# PPA builders' thread



## Voodoochile

w00t!





 Everything measures correctly, albeit only cranked up to 15v for this test. I've got sound! Running DIP OPA627As and one HA5002 per channel. I'm going to bed now. Away tomorrow, but hope to play with this at 24v and another set of three buffers on Monday afternoon. This is to be my bench-testing PPA, so it's stuffed with SIP sockets all over the place. I will at least mount it to a nice base, with jacks in angle brackets.


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## ablaze

wow, nice pic 
	

	
	
		
		

		
		
	


	




 what power supply are you using?


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## Voodoochile

Anything that makes less than 25v!
	

	
	
		
		

		
		
	


	




 (the value of my C1s)

 The PS in the pic is an Agilent (HP) linear. I'll probably go with a wall-wart or half of a PS1 for the interim.

 Off I go now...


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## dokebi

More close-up pictures please. Any chance of a buffer stack happening?


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## Voodoochile

The four locations on the board are effectively 'stacked', so hard to imagine ever wanting more than four per channel.

 Anyone else under way yet?


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## ablaze

voodoo,
 I've posted some of your pics in my forum thread too,
 hope you don't mind. they're just too purrty


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## morsel

My, that was quick work, and nice pictures too, Voodoo! Be careful about using caps with a WV rating too close to your PS voltage. You don't need much capacitance, 1000-2000uF is plenty. Room for 8 caps exists so 220uF 35WV Silmics or Cerafines can be used.


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## BradJudy

Very nice VC, you tempt the rest of us. It will be nice to see it completed and I'm guessing it won't take long.


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## peranders

Where did Morsel's PPA thread go, the one wich one swede got a little grumpy over the commercial thing?

 BTW: PPA is looking good.


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## mclaren20

any chance of getting pics of the underside?


 NICE amp btw.


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## Chipko

Quote:


 _Originally posted by peranders _
*Where did Morsel's PPA thread go, the one wich one swede got a little grumpy over the commercial thing?* 
 

Wrong forum Peranders


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## tbdoah

Nice voodoo!


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## peranders

Quote:


 _Originally posted by Chipko _
*Wrong forum Peranders * 
 

Obviously! It was Headwize but while we're at it, I get "communication exception -336" at headwize, since yesterday. Somebody who knows more?

 Sorry for threadjacking.


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## Chipko

It's related to the user agent string. Headwize doesn't recognize your browser/OS combo and won't let you see the pages.

 Thread dejacked


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## xtreme4099

honestly the buf634 doesnt sound good on the ppa compared to the current ha5002 as the prefered buffer ... sound good is the key phrase, thats what an amp supposed to do to your music.


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## Glassman

could someone explain me how does the 'amplified and buffered' ground work? I know that symetricaly driven headphones sounds better, but I don't understand the PPA ground circuit..


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## Arzela

I have an Elpac wm071 wall wart. It's a +15, -15 volt supply. Could I use this to power the PPA? I'd just connect the + and - leads from the wart and leave its ground unconnected.


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## peranders

But you mean BUF634 is OK at a meta42 pcb with same opamp and the same multiloop feedback? I don't the think the difference is that dramatic.


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## peranders

Quote:


 _Originally posted by Glassman _
*could someone explain me how does the 'amplified and buffered' ground work? I know that symetricaly driven headphones sounds better, but I don't understand the PPA ground circuit.. 
	

	
	
		
		

		
		
	


	


* 
 

This is only a active voltage divider. If you have done this with two resistors it would have been rather thirsty. This is an electronic way to create a low impedance node with too much current consumption.

 I personally don't understand the benefit of this if you have no trouble to get +- voltage.


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## Chipko

So the groundchannel is just a fancy TLE2426 that can be omitted and bridged if you have a dualvoltage supply?


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## peranders

It can certainly be omitted if you have a split power supply.


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## Glassman

I meant something else, not that TLE2426 rail splitter, I know how this works but there are 3 channels each with AD8610 and HA-5002s, one for left channel, one for right and the third is for ground and I don't understand this.. is that something like active current sink or what??


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## peranders

The ground channel serves as a power buffer for the rail splitter. It may seems to be a little bit odd but this is the designers priviledge to whatever he/she wants.


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## ppl

peranders> think of this as the headphone Equiv to a BTL (Balanced to load Amp with the exception of the Negitive part not Inverted as in a Normal BTL design and the Negitive portion operating at unity gain.


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## xtreme4099

again i believe all specs have been posted on the above websites ...

 If it Sounds Good, It is Good - Duke Ellington aka JMT sig.

 And it does sound good...


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## peranders

Quote:


 _Originally posted by xtreme4099 _
*again i believe all specs have been posted on the website ...
* 
 

Can't find anything really. Am i blind? Where do you find any figures?

 EDIT: I found it!


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## xtreme4099

in other words its something new and improved that hasnt been done before except by our fellow diyers .. thx everyone...


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## aos

Quote:


 The real problem may be that there isn't any sound card out there that can provide the performance necessary to elucidate the differences between a PPA and a META42, so RMAA dutifully reports that there is none - not something you'd really want to share with the masses, despite the fact that the lack of any difference might be entirely due to the sound card. 
 

Not true at all. You can very easily see differences in noise performance, dynamic range performance and especially channel crosstalk. I am not talking about PPA specifically as I haven't built it yet but I did measure different amps, sources and variations of the same design and you can always pick up differences. Distortion - unless to a headphone - is usually low enough that your point may have some merit but otherwise... Maybe what you need is a better soundcard. I bought a Revo just for the sole purpose of measurement as it has the second best ADC chip from AKM. And indeed it has 104dB + noise performance. Audigy is much worse and indeed if sound card is worse than what you're measuring then the results are meaningless.

 Also in my experience, test results are very repeateable and don't really vary from run to run. You can of course debate merits and demerits of the methods they use. For example the real value of channel crosstalk is masked by the noise floor, i.e. if it's better than noise floor then the value of noise floor will be shown. You could probably use auto-convolution over a long period of time to get the real value but of what use it would be is questionable. You can also debate if certain flaws are audible or harmful to the sound or even if the whole thing matters subjectively. But RMAA is very useful to pick up potential trouble with a particular amp.


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## Squalish

Controversy aside, I wanted to ask about something. How does the PPA do w/ EL2001's?


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## ablaze

*back to the topic*

 tangent's updated his step-by-step guide! 
	

	
	
		
		

		
		
	


	



http://tangentsoft.net/audio/ppa/amp/steps.html


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## aos

Quote:


 tangent's updated his step-by-step guide! 
 

Damn that "expedited" mail. It's been a week now (admittedly with a long weekend) and my board is still not here :~(. Should've taken the FedEx route, I'd have it finished long time ago.

 It's very nice with pictures and all. Say what you will (i.e. disagree with parts of the content or the way it's presented) but I think he's pouring a lot of time and effort into these guides. These things take time and your head will hurt after a bit, trust me.


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## Voodoochile

Well, this will all be very interesting to see pan out. I have a GTXP, a Phillips card, and the onboard Analog Devices Soundmax in various PCs, the soundmax has both toslink and coax digital outs which I can connect to the superdac. The superdac has balanced outputs...I have not yet really though about taking any measurements in RMAA, but perhaps it might be something to look into.

 On to the section for those curious but less technically astute (no offense to anyone, as this includes me). This testbed PPA was built to spec right off the schematic, and I had an issue with hiss at first, which turned out to be my negligence in jumpering the bass-boost switchpads (who really needs a feedback loop anyway?). Thought I had in the back of my mind, but I had actually done the power switch pads, and my mind was telling me it was all squared away. Anyway, now that they are closed*, the hiss is gone, and DC is down to 2.1mV and 1.9mV, which is super, and there is no hiss, of course.
	

	
	
		
		

		
			





 .
 I'm powering it off a bastardized version of a half-PS1 type PSU that is outputting a regulated 24.4v (my on-PPA caps are 25v r-t-r).

 It is a 'really nice amplifier' is what I have to offer so far. I have not had the luxury of extended listening periods as of yet, but do look forward to more time soon! It is still on the bench with the HD570s and Sony DVD player. Yeah the cans are a bit sketchy, but it's what is on my workbench. I hope to get the amp upstairs shortly to hook up to my HD580 C541i rig, which is a great workable rig, though not exotic. I'm not really the reviewing type, but the PPA is a very smooth and responsive amplifier. It initially seems very powerful, yet articulate/responsive. I have the OPA627s in it for now out of convenience, but plan to mount a few more 8610s onto Browndogs so I can load a set of them. I also have two buffers per channel at the moment (burning in for the last 20 hours now), but will populate the other six locations this weekend. I'll prolly replace the six in there now first, and repeat the burn cycle, then load all twelve buffers. I have not done any subjective testing side-by-side as of yet.

 *the S2 switchpads are for the bass-boost config, which I did not want to implement on this breadboard-style PCB. You thus leave out those components, but still need to jumper the pads to enable the feedback loop to function.


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## ablaze

aren't we going OT here? this thread was for PPA building experiences to share 
	

	
	
		
		

		
		
	


	




 can the mods split the relevant posts to a new topic on testing methodology?


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## ablaze

ppl,
 would the PPA be powerful enough to drive AKG K1000s?


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## ppl

Yes if you have a 24 volt power supply. BTW you are so Right this is a builders thred and all these apperent new concerns that people have should have been done in a timley manner in the thread located hear http://www4.head-fi.org/forums/showt...&highlight=PPA


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## ablaze

thanks ppl. I can't wait to start on it myself. 
	

	
	
		
		

		
		
	


	




 anyway, I've asked JMT to split the posts into a new thread..hope he checks his PM soon..


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## ppl

cool then this can be back to Building issues.

 The PPA will put slightly under 400 mW into the AKG K1000's and get about 100 dB of SLP. the K1000's require lots of voltage and that is why thay recomend driving them from a Loudspeaker amp. However if normal listening levels are used then the PPA will work


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## JMT

Quote:


 anyway, I've asked JMT to split the posts into a new thread.. 
 

 I gave it my best shot. Some of the posts I left intact so the subsequent posts would make sense, so you may see some duplications.


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## morsel

Sorry, but I am going to have to repeat these answers since my original post was moved to the other thread. Perhaps the original thread contents and order could be restored or a second attempt to sort the threads be made, as both threads are sort of scrambled now. 

 Peranders: 4 buffers result in less distortion, and tighter, gutsier, more accurate bass. One buffer is not as good. If you refer back to the many threads that discuss the HA5002 and BUF634 you will see that many people have listened to them and prefer the sound of the HA5002. It is also cheaper and has no output protection, which results in lower output impedance.

 Arzela: You can use your ±15V Elpac as you suggested only if you reduce the voltage or choose opamps that can handle 30V. The AD8610 should not be subjected to more than 24V.

 Peranders: The current META42 still uses Elantec buffers. The reason the BUF634 was chosen for the next META42 incarnation is because the EL2001/2002 are discontinued and the BUF634 can be operated in low or medium bandwidth mode to save power. The current META42 does not have differential output, either.

 (Glassman) "could someone explain me how does the 'amplified and buffered' ground work?"
 (Peranders) "This is only an active voltage divider."
 (Chipko) "So the groundchannel is just a fancy TLE2426 that can be omitted and bridged if you have a dualvoltage supply?"
 (Peranders) "It can certainly be omitted if you have a split power supply."

 Not true. I quote my description of differential output from the ppa website:
  Quote:


 The PPA has 3 amplifier channels: left, right, and ground, which use the same output buffers and noninverting opamp topology. The ground channel sources and sinks the return current from both drivers which would otherwise have been dumped into signal ground or power supply ground. This shifts responsibility for the high current reactive load of the headphones from signal ground to the supply rails of the ground channel buffer, thus removing the primary source of signal ground contamination. The drivers have symmetrical output buffers with equal impedance and transfer characteristics on both sides, rather than an output buffer on one side and the large capacitor bank of the power supply ground on the other. This results in lower output impedance and greater linearity.

 Standard headphones have 3 wires: left, right, and ground, which is tied to the negative side of both drivers. Standard headphone amplifiers have 2 channels: left and right, with signal ground or power supply ground used for the return path from the headphone ground wire. Fully balanced headphone amplifiers have 4 channels, require custom 4 wire headphones, and are typically operated in bridged mode, which doubles the output voltage and quadruples the power by using inverting and noninverting pairs, but does not offer symmetrical transfer characteristics due to the difference between inverting and noninverting modes. 
 

As PPL says, be sure to read the various PPA websites.


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## Voodoochile

Installed the other six buffers tonight. Here is an updated pic with the 24.4 volt PSU and the buffers...




 No, I have not measured it yet, but when I do, it will be in the other thread.


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## aos

Just finished mine. Listened only for a few minutes and with MP3's of all things. I'm gonna order some well deserved pizza now but the first impression - with just one HA3-5002 per channel - is that the bass is very powerful and well controlled.


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## dokebi

Based on current listening do you guys think the sound resembles the meta or any other amp?


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## xtreme4099

the soundstage is much bigger .. better imaging ... clearer, quicker more pronounced, snappier than the meta. ppa in a stock config is overall much better than a meta42 in a max config.


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## fewtch

Quote:


 _Originally posted by aos _
*Just finished mine. Listened only for a few minutes and with MP3's of all things.* 
 

Sorry to go partially off-topic again... IME, a better amp can actually make MP3s sound better, rather than be more revealing of flaws in this case. I believe this is because the psychoacoustic algorithms involved in lossy compression expect a theoretically "perfect" response from equipment -- part of the auditory prediction performed by lossy encoders. Something many people may not be aware of (and a welcome benefit for those of us who have our amps hooked to a sound card, and a few MP3's floating around).


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## ablaze

Quote:


 _Originally posted by xtreme4099 _
*the soundstage is much bigger .. better imaging ... clearer, quicker more pronounced, snappier than the meta. ppa in a stock config is overall much better than a meta42 in a max config. * 
 

what is a ppa "stock"? ie. 12 buffers or 1 per channel?

 just got my PPA boards todae


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## xtreme4099

1 per channel .. barebones ppa ...


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## Voodoochile

My guess is two buffers per channel... but that's like jumping almost all the way into the pool, I figure. You are only saving about 5% cost by going with 6 instead of 12. For those who think it looks outrageous having that huge swath of buffers, remember that even a meta often has 10 to 12 buffers in it. These will surely run cooler spead apart as they are, especially if you run them near their limits.

 I can see that one buffer is barebones, but I don't know if I'd consider it to be a base config. The improvement from two is very significant.


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## ablaze

you compared them? cool 
	

	
	
		
		

		
			






 hey guys, how do I solder my smd opamps to the board (ie. not using the DIP-8 adapter) more specifically, how do I know how to orientate the opamps?


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## ablaze

vc, could you post a nice big close-up pic of your updated ppa


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## Voodoochile

The chip on the top of this browndog is the same... see the notch near the lower left leg? That is pin one. The screen on the board shows the index notch... the pin one goes at that end.
Link


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## Voodoochile

Here is some detail, but remember that I'm presently using the OPA627s in mine:


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## aos

Snappier is a good term to describe it. The percussion really snaps at you now.


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## Voodoochile

I agree, aos. It sounds more 'discrete' to me than a META, if that makes sense. I hate to use the word dynamic, but it fits, I'm afraid.
 I'm not trying to start a war here, believe me.


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## morsel

The full configuration of 12 buffers, i.e. 4 buffers per channel is stock/standard as far as I am concerned. Tangent has this to say on his website:  Quote:


 You don't need to parallel buffers to get good sound. Just one per channel still sounds pretty darn good. Sticking with one buffer per channel is reasonable if you want to save money or reduce current draw when running from batteries. 
 

 I do not encourage using fewer buffers as sound quality is compromised to some extent and the remaining buffers become more vulnerable to damage from accidental output shorting. Tangent, PPL, and I do not agree on everything. Hopefully it is understood to be normal and inevitable that we have our own differing opinions on some issues.


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## Voodoochile

As I noted earlier, you don't really save much by going with 6 versus 12, either. It's too nice an amp to skimp on another few dollars in parts. After you have sprung the bulk of the outlay, at least!


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## Arzela

Do all three opamps have to be the same?
 I was thinking of trying 637's in the left/right channels and an ad8610 in ground (I have
 637's on hand, and no money to buy 627's 
	

	
	
		
		

		
		
	


	




 ).


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## morsel

The amp will work, but you may get a blend of Analog Devices and Burr Brown sound. I have not tried it.


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## aos

I am using AD8610 in ground and OPA627 in l/r. Works fine. Finally some use for OPA627, I got them as samples and never used them. I don't have any soic to DIP adapters (the ones tangent sent me were somehow destroyed during shipping) and I didn't want to solder AD8610 in l/r just yet. I don't think the ground channel's opamp should impact the sound much (or biased into class A) but for the heck of symmetry you should probably just make it all the same.


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## morsel

For the sake of flexibility and future upgrades I would not solder opamps to the so8 pads. Before you know it, the latest and greatest uber opamp will come out, and you will probably want to try it.


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## BradJudy

So what power supply designs is everyone using and are you planning on switching to the PPA PS once it's available?


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## morsel

The Elpac WM080-1950-760 24V wallwart is a good choice.


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## guzzler

i'm sure this has been answered before, but what is the difference between the different HA3-xxxx series?? RS seems to stock everyone apart from the HA3-5002, eg the HA3-5033... is this pin compatible and is it better or worse the 5002??

 g


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## guzzler

sorry, to elaborate:

 the HA3-5033 is in a TO99-5 package... the one i saw on RS in a DIP8 was the HA3-5020-5... same question above applies!

 g


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## morsel

The HA-5002 is not the same part as the HA-5033, or the HA-5020 for that matter, which is not even a buffer. The flavor of HA-5002 you need is the HA3-5002-5, which is the PDIP package. Do not use the HA-5033, it has a quiescent current of 21mA, lower output current, higher output impedance, and does not sound as good.

HA-5002
HA-5033

 Ah, and see below, PPL likes the HA-5033.


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## ppl

These are the Buffers that will drop right in the PPA sockets 
 (1)The recommended HA3-5002-5 in P-Dip
 (2)The Alternative HA3-5033-5 In P-Dip
 (3)The Alternative # 2 OPA-633KP In P-Dip

 The Above all will work great in PPA sockets. The HA-5033 and OPA633 are rated at half the output current of the 5002 so if these are used I recommend a full complement of buffers with any headphones. Also since each 5033/633 consumes 20 mA vs. the 5002 8 mA your Class A output is improved Heat sink these also as they get quite warm without one. Several glue on Dip sinks are available.

 The HA2-5002-5 is a metal can version of the Recommended HA3-5002-5, However the pinot is different and leads need to be bent to match the Dip versions.

 Links>
http://focus.ti.com/docs/prod/produc...pfsection=desc
http://www.intersil.com/design/param...asp?pn=HA-5033
http://www.intersil.com/design/param...asp?pn=HA-5002


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## Squalish

What about the el2001cn?


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## morsel

The EL2001 is not pin compatible with the PPA, and was discontinued last winter.


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## ppl

While I do Like the sound of the OPA-633 and HA-5033. I also like the HA-5002. my list is Buffers that are a plug in alternative to the 5002's. This will allow people to Roll Buffers just like thay presently do with op amps and Tubes. I leave what sounds best up to you the Builder.


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## 10SNE1

Per Tangent's guide to parts selection, R1 should be equal to the sum of R3 and R5 feedback resistors to balance the opamp input impedances.

 What would be the consequence of having R1 being 100 ohms less than the sum. (I have plenty of 4.22K resistors, the recommended is 4.32K if R3 is 3.32K and R5 is 1K).

 It seems to me that since it follows the 50K volume variable resistor, that 100 ohms is no big deal.


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## morsel

You are right, it's no big deal. These are FET input opamps, not bipolar input.


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## Arzela

I just built my PPA. It sounds great with the 637/ad8610 combo. Nicely detailed, dynamic, and well-defined bass. Great design
 ppl, Morsel, Tangent, et. all!

 A word of caution for others: I put a Molex connector in for the input near the pot. Consequently, the pot was a tight squeeze (even after repositioning its pins and
 cutting of a plastic tab on the back).

 The DC output is low. Average of 2 mv across the channels, but a max of 100 mv or so and a min of -100. Most probably my source...

 A question: I have 2240 uf in the big caps. Would doubling this (from 4 C1 positions filled to
 all 8) help or hinder?


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## ppl

DC offset should be measured with the Volume at Min so as to not be influenced by any input sources with potential DC on it's output. BTW did you add Bass Boost?

 Regarding the idea of using AD-8610 in the ground Channel and other types in the gain stage...... This will work and might impact the sound but as pointed out by Morsel any difference will be quite small and may not be heard.


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## morsel

2240uF is more than plenty. Adding more capacitance is unlikely to improve the sound of the amp. Extreme excess capacitance can cause power supply problems. I'd leave it alone.

 If you are using 1000uF Panasonic FC you only need 1 or 2. There are 8 positions on the board for high end audiophile caps such as the 220uF Elna Silmic. Kurt and I were unable to hear any difference between the Elna and Panasonic caps.


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## Arzela

No bass boost. Those DC figures were with
 the volume at 3/4 (loud!) . With the volume at min,
 the DC is stable at 1 mv or less.


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## morsel

Since you are not using bass boost, did you remember to jumper S2?

 BTW, Ding! 500 posts. Scary.


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## Arzela

Thanks to Voodoochile's post, yes the S2's are
 jumpered. 

 I'm going to bias the 627's into class A next. I hope Tangent's site explains
 how to match the trannies...


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## Arzela

Oh, just remembered. If only 6 Q3's are used (two for each channel), in each channel, which of the four
 positions are populated?


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## morsel

It does not matter much, I'd populate the upper ones.


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## aos

Quote:


 Per Tangent's guide to parts selection, R1 should be equal to the sum of R3 and R5 feedback resistors to balance the opamp input impedances.

 What would be the consequence of having R1 being 100 ohms less than the sum. (I have plenty of 4.22K resistors, the recommended is 4.32K if R3 is 3.32K and R5 is 1K).

 It seems to me that since it follows the 50K volume variable resistor, that 100 ohms is no big deal. 
 

Actually tangent's calculations are incorrect as they don't take into account the impedance of the pot. As the pot is variable, the way this is typically done (as per Walt Jung article I think) is to do the calculations assuming the value of the pot at the normal listening volume. Then you have the upper and lower part of the pot in parallel, and in series with the input resistor.

 In addition, it wouldn't be exactly 4.32k even at full volume of the pot because the 1k feedback resistor is calculated in paralllel with 10k, which yields 909 Ohms, added to 3.32k, so 4.22 is actually almost right. Of course, two 1M should be taken into account too but they are two to three orders of magnitude larger so their impact would be quite small. Anyhow this isn't critical, and with pot you can't get it right anyway. Also, I don't think all opamps benefit from matching the impedance (there's another reason as below).

 The other reason for balance of input impedances as seen from the opamp inputs - again according to Walt Jung - is because input impedances of the opamps are non-linear. But they will cancel each other out if they are at the same bias point on both input terminals, which balancing the impedance (not just resistance, impeedance) will achieve.


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## tangent

Quote:


 what is a ppa "stock"? ie. 12 buffers or 1 per channel? 
 

It's kind of a meaningless question. Contrast the META42 where going beyond 1 per channel meant stacking, which is not really part of the board, so you could reasonably argue that 1 buffer per channel is "stock" on the META42 board. With the PPA, anywhere from 1 to 4 per channel are equally supported.

 If cost is a big problem for you, it's okay to skimp on buffers. Just beware the safety risk Morsel alluded to (also discussed in my docs) and that you're not getting all of the potential out of the board that you could. You might study the distortion graphs in the Benchmarks section of the docs to understand what you are giving up in the way of quality.

 The best reason to use fewer than 4 buffers per channel is when you have a power supply current issue. Perhaps you're using batteries and want longer lifetime than 4 buffers per channel allows. Or, perhaps you've got a power supply that won't put out the ~150mA that a fully loaded PPA requires. Reducing the buffer count is a perfectly reasonable way to solve these problems.

  Quote:


 how do I solder my smd opamps to the board 
 

There's a silver dot on the board near pin 1 of each SO-8 position. Pin 1 on the op-amp is marked by a small divot or other marking. If you can't see it at first, use strong light and look closely -- it's there.

  Quote:


 the HA-5033...does not sound as good. 
 

I came to that conclusion when testing that buffer in a META42. It sounds veiled and slow in that amp. I haven't tried a HA-5033 (or OPA633 -- same thing, different suppliers) in a PPA, but I wonder if it might be a euphonic combination with a snappy op-amp like the 8610. I may indeed have to try that....

  Quote:


 I hope Tangent's site explains how to match the trannies... 
 

You don't need to use "matched" transistors in the PPA. You can use random JFETs and then put different R8 values in each channel to account for the differences in your transistors. If the docs aren't clear on this point, send me a message and I'll try to clarify the process.

  Quote:


 If only 6 Q3's are used (two for each channel), in each channel, which of the four
 positions are populated? 
 

The left pair in each group is on the negative rail, and the right pair are on the positive rail.


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## ablaze

thanks for answering our queries tangent 
	

	
	
		
		

		
			





 btw, need some help with configuring power rails. 
  Quote:


 You should have chosen your power rail configuration by now. Depending on what you chose, you will need 2 to 12 Q3s, and 1 to 3 TLEs.

 If you chose to have separate rails for each op-amp, add the 6 or 12 Q3s and the three TLEs.

 If you chose to have just one set of op-amp rails, put the 2 or 4 JFETs into Q3G, and populate TLEG. You will also need to add four jumpers to tie the left and right channel V+ and V- rails to the ground channel's V+ and V- rails; use the 8 wire pads near the centerline of the board, the ones with the dashed silkscreen lines going between them. Be sure not to mix up V+ and V-! 
 

this is my first amp, and I've really no idea whats the best configuration to use. I'll be using the 637s for the LR channels, and 627s for ground as you suggested, and using a 24v DC psu (won't be using batteries). opamps unbiased to class A for now. 12 buffers. what do you suggest is the best way to configure the power rails? (anything else you need to know to help you help me decide? 
	

	
	
		
		

		
		
	


	




)


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## tangent

Quote:


 need some help with configuring power rails. 
 

Read the section on Q3. It gives you a simple "default" configuration. At your level of experience, you shouldn't do anything different.


----------



## ablaze

pls del


----------



## morsel

(reply to a deleted wiring question)

 No, that would short out the power bus. The square pads are positive, the round pads are negative. Bridge the 3 positive rails together, and the 3 negative rails together. Please look at the pcb layout, that should make the connections obvious to you.


----------



## ablaze

thanks morsel. will do that. pardon the newbie questions. first diy amp


----------



## morsel




----------



## Arzela

Is this normal:

 Supply voltage: 23.82 V

 Potential across opamp power pins: 22.38 V


 Potential across buffer power pins: 23.53 V

 ??


----------



## morsel

1.15V drop from the buffer rails to the opamp rails is normal.

 .29V across the input protection diode is rather low, I would have expected more like .65V.


----------



## Arzela

Thanks Morsel, that clears things up 
 for me. I do have .324 across the diode.
 I'm not sure what the diode is excatly, but
 it's marked IN5819 (I guess I do
 know after all 
	

	
	
		
		

		
		
	


	




 ). I had some left
 over from my META 42.

 The voltages across the three opamps differ by .5 volts or so (22.44 left,
 23.05 ground, and 22.56 right to be exact). 

 I presume this is due to differences in the unmatched 5486's that I used to configure
 the rails (or perhaps, having 637's in L/R and an 8610 in ground). If it
 is due to the trannies, would correcting things lead
 to a noticable improvement?

 The L/R seem okay, they are within 1/2 a percent
 of each other. The ground seems high though...


----------



## morsel

The AD8610 draws about 3mA, the OPA637 draws about 7mA. If you are using 1 2N5486 per rail per channel, and they happen to have an Idss closer to 8mA than 20mA, that would explain the difference in voltage on your opamp rails. In any case, it's not a problem.


----------



## ablaze

Quote:


 _Originally posted by morsel _
*




* 
 

so I jumper across the holes you marked? thanks Morsel. you just saved me the "thinking". You guys are greeat


----------



## ablaze

a lil pic of my own!




 should I remove that damaged cap, or is it safe to leave it there?


----------



## eric343

It looks like you melted through to the internal metal plates. Remove the cap, short the leads, and check it with a DMM's continuity tester/ohmmeter function to make sure it isn't shorted. What you should see is that the resistance of the capacitor goes up over a short period of time, and gets reset when you short the leads. If the resistance stays low or reads <1ohm, toss the cap. If the resistance is immeasurably high *immediately* after shorting the leads (doesn't climb at all), then toss the cap. Otherwise, it's fine.


----------



## ablaze

thanks eric. ok, cap looks alive. resistance rises. then resets when shorted. thanks


----------



## ablaze

hmm. wired everything up. no power. argh.
 what voltages should I test? the LED doesn't light up. and I've checked that the DC jack's wired correctly, polarity-wise.


----------



## Arzela

Do you have S1- and S1+ jumpered?
 They are near the diode.


----------



## ablaze

i got them attached to a 2-pole switch. 
 if I posted a pic would it be better?


----------



## Arzela

A pic would be good...


----------



## ablaze

ok pics 

 (I'm waiting for someone to point out some silly mistake that I made 
	

	
	
		
		

		
		
	


	




)


----------



## ablaze

btw, those are 637s on the LR channel, and a 627 on the ground channel. 4x2N5486s at Q3, V+ V- of LR tied to G's V+ V-, following morsel's instructions earlier in this thread. RLED 10k resistor used.


----------



## Arzela

It looks fine to me.
 Are you getting power at the C1 positions? Is your
 switch wired correctly?


----------



## ablaze

yeah checked and double-checked the switch. 


 edit: maybe you should teach me how to test for power. multimeter with the leads at the populated or unpopulated C1s? voltage or current?


----------



## Arzela

Check voltage at an unused C1 position.
 You should get the input voltage minus around .6 volts. If you don't have voltage here,
 the next thig to check is the diode
 (You should have .6 v or so across the diode). Then the switch, then the dc jack wiring.

 [EDIT] Sorry, I meant "voltage" not "power" in my previous post


----------



## ablaze

ah crap. turns out the DC jack was screwy! alright, at least I see my LED light up now. testing voltages now..

 I'm getting near 0 DC offset on L and R, but the ground channel has continually rising DC..hmm..

 also, the buffers should get "warm" right. I've no idea what "warm" is, cos if you ask me its hot. but still comfortable enough to leave my finger there. is this "warm"?


----------



## Arzela

My buffers get warm, uncomfortable to touch, but
 bearable. Maybe 100-120 F.

 How are you measuring DC on ground?
 What matters is DC from left output to 
 ground output, and R out to G out.

 Though it might be anamolous to have
 large DC from a channel to signal ground
 (Morsel would know), it won't harm your
 phones.

 Sounds like it's time to test some
 (cheap) headphones


----------



## ablaze

measured L,R,G to input ground on the board. is that right?
 anyway, L/R output to G output produces that same continually-rising DC too. argh.

 also, I think my Q3s are configured wrong. I'm only getting 14-15v across each opamp. 4x5486s in Q3G (none in Q3 L/R) is wrong?


----------



## Arzela

You do want to measure the DC that
 the headphone sees; namely, referenced to
 output ground.

 How high does the DC rise?

 What is your input voltage?


----------



## ablaze

Quote:


 _Originally posted by Arzela _
*You do want to measure the DC that
 the headphone sees; namely, referenced to
 output ground.
* 
 

yeah, it keeps rising too, with ref to G-output . it just kept gaining, until I turned it off when it exceeded 20mV. didn't wanna damage anything 
	

	
	
		
		

		
			





 input voltage, measured across the C1 holes, is 23.85v or so. buffers have around there across, but across the opamps there's only 14v or so.


----------



## Arzela

Most probably, your jumpers are not
 soldered in correctly.

 I can't comment on your Q3's,
 but it does follow tangent's advice.

 Are you measuring the DC with a cd
 player (or other source) connected?
 The DC might then be the sources fault.


----------



## ablaze

you're talking about the V+ V- jumpers right?

 and no, I've got no sources connected yet. 

 anyway, I'll try resoldering the jumpers. hope that'll work


----------



## Arzela

Yes, the V+, V- jumpers. 
 Check the voltages here as well.
 If they are off, then your Q3's are most likely screwy (check for solder bridges).
 If they are correct, the TLE should be checked next.

 (ahem) 500'th post


----------



## ablaze

hey congrats! 
	

	
	
		
		

		
		
	


	





 checked the jumpers. getting +8v/-8v here. checked the jumpers, jumpered points have the same voltage. at least my soldering's passable 
	

	
	
		
		

		
		
	


	




 hah

 resoldered the Q3s. no bridges. 

 how should I check the TLE?

 btw, the TLE comes with 3 pins in a line, whereas on the board its staggered. 
 so the TLE looks like this
 1_2_3

 board looks like:
 1___3
 __2

 so I just bend pin 2 to fit on the board right?

 (ignore the underscore "_" I'm just trying to get the staggering to look right)


----------



## Arzela

Hmm, you should be getting
 higher figures at the jumper positions.
 About 1 volt less than the voltage across the buffers I think. Perhaps you should wait for
 some expert advice here...

 Your TLE sceme is correct, just check for
 bridges. And oops! I just noticed on my board, make sure
 all the leads are actually soldered to their
 pads!


----------



## ablaze

thanks arzela. I've checked and its all soldered properly, no bridges. thanks for helping me out thus far though!


----------



## morsel

The OPA627/637 draw about 7ma each. That's about 21mA total. You are bypassing the separate FETs and TLE for the L&R opamp rails, using 2 FETs per rail on the ground channel to power all 3 opamps. The 2N5456 has an Idss from 8 to 20mA. If yours are only 8mA each, that is 16mA total, insufficient to drive the 21mA your opamps require, not to mention cascode current sources for them which have not been added yet.

 In your configuration you either need to measure your FETs to be sure they can supply the current, use more of them, or use higher Idss FETs such as the 2N4392 with an Idss of 25-100mA. I would yank out your 4 FETs and measure their Idss. Assuming they are too low and you have more of them, try using 1 pair per channel if the Idss is sufficient for your opamp + future cascode current source. You can still use 1 TLE with the jumpers.


----------



## ablaze

shucks. looks like there's no way I can work around this. my initial plan WAS to use separate rails for each opamp, but I under-ordered the 5486s. I was hoping I could make do with this config for the time being. damn. looks like I'll just have to go get more..thanks again morsel


----------



## ablaze

morsel, one thing: is the rising DC offset on my ground output related to this issue?


----------



## ppl

ablaze> I noticed you do not have C6G installed. With the OPA-627 this will be unstable without C6G. this cap IMHO is not optional it is REQUIRED to asure stability. this is causing the High DC offset with the ground channel .


----------



## hornist

I notice that Panasonic FC capacitors are recommended. FK capacitors have lower ESR, better reliability, and are only a little more expensive. But they only come in surface mount - is that out of the question on these boards?

 Thanks.


----------



## ablaze

added C6. added separate rails. all the voltages look good now. do I dare to take a listen? 
	

	
	
		
		

		
		
	


	





 oh, whilst testing I accidentally shorted the V1+ and V2- pins on one of the buffers! sparks flew 
	

	
	
		
		

		
		
	


	




 how to tell if I killed it? voltages on it still look fine though..


----------



## ablaze

woohoo! its alive! 
	

	
	
		
		

		
			




 my first DIY amp hehe

 I'm getting a lot of noise from the middle position of the pot onwards..hmm..wonder if its my crappy interconnects..


----------



## ppl

ground the Pot shaft or install the Amp in a metal case


----------



## ablaze

my pot's already grounded to input ground. 

 more questions: when biasing the 637s and the 627 how much bias should I aim for? 1mA? 2mA?


----------



## ppl

Then disconnect the input cables and see if the noise goses away this would indicate that interfearence is being injected from the Input interconnect cable and thay would have to be real Junk cables or you have some serious RFI in the location of your system if this hum goes away with no input connected. By your statuing that the noise gets louder as the Volume is turned louder this may be what is happening to you so mabe move the equipment and or get decent cables.

 1-2 mA is fine anywhere in that range up to about 3 mA


----------



## ablaze

I suspect its my interconnect. its a crappily done up one to test the amp.
 and the hum is more apparent with the source disconnected. sounds like grounding issues? 

 anyway, biased L-G-R 
 1.67mA-1.72mA-1.58mA..


----------



## ppl

is this hum still apperent with no input connected? Your Biasing is ok


----------



## ablaze

ok. with source connnected, there's only noise from about 3o'clock onwards. hissing.

 with source DISconnected, there's a persistent hum, that increases with volume, apparent from about 11o'clock onwards. doesn't sound like hissing, more like a hum/buzz.


----------



## ppl

somthing is wrong this Amp should be Dead quiet with no source connected. check that Buffer that got shorted. remove it test. then try just one buffer per channel ones that were not in the same channel as the ones you shorted. also is the Bass Boost switch posistions jumpered. Can you post a clear pic of your board both top and bottom.

 BTW is the Amp encased if not this will cause your hum.


----------



## ablaze

alright. will do that later.

 quick question: bass boost switch you mean S2 right? thats the only bass boost switch right?


----------



## ppl

yes S2L & S2R and again try the amp inside a metal case hum should go away if the amp is working properly. what is the DC offset on each channel measured from the Input ground with the OPA's this should be less than 3mV on L & R ch and 0 on Ground 0.02mV typical


----------



## ablaze

thanks ppl. I'll try it out these couple of days. 

 dc offset's <2mV on L and R, and 0mV on the G output. referenced to input ground.


----------



## jasonhanjk

Are you using the 50k or 100k pot?


----------



## ppl

OK put it in the metal case and ill bet your hum will go away. I notice hum in uncased amps next to Monitors and floresent lights even 6 ft away but put in case gone Dead quiet


----------



## ablaze

ok found this:
 when my rcas are connected to the board, the hum is there.
 even with the source disconnected.
 but when I disconnect the rcas from the board completely, the hum goes away! is that of any significance?


----------



## ppl

sounds like you are indeed picking up outside noise and the Jacks are acting as an antenna Again put the amp in a case and make sure the jacks are grounded to the case and all should be well


----------



## Voodoochile

That is all true, but I'm still surprised you are getting that kind of noise. The picture I posted on page one of this thread showing my amp running on the bench, is underneath an eight-foot 2-tube fluorescent fixture, and there is a monitor right behind the resistor boxes in the pic, on top of the old receiver.

 Perhaps the shortcoming in the rail isolation config (as it is standing now while waiting for your other jfets) is also contributing to the sensitivity? Or maybe I have a well-behaved light fixture. Also, I'd replace that burned cap, even if it tests OK. They are not too expensive.

 Another question:
 Has anyone compared running the leads from the RCAs to the rear pads on the board versus through the front pads via shielded cable housing? I know that there is a ground plane above the traces on the PPA board, but they are straight and parallel, so I'm wondering if a shielded twisted cable config is better or worse that the board-routed traces. Just another conveniently-included option to consider.

 My leads are presently going to the front pads as a temporary measure, as I would like to use the rear pads when casing up, at least for aesthetic reasons.


----------



## aos

Quote:


 Has anyone compared running the leads from the RCAs to the rear pads on the board versus through the front pads via shielded cable housing? 
 

I did, measurements are in another thread.

 ablaze, use the shielded RCA cables. Those cheap $2 cables you get with every piece of equipment are not shielded or twisted so if it goes next to any kind of EMI source it'll pick up noise. You can also try ferrite cylinders on the cable (there were threads about this ferrite cylinders oh, 2 years ago on Headwize).


----------



## Voodoochile

Found it, thanks aos. Don't know how I missed that first time around.

 Maybe I'll keep it wired to the front, and run the cable under the board to the back.


----------



## aos

You'll have to run actual cable (as in shileded, twisted pair, whatever) to the front otherwise you stand to get worse results than using the rear pins - that shielding on the PCB will protect from noise and it's good it's there. You should run a measurement yourself to see if you're having the reduced crosstalk effect before going through the big trouble of wiring insides differently (a simple wire is simple, but a shielded cable is a royal pain).


----------



## Voodoochile

Yes, that's what I was contemplating. I braid some teflon and insert it into a copper braided sheath, then cover with fiberglass tubing. It's not difficult really, but it is surely more work than snipping and soldering a set of straightwires.

 Thanks for your input. I will try to get some measurements done soon.


----------



## ablaze

more details on the problem:
 source disconnected. IR,IL,IG connected to rcas.
 I tried turning off everything this time, so just the amp on the table, no electrical appliances around.

 lifting the amp off the table reduces the buzz about 20%
 but once I hold the rca jacks, or the knob of my pot, ALL the noise disappears! perfectly silent!

 so you think if I use a METAL case, my problem'll fixed?

 btw, voodoo, I've since added the remaining 2 TLEs and populated the Q3L/R with 4x5486s so its on separate rails now. why's my amp so vulnerable to noise


----------



## jtfoo

Have you try running from a battery? Sometimes a bad PSU might introduce buzz.


----------



## Voodoochile

I'm using the same jfets on my rails, ablaze... mine check out to about 12mA each. Did you remove the jumpers connecting the ground channel PS to your L/R channel PSs? With the extra TLEs and isolation jfets, they are no longer needed.

 What PSU are you using?

 Mine had a bit of hiss until I completed my feedback loop by jumping S2 (doh!), but is since silent. Your pot appears grounded. Do not connect your output common to your input common whatever you do. Your input common can be and should be common to the ground with your pot.


----------



## ppl

Yes or line the inside of your wood case with Aluminium foil and or copper sheet some are self adheasive then connect RCA and input ground to Foil and all should be well This is evident by the fact of you totching the RCA jacks or the volume the hum is gone seems to point in a shielding direction


----------



## morsel

"Did you remove the jumpers connecting the ground channel PS to your L/R channel PSs? With the extra TLEs and isolation jfets, they are no longer needed."

 Jumpers will defeat the purpose of having separate opamp rails and cause multiple TLEs to fight each other. Jumpers must be used with 1 TLE and never used with 3 TLEs.

 Ablaze, as was previously suggested, your RCA cables can act like antennas when not connected to anything. If you turn up the volume the amp will amplify AC hum picked up by the RCA cables. This can be exacerbated by ground loop problems and nearby motors, monitors, or dimmers.

 If you plug an RCA cable into a normally functioning amp and touch the signal pin, the amp will hum because it amplifies the signal picked up by your body acting as an antenna. The fact that your noise disappears when you touch parts of your amp indicates your body is grounding something that is acting as an antenna or is otherwise a source for AC hum.

 Your power supply must be isolated from AC ground. If one of the power supply outputs is tied to AC ground, internally or otherwise, it will drag one of the PPA power rails to AC ground, damaging the amp if it is connected to an AC grounded source.

 Read these links for more information on basic connections and grounding:

Rane Note 110 Sound System Interconnection
Rane Note 151 Grounding and Shielding Audio Devices


----------



## jamont

What is the purpose of the two notches at the top (logo end) of the PPA board?


----------



## morsel

Wire passthroughs. One of them aligns with a passthrough on the battery board.


----------



## jamont

Quote:


 _Originally posted by morsel _
 Wire passthroughs. One of them aligns with a passthrough on the battery board. 
 

OK, thanks! Does this mean that if you use the Hammond 1455N1601 case that there is no clearance at the ends of the case? (I'm still ordering parts... )


----------



## morsel

Correct.


----------



## ablaze

hi guys,
 I've removed the jumpers since I added the other 2 TLEs. I'm not THAT daft even if I'm a newbie 
	

	
	
		
		

		
		
	


	




 and the pot is grounded to input ground already, as I mentioned. S2 jumpered.

 I don't think I wired anything wrongly, from what you guys said. I'm using a cheap 24v regulated psu I bought locally for about US$18..I'm thinking now its this psu thats suspect. argh. looks like nothing else I can do other than encase the amp in a box. I'll report back when I do.

 (thanks for all the input!)

 edit: typos


----------



## jamont

One more board/case question. I'm using Pana FC 1000uF/35V caps for C1. Is there any clearance problem mounting a board so configured in the Hammond 1455N1601 case? Are the caps too tall?


----------



## morsel

Those caps will fit just fine. They and the 220uF 35V Elnas are the recommended choices for C1.


----------



## was ist los?

Where can i find the 220uf 25v and 35v elnas? Welborne only has 16v and 50v from Angela.


----------



## morsel

http://www.google.com/search?q=elna+silmic+cerafine
http://www.geocities.com/audiograde/elects.html
http://www.thlaudio.com/elnaitme.htm


----------



## ablaze

since we're on C1s:
 I've got 4x1000uF Pana FCs on the C1s
 is that overkill?
 I've got one more, should I add it in?


----------



## xtreme4099

hmm... i got some 220uf 25v premium blackgates from angela.com ... their were quite quick about ... cept in an seemingly unsecure way they accept your cc over email and fax... no ssl nothin ...well they've been in business for a while now ... but they were prompt and quick to get here ... 8 - 220uf/25 Premium Blackgates and 6 of the 47uf/16v standard Blackgates for C4.


----------



## morsel

Has anyone finished building their PPA?


----------



## Arzela

One here. At least the PPA board
 is configured as I want it.

 I'm waiting on some
 power supply parts and rotary switches,
 then I'm going to case it up.

 BTW, would using the L/R outs and input
 ground give a respectable line level signal?


----------



## aos

I did, the same day I received the board. If you mean finished with making panels and with battery board, I'm still waiting for 12 AAA batteries to arrive...


----------



## Voodoochile

Mine's done and I've been listening, but not in a case as of yet. Waiting for one to arrive that isn't cut to the wrong size.


----------



## morsel

For those of you with working amps, how goes the listening?

 Arzela says, "BTW, would using the L/R outs and input ground give a respectable line level signal?"

 Yes, that's how I would do it.


----------



## Bonkura

Im also still waiting to hear some more extensive comments on the sound, some reviews to post in the applification forum perhaps?


----------



## Voodoochile

I am a horrible equipment reviewer, because I do not know the vernacular. However, I'll try to register some mini-feedback.

 Disclaimer: First off, I want to be granted permission to use the word 'dynamic'
	

	
	
		
		

		
		
	


	




 without anyone thinking I am pimping the PPA as a replacement for the Gilmore Dynamic. Everybody seems to want to know which one is better, and I'm not about to go there... I don't want to go there. I will not vote for or say that one is better. And yes, I do have both amps in my posession, and yes, I do like them both very much.

 The PPA seems to have a wider soundstage to me than the META or CHA. It's not too wide, nor does it make me say 'I wish I had crossfeed right now', it's pleasantly wide. As though I were sitting nearer the source rather than in the back third of the room. The amp has an articulate nature to it that is both very fast, but not harsh or mechanical sounding (I told you I do not know the vernacular). I can't say that the bass extends deeper than the META per se, but it seems to have more 'oomf' or whallop. Again, this is a very crip and clean whallop, not heavy or burdened. I would say that if it were an athlete (no, not a pole-vaulter), it would be a very muscular and agile gymnast, as opposed to a sumo wrestler or a ballerina, for example. 
 The midrange is rich sounding, and the highs are very clean, but not hyper-analytical. Snappy and fast? I guess. I need a new adjective. The scope of the tonal range seems quite linear in scale, without anything sounding weak or recessed at any particular point. Very fluid throughout, and quite balanced. I like it.

 It is indeed a very full and dynamic amplifier, and it does share many of the characteristics of my Gilmore dynamic. It is not the same, however... they each have some small attributes that set them apart. I have not done a lot of A/B testing yet to try and pin these differences down, but have heard enough to know there is a difference. The sound is impressive thus far.

 Presently, the amp is populated with 627s in all three channels, twelve buffers, and is running off a 23.5 volt linear PSU. The META has four el2002 buffers per channel, and runs off a 30v dual voltage linear, with AD744s driving the buffers from the comp pins. I like this META very much, it is no slouch at all. The gilmore is built on Michael Lew's miniboard, with a 32.8 volt linear powering it. All three amps have the Alps blue in them.

 I'll try to post other impressions after I have had some extensive time with the collective group, if you can stand it.

 Edit: Can I keep my martini avatar, or do I have to don my fire extinguisher avatar?


----------



## jamont

Quote:


 Edit: Can I keep my martini avatar, or do I have to don my fire extinguisher avatar? 
 

I want the martini avatar, or at least a martini


----------



## xtreme4099

i can agree with voodoo in saying this amp extremely liquid fast ...and very articulate in all ranges ... not too much emphansis on any one range .... good wide soundstage .. experienced them in several configurations and can say that this is true for all, its wider than the sugden i heard at the meet, and dead quiet even with a standard ratshack wallwart, me thinks what a even better powersupply would do... hmm.


----------



## Arzela

I just replaced my ground channel 8610
 with a opa627. Powered the amp up with a 30 V supply. 

 Touched the ground buffers. 

 Owwee!! It's around 130-140 °F (guessing here; actually, I can touch
 the chip for a few seconds before I abandon any pretense of machismo).

 Is this safe? Expected? Anomolous? Perhaps a heat sink is in order?


----------



## morsel

Arzela, when Kurt and I were testing the prototypes I don't recall the buffers getting too hot to touch unless we were driving our 32 Ohm dummy load with a few volts of output. Are they getting that hot when the amp is idle? If so, is it only the ground channel buffers that get hot? If so, and you feel comfortable that the amp as a whole and all the voltages are OK, try swapping one group of buffers for another and see if the heat issue moves with the buffer group. Each buffer in a particular channel fights its mates a wee bit, but hopefully not too much. Perhaps there is one ornery buffer that doesn't play well with others.

 VC and Xtreme, thanks for your comments. Tell us more about the differences between the amps when you can.


----------



## ablaze

Quote:


 _Originally posted by Arzela _
*I just replaced my ground channel 8610
 with a opa627. Powered the amp up with a 30 V supply. 

 Touched the ground buffers. 

 Owwee!! It's around 130-140 °F (guessing here; actually, I can touch
 the chip for a few seconds before I abandon any pretense of machismo).

 Is this safe? Expected? Anomolous? Perhaps a heat sink is in order? * 
 

Arzela, whats the difference in sound switching from the 8610 to the 627s in the ground?


----------



## aos

The chips are hot and uncomfortable to hold a finger on for longer than a few seconds but you can hold it for 20 or so seconds for sure (I just did but I don't want a repeat). If they're so hot that just a simple touch will burn your finger then it is too hot. By the way, I measured consumption of the amp at 124mA.


----------



## Voodoochile

Quote:


 _Originally posted by Arzela _
*I can touch the chip for a few seconds before I abandon any pretense of machismo).* 
 

That's the funniest thing I've seen in quite a while.
	

	
	
		
		

		
			











 Thanks Arzela!

 As for your amp, something sounds askew... mine is very similarly configured, and does not run that hot at all. Nice and warm, but not uncomfortable. This is with 120ohm cans... I have not tried it with anything lower than that yet. Mebbe I need to get out the HD280s.

 I did make the Klaus Noll amp from Audio Xpress (still waiting for a few parts for the Jung/Didden regs, but running on another PS okay), and the second stage of that is super hot, but seems to hang in there. They are AD811 drivers, with the AD744 in front. Real hot, as in hotter than Buf634 in full bandwidth, but still runs fine for hours. Klaus did add a small heatsink to them, but I don't know that it's needed. Hard to tell how hot the junction is, but it's probably not anywhere near the fail point yet. I would get a blister instantly well before the published numbers hit. The numbers are astronomically high, it seems.

 EDIT: Mine is running from a 23.5V PSU... one difference. I doubt that matters much to your buffers though.

 Also, Morsel: I will be sure to follow up further when I've had some casual time to spend with these together. Much of my listening thus far is sitting at the workbench between 11:30pm and 1:30am. It's okay, but I don't juggle things around too much at that hour. The fact that it is outstanding remains, still.
 I think perhaps I need to read more reviews so I can sound like a cool guy when I critique things! j/k... but I should just the same. Right now it's as though english is a second language for me when I try to explain how something sounds relative to another point of reference.


----------



## Arzela

Morsel,

 At idle, the ground buffers are noticebly warmer than
 the L/R buffers. I might have exgagerated (sp) a bit in my last post. One can touch the ground buffers without permanent harm,
 but it gets very uncomfortable after two seconds or so. It won't burn ya, but
 it is painfull. 

 I switched out the ground bank with the left channel bank, but the behaviour remained unchanged.

 The amp seems to work, and in fact, sounds great (I'll elaborate on this after I've listened to
 the amp a bit more). Voltages are fine:
 after the ground bufs I have 28.21 V, 28.17 for left, 28.29 for
 right. This is with a supply voltage of 30.04 V.

 My amp draws 156 ma at idle. This is
 with 627 in ground, With the 8610, current consumption was 126 ma.

 Ablaze, there wasn't much difference, aside from a
 (ahem) smoother, more refined high end. Of course, this is a subjective immpression.

 Sorry for the wierd line breaks..I'll never get used to this...


----------



## Voodoochile

David: are you going to do another over-the-top-stunning case job as you did with your gilmore? I think you did very well to keep the inside of that looking as neat as you did (gorgeous). When you get into switched inputs and outputs, the inside can easily take on the appearance of many homemade computers.

 One of my pet peeves is a shoddy wiring job, especially in a PC.


----------



## ablaze

Arzela, thanks.
 I'm not sure I'm a big fan of the OPA sound.
 think I'm gonna try 8065s in the LR and an 8610 in the ground. 
 now where's that AD sample page..


----------



## Whit

Arzela,
 Did you place a cap for C6G? Ppl mentioned earlier in this thread that lack of C6G could cause instability and specifically mentions the 627. Here is what he said speaking to ablaze.


 "I noticed you do not have C6G installed. With the OPA-627 this will be unstable without C6G. this cap IMHO is not optional it is REQUIRED to asure stability. this is causing the High DC offset with the ground channel"


----------



## Voodoochile

Ablaze: Have you listened to the AD843s? Just wondering. If not, give them a whirl.


----------



## ablaze

whit:
 you're right. I had increasing DC offset on the ground channel >30mV until I added the C6G cap. 

 voodoochile:
 really? actually, I'm a big detail fan, and I don't feel that the OPA637s are giving me as much as I'd like. hence I'm thinking of the 8065s
 as described by ppl in this thread
http://www4.head-fi.org/forums/showt...ghlight=opa637
  Quote:


 When listening to less than perfect recordings from this same setup the highly analytical 8065 revealed every flaw in it. 
 

sounds like my kind of sound


----------



## Arzela

Whit,

 C6G! Thanks! Forgot about that. Now where did
 I put that there cap....

 Mark, thanks for the compliment. I'm
 going to make a unit similar to my Gilmore.
 In the same case size, in fact.
 With only one Nuetrik jack in front, the front panel layout
 will be considerably less cramped. 
 Unfortunately, after one too many slip ups with a file, I've 
 screwed up the front panel that came with the case. I'll probably have a replacement made by
 Front panel express; unless I can find someone
 who'll send me a nicely finished piece of Au sized to order.


----------



## morsel

12 x 8.5 = 102mA (buffers)
 3 x 3.5 = 10mA (AD8610) or
 3 x 7 = 21mA (OPA627)
 3 x 1 = 3mA (cascode current source)

 Our prototypes using AD8610 have an Iq of about 115mA. Using OPA627 the Iq would be about 126mA. 156mA is 30mA more than that. Arzela, perhaps your ground channel is oscillating. Do you have a scope? Omitting C6G could be the problem. I don't recommend omitting any parts.

 Ablaze, I think the AD8610 sounds better than the AD8065.


----------



## Arzela

Thanks Morsel and, again, Whit. Adding 
 C6 brought current consumption down to
 128 ma. Buffers are merely warm and the three banks have a uniform temperature.

 Splendid!


----------



## morsel

Cool beans, or in this case, cool buffers. 
	

	
	
		
		

		
		
	


	




 Your ground channel was definitely oscillating. Glad your amp is working better now.


----------



## ablaze

morsel, could you elaborate a lil WHY you prefer the 8610 to the 8065?


----------



## morsel

I listened to many different opamps a while back, including the AD8610 and AD8065, and subjectively thought the AD8610 was the best. To add a bit of technical rationale, the AD8065 is a low budget opamp with rail-to-rail outputs which typically compromise audio quality, whereas the AD8610 is a pricier precision opamp designed for high performance audio use, among other things.

 I don't wish to hijack this thread or start an opamp range war, just giving you my opinion, and suggesting these points are hints that the AD8610 is better. If you search past threads here and on Headwize you are bound to find more on this subject.


----------



## ablaze

as always, thanks morsel.


----------



## Voodoochile

Quote:


 _Originally posted by Arzela _
*Thanks Morsel and, again, Whit. Adding 
 C6 brought current consumption down to
 128 ma. Buffers are merely warm and the three banks have a uniform temperature.
 Splendid! * 
 

Sounds much more like mine now! Good deal.

 As for your front panel (doh!) Par will sell you a replacement front panel on it's own. (Or was it Sescom that will? I think Par will also.)


----------



## Voodoochile

Finally got this into a case:

















 and with the PSU that will end up powering it. It's running on the bench PSU in these pics.


----------



## was ist los?

Beautiful work voodoochile!!!! I love the case, what is it? Again, excellent work!!!


----------



## eric343

Very nice work, Voodoo!


----------



## morsel

Gorgeous work, Voodoo! That case is styling. Is it a Lansing MicroPak C?

 Arzela, I just saw your Par Metals case Gilmore, oh my god, drool city.


----------



## Voodoochile

Thanks for the nice comments, and sorry for the sparse post- it was late.

 Yes, it's a MicroPak C. I like the way that the cover wraps the sides as well. About 1/8" larger than the PCB (eurocard), and 1.5" tall. Shorter than the Hammond, so very snug. The Locking Neutrik was almost going to be on it's side. I think it would also be fine that way, with the button to the left.

 The inputs are Vampire CMHEX, with Canare Star Quad to the board. Other wiring is Alpha teflon on plated copper. To keep the wiring minimal, the inlet jack runs directly to the switch knives, then the power from the switch runs to the board. So the switch pads have jumpers on them for now. Both rails are switched.

 So this is about the size of a paperback book, and weighs similarly.

 edited for nearly fubar typing


----------



## ppl

Voodochillie> Glad you like your New Amp Hope you get a lot of enjoyment out of it on the upcoming Cold snowy New England Days ahead. I also like the Lansing cases and the Low profile is nice. I myself have been thinking of using one of them on my Next PPA. The standard Hammond case is more for those that wish to install the battery board. Also the Anodizing on the Lansing is a lot better than the Hammond. 

 My question is who will be the first to try the AD-8065 op amps with the HA-5033 or OPA-633 Buffers? BTW the AD-8065 is unity gain stable and as such will work well in the ground channel. I have in fact tried the AD-8065 in all positions and it works great with one exception and that is when using bass Boost the DC offset can get quite large (60mV) unless you hand select your OP Amp for low DC offset by trial and error. Out of (4) op amps you should be able to find two for the gain channels that are low enough to use.


 BTW i like the one peice construction of the D style myself with the Removable bottom pannel of the E style second the data for the d style is......

http://www.lansing-enclosures.com/me...d_techdata.pdf


----------



## ablaze

ppl, would there be any adverse effects using the 8065s with the default 5003 buffers?


----------



## Voodoochile

Thanks for the remarks, and also for all of your input in the project, ppl. I'm always game for some op-amp rolling.


----------



## ppl

The AD-8065 will work fine with the HA-5002 Buffers but the sound is better with this OPA on the HA-5033


----------



## jamont

Great job, Mark, as usual!

 My board is essentially done, as of about 30 min. ago. I'm using 3xAD8610 and a 2-2-2 buffer configuration. I've done the cascodes per tangent's excellent instructions, and I'm now enjoying listening at the workbench while I wait for case parts. The sound with AKG K501's is really excellent.

 Thanks to the PPA team for making this available, and to morsel for answering many questions!


----------



## Arzela

That's an ox-stunner of a book Mark.
 And a great read ! Nice 
	

	
	
		
		

		
		
	


	




 Now for something entirely
 different:

 My phones are set up for dual mono.
 Each cup has its own wire which terminates at the tip and base (ground) of a typical phone plug.
 These were for my Balanced Gilmore.

 If I set up two phone jacks for my PPA,
 wired appropriately, would I eliminate the
 danger of shorting the outputs when removing the plugs?


----------



## Voodoochile

If the ring is not connected to anything ( I think I follow you), then yes, that should alleviate any shorting of your outputs. 

 I would make a test jig first, to be sure... just in case your jack has some oddly long contact area.


----------



## tortie

Very beautiful work Voodoochille! 
	

	
	
		
		

		
			





 What will the case for your PS look like?


----------



## Voodoochile

This amp is mainly for use as a tool for me, for trying out different OPAs at different bias levels, as well as for trying out the amp with differing PSUs. So no specific PSU for it. Of course the amp will make it upstairs where I'll spend time just listening, too
	

	
	
		
		

		
		
	


	




 .

 When I do that, I'll use a linear that happens to be housed in a (approximate) 4x4x2 Hammond case. I could fit a PSU into a case of the same size, but would likely use a larger case and fit the amp and PSU together.


----------



## morsel

Congrats on your amp, Jamont. Do try it with the full 4-4-4 complement of buffers when you can.

 Arzela, using two phone jacks is somewhat inconvenient. Personally, I would not worry too much about the output shorting issue. If the PPA had 4 wire outputs and thus required specially modified headphones such as the Blockhead or Balanced Gilmore, I would use either a 4 conductor XLR connector or Neutrik Speakon connector as they have parallel conductors, not coaxial conductors, and thus do not transiently short when disconnected. However, one of my major reasons for going with differential output was to avoid the need for customized 4 wire headphones which do not work with ordinary equipment, while reaping some of the benefits of a 4 wire system.

 In keeping with this philosophy, I recommend using normal 3 wire headphone jacks. If you are really concerned about accidentally yanking the plug out partway by walking too far from the amp, you can either use a locking Neutrik jack (which I find rather heavy and clumsy to operate but which are nonetheless very popular) or you can fuse your amp such that the increased current draw from a dead short on the output blows the fuse, or you can use one of those resettable fuses if you don't like replacing real fuses. With 4 buffers per channel and 200mA of current per buffer, if your power supply is incapable of more than 800mA of output then you have nothing to worry about. This is perhaps the most convenient solution of all.


----------



## IMEP

Very nice case-work Voodoochile! You've raised the bar once again!


----------



## ablaze

got my hammond! here're the completed pics 
	

	
	
		
		

		
		
	


	




 as you can see its a "custom" model with dual inputs: rca and 1/4" line-in
 1/4" output

 front panel:





 back panel:





 another front view:





 another back view:





 front view of the amp:





 with the lights off:





 an a ****-style view 
	

	
	
		
		

		
		
	


	




)





 opinions? 

 btw, thats a Cliff-UK 1/4" non-locking jack for the input and output (hate locking jacks 
	

	
	
		
		

		
		
	


	




)


----------



## Voodoochile

How do you like it, Ablaze? I'm sure everyone is anxious to hear your thoughts.

 Nice job casing up. Are you going to trim your pot's shaft back a bit? Also, what RCAs are you using? They are massive!

 Thanks for lifting your shirt in the last pic, too.

 One other question: Which input pads did you use? I cannot see in the last pic. Good-looking braid job there, BTW.


----------



## ablaze

heh. building an amp for the first time is quite the experience. its like having a first kid I guess 
	

	
	
		
		

		
		
	


	




 hmmm..pot shaft. yeah I think I'll do that. thanks for the reminder!
 and those are CMC jacks. not too familiar with the brand, but its made in the USA! 
	

	
	
		
		

		
		
	


	




 It sounds great to me so far, and housing it has got rid of all the humming problems I previously had, now its perfectly silent! but I'll reserve formal listening opinions until I can get some one with more "experienced" ears to take a listen.


----------



## ablaze

btw, gotta thank each and everyone of you on this thread for all the help along the way. couldn't have completed without ya'all. thanks!


----------



## Voodoochile

Nice. Yep, casing up is often the hardest part.

 This is your first amp build? You have big balls, suffice to say. You have done exceptionally well.

 The only bad thing about building a PPA for your first amp is... what will you do next? Build a cmoy into an empty Bic lighter case?





 I'm thinking you might have used both sets of inputs, as you have two sets of jacks. If so, do you hear any difference between the two?


----------



## ablaze

yeah. foolhardy to attempt a PPA first lol 
	

	
	
		
		

		
		
	


	




 I'll check it out later and report back. there shouldn't be a difference should there?


----------



## Voodoochile

Well, you could easily get good results from either pad set... which is why they are there. But the differences are there. The rear pads lead to straight traces all the way up the board, albeit under a ground plane. Going to the front pads you have the opportunity to twist or braid or use shielded cable, but you are also shooting through the air over the baord (and ground plane).

 Ideally, you will not hear a difference.

 And yes, that is a very ambitious first project!


----------



## morsel

Congratulations on your amp, Ablaze! Good job. Before you saw off your pot shaft, consider using a larger, deeper knob. It might look and feel better than the knob you are currently using. Nah, on second thought, your existing knob is big enough.


----------



## ablaze

thanks morsel. hmm..bigger knob..yeah that might just up spruce up the front panel a lil. maybe I will 
	

	
	
		
		

		
		
	


	




 voodoo: actually I'm using both sets of rear pads for the inputs. didn't touch the front pads.


----------



## xtreme4099

Congrats ablaze, Glad you like your new Amp. Please tell everyone that you did mount the Op Amps on botton board supplyed SMT pads (Very Recomended). I can see people saying look it cant work! it has no op amps.......


----------



## Voodoochile

Not using any op-amps is what contributes to the very clean, clear sound!


----------



## ablaze

lol 
	

	
	
		
		

		
			





 no wonder there's no more hum


----------



## JMT

I just completed my PPA, using some OPA627s, Cerafines, etc.

 WOW!!


----------



## Voodoochile

It's pretty wild, isn't it?
 Congrats, Jon!


----------



## morsel

Yay Jon!


----------



## dd3mon

Quote:


 _Originally posted by JMT _
*I just completed my PPA, using some OPA627s, Cerafines, etc.

 WOW!! 
	

	
	
		
		

		
		
	


	


* 
 

Details! Details! How's it stack up against your Meta42s? Your Max?






 And when ya gonna start building them for others? 
	

	
	
		
		

		
		
	


	




 -dd3mon


----------



## aos

I've just got my battery board to fast charge batteries 
	

	
	
		
		

		
		
	


	




. Didn't want to cooperate for a while there.


----------



## picklgreen

I am curious if anyone has tried installing a DACT CT2 stepped attenuator or tried using AD825 opamps in their PPA?

 I replaced the opamps in my Rotel 071 cd player with these and it made a huge difference.


----------



## Voodoochile

I have a 50k Dact on hand, and it will fit even in the little case mine is in. No plans to install it just yet, it's really for another project. But I will likely put one in ultimately.

 No chip rolling yet, too many other projects consuming my time.
	

	
	
		
		

		
		
	


	



 This weekend is not looking too amp-fiddling-friendly, either.

 Jon- have you cased up yet, or still on the bench? What are your plans with this one?


----------



## JMT

Impressions: 

 Ok, WOW may have been a tad too under-descriptive. I got the same sense of awe listening to this amp (keep in mind, the active components have not had a chance to burn in) that I got when I listened to my first META amp over the CHA47 amps that I had been building. The PPA has authority, in all of the frequencies. But it absolutely shines on the mids/upper mids/treble extension. The bass is accurate, and at the same time is not overpowering. I was listening to my "test" CD (Lee Ritenour Live in L.A.) as I know this CD backwards and forwards. Drum hits are powerful, eye blinkingly dynamic. Acoustic guitar sounds like *acoustic* guitar....pick and all. I can hear some of that 3 dimensional soundstage that the CHA47 lacks, there is depth galore. I can only imagine what this bad boy will sound like once the OPA627s settle in.

 I don't think a comparison to the Max would be fair. The Max just does all of those things, but many times better. There is an ambience with the Max that I have not heard any amp come close to......ok, with the exception of the BlockHead. 
	

	
	
		
		

		
		
	


	




 One thing that I really love about the PPA board is the size, and how it fits snugly into the board slots of the Hammond 1455K1601 enclosure. The amp is all cased up and ready to rock, the internal after build look is very professional looking. No extra room anywhere with everything in it's place. 

 I will enjoy this amp through the weekend, and then it's destined for one of our members.


----------



## morsel

Picklgreen, the AD825 is generally considered to be inferior to the AD8610. The stepped attenuator is a nice upgrade, however.


----------



## aos

Quote:


 I don't think a comparison to the Max would be fair. The Max just does all of those things, but many times better. There is an ambience with the Max that I have not heard any amp come close to......ok, with the exception of the BlockHead. 
 

That's unfortunate. Initial reports were hinting at closer relation between two amps, especially since PPA is very expensive amp, probably on par with MAX parts-price-wise (so comparing them certainly is fair).


----------



## puppyslugg

Quote:


 That's unfortunate. Initial reports were hinting at closer relation between two amps, especially since PPA is very expensive amp, probably on par with MAX parts-price-wise (so comparing them certainly is fair). 
 

That was the hope, but JMT's findings are still in the preliminary stages. Opinions may change after burn-in. Besides, what does JMT know, anyway?


----------



## Voodoochile

Ouch!


----------



## aos

Well, he used OPA627 as I did originally, but some advocate use of OPA637 in L/R, claiming that 627 is too dark and lacks detail. I just got a pair of 637 those this morning. What is definitely true is that you must find a pair of opamp/buffer that has that special synergy. AD8610 and EL2001 were such a pair. HA3-5002 is new to us (certainly not new on market) so we have to discover what works best. E.g. ppl prefers AD8065 with OPA633/HA-5033.


----------



## binary_digit

ad8610x3+5002(4x4x4)= A big number and really nice all around sound. I consider this the base line for mine. 627 & 637 configs seem to dull things down a bit. el2009's were the bomb. They will be missed. 
	

	
	
		
		

		
			





 But not for long 
	

	
	
		
		

		
		
	


	




 Peace,
 B_D


----------



## puppyslugg

Quote:


 _Originally posted by binary_digit _
*el2009's were the bomb. They will be missed. 
	

	
	
		
		

		
		
	


	




 But not for long 
	

	
	
		
		

		
		
	


	




 Peace,
 B_D * 
 

Hi binary-digit,

 Are you going to be offering special edition PPA's with el2009's?Were the ad843 ever considered or tried in the PPA?


----------



## JMT

I like the sound of the 627s, but also have a few 637s here that I am anxious to try. I agree with aos in that it will be important to find the right combination for your particular ears. But, with three 627s in it, it does sound PFI!!
  Quote:


 _Originally posted by puppyslugg_
*Besides, what does JMT know, anyway?
	

	
	
		
		

		
		
	


	








* 
 

Just enough to be dangerous.


----------



## binary_digit

Quote:


 _Originally posted by puppyslugg _
*Hi binary-digit,

 Are you going to be offering special edition PPA's with el2009's?Were the ad843 ever considered or tried in the PPA? * 
 

The first question is not appropriate for me to answer in these forums. Never tried the ad843's, but I'm sure PPL will give you his thoughts on them in this application.

 Peace,
 B_D


----------



## binary_digit

Quote:


 _Originally posted by JMT _
*I like the sound of the 627s, but also have a few 637s here that I am anxious to try. I agree with aos in that it will be important to find the right combination for your particular ears. But, with three 627s in it, it does sound PFI!!* 
 

You own a couple of different headphones JMT. I have found the HD600's to be a allaround comfortable headphone to listen to. The inherant layed back sound seems to like the 8610 to deliver the distant highs. But the HP1000's on the otherhand have this in spades. I would expect the 627's to curb this a bit. What say you?

 Peace,
 B_D


----------



## Arzela

"PFI"? 

 = "Pretty [expletive deleted] incredible"?


----------



## picklgreen

Will it be safe to use the blackgate 220uf 25v for C1 and the blackgate 47uf 16v for C4 if I use the recommened 24v Elpac WM080 power supply?


----------



## eric343

Quote:


 _Originally posted by puppyslugg _
*Hi binary-digit,

 Are you going to be offering special edition PPA's with el2009's?* 
 

From my conversations with him, he's implied that he does this already.

 What he was talking about was something entirely different...


----------



## Voodoochile

I liked that too, David!
 It just screams 'custom title' for someone.


----------



## xtreme4099

what binary is implying is something good... very good and crunchy too.


----------



## puppyslugg

Quote:


 _Originally posted by xtreme4099 _
*what binary is implying is something that will equal or surpass the 2009s. * 
 

Possibly a discrete buffer?


----------



## xtreme4099

there coming out with something new and improved, with 25% more free, tide fresh, whiter whites, brighter colors, and minty fresh.


----------



## 10SNE1

Just completed the assembly and testing of my PPA.

 No problems by following Tangent's guide to assembly.

 I used a potpourri of parts including surplus Dale resistors, caps, Panasonic film and electrolytics and free sample OP627s and TLEs.
 I can't justify (for myself) gilding the lily with specialty ($$$) parts.
 Instead, I maxed out the buffers and power rail configuration.

 The most tedious part was finding a usable R8 to get the proper cascode current. I had to use 2n5457 devices in lieu of 2n5484 for Q1. I found that 820ohm for R8 got the current through the R9 position to about 1.2ma.

 The sound is just great, even uncased. What is really neat is the absence of any hum, even uncased and with long power and signal leads. The only hum I noticed was when I touched the pot and turned the volume up. That should be fixed by grounding the pot to the ground plane and enclosure.

 DC offset is ZERO for both sides.

 I powered the amp for testing using an old ELPAC +/-12v wallwart. I'm going to case it up in a longer version of the standard Hammond case and make a regulated 24VDC board that will slide into the extra space. The AC will be provided by a 24VAC/800ma wallwart.


----------



## binary_digit

I can't make out from your pic if boost is jumped. Congrats on the build.


----------



## 10SNE1

Quote:


 I can't make out from your pic if boost is jumped. 
 

I did have it jumpered until the basic amp operation was assured.

 Then I added in the bass boost cap and resistor and removed the jumper. Leads to the switch will be added when it is encased.


----------



## picklgreen

Quote:


 _Originally posted by xtreme4099 _
*hmm... i got some 220uf 25v premium blackgates from angela.com ... 6 of the 47uf/16v standard Blackgates for C4. * 
 

Are these rated at enough voltage (16v) if using the recommened 24v Elpac power supply?

 Blackgate also carries a 100uf/25v cap but it is 10mm x 20mm. Is this to big (8mm is the recommmened maximum size for C4)?


----------



## morsel

JMT: Quote:


 I don't think a comparison to the Max would be fair. The Max just does all of those things, but many times better. There is an ambience with the Max that I have not heard any amp come close to......ok, with the exception of the BlockHead. 
 

aos: Quote:


 That's unfortunate. Initial reports were hinting at closer relation between two amps, especially since PPA is very expensive amp, probably on par with MAX parts-price-wise (so comparing them certainly is fair). 
 

I wouldn't worry too much, aos. JMT has his opinion, and so do we all. Tyll and I compared the Max to a PPA w/AD8610 opamps at JMT's last meet. They were both very good. I preferred the PPA to the extent that I prefer the Analog Devices sound over the Burr Brown sound. (I would love to see Headroom produce AD8610 modules for their amps.) It's a matter of personal taste. I certainly would not say that either amp was "many times better" than the other.


----------



## xtreme4099

might i remind people that theres other configurations that would make it sound better even, the stock 444 here with 627s it seems is not the only game in town,the ppa is very configurable and upgradable, it depends on your tastes for one, how much your willing to dish out, and what your looking for.


----------



## Arzela

Looks nice 10SNE1 ! Are tose
 Vishay PTF resistors? Pretty


----------



## 10SNE1

Quote:


 Vishay PTF resistors? 
 

No, they are some surplus Vishay ERC milspec grade resistors.

 I happened to have picked some up a while ago and while they are a bit longer than the lead spacing on the board, a little bending makes them fit OK.

 They do have that royal blue color which is interesting.


----------



## aos

My new opamp favorite for PPA is LT1360. It brings out details that I've never heard before, particularly noticeable with violins but not limited just to strings (e.g. it's now easier to separate piccolo from flute). I'm talking real detail like microdynamics which you can pick if you ever heard a violine live, not the extra "air" that some people dismiss as just emphasized treble. I am still not convinced that there's no coloration with this opamp (in the lower treble) or that this is not all in my mind, but I'm definitely enjoying listening to it.


----------



## picklgreen

Who makes this and where can I get it?


----------



## was ist los?

I would like to know whether the ground buffers really make a difference. Does the amount in the ground really impact sound?


----------



## tangent

Quote:


 I would like to know whether the ground buffers really make a difference. 
 

Does this not answer your question?

http://tangentsoft.net/audio/ppa/amp...ml#par-buffers

 Short version: the number of ground buffers is a safety issue, not a sonic one.


----------



## morsel

I do not agree with Tangent's assumption if based solely upon RMAA tests. Listening to deep bass passages from well recorded music will tell you far more than RMAA about how many buffers are needed on the ground channel. I have not personally compared light ground channels with fully buffered ones in this fashion, but I would not conclude it is purely a safety issue without thorough listening tests.


----------



## Glassman

what about discreet buffer modules based on sijosae's Butterfly42?






 is the HA3-5002 really that important to the sonic performance? it would be interesting to build this discrete buffer on some breadboard and wire it into PPA just to hear how does it perform..


----------



## morsel

Discrete buffers are very tempting and no doubt will be the subject of research this winter. It remains to be seen whether we can have our cake and eat it, too. There is a long list of desirable traits that may be difficult to completely achieve:

 high output current
 low output impedence
 high PSRR
 low noise
 low distortion
 low dc offset
 low parts count
 low cost
 minimal manual component matching
 etc.

 Then there is the MOSFET .vs. BJT war to contend with, and all the different topologies to evaluate. It will be interesting.


----------



## ppl

I have also been reasearching this aproach. The above circuit lacks the required output current need for this amp since the above Butterfly version of the classic Dimond Buffer is limited to about 200 or so mA. paralelling more output transistors will bring this up into the desireable 1 Amp output current range. Remember the Butterfly Circuit as shown above like the Monolithic HA-5002 lacks output current limiting

 aos> LT1360. Op Amp interesting I have used these and the LT-1363 in other Amps and the 1360 works good with the 1363 having too high of input Bias current for the High Imput impedance of the PPA. However based upon aos glowing recomendation Ill try the LT-1360.
 Data sheet hear http://www.linear.com/prod/datasheet.html?datasheet=82 This opamp likes at least a 20 volt supply (+/-10 Volts) otherwise thay lose performance and sound quality. However this should not be an Issue in the PPA.


----------



## Glassman

no current limiting.. isn't it why you choosed HA3-5002 for PPA? 
	

	
	
		
		

		
		
	


	




 and what if I build just the ground channel and connect it to my Gilmore? I think it should work fine.. am I right? the ground channel is not so sonical dependant - it's just a lot better when it is, but it's not so important what particular opamp and buffer I choose..?!? 
	

	
	
		
		

		
		
	


	




 this should bring about the same improvements as going from META42 to PPA no?


----------



## ppl

Actually the lack of current limiting is why we used 4 of them. If you use the Diamond buffer then parallel 4 output transistors if that is the topology you want to use.


----------



## Glassman

so why did you choose monolithic circuit over some kind of discreete like the Diamond..?


----------



## eric343

Simplicity, cost, simplicity, and size. Also probably simplicity and board real estate.


----------



## Glassman

Quote:


 _Originally posted by eric343 _
*Simplicity, cost, simplicity, and size. Also probably simplicity and board real estate. * 
 

if those are the only reasons then I'm a lucky boy! (have you mentioned simplicity?) 
	

	
	
		
		

		
			





 I'm going discreet becouse the cost of 12 intersils is somewhat higher than that of say 50 trannies..


----------



## morsel

Theoretically it should be cheaper and better with a discrete circuit, but if PSRR is worse then a better power supply will be required. It may also require precise transistor gain matching, which is a nuisance, especially for those making many amps. For class A operation it will also draw much more current, making battery operation impractical.


----------



## Glassman

you are making me happy, morsel. I don't need to be batery powered nor I use cheap wall warts, so the discrete buffer seems like the best option for me..

 and what about my thought of adding PPA-ground channel to Gilmore amp?? could this improve it sightly?


----------



## ppl

Glassman: Remember that not only will the HA-5002 work but as I mentioned before the OPA-633 and the HA-5033 are a pin compatible drop in alternative. Just because somthing is made from Discreet Components is no reason to think it is any Better than a Monolithic alternative.

 Again i am working on a discreet component version of the Dimond Buffer that i hope can be made on a small Board that will plug in to the 4 Buffer sockets on the PPA. However as Morsel pointed out alot of design issues need to be adressed in order to offer this to Head-fiers. Moreover this aproach will not obsolete present PPA's as a plug in Discreet Buffer would be just as easy as changing Chips un-plug and plug in the Module. The Analog version of Plug and Play.


----------



## Voodoochile

That sounds excellent!
 (no pun intended)
 The four-up pads should make for a perfect daughterboard plug-in location.


----------



## Jupiter

Quote:


 _Originally posted by morsel _
*It may also require precise transistor gain matching, which is a nuisance, especially for those making many amps.* 
 

So the PPA project is also targeted towards people who sells DIY amps? If so, why? (Just curious.)


----------



## eric343

Because 2 or 3 of the people on Team PPA are planning to, or already selling them, for one...

 ...for another, the PPA is a hell of an amp, too good not to be made availible to those who don't know what end of a soldering iron to hold on to.


----------



## Jupiter

Quote:


 _Originally posted by eric343 _
*Because 2 or 3 of the people on Team PPA are planning to, or already selling them, for one...* 
 

Good point. (I guess that might also explain why erix was so critical about the PPA project, but that's another discussion.)

  Quote:


 _Originally posted by eric343 _
*...for another, the PPA is a hell of an amp, too good not to be made availible to those who don't know what end of a soldering iron to hold on to. * 
 

Their loss.


----------



## picklgreen

I want to modify my PPA to run fully balanced. (In and out). Can somene please draw me up a schematic to show me how to do this?


----------



## tangent

Quote:


 So the PPA project is also targeted towards people who sells DIY amps? If so, why? 
 

You're looking at it the wrong way around. The "DIY for Someone Else" (DIYFSE) market exists because there are DIY amps that sound good and are straightforward to build, so they become popular enough that even non-DIYers want them.

 If you make a design that's difficult to build, few will build it. If it's not popular within the DIY community, it will be almost unknown outside the DIY community. Therefore, no DIYFSEer will be making them. There's little incentive to make circuit boards for such designs.

 The DIYFSE market is a consequence of popularity in the DIY market. If you expect a design to be popular enough to justify circuit boards, you expect that DIYFSEers will want to build it for others.


----------



## tangent

Quote:


 I want to modify my PPA to run fully balanced. (In and out). 
 

No you don't, you only think you want that. 
	

	
	
		
		

		
		
	


	




 Balanced operation means four signal lines in and out, for stereo. You could do that by adding a fourth "channel" to the PPA, adding a 4-gang pot, and running the four input signals through the pot, through the 4 amplification channels, and out.

 Problems with this approach:

 1. The pot is going to reduce the CMRR of balanced operation in proportion to its channel mismatch. You'd need to go with a stepped attenuator to avoid this.

 2. What do you do with the four output signals once you have them? If you don't mod your headphones to have two separate cords, you won't get any benefit from this mode of operation. You'll just end up collapsing the signal back to single-ended at the headphone plug.

 This sounds like "lots of components for very little gain". 

 Balanced operation is all well and fine to talk about in power amps, because they have 4 output connections already. Driving each speaker with a balanced signal is perfectly reasonable. Headphones have 3 output channels, hence the PPA's 3 channel design.

 If you have a balanced source, a much better plan is to just add a balanced receiver to the PPA. You will get all of the CMRR benefits of balanced operation in the cabling from your source to the amp. Within the amp the signal stays clean as well, if it is built correctly.


----------



## picklgreen

So how does a circuit like the LC Audio Zap filter work that only uses 2 opamps but is fully balanced? Or is using two single opamps and a dual one at the top of the circuit board (probably for the ground channels?)






http://www.lcaudio.dk/com/zapfilter.htm


----------



## tangent

Quote:


 So how does a circuit like the LC Audio Zap filter work that only uses 2 opamps but is fully balanced? 
 

Without seeing the schematic, I can only speculate. Perhaps the op-amps are dual channel chips? Perhaps the op-amps are not directly in the signal path? I notice that they brag about the discrete circuitry on this card, so why could that not be two independent channels per side?

 In any case, this avoids the two objections I brought up in my previous post: you need a 4-gang stepped attenuator and 4 output connections to make any benefit from this in a headphone amplifier. Are you willing to do those things? If not, what's so wrong with just adding a balanced receiver to the amp, since the output is going to be single-ended anyway?

 EDIT: I have no problem modding a CD player to have balanced outputs. That's perfectly reasonable. But a CD player is not a headphone amplifier. They have different design requirements. Pointing to a CD player mod is no proof that it would be good to similarly mod a headphone amp.


----------



## picklgreen

I have no problem adding the 4 gang attentuator, and buying the balanced cables for my HD600's. My main concern is having to create a new PCB to facilitate the extra channel needed.

 Could someone draw me a schematic of how to wire in a stepped antenutor on the input channel? And according to its desgin i would only need a 4-gang right?







 or would this work?


----------



## eric343

Quote:


 _Originally posted by picklgreen _
*I have no problem adding the 4 gang attentuator, and buying the balanced cables for my HD600's. My main concern is having to create a new PCB to facilitate the extra channel needed. * 
 

No need. Just build it on protoboard.


----------



## Glassman

ZAP Filter is whole discrete design - those opamps are there just for DC servo operation.. this design is balanced from input to output - you can then connect + and - or just + and GND..

 but tangent? why do you thing that four channels are needed?? what about connecting the - input to inverting leg of the L & R channel's opamp? what exactly did you meant with 'balanced receiver'?


----------



## picklgreen

I think ill buy one of those zap filters and see how it sounds as a headphone amp! You can even buy a power supply for it so all i would have to do is add a volume control to it and instead of rca outs ill use xlr balanced outs


----------



## morsel

Jupiter: "So the PPA project is also targeted towards people who sells DIY amps? If so, why? (Just curious.)"

 Tangent already wrote a great reply to this question. My two cents: I am motivated to contribute to the DIY headphone amp community. If no one wanted a PPA, it would not be much of a contribution. I pushed for keeping the cost and parts count low, minimizing the need for manual component matching, and conforming to the standard 3 wire headphone system, to appeal to the broadest possible cross section of the community, not to make DIYFSEers rich.

 Glassman: "and what about my thought of adding PPA-ground channel to Gilmore amp?? could this improve it sightly?"

 picklgreen: "I want to modify my PPA to run fully balanced. (In and out). Can somene please draw me up a schematic to show me how to do this?"

 My quick and silly answer to the two of you is that Glassman should build a PPA and picklgreen should build a balanced Gilmore. 
	

	
	
		
		

		
		
	


	




 Building a PPA with discrete outputs (or something akin to a differential Gilmore) is on the list of winter research projects. As for a fully balanced PPA, assemble 2 PPA boards, omitting the ground channels. Use the two channels of board 1 as L±, the two channels of board 2 as R±, a nice 4 gang stepped attenuator, and custom wired Sennheiser HD600 headphones with Canare StarQuad cable and a 4 conductor XLR or Speakon connector.


----------



## aos

Kind of bizzare that LC audio uses those silver mica capacitors as through-hole, when they use all those tiny SMDs for the rest of the circuit. Especially since you can get silver mica in SMD...

 But it certainly looks like a discrete design - all those SOT-23's are transistors, and the four per channel on top that are a bit bigger are likely output transistors (probably a parallelled complementary pair). And the board has its own voltage regulator on the top left corner. Some relays and control circuit. This is all just a guess, of course.

 Also, if someone is going to try LT1360 (I always screw up and say 1630 which is misleading because there is such an opamp in fact I used them once), be careful about the DC offset! I measured 10mV (and my resistor values are not all as specified) so bass boost is out of the question without changing some resistors.


----------



## ppl

the Zap circuit uses only one pair of transistors per amp. one pair for the Pos output and one pair for the Neg output. Remember most balanced Amps are as tangent stated 4 amps per stereo pair two amps per channel. Thay do look like thay would drive headphones if the Emmitter resistors are low in value. Balanced Equipment is intended for 600 ohm balanced lines and as such the output must be able to drive lower impedances that the typical opamp will tolerate.


----------



## picklgreen

Does anyone know who I can contact to do laser engraving? I want to get the case of my PPA engraved with my brand name...

 Also I would assume the PPA is "open source" and redistributing PPA designed amps is legal? I know there are 2 companies currently that sell PPA based amps, do they have to pay any royalities or anything for it?


----------



## tangent

Quote:


 assemble 2 PPA boards, omitting the ground channels. 
 

That'd work. Kind of inefficient (lots of unused board real estate) but if one didn't want to create a new layout, that's a good solution.

  Quote:


 what about connecting the - input to inverting leg of the L & R channel's opamp? what exactly did you meant with 'balanced receiver'? 
 

What you describe _is_ a type of balanced receiver. These are also called baluns. However, I don't see that you can get custom gain levels from such an arrangement, and it seems to me that it wouldn't work with the multiloop components downstream. What you want is a separate balanced receiver that puts out a single-ended signal which you run to the + input of the PPA op-amp. You can make much better balanced receivers than using a single op-amp. Lots of circuits can be found online.

 Adding a balanced receiver to the front end of the PPA is a sensible way to go, but it doesn't fill picklgreen's requirements.


----------



## picklgreen

i see that most people have used the reccommended 1.ouf for C2/C5. Has anyone used the 3.3uf (mouser #75-mkt1826533055) They are much more costly but I am wondering if you did how did it effect the sound?


----------



## Glassman

What? 3.3uF polyester Roederstein for 5$?? they're selling for no more than 1$ here! ..and I thought it's all cheaper in US. 
	

	
	
		
		

		
		
	


	




 I think that it doesn't affect the sound, it's there just to cancel oscilations (if it's the one I think of)


----------



## Voodoochile

Correct.
 And it might make your PSU a bit more responsive to transient demands.


----------



## picklgreen

If you are using the OPA627 opamp in your ppa, i'd like to know what values of R8 and the corresponding mA value you measured across R9 for it. (Vishay sells quite a few values from 10-100 ohms so i want an idea of which ones to buy since I could easily spend $100 if i had to get them all to use trial and error!)


----------



## morsel

Picklgreen, C2 and C5 can be anything from 1 to 6.8uF (the largest that will fit). There is no need to go with expensive exotics. I suggest 1µF 50WV BC MKT 370 or Wima MKS 2 PETP polyester film caps as they are cheap and easy to get. If you can get higher capacitance for a similar or better price, then go for it.
  Quote:


 Also I would assume the PPA is "open source" and redistributing PPA designed amps is legal? I know there are 2 companies currently that sell PPA based amps, do they have to pay any royalities or anything for it? 
 

Anyone may build and sell PPAs using the boards available from Tangent. Anyone may make their own PPA board for their own personal use. We do not grant the right to make PPA boards for commercial purposes. Tangent invested his own money to pay for research and enable us to offer the PPA to the community at a dirt cheap price. He also spends a lot of time on the onerous task of distributing boards. We want to see him compensated for his investment and effort.


----------



## TommyTheCat

I was going to post those BC's for c2/c5 but morsel beat me as i was going to write!

 But yeah, i was looking at those. Something like 63V-1.0uf. They're a good size and about $5 for 10. I hoping they'll work out(when i actually build, need $ first 
	

	
	
		
		

		
		
	


	




 )


----------



## 10SNE1

I decided to build a simple regulated PS that would fit aft of the PPA board in the extended length Hammond box (1455N2201).

 24VAC wallwarts are cheap, and I had the parts on hand.

 This is a conventional design based on the LM317 voltage regulator with large ripple filter and bypass caps (10uf tantalum, .1uf ceramic) and will accept 24 VAC. It will provide regulated DC out up to 28 volts or so with that source.

 Depending on the height of the filter cap and/or heatsink, it may be necessary to slide it in the lowest card slot (slot 1) where the PPA board goes in slot 2.

 The overall size of the board is 100mm (3.925") * 57mm (2.25").

 A smaller filter cap can be used (2200uf); I just happened to have a bunch of 3300uf on hand).









 Foil side (if you want to use the iron-on masking technique):


----------



## Jupiter

Quote:


 _Originally posted by aos _
*Kind of bizzare that LC audio uses those silver mica capacitors as through-hole, when they use all those tiny SMDs for the rest of the circuit. Especially since you can get silver mica in SMD...* 
 

They're using some special custom made silver micas, so I guess they couldn't get these in SMD.


----------



## 10SNE1

Here are some pics of my completed PPA.

 It's housed in the 'stretch' model of the standard Hammond enclosure; I made a regulated 24v PS powered off an external AC wallwart.





 Amp has bassboost switch up front. Most of the rest of the components are plain vanilla, so this amp was fairly nominal in cost.









 It sounds terrific, although I do not have the most discriminating ear. Very quiet, no hum at all. When I have the volume cranked up full (no signal, of course), all I hear is some crackling like a quiet campfire. I would never listen at that volume so I guess it's academic that there is that noise.

 My compliments to the PPA team - a very nice design, not too difficult to build (the hardest part was casing it up - cutting that ALPS pot shaft is TOUGH. I had to use a diamond cutoff wheel in my Dremel and it still took some time).


----------



## ppl

10SNE1
 That faint noise sounds to me like Rectifier Diode switching noise. try some 470pF capacitors between all 4 posts of your Bridge rect. this requires 4 capacitors. What kind of sockets are the Buffers mounted in? look Blue to me rather than Black.


----------



## protos

Quote:


 _Originally posted by morsel _
*stepped attenuator, and custom wired Sennheiser HD600 headphones with Canare StarQuad cable and a 4 conductor XLR or Speakon connector. * 
 

 Is it really necessary to get expensive cables?Why not just get a replacement cable from Sennheiser , chop off the 1/4'' plug and put a 4-pole connector(s) of your choice . After all the original cable has four conductors.


----------



## Voodoochile

StarQuad is only about $0.50 a foot, so it's not expensive. There is labor invloved, however.


----------



## morsel

Protos, you are right, it would be easy to put your own 4 conductor plug on the stock cables. I also forgot about dealing with those custom Sennheiser connectors that plug into the ear cups, and the Cardas cables with molded on Sennheiser connectors. You could get the balanced version. Not sure what plug it comes with, but it would be simple to replace. A pricey choice, but so is building a balanced PPA.


----------



## 10SNE1

Quote:


 That faint noise sounds to me like Rectifier Diode switching noise. try some 470pF capacitors between all 4 posts of your Bridge rect. this requires 4 capacitors. What kind of sockets are the Buffers mounted in? look Blue to me rather than Black. 
 

I will try that in a revised version of the PS. Actually, the noise also contains a faint 'ticking' sound with the volume at max. But this may also be related to the diode switching noise.

 Edited to insert revised PCB:






 The buffer sockets are actually 16 pin sockets installed over two of the buffer locations. I had a bunch of these left over from other projects. Just have to remember that the dimpled ends of the buffer chips face each other in the middle


----------



## morsel

I will be out of town with no Internet access from September 24 to October 8. Have fun with your amps. See you in a couple of weeks.


----------



## Kadail

Well, a long while back I bought a pair of hd-600's and due to money constraints I never considered buying/building an amp. Thats changed now and I really want to try these out with an amp. I talked to my brother (hes just finishing his EE degree at college) and said he would probably be able to build me the PPA. I plan to get him the best parts possible for it, but am not sure what those might be. I did quite a bit of reading and saw that some people like to use black gate capacitors, so maybe those will fit the bill. Based on the builders current experiences with the PPA here at head-fi, which opamps/buffers (accessible) or anything else that effects the sound of the amp would sound best with the hd600's? My source currently is a m-audio audiophile 2496. I haven't upgraded any cables yet, I plan to do that once I get a hold of some kind of amp. Any feedback is very much appreciated, thanks!


----------



## Glassman

If you don't want to spend that much money, use decent parts, becouse anything else than opamps and buffers doesn't affect the sound that much.. possibly those C1 caps.. I think that Panasonic FCs are just fine and are relatively cheap..

 as for your Audiophile 2496 - seriously consider this -> opamp replacing


----------



## g14389

I chose a bigger case and PS than needed in case of future expansion to this amp.


----------



## Voodoochile

Cool amp! Nice job with the wiring.
 That PSU could power a whole bank of PPAs! HUGE transformer. Maybe you could expand into a 6.2 surround headphone amp later 
	

	
	
		
		

		
		
	


	




 . Set up the case like a Citrix frame!

 Edit: Welcome to Head-Fi, also. Thanks for sharing pics of your work.


----------



## ablaze

hey guys, one of my friends contemplating a PPA is considering STACKING the buffers eg. 2 per socket, total 24. is this possible?


----------



## ablaze

another question: how does one change the GAIN on the PPA?


----------



## tangent

Quote:


 STACKING the buffers eg. 2 per socket, total 24. is this possible? 
 

Yes, but due to the low output resistance, you should match the offset of your buffers so they don't get warm fighting against each other. Put them in a socket, measure the voltage drop from IN to OUT on each buffer and sort them by that drop. Then pair them up so that each pair is close to each other.

  Quote:


 how does one change the GAIN on the PPA? 
 

R4.


----------



## jtfoo

I find the Bass boost on my PPA too overwhelming.. I'm using 68nF // 15nF for total 83nF for C7 and R7 is 100K.. 

 I'm thinking of reducing R7 to 50K, how many dB boost will this give?


----------



## PeterR

about 15dB, 5dB less than now.


----------



## tangent

You might also consider increasing the value of C7. Even 220nF isn't unreasonable.


----------



## jtfoo

Quote:


 _Originally posted by PeterR _
*about 15dB, 5dB less than now. * 
 

Thanks, I guess 5dB I should hear a significant reduction in bass boost?

  Quote:


 _Originally posted by tangent _
*You might also consider increasing the value of C7. Even 220nF isn't unreasonable. * 
 

Hi tangent,
 Wouldn't increasing the value of C7 also increase the range of frequency to be boosted? How does this help?


----------



## tangent

Quote:


 I guess 5dB I should hear a significant reduction in bass boost? 
 

Yes.

  Quote:


 Wouldn't increasing the value of C7 also increase the range of frequency to be boosted? 
 

My docs said that up until recently, but they were wrong. The higher the value of C7, the lower the corner frequency of the filter.


----------



## jtfoo

Quote:


 _Originally posted by tangent _
*Yes.

 My docs said that up until recently, but they were wrong. The higher the value of C7, the lower the corner frequency of the filter. * 
 

Thanks for clarification, the last I read your tweak doc was sometime ago.. I'll try changing C7 first to maybe 0.1uF as I have plenty of these.


----------



## ablaze

hmm..is it normal for the amp to hum with no source connected, but for the hum to go away once a source is plugged in?


----------



## Chipko

Ablaze, yes, your input can act as an antenna when unconnected.


----------



## eric343

Quote:


 _Originally posted by ablaze _
*hmm..is it normal for the amp to hum with no source connected, but for the hum to go away once a source is plugged in? * 
 

No. No properly working amp I've ever had has done this... Even my KGSS with its gain of 1000 doesn't do this.


----------



## ppl

if your amp is at min Volume no Hum should be present regardless of wether or not any input is connected. If the Volume is set at any higher than min. yes hum can get in via the input on poorly shieled input cables or twisted pair.


----------



## ablaze

the hum kicks in at about 50% of the max volume. I've already taken pains to twist the input cables. I think I"ll try to shorten it, its about 3cm long now.


----------



## Voodoochile

I don't see that effect at all, ablaze... not even with the bare PPA on the workbench. And that is saying something because there is a fluorescent fixture 3' above, and a computer monitor about 10" away. Nothing like hum to report.

 My inputs are connected with some mini starquad.


----------



## jtfoo

Ablaze, a possibility could be your PSU. Try using a better one then the one from SLT. Or better use batteries.


----------



## tangent

Have you attached a ground strap to your pot, ablaze?


----------



## picklgreen




----------



## ablaze

tangent: done from the start

 jt: my psu's one of those with a 2 pin plug to the wall, no ground connection, could that be it?

 voodoochile: yes, I heard you at the beginning of the thread 
	

	
	
		
		

		
			





 anyway, I'll try shortening my input wires. hope that'll work.


----------



## jtfoo

Quote:


 _Originally posted by ablaze _
*jt: my psu's one of those with a 2 pin plug to the wall, no ground connection, could that be it?
 . * 
 

Use to think that my laptop PSU was good, becoz I paid more than $30. When I used it with my Meta42, there's some hum, despite I grounded the vol pot. Only when I change to a SLA battery supply, the hum went away.
 And my laptop PSU is a two pin type too.


----------



## ekwinix

Hey guys.
 I'm basically starting out in audio DIY and have a question that alot of you might find ameteurish, but why is it that the ground has the same setup (i.e. op-amp, buffer) as right and left channels? Especially since its not going to the output?
 Cheers.


----------



## tangent

The ground channel _does_ go to the output. The currents sourced by the right and left channels go through the drivers and come back to the ground channel on the positive swing of the AC signal, and the current for the negative swing comes from the ground channel. That's right, the ground signal has to do things that are very similar to what the left and right channels do.

 If you make all three channels as similar as possible, you get more symmetrical behavior. Even better might be to have _four_ channels, and rewire your headphones to use separate wires for the left and right drivers, but that's more work than most people want to go to.


----------



## phaedrus

I realized Saturday evening that I'd spaced ordering my buffers from newark. I've had quite a bit of bad luck with their system (deleted carts, unable to place orders, shipped the wrong parts). As newark's system didn't want my money, I started looking for someone who would be willing to relieve me of it. After a quick stop at Intersil, I wound up at www.arrow.com. The order and registration was pretty flawless and the prices on the two items not available at digikey or mouser were quite a bit less (MC33340P is $.84 vs $1.99, HA3-5002-5 is $3.07 vs. $3.85) . 

 I just received the confirmation email/invoice for my order, so it appears that it is a go for your random joe off the information highway. I'll be certain to post if any issues pop up, but I'd expect that the chips will be here Wednesday so I can finally fire my PPA up.

 [edit: fixed me bad grammah]


----------



## JMT

I just started using Arrow for some components, they are on my "Preferred Vendors" list.


----------



## picklgreen

To wire 2 headphone jacks do I just wire them in parrallel or do i need to add an isolation cap or anything?


----------



## binary_digit

We use multiple headphones with Y adapters, so paralleling should be fine.


----------



## tophu

If you parallel them, then they can interfere with each other. Also, since you've only got one volume control, it can be tricky to match the volume on both outputs if they are different types of headphones.

 If its an option, you're better off splitting the signal at the source output and using a separate amp for each headphone.


----------



## crane

The company I work for deals with arrow for many of our electronic needs. If your company deals with Arrow, contact them directly. The prices they quote on their web site are much higher than if you deal with them directly. 

 I paid $3.52 (CAN) each for the HA3-5002-5's +$7.50 (CAN) for shipping. 
	

	
	
		
		

		
		
	


	




www.Arrow.com quotes the HA3-5002-5's @ $3.07 (US) each.


----------



## Jupiter

Quote:


 _Originally posted by tophu _
*If you parallel them, then they can interfere with each other. Also, since you've only got one volume control, it can be tricky to match the volume on both outputs if they are different types of headphones.

 If its an option, you're better off splitting the signal at the source output and using a separate amp for each headphone. * 
 

What about using separate buffers for each headphone? Wouldn't that be almost as good? Except for volume, obviously.


----------



## tophu

Sure, volume issues aside separate buffers for each output would certainly work.


----------



## PeterR

Quote:


 _Originally posted by tophu _
*Sure, volume issues aside separate buffers for each output would certainly work. * 
 

With a PPA that won't work, as the buffers are in the feedback loop.


----------



## Jupiter

OK, I didn't think of that.

 I assume there is some reason why you can't add another feedback loop?


----------



## tangent

You could add another stage after the PPA outputs with no voltage gain, but you'd also have to add an op-amp to control the errors of the buffer, and then you'd want it to be Jung multiloop, and now you've basically doubled your PPA only now you're using 3x the components (1x input, 2x output) instead of just 2x. Doubling the entire amp and splitting at the input is a better plan.


----------



## Jupiter

I see. Thanks for the explanation, tangent.


----------



## doobooloo

I'm planning my PPA at the moment, and I have a few questions:

 1. Since I'm planning to use the OPA637/627 combo, I would need more than 12 cells to sound at its optimum, right?

 2. So, I was thinking of going with 18 AAA's, and I had a lot of trouble finding a >30V power supply. I found a few 36V and 48Vs but they were quite expensive, so... I was thinking of buying two Elpac WM080s and putting them in series to create 48V. Would this high voltage be a problem for the charging circuit/amplifier?

 3. Or, could I just buy similar spec'ed 12V Elpac and connect that in series with the 24V WM080? Would this be feasible? Or, does anyone know of a good, affordable 36V PS?

 4. I'm confused about the battery board power switch. It says that it will charge when external power is plugged in, and it will run from the batteries when it is not. Does that mean when external power is connected, I can only charge and can't run the amp from the external power source? (i.e. I can't have it as a home amplifier for most of the time?)

 5. Is it a good idea to have two power LEDs - one for the battery board, one for the main board? So, the battery board will indicate charge status and whether it is being used, and the main board will simply indicate whether the main board is being powered.

 Thanks in advance for all your help!


----------



## Jupiter

Did anyone try their PPA as a preamp, yet?


----------



## Glassman

and did someone ever tried comparing the sound of regular wired PPA vs. headphone ground hooked directly to PSU ground leaving out the ground channel..?..! I wonder how much this affects the sound..


----------



## phaedrus

Quote:


 _Originally posted by doobooloo _
*4. I'm confused about the battery board power switch. It says that it will charge when external power is plugged in, and it will run from the batteries when it is not. Does that mean when external power is connected, I can only charge and can't run the amp from the external power source? (i.e. I can't have it as a home amplifier for most of the time?)
* 
 

The PPA and BB are configured to use Molex KK connectors. Your power supply can send juice to both boards. The system of diode bridges between the two boards insures that the amp gets powered by whichever source has the best bang. Using the amp while charging the BB was a design consideration and has been built in.

  Quote:


 *
 5. Is it a good idea to have two power LEDs - one for the battery board, one for the main board? So, the battery board will indicate charge status and whether it is being used, and the main board will simply indicate whether the main board is being powered.
* 
 

Using two LEDs will do what you say. Assuming you configure your amp board LED with a ZNR or CRD, it will also tell you when it is time to get the amp hooked back up to the grid.


----------



## 10SNE1

Quote:


 I was thinking of going with 18 AAA's, and I had a lot of trouble finding a >30V power supply. 
 

If you are using NiMH rechargeables, remember that they are nominally 1.2 volts so 18 in series is 21.6 volts.

 Therefore, a 24 volt supply should be adequate to charge these; if not, you can easily make a regulated DC supply using a LM317 and a 24 - 30 v AC source like a transformer or wallwart to provide more voltage.


----------



## doobooloo

phaedrus - Thanks a lot for the info. 
	

	
	
		
		

		
		
	


	




 it really cleared up some things for me.

 10SNE1 - On Tangent's PPA site, it says for 18 AAAs to work with the fast charger, I'll need at least 33V... Or is there a way to make this work with the 24V supply?

 Also, in general, would 12 AAAs be sufficient to drive the OPA627/637s? If so, I guess I'll just go with 12 instead of the crazy 18 and save myself a lot of trouble... But I'm just afraid that the opamps will not sound its best with only about 12V of supply. (And since I'll be using the CD3Ks primarily, I would really like to have that warm BB sound...)

 Thanks again for all your help!


----------



## tangent

Quote:


 Since I'm planning to use the OPA637/627 combo, I would need more than 12 cells to sound at its optimum, right? 
 

I have one PPA with those op-amps running from 12 cells at the moment. It works well, though it does start clipping before the cells are fully dead.

  Quote:


 So, I was thinking of going with 18 AAA's, 
 

Why not go with 15 or 16, and use a readily-available 30V supply? The simplest would be an Elpac WM071 or 72 (I forget) which is +/-15V. Just ignore the ground leg.

 36V would be right on the edge of the maximum I would accept. You'd be straining the op-amps at that voltage level (even after counting the diode and JFET drops). And, you'd be generating a lot of heat due to the voltage drop across the battery board's regulator. 

 As for 48V, that isn't even workable. You'd blow up almost every active device in the amplifier with that much voltage.

  Quote:


 Or, could I just buy similar spec'ed 12V Elpac and connect that in series with the 24V WM080? 
 

Yes, this would work if you used isolated power supplies. Elpac's linears qualify. But, I have to wonder if it isn't worth going with a custom power supply at this point? I am working on such a design now, but unfortunately it will be weeks before anything is ready.

  Quote:


 Did anyone try their PPA as a preamp, yet? 
 

The PPA design is a bad one for a preamp. It is designed to power passive components (headphone drivers). If you want a preamp, look elsewhere.

  Quote:


 a 24 volt supply should be adequate to charge these; 
 

You don't know what you're talking about. For just one thing, NiMH cells will hit ~1.55V each before their voltage starts to drop under charge. There are other voltage drops in the PPA battery board charging circuit that you're not taking into account, too.


----------



## eric343

Quote:


 _Originally posted by tangent _
*
 The PPA design is a bad one for a preamp. It is designed to power passive components (headphone drivers). If you want a preamp, look elsewhere.
* 
 

That's a bit misleading, no? Headphone drivers are a bit more reactive (since they have inductance, capacitance, and low impedance) than the resistive load of an amplifier input (plus a few hundred pF for interconnects). 

 Of course, I don't know what kind of voltage swing is required, but I don't think it's that much - Kevin's dynamic amp reportedly makes an excellent preamp.


----------



## tangent

If you use a PPA as a preamp in most systems, that will basically short out the ground channel's input and output through the grounding of the interconnects, making it completely useless. It should work connected like this, but you'd be wasting its capability.

 The reason an amp like the KGCA works as a preamp is that the ground is basically just a wire. It doesn't matter if it's part of a greater path through the rest of the system.

 Now, one could either hack up a PPA board or make something similar on a new board, but then it's not a PPA any more. My original statement stands: the PPA is not a good design for a preamp.


----------



## eric343

Depends on how you wire it, actually... (if the input and output RCA jacks are electrically isolated, you should theoretically be able to have the ground terminals of the output jacks connected to the ground channel output)

 But you're right that the PPA (especially the ground channel) is really optimized for reactive loads and it would be pretty much overkill to use it as a preamp.


----------



## Jupiter

Quote:


 _Originally posted by Jupiter _
*Did anyone try their PPA as a preamp, yet? * 
 

To clarify: I'm going to build a PPA for headphone use. I was wondering if it would also perform well as a preamp, since that would be a nice bonus. I guess the answer is no.


----------



## doobooloo

Thanks for all your help so far!

 I think I'll just go with the WM080 + WM060 (24V + 12V) and use 18AAAs. In this case, I'll definately need to up the voltage specs of all the caps to 50V, right?

 Any other cautionary measures I would need to take by upping the voltage to 36V?

  Quote:


 But, I have to wonder if it isn't worth going with a custom power supply at this point? I am working on such a design now, but unfortunately it will be weeks before anything is ready. 
 

Do you know of any good >30V custom power supply designs that are available as kits/half kits? I see the Hagerman PS... (http://www.hagtech.com/bugle.html#powersupply)

 Also, if you have +/- 15V supply instead of single 30V, how would the PPA board power setup be different?

 Thanks a lot again in advance!


----------



## guzzler

Quote:


 _Originally posted by doobooloo _
*Also, if you have +/- 15V supply instead of single 30V, how would the PPA board power setup be different?* 
 

just connect the + and - lines from the PS and don't connect the ground. That gives you 30V onto the PPA board...

 g


----------



## tangent

Quote:


 I'll definately need to up the voltage specs of all the caps to 50V, right? 
 

Yes. All the more reason to build a custom power supply, so you can use ~32V to power everything, and thus stick with 35V cap.

  Quote:


 Do you know of any good >30V custom power supply designs that are available as kits/half kits? 
 

There's the Welborne Labs PS-1, which is a full circuit kit (no enclosure, jacks, etc.). It's about $100, IIRC.

 AudioXPress still offers the Didden-Jung super-regulator PCBs for about $25 for a positive/negative pair. (You only need to use the positive half with the PPA.) You need to populate the board, which isn't that expensive, and then add a transformer, diode bridge, and main reservoir capacitor off-board. The latter will account for most of the cost. Probably your total cost will still crest the $60 you'll be paying for two Elpac supplies, but the performance will be better.

 A cheaper alternative is the Velleman LM317 kit. It includes all the parts for the main circuit, and as I recall you just have to add a heat sink, transformer and any casework you want. At $13 for the kit and about $30 for the auxilliary parts, this should be cheaper than the Elpac path, and the performance should be basically equivalent.


----------



## doobooloo

Can I just use two WM080s and make a little voltage divider box thingy to supply ~33V?

 But the voltage be sort of variable with changing loads, right? (since it'll be driving some load) But how much of an effect will this have on the amp performance (is it a significant problem or can it be safely ignored?)


----------



## tangent

Quote:


 Can I just use two WM080s and make a little voltage divider box thingy to supply ~33V? 
 

If you're thinking "a pair of resistors", then the answer is "not sanely".

 You need to put about 10x more current through a voltage tivider than is delivered from it to keep the voltage from waggling too much under load. So let's see, about 300mA (at least) under full load means at least 3A through the divider. To get that much at 33V you need the divider pair to be 11 ohms (or less). A 5% resistor pair that seems to meet this criteria is 3.3 and 6.8 ohms. This gives you 32.3V when the input is 48V. If you take 300mA from the divider, that puts under 1/2W across the 3.3 ohm resistor. No problem. The remaining 3.2A must go through the lower resistor, requiring a 70W resistor AT MININUM. You'd probably end up with a much larger resistor because you'd have to derate it for the heat you'd produce.

 No, the right solution if you had to use two series supplies is to put a linear regulator after them. Then you ask, "Why do you need three linear regulators? Why not use two unregulated supplies?" Good question. But if you do that, you're on the road to building your own custom supply, so why not _just do it_?


----------



## Magic77

I'm 99% sure I'm going to build the PPA Amp and have a couple of quick questions:

 1. Q3: If I use 6 JFETS; Do I only use one TLE or 3? I'm not really clear about the TLE's and Rail Configurations.

 2.C2, C3 & C5: Is it OK to install these just to be safe? Or; are they only needed if there are oscillation problems?

 I do not think I am going to use Class "A" biasing.


----------



## binary_digit

Quote:


 _Originally posted by Magic77 _
*I do not think I am going to use Class "A" biasing. * 
 

Why would you not Bias to class A ?

 Just curious

 Peace,
 B_D


----------



## Magic77

Quote:


 _Originally posted by binary_digit _
*Why would you not Bias to class A ?

 Just curious

 Peace,
 B_D * 
 

Maybe since I've never built an amp like this before, I'd rather keep things simpler at first. Or; maybe I'll change my mind after my questions are answered.


----------



## binary_digit

Quote:


 _Originally posted by Magic77 _
*Maybe since I've never built an amp like this before, I'd rather keep things simpler at first. Or; maybe I'll change my mind after my questions are answered. * 
 

Cool

 B_D


----------



## tangent

Quote:


 If I use 6 JFETS; Do I only use one TLE or 3? 
 

2 or 4 JFETs on the Ground channel goes with 1 TLE, and you tie the three sets of rails together with jumpers. 6 or 12 JFETs with 2 or 4 on each channel goes with 3 TLEs because you keep all three rails separate. To put it another way, you use one TLE per set of rails, so you only use one TLE when you tie all of the rails together.

  Quote:


 C2, C3 & C5: Is it OK to install these just to be safe? 
 

C5 is pretty much necessary under all conditions. C2 is good to have, but not essential. C3 can be left out unless you have problems.

  Quote:


 I do not think I am going to use Class "A" biasing. 
 

Perfectly fine, at first. I do recommend keeping the amp config simple from the start, and then adding complexity later. You might order your biasing JFETs with the initial parts order, though, because a few JFETs will be under the ordering minimum from almost any supplier.


----------



## Magic77

tangent,

 Thanks very much for the reply, it helps a lot. One more question though about the Volume Pot:

 Is the ALPS Blue, the only pot that "should" be used? Or, can you use the Panasonic EVJ-C20 or the ALPS 9mm 50K as mentioned with the META project?


----------



## doobooloo

Hello,

 One more question arising from ignorance:

 Only caps C1 and C2 need to be over the PS voltage, right? C7 is in the signal path, and C4 and C5 are all post-TLE so they get half the voltage...?

 Basically, is it safe to use 30V rated caps on C5 when my PS will be ~33V?

 Also, how safe is it to have the PS voltage so close to the rated voltage of the caps? For example, is it reasonable to have a 35V PS with 35V rated C1/C2?

 Gosh, I should have picked EE over ME two years ago... 
	

	
	
		
		

		
			





 Thanks in advance for the help!


----------



## guzzler

Quote:


 _Originally posted by Magic77 _
*Is the ALPS Blue, the only pot that "should" be used? Or, can you use the Panasonic EVJ-C20 or the ALPS 9mm 50K as mentioned with the META project? * 
 

the ALPS Blue is the specified pot, the EVJ and 9mm ALPS would be false economy as they are nowhere near as good. Even better than the Blue would be a stepped attenuator, but we're talking serious cash for those!

 g


----------



## tangent

Quote:


 Is the ALPS Blue, the only pot that "should" be used? 
 

No, there are several fine alternatives out there.

  Quote:


 Panasonic EVJ-C20 or the ALPS 9mm 
 

Those aren't among them.

  Quote:


 Only caps C1 and C2 need to be over the PS voltage, right? C7 is in the signal path, and C4 and C5 are all post-TLE so they get half the voltage...? 
 

Yes, but as always, I recommend that you make the post-TLE caps at or above the PS voltage as well. In your case, 35V caps are readily available.

  Quote:


 how safe is it to have the PS voltage so close to the rated voltage of the caps? 
 

It depends on how well regulated your power supply is. If you're 2V under, it would take a pretty bad power supply to jump more than 2V and pop the caps. If you're 0.2V under, you're playing with fire.

  Quote:


 is it reasonable to have a 35V PS with 35V rated C1/C2? 
 

You don't want a 35V PS in your situation anyway. 32 or 33V is just right.

 A tease: http://tangentsoft.net/audio/ppa/ps/


----------



## doobooloo

Quote:


 A tease: http://tangentsoft.net/audio/ppa/ps/ 
 

GAH! Just when I make my big decision to spend $150 on the Welborne PS-1... I was like, two inches (?!) away from clicking that order button and you post that picture...






 It's really nice. I know this is a really a shouldn't-be-asked kind of a question, but in how many weeks/months will the PS be ready for us to purchase?

 Also, how much of a performance difference is there between the Welborne PS-1 and the PPA PSU? They're kind of different beasts, it seems like, but still... 
	

	
	
		
		

		
		
	


	




 More waiting...


----------



## jasonhanjk

Wah nice.
 At that size, the output of that transformer should be around 2A.


----------



## tangent

Quote:


 how many weeks/months will the PS be ready for us to purchase? 
 

Even if this were a PM and not a public forum, I wouldn't have a solid answer for you. I know for certain that the final version will be different from what you see. Since I don't know when I will be satisfied, I can't predict when I will order boards.

 If you want something right now, go with that Velleman kit I mentioned. (K1823) I finally got around to testing mine, and it actually beats my PPA PS prototype. I attribute the difference to superior layout on Velleman's part. That's one of several things I'll be fixing in my next prototype.

 Incidentally, both do better than the Creek OBH-2, so the difference between the Velleman PS and my prototype isn't a matter of "junky" vs. "less junky" but rather "pretty darn good" vs. "even better". I would be tempted to wrap up testing right now if I hadn't tested the Velleman. I have a new benchmark of price/performance, so I now have to improve my supply's performance to justify its higher parts cost. If I can't, I'll just start building Vellemans for my PPAs.

 Anyway, the Velleman kit is less than $14 from Parts Express, and you just have to add a transformer and a heat sink to it. You can probably get all that from PE for $25 or so. Add a box and some hardware, and you're still under $50.

  Quote:


 how much of a performance difference is there between the Welborne PS-1 and the PPA PSU? 
 

I don't know, since I've never tested a PS1. However, my first prototype is also an LM317-based power supply, and the schematics are similar. The differences in the PS1 are either 1) not useful for the PPA (e.g. dual rails) or 2) overkill (e.g. super-tweaky capacitor setup). I tried several of the "enhancements" in the PS1 on my first prototype, and they made zero difference to the test results. Also critical here is that the PPA is pretty tolerant of bad power quality, so I don't expect that a listening test would help sort this out. What I'm after here is a good quality power supply for not too much money. Since ultimate power cleanliness isn't going to be necessary for the PPA, I'm going to be stopping short of the best quality power designs that I know are possible. There just wouldn't be any justification for the higher parts cost and circuit complexity.

  Quote:


 the output of that transformer should be around 2A. 
 

The transformer is only 60mm square. Output is 500mA for this 30V version. You can get a higher VA unit in the same footprint (it's taller) and you can go with a lower voltage to get more amps. The biggest you can manage in this footprint is about 1.3A while still maintaining a good output voltage. I doubt I'll be going with the next size larger.


----------



## jasonhanjk

> The transformer is only 60mm square. Output is 500mA for this 30V version.
> 
> 
> 
> ...


----------



## jtfoo

I'm in the process of adding the battery board. From Tangent's site the calculator says I need >33V of power supply for 18 cells. I was wondering will 33V be too much for the AD8610 opamps to handle? the spec sheet says the AD8610 handles only +- 13V or 26Vdc.


----------



## Jupiter

Is there room for both the amp and battery board in one Hammond 1455 case?


----------



## phaedrus

26V is the max for the AD8610's.

 The battery board goes in slot 3 from the bottom face down and the PPA board goes face up on slot 4 in a Hammond 1455.

 If I recall this and other threads correctly, tangent recommends 12 AAA with a 24V PS, 15 AAA with a 30v (though you'll not be able to use the AD8610's).


----------



## aos

Quote:


 Yes, but as always, I recommend that you make the post-TLE caps at or above the PS voltage as well. In your case, 35V caps are readily available. 
 

I do the opposite. Electrolytics lose capacitance if they're run well below their rated voltage, and it's also a waste of space (i.e. you can use twice as much capacity at half the voltage).


----------



## jtfoo

Quote:


 _Originally posted by Jupiter _
*Is there room for both the amp and battery board in one Hammond 1455 case? * 
 

you can still fit both board in provided you're using AAA battery holder. But there's not much tolerance left for height.


----------



## doobooloo

I have a question regarding the Velleman kit.

 It says in its manual that the maximum input voltage is 28VAC, but I really want to use an Avel 30VAC toroidal available on Parts Express. I don't really see why the design would not allow 30VAC to run fine - or am I missing something in the circuitry that would cause problems with a 30VAC input?

 Thanks again! All the parts are now on their way - I can't wait to start building this amp! 
	

	
	
		
		

		
			





 [edit] Also, the manual recommends a 50VA transformer for 22!~35V output voltage, but the Avel toroidal is rated at 30VA. Would this a problem for the PPA?


----------



## Nisbeth

Deleted. Incorrect information 
	

	
	
		
		

		
		
	


	




 /U.


----------



## protos

Quote:


 _Originally posted by Nisbeth _
*If you feed it more than 28 VAC you'll exceed the max. input voltage limit on the regulator (see datasheet for the LM317).

 /U. * 
 

 Perhaps you misunderstood something.The maximum input to output differential is 40V.So theoretically you could have a 100v input and regulate until 60v.


----------



## Nisbeth

Oops, my bad 
	

	
	
		
		

		
		
	


	




 /U.


----------



## jasonhanjk

Quote:


 _Originally posted by jtfoo _
*I'm in the process of adding the battery board. From Tangent's site the calculator says I need >33V of power supply for 18 cells. I was wondering will 33V be too much for the AD8610 opamps to handle? the spec sheet says the AD8610 handles only +- 13V or 26Vdc. * 
 

It was assumed each cell gives 1.2V when at normal operating voltage. Adds up to 21.6V. It is not advise to charge the batt and using the amp at the same time.





 Post some **** at our forum leh...


----------



## tangent

Quote:


 the calculator says I need >33V of power supply for 18 cells. 
 

That's only if you use a standard regulator. Spend a little bit more on an LDO and you can get away with as little as 31V. Elsewhere here on Head-Fi I've talked about the reasons why the supply voltage number the calculator gives is not set in stone. Do a search for "LDO slack" or something like that. Or, look at the current vs. dropout voltage for the regulator you're wanting to use.

  Quote:


 the spec sheet says the AD8610 handles only +- 13V or 26Vdc. 
 

Indeed.

 I keep saying that 18 cells isn't required except in a few situations. If you step back to 15 cells, you can charge that with about 27V, and you can arrange the voltage drops along the rails (diodes, JFETs) to soak up that extra volt so you don't hurt the 8610s. Then on batteries, you get about 18V to the op-amps, which allows over 5Vrms to the headphones with this chip. _Very_ few headphones in this world require that much voltage. From calculation I think even the AKG K1000s only need around 3.5V to exceed 90dB. More typical headphones require 1.5V or less.

 The reason I left enough room on the battery board to accept 18 cells was for voltage-inefficient op-amps like the AD843. That one has about a 7Vp-p limit from the rails to the output, for symmetrical signals like audio. With 18 cells, you'd be able to get 5Vrms out, just like 15 cells with the AD8610.

  Quote:


 I don't really see why the design would not allow 30VAC to run fine 
 

It has to do with the way transformers work.

 The output voltage rating of a transformer is given at full load. At lesser loads, the output voltage rises. Few transformer datasheets tell you what voltage the transformer will reach under no load. Here's one of the few I've seen that does: http://amveco.com/Low_Profile_PC.htm

 Take a look at the 2x15V lines. Each one gives a different voltage under no load, due to design differences. The highest one is 2x21.4V. Assuming that this same sort of thing happens with transformers from other manufacturers, you might reasonably see a 40V no-load output from a "28V" transformer.

 It gets worse. When you run 40VAC through a diode bridge, you get 1.414x the DC voltage from it, so now it's 56VDC. In my kit, Velleman provided a 35V C4 cap. Already we're in trouble. Probably you can't actually get 35V out of this circuit without replacing C4.

 After replacing C4 with a 50V or 63V cap, you have to worry about the voltage drop across the regulator. Because this circuit is designed to give you full adjustability from 1.5V to 35V, you have to be careful that you've set it for 35V before turning it on. You can probably exceed the regulator's maximum voltage drop if you use a high-voltage transformer and turn it on with the trim pot set for 1.5V.


----------



## Voodoochile

The information Tangent posted about the load/no-load output of the transformers is really key. I think that it presents an opportunity for people to blow up some caps if they aren't careful.

 You not only have to account for the output of the unit under a given load, but also anticipate the voltage rise in the even that the load is unexpectedly lifted. This can also affect stability of the regulator in some cases. There is a lot more to this than initially appears.

 If you get some massive toroidal transformer, you are going to need some very sturdy caps to deal with it, which can be quite limiting. You also have to consider inrush when such caps charge.


----------



## doobooloo

Aah. Thanks a lot for the info... I'm learning so much on these forums... 
	

	
	
		
		

		
		
	


	




 I have a question about the bass boost. Sample values on Tangent's website and Morsel's website include those that boost bass upto +20db (according to the micro-cap file) with R7 = 100K...

 Aren't these values rather ridiculously large? I mean, +12db on equalizers is overkill, and most of the time I'm happy with +3db~+6db only at the sub-bass areas just to compensate for the natural roll-off of headphones... (like Jan Meier's Analoguer).

 But, even with C7 = .12uF, the bass boost extends up too far for my liking - and after experimentation I found that what I would really like is C7 = .22uF or .33uF.

 So, a few questions here - first, is the voltage db the same as the db scale used on equalizers? Isn't the voltage decibel defined as 10log(v2/v1) and SPL decibel as 20log(v2/v1) or something? This would make a lot more sense (I'll be halving the values I see on the Micro-Cap graph) since +20db of bass boosting sounds a little, well, too much. Or am I completely misunderstanding db?

 Second, are there any recommended caps for C7 that will have capacitances of 0.22uF or 0.33uF?

 Well - I guess what it all comes down to is, I'd like to have bass boost that starts boosting at around 100Hz (<+1dB), ~+3dB at around 50Hz, and 6~10dB of boosting by 20Hz. How should I tackle this?

 Thanks in advance!


----------



## tangent

Quote:


 Aren't these values rather ridiculously large? 
 

Depends on your situation and your tastes. But in general, I'm with you -- I want my corner frequency to be low and the boost amount to be much lower than 20dB. I wish I had some part values to recommend to you, but I haven't settled on a set I really like yet.

  Quote:


 is the voltage db the same as the db scale used on equalizers? 
 

Yes.

  Quote:


 Isn't the voltage decibel defined as 10log(v2/v1) and SPL decibel as 20log(v2/v1) or something? 
 

The other way around. 20dB in voltage is 10x.

  Quote:


 are there any recommended caps for C7 that will have capacitances of 0.22uF or 0.33uF? 
 

You'll have to go with polyester to meet that goal. Sorry.

  Quote:


 How should I tackle this? 
 

Download the MicroCap demo, download the starter circuit file from the bass boost section of the PPA docs, and start playing.


----------



## doobooloo

Thanks for the reply, Tangent. 
	

	
	
		
		

		
			





  Quote:


 You'll have to go with polyester to meet that goal. Sorry. 
 

So, polyester is not as sonically desirable as polypropylene, but in reality, how much of a sonic difference is it going to make?

 Or should I go with "creative mounting" and mount some big high quality polypropylene film caps in there somewhere?

 Thanks again! 
	

	
	
		
		

		
		
	


	




 [edit] OK, I just read up on The "Sound of Capacitors article linked from the META42 page, still not so sure...


----------



## doobooloo

Quote:


 _Originally posted by tangent _
*After replacing C4 with a 50V or 63V cap, you have to worry about the voltage drop across the regulator. Because this circuit is designed to give you full adjustability from 1.5V to 35V, you have to be careful that you've set it for 35V before turning it on. You can probably exceed the regulator's maximum voltage drop if you use a high-voltage transformer and turn it on with the trim pot set for 1.5V. * 
 

So, the LM317 regulator will tolerate the 30VAC power supply as long as I'm careful with the voltage drop, and the caps need to be replaced with higher voltage parts...

 So... it *is* possible to use that 30VAC toroidal as long as I'm careful and get my 33V from the Velleman kit?

 Thanks!

 [edit] Also, what's the max size for the electrolytic caps on the Velleman kit? Or should I just build an outboard "cap bank"?


----------



## Voodoochile

Might be comparing apples to oranges here, but when I make an adjustable PSU (like PS1), I am careful to set the trimpot I use from the adjust pin to the proper value before installing it, for that very reason. Don't want to have it power up way out of spec.

 By adjustable, I also mean within a preferred range as well.... not infinitely adjustable. When you start dissipating 10+ volts across the regulator, your heatsink needs start to go through the roof.


----------



## doobooloo

I found a capacitor that will fit the C7 board layout and be pretty good: the WIMA MKP-2 Metallized Polypropylene @ 0.22uF is 7.2mm x 7.2mm.

 These would be ideal for the bass boost cap, but how do I get my hands on them from here in the US? They don't seem to have an official distributor... and Welborne labs has some but NOT the MKP-2 series...

 *hopeful look*


----------



## Magic77

Quick Question about the Elpac WM080 24VDC power supply:

 Do these have a DIN Connector or a regular DC Jack Connector?

 If a DIN connector; do you have to solder up a 2.1mm or 2.5mm DC Jack connector and cut off the DIN?


----------



## Arzela

It's a phone jack. Elpac.com has
 the part number...


----------



## Magic77

Quote:


 _Originally posted by Arzela _
*It's a phone jack. Elpac.com has
 the part number... * 
 

When I bring up this part # at newark.com, it says it has a DIN connector. Are there 2 different part #'s for different connectors?


----------



## Arzela

I'm not sure.
 My wm80 is wm080-1950-760 (from Mouser)

 At the Elpac site, they say the wm80's have
 the pone jack connector. I would
 assume Newark has a typo (I think "DIN mounting"
 should be "wall mounting"); but it's
 best to call them up and make sure.


----------



## Magic77

sorry, double post.


----------



## Magic77

Here's the link for the PDF:

http://www.elpac.com/uploads/documen...%20REV%20A.pdf

 It says DIN or Barrel connector; but I guess it's only for specific models on the PDF that may be different.


----------



## Arzela

The DIN is for the tabletop models, and
 for dual output models, perhaps some others. The wm080's output is through
 a phone jack. 

 In any case, you could always terminate it as you
 descibed above.


----------



## jamont

If you get the Elpac WM080-1950-760 from Mouser, the DC output has a barrel connector. It mates with a 2.5mm connector such as Mouser #163-4305


----------



## Voodoochile

The WM080s I have bought always have ahd the barrel connector.

 I believe when Elpac's data sheet says 'either DIN or barrel', it means if it's single voltage, you get barrel, and if dual or triple voltage, you get DIN. Certainly it seems to hold true with the WM080.

 [sidebar]
 Nice avatar, John!


----------



## tangent

Quote:


 So, polyester is not as sonically desirable as polypropylene, but in reality, how much of a sonic difference is it going to make? 
 

One could argue that you're already screwing with the sound quality by adding bass boost, so why worry about ultimate quality?

 Another way to look at it is that you don't really have to fit in the C7 footprint. There's actually lots of space nearby for a somewhat larger cap, if you don't mind it floating over other stuff.

 Finally, I just tried 0.1uF and 10K for C7 and R7, and I find it to be nonintrusive. If there's no real bass to be had, you can't even tell when you turn it on and off. When there _is_ bass there, it adds a pleasant warmth that you miss when you turn it off. You end up scolding yourself that you're a PURIST, DAMMIT and you shouldn't be listening to bass boost circuits. 
	

	
	
		
		

		
		
	


	




  Quote:


 So... it is possible to use that 30VAC toroidal as long as I'm careful and get my 33V from the Velleman kit? 
 

Don't guess, run the numbers. 

 Multiply the rated AC voltage by 1.4 to get a good estimate of the no-load AC voltage: 42V. Multiply by 1.4 again to get unfiltered DC RMS voltage: 60V. So, we need a 63V cap to replace the one Velleman supplies, and due to the limits of the LM317 you only have about 10V of adjustability across the regulator before you damage it. Again, start with the voltage regulation high, or set to the expected point as Voodoochile recommends, and then tweak it carefully around that value after turning it on.

 Wear safety glasses. Caps and regulators can explode violently.

  Quote:


 what's the max size for the electrolytic caps on the Velleman kit? 
 

About 45 x 20mm if you want to stay within the silkscreened box on the board. You'll probably only be able to get 1000uF in that much space, with a 63V cap.

  Quote:


 By adjustable, I also mean within a preferred range as well.... not infinitely adjustable. 
 

Yes, this is a weakness of the Velleman circuit. By adding a fixed resistor in series with the trim pot and making the trim pot small, you end up with a small but useful adjustment range. My current PPA PS prototype has a 29 to 35V range.

  Quote:


 The wm080's output is through a phone jack. 
 

No, the others are right: it's a barrel connector. If the full part number has a "760" in it, it means it uses a Switchcraft 760 style connector, which is a 5.5/2.5mm barrel connector.


----------



## doobooloo

Aah. I just ordered some large 0.33uF popyprop caps to somehow fit on the board... I was using a software EQ (from ANWIDA) and matching it with values I get from Micro-Cap and I decided that I really won't be satisfied with 0.1uF... and I really love the results I'm getting from 0.33uF + 33K C7 +R7... 
	

	
	
		
		

		
		
	


	




 It really seems to fill in the deep, low bass that at many times seemed missing, but still leaves rest of the music intact.

 It's not really bass _boosting_, it's bass _compensating_. 
	

	
	
		
		

		
		
	


	




  Quote:


 So, we need a 63V cap to replace the one Velleman supplies 
 

Oh shoot. I thought, since Velleman allows upto 28V transformers and comes with 35V caps, I thought for the extra 2V incease in transformer voltage I could be safe with 50V caps... so just last night I bought two 2200uF caps that fit on that silkscreened area from Mouser... gah. But I have a question - why multiply the 30V twice with 1.4? I mean, I understand the first one, but aren't electrolytic caps rated at AC voltage anyway, so why convert to DC RMS...? Or are they rated at DC?

 Do I really have to go and place another order for these caps...?

 Oh, and how about the three other caps in the circuit? Do I need to buy replacement caps for those as well?

 Oh, and how big of a heatsink do I need for the regulator? Can I just use the little one that fits on the PPA battery board?

 Thanks!


----------



## phaedrus

My PPA with battery pack is complete and cased. I added a modified linkwitz crossfeed, otherwise it is all pretty standard stuff. Many thanks to y'all for nursing me through my apparent inability to read the current versions of Warren's docs, my Cerafine withdrawals and my testosterone overload with regards to batteries.

 The amp sounds good, well, the music passing through the amp sounds good to my ears. I may need to tweak the bass boost a bit yet, and I may go for round 3 on the front panel once my drill press arrives; but, I'm otherwise done for the present. As I post this, I'm listening to Leona Naess's new self titled album, enjoying my morning beverage and looking forward to several nights' sleep before I do anything else. 
	

	
	
		
		

		
			





 So without further ado, on to the marginal 8mm feed! As I'm aware of the general male fantasy of girl on girl, here come the barely legal, dancing amps:






 One of my recent Meta42's riding pig back on the new Pimp Portable Amp. Nice knobs! 

 And the caboose isn't too bad either...






 "No, I've never done this kind of thing before, but you seem like a nice guy and it is only my top..."






 Did I mention that this battery board is *BARELY LEGAL*!!!






 We now return you to your regularly scheduled questions about building the PPA.


----------



## doobooloo

Wow, wonderful job on your PPA phaedrus! 
	

	
	
		
		

		
		
	


	




 Congrats!

 Yes, the pictures are too explicit and seusual for me, as I'm only at the stage of gathering parts and planning... and I dream night and day of having a fine one like yours on my desk dancing for me... 
	

	
	
		
		

		
		
	


	




 I'm glad it sounds good! What a great duo of amps you have!


----------



## phaedrus

How warm should the hammond case get while connected to the grid? I pre-charged my AAA's while I was building the battery board. Voltage checked out once I unjumpered those AA traces and replaced the melted battery holders. The regulator did not make it to "hot" at any point while uncased. The bottom of the hammond is toasty warm at present.


----------



## PeterR

Quote:


 Oh shoot. I thought, since Velleman allows upto 28V transformers and comes with 35V caps, I thought for the extra 2V incease in transformer voltage I could be safe with 50V caps... so just last night I bought two 2200uF caps that fit on that silkscreened area from Mouser... gah. But I have a question - why multiply the 30V twice with 1.4? I mean, I understand the first one, but aren't electrolytic caps rated at AC voltage anyway, so why convert to DC RMS...? Or are they rated at DC? 
 

I haven't followed the whole thread, but a no load voltage 40% above rated voltage means tangent's playing it safe or a very wimpy transformer. Generally, the higher the VA rating, the smaller the voltage droop under load. Expect about 15% from a 50VA transformer. The caps see the DC voltage after the rectifier, which is about 1.4 times the AC voltage (minus 1V or so loss from the rectifier).


----------



## Voodoochile

Nice looking work, phaedrus! There should be an 18+ warning on the thread. I had to do a double-take at the topless shot or the PPA... at first glance it appears that one whole channel is unpopulated! I was wondering how you could enjouy the sound only with your left ear, then noticed the inverted crossfeed board.

 The casework is darn good, especially considering you don't have the press yet. Kinda odd to get it after building these two amps, don't you think? 
	

	
	
		
		

		
		
	


	







 Thanks for sharing the pics!


----------



## Magic77

Can anyone suggest hook-up wire for the PPA project?

 24 or 22AWG? Solid or Stranded?

 Thanks.


----------



## phaedrus

Well, it's closer to projects 7 & 8 (2 cmoys, 1 cmoy with upgraded PS, 1 a47, passive 3:1 channel mixer, modified linkwitz on protoboard, and a more or less canonical meta42 with doubled el2001's and crossfeed preceded). I'd not buy a drill press just for my new amp habit ("if you'll buy that, I'll throw the golden gate in free"); however, since it can and will be used for amps, woodworking AND ceramics, it seemed like the thing to do.


----------



## Voodoochile

That's a subject of much debate...

 I like 22g stranded Alpha or Belden, Teflon insulated and plated.
 Canare star quad makes a nice connection from the jacks to the board, but the Alpha or Belden also works well, twist or braid it. Do not twist your DC connections.

 Others swear by solid copper, some like pure silver.

 Edit: (phaedrus) Yes, they are super handy to have around. Would have been nice to have say, 8 amps ago?


----------



## phaedrus

Quote:


 _Originally posted by Magic77 _
*24 or 22AWG? Solid or Stranded?* 
 

I'm using 24AWG stranded canare hookup wire, though I just started with a roll of 24AWG stranded from Radio Shack. I tried the solid core stuff and did not care for it as much. The canare, for what it's worth, is donated by a younger sibling who finds it only marginally more annoying to bring his post job scraps to me than to the dumpster.

 GnD ran a recent thread on the subject which is available here:

http://www4.head-fi.org/forums/showt...stranded+solid


----------



## phaedrus

Quote:


 _Originally posted by Voodoochile _
*Do not twist your DC connections.* 
 

But, but, it looks nice... (May I have some cheese and crackers with my whine?) Why is twisting the DC bad? 

  Quote:


 *Edit: (phaedrus) Yes, they are super handy to have around. Would have been nice to have say, 8 amps ago? * 
 

 Yes, yes indeed.


----------



## Voodoochile

Quote:


 _Originally posted by phaedrus _
*But, but, it looks nice... (May I have some cheese and crackers with my whine?) Why is twisting the DC bad? * 
 

Meh, maybe I'm just paranoid, but I worry about such things as electromagnetism, inductance, and a host of other effects that might not even be an issue with DC feeds. But I also want things to look neat, so I tend to slide some fiberglass sleeve over the DC leads instead.

 I should have dispensed that tip with a disclaimer.

 Perhaps someone of authority will wander in and provide some cheese to go-with!


----------



## morsel

Tangent said: Quote:


 The PPA design is a bad one for a preamp. It is designed to power passive components (headphone drivers). If you want a preamp, look elsewhere.

 If you use a PPA as a preamp in most systems, that will basically short out the ground channel's input and output through the grounding of the interconnects, making it completely useless. It should work connected like this, but you'd be wasting its capability. 
 

There is a good solution to this issue. Use signal ground for the preamp line out, not output ground. This prevents output ground from shorting to signal ground. A PPA wired this way will work just fine as a preamp.


----------



## tangent

Quote:


 why multiply the 30V twice with 1.4? 
 

The first 1.4 accounts for the voltage rise of the transformer under no load. Peter's right, this number will vary from unit to unit. I only use the 40% rise because it's the highest value I've ever seen, so it seems a safe starting value. If you're feeling lucky, you can also observe that the transformer is never operated under a complete no-load condition: you have the regulator's idle current pulling the transformer's output voltage down at all times.

 My PPA prototype PS uses a +/-15V supply and it puts 52V across the reservoir cap under no load conditions. My power supply has a higher idling current than the Velleman design.

 The second 1.4x factor accounts for the RMS voltage increase due to the diode bridge. "Camel humps" have a higher heating ability than a sine wave with the same peak amplitiude.

  Quote:


 Do I really have to go and place another order for these caps...? 
 

You can stick the two in series to get a 1100uF/100V cap. That'll work until you can get a 2200uF/63V to replace it.

  Quote:


 how about the three other caps in the circuit? 
 

Two of them are films, so they should be 63V or higher already. The other is the ADJ pin cap, so it sees the output voltage of the regulator minus 1.25V. It's a 35V cap in my kit.

  Quote:


 how big of a heatsink do I need for the regulator? 
 

The one for the battery board will be okay for low output currents, but you'll want a bigger one when using the supply to run the amp and the battery board. It might even get too hot running just the amp, with that heat sink.

 Radio Shack may have a bigger heat sink in stock.

  Quote:


 My PPA with battery pack is complete and cased. 
 

Nice work!

 Shall I call you the Larry Flynt of DIY? 
	

	
	
		
		

		
		
	


	




  Quote:


 The bottom of the hammond is toasty warm at present. 
 

It will normally get a bit warm when the cells are charging. Even if the cells are charged, the '340 chip has a power-on minimum charge time that it must go through before it will start checking the battery voltage, to account for cold start-ups. If you're using the '342, it's about 3x longer than for the '340. During this time, the regulator will put put out heat.

 Heat comes from two sources under your control: the voltage drop across the regulator, and current across R2. You minimize the first by using an LDO and setting your power supply's voltage to be the minimum that can possibly work, and you minimize the second by choosing a moderate charging current.

  Quote:


 I worry about such things as...inductance 
 

DC sees inductors as no different from a straight wire. AC sees inductors as a resistor whose value varies with frequency. Inductors are _good_ for power connections; they block RF. Now, twisting your wires together doesn't make a very good inductor....but it's not harmful, so go ahead.


----------



## Voodoochile

I'll will sleep better now, thanks!
 I was worried about creating some sort of electromagnetic field.

 edit: With regard to twisting or not twisting DC feed wire.
 Twist away!


----------



## Nisbeth

Quote:


 _Originally posted by Voodoochile _
*edit: With regard to twisting or not twisting DC feed wire.
 Twist away! * 
 

 Thank you, I'll start right away 
	

	
	
		
		

		
		
	


	




 Tangent, if you use small, short-circuit proof transformators, they can give out up to twice the rated voltage when unloaded (!!). This drops very rapidly with increasing load though, so putting an LED permanently across the output (biased to maybe 5 mA or so) will usually drop the voltage significantly IME. This increase in output voltage is due to the the short-circuit protection (although I do not remember the exact explanation). 

 U.


----------



## phaedrus

Quote:


 _Originally posted by tangent _
*Shall I call you the Larry Flynt of DIY? 
	

	
	
		
		

		
			



* 
 

Only if I start hustling my amps. 
	

	
	
		
		

		
		
	


	




 Speaking of which, watch the for sale forum -- muahahahhahahahha!

  Quote:


 *It will normally get a bit warm when the cells are charging. Even if the cells are charged, the '340 chip has a power-on minimum charge time that it must go through before it will start checking the battery voltage, to account for cold start-ups. * 
 

I'm using the 340 chip, and rather than just ask how long I should expect heat, I was a good amp student and pulled the info sheet at newark. The chip on the data sheet is an 8 pin. The chips I received were 6 pins. Further, the marking diagrams don't sync up. *This* might explain why my amp was so toasty warm while connected to the grid? Now where did I leave that *BARELY LEGAL* great oogley google?

 ACK!!! Grrrrrr! Another newark fiasco for me. They sent me four of the $0.55/each 6-Pin DIP High BVceo Phototransistor Output Optocoupler and charged me for four of the $1.99/each MC33340P. No wonder it gets so toasty... Is there anything that I need to check for damage now? Aside from my pride, that is? And I thought I was showing such restraint not verifying that it plugged into the top three pairs of holes on the socket...


----------



## picklgreen

Mouser is out of stock of the Elpac power supplies (24v) until December 17th.


----------



## Whit

Quote:


 ACK!!! Grrrrrr! Another newark fiasco for me. They sent me four of the $0.55/each 6-Pin DIP High BVceo Phototransistor Output Optocoupler and charged me for four of the $1.99/each MC33340P. 
 

They did this for me also. An email to customer service solved this. They even shipped it out at no charge and let me keep the optocouplers.


----------



## tangent

Quote:


 Mouser is out of stock of the Elpac power supplies (24v) until December 17th. 
 

Allied and Newark also carry the WM080. If someone's got an emergency and really needs one, PM me; I've got a few I could let go.

  Quote:


 The chips I received were 6 pins. 
 

Ouch!

 I'd be curious to know if you could find the part number of those optocouplers. I wonder if it's really similar to the '340s part number.

  Quote:


 Is there anything that I need to check for damage now? 
 

It's hard to guess what's been happening on that board. 

 Take the battery board out of the case and look for indicators of heat damage: cracked components, discolored components, scorch marks on the board, open flames.... 

 If nothing obvious jumps out at you, apply power, then wave your hands slowly over the board until you localize the heat source. Whatever's getting hot is the most likely thing to be damaged, if anything is. The regulator should survive overheating pretty well. The optocoupler is almost certainly toast. Some of the diodes and resistors might be fried. R2 might have changed value. And I suppose depending on what the circuit became while the optocoupler was in there, the NiMH cells could be damaged.

 Is F1 in place? If so, the fact that it didn't break is a good sign. If not, you're going to order the parts now, right?


----------



## Magic77

Does anyone know if the OPA604 could be used with the PPA amp, using the Intersil Buffers?

 Also wanted to ask: If you are NOT biasing the PPA into Class-A; what would be better; more buffers? less buffers? Or is this basically subjective to individual preferences?


----------



## phaedrus

Hmmmm, F1 was in place and is intact. No evidence of flames, scorching, cracking, etc. The hot spot on the hammond was the regulator's location, though it never became so warm that it was uncomfortable to hold. As opposed to the battery array, for instance, when I jumpered the AA positions along with the AAA, heated the batteries up and melted a couple of the holders. 
	

	
	
		
		

		
		
	


	




 I'll have to check R2 this evening. 

 I did use it for a bit off of the battery board yesterday afternoon and evening, though that isn't much help with the recharge circuit. The battery array is putting out enough juice to keep the 8610's happy, at least.

 Newarks part number for the optocoupler is: 46F7752. Not real close to the part number you (tangent) listed for the charge controller (01F2049).

 Edit: fixed me bad gramah.


----------



## tangent

What value are you using for R2? The heat you felt might have been normal for the voltage drop across the regulator. One very likely possibility is that the optocoupler died an early death and didn't affect the circuit at all. You may have just ended up with a constant fast-charger.


----------



## tangent

Quote:


 Does anyone know if the OPA604 could be used with the PPA amp, using the Intersil Buffers? 
 

Yes, it can.

  Quote:


 If you are NOT biasing the PPA into Class-A; what would be better; more buffers? less buffers? Or is this basically subjective to individual preferences? 
 

These are independent features. You don't choose your buffer config depending on the biasing setup of the op-amps, or vice versa.


----------



## aos

Quote:


 Now, twisting your wires together doesn't make a very good inductor....but it's not harmful, so go ahead. 
 

Twisting wires together is not done to reduce the exiting HF noise in the wire but to effectively reduce the amount of EMI that will get induced in that piece of wire. Now I might be wrong as this is coming from 10+ years old memory but it's because it minimizes the surface between wires and the induced current is directly proportional to that. In addition, as both wires are very close, the magnetic field is almost the same in both wires at any point which makes induced EMI almost equal (of opposite sign if I remember) so it's a common mode signal that can be filtered out after the wire. That's why a lot of cables are of twisted type.

 Personally, I twist because it looks nicer and it groups wires together rather than making a mess of cables that makes it tougher to figure out which is which.


----------



## phaedrus

Quote:


 _Originally posted by tangent _
*What value are you using for R2?* 
 

I installed a 4.7 ohm 1/2 watt resistor there.


----------



## tangent

I'd use a 1W or larger resistor instead, just to spread the heat out a bit (more surface area) but you should be able to get away with 1/2W with that resistor value. 

 The current level is fairly low. The regulator should get warn enough when fast-charging that you wouldn't want to hold your finger on it for a few seconds. If you can't hold your finger on it for even a second, or if spittle sizzles on it, you've got a problem.


----------



## phaedrus

I picked up a 5W cement wirewound resistor for R2 while I was out for lunch. I'll replace the current 1/2W and then be in holding pattern for newark.


----------



## Magic77

Question: In the PPA Parts selection guide, it says that C6 is NOT optional. But, in the Required parts list, C6 is not listed? Just curious if this is a typo?


----------



## morsel

C6 is not optional. Note that Tangent's opinions on "optional" parts are not necessarily the opinions of the rest of Team PPA. Omitting parts may result in inferior performance and instability.


----------



## tangent

My criterion for optional parts is, "will the amp run correctly without this part?" Morsel would rather divide the parts with the criterion, "Could the performance be improved by adding this part?" Both are valid ways of dividing the parts.

 C6 is not optional under either interpretation.

 Thanks for letting me know about the misclassification in the parts list, Magic77. It's fixed now.


----------



## Arzela

I wish to integrate some input
 filtering caps for my PPA rig
 (readies fire extinguisher). Of course,
 I'll have to put the 1 uf film caps before the
 pot. My question is, should I put
 the companion resistor from cap to ground
 in? Or will the large value resistor R2
 in the PPA schematic serve as the "R"
 in the RC constant?


----------



## Magic77

Between the AD8610 vs. OPA627:

 How do you know which one of these chips would be a better choice?

 In other words: Does it depend on the type Headphones(Impedances) you will be using, or if you prefer more or less signal Gain?

 I'm almost done ordering all my PPA parts, but I'm trying to get a better idea about the Op-Amp I should choose. I know everyone's opinions are different, but maybe other PPA builders can state their Op-Amp preferences. 

 I don't mind spending the few extra bucks for the OPA627 if it's really worth it.


----------



## Arzela

I think its entirely subjective. Try both and
 see what you like. FWIW, the 637's are a bit more
 restrained on the high end than the ad chips; but, they both sound great to me.


----------



## tangent

Quote:


 readies fire extinguisher 
 

Better put on your asbestos underwear, too. 
	

	
	
		
		

		
			





  Quote:


 should I put the companion resistor from cap to ground in? Or will the large value resistor R2 in the PPA schematic serve as the "R" in the RC constant? 
 

If you don't put in a resistor, the pot will be the resistance following the cap. If you do put one in, you'd want it to be bigger than the pot's resistance, so the pot's resistance would still dominate.

 Suit yourself either way, but calculate the C with the assumption that R is 1/2 the pot's value. (You'd use the full pot value only if you kept the volume control near max all the time.)

  Quote:


 Between the AD8610 vs. OPA627: 
 

I have two PPAs, one with the 8610s and one with the 637/627. I haven't decided yet which one I prefer. They're unquestionably different, but I need to do more tests -- different sources, different headphones. I'm only replying so you don't think I'm ignoring you.


----------



## Magic77

Can someone please help me with wiring up the DPDT On/Off Switch for the PPA? I'll be using the Elpac WM080 only.

 I ordered the E-Switch RR3130B. I know the switch has 6 connections. 

 So; what switch contacts are going where on the PPA board?

 Sorry if this seems like a dumb question, but I don't want to mess this up. Thanks.


----------



## g14389

Quote:


 _Originally posted by Magic77 _
*Between the AD8610 vs. OPA627:

 How do you know which one of these chips would be a better choice?

 In other words: Does it depend on the type Headphones(Impedances) you will be using, or if you prefer more or less signal Gain?

 I'm almost done ordering all my PPA parts, but I'm trying to get a better idea about the Op-Amp I should choose. I know everyone's opinions are different, but maybe other PPA builders can state their Op-Amp preferences. 

 I don't mind spending the few extra bucks for the OPA627 if it's really worth it. * 
 


 On my first PPA I used OPA627s. I just recently finished 2 more PPAs using AD8610 for friends.

 This is just my opinion. The OPA627 sounds more accurate as far as vocals, well rounded in frequency response, better bass and warm to the ears. With the OPA627 I feel like the music is more life and closer to sound stage . The AD8610 were louder and accents the higer frequency and are not as clear (vocal).

 Keep in mind, I am speaking relative to each other (not saying AD8610 is bad at all). I know this is based on personal preference but I though this might or might not help you or someone else make a future choice.

 I would be intered in more opinions from others (no sure if my explanation was that good) or someone who may suggest yet another OPAMP to try that could be even better.

 Thanks.


----------



## Arzela

Quote:


 So; what switch contacts are going where on the PPA board? 
 


http://spec.e-switch.com/F-D/F030001B.pdf

 Refering to the above datasheet:




 pin 2 -> top of s1+

 pin 2b -> top of s1-

 pin 3-> bottom of s1+

 pin 3b-> bottom of s1-

 Run your power to V+ and V- on the board.


 ( As far as I can tell, with 3 and 3b, you'd depress the "dot" on 
 the switch to turn the power on.
 I may be wrong here,
 you should check with a meter.
 If you don't like this, use 1 and 1b instead of 3 and 3b.)


 This scheme will switch both power leads.


----------



## Magic77

Quote:


 _Originally posted by Arzela _
*http://spec.e-switch.com/F-D/F030001B.pdf

 Refering to the above datasheet:




 pin 2 -> top of s1+

 pin 2b -> top of s1-

 pin 3-> bottom of s1+

 pin 3b-> bottom of s1-

 Run your power to V+ and V- on the board.


 ( As far as I can tell, with 3 and 3b, you'd depress the "dot" on 
 the switch to turn the power on.
 I may be wrong here,
 you should check with a meter.
 If you don't like this, use 1 and 1b instead of 3 and 3b.)


 This scheme will switch both power leads. * 
 

Thanks. OK; I can understand that only 4 contacts on the switch would be used since there are only 4 positions on the PPA board(S1+ and S1-). 

 But; do I need to jumper the other 2 unused contacts? Switches like this always confuse me. Thanks for any more help.


----------



## Magic77

Question regarding R3 and R4 on PPA Schematic:

 R3(Ground Channel) says; "omit". Does this mean there should be NO resistor there? Should it be jumpered or left alone?

 R4 ground channel is 4.32K. R4 L&R channels are 10K. Is it correct that the ground channel R4 is a different value than the L&R R4 value?


----------



## PeterR

- leave the other contacts alone
 - no resistor
 - yes


----------



## phaedrus

Is the use of a 627 on the ground channel with 637's on L & R an economic consideration? Or, is there another reason?


----------



## bigcat39

No, the 637's and 627's are (about) the same price. 637's are not unity gain stable, and the ground channel is @ unity.


----------



## Magic77

Quote:


 _Originally posted by PeterR _
*- leave the other contacts alone
 - no resistor
 - yes * 
 

Thanks. So; I'm assuming no R3 resistor(ground channel only) and do not jumper?


----------



## Arzela

Definitely don't jumper r3. Morsel
 recommends putting a 1 meg resistor there.


----------



## morsel

Morsel recommends omitting R3G. Use a 1M resistor if you insist.


----------



## Magic77

Quote:


 _Originally posted by morsel _
*Morsel recommends omitting R3G. Use a 1M resistor if you insist. * 
 

Can you please explain why or why not you would use the 1M resistor opposed to leaving it empty? Thanks.


----------



## morsel

R3G is not needed for normal operation. Without it the ground channel operates at unity gain. Using R3G allows for a gain other than 1, and replacing C6G with a resistor further allows for a different inner loop gain at the expense of decreased stability in low gain configurations. Not that I recommend doing this, but it can be done. We played around with this a lot during the development of the PPA.

 Some people hate omitting parts regardless of how vestigial they are. For these people, a 1M resistor is pretty close to an open circuit as far as gain setting is concerned. Consider R3G a feature for the fringe experimenter.


----------



## picklgreen

Where can I buy Wima caps? The only place I have found is www.epassives.com but they seem a little pricey.


----------



## Arzela

Sorry for the misquote Morsel...lack
 of sleep.


----------



## doobooloo

Slept at 6 this morning. The result:





































 The big blue things are 0.33uF polypropylene caps for bass boost - the result of struggling to find suitable caps for the small footprint assigned to C7... and failing miserably. 
	

	
	
		
		

		
		
	


	




 The wire used is pure silver 22AWG from Homegrown. I will eventually wire everything with this silver wire for this PPA.

 Solder used is silver bearing solder.

 4 HA3-5002-5 buffers per channel, as you can see, and OPA637BPs for L/R and OPA627BP for ground.

 C1s are 1200uF 35V Panasonic FCs.

 And here is where I'm kicking myself in the butt. After installing these eight tall caps, I found out that it won't fit in the Hammond with the battery pack. Stupid me, I measured the height from the board to the "ceiling" at the center, ignoring the corner rails... 
	

	
	
		
		

		
		
	


	




 oh well. I ordered another set shorter 25mm caps to accomodate that, so I'll have to rip those off... gah! 
	

	
	
		
		

		
		
	


	










 Oh well. That's what I get for working while breathing solder fumes at 6 in the morning...

 [edit] Fixed pic linking...


----------



## Bonkura

Very nice hq closeup pics there!

 woah those caps are big


----------



## morsel

Hi doobooloo, Digikey sells .082µF BC MKP 416 polypropylene film caps (and various other values as well) that fit the PCM5 C7 spot perfectly.


----------



## doobooloo

morsel - Yeah I have the 0.12uF MKP416 metallized polyprop (the largest of the series that will fit on the PCM5 footprint) from Digikey as well, but after experimenting with EQs and Micro-Cap I decided that 0.12uF will boost too much into midbass... what I really want is a bass "compensation" circuitry where only the low bass rolloff of headphones is "corrected"... and with my CD3Ks I found that 0.33uF C7 with 33K R7 works extremely well.

 And I couldn't find any ~0.33uF polyprop caps that will fit in that area so I just decided to go creative.


----------



## tangent

Very nice construction work, Doo. Nice pictures, too. I like the use of sunlight instead of flash.

 The pics also settle the question of 10mm caps in C4....


----------



## Sovkiller

Quote:


 _Originally posted by doobooloo _
*morsel - Yeah I have the 0.12uF MKP416 metallized polyprop (the largest of the series that will fit on the PCM5 footprint) from Digikey as well, but after experimenting with EQs and Micro-Cap I decided that 0.12uF will boost too much into midbass... what I really want is a bass "compensation" circuitry where only the low bass rolloff of headphones is "corrected"... and with my CD3Ks I found that 0.33uF C7 with 33K R7 works extremely well.

 And I couldn't find any ~0.33uF polyprop caps that will fit in that area so I just decided to go creative. 
	

	
	
		
		

		
		
	


	


* 
 

Well I'm getting one myself, but IMO you do not need "bass compensation" for the CD3000 at all, the CD3000 is perfect the way it is, unless you have a roll off on the bass freq, due a bright source, etc...BTW you are using OPA627s right? Unless for the same cause I'm into, bass deficient recordings....


----------



## Arzela

I need about 35 ma to power some relays.
 Can I take the power from V+ high and signal ground of the PPA board, or will this
 cause problems? I need 12 volts. The above connections give 15 volts with my 30 volt power supply, which seems a reasonable size to step down. 

 I'd rather not grab power straight from the power supply, (30 volts)
 since then I'd have to dissipate 1/2 watt
 somewhere to no good end. (I need 30 ma
 into a 400 ohm load. With 30 volts the only
 way I could think of doing this is to use
 the load as half of a voltage divider, the other half would be a 600 ohm
 resistor/heat generator).


----------



## morsel

Magic77: I've been noticing an apparent trend towards the OPA627/637 over the AD8610 lately. I just want to reiterate my opinion that the AD8610 is the superior opamp, with great bass and more high end detail at a lower price than the OPA627/637. I suggest you only go for the Burr Browns if you find the Analog Devices too unforgiving, or if you know for a fact you prefer the Burr Brown sound. Don't waste your time with other opamps, these are about as good as it gets.

 Arzela: I would not take relay power from signal ground, as it is not designed to put out that kind of current. Signal ground is independently referenced by TLEs from each opamp rail pair, which in turn are isolated from V+ and V- by small FET current sources. You will need to find some other way to power your relays, sorry.


----------



## doobooloo

Quote:


 _Originally posted by Sovkiller _
*Well I'm getting one myself, but IMO you do not need "bass compensation" for the CD3000 at all, the CD3000 is perfect the way it is, unless you have a roll off on the bass freq, due a bright source, etc...BTW you are using OPA627s right? Unless for the same cause I'm into, bass deficient recordings.... * 
 

The CD3Ks have very respectable bass, but like all other headphones, it has a noticeable rolloff for very deep bass. (30~40Hz) On some recordings this deficiency bugs me, and plus my Echo MIA MIDI soundcard is rather bright sounding so... 
	

	
	
		
		

		
		
	


	




 It just makes great bass-maker even greater.


----------



## Sovkiller

Quote:


 _Originally posted by doobooloo _
*The CD3Ks have very respectable bass, but like all other headphones, it has a noticeable rolloff for very deep bass. (30~40Hz) On some recordings this deficiency bugs me, and plus my Echo MIA MIDI soundcard is rather bright sounding so... 
	

	
	
		
		

		
		
	


	




 It just makes great bass-maker even greater. 
	

	
	
		
		

		
		
	


	


* 
 

If I would choose to listen 80's rock instead of early 70's, I would get stock with the Perreaux the rest of my life, I like the sound of it, and the bass is incredible, nothing like succinct as bill said, I heard a trully real bass, just that with my old recordings is not my cup of tea, sometimes with new recordings, I heard like if the subwoofer was on, I even took the headphoens out to see if by mistake I left it on, but nothing it was the CD3000 alone, and it goes deeper than 30 Hz OK?...but a bit of more bass will be nice, just a little bit, to compensate some old recordings and to "basshead" the new ones....I agree on that...


----------



## was ist los?

For those of you who use bass boost, how many of you actually put a switch to defeat it? I like it, so i don't think i'll put a switch in amp.


----------



## Tuomaster

Can you use BUF634 instead of HA3-5002-5? Someone said that BUF634 won't sound as good on PPA so I presume that they are pin compatable.


----------



## dokebi

They are not pin compatible.


----------



## tangent

It is not necessary that two buffers be pin-compatible to try them both in the same amp design. You just have to spend the effort to adapt one set of chips, or build two different amplifiers. If you want to try it yourself, go right on ahead. 

 If you prefer a more rolled off sound like the BUF634 will give you, the OPA633/HA-5033 (same design) will give you this as well in a pin-compatible package. The OPA633 and the BUF634 do not sound exactly alike, just more similar to each other than they sound to the 5002.


----------



## Tuomaster

I don't know what got into me. Should have checked that from datasheets. 
	

	
	
		
		

		
			





 I don't want to adapt anything. The main reason why I am interested of PPA is that it is simple to build. Everything is thought for me and I just solder everything together. (I have built Gilmore Dynamic with my own pcb:s and my nerves deserve some rest now


----------



## protos

I finished my PPA board yesterday morning and hooked it up for a listen after a burn in of about 4 hrs.
 I am using 3x1000uf Pana FC as C1 , 47uf standard black gates , and 1uf polyst film caps, OPA 627BP.PS was a bench regulated at 24v or alternatively 2 x12v sla batteries.
 I have to say that I am little disappointed at the end of the day.I am not saying that the PPA doesn't sound quite good but it has a residual hardness or mechanicalness particularly in the mid-range that may sound tiring or uninvolving after a while.
 So what did I compare it to?
 The head amp I am using at the moment is a kind of hybrid invoving a BB DRV134 balanced line driver as input stage into a Pass X balanced line stage (for further info see diyaudio.com pages or Pass site) modified to run on +- 12v SLA batteries and heavily biased with about 70 ma per mosfet.The output is balanced and I have modified my HD-600's accordingly although surprisingly it still sounds the same with a common neg connection.Now this sounds more natural in the mid -range and seems to have a wider and deeper soundstage than the PPA. The PPA has great bass and might be slightly ahead there on points but the differences are not decisive.
 The PPA to my ears at least only starts sounding smooth enough after the 3rd buffer but even with 4 it doesn't sound as liquid as my other amp.
 What can I say - after spending the not so insubstantial sum required and reading about all the innovative elements I expected it and wanted it to sound better than my hybrid amp which was cheaper and not a design originally intended for powering headphones.
 The only caveat is that perhaps the sound may improve if I bias the opamps further into class a. At the moment I am using 2n5486 and bf 245a with the 1k and 100r resistors but I am not extremely optimistic about the degree this will change the sonics.
 I haven't worked it out yet but what is the effect on bias after removing the resistor network?


----------



## tangent

Quote:


 it has a residual hardness or mechanicalness particularly in the mid-range 
 

I don't know that I would describe it that way. 

 The PPA is not a forgiving amp. It is very fast and very transparent. The fastest and most transparent common configuration is the AD8610 with the HA-5002. Change to the OPA637 and it becomes a bit less transparent and a bit slower. Further down the line is the OPA627, and then you can change to the OPA633/HA-5033. I wonder if perhaps you are simply not far enough down that scale for your tastes and system.

 Another thing I want to try someday are the AD843 and AD845. These are much smoother chips than the others mentioned. The 845 is the smoother of the two, but at the expense of detail.


----------



## protos

I'll try the 8610's which I have already and which I like perhaps more than the 627AP's at least but the difference between them is not all that great and previous experience has shown that the mid hardness that I am talking about will probably not be cured substantially by them.
 I am not saying that the PPA is not very revealing and has a lot of detail and monitor type sound..Also perhaps I would not criticize it if I didn't have something to compare it with that to my ears sounded better.And of course this is only one persons opinion - somebody else might prefer it the other way round.But for sure it seems to me to lack that naturalness/smoothness/liquidity/musicality in the mid-range that I find essential .
 Could it be that it is more accurate and therefore unforgiving of source and recording.Hmmm... perhaps but that would also mean that certain recordings would sound much better which I did not particularly notice.
 And by the way no I'm not a SET or tube fanatic used to certain types of "presentation".


----------



## tangent

I think changing to the 8610s would be going the wrong direction for you. Go to the 843s, 845s, or change the buffers instead.


----------



## protos

Further audition yesterday was more positive.Perhaps as some people claim the solder joints need some time to settle in.Switched to 8610 on left and right channel which opened up the mids and at least now I feel that it is starting to approach within view of the other headamp. Bass is now quite bit tighter and more dynamic than other amp.However in terms of soundstage and airiness the PPA is still lagging a little bit behind but not as much as initial impressions.
 Batteries still continue to impress me how much better and natural they sound compared to regulated PS.
 I might try tweaking further with some extra bypassing on the caps.
 What about further class a biasing ?Nobody answered my question about this.


----------



## Voodoochile

The 8610 does not seem to show much (if any) benefit from class-A bias to me... or it is already running that way, perhaps. I'm not saying it sounds good or bad, but that the difference before and after is barely discernible. the OPA627 and 637, OTOH, are quite responsive to biasing. I do find that more than 1mA is beneficial, about 2 to 2.5mA seems to work well, and does not lead to overheating.

 Hope this is useful to you, Protos. Any pics to share of your handiwork?


----------



## morsel

Protos, since you like the AD8610 better, why not go whole hog and replace your ground channel opamp as well.


----------



## phaedrus

The proper charge controller replaced my somewhat less useful optocontroller yesterday evening. I also switched out C7 and prefer the reduced range of boost, but will continue to experiment with a couple of values above .1 for which I'm currently waiting. I also swapped out the 1/2W R2 on the battery board with a 5W cement wirewound resistor.

 The batteries charged as intended last night. The chasis warmed slightly, but no where near the "toasty warm" of the optocontrolled charge cycle. 
	

	
	
		
		

		
		
	


	




 I managed to leave my elpac power supply at home, and the charge circuit's LED behavior on my emergency-especially-for-days-when-the-old-timer's-kicks-in power supply (19V) begs clarification. Last night, connected to 24V, the charge LED lit up and began flashing at the typical 1.38 second interval. This morning, connected to 19V, the charge LED flashes at its interval, but is not lit up. I infer this is a result of the lowered supply voltage, but I don't understand why. May I solicit clarification?

 Also, I hope which ever of you snagged Allied's last Elpac 24V out of my shopping cart is very happy with your purchase. 
	

	
	
		
		

		
		
	


	




 No, really, I hope it works really well for you.


----------



## tangent

Quote:


 connected to 19V, the charge LED flashes at its interval, but is not lit up. 
 

Naturally if the supply voltage is too low, the circuit will behave strangely. If you want to be able to plug in this low supply voltage and leave the battery charger out of the circuit, you might add a switch that cuts the V+ line to the battery board. Then you can plug in low-voltage supplies and it will power the amp only.


----------



## phaedrus

I assumed from our previous discussions that the circuit would be in some variation of trickle mode, and was mostly curious as to whether or not this was expected/explainable behavior. I'm planning to pick up another elpac and will build the PPA power supply when it becomes available. Will I damage something if it occasionally runs on the low supply (I'm with it 90% of the time with regards to getting the 24V from work to home). Am I better off adding the bypass switch and, if so, will a spst on v+ be sufficient?


----------



## tangent

I think you're misapplying some facts I gave you. 
 I've said that you don't have to have exactly the supply voltage my battery board calculator recommends. 0.5V under the recommended value is almost always okay. Dropping 1V might even be okay in some situations. Dropping 5V is virtually guaranteed to give dissatisfying results.

 Probably what is happening is that the regulator isn't even trying to charge the batteries, but since the charge controller has enough supply voltage and the Vsen pin isn't showing the batteries as out of range or done charging, it is leaving the path through pin 2 or 3 closed, so the LED stays only partly lit.

 If you want it to degrade to trickle-only mode with the LED solidly lit when the supply voltage is too low to fast-charge, you might just add a third function to the battery board like that of pins 2 and 3 on the '340. Pins 2 and 3 put a transistor inline with the regulator's ADJ pin to ground, right? You could add a discrete transistor and some voltage sensing mechanism to turn the transistor on. A zener and a few conditioning resistors should do the trick. Then when your circuit triggered, it would turn the LED fully on and disable the regulator, just as the '340 does.


----------



## phaedrus

I'll run a 24V PS (barring senior moments 
	

	
	
		
		

		
			





), at least until the custom power supply is ready for the masses. It appears that newark has them in stock, and I'll try an order there again.

 I thought that at 19V it would be trickle charging and expected the LED to be on, though perhaps dimmed. However, the actual condition was LED not lit and flashing at the fast charge interval. The LED has since stopped flashing and is lit steady now, as it was once it finished charging off the 24V supply last night. I don't think I described the conditions adequately at the outset -- sorry.

 If I'm potentially running into a problem occasionally running off 19V until a second elpac arrives, I'll install a switch on V+ to the battery board. If it is mostly safe, I'll bide the odd behavior until I've a PS for home and for work.


----------



## tangent

Yes, it should be flashing, since as I said the '340 believes the batteries are still in need of fast-charging. The fact that it wasn't a bit dim in between flashes is a function of the idle currents of the nearby TLEs.

 It isn't so much a problem to run from 19V, you're just confusing the charging circuit. You could leave out the '340 and temporarily run a wire from pin 2 or 3 of that socket to ground to disable the fast-charging scheme to get constant trickle charging.


----------



## Magic77

WOW!! I didn't realize the AD8610AR's were SOIC instead of DIP. So, I ordered a few BrownDog adapters.

 Maybe I missed something in the PPA parts selection guide or parts list?


----------



## myself, aka me

I think most order sites the information about the opamp shows what form it is - 8 pin DIP, SOIC-8 etc. If not then the datasheet most certainly does


----------



## tangent

Quote:


 Maybe I missed something in the PPA parts selection guide or parts list? 
 

I don't see what you think it should say. Observe these facts:

 - The PPA is not tied to any particular chip. I can't very well list specific warnings about every possible chip you could use in the PPA.

 - There are SOIC-8 pads on the board, so you don't actually require those adapters. They only allow you to socket the chips.

 - The 8610 is available both mounted and unmounted on my ordering page, which should serve as a fairly big clue for that particular chip.

 - 'myself' has a good point: are you not reading the docs for the chips you plan on using? Sorrow lies down that path.


----------



## Magic77

Quote:


 _Originally posted by tangent _
*I don't see what you think it should say. Observe these facts:

 - The PPA is not tied to any particular chip. I can't very well list specific warnings about every possible chip you could use in the PPA.

 - There are SOIC-8 pads on the board, so you don't actually require those adapters. They only allow you to socket the chips.

 - The 8610 is available both mounted and unmounted on my ordering page, which should serve as a fairly big clue for that particular chip.

 - 'myself' has a good point: are you not reading the docs for the chips you plan on using? Sorrow lies down that path. * 
 

OK, OK, Take it easy!! I was blaming myself for possibly missing something. I'm not pointing fingers at anyone or saying that YOU made a mistake with your instructions.

 Sorry I made the post in the first place.


----------



## protos

Played around with the bass boost yesterday but couldn't get a satisfactory result 10k and .01uf was still too much mid-bassy for me.Tried 6.8k but not happy either.Even tried 3300pf which gives a very slight boost but I can't seem to get the quality I want.I guess the cans just won't give it.
 Funny thing is I prefer the sound with no cap and the 10k resistor in.Of course I adjusted for gain and it seems that highs are more extended.Even more funny is that a lower quality metal film resistor of the same value doesn't give me this effect.I am using Welwyn rc55 precision resistors.So resistors do sound different , at least in this application.
 As to 12v operation although it works fine there seems to be a slight thinning of the lower frequencies.


----------



## morsel

I can see a couple of disparate uses for bass boost. A more subtle use is a very mild boost to compensate for bass weak headphones. The original intended use was for more extreme boosting to compensate for bass weak recordings, of which there are many. Using a pot instead of R7 will allow for user controllable boost. If you are really determined you could include a rotary switch to select different values of C7 to vary the cutoff frequency as well.


----------



## crane

I just finished building my PPA and hooked it up to power, measured the DC offset from the ground plane to each of the output (OL,OR,OG) pads and found that I was getting in excess of 600 millivolts. I then (just for the hell of it) hooked up a cheap pair of headphones to the amp and got a loud buzzing noise even a 0 volume.

 Currently the amp is wired with the base config, 1 buffer per channel.

 I don’t have any resistors in R3G, R7, R8 or R9 and I did not install the bass boost circuit. I used standard resistors values from the schematic from tangents site.

 Any ideas of common problems that could cause this problem ?


 Thanks
 Crane


----------



## Voodoochile

Did you jumper the switchpads for the bass boost? (S2)

 Edit: Don't even connect your junk cans if you have that kind of offset.


----------



## 10SNE1

Quote:


 measured the DC offset from the ground plane to each of the output (OL,OR,OG) pads 
 

 Shouldn't the DC offset be measured from OG to OR and OG to OL?

  Quote:


 got a loud buzzing noise 
 

 Sounds like something is oscillating. Did you install C6 on the ground channel?


----------



## doobooloo

Quote:


 _Originally posted by protos _
*Played around with the bass boost yesterday but couldn't get a satisfactory result 10k and .01uf was still too much mid-bassy for me.Tried 6.8k but not happy either.Even tried 3300pf which gives a very slight boost but I can't seem to get the quality I want.I guess the cans just won't give it.
 Funny thing is I prefer the sound with no cap and the 10k resistor in.Of course I adjusted for gain and it seems that highs are more extended.Even more funny is that a lower quality metal film resistor of the same value doesn't give me this effect.I am using Welwyn rc55 precision resistors.So resistors do sound different , at least in this application.
 As to 12v operation although it works fine there seems to be a slight thinning of the lower frequencies. * 
 

Hey protos,

 It seems like you're lowering your C7 values to lower bass boost as well - but it's actually the other way around. You need to increase C7 values to the 0.22uF ballpark to actually get rid of midbass boost. That's why I'm using a 0.33uF C7 capacitor with a 33K R7 on my design so that I only boost the very low frequencies and have almost no boosting from 100Hz upwards.

 Your 0.01uF and 3300pf would REALLY go up in the frequency range - have you tried Tangent's sample circuit for Micro-Cap? I used it to tune the boost the way I wanted it to be, and it proved to be very useful:

 Micro-Cap demo from here: http://www.spectrum-soft.com/
 Tangent's circult file from here: http://www.tangentsoft.net/audio/ppa...bass-boost.cir


----------



## Sovkiller

Well it seems that I may need to ask directly I was reading and reading, and I found nothing in the thread, that should make me go in either direction, I have a to choose between 3 X OPA627, or 2 X OPA637 and 1 X OPA627 for the ground channel (the AD IMO I think that should be a way too bright for the CD3000, I know that morsel will disagree, as she seems to love the sound of the AD, but paired with the CD3000 I don't think it should be a good combo, anyway if someone had tried it just please post your impressions) which should be the best way to go and why, in your opinions of course.....morsel tangent, ppl, or any other members that have tried both configurations???


----------



## morsel

If you can't decide which opamps to use, just buy or borrow both kinds and listen to them. Then you will be sure to know which you prefer.


----------



## Sovkiller

Sorry I'm not a DIY guy in any way, if I get some OPamps I will keep the ones I won't use in vane for the rest of my life without use, or sell them later, about to borrow some, who's gonna be Mr. nice guy??? I promise I will take good care of them....


----------



## morsel

Pay your DIYFSEer to give you both sets of opamps, try them out, then send back the ones you don't want.


----------



## doobooloo

Hehe... is that an official term, DIYFSEer?


----------



## Sovkiller

I have another idea: why not posting your opinions on how they may sound, one of each of them, 627, 637, 8610, of course subjective personal opinions, and maybe the cans used for those auditions, and this is for the ones that have tried the two or three more common, this way we could have a better idea on where to start, and later on, once we get used to the way the choosen pair sounds, try the rest.... 

 morsel, consider also that we may not have more money to spend on that, right now, we are talking of 50+ (always people forget an important issue *"BUDGET"*) Sorry I simply can't afford to pay more of what I'm just paying for it, unless I sell other items first...the beloved Perreaux may go...


----------



## Sovkiller

Yes....DIY (For Someone Else) er...


----------



## morsel

Sovkiller, there are probably over a hundred posts discussing how these opamps sound. Just about everything that can be said has already been said many times over. If you have already searched for and read all the threads that discuss these opamps and you are still not satisfied by what you have read and can't afford to try both opamps for yourself or talk someone into lending them to you, then perhaps you should give it a rest.


----------



## Sovkiller

Well I do not see anything wrong in find out for some info that I think is still missing, I do not want you to give me anything not trying to make someone do it, I just wanted your opinion, but if this seems to bother you, sorry, then not even your opinion then, when I agree that it should be very useful in this case.....

 And sorry morsel, but I was not able to find anything, just a few isolated words like that this is dark and the other is detailed, and such things, or isolated words, that says nothing without the contest they are in, or the setup they were tested, an objective comparison or even a subjective one, between both with one same headphone (any could be is just ot have an idea) in one same setup, has not been posted yet, or at least I was not able to find it, in the PPA threads at least, if someone knows of any post, please just point me to them, if you don't mind, please....I was reading for some days now, and I was not able to find anything really useful or what I was looking for, sorry if I bother you....


----------



## Whit

Opamp rolling: AD8620 & OPA627


----------



## Sovkiller

This is the one, for some reason it didn't show up while I was searching, maybe the way I typed the OPA 637 with the space in the middle was the cause, sorry if I bothered you guys...


----------



## morsel

Om, om, resistance is useless if less than 1 Ohm...


----------



## PeterR

Quote:


 _Originally posted by morsel _
*





 Om, om, resistance is useless if less than 1 Ohm... * 
 





 Assimilating that EE had side-effects on the collective the Borg weren't expecting...
 Anyhow, like that smiley...


----------



## Tina

Quote:


 _Originally posted by Sovkiller _
*the AD IMO I think that should be a way too bright for the CD3000* 
 

where in the world did you get such info? the ad8610/20 sounds a bit more detailed and extended. the opa627/37bp is more on the darker and bassier side that's why some ears percieve it to be nicer. now this is where the quality of your source etc. comes to play. but then again, like morsel, i prefer the ad86x0 transparency over the burr brown's
	

	
	
		
		

		
		
	


	




.


----------



## tangent

Quote:


 Did you jumper the switchpads for the bass boost? (S2) 
 

That sure sounds like the problem to me. High noise and a large offset are big clues that your outer loop isn't closed.

  Quote:


 Shouldn't the DC offset be measured from OG to OR and OG to OL? 
 

It depends on what you're trying to figure out.

 If you measure from the ground plane to OG and get almost no offset (normal), then you can measure from either OG or the ground plane to the other channels. But if you get an offset from the ground plane to OG, something's wrong with OG and you shouldn't use OG as a reference to measure against. Remember, voltage is relative -- if your reference is bouncing around, your measurements will probably confuse you more than they help.

  Quote:


 why not posting your opinions on how they may sound, one of each of them, 627, 637, 8610, of course subjective personal opinions, and maybe the cans used for those auditions 
 

Number of chip configurations in question: 3. 

 Number of high-fidelity headphones worth considering: let's call it 10 for the sake of argument.

 Number of high-fidelity sources worth considering: way more than 10, but let's pin it at 10.

 Combined, that's 300 different reviews. Only one of them may include your favorite headphones and source, and even that one doesn't involve your ears, Sovkiller. So even if we give you what you're asking for, it won't tell you what you really want to know: "what op-amp set will I like in my system?"

 The best we can give you is the results of a popularity contest, and even that doesn't answer your question. 

 If you want to know how they sound to you in your system, there's only one way to find out.


----------



## crane

I powerd up my newly built PPA, and no sound, just a very slight hum.

 Currently using (L&R channels):
 - R1 = 4.3k ohm R4 = 9.0K ohm
 - R2 = 1.0M ohm R5 = 3.3k ohm
 - R3 = 1.0k ohm R6 = 1.0M ohm
 - R11-R14 = 1.0k ohm


 - Pot is grounded, 
 - C6G populated
 - Using OPA627AP, 1 buffer per channel.


 Checked power, Measured:
 - V- to v+ : 22.85
 - V- to IG : 21.45
 - V- to Buffer : 22.10
 - V- to C1+ = 22.10



 Any help would be appreciated.


 Thanks
 Crane


----------



## morsel

Crane, did you follow Tangent's step by step assembly guide?

 Take out all your ICs before doing anything else. Make sure your power voltages are OK. Here are some approximate expected voltages for a 24V power supply:

 V+ to V- : +24
 for each opamp:
 opamp rail+ to opamp rail- : +22
 opamp rail+ to IG : +11
 opamp rail- to IG : -11

 If any of these are not within 2 volts or the polarity is reversed, let us know.


----------



## crane

Quote:


 _Originally posted by morsel _
*Crane, did you follow Tangent's step by step assembly guide?

 Take out all your ICs before doing anything else. Make sure your power voltages are OK. Here are some approximate expected voltages for a 24V power supply:

 V+ to V- : +24
 for each opamp:
 opamp rail+ to opamp rail- : +22
 opamp rail+ to IG : +11
 opamp rail- to IG : -11

 If any of these are not within 2 volts or the polarity is reversed, let us know. * 
 

I get 22.85 volts between V+ and V- and about 22.19 across C1.

 I only get 0.300 volts from opamp+ to IG (same for opamp- and IG)


 Crane


----------



## Sovkiller

Quote:


 _Originally posted by Tina _
*where in the world did you get such info? the ad8610/20 sounds a bit more detailed and extended. the opa627/37bp is more on the darker and bassier side that's why some ears perceive it to be nicer. now this is where the quality of your source etc. comes to play. but then again, like morsel, i prefer the ad86x0 transparency over the burr brown's
	

	
	
		
		

		
			





. * 
 

Why always blaming what is above or below and not the thing itself???
 Maybe what is detailed for you, is not tolerable for others, and others will consider harsh, or bright, I'm not saying that it is, I have not heard any of the two, I just get this info from some other members that have tried both also, I was asking to all of them, even the designers of the PPA themselves, IYO if a chip sound good, excellent, in one system and other sound a little bit different and you do not like it, the problem is on the system right? IMO is on the chip, I do not think any source will sound really bad to make a chip sound really bad, if it is good one, and OTOH people who prefer the burr brown sound, will prefer it always, it is a matter of prefference.............I will try both though, just that I will begin with this first, those are the more expensive anyway, and this suggestion was the only really objective and proved one, I got from a PPA/CD3K combo owner, but I'm open to try both and I will try the AD also later on, and if I like the AD better, good, I will swap them and period that is why I request sockets....this is a versatile amp, and I do not think that those will be the only two Op amps, later maybe will show up another and everybody will run to try this new one....this is a long process, with no end BTW....


----------



## tangent

Quote:


 I only get 0.300 volts from opamp+ to IG (same for opamp- and IG) 
 

What's in Q3?


----------



## crane

Tangent,

 I have 2 PN4392s per channel (put them in the top Q3 positions on each channel). I have a TLE installed for each channel as well.


 Crane


----------



## morsel

Crane, either you have no power to your opamps, or more likely, you are confusing the + and - inputs of the opamp with the + and - power rails of the opamp. Please measure the voltage from each opamp power rail to signal ground.


----------



## JohnFerrier

As far as op-amps, I'd like to suggest the OPA134 (SoundPlus High Performance Audio Operational Amplifiers). Though some may think that it may be too much like the OPA627, it is several years newer and seem tuned for audio purposes (rather than just a very good precision op-amp).

http://focus.ti.com/lit/ds/symlink/opa134.pdf

 If you look at the spec sheet. There is much more focus on audio performance. Much more THD information than the OPA627 or AD8610. For those two parts it is actually sketchy. For example, the OPA627 it says output +/-10V. Is that rms or peak? What does "+/-10V" mean? Lower voltages would be more meaningful. For the AD8610, the one THD graph is really just a comparison to the OPA627. The text indicates that the AD part is better, but to my eyes it seem like the graph still shows the OPA to be slightly better.

 For unity gain, the OPA134 actually has lower THD specs than either of the other two, for 1-20khz.

 AD also has new parts AD8027 and AD8029 that have selectable biases. I haven't looked at them too much.


 JF


----------



## eric343

Funny, but I thought that everyone preferred the AD8610/OPA637 to the OPA134, soundwise... I mean sure, I keep a few around for amp testing (from the Cmoy days), but I've never thought of them as terribly hi-fi.


----------



## JohnFerrier

What I think is funny is how there is no decisive "hi-fi" solution. It doesn't appear that anyone is happy with anything in particular. This leads me to question how possible faithful reproduction of music/sound is. Personally, I think we're stumbling in the dark.


 JF


----------



## tangent

If by "stumbling in the dark" you mean there is no way to "engineer" an amplifier that will please everybody, then yes we most certainly are stumbling in the dark.

 But I think everyone can agree on one thing: listening tests are the final arbiter of quality. I don't think I've ever seen a report from someone who has listened to both chips say that the OPA134 sounds better than the OPA627. There may be claims out there that the OPA134 is a better value for the money or is a better choice for product X which must meet some given price point, but audiophile DIYers generally put absolute quality above cost/performance issues.

 Datasheet reading is a good way to investigate new, unfamiliar parts, but trying to dethrone estabished ones via the datasheet isn't a terribly good way to go about it.


----------



## morsel

I suggest discussing opamps in one of the many existing opamp threads, after reading the existing wealth of information on the subject. This beating of dead horses is wearisome.

 I wonder if it is possible to get headbang.gif 
	

	
	
		
		

		
		
	


	




 into the list of available smilies?


----------



## Steve Eddy

Quote:


 _Originally posted by JohnFerrier _
*What I think is funny is how there is no decisive "hi-fi" solution. It doesn't appear that anyone is happy with anything in particular. This leads me to question how possible faithful reproduction of music/sound is. Personally, I think we're stumbling in the dark.* 
 

The "problem" is that we're humans. We're emotional. Subjective. And just because something may be "better" in absolute objective terms, it doesn't mean that it will necessarily be universally perceived as "better." The only ones stumbling in the dark are those who believe there is any singular "best" solution for everyone.

 Just as beauty is in the eye of the beholder, sonic bliss is in the ear of the beholder.

 se


----------



## JohnFerrier

Quote:


 _Originally posted by tangent _
*Datasheet reading is a good way to investigate new, unfamiliar parts, but trying to dethrone estabished ones via the datasheet isn't a terribly good way to go about it. * 
 

No, I was just suggesting the OPA134 because I hadn't read that people had determined that it wasn't up to par. I could have done a search, but for myself I think I'll try discrete. So, what am I doing in the PPA thread? Again, I just wished to suggest a part that maybe people hadn't considered. And I think I share an interest in building good headphone amplifiers.


 JF


----------



## ppl

John the OPA-132 and 134 are intended for low cost. I have found more often than not that when a Op amp is specified for Audio they assume that low cost is one of the requirements. That low cost is just as in portent as low noise and distortion. For volume manufactures this is indeed the case. BB made several attempts at products aimed at mass market Audio, The OPA-2604 being one of them. IMHO nether of these are as good as it gets they are not built upon BB’s Di-fet platform Burr Brown Trade name for Dielectric isolation as the OPA-627/637 and the OPA 2107.

 It is also nice to remember that data sheets are the equivalent to a sales brochure. So if a device is aimed at a specific market then the data presented is going to be what that market wants to see and in the case of Audio that is THD graphs frequency response and noise. Also the application circuits are also end market related. 

 An interesting comparison is the OPA132 and OPA134 data sheets one is intended for Audio and as such is less costly and also has relaxed DC specs. Since most commercial Audio circuits are ether AC coupled or not concerned with the absolute best in DC precision it makes little since in charging a premium for the part for this added DC precision. The Output rating of +/- XX volts is a carry over from when op amps were primarily used in DC only circuits, hence the max positive DC output Voltage and Max negative output voltage. This is why still today we have specs that refer to an OPA’s output potential as both a + and – output voltage. Also note that in some cases notable with older devices that this specification can be different for positive and negative outputs, moreover the difference can get quite dramatic under heavy loading. (see BUF-634 data sheet Pg.6) the graph in the upper left of the page output voltage vs load current.
http://focus.ti.com/lit/ds/sbos030/sbos030.pdf

 The OPA 132 data sheet is http://focus.ti.com/lit/ds/symlink/opa132.pdf
 The OPA 134 data sheet is http://focus.ti.com/lit/ds/sbos058/sbos058.pdf


----------



## protos

Quote:


 _Originally posted by crane _
*Tangent,

 I have 2 PN4392s per channel (put them in the top Q3 positions on each channel). I have a TLE installed for each channel as well.


 Crane * 
 

 Check
 1. jfet orientation
 2. tle rail splitter voltages
 3. op-amp orientation from data sheet
 If the jfets are conducting and the rail splitter is working then the op-amps should have the correct voltages to ground.


----------



## crane

Quote:


 _Originally posted by morsel _
*Crane, either you have no power to your opamps, or more likely, you are confusing the + and - inputs of the opamp with the + and - power rails of the opamp. Please measure the voltage from each opamp power rail to signal ground. * 
 


 Morsel, thanks for all your help. I finally got the amp to work. I installed the Q3's in the wrong spot (newbie error) 
	

	
	
		
		

		
		
	


	




 I have only been listening for about 10 minutes, the amp sound great. 

 Thank you for your help, and to the entire PPA for their work on the PPA. Can we ask what is next ?


 Crane


----------



## morsel

I'm not sure what I'll be doing next. There are still things to be done with the PPA, and the new META42 boards are not out yet. Once things quiet down I'll think about it.


----------



## tangent

Quote:


 I installed the Q3's in the wrong spot 
 

What exactly did you do? I don't ask to embarrass you, but so that I can possibly improve the docs. PM me about it if you don't want to say publically.

  Quote:


 Can we ask what is next? 
 

The power supply project is still creeping along, and ppl's working on a plug-compatible discrete buffer for the PPA.


----------



## jtfoo

Just finished building a 27.2V PS and installing the battery board. I'm using 2.3hrs fast charging for 15 NiMH 800mah batteries. The resistors values are based on the config calculator from Tangent's site. The initial fast charging(blinking LED) took around 3hrs 10mins to go into trickle mode(LED light up all the way). Is it normal for the initial charge taking longer than what was calculated?

 Here are some measurements.

 During fast charging, 
 Supply voltage drops from 27.2V to 27.01V. (should be alright). 
 Voltage across R2(3.6R) is 1.21V, so roughly 336ma fast charging.


----------



## tangent

Quote:


 Is it normal for the initial charge taking longer than what was calculated? 
 

Yes. The calculator assumes 100% efficiency, which is of course not going to happen. Also, past the full charge point, it takes some time for the slope of the battery's voltage to start dropping fast enough for the chip to 'see' it.


----------



## protos

Tried the PPa as pre-amp yesterday. Excellent bass and dynamics ,in fact at some stage I thought that I hadn't switched off the bass boost.Of course used IG and two caps on out to get rid of slight 3.5mv offset.
 However I think to get the tightest bass you have to use either a very good regulated supply or the battery board which is much preferable all round.Even with 10 AA's it sounds very good on cans or as pre even though I had some misgivings about the low voltage.
 I love the dynamics of this amp but I am still not completely convinced with the midrange.It does sound clean and detailed but I felt a little bit of listening fatigue creeping in after about 30-40 mins.It's that annoying feeling that the volume is starting to be too loud although decreasing it a little doesn't help a lot. I don't get this with my other amp.
 Source is a Teac VRDS 25 that is clocked and opamp upgraded.Also using Perp Technologies modified P3 dac.


----------



## fewtch

Quote:


 _Originally posted by morsel _
*I'm not sure what I'll be doing next. There are still things to be done with the PPA, and the new META42 boards are not out yet. Once things quiet down I'll think about it. * 
 

I think you guys have really taken op-amp based designs to the limit (at least from what I can gather, in my very limited experience)... perhaps some sort of an all-discrete design next?


----------



## protos

I still believe that a true balanced PPA would sound better.


----------



## morsel

We decided not to go that route because only a very tiny percentage of DIYers would want one. You can build a fully balanced PPA by using 2 PPA boards. Ignore the ground channels, use left and right as plus and minus, board 1 is left, board 2 is right. That and a nice stepped attenuator would be killer, but probably overkill for most people.


----------



## JohnFerrier

Quote:


 _Originally posted by morsel _
*We decided not to go that route because only a very tiny percentage of DIYers would want one. You can build a fully balanced PPA by using 2 PPA boards. Ignore the ground channels, use left and right as plus and minus, board 1 is left, board 2 is right. That and a nice stepped attenuator would be killer, but probably overkill for most people. * 
 

You are right, only people that have or can modify their headphone cable to seperate the common "ground" channel will be able use bridged PPAs. Unfortunately, this rules out (without a lot of work) some nice headphones. To bridge PPAs though, I think that the boards would need to be modified to also provide inverted signals.


 JF


----------



## ppl

You actualy could with two boards and do a bloackhead style dual mono and put wto boards in one case and do not install parts for the ground channel and yes interchange the resistors going from the inverting and non inverting inputs and a dual stereo alps bule as an mono volume control with one secting controling each polarity. alot of thought in doing the rework properly would be required


----------



## Sovkiller

Quote:


 _Originally posted by protos _
*Tried the PPa as pre-amp yesterday. Excellent bass and dynamics ,in fact at some stage I thought that I hadn't switched off the bass boost.Of course used IG and two caps on out to get rid of slight 3.5mv offset.
 However I think to get the tightest bass you have to use either a very good regulated supply or the battery board which is much preferable all round.Even with 10 AA's it sounds very good on cans or as pre even though I had some misgivings about the low voltage.
 I love the dynamics of this amp but I am still not completely convinced with the midrange.It does sound clean and detailed but I felt a little bit of listening fatigue creeping in after about 30-40 mins.It's that annoying feeling that the volume is starting to be too loud although decreasing it a little doesn't help a lot. I don't get this with my other amp.
 Source is a Teac VRDS 25 that is clocked and opamp upgraded.Also using Perp Technologies modified P3 dac. * 
 

Have you ever tried a different chip, maybe another more "smooth" or "dark" os so... 
 Not everybody likes the same chips, some find then AD a little "bright" or "harsh" , depending on the headphone used of course, and some others will find the BB too dark...


----------



## Cyntax

Hey guys,

 Just in the process of building my PPA. I'm at the "testing power supply" phase, and when I plugged in the power supply the LED didn't light up. So i'm going through and trying to debug what the problem might be. Any suggestions on where I can start looking?

 I have a multi-meter and have been poking it around where the power should be going to the LED, althought i'm not sure what values I should be expecting. I'm using the elpac 24v power supply that is recommended on tangents website. 

 Any help or advice would be greatly appreciated 
	

	
	
		
		

		
		
	


	




 Thanks,
 Cyntax


----------



## JMT

Quote:


 I'm at the "testing power supply" phase, and when I plugged in the power supply the LED didn't light up. So i'm going through and trying to debug what the problem might be. Any suggestions on where I can start looking? 
 

Did you jumper the S1+ and S1- positions?


----------



## Cyntax

Quote:


 _Originally posted by JMT _
*Did you jumper the S1 and S2 positions? * 
 

Yes


----------



## JMT

Can you post a photo of your board? Also, all your TLE's in place?


----------



## Cyntax

Quote:


 _Originally posted by JMT _
*Can you post a photo of your board? Also, all your TLE's in place? * 
 

Yup all TLE's are in place.

 Here are some pics.


----------



## picklgreen

How is the power supply board coming along?


----------



## Cyntax

OK this is what i've figured out so far. 

 Using my multimeter if I measure right from the power + to the power - before it even touches the board its reading 0.24 on my meter. If I measure + and - in one of the empty C1 slots it reads 0.007. So then I back traced to D1. If I measure from - where the power enters the board to just before it hits D1 it reads 0.24, but if I measure it right after the D1 it reads 0.11. 

 Before I go to all the trouble of desoldering D1, does this make sense to anyone? Looking at the picture above is it possible I have the D1 backwards?


----------



## JMT

No, your D1 looks fine. What is difficult to see is how you have your V+ and V- wired. Althought is looks like it is correct, it's hard to be sure. You don't have either of the connectors going to B+ right?


----------



## Cyntax

Quote:


 _Originally posted by JMT _
*No, your D1 looks fine. What is difficult to see is how you have your V+ and V- wired. Althought is looks like it is correct, it's hard to be sure. You don't have either of the connectors going to B+ right? * 
 

Nope nothing is connected to B+. 

 But should the voltage be that much different after it goes through D1?


----------



## 10SNE1

Quote:


 Using my multimeter if I measure right from the power + to the power - before it even touches the board its reading 0.24 on my meter. If I measure + and - in one of the empty C1 slots it reads 0.007. So then I back traced to D1. If I measure from - where the power enters the board to just before it hits D1 it reads 0.24, but if I measure it right after the D1 it reads 0.11. 
 

What are the units of measurement for '0.24' and '0.007'? If volts, something is wrong with either your meter or power supply.
 The voltage reading across D1 should be very small.

 You should be reading approximately the same value across C1 as the voltage provided by the power supply.

 The voltage reading across RLED should be roughly the power supply voltage minus the voltage rating of the LED (roughly 1.6 - 1.8volts). Your LED is wired in with the proper polarity, right?


----------



## Cyntax

AHA! Got it working. Somehow I must have toasted my DC jack. I wired up a new DC jack and the light came on right away.

 Now, where is virtual ground and how do I test to make sure everything is cool?


----------



## protos

I have to report something that might cause some surprise to the PPA team and fellow builders.
 I spent some time auditioning the amp with or without the groung channel (i.e. switching between OG and IG as output ground) and I find that the ground channel is not preferable !!
 It seems to slightly smear and darken the sound.The difference is small but it is there.
 As some of you may have noticed in my previous posts I find that the midrange quality of the PPA could be better.Well by bypassing the ground channel this problem is less severe.
 Of course I expect a lot of flak here and people telling me it's my set up or my choice of op-amps (all ad 8610) or that the 3 channel PPA is revealing faults in my CD player that the 2 channel doesn't or that I am listening to a META etc..
 However in the end I always trust my ears. In any case it is very simple for anybody to try out at very little inconvenience so it would be interesting to see what others think of the ground channel's contribution (or not) to the PPAs' sonics.


----------



## tangent

Quote:


 How is the power supply board coming along? 
 

I've built a couple of LM317-based supplies, and they do work, but I'm not satisfied with their performance yet.

  Quote:


 Somehow I must have toasted my DC jack. 
 

If it's the plastic one from Mouser, you might just be using the wrong connections. There are three lugs, and one of them shouldn't be used with a PPA. It's a normally-closed circuit, often used to switch battery packs in when the wall wart is removed. That's not necessary in a PPA due to the input diode arrangement.

  Quote:


 Now, where is virtual ground and how do I test to make sure everything is cool? 
 

It's that big copper rectangle that the input traces run under from the 'I' pads to the pot.


----------



## picklgreen

Quote:


 _Originally posted by tangent _
 If it's the plastic one from Mouser, you might just be using the wrong connections. There are three lugs, and one of them shouldn't be used with a PPA. It's a normally-closed circuit, often used to switch battery packs in when the wall wart is removed. That's not necessary in a PPA due to the input diode arrangement. 
 

Which ones do we use than? The one on the top and the big one from the center?


----------



## Sovkiller

Quote:


 _Originally posted by protos _
*I have to report something that might cause some surprise to the PPA team and fellow builders.
 I spent some time auditioning the amp with or without the groung channel (i.e. switching between OG and IG as output ground) and I find that the ground channel is not preferable !!
 It seems to slightly smear and darken the sound.The difference is small but it is there.
 As some of you may have noticed in my previous posts I find that the midrange quality of the PPA could be better.Well by bypassing the ground channel this problem is less severe.
 Of course I expect a lot of flak here and people telling me it's my set up or my choice of op-amps (all ad 8610) or that the 3 channel PPA is revealing faults in my CD player that the 2 channel doesn't or that I am listening to a META etc..
 However in the end I always trust my ears. In any case it is very simple for anybody to try out at very little inconvenience so it would be interesting to see what others think of the ground channel's contribution (or not) to the PPAs' sonics. * 
 

I would like to hear from other members as well, and from the designers....morsel, tangent, ppl, what is the benefit of the ground channel then??? I know that has to be a reason....


----------



## morsel

Quote:


 I would like to hear from other members as well, and from the designers....morsel, tangent, ppl, what is the benefit of the ground channel then??? I know that has to be a reason.... 
 

Sovkiller, you can read about the ground channel at http://elvencraft.com/ppa/ under the differential output section.


----------



## JMT

[size=xx-small] Quote:


 _Originally posted by Tangent:_
*If it's the plastic one from Mouser, you might just be using the wrong connections. There are three lugs, and one of them shouldn't be used with a PPA.* 
 

 [/size]
 [size=xx-small] Quote:


 _Originally posted by picklgreen:_
*Which ones do we use than? The one on the top and the big one from the center?* 
 

 [/size]

 Use the one on the left (positive) and the one in the center/top (negative). This will make the polarity of your jack center positive.


----------



## Sovkiller

According to your website:

 ".....the PPA has 3 amplifier channels: left, right, and ground, which use the same output buffers and noninverting opamp topology. *The ground channel sources and sinks the return current from both drivers which would otherwise have been dumped into signal ground or power supply ground. This shifts responsibility for the high current reactive load of the headphones from signal ground to the supply rails of the ground channel buffer, thus removing the primary source of signal ground contamination.* The drivers have symmetrical output buffers with equal impedance and transfer characteristics on both sides, rather than an output buffer on one side and the large capacitor bank of the power supply ground on the other. This results in lower output impedance and greater linearity.

 Standard headphones have 3 wires: left, right, and ground, which is tied to the negative side of both drivers. Standard headphone amplifiers have 2 channels: left and right, with signal ground or power supply ground used for the return path from the headphone ground wire. Fully balanced headphone amplifiers have 4 channels, require custom 4 wire headphones, and are typically operated in bridged mode, which doubles the output voltage and quadruples the power by using inverting and noninverting pairs, but does not offer symmetrical transfer characteristics due to the difference between inverting and noninverting modes....."


 Morsel, do you think that this could be possible??? That the PPA with the ground channel activated will sound worst that one without it, I refuse to believe that, according to what I have read, but here is just an electronic explanation of the ground channel, nothing about the sonic improvements it will offer over a regular design. I would like to hear your opinion, or any other about that, all the PPA to the date have being implemented with the three channels, even mine......


----------



## morsel

Sovkiller, I'm off to see a movie.


----------



## Sovkiller

Don't worry morsel thanks for your help anyway, the last thing I wanted, was to bother you while watching TV, as usual, I will PM ppl then, for an answer, maybe he will have a better answer that your willing to watch TV. 

 BTW this time this matter was not brought to the table by me, and others may have the same question, and maybe it looks silly to you, because of your knowledge, but to us are not, and sometimes the better solution electronically, is not the best sonic solution.....


----------



## Jupiter

Sovkiller,

 The ground channel has been mentioned before, so you might find an answer if you do a search.


----------



## Sovkiller

Jupiter: Maybe after almost 3000 post and more than a year here, I don't know how to use the search field, who knows? Maybe, sorry....

 BTW I already did, and the PPA threads are extremelly long, and too many more than 20.....sorry in this case the search does not work for me, at least.....anyway, nevermind I just PM a couple of guys for an answer, maybe I will get it, or maybe not, but I will not read 300 pages just to find out, sorry and call me lazy, if you want...


----------



## morsel

As it happens, I was going to see a movie in a theatre with a friend, but I was delayed, so we canceled.

 Sovkiller, you seem to want me to refute Protos post. I have no desire to do that. Protos has 15 posts to his name. We know nothing of his skills or background. We don't see dozens of posts by other DIYers saying differential output is bad. Team PPA spent months designing and testing the PPA. Draw your own conclusions. Speaking of which, why don't you just try it yourself?


----------



## Sovkiller

First I do not have mine here yet, I will have it, by monday or tuesday finally, and believe me, that if I like it, you will have an unconditional fan here, and you know my loyalty just following my CD3000 posts....LOL....second, I don't know how to do it, sorry, what do I have to jumper in other to bypass the whole ground channel, OTOH, I will try of course, I will try all the options I can afford with the the PPA so far by now the AD and the OPAs, and some setups for bass-boost, to see which is the one is best suited for me, nothing against you or the other poster, sorry if it comes that way, anyway, I don't know if this could be possible under some specific circumstances only, maybe this or that load of Z, or maybe in this or that conditions, I don't know, that is why I'm asking you....nothing that I want anybody to refute anything, just your honest opinion...period as you were the designers, not him, not me, you are the best entitled to do that....


----------



## tangent

Quote:


 what do I have to jumper in other to bypass the whole ground channel, 
 

Desolder the wire going to the OG pad and connect it to one of the many spare ground pads connecting to the big ground plane.

 If you want to make absolutely sure the ground channel is not affecting anything, you could also remove all the chips in the ground section.


----------



## Cyntax

fewf..things are finally wired up on my amp and its looking good.

 I'm doing the last test that tangent suggest on his website. 

_Then, take your meter and put it on the DC millivolts setting and measure from the ground plane to the output of each of the three channels; you should only be getting a few millivolts at most. If you are getting a few tens of millivolts, that's still okay, but you can't safely add the bass boost; you'll need to find out what's causing this offset and fix it before adding bass boost because it will exacerbate the problem. If you're getting more than a few tens of millivolts, you'll need to fix the problem regardless, as excessive DC offset will damage headphones._ 

 I put my multimeter on 200m on the V side (I assume this is the millivolts?) And this is what I found:

 Right Channel: 2.0
 Ground Channel: 1.2
 Left Channel: 0.2

 Are these values ok? Is there anything I can do to better them?

 Will post pics once its all done.


----------



## protos

Quote:


 _Originally posted by morsel _
* Protos has 15 posts to his name. We know nothing of his skills or background. We don't see dozens of posts by other DIYers saying differential output is bad. Team PPA spent months designing and testing the PPA. Draw your own conclusions. Speaking of which, why don't you just try it yourself? * 
 

 I didn't realize that the number of posts were an indication of somebodys skills or background.
 Of course though, I agree with morsel in principle.When somebody makes a claim in a forum and his "pedigree" is not known it is always wise to take his/her opinion with some reservation. I am not trying to impose my personal views on the PPA here just trying to provide what I hope is constructive criticism in the hope that someone may find it useful.
 In any case my final point was that bypassing the ground channel is extremely simple and PPA owners can easily try it for themselves.
 I would appreciate the feedback not because I am hoping to prove my point but mainly to see if others hear what I am hearing and in case this is not so for me to look at my PPA and see if there's a possibility something is not working as planned.Since I have invested time and money in the project I would really like it to be the best sounding head amp.


----------



## ppl

Most people have found the explanation of the ground channel on Larrys site more understandable.http://laroccoaudio.com/DifDrive.html

 I would advise against using the input ground as a ground return for Headphones as there is not enought current there to support low impedance loads. For use as a preamp the input ground as opposed to the Ground channel ground is ok to use since a power amp has a high input impedance. 

 regarding not using the ground channel output as opposed to the using a virtual ground sounding better. Anything is possible in Audio and i would not discredit anyones subjective evaluations of a component and if someone finds the another configuation that makes there PPA sound better to them that is great, It is an easy test without disturbung anything just remember with low impedance headphones when you exceed the available current from the Jfets the all kings of undesireable things like high DC offset can happen. People that wish to exparament with this are free to do so however remember if somthing goses wrong please don't complain


----------



## erix

Quote:


 _Originally posted by protos _
* In any case my final point was that bypassing the ground channel is extremely simple and PPA owners can easily try it for themselves. * 
 

Indeed, very simple, all it takes is a SPDT switch.

 Run a wire from center lug of the switch to your headphone jack ground lug.

 Take the output of the ground channel and run it to the one side of the the switch.

 Run another wire from the other lug of the switch to the point on the board where the input ground is connected.

 You will now be able to switch between an amplified ground channel and a normal ground. 

 Note that the input of the ground amp channel is always connected to ground.
 Also note that at the point in the switch's travel when it is connected to neither pole the amp will not have a ground connection. You may want to turn off power before switching between modes or else move that switch _really_ fast.

 Do try it and tell us what you think.

 edit: In fact, try it and MEASURE it - I'd like to see what difference it makes and I don't have the test equipment to tell me if it sounds good or not. Thanx.

 ok,
 erix


----------



## morsel

Quote:


 I didn't realize that the number of posts were an indication of somebodys skills or background. 
 

That was not my intended meaning. The point I was trying to make is that you are new to us and we don't know much about you. I was trying to temper Sovkiller's reaction without stepping too hard on your toes. It was not a position I relished. I don't want to say you are wrong, nor alienate you from these forums. I think it likely there is some peculiar extenuating circumstance which is responsible for your observations, but that's just my opinion.

 While we are on the subject, PPL is right as usual: using signal ground instead of output ground for driving headphones is not a good idea, as the input stage is not designed to handle the load. It was irresponsible of me to suggest people simply try it for themselves. It is my belief that the PPA sounds and performs better as designed.


----------



## ppl

For those that may not know the Lineage of the PPA my pocket Amp as depicted in this old thread is 2/3 a PPA using a conventional Virtual ground. This Amp still today is considered the Definitive Reference standard of Portable Amp's. Photos and schematic are included.
http://www4.head-fi.org/forums/showt...+my+pocket+amp


----------



## Sovkiller

Quote:


 _Originally posted by morsel _
*I was trying to temper Sovkiller's reaction without stepping too hard on your toes. It was not a position I relished. I don't want to say you are wrong, nor alienate you from these forums. I think it likely there is some peculiar extenuating circumstance which is responsible for your observations, but that's just my opinion.* 
 

morsel as I explained before there is no need of temper anything, this was not my intention neither, I was just trying to find out, maybe you guys, have tested this option also, and for any unknown reason, this could not be safe, or maybe it is not possible, unless something was wrong in any other place, as we see now, and as ppl stated, also there are other implications on that, and not only the preference, I was driving very low Z cans, 32ohms, so for me is not even safe, to try it, if I would test it, maybe some undesirable effects should appear....but nevermind...

 Now the good part, I'm listening right now the PPA, it is a hell of an amp, I'm using the BB not the AD, and the sound is just right, not too bright, not too dark neither, just right, perfect if you ask me twice, I was listening just for one hour or so, is too early for a real impression, but I think that you guys hit the nail in the same HEAD....period....thanks very much morsel, ppl, tangent, kurt, and other that have work on the project, for so delicate design, I will post my impressions later....another thing............the Perreaux is not so far from it soundwise.......but is too early.....


----------



## protos

Quote:


 _Originally posted by ppl _
*

 I would advise against using the input ground as a ground return for Headphones as there is not enought current there to support low impedance loads. For use as a preamp the input ground as opposed to the Ground channel ground is ok to use since a power amp has a high input impedance. * 
 

 There is something here I don't understand. Your previous amps and the majority of head amps either DIY or production don't have a ground channel but use the usual grounding scheme where signal ground and output ground are the same thing.Are you saying that all these amps are inherently unstable and dangerous for low impedance headphones?


----------



## PeterR

The problem here is the use of a single supply and therefore the need for a virtual ground. This is supplied by the TLE2426s, whith a current capability of about 20mA. If you use the unbuffered signal ground, (i.e. w/o 'ground channel'), it needs to handle the combined current output of the left and right channel (4 5002's per channel, so really not a fair fight). In a conventional virtual ground setup you therefore probably would like to buffer the output of the rail splitter, like e.g. in the META.


----------



## jeffreyj

Quote:


 _Originally posted by protos _
*There is something here I don't understand. Your previous amps and the majority of head amps either DIY or production don't have a ground channel but use the usual grounding scheme where signal ground and output ground are the same thing.Are you saying that all these amps are inherently unstable and dangerous for low impedance headphones? * 
 

I believe what you have not considered here is that, for example, the META42 does not have it's signal level amplifier isolated from the power supply rails by JFET constant current sources as is done in the PPA. Trying to demand more current from a CCS than it is programmed to give will result in its terminal voltage going to zero. Think of the PPA's input amplifier as being powered by one set of batteries while the output buffer is powered by another set. Now imagine that the battery packs' center-taps (virtual ground provided by the TLE2426's, in the actual case) are joined by a 1k resistor. As long as their is little current flowing between input amp and buffer amp, the voltage drop across the resistor will be minimal (ie - as long as the only load on the input amp is the buffer amp's high input impedance, things are kosher). But if you were to return the buffer amp's output current through the input ground connection it would have to flow back through the 1k resistor.

 Is this how it actually works? No, but it is a good analogy of why the input ground and output ground _in this particular power supply scheme_ must be kept separate.


----------



## protos

Oh , I see the problem area now. How much current would low imp phones need normally?


----------



## jeffreyj

P = I^2 * R

 Eg - 10mW into 32 ohms requires ~18mA.


----------



## protos

Are you sure they need that much?I had a look at grado site and the rs1 is 98db for 1mv.So a few ma should be enough to drive them to deafening levels.
 In fact I think with 5.6 ma you can get 113db.


----------



## PeterR

Quote:


 _Originally posted by protos _
*Are you sure they need that much?I had a look at grado site and the rs1 is 98db for 1mv.So a few ma should be enough to drive them to deafening levels. * 
 

98dB/1mV would be insane, that's most likely 98dB/1mW.
 1mA into 32ohm equals 0.032mW, or 83dB SPL output from the Grados.

 Edit: Did your edit your post between me reading it and hitting reply, or did I dream those 1mA/112dB you were talking about?

 Edit: And another one, it's really hard to keep up with your edits...5.6mA is about 1mW, therefore 98dB SPL.


----------



## jeffreyj

Quote:


 _Originally posted by protos _
*Are you sure they need that much?I had a look at grado site and the rs1 is 98db for 1mv.So a few ma should be enough to drive them to deafening levels.
 In fact I think with 5.6 ma you can get 113db. * 
 

I gave you an example, not a definitive statement as to how much current a particular brand of headphones would require.


----------



## protos

http://www.gradolabs.com/product_pages/rs1.htm

 Maybe, but that is what the official site is quoting.


----------



## protos

Looking at AT which is more inefficient : 100db/mw you can still get 103 db with 7ma.
 However I can understand that if you have low imp headphones and plan to listen at levels much above this then the TLE's might start to have a problem .


----------



## morsel

Peter and Jeffrey are correct. The PPA input/signal ground is not designed to source or sink headphone currents. Even if your headphones don't draw that much current, you are depending upon wimpy TLE rail splitters and electrolytic capacitors to do the job of 4 studly HA5002 buffers, and you are polluting signal ground with output currents, thus simultaneously sacrificing low impedance control over the headphone drivers and isolation of the input stage.

 I don't know why your amp sounds better when not using the ground channel. My best guess is that something is ailing it. You could try swapping opamps, examining connections, making sure all parts are of the correct value in the right location, etc. You could also take another look at Tangent's detailed assembly guide at his site and my brief section on wiring considerations at mine. Perhaps something will jump out at you.

 (rereading all of your posts in this thread)

 You started with OPA627 but replaced the left and right channels with AD8610 which you seemed to prefer. Did you ever replace your ground channel opamp with an AD8610?

 You used the PPA as a preamp. Hopefully you used signal ground, not output ground, for the line out connections.

 If all else fails, sack your PPA and build a class A power MOSFET monster: SDS Labs Headphone Amplifier


----------



## protos

I have ad 8610 on all channels now. I don't really believe there is something wrong with it.As a pre-amp using the signal ground it sounds very very good.Better than my existing pre's (Naim,Pass etc). The only possibility is there is something wrong in the ground channel but I doubt it since it measures correctly in all senses.As I said before the sonic differences between using or not using the ground channel are quite small and are not apparent unless you do a direct A/B.There is no obvious distortion or frequency aberration with the ground channel.However I find the PPA to sound more open without it and I have rewired the output.I am using hd-600 so I can't say if this would be apparent on other 'phones especially low impedance ones.
 Perhaps comparing the PPA to a balanced amp is a little unfair.The balanced one I have has a wider soundstage and sounds a bit smoother and is quite musical. The PPA which seems to have broken in more now gives a liitle more precision and punch but may also sound slightly narrower. I was playing around with the buffers yesterday and it sounds to me that perhaps 3 gives the ideal balance with 4 sounding a touch overblown. I haven't made up my mind yet.


----------



## crane

Well, I thought that my PPA was working properly, they I started doing a listening test and found that there is a problem.

 Everything is o.k. when I am listing with the volume at a moderate level, but when I turn it to a louder level, there is a loud clip/crackle.

 I started to debug with the multimeter. I measured from IG to OL/OR/OG and found that there was a sudden spike in the DC voltage (at about 3oclock). The DC voltage jumped from the 0.1-0.9mv range to 400-600mv range.

 Any help would be appreciated.


----------



## Cyntax

Hey guys, 

 I posted this a few pages back but I think it got lost 
	

	
	
		
		

		
			





 I'm about to add in bass boost to the PPA and I am measuring the DC offset on each channel.

 I put my multimeter on 200m on the V side (I assume this is the millivolts?) And this is what I found:

 Right Channel: 2.0
 Ground Channel: 1.2
 Left Channel: 0.2

 Are these values ok? Is there anything I can do to better them? Its kinda strange there is such a difference from the left channel to the right channel.


----------



## tangent

Quote:


 The DC voltage jumped from the 0.1-0.9mv range to 400-600mv range. 
 

It would be interesting to know what the supply current to the amplifier does when this voltage spikes. While you test these things, don't have the headphones plugged in.

 Is C6G populated?

  Quote:


 Are these values ok? Is there anything I can do to better them? 
 

They'll probably be okay, especially if the R7 value is close to the value of R4. The bigger R7 gets, the more the bass boost will magnifiy your DC offset. Eventually it can become a problem. I wouldn't worry about a 20mV offset (i.e. 2mV x g=10)


----------



## crane

I do have C6G installed.

 I measured from IG to Pin 8 of the op-amp. When the voltage between IG and OL/OR spikes, the voltage to Pin 8 drops by about 2 volts.

 Crane


----------



## Jupiter

Quote:


 _Originally posted by crane _
*I don have C6G installed.* 
 

You do or don't? By the way, that cap is not optional.


----------



## crane

Sorry, mistype. 

 I have C6G installed.


----------



## tangent

We're using single-channel op-amps in the PPA. Pin 8 on singles is used for various things. If you measure against pin _7_, that might be interesting. But I'm still more interested to know how the supply current to the amplifier changes.


----------



## DCameronMauch

Question about the ground buffers... Since the ground channel must source/sink twice as much current as either signal channel, shouldn't the ground channel have twice as many buffers as either signal channel? With the maximum 4x3 configuration, the buffers will not have consistent loading. The ground channel buffers will be worked harder than the signal channel buffers. Just seems pretty logical to me. Or am I missing something?

 Also the jfet isolation in the power supplies. What is the theory of how that works? It looks like a two parallel constant current sources, but with a variable load. Could someone please explain this a little please? Thanks!


----------



## tangent

Quote:


 Since the ground channel must source/sink twice as much current as either signal channel, shouldn't the ground channel have twice as many buffers as either signal channel? 
 

That applies only when both output channels' signals are in phase and of similar amplitudes, and when the output current of each buffer is high. So if you're using your PPA to drive small speakers with mono source material, yes, a 1-2-1 multiple makes sense. Otherwise, it really doesn't matter.

  Quote:


 Also the jfet isolation in the power supplies. What is the theory of how that works? 
 

Standard constant current source theory: a current source maintains a constant current despite voltage changes across them. The implication of that is that voltage changes are not transmitted through a useful current source. This happens even when the current source is not fully loaded.


----------



## DCameronMauch

Hello. Thanks for the response.

  Quote:


 That applies only when both output channels' signals are in phase and of similar amplitudes, and when the output current of each buffer is high. So if you're using your PPA to drive small speakers with mono source material, yes, a 1-2-1 multiple makes sense. Otherwise, it really doesn't matter. 
 

I am a little confused. It sounds like you are basically saying that for more reasonable headphone loads, it is not a big deal. But I keep reading about how important it is to use all 4 buffers on each channel. Which tells me it is a big deal. Also average source material is 60% mono (and 80% mono in the bass). So I am left unclear on this point.
  Quote:


 Standard constant current source theory: a current source maintains a constant current despite voltage changes across them. The implication of that is that voltage changes are not transmitted through a useful current source. This happens even when the current source is not fully loaded. 
 

I don't think I am quite getting it. Because it looks like it would create a rather undesireable effect. A constant current source would look like a very high power supply source resistance at
 any audio frequency. So, unless all your circuitry runs full class A all the time, the power supply rails would modulate badly. Given a heavy load, the HA5002 used in the PPA would not meet this requirement. The idle current is would not be high enough. So, again, I must not be understanding how this works correctly. Thanks alot for helping with this!


----------



## morsel

DCM: Regarding buffer configurations, extensive testing shows that there is no benefit to putting more buffers on the ground channel than on the left and right channels. 4 buffers per channel assures good sound quality and resistance to output short circuiting. Check out the benchmarks and huge body of past posts for more details.


----------



## tangent

Quote:


 I keep reading about how important it is to use all 4 buffers on each channel. Which tells me it is a big deal. 
 

It's important for the _output_ channels to have 4 buffers, because this has known safety and quality benefits. I cover these issues in the docs.

 Four in the ground channel is less important from a quality standpoint. Probably you could get away with 1x buffer there if that was all that mattered. 4x in the ground is mainly a safety issue. Yes, it would be nice to have 8x in the ground channel, but the space for this just does not exist. Also, the most likely time you're going to strain the current drive of a channel is if you pull the headphone plug out while music is playing. Since you can't short both channels to ground at once with TRS plugs, 4-4-4 is just as safe as 4-8-4 would be. If you plan on shoving a 1/4" steel rod into your output jack, 4-8-4 would have an advantage.

  Quote:


 average source material is 60% mono (and 80% mono in the bass). 
 

When the load is headphones, the current is in the low milliamps range, so even 1-1-1 is sufficient. When you're shorting the output, it's only one channel at a time so having the same number of buffers in all channels is the safest course.

  Quote:


 A constant current source would look like a very high power supply source resistance at any audio frequency. 
 

I understand what you're thinking, and I'm not sure I can explain to you why what you're thinking does not apply. Before I try, let me point out that this feature of the circuit is not voodoo. I have done ripple rejection tests on it, and the reduction is obvious. I'm talking on the order of 15-30dB without any special effort.

 Like I said, I'm not certain I can explain this. Let me just make some observations. Maybe you can stitch them together into a picture that makes sense to you.

 1. The voltage drop across the current source is roughly constant, being a function of current draw. That current draw is mostly composed of the class A biasing current and the op-amp's quiescent current.

 2. The variable part of the op-amp's current draw is on the order of microamps.

 3. The caps on the op-amps' rails further helps stabilize the voltage on that side.


----------



## ITZBITZ

It's completely built, works great. 2x637, 1x627, 12 buffers, 8x1000 uf Panasonic FC caps (which I'm about to reduce to 3 or change out with Muse KZ). 15xAAA pack lasts almost 8 hours.

 Cased (front only, waiting for huge bit to make switch hole):






 Amp Board (click for full image):




 From Behind:





 From the Top:





 Enjoy!


----------



## morsel

Congratulations, Itzbitz!

 I think you may need a smaller Molex connector for the battery board coupling cable so the wires can pass through the board slot. The Molex you are using may not allow the rear panel to be seated properly.


----------



## Voodoochile

Nice job! How do you like it? (it's early on, I realize)

 I agree about your battery board molex. Another option is to solder the wires direct to the battery board, and just have the connector on the amp side. Still comes apart when needed.

 Nice touch that you soldered your buffers directly, too. Go forth boldly!


----------



## nanahachi

ITZBITZ, 
 that looks fantastic. so nice and clean. it makes me want to spend my winter break brushing up on DIY skills (and somehow scrounge up enough cash to buy PPA parts 
	

	
	
		
		

		
		
	


	




)

 great job!


----------



## ITZBITZ

Quote:


 _Originally posted by morsel _
 I think you may need a smaller Molex connector for the battery board coupling cable so the wires can pass through the board slot. The Molex you are using may not allow the rear panel to be seated properly. [/B] 
 

I was wondering about that. I used the parts on the listing on Tangent's site and wondered about the clearance on the back panel with those wires. I will probably just cut back the connector with a dremel if possible, or hard-wire the leads to the board and only have the quick disconnect on the amplifier board side.

 Thanks for the comments, patience is the key!


----------



## tigger

Quote:


 _Originally posted by ITZBITZ _
*I was wondering about that. I used the parts on the listing on Tangent's site and wondered about the clearance on the back panel with those wires. I will probably just cut back the connector with a dremel if possible, or hard-wire the leads to the board and only have the quick disconnect on the amplifier board side.

 Thanks for the comments, patience is the key! * 
 

Another possibility is to bend the legs of the Molex closer to the body, this gives enough clearance for the wires to pass through without fouling the rear panel.


----------



## Dean Coop

I'm stumped, for some reason my right channel is a lot quieter (half the volume) than the left. It sounds clear, but not as full in the range and I can't for the life of me figure out whats going on. I've tried changing the opamps, buffers and inputs with no change. Any suggestions?
	

	
	
		
		

		
		
	


	




 Thanks,

 Dean


----------



## jasonhanjk

Have you bias to class A correctly?


----------



## Dean Coop

No I haven’t. Right now R9 is open, Q1 and Q2 are installed and I have a jumper across R8.


 Edit

 Ok this is starting to get frustrating...
 I must be reading the instructions wrong because I can't get the current to change across R9 at all. This is what I'm doing; I have a 1K resistor and my meter in series across the R9 slot. Then I have a 2K pot in R8. Right now I'm not seeing any current across R9 and I can't get it to change by adjusting R8. What am I doing wrong?


 Any other suggestions on getting this thing working?


----------



## hifi

How would the SDS labs design stand against the PPA??

 (i got a board for the SDS)


----------



## morsel

Build your board and let us know. I've had my eye on the SDS Labs Headphone Amplifier for some time now, but I have never heard one. A modified differential SDS would be interesting to try.


----------



## hifi

Hello,

 Im at a loss what to build I did put some effort into the SDS board I made, (added ground plane, CLC filter in the psu dicrete diodes, and incorprated the addendum recomendations) but i did never build it because i needed the Talema toroid for another project, the board just lies in a drawer gathering dust... anybody with a spare PPL board want to take it of my hands? 
	

	
	
		
		

		
			





 JWB over at www.diyaudio.com have made a really nice Aleph headphone amp. witch might just be the ultimate when it comes to stationary amps... I dont know how good the Pimeta/PPL really is?!... (my headphones are Grado SR125 / Shure E2C) i mean when it sure looks great when it comes to portable gear but still..

 (a short questions i have not reachered the desgins enogh jet but why don´t the Pimeta board utilise the HA3-5002 bufferts?)'

 / Micke


----------



## morsel

Regarding the PIMETA, Tangent and I talked about buffer options, basically the bottom line is that the BUF634 is BW/Iq adjustable whereas the HA5002 is not, making the BUF634 a more flexible choice.


----------



## Dean Coop

Well I've managed to figure out how to bias the amps in to class A properly but I'm still having a problem with the channels not matching in volume...

 edit...Well after a lot of screwing around, I found that there was nothing wrong with the amp at all. It was the damn cheap "tester" headphones that was causing the problem.

 Anyway, using my good headphones I have been really enjoying this amp, actually the only thing wrong with it is the trouble I'm having turning it off because I'm liking it so much. Hopefully I can find a digital camera that I can use to take some pictures of the finished product.


----------



## jasonhanjk

Dean, could you measure the voltage with reference from IG to OL, OR and OG?

 You start a new thread and we would be in better position to help you.

 Regards,
 Jason


----------



## Voodoochile

Quote:


 _Originally posted by jasonhanjk _
*You start a new thread and we would be in better position to help you.
 Regards,
 Jason * 
 

Excellent advice! This thread is virtually unsearchable given it's massive proportions. Please use a good descriptive title as well, rather than (for example) 'need PPA help'.

 Thanks Jason.


----------



## hifi

Also i wonder...is the performance of the PPL better with the battery board or with a propper regulated PSU?

 I mean is the battery board nor for portable use or for enhanced performance?

 /micke


----------



## jasonhanjk

Quote:


 _Originally posted by hifi _
*Also i wonder...is the performance of the PPL better with the battery board or with a propper regulated PSU?

 I mean is the battery board nor for portable use or for enhanced performance?

 /micke * 
 

Some say yes, others no. You have to try it yourself.


----------



## hifi

Okie..It should be pretty battery dependent the NiMh cells do range from 500-2100mA and so should the source resitance of them aswell...

 so how does a maxed out Pimeta stand against the PPA?


----------



## Voodoochile

The PPA measures quite a bit better. Tangent's site lists RMAA graphs showing the Pimeta vs META42, and also PPA vs META42.

 Crosstalk and noise level are markedly better with the PPA, for instance. Mind you I am not saying the LETA42 or Pimeta are not good, just that the PPA is a better performer.

 It's not that surprising, as the Pimeta was not made to be a competitor to the PPA, but rather to replace the META42, which enjoyed a nice little niche of it's own.


----------



## hifi

hello,

 okej, jet at a glance the toplogy of the Pimeta and the PPA is quite similar, one could make the Pimeta use HA3-5002 buffers.. 

 As i staded before i have made a nice board for the SDSlabs headphone amp and i think i should build it before buidlign a PPA but a Pimeta would be cheaper to build...just to get my feet wet regardings to the concept of the two amps.. 

 anyway drawing a new board for the Mint/Pimeta with all smd parts and a DCDC converter maybe a digitalpot or none at all.. would better suit my portable needs (my mp3 player is 83x25x18mm and i dont want to carry another box that is larger than that) and i think it possible to accomplish that im thinking of make ing something lite this: 

 ----------- 3,5 plugs in this emty space
 ----------- smaler boards with one op amp and one buffer 
 ------------------------- Psu with DCDC reg
 battery compartment one AA or AAA 

 anyway i have not done anywork on this jet (just wrote down my thougts) well the chrismass break is comming up and i plan on doing much hifi building the last few days this year 
	

	
	
		
		

		
		
	


	




))


----------



## tangent

Quote:


 The PPA measures quite a bit better. 
 

Beware of reading too much into the measurements. They exist to show that there are no major flaws in the design. That is, distortion is under control with all of these amps, crosstalk is within reasonable limits, etc. You'll notice that the PIMETA and META42 measure quite closely to each other, but I assure you that they sound quite different.

  Quote:


 one could make the Pimeta use HA3-5002 buffers.. 
 

Yes, and then its minimum quiescent current would be two to three times higher as one with BUF634s. Further, it would have a less forgiving sound. Both are fatal mistakes for a small portable amplifier designed to go with small portable sources. I chose to go with the BUF634 quite deliberately.


----------



## hifi

hello,

 Yes i know, but the pimeta is still to large to fit my portable needs so portable will not be its primary use, more like computer amp perhaps... or just something to keep me ocupied during the holidays 
	

	
	
		
		

		
		
	


	






 / Micke


----------



## eric343

I'm curious why the PIMETA doesn't have a virtual ground buffer...


----------



## tangent

Quote:


 I'm curious why the PIMETA doesn't have a virtual ground buffer... 
 

Same reason the PPA doesn't: if you make the ground buffer take the load of the returning currents from the headphones, the TLE only has to cope with tiny currents. Since a TLE has much lower output impedance than a buffer, it's a better solution when you can get away with it.


----------



## feles

I just got all the goodies together and im gonna start tonight. im taking lots of pictures for your enjoyment. wish me luck.


----------



## Duncan

Quote:


 _Originally posted by feles _
*wish me luck. * 
 

Good luck!

 As and when I get around to it, i'm going to take the wimps way out, and get someone to build one for me


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## ppl

ITZBITZ I noticed your headphone jack is not insulated from the chassis.This is a bad idea as it will cause the ground channel to misbehave. The Nutrik jack is specified for its isolated ground and locking feature both are considered required on the PPA.


 Dean Coop Please elaborate on your volume inbalance? have you tried swaping op amps from one ch to the Other? Might reveal a defective OPA. also do the asme with the Buffers starting with only 1 buffer per ch to test. Measure the DC offset on each ch and note any large differences. hope this helps


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## ITZBITZ

Quote:


 _Originally posted by ppl _
*ITZBITZ I noticed your headphone jack is not insulated from the chassis.This is a bad idea as it will cause the ground channel to misbehave. The Nutrik jack is specified for its isolated ground and locking feature both are considered required on the PPA.
* 
 

Really? Ok. I guess I'll order one.

 What about the input jacks? Do they also need to be insulated?

 Is this the ticket? 

http://www.partsexpress.com/pe/showd..._ID=2508&DID=7


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## tangent

Quote:


 What about the input jacks? Do they also need to be insulated? 
 

It's one or the other, or both. If neither are insulated, you short OG to IG through the case, which is what ppl is talking about. You could avoid getting an insulated output jack by insulating the input jacks, but I'm not sure the OG channel is a good place to dump interference that the case will pick up.


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## feles

Ive got pretty much everything on the board, i got a little carried away with the sockets though... (i hey i was on a roll). Oh, yeah, soldering irons ARE HOT!!! I managed to give myself a 3rd degree burn on my pinky by brushing against mine. its the first time ive ever actually burnt myself with one, and i hope its the last. 

pic1 

pic2 

pic3

pic4


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## ppl

feles
 why are you only populating 3 C1 posistions. Some people claim that the amount of capacitence hear is unimportent however IMHO it really matters.


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## feles

They are panasonic FC 1000uF, so I've already got 4000uF... I have a bunch more of them so if you really think I should fill them all up I will. I was just going to reverse-current on the extras and watch them explode in my back yard anyway


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## ppl

Quote:


 _Originally posted by feles _
*They are panasonic FC 1000uF, so I've already got 4000uF... I have a bunch more of them so if you really think I should fill them all up I will. I was just going to reverse-current on the extras and watch them explode in my back yard anyway 
	

	
	
		
		

		
		
	


	


* 
 

Well since you have them already and you are just going to pollute your yard with toxic chemicals and probably contaminate the ground water in 50 years why not yourself and our earth a favor do and put them in your amp.


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## ITZBITZ

Quote:


 _Originally posted by ppl _
*Well since you have them already and you are just going to pollute your yard with toxic chemicals and probably contaminate the ground water in 50 years why not yourself and our earth a favor do and put them in your amp. * 
 

When I mentioned I had 8000 uF of capacitance, I was told that it was probably too much and that it could cause power supply problems. Is this not the case?

 I have 8x 1000uF Panasonic FC's on my PPA now.


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## ppl

8,000uF of primarry rail caps is not large at all considering alot of High end preamps sport 10,000uF of primarry capacitence. If you power supply is so wimpy it can't cope with 8,000uF then consider getting a better supply.

 one big reason to populate all C1 posistions is to prevent excessive inductence on the Power Buss lines. consider that you have less space between capacitors with fully populated C1's and thus a shorter foil lenght between capacitors. this results in less unchecked inductence. Also now consider that if the output Buffers just so happen to fall in one of those unchecked (Unpopulated) C1 posistions then you have the potential for some real untidy supply ringing just from the inductence of the foil alone. one of the design considerations in the PPA is this issue so it is my recomendations that if you wish to use less capacitence then just use smaller C1 values and still populate all the posistions. moreover evean if you dont hear anny difference between 500uF and 8,000uf consider that the 8,000uF will provide lower Ripple and generaly a lower impedance within the audio range than a smaller capacitence.


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## feles

ok well I've added 4 more C1 skyscrapers to my little city here... while I'm around to post here, I just noticed your sig ppl, what are your recommendations for C7 and R7 so that i get the full "spring morning" effect?


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## ppl

Humm max spring morning effect. Well if your a bass head like i am then 0.068uF if you want less intrusion in the lower mids then0.1uf and if you only want to boost the low rumbel and have basicaly no effect on most music then 0.22uF Team Sony recomends 0.056uF


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## feles

Everything is done, although I dont have it in a case yet, i hooked up to 2 9 volt batteries and input from my minidisk, this think rocks! Do I win a prize for getting it to work on the first try?


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## picklgreen

I finally got around to finishing my PPA! I actually forgot all about it. I started it a long time ago so it was built on the V1.0A board. I guess they have since had 2 major revisions. Oh well....

 So it powered up right off the bat and sounded pretty good. I prefer the sound of the OPA 627.637 mix. Just the 627 in all 3 channels was to laid back for me.

 Had a bit of a problem doing the class A bias but i got help with that. Have them set to 2mA bias.

 I will post some pics when i figure out how to post them.

 For my next project I would like to build either the PPA V2 or an M3. Any thoughts?


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## dhp

anyone have 3 2N5088s and a 2N5087 transistor? They're used in the discrete buffer stages of the PPAv2. Shoot me a PM and it'll be greatly appreciated. Thanks


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## luvdunhill

reviving a dead thread 
	

	
	
		
		

		
			





 Anyways, can someone give me some insight in how to choose a CRD for the PPAv2? values go from 0.24mA - 4.7mA in the range given on Tangent's website. My gut is to go for a higher value, but I thought I'd ask and get the mathematical answer


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## tangent

Quote:


  Originally Posted by *luvdunhill* 
_reviving a dead thread 
	

	
	
		
		

		
		
	


	




 Anyways, can someone give me some insight in how to choose a CRD for the PPAv2? values go from 0.24mA - 4.7mA in the range given on Tangent's website. My gut is to go for a higher value, but I thought I'd ask and get the mathematical answer 
	

	
	
		
		

		
		
	


	


_

 

There are several places in the PPA you could use a CRD. Which one are you talking about?


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## luvdunhill

In the PPAv2 PCB position marked CRD. It's for the LED


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## tangent

Okay, so technically, there is indeed a mathematical answer. You would have to talk the LED's manufacturer out of its lumens vs. current graph -- I've yet to see one in a datasheet -- and then decide how many lumens is "bright enough" for you. That'll give you current.

 Or you can do what the rest of the world does and fiddle with it until you find a brightness level that makes you happy. With most LEDs and most eyes, this will be somewhere around 2 mA. It may need to be as high as 5mA, and some may tolerate values under 1 mA. You'd do this with a resistor and a fixed power supply voltage, then calculate the correct CRD value from that.

 If you must know the correct answer before buying parts, you're out of luck. There is no easy answer. If you had to pick a value blindly, I'd do 1 mA for a red, green (the sickly yellowish green traditional color -- not the new "true" greens) or amber LED. For the newer types -- white, blue, pure green, violet... -- I'd probably do 2 mA.


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## ozshadow

I have yet to find the perfect blue LED. The 1500 brightness 5mm Radio Shack ones light up half my bedroom at night with a 10k resistor - and its purple looking.


 Trying this one next with 10k resistor
http://www.mouser.com/search/Product...04-WP7104QBC/D


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## picklgreen

I have several different blue leds in 3mm and 5mm that work great! And yes they are brighter than red ones but that is because of the spectrum of light blue falls in. But when i use resistors, it does not make them purple...they are still blue!

 I have some pink ones also that look sweet.


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## luvdunhill

Hi all fellow PPA builders 
	

	
	
		
		

		
		
	


	




 I was wondering if using a 475k instead of 470k resistor for R6RL would make any difference other than a slight increase in gain? 

 Also, when connecting the BBR and R7R pads, should I run the wires on the bottom or the top of the board? Also, Tangent suggests testing the amp before adding the bass boost, but I should be able to just jumper the S2RL pads and still run the BBR->R7R wires before hand, right? In other words, I'd rather add the BBR-R7R wires, jumper the BBR->R7R, test the PPA, unjumper and test the bass boost.

 Thanks!!


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## tangent

Quote:


  Originally Posted by *luvdunhill* 
_I was wondering if using a 475k instead of 470k resistor for R6RL would make any difference_

 

Not a whit.

  Quote:


 should I run the wires on the bottom or the top of the board? 
 

I'd do it on the bottom, only because there aren't any components in the way. If you had to do it on the top for some reason, there's no great problem with that.

  Quote:


 Tangent suggests testing the amp before adding the bass boost, but I should be able to just jumper the S2RL pads and still run the BBR->R7R wires before hand, right? In other words, I'd rather add the BBR-R7R wires, jumper the BBR->R7R, test the PPA, unjumper and test the bass boost. 
 

I'm not understanding which end you're jumpering. 

 If you're soldering the boost control wires together, then no, that's not a good plan. Part of the reason I say you should test without bass boost is because the smaller the feedback loop, the fewer the chances for problems.

 If you're shorting it so the wires aren't in the loop, I suppose that would be okay, but I don't know that you'd get a great amount of advantage from this. Regardless of how you do this, you're going to have to desolder something, so...


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## luvdunhill

hi Tangent! Basically, I was wondering if I could go ahead and run the two wires from BBR to S2R and *also* jumper S2L and S2R.. test and then remove S2L/S2R to test the bass boost.. I just would like to go ahead and run the wires now 
	

	
	
		
		

		
		
	


	




 Since you recommend putting them on the bottom of the board, I'm not sure how to do this!! Do I solder on the front side of the board? There's no way I can really do this with all the parts already on the board.. so I assume that I would just tin the wire, shove it in and flow solder around the wire on the back?

 Also, I'm thinking about trying the OPA637BPG4 op amps first (I have no idea what the G4 means, as there's no difference I can see on TI's website) so wish me luck! I also have OPA134PA and OPA227PA single channel opamps on hand as well if the former turns out to be cranky!


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## luvdunhill

hm, quick question. What could cause a different DC bias in one channel but not the other? I have 2.2mV in the right channel and 0.5mV in the left channel. I have set R24/R34 to 44mV in all three channels and have biased the opamps with 1.0V across R10 in all three channels as well. I'm just using two 9V batteries right now to test, until my Elpac arrives, in case that is of interest.

 edit: my input voltages are off my a half volt or so to my opamps, so I'm going to assume that I testing with two 9v batteries in series is the problem. Also, I'm measuring the above voltages from IG to OL/R... I'm not sure if this is the correct way to do this.

 edit: ok, to OPAL I have 4.84,-4.85 and to OPAG I have -5.30,5.35 and to OPAR I have -5.55,5.54. Also, I tried to enable the bass boost, and the DC offset voltages are still disproporinate... now, with the knob in the off position, I get 1.9mV DC offset in the right channel and with it fully turned I get 7.4mV DC offset. In the left channel I get 0.5mV and 6.06mV. I also measured both channels of the pot, and they are a little off, the right channel of the bass boost pot is 1.4-45.8k and the left channel is 1.6-47.0k. Also, R4R = 10.0k and R4L = 9.98k.

 I just ordered my Elpac, so unless there is something I can do with the 9v batteries, I'm going to retest after I get the regulated wall-wart power supply.

 -Marc


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## raduray

I have a LaRocco PPA which is a PPA v1 board with the LaRocco Diamond Buffers. It's powered by an Elpac 24V Power Supply. Currently it's running OPA627 op-amps and I'm wondering if it will support AD843?


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## quicksilver96

Yes, an AD843 will work in place of an OPA627.

 Edit for luvdunhill - 

 About the DC offset: small differences like this can be attributed to manufacturing tolerances. The difference you have described is very small and will not effect the operation of your amplifier. Some opamps such as the AD843 and OPA627 have pins dedicated to setting this offset exactly the same for applications where a few mV of DC offset will matter. The PPA (v1 or v2) does not connect anything to these trim/offset pins and there really is no need. If the offset difference is really high, there is something wrong with the build or the opamp itself.

 About the input voltages: again - manufacturing tolerances. Tangent has an individual TLE, JFETS, R8 resistors, C4, and C5 for every opamp. Each of these parts has certain manufacturing tolerances and the V+/V- output to each individual opamp will be slightly different, though 1/2 volt seems slightly high, I don't think it will effect the operation of the amplifier. The "virtual ground" ouput of all the TLEs are tied together, and I think this is more important than the V+/V- levels being exactly the same at each opamp.


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## tangent

Quote:


  Originally Posted by *luvdunhill* 
_Do I solder on the front side of the board? There's no way I can really do this with all the parts already on the board.._

 

I doubt there's really "no way" to do it, but no, that's not what I had in mind. With hookup wire, if you simply don't push the wire all the way in the hole so there's a gap between the insulation and the pad, you can heat the wire+pad up and flow solder in there from the same side as the wire.

  Quote:


 I have no idea what the G4 means 
 

I haven't bothered to look, but I'll bet it's a RoHS code...Google it if you don't know about RoHS yet.

  Quote:


 What could cause a different DC bias in one channel but not the other? I have 2.2mV in the right channel and 0.5mV in the left channel. 
 

First, the correct term for that is a DC offset, not a bias. EDIT: The distinction is one of intent: an offset is an error, whereas a bias is created purposefully.

 As for what causes it, basically it's a difference in part tolerances. It's exceptional to have two circuits have the same DC offset, if you don't take special measures to ensure it. Mismatch is the common case. But as long as they're all within some reasonable range, it's fine, which is your situation.

  Quote:


  Originally Posted by *raduray* 
_I'm wondering if it will support AD843?_

 

We had problems with the 843 in both the v1 and in the v2. Do a search here...tips for increasing the amp's stability margin have been posted several times. A good first search would be for *PPA* and *AD843*.


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## luvdunhill

Thank you Tangent! The amp sounds great! 

 I'd like to go back and add ZNR, which is now jumpered. I am using a CRD(1N5304) which is rated at 1.8mA. I am using a LED that has 4.9V forward voltage and If = 20mA. If I use 12 x AAA battery pack and I would like the LED to shut off at 12V, then will a 6.8V or 7.5V zener work, right?


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## luvdunhill

so today I had the pleasure of upping the buffer bias from 10mA to 30mA. Wow, a HUGE improvement!! I was wondering if anyone had any luck with increasing the opamp bias point from 1mA and what value would be considered reasonable.

 Also, I'm running OPA637BP x 2 + OPA227PA for the ground channel. I also have three each of OPA602AP, OPA228PA, OPA227PA, OPA637AP and OPA134PA on hand and would appreciate any recommendations on what combination to try until I get a OPA627 to put in my ground channel 
	

	
	
		
		

		
			





 edit: oops, I almost forgot... when using the OPA627 in the ground channel, do you recommend bumping C6 up to 100pF? Currently, I have 10pF silver mica in C6. Would this be a good location to try out a polystyrene capacitor?


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## tangent

Quote:


  Originally Posted by *luvdunhill* 
_I'd like to go back and add ZNR, which is now jumpered. I am using a CRD(1N5304) which is rated at 1.8mA. I am using a LED that has 4.9V forward voltage and If = 20mA. If I use 12 x AAA battery pack and I would like the LED to shut off at 12V, then will a 6.8V or 7.5V zener work, right?_

 

Yes, something like that. Getting the exact behavior you expect may require some experimentation, because the zener's knee is fairly soft. You get the most abrupt shut-off if you set it to a lower voltage, but then that gives you less warning that the battery pack is about to crater.

 Oh, and so you understand, the CRD's value and the LED's If limit are irrelevant here. All that matters is the LED's forward voltage and your desired cut-off point.

  Quote:


 when using the OPA627 in the ground channel, do you recommend bumping C6 up to 100pF? 
 

Can't hurt, but I wouldn't do it in advance. Do it later, if you have problems.

  Quote:


 Currently, I have 10pF silver mica in C6. Would this be a good location to try out a polystyrene capacitor? 
 

Yes. The only reason I recommend micas by default is that they're a whole lot easier to find.


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## mik000000

Is there any reason I can't put the TO92 transistors in SIP sockets? Not that I think I am going to mess up, but it would make fixing it much easier.


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## mik000000

I followed Tangent's guide for C2 selection and got 2 x .22uf and 3 x .024uf. (Digikey BC2100-nd) Only problem is the .024 are too small for the board. Are these the right parts?


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## Polaris111688

In C2, you'd probably want axial-leaded capacitors, rather than box or radial. Check these out:
http://www.mouser.com/search/Product...-MKT1813410254


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## mik000000

the .22uf box caps fit fine. I cam mix in the radials? or should i replace all 5?


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## Polaris111688

Yeah, that's fine. You can mix in radials and box. It won't affect functionality. The only thing that matters is if it physically looks good to you.


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## luvdunhill

I was wondering if I could get away with 4.7k instead of 4.32k for R1. I understand that R1=R3+R5 but was wondering if this was a hard and fast rule.

 Thanks!


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## luvdunhill

Quote:


  Originally Posted by *luvdunhill* /img/forum/go_quote.gif 
_I was wondering if I could get away with 4.7k instead of 4.32k for R1. I understand that R1=R3+R5 but was wondering if this was a hard and fast rule.

 Thanks!_

 

^ polite bump ^

 I'd like to understand how I can change R1 to another value


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## FallenAngel

To change R1, it still must follow these rules:

 Right / Left Channels:
 R1 = R3 + R5

 Ground Channel:
 R1 = R4

 If you want to change R1, feel free, but remember to change R4 on the ground to be the same. Also, remember the whole optimizing loops thing. Usually, you would only change R4 to set the gain because R1, R3 & R5 are closely linked together.


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## ablaze

hey guys,
 anybody started on their PPA yet? Do share your experiences on this thread.

 me, I'm waiting for my PPA boards to arrive from tangent before I start trying to figure the whole thing out


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## xtreme4099

waiting for parts ...


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## Voodoochile

Got boards... got parts... got milk...
 need time.

 I hope to start tonight.


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## ablaze

keep us updated voodoochile 
	

	
	
		
		

		
		
	


	




 tangent, when's your site going to be updated for the step-by-step assembly page?


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## morsel

I just updated the PPA website at http://elvencraft.com/ppa/ with a small section on wiring considerations:

 Signal ground is input ground, not output ground. Output ground is the output of the ground channel. It exists solely to drive headphones. It is not a true ground. Do not connect signal ground to output ground. This defeats the purpose of differential output and may cause amplifier instability. Do not use the headphone output as a line level output as this may short signal ground to output ground. Use signal ground instead of output ground for line level outputs.

 Do not connect V+ or V- to the case. This may cause damage to the amp or other components.

 Connect the case and pot housing to signal ground. This will shield the amp from hum and noise.

 Do not connect AC ground to signal ground or the case. This may cause ground loop problems.


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