point is a tad bit meh.
> I thought about it a bit, and maybe (with tangent's blessing) we could get another DIYer with a storefront to carry the boards?
> Ti Kan (AMB) has a pretty robust storefront already with multiple boards and other products for sale. Although I'm not sure how keen he'd be on selling a second 3-channel board (his M^3 design is also 3 channel).


 
 I would definitely be in on this. I would probably want a couple at least for op-amp swapping, gifting to friends and family and such.
  
 The storefront idea would actually be quite simple for me to pull off. I own a URL ( theheadphonehub.com ) that I have wanted to get off the ground for some time--originally for an ad-based headphone review site but listen here, I have an even better idea. Instead, I could set up a non-profit circuit board group buying and non-profit headphone information site. I would first have to get permission from the higher ups here and possibly apply for MoT status to post anything about it. I mean, I could buy the batches, sell them on a slightly above for-cost basis, use the excess money to pay for renewing the site subscription and lowering the costs on future board runs, and finally donating whatever extra is left after all is said and done to a non-profit charity like The Red Cross.


----------



## 3l3tric

hifihedgehog said:


> I would definitely be in on this. I would probably want a couple at least for op-amp swapping, gifting to friends and family and such.
> 
> The storefront idea would actually be quite simple for me to pull off. I own a URL ( theheadphonehub.com ) that I have wanted to get off the ground for some time--originally for an ad-based headphone review site but listen here, I have an even better idea. Instead, I could set up a non-profit circuit board group buying and non-profit headphone information site. I would first have to get permission from the higher ups here and possibly apply for MoT status to post anything about it. I mean, I could buy the batches, sell them on a slightly above for-cost basis, use the excess money to pay for renewing the site subscription and lowering the costs on future board runs, and finally donating whatever extra is left after all is said and done to a non-profit charity like The Red Cross.



That's an excellent idea!
I wouldn't necessarily count out the reviewing part of the site, though. We could put comprehensive reviews of different DIY equipment and articles about different DIY related stuff like cable braiding, DIY cable building, soldering techniques, opamp reviews, and the like.


----------



## tangent

Okay, this time for sure.  I dug the design files out of the email archive, so they have to be correct now.


----------



## Hifihedgehog

I just ordered what appears to be the greatest deal in PCB fabrication history. I will post the pictures when my PIMETA V1 boards arrive. I ordered from Maker Studio which charges only $10 plus about $6 shipping and handling for ten 10x10cm boards. Insanely cheap but it is 100% legil. They seem to be the new benchmark for this price point. The only noted problem is just a very minor ~1mm offset in the silkscreens which is nothing big at all to worry about in projects like these. See examples of the quality of the boards here:
 http://www.edn.com/electronics-blogs/all-aboard-/4437745/Quick-Turn-PCB-shop-review-project--Maker-Studio
 http://www.protonbasic.co.uk/showthread.php/72429-Anyone-used-PCB-Maker-Studio
  
 Also, a quick question for Tangent: Are we authorized to resell any boards (for profit and/or non-profit) we have made from your designs? (The boards will have the original, unaltered attributions and design layout that you provided. One exception: On the PIMETA V1, I had to remove several silkscreen lines that went off the board of the ALPS pot that resulted from the import of the original Express PCB diagram.) If so, I may sell off a few of the extra boards on eBay if they all pass my probing tests.


----------



## tangent

I have not formally released any of my hardware designs under an open hardware license, which means they're still under copyright.
  
 I put the files up there for people to riff off of, not to copy wholesale.
  
 I don't care if make a few for yourself or friends.
  
 But if you're going to involve money, I'd ask you to create your own design. Go do something interesting.  Add something different to the world.


----------



## Hifihedgehog

tangent said:


> I have not formally released any of my hardware designs under an open hardware license, which means they're still under copyright.
> 
> I put the files up there for people to riff off of, not to copy wholesale.
> 
> ...




Understood. If even a group buy ever happens, it will happen under your go ahead to respect your hard work for the community these many years. Speaking of creating something new and interesting on someone's own, I do have an idea of a more advanced DIY device I have been wanting to make for some time: a digital ADC-DAC interface and headphone amplfier combo with a digital crossfeed filter. I think the merits of crossfeed have been getting pushed under the rug lately because of the flagship price battles that been a-waging the last decade. And many people have long forgotten that one limitation, the superstereo effect, can only really be overcome by advanced channel filtering and mixing that crossfeed and other virtualization techniques provide. As for implementing this, I will have to do some heavy reading and mega prototyping this summer if it is ever going to see the light of day.


----------



## 3l3tric

Question for you guys:
 I want to integrate a battery charge indicator board to my amplifier. I want it to have 4-5 LEDs and a push button that, when pushed, lights up the LEDs to indicate the charge. 5 LEDs would be 100-81%, 4 80-61%, so on.
 I found the link below, but it looks like this board is for 5V batteries, instead of the 9.6V setup I have.
 Any suggestions?
  
 http://ru.aliexpress.com/store/product/Single-section-lithium-battery-LED-power-indicator-display-voltage-lithium-battery-voltage-indicator/914980_955703587.html


----------



## MisterX

A LM3914 would be an easy way to add a voltage level indicator.
 http://www.ti.com/product/lm3914


----------



## 3l3tric

misterx said:


> A LM3914 would be an easy way to add a voltage level indicator.
> http://www.ti.com/product/lm3914



How easy would it be to both power the chip and measure battery charge with it?
I coud be reading wrong, but it sounds like the source is only measurable between 0-5V, not 9.6.
EDIT: Nevermind, I was looking at an example diagram.
My question about the input measuring battery charge and the whole chip being powered by the same battery still stands, though


----------



## MisterX

Put a voltage divider between V+ and the signal input.
 (trimmers are frequently used so the "scale" can be calibrated)
 IIRC there was a schematic posted somewhere in this thread.
  
  
 Edit: check page 30.


----------



## 3l3tric

Thanks!
 One question, though: How would I go about running the indicator with only 5 LEDs? I don't have room for and really don't want all 10.


----------



## MisterX

You don't have to use all 10 LED positions.
 Put it all together on a breadboard and then pick which terminal (on the LM3914) best suits the desired behavior for each LED.


----------



## 3l3tric

misterx said:


> You don't have to use all 10 LED positions.
> Put it all together on a breadboard and then pick which terminal (on the LM3914) best suits the desired behavior for each LED.


 
 Alright, thanks.
 After further research, I found a design that uses Zenerdiodes in combination with resistors and LEDs to conduct the indication.
 Each zenerdiode's tolerance voltage goes up, from the battery-nearly-dead voltage to the battery-nearly-full voltage.
 I looked on digikey, and they seem to have all the necessary parts in a good accuracy space (I found 9.0V, 9.1V, 9.6V, 9.3V, 9.4V, and others).
 Is there something I'm missing that would result in this circuit not working?


----------



## Hifihedgehog

*Drum roll*

First off, a huge thanks to Tangent for releasing the board designs. Without a doubt, I cannot thank you enough for this and all your numerous contributions to the world of audio and electronics. Just minutes ago, I got my 10 Pimeta V1 boards in from Maker Studio, neatly and nicely packaged with all the goods. Call me overwhelmingly impressed. For 10 PCBs at around $17 shipped, this is the bargain bin deal of the decade for electronic hobbyists and audio hacking geeks who need PCBs fabricated.





Slightly related, I also got these resistive puppies in the mail today as well. I won't be needing to order parts for a long, long time now:
http://www.amazon.com/gp/product/B00H703OKE/ref=pd_lpo_sbs_dp_ss_3?pf_rd_p=1944687642&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00FVT8I22&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0997HY0FJ8SGE31JYHXM#productDetails


----------



## tangent

hifihedgehog said:


> First off, a huge thanks to Tangent for releasing the board designs.


 
  
 I'm glad you're getting some utility out of them.
  


> I won't be needing to order parts for a long, long time now:


 
  
 Why such a large value? I don't mean why 1.28 k ct resistors, I mean why 10 MΩ? You have a lot of use for such things?
  
 I guess it's one way to create power resistors. Gang up a hundred of those in parallel, and now you have a 100 kΩ 25 W resistor. 
	

	
	
		
		

		
			




  
 Hmmm, "low noise."  Someone doesn't know the Johnson-Nyquist formula, I see... A single resistor creates about an -84 dB noise floor on a line level signal all by itself. Now add a few more resistors, then follow that with some gain stages...we're getting up to LP noise levels now.
  
 (Yeah, heresy, I know, never diss the vinyl...)


----------



## Hifihedgehog

tangent said:


> Hmmm, "low noise."  Someone doesn't know the Johnson-Nyquist formula, I see... A single resistor creates about an -84 dB noise floor on a line level signal all by itself. Now add a few more resistors, then follow that with some gain stages...we're getting up to LP noise levels now.
> 
> (Yeah, heresy, I know, never diss the vinyl...)


 
 Yes, oh, yes. Scarcely mention distortion or noise and vinyl records or resistors in the same breath and you may become this furry guy's midnight snack. As in, ohm, ohm, ohm... *gulp* *licks lips* Moral of the story: treat this master ohm guard dog with care and kindness and it will stay ohm, sweet, ohm. You have been warned. 
  




  
 The funniest thing happened today. Today, my circuits class began building the power supply portion for their speaker amplifiers. With excitement, the TAs were rooting, almost chanting, in going around the workstations saying things like, "This is the most exciting day of the semester. Finally, exploding capacitors! Inevitably, at least one of you guys will accidentally place their capacitors in reversed polarity. Then boom!" Mind you, these aren't those little party popper kind of capacitors that most measly headphone amplifiers sport. These are 5 to 20 farad, jumbo, ACME firecrackers that will literally blow up into the roof if not used properly.
  
 And you know what? They were right. Someone did blow one up--the group seated right next to me and my lab partner. Yes, KABOOM! In the wake of the explosion, that pitch black, torn-to-shreds sucker was smoking like a miniature mushroom cloud, so much that they were worried about the fire sprinklers going off. Luckily, no water accompanied this unintentional electronic "fireworks display" but it sure added to the atmosphere of today's class. Popping caps, smoking pots and using opamps. I swear, people sometimes must think we are on drugs or something. _Punny_, I know.


----------



## Hifihedgehog

Hey @tangent! Just as a quick sanity check, if I were setting up a unity gain loop in a Pimeta-V1 board, I obviously would leave out R3 and jumper R4 in the LR (or left and right) channels. But as for the ground channel, if my R1 were 3.3 KΩ in the LR channels, R1 and R4 in the G (or ground) channel would be 3.3 KΩ as well and R3 would remain open, correct?


----------



## tangent

Sounds plausible.


----------



## Hifihedgehog

Day one is done and progress for my first PIMETA V1 board is coming along quite nice. Excluding a few parts here and there, I was able to solder on all the resistors, capacitors, sockets and ICs. It is likely impossible to make out on the board, but those op-amps are OPA627's, nestled securely in their sockets and ready to bring the house down! I also have some AD797's, AD8620's and AD843's on standby for some fun op-amp rolling! Not shown are the buffers, quad-stacked BUF634's and soon-to-be-modified LMH6321's, which will also take their positions in the ranks when the time comes.
  
 Still on my to-do list is to get in my four Panasonic FM series 1000 uF 35V capacitors, one ALPS RK097 potentiometer and two 1/8" TRS phone jacks, install those components and then do the front panel work. I must admit that my expertise with front panel work leaves much to be desired so I might rely on a friend or my university shop to pull this final step off. Even it is only plastic, I only have one front panel and one panel only in my Hammond case and I am not about to ruin it by practicing my drilling skills on it. I will leave that battle for another day and for the assorted junk heap of parts I have from years long past.


----------



## Hifihedgehog

The headphone amp monster lives!


----------



## Hifihedgehog

Sorry for the triple and quadruple posts. I am currently listening to my stash of op-amps and I must say, op-amp rolling is no myth. Quite far from it, as a matter of fact, and I can finally confirm all the good things and the bad things that people say about these individual parts, and put in my two cents as well. After rolling a few of them, here is a ranking of some op-amps.
 
1. AD797ANZ: _The last word in detail, balance and energy;_ The AD797 takes things to a whole other level, where bass is fast, punchy and tight as ever, midrange is coherent and emotive, and treble is crystal clear and precise. However, such fidelity does not come without its price, meaning the AD797 is so true and exacting that it brutally reveals all problems in your signal chain and in the original recording down to very last reverbation and electronic buzz, even when having no gain at all. It is a wide-open window to your music, but you may not want to know all the dirty details this op-amp sets in plain view to you. It is analogous to the Sennheiser HD 800, so for those who do not like hearing absolutely everything in such a garbage-in, garbage-out fashion, you may want to try the second place contender.
 
2. AD843JNZ: _Fun and detailed;_ Although with a smidge of blurring here and there, the AD843 is actually a bit more detailed than the OPA627. The only drawback is its very, very slightly less refined nature in the bass or midrange. In its favor, however, unlike the OPA627, there is no slight blanket of warmth over the sound which I consider a huge plus in my book. Bear in mind that, while it is more neutral than the OPA627, it still does not have the laser precise, all-revealing nature of the AD797. For some, this slight deviation of neutrality can be a benefit when you do not want to hear everything in the signal chain, including in the original recording itself. However, for the most diehard purists, this will still be a turn-off.
 
3. OPA627AP:_ Warm yet accurate_; This is a substantial upgrade over the OPA132/OPA134 but, unlike its price would suggest, it is nowhere near as revealing as the AD797. In practice, OPA627 editorializes over hiss, grit and noise, which can be good, but it adds its own take on the music in the process. And yet, it is still detailed and resolving at the same time with a nice hint of crystallity in the upper registers. Think of this as the classic Sennheiser of op-amps, somewhere in-between the HD 650 and HD 600 in terms of tone. It is quite nice in this regard but it lacks that wow factor with genres which rely on drive and punch. As such, it is not my cup of tea. For those who thirst for a romanticized retelling of their music or have an affinity towards tubes, this just might be your thing.
 
4. LM6171/LM6172: _Detailed and accurate;_ I was surprised by this op-amp's ability to project air, space and detail. What was not so compelling was its noticeable lack of dynamics and energy. In a way, it models the classic list of complaints against the K701 and, for some, the DT 880; there is just not enough oomph and verve for musical pleasure. This is essentially the classical side of the op-amp sound coin, whereas the OPA627 is set on the opposite romantic face. If you savor some dynamics and warmth to round out your listening session, the OPA627AP is a better choice. If you crave exactness and detail, the LM617x is the better choice of the two.
 
More coming!


----------



## alphaman

Good to see this thread active again.
  
 One of my daily-portable-use HAs is a Pimeta2 -- a unit that has been going strong for over 5 years (some early issues -- see way back in this thread -- but after those resolved, all good and RELIABLE).
  
 Some noted tweaks/upgrades I added to Pimeta2:
  

tri-color-LED battery condition ckt (a mini daughterboard on Vero)
12v battery pwr using AA NiMH [the AD825 _really_ need more than 9v]
AD825 opamps
  
 One specific mystery at early (post-build) stage was weird turn-on transients (loud pops) ... search this thread for that discussion. It turned out that _two 9v batteries wired in series_ (18v) was the culprit. I now use either one 9v, per orig. case design, or a small multi-AA external battery box (the AA cells are in series), similar to this...

  
I only use the Pimeta2 for IEMs as I don't think they drive my full-size cans as well as other HA's I currently own.


----------



## Hifihedgehog

Quick question: Is there a low noise and ripple battery board design online that I could use to charge 9V batteries with a wall wart? I have the older PIMETA V1 and I am very much interested in a charging board so I can just plop in the batteries and never have to switch or replace them every 3 hours. I have quad-stacked BUF634 buffer stages which makes battery life very, very short.
  
 I must say, by the way, that the sound quality is nothing short of spectacular! With my HiFiMeDIY as source and my Phonak PFE's, I seriously enjoy this loads more than any of my past Objective2's. It's got such energy and drive and PRAT and all those audiophile terms you would associate with perfect synergy. 
  
 EDIT: Another quick question: What would cause a PIMETA V1 with quad-stacked BUF634's to get unstable at a certain pot position when using OPA2132's? I am measuring zero DC offset, and I do not have this issue at all with the op-amps listed above.  For some reason, I get a somewhat noisy pot and distortion centered around a certain pot position (roughly 10 o'clock/25%) whenever I use the OPA2132. I have five of them at my disposal and they all behave the same, which is strange for an op-amp which is commonly recommended to beginners because of its renowned stability. Would it be that I need to add the bandwidth resistors on the buffers? Would it be that I need to mod in some 10 pF capacitors? (I am thinking this second case is much less likely, but I thought I'd ask anyway.) Technically, the buffers are still faster than the OPA2132 according to the datasheet, but maybe they need to be faster just in case. It just doesn't make any sense why it is behaving this way.
  
 EDIT: I just answered my own question where I asked "Would it be that I need to add the bandwidth resistors on the buffers?"
 Per the BUF634 datasheet: "High speed or _fast-settling_ op amps generally require the wide bandwidth mode to remain stable and to assure good dynamic performance."
 And per the OPA132 datasheet: "The combination of high slew rate and wide bandwidth provide_ fast settling time_."
 That would be an affirmative to that question.
  
 The other question is irrelevant, but if I added some 10 pF capacitors to the knock-off Browndog I have, it might very well remove the very very very slight hum in the LM6171 I only hear at eardrum-bursting volumes (and no music playing--heaven forbid I accidentally press play).


----------



## Hifihedgehog

I have found a problem with DC offset in my PIMETA V1's ground channel, and would like some feedback and suggestions. I am measuring 5 mV DC offset from input ground to output ground. Unlike offset of this magnitude in the left or right channels which would be acceptable, apparently, this amount of offset is not acceptable here. See here: http://tangentsoft.net/audio/trouble.html#loudclick (Out of curiosity, why would that be?) I looked at my ground channel where there is a double BUF634 buffer stack and an AD797, and I am at a loss as to what to be looking for. Please help. I can offer more information about my particular implementation as needed. 

EDIT: Additional information for this mystery: This PIMETA V1 is set up in a unity gain configuration. Resistors were hand matched and were already 1% precision resistors to boot. R1L/R/G is 3.3 KΩ, R2L/R is 1 MΩ, R3L/R/G is open, R4L/R is jumpered, R4G is 3.3 KΩ, R5L/R is 3.3 KΩ, R6L/R 1MΩ, R8L/R is jumpered, R10L/R is 1 KΩ, R11 is open and RLED is 10 KΩ. C6G is installed as well, and C6's were soldered on the back side of the boarf to the LR opamp socket's associated pins as well. Just to make this caper even more intriguing, the offset occurs independent of the model of opamp installed.


----------



## tangent

hifihedgehog said:


> Unlike offset of this magnitude in the left or right channels which would be acceptable, apparently, this amount of offset is not acceptable here. See here: http://tangentsoft.net/audio/trouble.html#loudclick (Out of curiosity, why would that be?)


 
  
 The only reason we expect the ground channel's DC offset to be lower is that it's always unity gain, whereas the other channels can be higher, which magnifies any inherent DC offsets.
  
 Given that all three of your amp channels are G=1, I'd expect them to _all_ be well under 20 mV.
  


> Just to make this caper even more intriguing, the offset occurs independent of the model of opamp installed.


 
  
 If you're changing OPAG and nothing changes, then the problem almost certainly isn't the op-amp, since there are manufacturing variations in op-amps that ensure variable DC offset. I would measure DC offset across the buffer stack only.
  
 I hope you're not changing _OPALR_ and expecting to see a change in the ground channel.
  
 Personally, I wouldn't have recommended the AD797, because it's a bipolar-input op-amp, which you were warned about in the parts selection guide.
  
 Have you gone through my generic troubleshooting guide?


----------



## Hifihedgehog

Thanks for the reply! Hopefully, these symptoms help me in reaching a valid diagnosis. 
   Quote:


tangent said:


> I hope you're not changing _OPALR_ and expecting to see a change in the ground channel.


 
  Nope. That would be like a dog chasing his tail, with no foreseeable resolution in sight. I am not madly beating my head in agony and bewilderment... yet.
  
 Quote:


> The only reason we expect the ground channel's DC offset to be lower is that it's always unity gain, whereas the other channels can be higher, which magnifies any inherent DC offsets.
> 
> Given that all three of your amp channels are G=1, I'd expect them to _all_ be well under 20 mV.


 
  That is my understanding as well. Following math and real world experience, I would expect the DC offset to increase as a multiple of the gain or thereabouts.
  
 Quote:


> If you're changing OPAG and nothing changes, then the problem almost certainly isn't the op-amp, since there are manufacturing variations in op-amps that ensure variable DC offset. I would measure DC offset across the buffer stack only.


 
  Bingo. More precisely, I am measuring across from the ground output to the ground input. So instead, I should measure from the ground op-amp output to the headphone ground output, right?
  
 Quote:


> Personally, I wouldn't have recommended the AD797, because it's a bipolar-input op-amp, which you were warned about in the parts selection guide.


 
   Thanks. Already seen and duly noted. As mentioned, I have this issue with any op-amp in the ground channel, be it an OPA134 or OPA634 or an AD843 or AD823, etcetera, etcetera, etcetera. 


> Have you gone through my generic troubleshooting guide?


 
  
  I have, and I plan on going through the Trace a Signal through the Amp section next. That is where, I wager, I am bound to find the underlying cause(s). As recommended, I will first skip ahead to the buffer section and measure for offset. Much to my chagrin, I may very well have a set of misbehaving buffers on my hands. We will see soon.


----------



## Hifihedgehog

I am getting roughly 24 mV offset from opamp ground output to output ground. Now, for the strange thing. It is the same result regardless of the buffer stack I place there. I also measured -30 mV offset from the opamp. The opamp appears to be overcompensating, and it does this, again, regardless of the opamp being used. Thoughts? I'm near agony and bewilderment. jk. Seriously, this is rather puzzling.

EDIT: From what I am reading around the web, if all it is is only around 5 mV, I shouldn't really be too worried about it. I mean, it is still three quarters of the way from the 20 mV mark. Previously, in a different thread, someone had 8 mV in a similar configuration, only it was when using fully discrete components and it was only in their left and right channels. I am totally willing to live with this seeing how the amp actually sounds so wonderful already--ultra low noise, dynamic and detailed. I just saw the number in reading through your website again and it caught my eye in the reading. If it really isn't a big deal and I am getting what I want, maybe I shouldn't be all too worried about it and I should just move on and enjoy my tunes. I can get all worried about DC offset with the next PIMETA I build from the stack of boards I have. After all, I want to build my little brother an amplifier as a gift and I want to get some more practice in so I can be a headphone amp samurai when I build him the perfect one when the time comes. This one is good enough for me.


----------



## quangngaicity (Feb 3, 2018)

Nho quyet tam va dinh huong dung dan, nam 2015 kinh te - xa hoi cua huyen Thap Muoi da co nhung buoc phat trien moi, chuong trinh xay dung nong thon moi va thu hut dau tu vao dia phuong co nhieu dot pha. Huyen Thap Muoi cach TP.HCM 90 km, cach TP. Can Tho 95 km va cach TP. Cao Lanh 32 km.

Huyen Thap Muoi nam o vi tri trung tam cua vung Dong Thap Muoi, la vua lua lon cua tinh va khu vuc. Thap Muoi cung duoc biet den la dia phuong co nhieu tiem nang phat trien du lich voi nhung canh dong sen bat ngan, la noi gin giu nhieu net van hoa - nghe thuat truyen thong. Nho phat huy tot tiem nang, loi the cua dia phuong nen kinh te - xa hoi cua huyen Thap Muoi da co su but pha manh me, dong bo. Nam 2015, san xuat nong nghiep tiep tuc phat trien, dien tich, nang suat, san luong va gia ban deu tang. Gia tri san xuat cong nghiep uoc dat 764 ty dong, tang 14% so voi nam 2014. Thuong mai dich vu tiep tuc phat trien, tong muc ban le ca nam uoc dat 5.582 ty dong.

Thap Muoi la huyen co loi the la trung tam cua vung Dong Thap Muoi, co vung nguyen lieu la vua lua lon cua tinh va khu vuc; chu dong san xuat ca ba vu va dien tich tuoi tieu bang bom dien tren 93%. Ben canh do, luc luong lao dong doi dao, co trinh do va kinh nghiem san xuat, san sang dap ung nhu cau cac du an su dung nhieu lao dong hay nhung du an co trinh do cong nghe cao. Hien tai, huyen Thap Muoi co 02 Khu Cong nghiep voi dien tich giai doan 1 la 150 ha/khu va 01 cum cong nghiep Truong Xuan, voi dien tich 93 ha da duoc dau tu ha tang ky thuat day du, san sang don nhan du an dau tu ngay.

*I. Dich Vu Internet FPT Thap Muoi. *

Voi quyet tam day nhanh tien do thuc hien, tao dot pha moi trong xay dung nong thon moi, huyen Thap Muoi da chu dong chi dao thuc hien nhung nhiem vu trong tam cua nam doi voi cong tac ra soat va thuc hien quy hoach, tang cuong cong tac tuyen truyen van dong, nang cao hieu qua trong phat trien san xuat, dau tu tap trung ha tang tai 3 xa diem, tap trung chi dao sau sat trong xay dung nong thon moi doi voi xa Thanh My, My Dong, Doc Binh Kieu va Truong Xuan.

Voi nhu cau su dung ngay mot cao. Cong ty vien thong fpt Dong Thap da dau tu ha tang de phuc vu cho ba con.Ba con va cac ho gia dinh tai huyen Thap Muoi tinh Dong Thap co the lien he ngay hotline tong dai de duoc gioi thieu cac goi cuoc internet cho phu hop tu 6 Mbps - 32 Mbps voi cuoc tron goi chi tu 150.000d - 330.000d kem theo cac chuong trinh ap dung cho khach hang tra truoc se duoc mien phi lap dat + tang cuoc su dung cho khach hang.

*II. Lap Mang Internet FPT Thap Muoi. *

Trong giai doan 2016 - 2020, fpt telecom du kien se bo sung them ha tang internet fpt tai 1 so xa khac tren dia ban huyen Thap Muoi Dong Thap de khach hang co the su dung dịch vụ *lắp mạng fpt lai vung*, mang internet fpt de dang hon va nhanh chong hon. De biet them chi tiet ve chuong trinh khuyen mai, cac khu vuc da co ha tang internet FPT vui long goi ngay hotline tong dai FPT. Bang gia cuoc danh co ho gia dinh, hoc sinh, sinh vien ma FPT telecom dang khuyen mai tai huyen Thap Muoi.

 Toc do duong truyen internet FPT tu 6 Mbps - 32 Mbps dap ung cho ho gia dinh su dung tu 1 - 8 nguoi xai cung 1 luc. Khach hang co the tham khao bang gia cuoc internet FPT tai huyen Thap Muoi truoc khi goi dien dang ky nhe. FPT telecom gui den quy khach hang bang bao gia cuoc *lắp internet fpt lấp vò*, internet FPT + truyen hinh FPT tai huyen Thap Muoi, Dong Thap voi toc do duong truyen internet FPT cao va hon 100 kenh truyen hinh dac sac trong va ngoai nuoc kem nhieu ung dung thong minh khi su dung truyen hinh FPT tai huyen Thap Muoi, Dong Thap.

De dang ky mang internet fpt Thap Muoi khach hang co the goi ve cho chung toi qua duong day nong 0971.620.836
website tham khảo: http://www.internetvietnam.net/


----------



## Hifihedgehog

quangngaicity said:


> It would work, but it would probably be pretty noisy.
> 
> Might be better to at least power a seperate linear PSU from the 12v rails of the computer's PSU.




I have no issues with power supply noise or noise on the output when using IEM's even. I don't quite understand where you are coming from as far as the computer power supply is concerned unless you a suggesting a true dual supply with a real ground.


----------



## tangent

hifihedgehog said:


> if all it is is only around 5 mV, I shouldn't really be too worried about it. I mean, it is still three quarters of the way from the 20 mV mark.


 
  
 This is true.  However, it does seem to be a legitimate mystery, rather than something like some meaningless process variation.  I recommend that you pursue it only if you would be gratified to know the answer.  If you don't care why it's happening, don't waste your time. 
  
 Rotating the buffers was a good test.  I should have thought of that myself.
  
 You've already rotated the op-amps, which means you're now down to the passives.
  


> I plan on going through the Trace a Signal through the Amp section next.


 
  
 That's only likely to find problems in the signal channels, not in the virtual ground.
  
 I was hinting that you might check the amp's quiescent current.  It even walks you through how to add the BUF634 contributions to the supply draw.


----------



## Hifihedgehog

Thanks! I will do that--I especially don't like this being left unanswered, since electronic analysis and diagnosis and all should be my forte as a computer engineer. Once I have college finals in my wake, unraveling this mystery will be my next task at hand. It may just be a matter of a bad solder joint somewhere down the line, so I will reheat and redo the joints to cover my bases there. The resistors measured okay, but I will double and triple check everything in the ground channel to see if I may have past over something.


----------



## Hifihedgehog

To those who have eyed the recently released PIMETA V1 design in this thread: if you were leery of using this design with the LMH6321 on account of the short circuit issue while disconnecting headphones that would burn up those buffers, worry no longer. MAGNEZ on Kickstarter is a new kind of audio jack adapter that solves not only the breakaway issues that jacks have but this shorting issue as well. 
  
 Link: https://www.kickstarter.com/projects/magzet/magzet-the-audio-jack-reinvented-with-the-power-of/


----------



## tico420

Had a v2 board laying around for years, finally got around to finishing it. Sounds great, thanks.
  
 OPA637 on left right channels, AD8065 on ground.
  
 Alps big pot
  
 24V tread


----------



## whitelabrat

I've had a board laying around too and I'm just waiting on four resistor values to show up.  Accidentally ordered 0402 package sized resistors.  Ha!  So small.
  
 But yeah, hoping to brown dog some OPA637 as well.


----------



## whitelabrat

Got it working, and it sounds really good. So happy. The OPA37 opamp for the ground channel is crazy hot though so I'll need to tinker with that. Running about 0.60 mA for the class A bias.

I really like having the option to do SMT or through hole. 

Photos: (my soldering is not super)


----------



## tangent

The OPA637 isn't unity-gain stable; the ground channel is unity gain. That's why they make the 627.


----------



## whitelabrat

Heh. I put the opa37 (not 637) in backwards. Perfect now.


----------



## tangent

The OP37 is _also_ not unity-gain stable. From the datasheet:
  


> the design is optimized for circuits with gains greater than five.


----------



## whitelabrat

WAT?  _looks at datasheet_.  almface:
  
 Ok.  I do realize I'm one of the knuckleheads often referred to in the instructions.    Popped in an OPA27GP.  Because I have some.
  
 @tangent nice.


----------



## Hifihedgehog

Keeping this thread alive and sharing a hot deal for makers! I simply joined PCBWay and I recently received a $45 credit that was enough to cover both the fabrication and shipping and handling costs of *20 *100 x 80mm 2-layer PCBs, absolutely free for me! For potential makers of the Pimeta V1 and he-who-shall-not-be-named's dioxygen amplifier, I cannot recommend PCBWay enough for their quick and impeccable service.
  
 http://www.pcbway.com/


----------



## spbkaizo (Feb 5, 2019)

Firstly, Apologies for dragging up a rather old thread - but I'm out of ideas.

I decided to build some of these, so I ordered some boards which arrived and I started to populate 3 of them.

One board became leader, and once I got to the section "check power" and everything was fine (voltage split +/-V correctly) on the op-amp pins, I then proceeded to populate the buffers, op-amps, etc as instructed.  First test after that revealed there was the following voltages on the following pin combos (18v bench supply):


PG/OPALR V- = -9V
PG/OPALR V+ = +9V
PG/OPAG V+ = +9V
PG/OPAG V- = -9V
So, all still ok.  Moving onto check the IG to Outputs revealed some scary results:


IG-OG = +8.5v
IG-OR = +7.4v
IG-OL = +7.4v
OG-OR = 110mv
OG-OL = 110mv
OK, so clearly not right.  Been unwinding the build and rebuilding it, checking as I go.  I was stumped.

As always, try to reproduce.  So I got one of the other boards, and started to build slowly and checked everything as I went along.  I got as far as installing the Op-Amps, and checked the input signal of a sine wave on a scope - perfect, on both pins 3 & 5.

Moving on, I checked the output of pins 1 & 5 - again, perfect, and absolutely in line with my gain settings.  So, I decided to solder 1 of the buffers into place.

And this is where things get weird.

Pin 2 of the output buffer goes to R11 - I carefully made sure that Pin2 did indeed go to R11 (currently unpopulated), soldered down the legs and re-checked.  Now, output from the corresponding OPALR Pin 1 is near zero, but the other output on Pin 7 remains fine.  I believe something to be amiss with the buffers - but would like support in this conclusion, as well as any other pointers you may have.

https://photos.app.goo.gl/RRdrY7HU1VgUvSiQ9
https://photos.app.goo.gl/6YTiRAXQCXPXUd8cA


----------



## tangent

spbkaizo said:


> I ordered some boards


Do you mean that you found a store selling simple copies of my board, against my wishes, or that you took my Gerbers and had a board house make some for you, in accord with my wishes?

If the latter, did you tell them it needs to be a 4-layer board? If you made it as a 2-layer copper board, that'll explain a whole lot of trouble.

Your close-up photo of one of the buffers (BUFR?) shows a number of problems with the physical realization of these boards relative to an original I've got sitting around here still:

Pin 4 appears completely flooded, not fenestrated into the plane.
The originals don't have those thin fingers between the pins, most egregiously between 2&3, and between 6&7.
Whoever ordered the boards elected not to include the bottom side silk layer, which means you might not be populating the components in the right spots or in the right orientation
Observations 1 & 2 call into question whether these boards do in fact express the schematic correctly. What other creepage and tolerance problems are there, which could cause shorts, opens, and parasitics where we don't want them? I've made a close-in screenshot of what my Gerber viewer shows for BUFR in the bottom copper layer, which I believe is what you're showing in the second picture. _Quelle différence!_

Observation 3 means we're reliant on your photos to tell whether your buffers are oriented correctly on their pads. It _looks_ like two of your buffers are oriented on the pads correctly; you don't show the third.



> Moving onto check the IG to Outputs revealed some scary results:


What op-amps are you using? Maybe post pictures.



> I checked the output of pins 1 & 5 - again, perfect, and absolutely in line with my gain settings.  So, I decided to solder 1 of the buffers into place.


I don't see how your op-amp tests gave sensible results without the buffers in place, especially the gain, since that means you'd be running on the inner Jung loop, which has a gain far higher than you'd be expecting.

Unless you shorted the buffer positions, you should _not_ have gotten sensible results from that test.



> Pin 2 of the output buffer goes to R11 - I carefully made sure that Pin2 did indeed go to R11 (currently unpopulated), soldered down the legs and re-checked.  Now, output from the corresponding OPALR Pin 1 is near zero,


I can't tell whether this is a grammar error — should these be two separate paragraphs? — or you're trying to get some point across to us that I'm missing. There's nothing about sentence 1 that leads us to sentence 2, and sentence 2 doesn't in any way clarify sentence 1.

OPALR pin 1 is a signal output pin, and BUFL pin 2 is a power modifier. You would not expect any connection between them, nor is there supposed to be.



> I believe something to be amiss with the buffers


Did you get them from a reputable source?

Maybe someone who's bought some of these recently could tell you whether they're still marking these chips with the Nat Semi logo so many years past their absorption into TI. Mine are so-marked, but they're from before the merger.



> any other pointers you may have.


The board could use a cleaning. It wouldn't be the first time I saw that solve a problem.


----------



## spbkaizo (Feb 6, 2019)

Would just like to say thanks for your time, in writing your response, as well as for the original work you did.



tangent said:


> Do you mean that you found a store selling simple copies of my board, against my wishes, or that you took my Gerbers and had a board house make some for you, in accord with my wishes?




I had the boards made, from your Gerbers.



> If the latter, did you tell them it needs to be a 4-layer board? If you made it as a 2-layer copper board, that'll explain a whole lot of trouble.


Was done as a 4 Layer Board.

The order artefacts are available for download from them, https://jlcpcb.com/file/download?uuid=135a5870c7d84874a24e2abef588ca54&businessType=example



> Your close-up photo of one of the buffers (BUFR?) shows a number of problems with the physical realization of these boards relative to an original I've got sitting around here still:
> 
> Pin 4 appears completely flooded, not fenestrated into the plane.
> The originals don't have those thin fingers between the pins, most egregiously between 2&3, and between 6&7.
> ...


I've done a side by side image of the viewer in Eagle, vs the Board - I'm not clear how I could have gone wrong.

Here's a better picture of the board: https://photos.app.goo.gl/7g3BySSVFQnZqyQy8



> What op-amps are you using? Maybe post pictures.


For testing, an OPA2134, OPA2132, OPA134.



> I don't see how your op-amp tests gave sensible results without the buffers in place, especially the gain, since that means you'd be running on the inner Jung loop, which has a gain far higher than you'd be expecting.


Indeed - I meant to demonstrate the opamp was in fact increasing gain, and therefore was alive.



> I can't tell whether this is a grammar error — should these be two separate paragraphs? — or you're trying to get some point across to us that I'm missing. There's nothing about sentence 1 that leads us to sentence 2, and sentence 2 doesn't in any way clarify sentence 1.
> 
> OPALR pin 1 is a signal output pin, and BUFL pin 2 is a power modifier. You would not expect any connection between them, nor is there supposed to be.


Apologies.  I meant that I output on PIN1 of opamp drops to 0 after soldering the buffer to the board.  Removing the buffer causes the signal to reappear.

I was referring to BUFL2 in that statement as a chip orientation hint.



> Did you get them from a reputable source?



No, I'd have to say I didn't.  They're hard to track down, at a reasonable price so I ordered 10x from a Chinese supplier.  Caveat Emptor.

As it stands, I have 10 boards.  I've traced the schematic through the board, and all seems reasonable.  Some questions if I may:

Is there a way to test that the inner layers are in fact present, and correct?
I have a "reusable" SOIC8 - DIP8 adapter with more reasonable pin distances for testing.  If I pop a buffer in there, is there a way to test the operation of it you can recommend?
In addition, I'm going to order another single buffer from a reputable supplier.  However, if you think the boards are a lost cause then maybe I won't 

TIA,

S.

Thanks for replying.


----------



## tangent (Feb 6, 2019)

spbkaizo said:


> I had the boards made, from your Gerbers.


What it looks like is that someone took my EAGLE files and ran their own hand-rolled CAM processor against it instead of running the included CAM processor, so that all of the DRC rules have potentially changed.

You didn't, by chance, send the EAGLE files to your board house, too? As a rule, you should only send Gerbers to a board house, specifically in order to prevent them from second-guessing DRC rules and such.

Here's a better screenshot of the Gerbers from the bottom side near BUFR, this time oriented the "natural" direction and with the bottom side silk and drill hits in place:







I've been careful to do this on the Gerbers in the ZIP file on the web site, rather than the original versions here in my personal documents folder, just in case there's some important difference.

As you can see, the fenestrations are present, and there are no stray copper fingers going between the buffer pins.



> OPA2134, OPA2132, OPA134.


And just to be sure, one of the OPA213x chips are in OPALR at a time, and the OPA134 is in OPAG, right?



> I meant to demonstrate the opamp was in fact increasing gain, and therefore was alive.


You mentioned a scope: if you look at a sine wave going through the op-amp with the buffer missing (not shorted) a sine wave should look like a near-square wave unless the input signal is very tiny, since it'll be at gain of 100x or so.

Actually, it might not be very square, because many chips behave badly when you drive their inputs or outputs to the rails like that.

You really want to do this sort of test with the buffer shorted, so the outer feedback loop dominates, being lower in parallel resistance.



> They're hard to track down, at a reasonable price


Maybe it matters that you're in the UK, but I see ready stock of about 20000 of them in onesy twosy quantities.

The question, then, is are those in fact LMH6321MRs?

You can partially answer that question by hooking them up to power and seeing whether they pass a signal with unity voltage gain, as they ought to. It's not absolute proof, because sometimes fraudulent designs will be something like a repurposed op-amp, so the main 4-5 pins will work as they're supposed to at low loads, but they won't put out the full power they're supposed to, and the other 3-4 pins might be disconnected or have other functions than the real thing.

Do your chips have the exposed solder pad on the bottom, or are they fully-encapsulated down there?



> is there a way to test that the inner layers are in fact present, and correct?


Sure, but it's best done in conjunction with a copy of EAGLE and the *.brd file loaded, so you can get a picture of what's supposed to be connected where.

The file *.ic1 in the dfiles package is EAGLE layer 2, and it contains the V+ plane. Anything connected to V+ on the schematic goes through this plane.

File *.ic2 is the GND plane, and it's EAGLE layer 15.

The bottom copper layer is *mostly* V-, but it's also used for signal traces, as you see in the above screenshot. (I tried to keep most signal traces on the top layer, but sometimes I needed to pop down to the bottom copper layer to make things work.) This is what those fingers intruding between the buffer pins are.

Mostly you can answer this question by heeding the first commandment of troubleshooting: thou shalt check power and ground connections. For that, you don't need EAGLE, you need the schematic and a clear idea of which pads on the PCB connect to which power or ground nets.



> I have a "reusable" SOIC8 - DIP8 adapter with more reasonable pin distances for testing.  If I pop a buffer in there, is there a way to test the operation of it you can recommend?


Not on this board. On the PIMETA v1, yes, because there were both DIP-8 and SOIC-8 footprints for the buffers, but not on v2, since the LMH6321 isn't available in DIP-8.



> if you think the boards are a lost cause then maybe I won't


I think they're _questionable_, but you can prove them worthy through testing.

I think there's a pretty good chance your boards are more prone to oscillations than the originals due to parasitic capacitive coupling to V- on the high impedance input pin on the buffers, but realize that that isn't a failure guarantee. If true, it just means there are some configurations that won't work on that board that would on a "real" PIMETA v2.

With those slow-ish op-amps, you're going to have more margin to cope with such problems than if you were trying to use something really fast and touchy.


----------



## spbkaizo

I'll reply more fully once digested, tested and evaluated. For now though:



tangent said:


> What it looks like is that someone took my EAGLE files and ran their own hand-rolled CAM processor against it instead of running the included CAM processor, so that all of the DRC rules have potentially changed.
> 
> You didn't, by chance, send the EAGLE files to your board house, too? As a rule, you should only send Gerbers to a board house, specifically in order to prevent them from second-guessing DRC rules and such.


I put my hands up - I imported them into EasyEDA and then sent the output to the board house.  Mea Culpa, entirely.



> And just to be sure, one of the OPA213x chips are in OPALR at a time, and the OPA134 is in OPAG, right?



Indeed 



> You mentioned a scope: if you look at a sine wave going through the op-amp with the buffer missing (not shorted) a sine wave should look like a near-square wave unless the input signal is very tiny, since it'll be at gain of 100x or so.
> 
> Actually, it might not be very square, because many chips behave badly when you drive their inputs or outputs to the rails like that.



Can confirm this happened - I turned to pot down to maybe a 1/4 turn.



> You really want to do this sort of test with the buffer shorted, so the outer feedback loop dominates, being lower in parallel resistance.



Interesting - this makes sense.



> The question, then, is are those in fact LMH6321MRs?
> 
> Do your chips have the exposed solder pad on the bottom, or are they fully-encapsulated down there?



No, they do not.  Guessing this is a red flag?

Will investigate the other stuff - apologies for splitting the post.


----------



## tangent

As far as I'm aware, you can't buy an actual SOIC-8 version of the LMH6321. You have a choice of the PowerPad/PSOP version or the DDPAK version, that's it.

I think there's an excellent chance those aren't actually LMH6321MRs. It'd explain everything.


----------



## spbkaizo (Feb 7, 2019)

tangent said:


> As far as I'm aware, you can't buy an actual SOIC-8 version of the LMH6321. You have a choice of the PowerPad/PSOP version or the DDPAK version, that's it.
> 
> I think there's an excellent chance those aren't actually LMH6321MRs. It'd explain everything.



Let's assume so.  The chip from a reputable supplier arrived today, I only purchased one so I expect the tests will not quite be meaningless, but they did provide a strong level of reassurance.

DC Offset on the lucky recipient (on OPALR buffer) is now down to 23mv, so managed to lose what I assume must be a short from the 'fake' chips.  I ran a 10khz signal through it, and the results were the square wave from the tests without the buffer, as with the new buffer installed.  The signal is now making it to the buffer.

Time to buy the remaining 5, that I initially need.  Confidence remains high, budget remains low 

Image of the two chips is side by side.  The marking on the original (05AC) is actually worse than the counterfeit (54RD).  Shame they couldn't get the insides right...https://photos.app.goo.gl/wbtBD5hnCMaPxvAn8


----------



## spbkaizo

Update: It works 

Installed the new chips, and just doing some testing, but it's all good so far.  DC Offset is 9.4mv on one channel and 16.2mv on the other channel.  Signal is clear, and VPP from 1v input is 5.2v output.

Now I can finally breathe again - thanks for the support.  You've got me over this being a doomed project.  

I'm going to go through more and more tests, before moving on.  But, at least the project has moved back into 'fun' status.


----------



## tangent

I'm glad to hear it.

Care to name-and-shame the retailer who sold you those bogus buffers, so others can avoid them?


----------



## spbkaizo

Absolutely, I sourced them from AliExpress, seller was XYWElectronic Store.

I've known, and found it fascinating, that there are counterfeit chips around, and I'm certain I must have had some in the past.  

Another lesson learned, to only buy from reputable suppliers - in my case, RS Components in the UK, who offered free delivery and they arrived in less than 24 hours on both occasions!

Thanks again.  I've now got the following back in flight:

Desktop/Portable Headphone Amp
Purely Portable Headphone Amp
Pre-Amp with Dual Rails supply (waiting on some power supply components)

Mainly SMD based Headphone amp
This leaves me another 6 boards to study and learn with, so should keep me quiet for some time...


----------



## tangent (Feb 9, 2019)

spbkaizo said:


> I sourced them from AliExpress, seller was XYWElectronic Store.


I think I found the listing you mean. It gives the brand name as PSTQE, not NatSemi or TI. A search for that brand on AliExpress suggests they're a maker of knock-off electronics.

Another red flag is that there are only two votes on the product, neither with commentary.

You might give this product the single star it deserves, and a reason why it deserves that. I think the single star is greatly overused, but in a case like this, where the product doesn't even try to do what its label claims, I think it's justified. If it even had a datasheet showing that it provides some other function and that they just HAPPENED to have picked the same part number as something else (yeah, right) it'd be worth more than a single star, but if all they're giving is a misleading part number...yeah, one star it is.

I don't consider the lack of a photo or the 3D rendering that doesn't match the actual item — missing PowerPad — to be a red flag. Legitimate resellers do this, too. *EDIT 1: *Digi-Key's 3D rendering shows the PowerPad, though; good on 'em!

*EDIT 2: *The price should also have been a clue. Digi-Key wants US $5.57 per buffer in qty. 10, whereas this AliExpress listing I found says $16.15 for 10. You can't explain a 3.45x difference between resellers any way other than "too good to be legitimate."


----------



## spbkaizo

Yes, I was hoping that mass economies of scale explained away the price.  Remarkable how easy it is to delude yourself.

Finished one of my builds now, sounds good and happy so far - 8.4v (2 * 4.2v Li-ion '9v battery') powered portable, running with the buffers and an OPA2227/OPA134 combo.  Battery life seems OK down to around 3.8v per cell, and they have a 600mah capacity.  Consumption runs at around 60mah, I'm getting about 5 hours of use before things are noticeably `wobbly`.  They have a charging circuit built in, and charge from that level in about an hour (at around 600mah, assuming split so 0.5C) which helps via micro-usb, so one less cable to carry....

The biggest surprise was that I seem to have managed to get around 6.5mv DC offset, so pleased with that!

https://photos.app.goo.gl/BhaBHTscjCzYdLSL9
https://photos.app.goo.gl/fUKC9fJV2ecjZmQg6

Going to focus on the pre-amp next, more free space to place components and the PSU.

Thanks again for the help.


----------



## tangent

spbkaizo said:


> Consumption runs at around 60mah


mA, not mAh. Divide milliamps into milliamp-hours to get hours.

That tells you in this case that you'd expect 10 hours of runtime, which is enlightening because it means your amp isn't draining the battery fully, since you're only getting half that runtime.

You probably can't fix it with a DC-DC converter. If you double the voltage to the PIMETA v2, you double the current draw on the battery, which nets you the same 5 hour runtime.

If it were me, I'd ignore it, since you don't want to fully drain a lithium chemistry battery anyway.

I don't think I've seen that case before. Has Serpac come out with a new color since I last looked, or has someone cloned the case closely enough that the PIMETA v2 fits into it the same way?



> the pre-amp next


You'll want to build that as a 2-channel amp. Preamps normally short IG to OG, since the input and output grounds are normally shorted together, which at best makes the ground channel on the PIMETA v2 useless, and can actually cause it to misbehave.


----------



## spbkaizo (Feb 19, 2019)

tangent said:


> mA, not mAh. Divide milliamps into milliamp-hours to get hours.
> 
> That tells you in this case that you'd expect 10 hours of runtime, which is enlightening because it means your amp isn't draining the battery fully, since you're only getting half that runtime.
> 
> ...


Yep, this is my 'travelling amp' for planes, trains, etc.  5 hours is plenty for these scenarios I estimate.



> I don't think I've seen that case before. Has Serpac come out with a new color since I last looked, or has someone cloned the case closely enough that the PIMETA v2 fits into it the same way?



It's close, but not the same - there's no mounting posts inside for example, and I've ignored the fixing points as it holds together nicely with just an elastic band.  I liked the colour...



> You'll want to build that as a 2-channel amp. Preamps normally short IG to OG, since the input and output grounds are normally shorted together, which at best makes the ground channel on the PIMETA v2 useless, and can actually cause it to misbehave.


[/quote]
Indeed - I've read and re-read the docs and believe I know what to do (ditch the ground channel entirely, run real gnd into the voltage divider vgnd location) amongst others.

So, I've now finished the second one, and I'm blown away by the difference between the two sets of op-amps.  This one is a semi-permanent (i.e. I take it home) installation on my work desk, running at 18-20v.  I get 3 hours on battery power from this one.  I'm intending to run it down each day for an hour or so, then plug it into charge throughout the day.  I'm using a Lenovo laptop power supply for this, they're pretty quiet from what I can hear.  Any tips for measuring actual noise?

I've gone with the AD8065/AD8066 combo in this one.

https://photos.app.goo.gl/QyGUFS5FFdxDb9zn6

I've got quite a few op-amps lying around, so I'll start rolling them around the handheld one to see if it improves.  I'm so happy with the desktop one I'm not going to touch it.


----------



## spbkaizo

I've started on another Pimetav2 portable amp, and wanted to just document and seek others opinions into my approach.

*POWER SUPPLY*

I'm intending to power this one from a Li-On battery, with the battery connected to a DC boost converter with dual voltage output, negating the ground channel and components, using a module I've found.  I'm still waiting on delivery of the module, but it is a buck boost converter which outputs to an arbitrary dual voltage power supply (+/-5v in my case).  The module is one of these https://www.aliexpress.com/item/32817163270.html

I'm intending to connect the power outputs into the respective rails, with V+ being connected to B+ on the PCB and the power switch being jumpered, with power being controlled via another switch on the batteries + line. 
*QUESTION*: The module claims to have 'soft start' but I'm curious about the supply to the pimeta, give the soft start on the amp is designed to operate with pre-charged capacitors.  Insights as to potential issues would be appreciated. 
*QUESTION*: The module has a switching frequency of 400khz.  Should I consider attempting to add in a LPF into the circuit, and if so where would be preferable?

The boost converter supply has standard PCB pin spacing, in a row.  As a result I'm going to effectively mount this on the scratch pad area, as it will keep things neat and tidy.  For the most part, this will be another SMD build so the only topside items will be the C2 caps, and the C1 caps. 

*BATTERY CHARGING*

For this, I'm going to mount a TP4056 onto a SOIC->DIP adapter as again, this give reasonable pins which will sit alongside the above DC boost converter.  The pins on the TP4056 are very low component requirements count, and I'm confident I can fit the required pin 2 resistor to ground by bridging it to either Pin1 of Pin2 on the same PCB (both GND), leaving 4,5,6,7,8 with appropriate connections.  I think it'll fit alongside the above module neatly. 

*CLASS A BIASING*

I've decided against this part of the circuit to save space, and allow integration of the power module.
*
BASS BOOST
*
For the first time, I've decided to incorporate a Bass Boost via the addition of a cap to R4.  This unit will be driving some open back headphones, which suffer from weak bass response.  R4 will be 1.8k, and the cap will be a Panasonic 1uF SMD PPS film cap.  I've gone this route as I don't want too much gain, but still want increased bass response.  I'm not adding a switch as I want it on by default.
*
TARGET HEADPHONES*

Headphones have high impedance drivers, 500ohm and are openback. 
*
OPALR
*
I've decided to give the new(ish) ADA4625-2 a spin in the first instance.
*
BUFFERS
*
I'm leaving the BUFL/BUFR out this time, as the ADA4625-2 datasheet indicates it can drive 600ohm loads, and I'd like to see how it performs.
*
COMPONENT VALUES
*
For completeness, here's the component values for the rest that I'm considering.
R1 = 1k or 2k, or 4.7k? (*QUESTION*: looking for aadvice here!)
R2 = 100k
R3 = 1k
R4 = 1.8k (+1uF PPS cap) = 2.8x Gain
R5 = N/A
R6 = N/A
R7 = N/A
POT = 10k
C1 = 0.22uF (==7hz cut off)
C2 = 330uF 16v
C3, C4, C5 as schematic.

Comments solicited, education welcomed


----------

