# PPA Project Announcement



## morsel

The PPA (PPL's Portable Amplifier) is a new headphone amplifier that PPL, Morsel, and Tangent have been working on since last fall. Over the past few years, PPL created a series of pocket headphone amplifiers using opamps and open loop buffers which were the inspiration for Apheared's #42 and the META42. The PPA incorporates a mixture of technologies from several PPL pocket amps, the META42, and new techniques such as differential output on a Eurocard format board. Testing of the first prototypes is underway and the initial results are promising. Our apologies for keeping this a secret for so long, but we wanted a reasonably detailed and substantial platform to initiate discussion.

 Please visit the PPA website for more information including features, technical comments, issues, schematics and layout. This is your chance to post comments, suggestions, and requests. We look forward to hearing from you.

 [size=small]http://elvencraft.com/ppa/[/size]

 -Morsel, Team PPA Slave Driver

 (Edit: I replaced the small layout with the full size one.)


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## x1lexure

OHHH NOOOO!!! Another one!!!!!


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## puppyslugg

Congrats, ppl, morsel, and tangent!!


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## 00940

nice design but ... 18 AAA NiMH batteries 
	

	
	
		
		

		
		
	


	





 congratulation for the new baby anyway


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## morsel

Thanks. 
	

	
	
		
		

		
		
	


	




 After more people have had a chance to read the material on the PPA website I will discuss the issues list in detail.


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## eric343

You're all crazy...

 ...for not doing the full-on PPL Home design. 
	

	
	
		
		

		
		
	


	




 I'm kidding of course - I look forward to seeing Kelly's glowing review of the PPA, and finally an amplifier that can make the Sony V700s sound less than totally awful without needing EL2008s!


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## puppyslugg

Quote:


 _Originally posted by eric343 _
*You're all crazy...

 ...for not doing the full-on PPL Home design. 
	

	
	
		
		

		
		
	


	


* 
 

I have to admit, I am a little disapointed it isn't a full blown ac powered amp.


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## eric343

It is. Even the PPL Home doesn't include a power supply IIRC, the only difference is that the Home is a discrete transistor design.


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## morsel

We hope the PPA will be all you ever need for home use. I'm guessing most PPAs will be built for AC operation. We have temporarily set aside the NiMH charging issues so we can focus on the amp itself.


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## puppyslugg

Quote:


 _Originally posted by morsel _
*I'm guessing most PPAs will be built for AC operation. * 
 

I have no doubt that will be true. I just would liked to have seen what you guys would came up for the ps.


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## kheldar

wow.. i remember this amp.. or at least the original which i built on a breadboard. It was amazing sounding, but my board design skills weren't up to making it.

 when is this one expected to be finished board wize?

 I finaly convice myself to get rid of the META42, and you guys come up with something new and interesting... my poor wallet..

 on the technical side, which buffer is in the lead? i know how much you dislike the burr brown one... One thing that you might want to consider is the buf634 in the to220 package, they are realy easy to stack since the pins line up in a single line. or so i found on the last amp i built.

 its nice to see one thats not "ultra" small in size. room to play in =)

 congrats =)


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## Whit

Could you increase the size of the C1 and C3 caps to 16mm so the 1000uf cerafines and blackgates would be usable? I know it sounds crazy but some people may want to use all boutique caps. 

 Whit


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## morsel

We have some power supply sketches but we need to perform more amp tests before we develop the power supply further.

 Differential output is a radically different topology that eliminates the primary source of signal ground contamination by shifting responsibility for the return path from the headphones from the power supply to a ground channel. This should make the PPA far less dependent upon the power supply to sound good than the META42 or Gilmore.

 We will have detailed test results for you once we resolve some testing inconsistencies. We have been using RightMark as well as some other programs that perform FFT analysis. I will guess we can get about .001% THD accuracy and .01% IMD accuracy with the new setup.

http://audio.rightmark.org/download.html


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## dta116

Kudos:
 For the choice of a Capacitor Multiplier Power Supply.
 For the OpAmp choices.
 For the design implementation of a charging ckt. (if battery Powered.)
 Just love the idea of ground amp !! (just don't get it yet)

 Questionable:
 The thought of multilayer PCB. (this is leaving the realm of DIY)
 The use of Elna Caps, They are extremely difficult to obtain.

 Suggestions:
 Using a rotary switch for crossfeed will reduce real estate and multiple switches.
 Incorporate Hi Z and Lo Z output jacks.

 Love the Idea....

 MANY Kudos to PPL, Morsel and Tangent.

 The NEW PPA Project gurus'


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## morsel

Hi Whit,

 We have talked about enlarging C1 but growing C3 is out of the question due to space considerations and would not do anything for the amp anyway. If we did make C1 bigger we would probably go to 18mm and have 6 of them across the top of the board. We are not sure it will actually be useful to have that much capacitance, and it might actually harm the amp, but we will know more as testing progresses.

 Hey Kheldar,

 The PPA is different from amps you have seen before. As I said on the website, there is no ETA on boards. We prefer the HA5002 (which is the currently implemented buffer as shown on the website) but will listen to arguments in favor of the BUF634. The HA5002 is cheaper and sounds better.


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## eric343

In the schematic, why are R10 and R11 1K? I was under the assumption that people usually used values <500ohms or so.


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## jamont

This looks like a great project!

 Do you intend this design to be less user-configurable than the META42? The recent distortion measurements by KurtW suggest that the extreme configurability of the META42 is perhaps a mixed blessing. I think it would be desirable for the PPA (and the META42 for that matter) to have a well-tested reference configuration that sounded good and was specified in detail.


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## morsel

Yes, it is intended to be less user configurable. The testing I had hoped would happen with the META42 resistor configuration got swept under the rug and forgotten early on. This time we are not leaving such things to chance.

 1k is a reasonable value for the buffer input resistors. They could be higher or lower. The choice is not critical.

 Incidentally, Kurt will be joining Team PPA when he gets back from vacation in a week or so.


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## puppyslugg

Quote:


 _Originally posted by morsel _
*Incidentally, Kurt will be joining Team PPA when he gets back from vacation in a week or so. * 
 

Yay!


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## Voodoochile

Yummy!

 Nice work, everyone... I'm looking forward to seeing how this unfolds.


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## aos

Issue: Ground plane over high impedance input area - definitely something I recommend you do. Production version of my PDAC does that and it made a big difference. Granted I do have sources of EMI within few cm but still, the noise at the output is unmeasurable on my oscilloscope. It might or might not be audible but it sure is measurable. 50k Alps Blue is also a good choice IMO.


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## was ist los?

If crossfeed was used, would it be on the same board, or seperate like the meta42?


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## morsel

Hi Aos, as you can see from the layout we do have a mini ground plane over the high impedance area but not over the whole board. We started out with a star ground configuration but switched to the ground plane a couple of months ago.

 We are seriously considering separating signal ground from opamp power ground with a 10 Ohm resistor and possibly a small cap in parallel to further reduce noise and hum. To break ground loops between the amp and other equipment we might want to put 10 Ohm resistors in series with all input connections as well.

 I have tentatively split up the ground connections into two groups, let me know if you think any of them are in the wrong group:

 signal ground connections:

 input grounds
 pot grounds
 opamp input resistors
 opamp feedback resistors

 power ground connections:

 opamp bypass caps
 TLE output
 ground plane
 case
 pot shaft and panel switches

 We haven't talked much about crossfeed. There is no onboard crossfeed atm. I'm thinking it should go on a daughterboard due to space considerations. There is onboard bass boost at the moment, but not yet room for the polypropylene BC Components cap we want to use.


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## mekanoplastik

hi Morsel

 this project looks like it will be the ultimate opamp based amp...
	

	
	
		
		

		
		
	


	




 just one question, why using bass boost ? i thought such type of implementation was not welcome in the high-end world. 



 m.


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## Possum

Quote:


 just one question, why using bass boost ? i thought such type of implementation was not welcome in the high-end world. 
 

I believe it's a ppl thing. You see the bass boost often in ppl's designs.


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## puppyslugg

Quote:


 _Originally posted by Possum _
*I believe it's a ppl thing. You see the bass boost often in ppl's designs. * 
 

PPL is a basshead!! 
	

	
	
		
		

		
		
	


	





 MekanoPlastik:

 You can just leave out the bass circuit, too. It's not required by law to have to intall it.


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## jamont

Do you see availability of the ALPS Blue as a problem? I agree that it's an excellent choice, but it's not so easy to get. Maybe tangent would sell them on his website with the boards, as he does now with the Elantec buffers for the META.


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## guzzler

can't say I really call it portable, more luggable! seriously though, this thing looks awesome, and its great to see radically new topologies coming through!

 nice one, dudes and dudette!

 g


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## morsel

Since Tangent is selling the Alps Blue there should be no problem with availability.

 Time to tackle some of the issues. Comments are welcome.

 You may have noticed that there are two LED modules on the board, one centered and one on the left side of the faceplate. While it is possible we might leave both of them, it would be useful to hear how people feel about positioning the power LED and the headphone jack.

 My opinion is the headphone jack should be in the center of the front panel so left and right handed people who use 1 hand to pull their plug out will both be able to do so easily. Putting the LED in the center and the jack on the left means that left handed people will not be able to brace their fingers against the case to withdraw the plug, thus causing the entire unit to shift on the shelf. Some people don't care or use two hands and find the centered LED more asthetically pleasing. I think that since one of the two has to be on the side we might as well make it more ergonomic for everyone.

 This leads to the issues of panel mount .vs. board mount components and custom cut panels. The pot is board mounted, that is a done deal. At the moment nothing else is board mounted and there is a 1 inch no parts zone at the front and back of the board to allow for panel mount components. This gives the most flexibility in choosing parts, but means more work during assembly. If we used board mount parts or rigidly specified panel mount components we could then offer custom cut panels.

 The so called locking silver tab Neutrik jacks are board mountable but do not in fact lock. The red tab locking jacks do lock but are not board mountable. If we are going for board mountable jacks we might as well go for some of the more sleek and asthetic jacks that don't lock.

 Nonlocking jacks can result in shorting the amp outputs. The amp does not have any output protection at the moment. Shorting the outputs for more than a few seconds with the volume at a high level could blow the output buffers. (Imagine yanking the cord 1/2 way out from across the room.) That leaves us with 3 options: live with the risk, use locking jacks, or provide output protection.

 I think DC servo circuits like the Gilmore uses are the best thing since sliced bread, but PPL hates them. Other options include fuses, thermal resetting fuses, current regulators, or foldback current limiters, either in the power supply, on the buffer rails, or on the outputs. All of these solutions have the potential to harm the sound quality.

 Of all these options, perhaps the least intrusive and complicated is to current limit the power supply and not use too much C1 rail capacitance. The capacitors would still be able to provide power for dynamic passages, but a dead short would quickly drain them and be limited by the maximum current of the supply. Going from 2 to 4 buffers per channel would help distribute load among the buffers, reducing the chance of damage while increasing the ability of the amp to handle dynamic passages, however, doubling the buffers will consume more current and make the amp less portable friendly. PPL's Not So Portable Amp? Perhaps. Maybe all that matters is that it's easy to carry around, not that it will run on rechargable batteries.

 Moving to 4 buffers per channel will eat into board space, forcing a reduction in C1, which is OK as there is probably too much C1 capacity anyway.

 Alternatively, we could switch to TO-220 package BUF634 buffers, which cost twice as much and don't sound as good but take less space and have built in output protection.

 Isn't it interesting how all these issues are interconnected?

 We are currently testing the 3 FET isolated opamp power rails configuration to determine how much if any benefit it provides over using a single FET isolated rail for all 3 opamps.


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## puppyslugg

Hi morsel,

 I vote for 'PPL's Not So Portable Amp'. 
	

	
	
		
		

		
		
	


	




 I guess I'm a little disappointed that there has to be such compromises in the design. Designing for portability, limits board size, circuit implementations, etc. I would have much prefered a full blown ac PPA. 

 Excuse my snivelling and whinning!


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## mekanoplastik

Quote:


 Excuse my snivelling and whinning! 
 

do not panic Puppyslug 
	

	
	
		
		

		
			





....i have the feeling they are already changing their mind about portability..

 ..in Morsel words: "(Imagine yanking the cord 1/2 way out from across the room.) " .....mmmm...across the room ?? shouldn’t it be "...across the bag" ?? 
	

	
	
		
		

		
		
	


	








 m.


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## morsel

Hi PS,

 Realize that all designs are compromises. Eurocard format is a nice standard size for which there are ready made cases. We could consider a larger board and case format if you have one to suggest.

 The PPA will be full blown, as you say. It may not be necessary to have 4 buffers per channel, for example. These choices are interrelated. On the other hand, we may have 4 buffers per channel if it turns out to make sense to do it that way, which will draw more current but does not have to change the board or case size.

 The design is not set in stone. That's why we are talking to you. It is possible to turn it into an AC only amp. As it stands now, it can be used for either, and early reports indicate the prototypes sound great.


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## puppyslugg

Hi Morsel,

 I realize everything is a compromise. I just hope the performance of the PPA, is not compromised for portability. But whatever you guys come up with, I'm sure I'll be happy with it! 
	

	
	
		
		

		
		
	


	




 ps


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## tangent

Quote:


 Using a rotary switch for crossfeed will reduce real estate and multiple switches. 
 

The issue isn't "rotary vs. toggle", it's "crossfeed on the board or not". Among the current PPA team, the consensus is "not". Therefore, the current idea is to maybe have a META42-like situation where there's a daughterboard you mount on the PPA board that adds crossfeed. I had in mind to float it over the input pads at the rear of the board, so the RCA jacks go instead to the crossfeed board, then make a short trip through the crossfeed and then down to the PPA's input pads.

 I still like the modified Linkwitz crossfeed design, and you can use rotary switches with it if you want, as discovered by Scott Lindeman. I'm considering making a new modified Linkwitz board especially for the PPA to allow boutique caps and with wire pads labelled to use one of Scott's rotary switch schemes, probably the simplified one. (See the META42 crossfeed page if you don't know what I'm talking about.)

  Quote:


 The thought of multilayer PCB. (this is leaving the realm of DIY) 
 

Since the idea is for me to have the boards manufactured, and not to provide files for people to etch their own boards, what does it matter how many layers there are, from the DIYer's perpective? You still plug components into holes and solder to pads on the outside layers, just as with the META42. What's the difficulty?

 The real issue is whether it's worth the cost or not. It means we have to buy 4-layer CAD packages for all those hacking on the board, and it means the cost of the board goes up by at least 2x, and more if we get the boards tested. Automated testing of the boards is very tempting for 4-layer boards since you can't just look at them and tell that there are shorts or breaks.

 The benefit is that we could add better shielding and such to the board, so channel separation would be better. 

 So given all that, would you be willing to pay 2 or maybe 3x more per PPA board if it were 4-layer vs. 2-layer? We're happy to consider the idea if people think it will be worth the cost.

 One thing to note, though: we already have a working design on 2 layers with no vias so far. We don't absolutely _need_ 4 layers to succeed.

  Quote:


 The use of Elna Caps, They are extremely difficult to obtain. 
 

We're not telling you to use ELNAs. We're telling you that they fit, if you want to use them. Use Black Gates, Nichicons, Panasonics, whatever strikes your fancy.

 What we may say "no" to is designing the board so that only one particular rare cap makes sense in the board. We'd have to have a compelling reason to use that cap, like C4 on the META42. And if we do that, I'll again provide access to the part, just as with the META42. This isn't to say that people should feel free to request any strange part they might want and know that Tangent Will Provide, but we will at least consider the merits of rare parts.

  Quote:


 Incorporate Hi Z and Lo Z output jacks. 
 

Several thoughts on that:

 1. None of the current PPA team members are in favor of anything but 0 ohm output impedance, for most headphones. The only argument in favor of a nonzero output impedance that I can get behind is a 75 ohm jack for Ety-4P users who want their phones to sound like 4Ses.

 2. If you just want a single nonzero Z output jack, you can easily wire the extra resistors inline with the wires going from the board to the jack.

 3. If you want two output jacks with different impedances, it's the same situation, but you jumper from one jack to the other at the panel, adding resistors as necessary.

 4. You'd have to use a smaller jack than the ones we have in mind (Neutrik NJ3FP6C) in order to fit both jacks on the panel of a Eurocard-size enclosure.

 The thread running through all these points is that this is a nonstandard configuration. We won't try to stop you from doing one of these setups, but we aren't going to add stuff to the board to make it easier to add these features, either. It's easy enough as it is, given how rarely we expect these features to be used.

  Quote:


 Do you intend this design to be less user-configurable than the META42? 
 

Nothing's stopping you from populating a PPA with wildly different configurations, just as you could with the META42. I'd say they're similarly configurable. But, what we do intend to do is make it clear in the docs that certain configurations were arrived at with painstaking research and that you should stray from them only at your own peril. At the same time, I don't want to be in a position to say, "that's not a PPA you've built because it doesn't use our exact resistor values".

  Quote:


 why using bass boost 
 

Why not? Since it's finely tunable if you like the idea and 100% defeatable if you don't, there's little reason not to add it, since we have the space.

 The idea is for the bass boost to compensate for bass-weak headphones or bass-weak recordings. It's not to pull a Sony move and get throbbing bass from a violin concerto.

  Quote:


 Tangent is selling the Alps Blue 
 

Ummmm, sort of. I have surplus and I have been known to sell a few on the side, but I'm not providing them explicitly on my orders page. Until I do that, you can't really say the question of availability is answered, since I don't currently want to be in the pot distribution business. (Hah ha!) Seriously, these little things are too expensive and too hard to get for me to go offering them on a high-volume basis.

 We should indeed consider alternate volume controls for this design. I think low-end pots like the Panasonic EVJ are totally out of the question for this amp. What does the Head-Fi public think of the idea of using the Nobel 25mm pot from Michael Percy, or perhaps adding pads for one of the cheaper stepped attenuators? (DACT, TKD...)

  Quote:


 Maybe all that matters is that it's easy to carry around, not that it will run on rechargable batteries. 
 

I for one intend to build a PPA with a rechargeable battery setup, and live with the size of the amp. I will also be building at least a few wall-only ones. That's what I like about the PPA design as it currently is: the ability to have excellent sound on the go if you want, yet not be limited w.r.t. sound quality when you don't mind being tied to a wall outlet.

  Quote:


 I guess I'm a little disappointed that there has to be such compromises in the design. 
 

From one who has actually listened to the PPA: it ain't too shabby already! Sure, it could be even more over-the-top, but the PPA's place in the world will be useful anyway. The impetus behind the PPA is all these people making META42s that push that design so hard that they're deep into diminishing-returns territory. What you really need instead is a new design, not to keep putting ever more exotic components into such a small, portable board. The PPA is that new design.

 After the PPA gets going we can talk about a completely unportable design. I still wouldn't presume to say that such a thing could be made without compromises. Morsel's right -- no amp design is without compromises.

  Quote:


 across the bag 
 

Not at all. I'm sure a great many PPAs will be used as wall-powered amps. Remember, it's about the size of a large brick, if not quite as heavy. Not everyone will be willing to lug that big an amp around. So, imagine that you're sitting in your listening room, rockin' out to some great tunes on some great, comfortable headphones, the phone rings, and you unthinkingly get up to answer it, yank on the cord, pull it out halfway, curse, have to go answer the phone anyway and tell the caller to hang on, then get back to the amp to either unplug the phones or plug them back in. This whole sequence has taken long enough that the buffers could be killed.

 Jan Meier chose to go with 1/8" jacks in his HA-1 to solve this problem, but that was an unpopular decision. People want 1/4" jacks on higher-end amps. Thus the choice: add output protection, current-limit the power supply, use locking output jacks, or none of the above and laugh cruelly at those who burn their buffers?


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## jasong

Can I assume there is a noise reduction reason for the signal outputs not being grouped together and/or brought to an edge of the board? 

 Or, as another thought slowly enters his stunned mind, this is an interim position as the board-mount (or not) decision progresses?

 --Jason


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## morsel

Apparently Team PPA needs to discuss the pot issue. I assumed that since every PPA needs an Alps Blue and Tangent uses them for the META42 he would proceed to stock them since he would sell one with every board. We will get back to you.

 Now where did I put that whip..


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## morsel

Hi Jason,

 Good question. The current layout would be compromised by running the outputs as traces. Our strong recommendation is to solder wires to the output pads, bring them straight up (perpendicular) from the surface of the board, and then forward to the headphone jack. If we switch to TO-220 BUF634s, 4 layer boards, or board mounted jacks this will change.


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## jasong

Thanks Morsel (and the entire PPA Team for that matter).

 Gad zooks though, a design where the low end volume control choice may turn out to be the Alps Blue. Cool.

 Might there be some documentation on differential output that has been shared by the team that could be unleashed upon us also?

 --Jason
 way too interested for his own good in the new "whippy" design.


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## morsel

I just rewrote the differential output section on the PPA website:

http://elvencraft.com/ppa/


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## tangent

Quote:


 I assumed that since every PPA needs an Alps Blue and Tangent uses them for the META42 he would proceed to stock them since he would sell one with every board. We will get back to you. 
 

It's not entirely out of the question, I'm just not eager to do it, that's all. I'd rather that we at least consider adding one other high-end attenuator choice to the board. I'm sorry you're feeling blindsided, Morsel, since I only stayed mum on this issue since it seemed like something that should be discussed by the masses. During the design phase, standardizing on just the ALPS Blue for simplicity's sake was perfectly reasonable.

 So, you masses, what do you think? Is the ALPS Blue the only thing we should consider for the amp, or do you want the freedom to use alternate high-end attenuators? At the very least, I'd like to see pads for the DACT CT2 added. 

 Again, low-end attenuators will not be tolerated for this board. Don't even think of asking for pads for the Panny pot.


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## Squalish

Quote:


 _Originally posted by tangent _
*
 Again, low-end attenuators will not be tolerated for this board. Don't even think of asking for pads for the Panny pot. 
	

	
	
		
		

		
		
	


	


* 
 

.35db mismatch and semi-logarithmicism doesn't seem THAT bad, but I agree w/ you. 

 In other news, what is happening with the blue traces here(If I'm showing my ignorance of common knowledge, feel free to mock me):


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## Voodoochile

We still have the META42 for portability. I think a META configured for battery operation is pretty hard to beat, and still be considered a truly portable amp. It's a lot of amp in a small package, with good battery life even from 1 or 2 9v batteries.

 I do think you loose a little something when you try to be all things to all people. Personally, I seem to know of more people interested in a major-league stationary amp than a little portable. We have LOTS of little portables to choose from, many of which sound very nice. I figure if you want something more than a META, go whole-hog, and make a nice, mains-powered amp, in a substantial case, with a substantial PS, possibly the DACT or TDK, beefy jacks, etc. We have lots of little amps, and many of them end up fastened to wall-wart anyway.

 If it's a portable, I like it to be not much bigger than a mint tin, or the small serpac cases. And no outboard battery packs, or 16-AA cells in a case the size of my grandmother's kodak.

 But that's just me 
	

	
	
		
		

		
		
	


	




 .


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## JMT

Quote:


 Is the ALPS Blue the only thing we should consider for the amp, or do you want the freedom to use alternate high-end attenuators? At the very least, I'd like to see pads for the DACT CT2 added. 
 

I think that the Alps Blue should be the _minimum_ that is considered for this amp, but with the flexibility to step up to an attenuator.

 Regarding panel vs. board mounted components. I understand the possibility of custom panels, but part of the fun of building it yourself is the ability to find the right enclosure. Won't board mount/custom panels drastically limit that to a few specific cases? Pardon if that's a dumb question.


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## eric343

Tangent - why not go with a transformer attenuator while you're at it? 
	

	
	
		
		

		
		
	


	




 Seriously, though, pads for both the Alps Blue and DACT CT2 would be a nice compromise and offer lots of flexibility.

 The Alps Black Beauty is sort of an interim step that I'm not sure can be board-mountable.


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## Dreamslacker

Quote:


 _Originally posted by Squalish _
*.35db mismatch and semi-logarithmicism doesn't seem THAT bad, but I agree w/ you. 

 In other news, what is happening with the blue traces here(If I'm showing my ignorance of common knowledge, feel free to mock me):



* 
 

The blue traces are on the back of the board for you to directly solder on SOIC opamps rather than to use soic to dip convertors. It's also found on the META42 board.


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## mekanoplastik

Quote:


 But that's just me . 
 

not really..i also think a portable amp the size of a brick +18AA'a that "requieres" an stepped att. is not very apealing....the fact the amp is a ppl design is enaugh reason for me to build it but i also would rather a no-limits amp.


 but that is just us 
	

	
	
		
		

		
			








 m.


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## Nisbeth

Quote:


 _Originally posted by eric343 _
*Tangent - why not go with a transformer attenuator while you're at it? 
	

	
	
		
		

		
		
	


	




 Seriously, though, pads for both the Alps Blue and DACT CT2 would be a nice compromise and offer lots of flexibility.

 The Alps Black Beauty is sort of an interim step that I'm not sure can be board-mountable. * 
 

The Black Beauty is board-moutable AFAIK, but it's bloody huge and where do you get them at a reasonable price 
	

	
	
		
		

		
		
	


	



 I think the Alps Blue would be a good, solid option for most people, but if you want to go all-out, by all means include the option of adding an attenuator. (just out of curiosity though, how much is a CT2 in the US ?) 

 BTW, tangent, have you checked volume pricing for the alps blue? I imagine that there will be quite a big interest in buying these so the price could come down to a very different level because of the quantity. If the only other feasible option is the DACT, and the alps is difficult to get via normal channels, my guess would be that a large percentage of buyers will buy the pot from you along wth the board. (but of course I realise it'll be a big outlay for you
	

	
	
		
		

		
		
	


	




)


 Hmm, just writing random thoughts, mainly because I am a little overwhelmed at the thought of a brand new amp design to build (but also because it's 3 a.m. here
	

	
	
		
		

		
		
	


	




.) Good work Team PPA 
	

	
	
		
		

		
		
	


	




 /U.


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## puppyslugg

Quote:


 _Originally posted by Voodoochile _
*We still have the META42 for portability. I think a META configured for battery operation is pretty hard to beat, and still be considered a truly portable amp. It's a lot of amp in a small package, with good battery life even from 1 or 2 9v batteries.

 I do think you loose a little something when you try to be all things to all people. Personally, I seem to know of more people interested in a major-league stationary amp than a little portable. We have LOTS of little portables to choose from, many of which sound very nice. I figure if you want something more than a META, go whole-hog, and make a nice, mains-powered amp, in a substantial case, with a substantial PS, possibly the DACT or TDK, beefy jacks, etc. We have lots of little amps, and many of them end up fastened to wall-wart anyway.

 If it's a portable, I like it to be not much bigger than a mint tin, or the small serpac cases. And no outboard battery packs, or 16-AA cells in a case the size of my grandmother's kodak.

 But that's just me 
	

	
	
		
		

		
		
	


	




 . * 
 

Welcome to Team 'PPL's Not So Portable Amp'!!


----------



## Squalish

Quote:


 _Originally posted by Nisbeth _
*The Black Beauty is board-moutable AFAIK, but it's bloody huge and where do you get them at a reasonable price 
	

	
	
		
		

		
		
	


	



 I think the Alps Blue would be a good, solid option for most people, but if you want to go all-out, by all means include the option of adding an attenuator. (just out of curiosity though, how much is a CT2 in the US ?) 
* 
 

I believe that Partsconnexion has the black beauty, either the real black beauty or the same part as WKLeung's ebay "alps blue" stepped attenuator, for $50.


----------



## mhamel

I for one would much perfer a no-holds-barred AC powered amp to compliment the Meta and all of the other portable designs that are popular here and on Headwize. 

 I also see the Alps Blue as the "minimum" pot for this. And slightly off-topic, but don't count on Mr. Leung's attenuators. I purchased 12 of them from him in various values and none of them are built with resistors - he denied that they were any different until I told him I took a couple of them apart and sent him photos of the two different styles. He's still "looking into it," but I'm not sure how much chance we have of seeing more of those Alps-sized attentuators from him.

 Whatever way the PPA design comes together as, I'm really looking forward to building one! 

 -Mike


----------



## Squalish

Quote:


 _Originally posted by mhamel _
*I for one would much perfer a no-holds-barred AC powered amp to compliment the Meta and all of the other portable designs that are popular here and on Headwize. 

 I also see the Alps Blue as the "minimum" pot for this. And slightly off-topic, but don't count on Mr. Leung's attenuators. I purchased 12 of them from him in various values and none of them are built with resistors - he denied that they were any different until I told him I took a couple of them apart and sent him photos of the two different styles. He's still "looking into it," but I'm not sure how much chance we have of seeing more of those Alps-sized attentuators from him.

 Whatever way the PPA design comes together as, I'm really looking forward to building one! 

 -Mike * 
 

I need more empirical evidence, but based on what people have said, it appears that the RH2702's are stepped attenuators, and the RH2701's are crappy pots. Some of the auctions he has up now show pictures with RH2702 as the serial, some show RH2701. Also, based on pics from auctions, I think the RH2701 has 30 steps, and the RH2702 has 21(audiotronics advertises 22). I know all of yours are 2701, but do are your pots 30step or 21/22step? In that thread, ffish posted this, taken from the partsconnexion newsletter:

  Quote:


 "Alps "Black Beauty" 21-step Dual/Stereo Series Attenuator $39.95 (US)

 For years, Alps was "the" name in conductive plastic potentiometers. Used by countless consumer and pro-audio companies, Alps was the market leader. However, they no longer make conductive plastic pots at all. The "Black Beauty" pot was so called due to its case color and size - differentiating it from their other, smaller, "Blue Velvet" potentiometer series. However, Alps also used this same case style to build a special order "series attenuator" as well, primarily for the pro audio market. pcX was lucky enough to find a large NOS quantity of these RARE controls. Substantially superior sonically to any pot, this series attenuator has 21-steps, a 60dB range and superior Channel-to-Channel tracking. This control should be compared to many other discrete series attenuators at well over $100 US, making our price of $39.95 US an absolute best buy! Anyone looking for a stereo volume control between 50K and 250K, should consider this part!" 
 

The 100k version of this is still selling on their website for $50.


----------



## puppyslugg

Quote:


 _Originally posted by mhamel _
*I for one would much perfer a no-holds-barred AC powered amp to compliment the Meta and all of the other portable designs that are popular here and on Headwize.* 
 

Welcome, Mike!

 Yet another enlightened member of Team 'PPL's Not So Portable Amp'!


----------



## ppl

The Absence of a Dc Servo. The Inclusion of Bass Boost items are things that I my self insisted upon in addition to Power supply isolation To be considered a true Design of Mine. 

 Bass Boost is real useful with headphones more so than with loudspeakers. When the Amount of Boost and turnover points are chosen, The Low bass can be boosted while leaving the Critical midrange like voice intact. The action of the Boost would not be noticed on most recordings with the bass boost set this low. The availability of selecting several preferably ideal turnover points to accommodate different situations. for example if the bass was to be used to improve the almost no low bass output of small street style Phones or just correcting for lack of low bass in the recording like most 60's and 70's Rock. In these cases I find 90% of the time these recordings need Bass boost unless a quality Mined Artist like Pink Floyd, However these are rare and most Doors and Led Zeppelin sound Thin in the Bass. The Bass boost circuit employed in the PPA is of about the Simplest topology and IMHO the Least sonically intrusive Eq technique Available. Unlike other Tone Control Schemes no additional circuitry need be added eliminating one entire stage of Circuitry the Signal has to go through prior to the Input of the Amp. The PPA method simply adds a gentle first order Ring free Bass Boost with one capacitor and one Resistor added within the Existing feedback loop. This topology has many other performance enhancing properties like increasing the output impedance proportionally to Boost. good Idea. Lastly but not least if total accuracy is desired then with the bass boost bypassed or turned off there is no reactive components reaming in the feedback loop and all is as if bass boost was never an option. But for me it is a must have option.

 the finest home High End Audio power Amplifiers employ some sort of separate power supply for the voltage gain stages and the Output stages. I Believe a headphone amp is nothing more than a low powered loudspeaker Amp. All the Performance qualities that separate the Common from the truly great stuff is real world Operating potential. 

 this implies High output current, A low and constant output impedance over the Audio range ( The PPA continues this well outside the audio range from DC-80,000 Hz.) A low noise output. headphone Are quite revealing of noise and distortion, thus the Amp must have as small amounts of these as possible. An Amp that is noise free with Loudspeakers can be very noisy over Headphones. this makes the low noise requirement real important on Headphone Amps and the PPA is Dead Quiet. The Preliminary Tests on the PPA's performance indicate more than Adequate for First Class Audio reproduction. 

 The Intent on Making the PPA portable was not to have an Amp you can carry around in your Shoulder bag Although you could if Desired. Anyway My pocket Amp serves me well while on the road. The Portability of the PPA comes into play if for example you like to use it camping or other places other than home where you want portable entertainment Just hook up the laptop and watch DVD's True you could use a small Pocket style amp for this Also But you also will not get the sound quality out of the Pocket style you get with the PPA.

 The PPA can be a power Guzzler up to 200 mA if ICq is possible with the AD-843's and (4) Buffers per channel and we have not two but three channels in the PPA. A normal PPA configuring of an OPA-627, AD 825 and other 6 mA Op Amps with only (2) buffers per channel is about. 76 mA. not all that Battery friendly But still manageable.

 While some might object to the compromises required to maintain portability the PPA in the tradition of my other Portable offerings include an isolated Supply Voltage for the Op Amp stages. thus not allowing contamination of the output rails to enter the Supply feeding the sensitive voltage gain circuits. this IMHO provides a blacker Background and more detailed Micro dynamics similar to what is obtained in High End Home Loudspeaker power amps. The PPA uses separate isolation circuits on each channel including that elusive third channel, Kind of reminds me of the third Eye. This provides Virtual dual mono for the Voltage gain stages and improve imaging and 3D Ability a lot vs just one isolated supply supplying all three channels. However even just one isolated power supply is an order of magnitude improvement over the conventional method of jut connecting the rails from the power output stage directly to the Gain stages.


 This is all I can write at the moment


----------



## tangent

Quote:


 I do think you loose a little something when you try to be all things to all people. 
 

I know where you're coming from, but this amp is only compromised relative to The Absolute. Again, we can talk about building the greatest amp in the world sometime later. Meanwhile, we have a middle ground that needs filling.

 All of you who are worried that this amp won't be extreme enough need to be a little patient. I've listened to it, and I'm telling you that it will be a very worthwhile upgrade from a META42. Comparing a META42 with components as similar as possible to a test PPA -- which was deliberately crippled for the purposes of the test -- showed the PPA to be the clear winner. The test results that I'll have soon will bear this out, as will listening tests if some of you people out there want to take the schematic on Morsel's web page and build your own version of this amp.

 Will the PPA be the best possible amp in the world? Well, no. But I do think there's a place in the world for a pretty damn good amp that whomps the META42 yet can still be taken with you if you choose. I do realize that this is the very limit of "portability" for most people, but that's no excuse to just forget portability and go positively insane.

 I'm willing to cede the ultimate high end. For now. 
	

	
	
		
		

		
		
	


	




 I don't know if it's clear from what you've seen yet, but this amp's minimum parts cost will already be something like 3x higher than the META42's. Once you do a few upgrades ton the main amp board, add the custom power supply, maybe add crossfeed and perhaps add the battery board, it'll be more like 5-6x the cost of a minimal META42 and probably take you 2x as long to put it all together. This is not a timid upgrade to the META42.

  Quote:


 i also think a portable amp the size of a brick +18AA'a that "requieres" an stepped att. is not very apealing 
 

I don't know if it's been made clear yet or not, but the battery configuration for this amp is _only_ for rechargeables. Partly because they sound better, but also for economics. That's why we're talking about a charging circuit -- not just because it's a neat idea, but because it's essential to the usefulness of the amp as a portable. Oh, and it's AAA's we're talking about, not AA's. It shouldn't add much to the weight of the amp, and they are expected to last 7 to 15 hours. The battery board, circuitry and batteries won't be all that costly, either -- about the price of a high-end linear power supply. Emminently workable.

  Quote:


 i also would rather a no-limits amp. 
 

Some day, perhaps. Let's get this one rolling first, okay?

  Quote:


 how much is a CT2 in the US 
 

diycable.com offers them for $151, but I got mine for about US$112 from THLAudio in Hong Kong.

 We might also think about the TKD's, as those are considerably cheaper -- more like $90 through THLAudio.

  Quote:


 have you checked volume pricing for the alps blue? 
 

The price of the individual pots in volume isn't the biggest problem. It's that it takes so long to get them, and they're so big and heavy that shipping costs aren't inconsiderable. See, if I started offering them, I'd have the people making META42s, PPAs, and other amps all draining the stock. In order to keep the frequency of orders low, I'd have to order something like 1000 at a time. Now, just how low do you think I could get them? Even at $5 apiece (1/5 to 1/6 what most people are charging onesy-twosy!) you're talking about a $5000 outlay.

 If it has to be done, it has to be done. But for now, I'd rather fob the responsibility of supplying pots off on someone else. They're really not all that hard to get. I list something like 6 different suppliers in the META42 docs.


----------



## ppl

Yes this amp requires a quality Pot for sure a Alps Blue as the Min. stepped attuators are nice also as maby is possibly that counterfit switched attuator that is similar to the Alps Blue case and pinout. 

 This amps is alot more articulate that similarly confogured Amps nou using our differential Output Drive technique. This has showen in listening test to drmaticaly improve transients and Imaging over conventionaly configured Virtual ground supplys. the Mids and highs are well represented and the Bass is alot faster sounding than Conventional Virtual ground Configuations. The HA-5002 provide more quality than the BUF-634 in Hi Bias mode. with a real potent high end that the Differential drive just inhances. the BUF-634 provides a warmer Fuller low end with loss of microdynamics but still an extended High end. This Amp High lights the qualties of the IC's used in the Signal path and thus is sonicaly more sensitive to op amp and buffer changes than most amps


----------



## mekanoplastik

PPL

 thank you for such a detailed explanation of the bass boost 
	

	
	
		
		

		
		
	


	




 m.


----------



## JMS

Hi. I'm one of the masses here to give my opinion. I'm also in favor of an all-out non-portable amp, but mainly I want to say that I would love to use board-mounted parts and a custom case, for the following reasons: 

 a) the amp can look more professional

 b) there would be less effort in building the amp - with the META42 the effort required to drill the Hammond case was at least as much as to populate the board (for me), and it was rather frustrating work. Also there's the danger of ruining the case, etc.

 c) less equipment required for the builder - no drill/bit set/file/rasp/etc.

 d) more flexibility - a "board-mount" board can still be used with panel-mount components with more effort, but not the other way around.

 I understand that panel-mounted components allow for more flexibility, but I think it would be better to optimize for the common case, which I assume to be people (like me) who just follow what the designers have chosen. Those who want to customize probably know what they're doing and can work around any peculiarities of the board anyway.


----------



## Whit

Why is a capacitance multiplier being considered instead of a full out regulated one? Also, if the board is populated with the 2200uf Panasonics this would create 26,400uf of filter capacitance. Wouldn't this create a potential huge drain on the batteries upon turning the amp on? Also I think that the 4 C1 caps should be sacrificed for 2 16mm caps per channel. The 2200uf FC caps that do fit the 12.5mm spacing are only rated for 25V. 18 AAA batteries voltage is 27V. Also the 25V is very close to the 24V that I assume most people will use with this amp. Bumping up the spacing would allow for the use of a 16mm 2700uf FC cap at 35V as well as the larger BG and Elnas.

 Whit


----------



## eric343

Quote:


 _Originally posted by JMS _
*I understand that panel-mounted components allow for more flexibility, but I think it would be better to optimize for the common case, which I assume to be people (like me) who just follow what the designers have chosen. Those who want to customize probably know what they're doing and can work around any peculiarities of the board anyway. * 
 

That's a good point - if you put the pads in a form that accomodates a certain board-mount component, but label them, then people who want boardmount can do that and people who want panel-mount will be able to panel-mount.


----------



## tangent

Quote:


 I would love to use board-mounted parts and a custom case 
 

We've had this very argument within Team PPA, and you've pretty well covered all the positive-side arguments. Here are the downsides:

 1. Board-mounting everything requires snakng traces across the board when many times that is highly inconvenient from a layout perspective. You'd end up having to go 4-layer or damaging the current optimized layout. For examples, take a look at the output holes and the bass boost switch pads. Realize that the big power rails coming down from the capacitor bank run on both sides of the board: V+ and V- on top of each other, to maximize the ability of the op-amps' CMRR. You can't cross those barriers without jumpers or without separating the rails and then using vias. Bleh.

 2. Custom panels aren't cheap. This is not a fatal argument, just realize that it isn't free to do this.

 3. Before we can even think of board mounting everything, we have to get everyone to agree on a single set of components. Once again for the slow of brain: you have to get a bunch of audiophiles to agree on a common set of components. I realize that those who disagree with the choices we come up with can just make their own panels, but it's still a problem we'll have to at least try to address.

 4. One of the panels must be limited to components that either don't mount to the panel (i.e. that just poke through), or can be unbolted from the front. This is because the Hammond and Lansing cases we're looking at have a top/bottom panel that can only be removed when you remove one of the end panels. You have to remove the top/bottom panel for amp tweaking and maintenance, like changing the rechargeables every few years, or rolling op-amps. I really don't like the idea of using outside-mount RCAs and switches -- they're ugly -- so it has to be the front panel that you remove first. The LED and bass boost switch aren't a problem -- they can just poke through the panel. The pot isn't a problem -- it has a mounting nut, but it's hidden under the volume knob. The output jack will either have to be a poke-through type or panel-mounted, since a board-mount-with-nut type is ugly. Poke-through for 1/4" jacks requires a very strong mountng setup where the board takes the strain. Crossfeed there's no help for -- its switch will have to be panel-mounted, since the circuit won't be going on the board anyway.

 5. Not everyone wants crossfeed, so do I have to make two kinds of front panels, one with a crossfeed switch hole and labelling, and one without? What about bass boost? This multiplies the combinations to 4 front panel types, all of which I have to prototype and stock. What about those who want 1/8" jacks? You can see how the combinations start to explode here.


----------



## ppl

I hear Ya! That I lobbied the other Team PPA members for from the onset and got voted out. 

 However in lue of the Non short circuit protection The True locking non Board mounted jack with pads located right at the Necessary point by the required jack lug for a short connection. As it is now requires care on the part of the assembler but this was assumed due to the nature of the Beast. 

 I also wanted a board mounted bass boost switch as it also requires care in routing on the Builder. so if ya all want to support me on this maybe the other team members will accommodate


----------



## tangent

Quote:


 Why is a capacitance multiplier being considered instead of a full out regulated one? 
 

Several reasons:

 1. It's neat, and you can't get them anywhere else. If you want a linear regulated supply, many DIYable choices exist already: the Gilmore, the Wellborne PS1, one or two from Rod Elliott, Velleman... And in the commercial market, there are many more.

 2. A properly-done capacitance multiplier should be able to have stability every bit as good as a regulated supply over the short term, which is what you care about. For long-term wall voltage changes, the output will also slowly change, but op-amps can cope with this no problem.

 3. I'm fairly sure that it's more efficient. No turning excess voltage into heat.

 4. Morsel and ppl had some neat ideas they wanted to try out, and I'm willing to go along with them.

  Quote:


 if the board is populated with the 2200uf Panasonics this would create 26,400uf of filter capacitance 
 

I agree that this is probably overkill. The other side of the argument is that it's nice to have the ability to do this if you want to try it, and we don't really intend that you use generic capacitors with this amp anyway. At the very least, dig up some nice Nichicon Muse series or something. Then you can have merely a moderately insane amount of high-quality capacitance -- a few thousand mics is easy to hit, even with exotics.

 I should point out that the second row of C1's is the first thing that will go if we need space. We're not dead-set on keeping all those caps if we have a better idea of how to use all that space. 

 Also, Morsel brought up an alternative earlier that people need to consider: is it better to use one row of 16 or 18mm diameter caps instead of two rows of 12.55mm ones? To decide this question, we need people to provide specific capacitor examples and show that the alternative with 12.5mm caps is in some way less appealing. The only one given so far is the Cerafine 1000uF/35V. Besides being hard to get, this cap is very tall: we only have about 31mm of space above the board for C1 if you put a battery board in the case, too, and this cap is 37mm tall. We'll need better examples than this to convince us to go to a single row of fat caps.


----------



## tangent

Quote:


 I lobbied the other Team PPA members for from the onset and got voted out. 
 

My objections to this haven't changed from what I said in my post on this subject above. However, I'm willing to be swayed on the matter. I just want to make sure that people who request this understand the consequences. It's expensive in at least a couple of senses of that word.

  Quote:


 I also wanted a board mounted bass boost switch as it also requires care in routing on the Builder. 
 

I offer a challenge to anyone who wants to board-mount everything: how would you route S2R's pads to the front of the board?


----------



## eric343

Can you post a picture of the layout without the ground plane?


----------



## Whit

Quote:


 To decide this question, we need people to provide specific capacitor examples and show that the alternative with 12.5mm caps is in some way less appealing. 
 

The 2200uf FC cap that is mentioned on the PPA site would be 35mm tall as well as rated for only 25V. If the diameter is boosted to 16mm then the 2200uf cap would be 31.5mm tall and rated for 35V. If a 35V, 16mm, 1800uf FC cap is used then the height is 25mm. In short, the larger diameter caps would allow for more vertical space for things such as the battery board. If the vertical space is not needed then boutique caps could be used such as the cerafines or blackgate. All of the 12.5mm caps on the PPA site are only rated for 25V. Since they will be seeing the full 24V(or whatever Voltage) this time versus the meta42 a 25V rating is too close for comfort. 

 Here are three black gates that would work with the 16mm spacing. 

 BlackGate STD 470uf 50V [16mm x 36mm] 
 BlackGate NX 680uf 35V [16mm x 24mm] 
 BlackGate STD 330uf 50V [16mm x 32mm] 

 Here is a nichicon muse:
 470µF..................50V KZ ......... 1.75 ........16mm x 35.5mm

 Here is a elna silmic:
 35/470uf 16 x 33mm 

 Whit


----------



## tangent

Quote:


 The 2200uf FC cap that is mentioned on the PPA site would be 35mm tall as well as rated for only 25V. 
 

You're right, Morsel should probably remove mention of that cap and maybe use one of the 1500s or something instead.

 If we go with board-mount everything and the custom panels that that requires, we'll have to require that everyone mount their PPA board in the case such that a battery board could fit underneath even if you don't use it. I don't want to multiply the number of panels I have to prototype and stock by another 2x. Thus, 31mm or so above the board is pretty much a hard limit. 31.5mm is probably do-able, but we haven't tested case space issues in detail yet.

 It's just as well -- 12x 2200uF is pretty silly. Again, the idea is to use smaller capacitance, higher quality parts rather than huge capacity generics.


----------



## tangent

Quote:


 Can you post a picture of the layout without the ground plane? 
 

What's under there are the traces from the input pads at the rear of the board going to the pot, and then the traces coming from the pot's wipers to R1 on each side. 

 I'm assuming that you're asking in response to my challenge, so I'll just tell you that the idea won't work. Since the trace on the bottom of the board going from the pot wiper to R1R extends virtually clear across the top edge of the ground plane, you can't get underneath the ground plane from its top edge except to the right of R1R. And you don't want to move the R1R trace out from under the ground plane because that's one of the traces the ground plane is there to protect. You also can't play games with vias to get under there unless you manually cut a hole in the ground plane to go around the via, since ExpressPCB doesn't know how to do that itself. That means cutting a perfectly good ground plane into at least four pieces. Bleh.


----------



## ppl

When the Board is mounted in it's uppermost posistion so the top of the Vol pot just clears the Top corner of the hammond Enclosure so as to make room for the battery board then 30 MM High caps ar the largest useable as that just clears the inside top of the case and 25 MM for the caps on the outer edge of the Board.

 The Quality of the capacitors will have less of an inpact on the sound than thay would on conventional Grounded Headphone Configuation But still quility caps Proabaly make a difference I'll report on this when i replace the Nitchicon 1000uF 35 Volt 12.5 x 30 MM types of whitch (6) are installed with silmics II's at a later date in the prototype. if you are going to use the AD_8610 opamp your supply is limited to 25 volts or less anyway and thus 25 volt caps would be best as you will be operating the caps in there most linear range there working voltage. while Higher voltage caps work you lose capacitence as the actual operating voltage is reduced from the Working voltage.


----------



## tangent

I've got a better idea than an image without the ground plane: one with overlapping traces in purple. If it's purple, you can't cross it.


----------



## JMS

Tangent: I hadn't thought about the routing issues you brought up. Thanks for pointing them out.

  Quote:


 Before we can even think of board mounting everything, we have to get everyone to agree on a single set of components. 
 

What I had in mind was that the designers will choose a single set of components and layout -- just like the set of resistor values. You don't have to please everyone exactly. It will be a compromise: people who use the "reference" design may not get exactly what they want, but in exchange they will get a better-looking amp that's easier to build. Those who must have something else can still make it themselves. Thus, you don't have to make 4 kinds of face plates for bass boost/crossfeed/etc. combinations -- just one for everyone. 

 Thanks for considering our suggestions!


----------



## tangent

Let's start getting down to brass tacks, then. For all those who want board-mount everything, what are your views on the following issues?

 1. Which type of RCA input jacks to use?

 2. How many sets of RCA jacks? Just one input? Two inputs, switchable? One input and one passive or buffered pass-through?

 3. What 1/4" output jack to use?

 4. ALPS Blue I presume?

 5. Bass boost switch?

 6. Crossfeed switch?

 7. Where does the LED go, centered or to the left side of the panel? If centered, does it go near the top, down at board level, or centered precisely within the panel area?

 8. Ditto for the output jack: is it centered so you can unplug even the stiff locking Neutrik jack one-handed with either hand, or on the left side like most amps do it, but requiring two hands to unlock it for lefties, and maybe righties, too?

 9. What kind of power connector?

 10. How big should the volume knob be? Style?

 11. What style of power switch?

 12. Allow space for 1/8" jack holes to be drilled near RCAs and 1/4"? Surely you wouldn't want holes in the panel that you have to plug if you don't want 1/8" jacks as well.


----------



## eric343

Tangent, thanks for posting a much bigger and more readable layout 
	

	
	
		
		

		
		
	


	




 For the S2R routing, move the trace that's right under the C4x text onto the left side of the C4x's left pads. Use the vacated space to run two parallel blue traces from S2R (actually, C5R) under the C4s and under R1L-R3L. Alternately, put the bass boost switch on the back and route the blue trace under R1R-R3R, which might need to be moved a bit.

 An in-optimal solution to be sure, but it would help if the amplfier/buffer blocs were closer to the C1s.


----------



## tangent

Quote:


 move the trace that's right under the C4x text onto the left side of the C4x's left pads. 
 

You mean to the right, surely.

 Still and all, your solution would probably work. Bonus: it goes under the ground plane, which may help considerably.

  Quote:


 Alternately, put the bass boost switch on the back 
 

Then you have similar problems with S2L. Besides, it belongs on the front.


----------



## eric343

Yes, to the right of course... what can I say, it's midnight. 
	

	
	
		
		

		
		
	


	




 And yes, good point... maybe separate the two??

 ...hey, this is supposed to be a 'no-holds-barred-mostly' amp, it's not hifi if it isn't at least slightly inconvenient...


----------



## JMS

My preferences:

 1. Any gold-plated RCA jacks, such as Radio Shack's.

 2. One set of input RCA's, one set of output RCA's in parallel with headphone jack. Both sets on the back panel.

 3. Any good-looking 1/4" jack is fine. I don't care about the locking part. In fact, I'd rather pull the jack out by accident than rip my headphones off my head by accident. The possible accidental output short, to me, is a very low expect cost of not more than a dollar, given the low probability with which it happens. 

 4. ALPS Blue.

 5. Bass boost switch (on/defeat) if bass boost circuit is in, although I don't need the bass boost.

 6. Crossfeed switch (on/defeat) if crossfeed in. Crossfeed would be nice but not necessary. 

 7. Headphone jack on the left. Volume on the right. Switches and LED(s) in between. All vertically centered.

 8. Headphone jack: two-handed plug/unplug is fine. I'd think that carrying around this amp and having to unplug it with one hand is a very rare ocasion.

 9. Power connector: A DC jack? Any is fine.

 10. Volume knob: big, shiny metal, such as Kilo DDS-90-1-5 (Allied Stock # 664-2451) which has a nice skirt. 

 11. Power switch: any is fine.

 12. No space needed for 1/8" jack for me.


----------



## tangent

Quote:


 Any gold-plated RCA jacks, such as Radio Shack's. 
 

I used to use those until I discovered that like everything else at Radio Shack, you can do better for the same price elsewhere. Just one example: items 50-2110 and -2105 at MCM. Virtually the same price as Radio Shack's gold-plated panel-mount jacks, and a good 80% of the quality as the Cardas CTFA.

 But we're talking board-mount here, remember?

  Quote:


 one set of output RCA's in parallel with headphone jack 
 

Tricky. We'll consider it.

  Quote:


 very low expect cost of not more than a dollar 
 

You're not willing to spend, say, $4 for the possibility of saving the cost of 6 buffers costing about $20 total? Sounds like a good insurance policy to me, especially when the $4 buys you looks in addition to safety.

 Besides, you would have a very hard time pulling the plug out of a solid 1/4" jack by the cord simply by pulling with your headphones while they're on your head. Either your headphones will come off your head or the amp will come off the shelf, locking jack or no. If you want the plug to come completely out of the jack when you tug on it, only the 1/8" size has friction low enough. What we're worried about is the middle ground -- the plug doesn't come entirely out, just comes out a bit, enough to cross the R and G channels. 

 I'm with you on the likelihood issue: it's more of a "this is possible" issue than "this is likely to happen" one.

 Thinking more about it, I think the chances of pulling the plug out only partway with a 1/4" jack is pretty low. It's actually higher with 1/8" jacks based on my experience. Too bad there aren't locking 1/8" jacks...

  Quote:


 Bass boost switch (on/defeat) if bass boost circuit is in, although I don't need the bass boost. 
 

You don't get that choice. Either there is no bass boost switch for all amps using the board-mount configuration, or all board-mount amps have it, wanted or not. If we decide more people want it than not, the hole will be put in the custom panel, so even if you don't want the bass boost you'll have to plug the hole with something. It might as well be a switch, and then you might as well add the 4 resistors and caps as well.

  Quote:


 Crossfeed switch (on/defeat) if crossfeed in. Crossfeed would be nice but not necessary. 
 

Again, you can't say that the hole should be there only if crossfeed is wanted. Unless I make N panels, one for every possible configuration, all panels have the same number of holes. You could say that since the crossfeed switch is panel mount, that you could make the builder drill that one, but you'd also want to label the switch positions since everything else on the panel will be labelled. And if it's labelled, it will have to have a hole, unless you do something nasty like use paint remover to dissolve the silkscreening on that part of the panel.

  Quote:


 All vertically centered. 
 

Sorry, that won't happen, due to the slot in the case we must use. To center the pot, the amp board would have to be one or two slots lower in the case, as I recall, and that eliminates the possibility of using the battery board.

  Quote:


 A DC jack? Any is fine. 
 

I asked because some people may have preferences. Personally, I'm a fan of the 5.5/2.5mm barrel connector, since that's what Elpac uses on its single-voltage supplies, and I like Elpac's stuff.


----------



## Voodoochile

Just so you all know, I appreciate and support your reasons for portability. Most importantly, this is your collective design, and should remain what you want. Isn't that the driving force behind designing your own equipment, after all? The desire for a larger stationary amp is only my opinion on the matter.

 Regarding the fact that the PPL Portable will 'whomp' the meta- I wouldn't doubt it at all, based on what I've heard. I was only trying to illustrate that the meta is still quite an amp, and a giant step up from source's amp alone, and even the cmoy.

 I'm also willing to make some sacrifices in the name of portability, but we're all different here. My rationale is that a source suitable for driving such a high-end amp is not exactly portable, either, and I try to keep all these things in balance. I'm not thinking that my PCDP is any better suited to feeding an amp of this level than I am thinking that the EVJ would be at home in it, either. Do remember that this is only my own preference.
	

	
	
		
		

		
			





 All that said, I'll build more than one, regardless of how big or small it is, and enjoy them thoroughly. There is no question about that! (that faint weeping sound you might hear is the muffled cry of my wallet)


----------



## ppl

This Amp is articulate and with some Op amps like the OPA-637 in the gain channels and the OPA-627 in the ground driver Channel MP3's are unlistenable Analog LP recordings most importently ones recorded in the 1950's on Columbia masterworks I have some virgin demo Classical i just played throught the PPA and the afore mentioned BB op amps. Wounderfull reproduction I can't imagine how thay got vinyl that quiet it was almost dead quiet with spirts of noise at time's and static discharging through my Pic up since i left it's carbon fiber Brush up rather than in contact with the record. this gives slightly extended Low end cut off with this Arm picup combo. 

 If mp3's are to be tolerated then an AD-8610 or OPA-627 is to be used. The AD-744, OPA132 & OPA-134, and similar are to dirty for this class of amp. this Amp highlights all the slight imperfections of the Op amp and Buffers used. 

 The Only recomended op amps that i have so far used are the AD-825 real nice and fast sounding somewhat High DC offset compaired to others. OPA-637/627, AD-843, Not as articulate as the OPA-637 but better than the OPA-627. Best bass of the Bunch Extreamly High DC offset over 7.4 mV no Bass Boost and 75 with bass Boost. while OPA-627/637 were less than 1mV with Bass boost and unmeasureable without. AD-8610 detailed and airy .lots of midbass punch Natural sounding voice probaly the most nutural sounding midrange i have ever heard in an Op amp. The PPA really highlight's the exalent qualities of this fine Device. AD-845 warm and somwhat dark sounding DC offset on this also under 1 mV with bass boost.

 The Best of overall in opamps IMHO is the AD-8610 unlike the OPA-627/637 the sound remains constant over quite a large supply voltage range. the OPA's start to noticable degrade below 20 Volts. that's +10/-10 on the Op amp rails.

 as warm and lush sounding as vinyl is the Bass boost was required on then New now classic Rock still as on CD sounding Thin in the Bass. Thank god for bass boost with well chosen operating points.


----------



## tangent

Quote:


 The desire for a larger stationary amp is only my opinion on the matter. 
 

Without changing the design radically, the only thing I can think of that would take tremendous amounts of additional space is a discrete output stage. Given that we've already got a pretty nice output stage as it is, I'm not sure what this would buy us.

 How about this: come up with some ideas that eat space, and we'll see if we can meet your "large" desire. This is not a goal, but an exercise. What does it take to make this amp bigger?

 I rule out one thing from the start: an internal AC power supply. There's no reason not to put that in a second box except to save money. Besides, did you not see the title of the pic ppl most recently posted?

 As for drinking more current and thus eliminating the possibility of portability, the only thing I can think of that _might_ justify the additional current is more buffers. But our measurements indicate that going beyond 2 buffers per channel is of dubious benefit. There's an open question of doubling the ground channel buffers, but all three channels? It doesn't seem to be in the cards.

 So again, what do you think would be helpful but which would require higher current levels?

 One thing to keep in mind is that the current draw of this amp varies pretty drastically based on configuration. With 1 buffer per channel and AD8610s biased lightly into class A (~1mA per), quiescent should be a smidge under 50mA. If you switch to AD843s biased heavily into class A (5mA+) and double the buffers, the quiescent current will crest 100mA. Yet, with the large battery power supply we're proposing, that still allows for about 7 hours of run time! Your average META42 draws less than 20mA. By comparision, the PPA drinks current like a horse drinks water.

 It just seems to me that people are talking like the PPA is full of half-measures. Like, if it doesn't weigh 10 pounds and warm the room that we're doing it wrong. 
	

	
	
		
		

		
		
	


	




 Portability is within reach with this configuration, so I defend it. I don't like to lose features for silly reasons. Based on what's been going on with META42s, I imagine that most PPAs will be used solely as home amps, but that doesn't mean we should remove the possibility of portability.

 Another thing to consider: batteries enable portability, but that's not the only reason they're going to be part of the final design. Rechargeable batteries have effective impedances of a fraction of an Ohm, and they also have no ripple or noise output. They're also independent from your wall power. They're nearly the ideal power supply for an audiophile amp.

  Quote:


 the meta is still quite an amp 
 

Indeed. I don't mean to imply that the META42 sucks or anything like that. But you want to talk about limited designs and half-measures, the META42 is _it_. Yet, it succeeds, because it fits its niche well. I think the PPA will do the same, for the same reason. They're both well balanced for their roles in the world.

 I point out that the PPA "whomps" the META42 not to hype it, but because I think people are seeing a similar-looking schematic and thinking that it's just a META42 with a flabbier PCB layout. There was a point right after I'd populated my PPA prototype board and made sure it was working, but before I'd done any critical listening where I said to myself, "If it doesn't clearly ace the META42 in terms of sound, we're going back to the drawing board." It had to be that way: the parts cost went up way too much to tolerate a piddly sound improvement. It had to be great or it would be scrapped. You're hearing about the PPA now because it didn't get scrapped.

  Quote:


 My rationale is that a source suitable for driving such a high-end amp is not exactly portable, either, and I try to keep all these things in balance. 
 

An amp is about passing the signal from the source without distortion and delivering the headphones the power they need without allowing the reactive load to create new distotions. Sources can always use more transparency, headphones can always use more power, and distortion in a portable META42 is still higher than we'd like. (See KurtW's buffer tests, particularly the ones for a single EL2001 in a META42 when it's driving headphones.) Given all that, it's reasonable to upgrade the amp ahead of the source and the headphones, as long as they aren't complete junk. It's true, you have no business plugging a Cassette Walkman and a pair of $5 earbuds into a PPA. But a Panasonic CT-570 and a pair of Grados plugged into a PPA makes a perfectly sane system.


----------



## guzzler

i think we should all take a look at the rev. number on the board: 0.014 This board has an awful lot of development still to go, and I think it's unfair to so comprehensively dismiss already. Tangent et al are specifically posting here because its _us_ that will ultimately buy it, not them so its in their interest to gauge opinion!

 g


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## Voodoochile

Quote:


 The desire for a larger stationary amp is only my opinion on the matter. 
 

I worded that poorly, my bad. I'm not interested in making it larger so it can be big. I'm just not striving for portability, as I already have that in other very capable amps.

  Quote:


 There's no reason not to put that in a second box except to save money. 
 

 Sure there is. Simplicity and an all-in-one chassis aesthetic is another. Inversely, what advantage does an outboard box have over residing in the same chassis? It has been demopnstrated that EMI and RFI are not difficult to overcome. Even a dubious 'box within a box, though unneccesary, could work.

  Quote:


 Besides, did you not see the title of the pic ppl most recently posted? 
 

 Yes. It was funny, but not educational. Looked like something I might post
	

	
	
		
		

		
		
	


	




 .

  Quote:


 So again, what do you think would be helpful but which would require higher current levels? 
 

Nothing. I am in full agreement that a pair of buffers is a proper balance of benefit. I do think that the current draw is already bordering on too high to be practical in a portable design. Quote:


 Your average META42 draws less than 20mA. By comparision, the PPA drinks current like a horse drinks water. 
 

 My point exactly.

  Quote:


 Portability is within reach with this configuration, so I defend it. I don't like to lose features for silly reasons. Based on what's been going on with META42s, I imagine that most PPAs will be used solely as home amps, but that doesn't mean we should remove the possibility of portability. 
 

An I do respect that, very much. I can case this up in a woodstove if I want to. I did not mean to imply that it was full of shortcomings or compromises to save space, rather that we have some nice amps already that fill this niche very well, and perhaps it should not be the focus of design. It was a solicited comment only. I do not think your design is poor or compromised by any means... it looks quite smashing, actually.

 I'm not trying to run over anyone's nerves with a rasp, and I do not have issues with the design, per se. I was merely offering my thoughts on the direction of the end use. Certainly, if you design the board for portability, we have the option of chasing either direction, which would not be the case with a larger or more power-hungry design. Beside, we always have tubes for that. I have not seen fixup posting any plans for the fixup super-mini-melos-sha-gold-reference-clone, with power booster.


----------



## Voodoochile

And another thing...
 This whole discussion (at least the part involving me) is largely rhetoric.

 I don't think you can go wrong with this amp. ask anyone, and they will probably say "I love it except for one little thing..." and that little thing will probably be different depending who you talk to. 

 But the fact would remain- it will be an outstanding example in it's field. I'm thoroughly impressed with it, and I think most people will be, also.


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## jamont

Quote:


 _Originally posted by Voodoochile _
 I worded that poorly, my bad. I'm not interested in making it larger so it can be big. I'm just not striving for portability, as I already have that in other very capable amps.

 Sure there is. Simplicity and an all-in-one chassis aesthetic is another. Inversely, what advantage does an outboard box have over residing in the same chassis? It has been demopnstrated that EMI and RFI are not difficult to overcome. Even a dubious 'box within a box, though unneccesary, could work. 
 

I'm with VC here. This is one thing the Corda HA-1 got right. It's a nice single box amp with IEC power connector on the rear and it's very quiet. I will build the PPA either way but I would really like a single box AC powered unit.


----------



## Squalish

oops - bad post


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## Squalish

*tries to post pics and fails*


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## Voodoochile

Quote:


 It has been demopnstrated... 
 

 I bet you guys don't even know what I'm talking about!

 "demopnstrated"? Sounds like harsh punishment to me.


----------



## Squalish

Quote:


 _Originally posted by tangent _
*
 I should point out that the second row of C1's is the first thing that will go if we need space. We're not dead-set on keeping all those caps if we have a better idea of how to use all that space. 

 Also, Morsel brought up an alternative earlier that people need to consider: is it better to use one row of 16 or 18mm diameter caps instead of two rows of 12.55mm ones? To decide this question, we need people to provide specific capacitor examples and show that the alternative with 12.5mm caps is in some way less appealing. The only one given so far is the Cerafine 1000uF/35V. Besides being hard to get, this cap is very tall: we only have about 31mm of space above the board for C1 if you put a battery board in the case, too, and this cap is 37mm tall. We'll need better examples than this to convince us to go to a single row of fat caps. * 
 

Taking out half the caps is not necessarily needed to get it all in 1 row. I did this last night, when I lost internet access, so pardon the lack of purpality. Also, sorry about the choppyness, PCBs are hard to photochop. Likewise the text, I accidentally deleted it and failed to correctly remember the version number.

 Next up on my list when I was doing this was to move C2 below the R11-R5 resistor bank, possibly by moving Q3 to the left a quarter inch, and stretching out R8/R9 group. After that, I would change the connections to ground to be straight, for aesthetics, and make them conform to the revised purple-traced pic, incl changing R2L and R3L to have underboard traces. The connections to ground are all connected to it via through-holes, going under the board until they hit the hole. The idea is that you can use whatever you want on the top layer, in order to snake traces across the board, as tangent said would be difficult.


----------



## JMS

Quote:


 Again, you can't say that the hole should be there only if crossfeed is wanted. 
 

Oh, absolutely. What I mean is, crossfeed (or bass boost) is not too important for me, but if the reference design/face plate comes with it, I'd be happy to add it, if only to fill up the holes. In summary:

 "I don't think you can go wrong with this amp. ask anyone, and they will probably say 'I love it except for one little thing...' and that little thing will probably be different depending who you talk to." (Voodoochile)

 but

 "I will build the PPA either way..." (jamont)


----------



## jamont

My comments on some of tangent's laundry list :

 1. I think that the RCA jacks should be panel mount, not board mount. I don't know of any high quality PCB mount RCA's - there are lots of good panel mount ones. These tend to get a lot of strain from stiff audiophile cables and panel mount would probably hold up better. Look at the Corda HA-1 for a good example of what to avoid (I speak from unhappy personal experience here).

 4. ALPS Blue is fine if sourcing is not an issue.

 7,8. If the lefty/righty thing is a concern, how about this:

 on/off bass boost xfeed 1/4" phone volume 

 in a row across the front panel. LED underneath the power switch.

 9. I'm with tangent here, the 5.5/2.5mm barrel connector is a winner. In addition to working with the Elpac PS, this is easy to hook up to a DIY PSU.

 10. I want a big volume knob, 1.25" would be great. Styling like the small Kilo knobs would be great. Simple, black, round.

 11. Small rocker on fron panel (see above).

 12. I don't need the 1/8" jacks.


----------



## eric343

Board mount RCA jacks - Cardas makes the GRFA in a boardmount formfactor, and they're one of the best IMHO. Also, I believe the GRFAs are 'hybrid' - though they mount to the board you still secure them with a nut, eliminating strain problems.


----------



## antness

Vampire also makes a very nice board mounted RCA which costs about $15 a pair


----------



## aos

I've never managed to tighten a panel mount RCA jack good enough so that it won't get loose sooner or later. PCB mount is the way to go. Besides, you don't **HAVE** to get custom panels, you can do it yourself. It does require being careful and measuring thrice but it's not THAT hard.


----------



## antness

Another problem with the PC mount RCA jacks is that if you buy stereo units, the jacks are always way too close together to use the thicker cables that many have, as well as too weak.


----------



## Voodoochile

I've noted the too close problem antness points out. As far as keeping the panel mounts tight, I have used a drop locktite on the threads.


----------



## tangent

Quote:


 I'm not interested in making it larger so it can be big. 
 

Naturally. I simply mean, what features do you want that would require to be larger than it already is. If it's just to put an AC power supply on the same board, well, I'm pretty sure that will end up being a separate board. It's not out of the question, but probably not something we'll tackle immediately.

  Quote:


 what advantage does an outboard box have over residing in the same chassis? 
 

We need an outboard power supply anyway, for those who want to use the PPA in a battery setup. The reason is, we need a fairly high voltage to charge 18xAAA -- something on the order of 30V -- and good high-current high-voltage linears seem to be very hard to find. Therefore, we're already talking about building our own. For the first run, that might as well be the same solution used by those building AC-only amps. Later we might integrate that power supply circuit onto a larger PPA spinoff board.

  Quote:


 It was funny, but not educational. 
 

You missed the lesson: There was indeed humor there, but ppl was also making a point: he really likes rechargeable battery powered amps.

  Quote:


 we have some nice amps already that fill this niche very well 
 

We have amps that fill lower niches very well. I'm not aware of any portable amps in the PPA's class.

  Quote:


 I'm not trying to run over anyone's nerves with a rasp 
 

I must have come across as upset, or defensive. I'm just defend*ing*, that's all. Your opinions are quite welcome; I don't want to discourage them or any like them. I'm simply responding, from the perspective of the PPA's current design concept.

 It appears that we're going to end up dividing comments into three categories: 1) won't ever do it to a PPA, 2) might do it in a future variant of the amp, and 3) probably a good idea to do that to the current PPA. I know being put in category 2 is a disappointment, but some things we just can't do without changing what the PPA _is_. Doesn't mean they aren't good ideas, though.

  Quote:


 fixup super-mini-melos-sha-gold-reference-clone, with power booster. 
 

He told me not to talk about it, but that's v6. In v7, he's adding bass boost.

  Quote:


 I don't think you can go wrong with this amp 
 

Thanks for your vote of confidence! I do think your ideas have some merit. We just can't make the PPA all things for all people.

  Quote:


 Taking out half the caps is not necessarily needed to get it all in 1 row. 
 

Thanks for all the work, Squalish. I know it must have taken you quite a bit of time and thought to come up with that layout. Unfortunately, it violates several of the rules we've set for ourselves.

 One is that it puts things too close to the front and back of the board, which limits what you can put on the panels and where you can put it. We have an informal one-inch "keep-out" area at the front and back of the board to allow for panel components. We haven't had to violate that keep-out area yet; we may yet break into the keep-out area as the layout firms up and it becomes clear what we can get away with, but it's too early to do such drastic things at the moment.

 (For what it's worth, you truly don't have to eliminate 1/2 of the caps. There are 8-cap arrangements possible in a single row. The only downside is that it's not as pretty as the current configuration.)

 Another rule we didn't tell you about that you violated in your layout is that the C4s are now farther from the op-amps. The C4s are there partially for bypass, so they really ought to be as close to the chips' power pins as we can reasonably make them.

 Finally, I'm not thrilled with the addition of what amounts to several vias. Call them what you like, they're still vias.

  Quote:


 I think that the RCA jacks should be panel mount, not board mount. 
 

One real advantage of panel-mount inputs is that it makes hooking up a crossfeed easier. With board-mount jacks, we'd have to have some way of cutting the input trace in order to force the input signal to go through the crossfeed circuit instead of straight to the pot.

 The advantages and availability issues the others have brought up are noted, though.

  Quote:


 Small rocker on fron panel 
 

Hmmm, a quandary. Power on the front is good for portable amps, especially when they're in a bag. For home amps I prefer to keep it on the back, since it's cleaner and I don't need to get to the switch often. In the PPA, all of the power inputs will be at the rear of the board already, so I'm inclined to put the switch on the back.

 People, let me know what you think about this particular issue. Putting the switch on the front panel wouldn't be too difficult to do (the traces above the cap bank could be reworked for the purpose), but it's a matter of taste as to whether it's a good idea. Do you go for usability, with the switch on the front of the case, or do you go for esthetics, keeping the front panel as clean as possible?

  Quote:


 you don't **HAVE** to get custom panels, you can do it yourself. It does require being careful and measuring thrice but it's not THAT hard. 
 

One of the arguments in favor of board-mounting everything is that it's faster to build the amp. If you measure thrice and take extra care when machining the panel, you could soak those savings right up. If we're going to offer the option of board-mounted components, it will be accompanied by a custom panel. The only issue in question is, how many combinations of panels will there have to be, and if we can get away with only one, what is the feature set supported by that panel?


----------



## ppl

With good quality silver contact switches there is no reason that with the Bass boost defeated that the same quality of sound can be obtained as if there were no prevision available.

 Yes i like rechargable batteries, see my frends don't let frends use AC on an earleyer post. AC is nasty unless you use all Kinds of EMI filtering and a quiet Circuit design.


----------



## eric343

Regarding the whole custom front panel thing, can't you get black plastic 'plugs' that will cover unused holes in panels? If you could find ones with a wide enough 'flange', then they'd cover the silkscreen label for that hole, too.

 Alternately, silkscreen *both* sides of the panel and have "drill here" circles with small center holes (that don't go all the way through).


----------



## ppl

Somewhare is a post on Custom Pannels up to 1/2' thick I belive and available in stuff like brass. if i remember right it like express pcb has software that you use to design the pannel and have them make it.


----------



## eric343

Hmm... I wonder if you can get glass/brushed steel faceplates... see, have all the silkscreeing behind the glass, and have the blue LEDs light up the glass... mmmmmm....

 Better yet, get some plexiglass/acrylic stuff and "bend" the top or bottom edge using a thin straight heating element made for the purpose... the bend would project the faceplate into the case where a row of LEDs can shine directly into the edge and the light travels via internal reflection to the front panel where some strategic routing creates floating, luminescent labels...


----------



## Squalish

Quote:


 _Originally posted by ppl _
*Somewhare is a post on Custom Pannels up to 1/2' thick I belive and available in stuff like brass. if i remember right it like express pcb has software that you use to design the pannel and have them make it. * 
 

Frontpanelexpress. Their prices are actually pretty reasonable for a DIYer, around $10-30.


----------



## Squalish

Quote:


 _Originally posted by eric343 _
*Hmm... I wonder if you can get glass/brushed steel faceplates... see, have all the silkscreeing behind the glass, and have the blue LEDs light up the glass... mmmmmm....

 Better yet, get some plexiglass/acrylic stuff and "bend" the top or bottom edge using a thin straight heating element made for the purpose... the bend would project the faceplate into the case where a row of LEDs can shine directly into the edge and the light travels via internal reflection to the front panel where some strategic routing creates floating, luminescent labels... * 
 

You really don't need an acrylic heater if you're doing it on a onetime basis, just a cheap heat gun and a template(Even if you mess up, acrylic is insanely cheap, I got something around 18x24" for $2.50), but if you're doing it in production, it should help a lot. I think the best option for doing this is, for ex a 5" panel, to heat it and let it flow over a 4" piece of rectangular balsa, then cut two vertical notches in the metal panel .5" from each side, push it in, cut excess length off, and flow both ends inward, to lock it in place. This is the only way I can think of to do it without messing up the typical way of mounting panels.
 I don't know how well light carries in hard preformed plexi that's been reshaped, but it works great in flexible things like venetian blind turners and heavy fishing wire, which is basically fiber-optic cable.
 You would need to use 1/8 acrylic, and >1.5mm metal, to keep panel thickness down.

 That said, I doubt they want to spend nearly this much time on something so cosmetic.


----------



## eric343

Quote:


 _Originally posted by Squalish _
*You really don't need an acrylic heater if you're doing it on a onetime basis, just a cheap heat gun and a template(Even if you mess up, acrylic is insanely cheap, I got something around 18x24" for $2.50), but if you're doing it in production, it should help a lot. I think the best option for doing this is, for ex a 5" panel, to heat it and let it flow over a 4" piece of rectangular balsa, then cut two vertical notches in the metal panel .5" from each side, push it in, cut excess length off, and flow both ends inward, to lock it in place. This is the only way I can think of to do it without messing up the typical way of mounting panels.
 I don't know how well light carries in hard preformed plexi that's been reshaped, but it works great in flexible things like venetian blind turners and heavy fishing wire, which is basically fiber-optic cable.
 You would need to use 1/8 acrylic, and >1.5mm metal, to keep panel thickness down.

 That said, I doubt they want to spend nearly this much time on something so cosmetic. * 
 

 \

 Good ideas 
	

	
	
		
		

		
			





 And come on, man, in the world of Hi-Fi, looks are just as important as sound... Case in point, the Shanling T100, which survives almost entirely on looks... now obviously, the PPA is going to sound way better than the Shanling, but hey, why not make it look professional, too?


----------



## zzz

Quote:


 _Originally posted by aos _
*I've never managed to tighten a panel mount RCA jack good enough so that it won't get loose sooner or later.* 
 

cover the nuts with clear varnish (this can be done from the inside, between, or wherever, depending on the jacks).


----------



## Squalish

Quote:


 _Originally posted by eric343 _
*\

 Good ideas 
	

	
	
		
		

		
		
	


	




 And come on, man, in the world of Hi-Fi, looks are just as important as sound... Case in point, the Shanling T100, which survives almost entirely on looks... now obviously, the PPA is going to sound way better than the Shanling, but hey, why not make it look professional, too?




* 
 

The thing is, do we want Tangent spending 15 minutes on each and every panel, or do we want him working on the PPA board itself? I think there might be places that do this stuff for you, but they are probably too highvolume to be within reach. It is quite easy to mess up and brown or burn acrylic when doing this(I don't recall the melting/burning temps, but they were something like melt at 370f, brown at 390f, flame at 400f), too.


----------



## morsel

Heehee, clearly I have been away from my computer too long. 
	

	
	
		
		

		
		
	


	




 There are so many pages of new posts I will answer with soundbites.

 The DACT CT2 is nice, but pricy at ~$112-150. I suspect most people will prefer a $20 pot. We can look into providing pads for the DACT as long as it does not wreck the layout. No point in turning things upside down for a part few will use.

 The Leung "Alps" stepped attenuators are not in consideration as they are way too stiff and audibly click when turned.

 The PPA is not seriously compromised .vs. an AC only configuration. Before you get all hot and heavy about the PPA being portable you should wait for the test results.

 I do not share Tangent's expectations for the PPA. My goal is to make the PPA as good or better than the Gilmore and Corda PreHead. If I did not believe it was possible I would not have started this project.

 Whit, regarding C1 caps, I must have read the Panasonic FC chart wrong. I'll change that to 1000uF on the website. We definitely want 35WVDC.

 A capacitance multiplier is not vulnerable to dropouts because it has no set voltage like a voltage regulator.

 Eric and PPL, I don't think we can do an onboard bass boost switch without running shielded jumpers, messing up the layout by running the right channel feedback leads through sensitive parts of the left channel circuit, or going to a 4 layer board.

 Further testing is needed before we will know whether 2 or 4 buffers per channel is the best choice.

 Do not underestimate the significance of differential output.

 The notion of a single box ac powered solution is very appealing, but as project manager I have to balance many issues including honoring PPL's wishes, assuring we don't compromise sound quality, and offering a sane end result that most of us can be happy with. I think we need more time to gauge public feeling over this issue.


----------



## Squalish

Quote:


 _Originally posted by tangent _
 Thanks for all the work, Squalish. I know it must have taken you quite a bit of time and thought to come up with that layout. 
 

No problem, just a bored insomniac's timesink. It was less boring than anything else you can do at 3AM without internet access and without waking anyone up.

  Quote:


 Unfortunately, it violates several of the rules we've set for ourselves. 
 

I made it partly to find out those rules, partly just to point out the length.
  Quote:


 One is that it puts things too close to the front and back of the board, which limits what you can put on the panels and where you can put it. We have an informal one-inch "keep-out" area at the front and back of the board to allow for panel components. We haven't had to violate that keep-out area yet; we may yet break into the keep-out area as the layout firms up and it becomes clear what we can get away with, but it's too early to do such drastic things at the moment. 
 

I should adjust my pic so that the 3 main sections are 12mm higher, the LEDs and power are 12mm to the left, and there is a lip on the top and bottom of the row of C1's.
 **
 *R
 *
 *G
 *
 *L
 **
 I guess it doesn't make as much difference from teh current layout like that, but it gives you a little headroom, and uses some of the unusable C1 to LRG space.

  Quote:


 Another rule we didn't tell you about that you violated in your layout is that the C4s are now farther from the op-amps. The C4s are there partially for bypass, so they really ought to be as close to the chips' power pins as we can reasonably make them. 
 

I left the C4s there because I wasn't sure if anything important was connected to them on the underside of the board. With the purplized layout, I see I could have just moved them with the rest of the group. Is it bad having them connected to teh ground by traces, instead of directly?
  Quote:


 Finally, I'm not thrilled with the addition of what amounts to several vias. Call them what you like, they're still vias. 
 

Now I see what you were saying before(I didn't know what "via" meant until 5 minutes ago). What's the downside to using them? Since we seem to be exploring panelmounting, the only alternative looks like jumpers.
  Quote:


 Hmmm, a quandary. Power on the front is good for portable amps, especially when they're in a bag. For home amps I prefer to keep it on the back, since it's cleaner and I don't need to get to the switch often. In the PPA, all of the power inputs will be at the rear of the board already, so I'm inclined to put the switch on the back.

 People, let me know what you think about this particular issue. Putting the switch on the front panel wouldn't be too difficult to do (the traces above the cap bank could be reworked for the purpose), but it's a matter of taste as to whether it's a good idea. Do you go for usability, with the switch on the front of the case, or do you go for esthetics, keeping the front panel as clean as possible? 
 

IMO, PCmounting itself, and constraining someone to use a premade frontpanel, is an adjustment for usability. If someone wants better aestheics, let them panelmount. Give everyone else usability. general priorities:1)sound 2)usability 3)buildability 4)looks.

  Quote:


 One of the arguments in favor of board-mounting everything is that it's faster to build the amp. If you measure thrice and take extra care when machining the panel, you could soak those savings right up. If we're going to offer the option of board-mounted components, it will be accompanied by a custom panel. The only issue in question is, how many combinations of panels will there have to be, and if we can get away with only one, what is the feature set supported by that panel? 
 

I think you need to explore what case people will be using the panel with. A lot of it depends on the dimensions of the front panel, which fluctuate a ton with the presence of a battery pack and the dimensions of the box. 7"x4"x1.5" is required for the board, if a flat battpack is gonna be above the board that adds another .5" minimum of height

 If you decide to use a specified panel/case and are having trouble fitting in components that will be acceptible to everyone, you could always go all-out, redesign the board a bit, and make the front of the board to the right of the ground plane. This might necessitate 4layer, though, and seems like too drastic a solution. A daughtercard is an option too, to take advantage of the height the box will need to be.

 On which options come standard: I wouldn't mind 2xRCA ins, 1xmini in, 1x1/4out, 1xminiout. You could use a DPDT for off-charging-battery, Xfeed adds 2 DPDTs, the bass a DPST. If you can find a good-quality vertical mount mini slide switch, it would save a ton of space. Ideally, you will have 1.25" space for a large-sized knob.
 If you have trouble w/ the above, remove components in this order:

 bassboost
 1xRCAin
 shorten 1.25" knobspace to 1"
 XfeedS1
 XfeedS2
 miniin
 miniout

 The big question: Will this fit in a jumbo altoids?


----------



## Squalish

Idea about the acrylic. This would take a little doing(lettering is difficult to cut through metal), but why not use the metal as a Light-Bright filter, and put the acrylic on the other side? It wouldn't look as good, but it would be doable.

 I don't know about the results(I would imagine you need 1mm or lower thickness of metal for it to show through correctly), and I think extremely small bit etching is hideously expensive for machine shops, but it would alleviate the labor of using heat to connect the plexi and the panel, you could just use screws.


----------



## Arzela

Has anyone dealt with www.emachineshop.com ?

 They have a software CAD package to download. You design your part and send
 them the drawing for them to machine. 

 Lots
 of available materials, e.g., aluminum, brass,
 titanium (!)... Lots of finishing options, e.g., brushed, chrome, gold plate (!)...

 Perhaps this would be a good place to do a group buy....


 Just a thought.


----------



## Nisbeth

Quote:


 _Originally posted by Squalish _
*
 I think you need to explore what case people will be using the panel with. A lot of it depends on the dimensions of the front panel, which fluctuate a ton with the presence of a battery pack and the dimensions of the box. 7"x4"x1.5" is required for the board, if a flat battpack is gonna be above the board that adds another .5" minimum of height
* 
 

Morsel, Tangent: What are the preliminary plans for the batterypack? Will that be in a 2nd enclosure or some form of stacked configuration with the amp board?
 Because then portability will probably be compromised severely or? Anyway, AFAIK AA batts weigh ~1 oz/pc, which brings the battery pack alone to ~18 oz or ~500 grams. Not exactly lightweight, and with a charging circuit etc, you risk having to lug around something that looks like this 
	

	
	
		
		

		
			







 IMHO the power-supply issue needs to be resolved fairly quickly, because this pretty much dictates the size of the enclosure and thus how much space is "left over" for other things. Even with two modules like these, (but with 9 cells each of course) you're talking quite a lot of space. 
	

	
	
		
		

		
		
	


	



 Regarding the potentiometer issue, I personally think the Alps blue should be the first choice. If you can provide pads for the DACT that would be great (could be difficult when you look at the drawings ), but IMO this is important, since the project looses quite a lot of it's "mass appeal" if a 150$ attenuator is required. As much a we'd all like to, not every one is able to pay that kind of money for audio gear. And a lower interest will reflect negatively on the price of the boards and other components, which noone could be interested in. Having the DACT or something similar as an option (possibly for later upgrades) is fine with me though. 
	

	
	
		
		

		
		
	


	




 Questions, Questions.... 
	

	
	
		
		

		
		
	


	




 /U.

 Edit: More pictures of that battery supply here


----------



## Squalish

Quote:


 _Originally posted by Arzela _
*Has anyone dealt with www.emachineshop.com ?

 They have a software CAD package to download. You design your part and send
 them the drawing for them to machine. 

 Lots
 of available materials, e.g., aluminum, brass,
 titanium (!)... Lots of finishing options, e.g., brushed, chrome, gold plate (!)...

 Perhaps this would be a good place to do a group buy....


 Just a thought. * 
 

I just downloaded and checked this out. It's VERY economical in large quantities compared to frontpanelexpress, and a huge ripoff if you are only ordering one. Also, it's very ignorant of the size of the board. You can get 100 10"x15" panels for about the same price as 100 1.5x5" panels ($650 for aluminum)


----------



## was ist los?

This amp is almost like a kit now, we are going to share same panels, cases, parts, etc.


----------



## Arzela

Quote:


 Also, it's very ignorant of the size of the board. You can get 100 10"x15" panels for about the same price as 100 1.5x5" panels ($650 for aluminum) 
 


 Yes...

 I noticed that the price barely increases if you
 order a panel with one hole verses a panel with ten recessed holes of various sizes.

 Strange...


----------



## morsel

Hi Nisbeth,

 We are hoping to delay discussion of the battery pack until we get the amp nailed down a bit more. To answer your question, our plan calls for a 3x6 array of AAA NiMH cells and a charging circuit on a battery board underneath the main board. We have already made sure it will fit the current amp design. As you can see from the existing documentation, the board and case size have already been determined. It would take some major convincing to get us to go bigger than Eurocard format.


----------



## sTaTIx

Quote:


 _Originally posted by morsel _
*I do not share Tangent's expectations for the PPA. My goal is to make the PPA as good or better than the Gilmore and Corda PreHead. If I did not believe it was possible I would not have started this project.* 
 

Hmm, that's interesting. Tangent says that the PPA will be WAAAY better than the Meta, and I recall you saying that the Gilmore was only slightly better than the Meta. So, by all accounts, you and Tangent should be in agreement that the PPA will be better than the Gilmore, right?


----------



## morsel

I'm not going to get into that with you, Statix.


----------



## ppl

Ah yes a true Virtual battery supply for all. However the PPA is more modest with only one layer of AAA's on just one Board that slides below the Amp Board.


----------



## Voodoochile

...ppl... Quote:


 Yes i like rechargable batteries, see my frends don't let frends use AC on an earleyer post. AC is nasty unless you use all Kinds of EMI filtering and a quiet Circuit design. 
 

 Thanks, that was enlightening. People don;t like AC for many reasons. As for your observations of cheap and noisy supplies, I hate them with a passion. If you don't do AC right, then don't do it at all.

 ...morsel... Quote:


 Before you get all hot and heavy about the PPA being portable you should wait for the test results. 
 

But I _like_ to get all hot and heavy! Especially about this stuff
	

	
	
		
		

		
		
	


	




 .

 ...tangent... Quote:


 He told me not to talk about it, but that's v6. In v7, he's adding bass boost. 
 

 I knew it! Did you know it's going to reside in a chapstick container?

 ...tangent... Quote:


 We just can't make the PPA all things for all people. 
 

Please _don't._ I believe that was one of my initial concerns. I hate it when that happens.

 So, these will be done by Thursday, right? I need five boards by Saturday if at all possible.


----------



## aos

So then the proper course of action is to order a prototype from front panel express and then order production quantities from emachineshop.com.

 This thread has grown increcibly in just one day. I don't think even original META42 caused this much stir.

 Also, be careful with recharger. At 18 cells it's going to generate a lot of heat during charging and you'll need to cool the regulating transistor, meaning a heatsink is in order. That might affect the space arrangement. Also, chargers get more complicated with so many cells and usually need extra circuitry to handle it.


----------



## Arzela

Shall we vote on a finish for the panel?

 I'd wan't satin nickel.


----------



## eric343

Hey, if eMachineShop has such good prices for BIG panels...

 ...do they do bending and welding? Because for a portable amp, a professionally cut, welded seam titanium case would be SCHWEEEET and ultra-tough...


----------



## Squalish

Quote:


 _Originally posted by eric343 _
*Hey, if eMachineShop has such good prices for BIG panels...

 ...do they do bending and welding? Because for a portable amp, a professionally cut, welded seam titanium case would be SCHWEEEET and ultra-tough... * 
 

Right now, it LOOKS like they do everything - they let you specify which machine you want to do what with.


----------



## Voodoochile

I'm not real big on the pre-fabbed front panels, but if they were made available, I'd go for one anyway. Stainless is nice. Otherwise I second a brushed nickel finish.

 Or, either one in a bead-blasted matte.


----------



## puck

i have to say that i'm not for the all board-mounted components with standard faceplate and case idea. if everything is pre-made, its not diy anymore because you are not "doing it yourself." also, a lot of the chassis mounted components are nicer looking than board mounted stuff because they can have trim moldings. 

 anyway, my vote goes for optimizing traces and not worrying about making everything board mounted, especially if this would eliminate the need for a 4 layer board. i like to be able to see the traces when trouble-shooting and the savings on cost would be nice.

 for those of you who want a standardized faceplate, you can get them made just as easily for chassis mounted as for board mounted stuff.

 i'd also like to throw in a vote for larger capacitor pads. i think that many people will end up mounting bigger caps off board if the pads only allow 12.5 mm caps.


----------



## Squalish

Quote:


 _Originally posted by Voodoochile _
*I'm not real big on the pre-fabbed front panels, but if they were made available, I'd go for one anyway. * 
 

My opinion exactly.


----------



## x1lexure

THE FOLLOWING IS JUST MY PERSONAL OPINION AND CAN BE IGNORED AT YOUR CHOICE:


 Seeing as how some have talked about not working on the Power Supply just yet I must object. If this is to be a prtable the powersupply size MUST be considered at the same time as the make up of the amp itself. Disappointment would surely follow after the exhausting hours the team will probably put into the amp itself.


----------



## joe_cool

I disagree to a small extent. If you make the choice for a portable then you limit yourself to a 9-volt, 2 x 9-volts, or some combination of single-cell devices. In this case you do what is necessary, not that which is optimum.


----------



## morsel

Hi Puck,

 I'm mostly in your camp. One comment about caps, though. More capacitance is better only to a point. It is actually possible to create problems with too much power supply capacitance. We will determine the proper amount of capacitance and provide appropriate space for it.


----------



## morsel

X1lexure,

 Seeing as how some have talked about not working on the Power Supply just yet happen to be the project manager who graduated from college before you were born, 
	

	
	
		
		

		
			





 it is my judgement that it is hard enough to focus on all of the amp issues at hand without dealing with the AC supply and NiMH charging circuit as well. All in good time. Also realize that some amp choices may affect power supply choices, so the amp comes first.

 I invite you to scroll back to some of my earlier posts to see some of the amp issues that have not been addressed. Once we have firmed up the amp a bit more and the team feels ready we will cover power supply issues.


----------



## tangent

Quote:


 in the world of Hi-Fi, looks are just as important as sound 
 

Sure, but shouldn't that be the _last_ thing we focus on?

  Quote:


 Is it bad having them connected to teh ground by traces, instead of directly? 
 

It's probably better to do that than what you originally did. But here's another thing to consider: the TLE's should definitely be close to the ground plane, and in the case of the ground channel it should be near the op-amp's input. Also, do you really want to be running signal traces underneath a bunch of dump-to-ground traces?

 Since the alternatives aren't terribly appealing either -- 4 layer boards or running shielded cable assemblies to the front of the board -- I'm not dismissing your ideas totally. We may end up doing something like that. I'm just saying that it's also less than perfect.

  Quote:


 What's the downside to using [vias]? 
 

Vias act like tiny inductors, and they force the signal to bend sharply. The radiation pattern coming off a via is actually pretty ugly.

 Does it matter? Well, maybe not. But my philosophy is that a via is a sign that you probably haven't tried hard enough to come up with a better route, one that avoids vias altogether. Sometimes you just have to use a via, but so far I've been able to remove vias in my layouts several times simply by staring at it a little harder. And sometimes I have no choice but to use a via, but at least when I give up I know I tried.

  Quote:


 At 18 cells it's going to generate a lot of heat 
 

Yep. The plan is to build some lash-up prototypes after we've nailed some of these niggly amp circuit details down and see how it performs. Then we'll know whether we can get away with 18 cells or not. There are numerous reasons we may have to come down from that number -- it's a good working number, but we may not be able to get away with it. We've got provisional designs for all this already, but nothing that's fit to show the world. It's just enough to convince ourselves that it's practical to even be thinking along these lines. We'll know more when we can spare the time to investigate this in detail. 

 In the meantime, back to the amp. 
	

	
	
		
		

		
		
	


	




  Quote:


 chargers get more complicated with so many cells and usually need extra circuitry to handle it. 
 

Also already under control. We've got three circuits we're looking at, and we have planed experiments on them to find out which ones we want to tell the world about, and which we want to throw away and pretend we never even discussed privately. 
	

	
	
		
		

		
		
	


	




  Quote:


 my vote goes for optimizing traces and not worrying about making everything board mounted, especially if this would eliminate the need for a 4 layer board. i like to be able to see the traces when trouble-shooting and the savings on cost would be nice. 
 

Wow, there's some sanity in the audiophile world! Thanks, puck. It's so easy to propose work for someone else....

  Quote:


 If this is to be a prtable the powersupply size MUST be considered at the same time as the make up of the amp itself. 
 

We're not ignoring the power supply. In fact, we've got some pretty good ideas of what we expect to implement already, just like with the battery board. Just trust that we know that it's possible to power the board reasonably so that we can focus on the amp circuit. I'm sure it seems to you that there are a million things we're ignoring, but in fact it's that we've already discussed those million things privately while we nailed down what you see now, and now we're trying to get comments on these issues one at a time. 

 At the moment, we'd rather be focusing on the amp circuit itself, not on all this casework and power stuff.

 Hint, hint.


----------



## Voodoochile

Ack... I don't even remember if I spoke up on the connectors issue.
 Other than perhaps the volume pot, I'm opposed to board-mounted connectors.

 I'm building Pete Millett's Hybrid right now, just for fun. It's a pretty cool amp, but I can already see that I will be hanging some wires from under the board to lead to panel-mounted jacks in a chassis under the board instead of the topside board-mounted stuff that's on there now. Later, if I really like it. Meanwhile it's all as Pete planned it. Nice for a quick and easy demonstrator, but not sure I would want it like that forever.


----------



## ppl

board mounting the bass boost switch is in line with an optimized layout. One thing that can make a good layout real bad quickly is wires running all over the place. With as much of the wiring put onboard then this can be included in an Ideal board layout and leaves less chance for error on the part of the Builder. I have several solutions for routing the bass Boost foils to the Front of the board and will perpose them to other team members. as it sits now i would have no problem with the headphone jack as it is but would perfer it board mounted. The bass boost i would be more strongly inclined to board mount as this is in the feedback loop and is importent.

 The power supply is not an afterthought on this Amp it is considered in totality and we may offer two choices one for recharging Batteries and another dedicated AC only to include things like EMI filtering and other Trapings. Moreover the power supply can be the users choice like the Schultz that is so popular in some places. As morsel pointed out this issue is moot at the moment and we are just considering our options. the main focus at this time is the Amp proper itself.


----------



## mhamel

I'm on the fence about board mount vs. panel mount. On one hand, the convenience of board-mounted components is appealing. Solder everything to the board, put it into the recommended case with pre-made end panels, and its done. On the other hand, a good part of the enjoyment of building these things, for me at least, is doing the enclosure work and getting creative with it.

 Obviously with board mount pads, there's always the option to panel mount and run leads, so I think ultimately my opinion would be that the main focus should be optimizing the board layout for the best possible performance, then provide board-mount pads for whatever makes sense to.

 As for any sort of pre-made front panel - there probably isn't any way to come up with something that would make everyone happy, so maybe there's a middle ground...

 If the decision is made to make/sell a panel for the 'recommended' enclosure, pick a vendor that would also allow one-offs, and supply links to download the design/layout file. That way those who want a different finish, material, overall size, etc. could download the file, customize it and have their own panel made and those who don't can just buy the standard version along with the recommended parts that fit it.

 Depending on the vendor, maybe they would provide a discount on the service for the first 30 or 60 days to those ordering a customized panel for this project, based on the total business they get from the initial standard order + the various customized orders.

 Building one for myself, I'd want to take the time to get creative and customize. In the case of building one for someone else, I'd probably opt for the standard enclosure with pre-made panels to save build time and money for the person purchasing it.

 I also agree strongly with Morsel about focusing on one part of this at a time. It's important to take the overall project goals into consideration and keep those in mind, but once the amp board details are worked out, then the power supply can be addressed. It seems to make more sense to me to choose appropriate components, have a final design and know exactly what the power requirements are before designing the supply. That way the design of the amp drives the design of the power supply (or supplies, if there are to be options).

 -Mike


----------



## aos

>>Does it matter? Well, maybe not. But my philosophy is that a via is a sign that you probably haven't tried hard enough to come up with a better route, one that avoids vias altogether. Sometimes you just have to use a via, but so far I've been able to remove vias in my layouts several times simply by staring at it a little harder. And sometimes I have no choice but to use a via, but at least when I give up I know I tried.

 From an aesthetic point of view I agree. When I started designing boards, I spent days and weeks "optimizing" the layout in exactly such a way, re-grouping parts, re-orienting chips, moving them from top to bottom etc. This consumed by FAR most of my time. But my philosophy has changed now. Look at what parts do, how could they impact others and how could they be impacted. Group the parts functionally, then optimize the critical traces and then route the rest with what you have left. Do not be afraid to use vias. I read a scientific document investigating effects of vias on impedance, EMI etc. and they concluded that single via on a trace won't change much. Only 3 on the same trace started showing non-negligible change. And we are talking very high frequencies. In an audio amp they are totally a non-issue, except that from my experience you better not trace larger currents through a via if you're using a low quality board supplier as the plating will die. Anyhow I have a huge number of vias in my DAC - between 50 and 100 on such a small board - and having high impedance traces shielded and physically separated from the ones carrying digital currents made all the difference in induced noise, not cutting down vias. Of course if you need to shield a trace then a via might screw your shielding but sometimes you have to do it anyway and shield as much as you can. I'd say don't waste your time trying to get rid of ALL vias. Avoid them on critical path and shield with ground plane but for other stuff, rather keep the part grouping optimal than move the stuff around just to get rid of a via. On, and having properly sized bypass caps where needed. It took me some time, spent with oscilloscope measuring noise, to discover causes of noise and figure out ways to eliminate them but in the end it was not the vias that were the problem, it were too large pot values, not enough capacitance on certain digital chip bypasses, no shielding of certain signals that were actually sending tons of EMI, and no resistors in series with those same signals to have them. But I had a a mixed signal board- your job should be at least in that department MUCH easier.


----------



## tangent

Quote:


 keep the part grouping optimal than move the stuff around just to get rid of a via. 
 

These are not incompatible goals. A via is telling you, "this part is too far away from the other parts that it connects to, and so the trace has to cross a bunch of unrelated stuff to get over there". When related parts are close together and oriented so that related pins are facing each other, the via count naturally drops.

 Your DAC is largely surface-mount, aos. That changes things, because you have to use vias just to get from one side of the board to the other. How many vias do you have that are right at a component pin? That's equivalent to a component pin in a thru-hole design, and that kind is okay. The "capitulation" kind of vias are the ones that you put in the middle of a trace, where you're jumping to the other side of the board just to avoid a trace that's in the way.

 I'm not saying that vias are evil, just that they're a hint. It tells you that you haven't thought the layout through carefully enough.

 Perhaps this will help you to understand where I'm coming from, aos: open your DAC's board file in Eagle, rip up all the routed traces and ask it to autoroute the board. Ensure that you use the default via cost of 99 -- that vias should be avoided at all costs. Then look at the *.pro file and see how many vias it had to use. I'll bet the via count went way up. The point is, an intelligent person did a much better job than the unthinking machine. People are sometimes lazy and machine-like.


----------



## morsel

I agree with Aos in principle, but Tangent also has a point. Digital circuits tend to need many more vias than analog headphone amplifiers.

 I am responsible for the layout. So far I have not used vias or jumpers, but I will not shirk from them if need be. The problem with vias on our layout is that a via can't cross superimposed dual power rails with one voltage on each side of the board. Ironically, we decided on superimposing the power rails to make routing power easier and to reduce noise. We could abandon that approach if there was good reason to.


----------



## aos

>>this part is too far away from the other parts that it connects to, and so the trace has to cross a bunch of unrelated stuff to get over there". 

 Sometimes. And sometimes it tells you that you have too many parts in too small a space. And if you can't change the space size, then you have no other choice than to use a via.

 >>That changes things, because you have to use vias just to get from one side of the board to the other. How many vias do you have that are right at a component pin? That's equivalent to a component pin in a thru-hole design, and that kind is okay. 

 You do have a point here. However I do have a lot of vias that go accross things such as power rails. Some traces you just don't want to break (power rails, primary signal traces etc.) and therefore it's either use a via (two of them actually, to create a jumper of sorts) or trace it all the way around - which ain't pretty or good for the signals. There's often another and very elegant solution however - if there's a through-hole component such as resistor (they're the best for this), then place it over the un-viable trace and kill two flies with one hit.

 All I'm saying here is not to get too attached to idea of no vias at the expense of time and even performance (having traces go around). If you can manage it fine without, that's cool.

 Another thing from someone who did a fair bit of different projects - time needed to build a device which has board-mounted jacks, connectors etc. is typically considerably less than having them panel mount and then solder wires, not to mention not optimal signal-wise. Furthermore, it makes it MUCH easier to test once it's done - you don't have to solder a bunch of wires and connectors just to see if it's working. If you're making one device, it doesn't matter that much (except for testing part) but if you're building many of them you're going to find advantages of board mount very quickly. There's a reason Jan Meier and Headroom do this. HOWEVER, there is one valid argument to mount at least some of the things on the panel - if not doing so would compromise the parts layout and negatively impact the performance (e.g. forcing a RCA jack carrying digital signal right in the middle of the amplifier just because it has to be on the back of the device). In such cases I'd use panel mount. But imagine, you finish soldering, plug in everything to test it, and then just slide it in the enclosure, snap in the front and rear panels, screw the screws and you're done! Instead of spending two-three hours toiling over drill press, measuring and marking and filing and praying you won't make a mistake. That's hard work and one that won't get appreciated at that, in fact quite the opposite as you're not likely to get it to look as good as professionally machine made panel. Unless you're a metal worker and can enjoy it - I am an electrical engineer and love soldering but drilling... and the mess it creates, who has the money to buy a house with a workshop these days?

 I'll try to find some time and see if I'll have any concrete ideas concerning the layout.


----------



## morsel

Disclaimer: I don't benefit financially from the PPA or META42.


----------



## JMS

Thanks for your efforts, morsel, and the rest of the PPA team.


----------



## ppl

One of the Reasons the PPA is designed like it is was to acomidate a two wire power supply while avoiding the Problems of Conventional Virtual ground driver's. Most VGD use an open loop Buffer and most of these devices have a High output Impedance. The Power supply rail capacitors across the rails help to stablize the effects of this High impedance. the Downside is that the Controling impedance is from the capacitors and thus imparting the quality of the cap's upon the sound. moreover since the VGD lacks Feedback large output currents that last longer than the charge available on the cap's to maintain that output current will pull the signal on the VGD twards one rail or the Other. I have thus used large rail capacitors on my VGD Amps and Now use a Current feedback Power op Amp for Virtual ground's.

 The PPA compleatly bypasses this problem by use of the Ground channel. this is pointed out on Morsel's site. To futher remove the sound of the capacitors from the Amp as much as possible. The Electrolytic on the Op amps are from rail to rail. Only Quality Film caps are from rail to ground on the Op amp Supply only. the output Rails are not grounded anywhere, also there is not any cap's from any output Rail to ground. this alone removes a source of Noise from contaminating the ground that is only used for signal. this is the beauty of differential drive. The Current sources along with the TLE's form a voltage devider that attuates Noise by 35 dB, In addition the Current sources will not Pass AC so again improving the isolation.

 Considering the above it makes no sence to me why batteries can't be used evean if a long run time is not possible. batteries are almost the perfect power source, more and more Audiophiles are finding this out and this is showing up in the Number of High End Components that are being powerd by batteries.


----------



## morsel

That was very well said, Phillip.


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## kerelybonto

ppl, can you explain your dislike for output DC servo circuits like the one in Gilmore's dynamic amp? Are you using output caps in the PPA, or what?

 kerely


----------



## Voodoochile

Indeed. Thank you for the added insight.


----------



## ppl

With Most op amps the DC offset is under 1mV even with bass boost, so no Coupling capacitors or servo is needed. and with op amps that have a DC offset that could be a problem I have sugested the ground channel Be Multi-Looped so as the same amount of Feedback that is used on the Voltage gain Channels can also be used in the Ground channel. This will asure that if the same Type of Op amp is used in all three channels the DC offset will still be low since all three channels will have the same amount of offset and so the amount of DC present at the Output of each of the three channels will also be the same. it is this relitive relationship that will keep DC on the Output low with most any Op amp with the possible exception of some Bipolar input op amps that would produce several volts of DC offset. in this case i would not use myself or recomend such a device. 

 The PPA followes one of my hard and fast design rules that operating parameters be natural to the device and everything work together in Harmony with out band-aids. It should not be required to correct problems that should not be present in the first place with additional circuitry. 

 maintaining simplicity, while obtaining the desired result is IMHO the true measure of an Elegant design. The Amp should also not be required to correct for problems in the source components, so if the source has DC upon it's output it is to be considered defective and repaired or replaced but surly not used with any Amplifier DC coupled or not. I think I have been hear before


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## morsel

Kerelybonto, you can see from the schematics and large gif of the layout viewable at the PPA website that there are no output or input caps.

http://elvencraft.com/ppa/

 I'm going to repost the following paragraphs from a few days ago because I was really hoping for feedback on this:

 We are seriously considering separating signal ground from opamp power ground with a 10 Ohm resistor and possibly a small cap in parallel to further reduce noise and hum. To break ground loops between the amp and other equipment we might want to put 10 Ohm resistors in series with all input connections as well.

 I have tentatively split up the ground connections into two groups, let me know if you think any of them are in the wrong group:

 signal ground connections:

 input grounds
 pot grounds
 opamp input resistors
 opamp feedback resistors

 power ground connections:

 opamp bypass caps
 TLE output
 ground plane
 case
 pot shaft and panel switches


----------



## puppyslugg

Hi morsel,

 I wonder if the pot shaft is in the right group? *shrug*


----------



## aos

I originally wanted to separate digital and analog grounds in my PDAC with a 10 Ohm resistor (as I have done before in someone else's design where it worked) or with a ferrite. Once prototype was built, I could hear and measure the hum with resistor which would go away only if a jumper was used instead. In the end I had ferrite beads on rails but not on grounds, just had them directly connected with a jumper at one point. I guess this is something that is of more experimental nature. Leave the place for resistors since you can just as easily put a jumper, and then experiment with oscilloscope in your prototype and figure out what works best. I hope you're not expecting the very first board to perform 100% 
	

	
	
		
		

		
		
	


	




.


----------



## morsel

We have been testing the first prototype for some time now. I am looking for feedback on the pros and cons of separating signal and power supply ground, and whether the two groups I split the various parts into sounds reasonable.

 PS, the pot shaft makes contact with the case so clearly it is in the same group as the case. The case shields the amp from external noise, so putting it on signal ground instead of power supply ground is probably not a great idea. Of course, if the grounds are not split then signal ground would be power supply ground so this point would me moot.


----------



## Whit

I have a few questions regarding the charging circuit. Are the circuits you're looking at a rapid charger or a slow trickle charger? Also, since the max voltage attainable by 18AAA NiMHs is 21.6V doesn't this rule out the AD843? Will it have some sort of thermal protection for the batteries? I've read that if the temperature exceeds 120F then the charging cycles of the battery is greatly reduced.

 Whit


----------



## tangent

Quote:


 Are the you're looking at a rapid charger 
 

With NiMH, the proper cycle is a constant high-current charge to a certain point, then dropping to a trickle charge which (ideally) cuts off after some period of time. The latter step may not be part of our design. The first two steps definitely will be.

 This is why we're talking about building our own power supply: there are several commercial supplies in the 30V/0.25A range, but what we probably need is a 28V/0.75A or 32V/0.5A supply or something strange like that.

  Quote:


 since the max voltage attainable by 18AAA NiMHs is 21.6V doesn't this rule out the AD843? 
 

Who says the 843 won't run on 21.6V? I find that it does well down to about 12V. Also, 21.6V is not the max voltage, that's the running voltage. They start well over that, drop quickly to 21.6V, then later drop quickly to about 16V before they're deemed "dead". We stay above 12V the whole time.

  Quote:


 Will it have some sort of thermal protection for the batteries? 
 

We have that option if we choose to add it. Whether we do or not depends on whether we have enough space or not.


----------



## aos

Wait, I'm getting confused here (blame my co-worker who is delaying our coffee break) how could the grounds be not split, isn't the separate multiloop buffer what creates signal ground from power ground, so they cannot be separate? Also, I wouldn't necessarily make a pot case being power ground instead of signal ground a big deal. Take oscilloscope and measure. You can't avoid doing that unless you're a genius 
	

	
	
		
		

		
		
	


	




.

 tangent, as far as I know Maxim charger chips have that two-cycle charging protocol so it's not something you need to worry about - unless you were planning on not using a dedicated charge controller chip.

 Also, why do you need the +- regulator when you are generating your own (virtual) ground? Or am I missing something?


----------



## tangent

Morsel's talking about a 3-way split. Currently there's the ground channel and all the other grounds. She's talking about splitting the latter set into two.

 And yes, we're aware of the charge controller chips, and again we're straying from the issues we want to talk about right now. We don't want to get off on this side track yet. Again, we're not ignoring the battery board; we've thought about all of this already and we're satisfied with its current provisional state. We can talk about implementation details later.

 FWIW, we've already eliminated the MAX712/713 series.


----------



## Whit

Quote:


 Who says the 843 won't run on 21.6V? 
 

Sorry. I didn't mean to imply that it wouldn't work, just that it might not work well. PPL said to not even consider using the 843 with less than +/- 12V in this thread:
Meta42 builders.. help me choose a new opamp 

 This is what I based my reasoning on.

 Whit


----------



## tangent

He's talking about for best performance of the op-amp. He's right, but that doesn't mean the op-amp totally sucks on 21V. It's not the "reference" chip for this amp on batteries anyway. It's just something that will work if you want to try it. For most uses, we recommend the 8610 instead.


----------



## aos

From what I saw so far you are asking for trouble if you're going to splice the ground so much. There's no substitute for experiments and I have to add the standard disclamer for my brain cells, but I wouldn't do it that way.


----------



## ppl

Thanks for all your input Folks. I can totaly relate to the grounding concerns that aos has. Splitting grounds can be a problem and this gets more importent with Mixed signals like a DAC. I however had great luck isolating the Analog and Digital ground on my Old magnavox CD player I upgraded years ago. A jumper was even provided on Board so it involved removing the Jumper and replacing it with a 4.7 Ohm Resistor. This reduced the digital noise present between the I/V conv. Op amp's + & - inputs by 20 times less than it was as viewed on my old analog scope.

 The Ground as it is now in the PPA works and is quite stable. Measured performance of the Amp like THD and the like are low enough that it is unlickly that any instability is going on or it would show up. However i have on other Amps needed an isolating resistor for the Input Ground. I now do this by default and as of yet has not caused a problem (See schematic pocket amp attached) while the pocket amp used a full ground plane it like the PPA worked quite well without the resistor R8 in the pocket amp's Schematic. But on the PPA, if it works why mess with it. One could logicaly state that age old saying "if it Ain't (IS NOT) broke don't Fix it".

 Fried brain cells LOL Boy I sure can relate to that.


----------



## morsel

I am working on a 4 buffer per channel version with one row of (8) 500mil diameter caps but no separate signal and power supply ground. Normally I bang these layouts out pretty quickly, but various distractions are keeping me occupied atm.

 Back in META42 days there were many layout objections, most of which we had to ignore due to space limitations. Does anyone have issues with the current layout?


----------



## jcx

Too many grounds!

 I would loose the L&R TLE2426 and split C3 into 2 big-ish Caps screwed into signal ref ground (with C4+/-), op amp power is best referenced to the signal and feedback reference ground and given the high impedance load provided by the buffers I wouldn’t worry about the op amp contaminating the quiet ground

 OC is then connected to (and the source of signal reference ground) by a fat trace that carries none of the output current – this is the center of the “star” ground, large headphone currents to the left, quiet signal and feedback reference ground to the right
 (re layout V0.014 4th? page this thread)

 Then inspection of the actual output buffer-headphone-OC buffer current loop suggests that the power distribution traces should move much closer to the buffer chips – if you want to get fancy the power could be distributed by a balanced quad transmission line structure to reduce the external magnetic field (just run another top/bottom power pair as close as possible to the present pair with +/- switched top to bottom) – vias required to balance the power taps at each buffer – an alternative low EMI power distribution structure that uses only one side of the board is to sandwich one double width power trace between two closely spaced single width traces of the opposite power polarity: 0.060” board thickness is actually a rather large magnetic field radiating gap compared to 0.010” surface trace separations

 Local SMT cap patterns near buffer and op amp power pins also could be helpful – NP0 ceramic is available up to 0.01 uF which is much more appropriate to bypassing 100 MHz buffers than any leaded cap, the complete film snob could use PPS SMT caps

 with nothing more than trace resistance and inductance separating the 3 big Cap pairs, there is little added by this physical grouping, I would rather see just 2 pair situated astride the (much shorter) power connections between the OC buffers and the 2 output channel buffers, if AC power adapters are to be accommodated, a 3rd pair at the board power entry with some RF suppression options might be good


----------



## morsel

Thanks for your detailed post, jcx. Your email address is not in your profile, send me an email so I can reply to you offline.


----------



## ppl

jcx. why would you not use the separate Power rails for each opamp. this creates greator isolation between Op amp Channels and thus should provide better channel seperation.The other sugestions seem Ok to me. Thanks for the sugestions.


----------



## jcx

I think the op amp power supplies are somewhat separated, the Q3 series fets (given their nonlinear triode mode operation and huge part-to-part variations) provide isolating series impedance, better IMHO would be current sources working into shunt regulators with the capacitance multiplier being a good compromise that doesn’t require so much headroom and automatically adjusts to the battery voltage

 My question would be what is voltage induced in the quiet ground by different arrangements?

 A capacitance multiplier could easily have 2-5 KOhms series base resistance that forms a divider (at audio frequencies where the filter cap is an AC short) with the quiet ground return resistance of ~10-20 milliOhm? giving at least 100 dB attenuation of power supply (load current induced) ripple which itself is attenuated by the ratio of the supply impedance to the load; say 200 milliOhm?(will vary with battery size, chemistry and stacking) vs 16 Ohm(lowest Z headphone I’ve heard of) for another 35 dB – together this gives ~ -135 dB surely enough power supply/channel isolation for portable audio

 Even with 100-200 Ohms of Q3 fet incremental resistance (or linear, precise real resistance) the distortion from this coupling at -110 dB still betters any CD source S/N


----------



## morsel

Hi jcx,

 We talked about using capacitance multipliers instead of FETs to isolate the opamp rails. We decided to start with the FETs since they are simpler and only move to the CM model if necessary.

 As to your question, we are waiting for the test results. Tangent has a long list of tests to perform. He will get back to us when he is ready.


----------



## ppl

jcx> My first suggestion was capacitance multipliers. My early portable Amp designs all used capacitance multipliers in addition to Current sources. yes this gives the virtues of voltage regulation with out the Dropout concerns of voltage regulation yet still provides Isolation for the op Amps from Power supply Noise.

 As morsel pointed out The use of only current sources was chosen because of low parts count. the PPA must remain affordable and most of My designs tend to be not cost bared approach so this compromise was reached if it were only up to me this amp would have capacitance multipliers on each op amp rail and a current source and TLE for all the Op amps. 

 Regarding the use of isolating each op amp with separate TLE's and current sources my listening tests show that this gives better Imagining and space localization than just one. I did not measure the Difference since while measurements can be useful I am a subjections type of person. that After seeing many Amps test the same yet sound totally different over the last few decades I have tended to place sound quality first and measurements last. However the Preliminary measurements on the PPA with all op amps operating on one rails produces great numbers and using separate isolation on each rail should improve channel separation somewhat. it still sounded noticeably better than just one isolation for all the op amps. Thanks for your input


----------



## was ist los?

What's a rough estimation of the cost of a fully completed PPA?


----------



## JMS

...and how much longer till completion?


----------



## morsel

According to the PPA website:

  Quote:


 There is no ETA on boards as it will take months to complete development. 
 

It is hard to give a good cost estimate since we are still working on the design.


----------



## jamont

I'm just curious, have you made use of circuit simulations (like PSpice or Micro-Cap or similar) in the design of the PPA?


----------



## morsel

I only used MicroCap to come up with the bass boost graph and equations.


----------



## tangent

Quote:


 Tangent has a long list of tests to perform. 
 

I've more or less finished all of them now. The results are online now on my PPA site.

  Quote:


 What's a rough estimation of the cost of a fully completed PPA? 
 

Probably the bare minimum for parts will be well over $100. Current estimates put parts costs in the $200 range for a typical configuration. It may well go higher, but it should stay under $300 for a pretty well maxed-out PPA. Specifics depend not only on the circuit features we eventually end up with, but also on things like what kind of panel components we agree on, what kind of case stuff happens, what kind of power systems we support, etc.

  Quote:


 how much longer till completion? 
 

"Are we there yet?" 
	

	
	
		
		

		
			





  Quote:


 have you made use of circuit simulations (like PSpice or Micro-Cap or similar) in the design of the PPA? 
 

Full system sims, no. ppl has probably simulated most aspects of the circuit separately, though, and Morsel and I have been playing with simulations of the bass boost circuit in order to better learn how to describe its action to you. You can see some of the results of that at Morsel's site, and eventually when my documentation comes online there will be many more graphs.


----------



## aos

Now that you have some results and some input (only about 9 pages 
	

	
	
		
		

		
		
	


	




 ) you might want to open a follow-up topic instead reusing this one as it's getting out of hand. Your presentation of results is cool by the way. I haven't managed to get meaningful results with my soundcards yet, I keep getting at most -80dB noise with M-Audio Revolution and as low as -67dB with SB Audigy (platinum) so results are pretty much useless. How do you set levels in the mixer? I'm also guessing a pretty substantial shielding of the 3.5mm minicable is required.


----------



## tangent

Quote:


 you might want to open a follow-up topic 
 

Back when we did the META42, we had at least half a dozen threads spread over two forums and each thread spawned the same questions over again and we'd have to keep pointing people to the previous threads.

  Quote:


 I keep getting at most -80dB noise with M-Audio Revolution 
 

It might be educational for us if you post the test results of a simple loopback test, and we can compare them with other RMAA tests of this card.

  Quote:


 How do you set levels in the mixer? 
 

The Revolution comes from an entirely different division of M-Audio than the Delta series, so I don't know if this applies: but on the last tab of the M-Audio mixer applet/control panel, you have the option of choosing between +4dBu, Consumer, and -10dBV levels.

  Quote:


 I'm also guessing a pretty substantial shielding of the 3.5mm minicable is required. 
 

That's one of several advantages of the Delta 44: it uses 1/4" mono jacks instead of 1/8" stereo jacks. You can readily get pro-quality instrument and patch panel cables that are well-built and well-shielded in this style, but decent 1/8" cables are rather harder to find.


----------



## aos

>Back when we did the META42, we had at least half a dozen >threads spread over two forums and each thread spawned the >same questions over again and we'd have to keep pointing >people to the previous threads.

 But of course. Where's the challenge otherwise? Also when you have everyting in one thread it is very hard to find what you want as you defeat the topic interface. But I'll live with ultralong thread if I have to.

 I will do loopback tests again. I did it several times already and was never happy. Input mixer has a slider and naturally as you slide it up the noise floor goes up too. When it's at the bottom, it's probably at gain=1. There's dB rating on the scale but it's tough to read and possibly more of a decorative gimmick than really a useable metric. Using one of the real-time spectrum analyzer programs M-Audio looks like it has way better noise floor than Audigy but then you must have equal input gain set for both for the comparison to have any meaning.

 I guess one of the benefits of professional card is that you have calibrated input/output settings. I thought Revolution is at least semi-professional - the SOLE reason I got it is to do these measurements - but from the drivers you wouldn't say that.


----------



## tangent

That other M-Audio division I spoke of is the consumer division. No, not even semi-pro. The only thing to recommend that card (besides all the 7.1 and gaming BS) is the fact that M-Audio put their stamp of approval on it. Which means it doesn't completely suck.

 Seriously, you should be getting better results than that. Here's a RightMark test of that card vs. some others:

http://members.cox.net/deadduck/Comparison.htm


----------



## aos

Gaming BS? Gaming is the PRIME reason to choose a particular soundcard for general usage (hence Audigy in my system). Games are where the fun is.

 Those measurements imply that the card is actually pretty good - comparative to your professional one. However, this tests the output side only, not the input side, which was the reason I bought the card anyway.


----------



## erix

Quote:


 _Originally posted by tangent _
 Back when we did the META42, we had at least half a dozen threads spread over two forums and each thread spawned the same questions over again and we'd have to keep pointing people to the previous threads. 
 

And, as we all know, the META42 turned into quite the little commercial venture. 

 I mean, you are the person making the boards.
 You are the person selling the boards...

 Doesn't that make you a manufacturer or "Member of the Trade"?

 From the Head-Fi Posting Rules and Terms of Use

  Quote:


 "Member of the Trade" includes manufacturers, dealers, distributors, manufacturer's representatives, importers, magazine and e-zine writers and others. 
 

 Quote:


 "General Forums" are those forums within Head-Fi not specifically designated as areas for commercial advertising by Members of the Trade. 
 

 Quote:


 A Member of the Trade may not volunteer any information about a specific product that he is selling or making, in response to a general request for information about a type of product or in any other discussion in the General Forums 
 

 Quote:


 A Member of the Trade may not post announcements, advertisements, sales information or the like about a product he makes or sells in the General Forums. 
 

 Quote:


 Head-Fi is most definately NOT anti-trade. In fact, trade members are a welcome and vital part of the Head-Fi community. However, Head-Fi's General Forums are not the place for self promotion and advertising of audio products or services. 
 

Justify this thread.

 ok,
 erix


----------



## aos

The fact that schematics and PCB layout are available for everybody's use. Discussion is limited to technical discussion which is explicitly allowed. You can make this amp yourself and sell it if you wish (or maybe not but you can certainly make one for yourself without buying anything from META team). It can be hard to draw the line but if you didn't have discussions like this than this forum (DIY) would be completely useless as you wouldn't be able to post (almost) anything.


----------



## Squalish

erix - I'm curious where we draw the line too.
 3 examples:
 Voodoochile sold 5 assembled meta42 boards via FS forum, with all onboard components.
 Jiggler got his FS post for an RA-1 clone, cased and finished, deleted.
 Subsonic's gilmore PCB group buy, which ended up being nonprofit, but had the possibility of being profit, was removed.

 Tangent does have a mall-fi ad, but I think members of the trade aren't allowed to make announcements about products.

 Of course, I'd prefer to have all the guidelines less strict, and I detest the information wasted when one of these big threads(same thing happened with subsonic's gilmore PCB thread) is removed, but within the rules, I don't know about the validity of this thread.


----------



## morsel

Quote:


 Justify this thread. 
 

Erix, this is my project and my thread. As I stated before, I don't benefit financially from the PPA or META42. Since Tangent sells boards and parts he has to watch what he says, but I do not. Tangent has a real job and only makes enough to cover his costs, time, and trouble. He is not getting rich selling META42 boards. We do this so the community can have access to cheap good DIY amps.


----------



## puppyslugg

Quote:


 _Originally posted by morsel _
*We do this so the community can have access to cheap good DIY amps. * 
 

For that, I applaud you and the PPA Team!! 

 Not only is the Meta relatively inexpensive to build, it also performs as well or better than many commercial products. I have even higher expectations for the PPA!!

 Thanks!


----------



## Voodoochile

Quote:


 Voodoochile sold 5 assembled meta42 boards via FS forum, with all onboard components. 
 

FWIW, those were all used amps, in essence. I built them for my own purposes, to my specs. When I was finished with my testing activities, I needed to 'lighten my load'.

 I guess my posture is that they were not built to order, nor was it a solicitaion to build to order.

 I will likely do the same with the PPA, but not on the same scale, for sure.
	

	
	
		
		

		
		
	


	



 Edit: I apologize for posting this here- I don't mean to drift all over this thread. Just wanted to offer some clarity from my perspective. I'm not defensive, and have no issues with squalish or anyone else, for that matter.


----------



## aos

I managed to get RMAA and M-Audio Revolution to work. I'm getting very decent results - in loopback, at 32bit/96kHz, noise level is -102dB and dynamic range is 101.5dB, THD is 0.0024% and IMD 0.0067%, stereo crosstalk -100.7dB, and the results when using an amp are just slightly worse (except for stereo crosstalk), so I'd say this card can be used for measurements.


----------



## Voodoochile

Quick question: The stereo crosstalk results, particularly with the Grados... any thoughts on the META's relatively poor showing there?

 In the tests, the Meta seems to hang pretty close, all in all, for a little guy. Just wondering what that is attributed to, if you know.


----------



## aos

Quite simple, when you have a heavy load, large current will flow through the buffers and hence through the power rails too. If the rails for different channels aren't isolated, and if the power supplies have impedance - and they always do - this signal will feed through to the other channel directly through the shared power rails. This effect is reduced the lower the impedance of the power supply (or virtual ground driver). META42 uses relatively high impedance open loop buffer, and therefore capacitors between ground and rails are there to help minimize impedance. But in the end some of it makes to the other side. That is why you have those FET isolators in PPA, to isolate chips from one another and among other things decrease crosstalk, and a dedicated ground channel driver helps reduce power supply impedance through wonders of negative feedback (open loop buffer alone can't achieve such results and what's worse, it varies with load). The other solution (which I employed) is to use separate voltage regulators for each channel, and this also works very well. By the way, what is Grado SR-60's impedance?


----------



## Voodoochile

32 ohms, I'm told.
 That all makes some sense to me, believe it or not! Thanks, aos.


----------



## KJ869

I would like to have crossfeedswitch options: off, litle,medium, full. and 1 switch for the powersource would be nice if you want it to be userfriendly all around amp: Battery, recharge, Wall. Just to make it more handy


----------



## Squalish

Quote:


 _Originally posted by KJ869 _
*I would like to have crossfeedswitch options: off, litle,medium, full. and 1 switch for the powersource would be nice if you want it to be userfriendly all around amp: Battery, recharge, Wall. Just to make it more handy 
	

	
	
		
		

		
		
	


	


* 
 

I believe the Modified Linkwitz Crossfeed, which is my guess as to what will go on here, if anything(tangent already sells them to go with the meta), has two 2-position toggles in addition to an optional bypass toggle, making 5 different positions. They don't correspond exactly to low, medium, and high, look into it.


----------



## Squalish

It just occured to me that if one wanted badly to miniatureize this(and wanted it enough to fabricate their own PCBs), making each channel a daughterboard, with sockets, wouldn't be too hard. I figure each channel is about 1.5" wide, that would form the height limitation. The width limitation would be either the diameter of 6 C1 caps(these could possibly be arrayed along the motherboard between daughtercards, for only 3x diameter, but one would have to add board component height), or the height of 3x the board components, whichever is higher, plus the side stuff for power, volume, etc. It's hard to describe what I'm visualizing, but the boardmount stuff could be behind the ground plane, and one could use thick guage wires or ribbons to connect each ground plane. Or, just use one on the motherboard.

 Of course, this is infinitely more complicated than a single board, and it would introduce dozens of design problems I know nothing about, but it is an interesting topic. I figure the end result might just fit in a 4x5x1.5" box.


----------



## Squalish

sorry, bad post


----------



## Squalish

Visualization of above idea:


----------



## ppl

The Board on this amp is a Eurocard size and that is about 4"" X 6" and if you have not looked on tangents site yet the Board is quite populated as it is. regarding crossfeed we have not ruled out this but it would be hard to acomidate since the caps are 30 MM and come up to the top of the Hammond case and the battery board is below the main Board thus taking making this amp a tight fit. Our gole for the PPA is all sound with Minimum frills. Cross feed can be added on later or an external box. mabe a external cross feed plus Eq could be devoloped.


----------



## tangent

Quote:


 I believe the Modified Linkwitz Crossfeed, which is my guess as to what will go on here, if anything(tangent already sells them to go with the meta), has two 2-position toggles in addition to an optional bypass toggle, making 5 different positions. They don't correspond exactly to low, medium, and high, look into it. 
 

CMoy designed the modified Linkwitz to use two DPDT switches for control, but Scott Lindeman figured out two different ways to use a rotary switch instead. And since you can simply add more S1s to get different crossfeed levels, 4-setting crossfeed is entirely possible with this circuit.

  Quote:


 the Board is quite populated as it is 
 

Certainly we won't be putting crossfeed on the main PPA board. Like with the META42, it will be an add-on PCB, but it probably won't be the same PCB as for the META42, since the space constraints aren't the same. Likely it will be larger, and it will have wire pads set up to make the rotary switch setups simpler to implement than on the META42's crossfeed board.

 But, this is not really on the radar at the moment. All we plan to do in the immediate future is figure out what kind of mounting options we want for the daughterboard and then table the issue until the PPA is closer to being finished. Then we may come back and hack out a crossfeed board to match up with that mounting scheme.


----------



## ppl

And there you have it from the Project leader. tangent is great at knowing what will fit. so the cross feed is his deal as I my self do not like cross feed. maybe one day ill hear one I like.


----------



## morsel

PPL, I am the project leader. 
	

	
	
		
		

		
		
	


	




 Speaking of which, check out the new v0016 board and schematic I just put up on the PPA website:

http://elvencraft.com/ppa/

 Changes:

 4 buffers per channel
 moved C2
 one row of C1 and less of them (from 12 to 8)
 rearranged the power bus
 2 C3 per channel
 rear input pads brought in behind the no fly zone
 power pads and diodes rearranged
 spacing between major component blocks changed

 Resistor values were lowered since 3M Dale Vishays cost 10x more than 1M and below. Gain of the ground channel was reduced from 2 to 1.004, pending removal of R3G and R5G after we finish testing the proposed ground channel changes.

 Let me know what you think.


----------



## ppl

Sorry


----------



## dta116

Morsel,

 Just took a look at the schem. and there are questions....

 What is the purpose of r7-c5 in the L-R channels and not in the Ground channel?

 Why 4 output buffers?

 The Layout is too small to see if the Low-current Power section is parralleled to the High-current section. and the purpose of two FET's before the rail splitter.

 I guess I could wait for Tangent to finish his write-up on his website.......but hey! i'm impatient...

 Not really, but I am curious. 

 Thanks.


----------



## dta116

Nevermind the r7-c5 question, I got stupid......

 Bass Boost !!


----------



## tangent

Quote:


 The Layout is too small to see if the Low-current Power section is parralleled to the High-current section. and the purpose of two FET's before the rail splitter. 
 

Look at the VL and VH symbols on the schematic. These are telling you that VL is derived from VH, and the two are separated by the JFETs. The JFETs isolate the low-current rails from the high-current rails, so that any ripple and such induced in the high-current rails does not bother the op-amps. This isn't quite the same thing as entirely separate supplies for each chip, but it is close.


----------



## morsel

4 output buffers per channel results in lower output impedance, superior control of low impedance drivers, and increased resistance to output shorting, greatly reducing the possibility of blown output devices without having to add output protection.

 The layout is 600x950 and shows all details. It seems people are not scrolling down to look at the full size layout. I am including the layout and schematic inline. Sorry for the waste of bandwidth.


----------



## dta116

Okay, clears that up, 

 Why not dual opamps.....?

 Why not stack the buffers rather than discrete......?

 Just more stupid questions.

 The value of R1, why a precision value in series with a pot?

 Thanks again for putting up with a dense mind.....


----------



## tangent

Quote:


 Why not dual opamps.....? 
 

Because this is a high-end amp.

  Quote:


 Why not stack the buffers rather than discrete 
 

You can't safely stack the HA3-5002.

  Quote:


 The value of R1, why a precision value in series with a pot? 
 

To balance the resistances seen by the two op-amp inputs. 4.32K == 3.3K + 1K (R5 + R3)


----------



## morsel

Single opamps have less crosstalk, thermal coupling, and enable the channels to be completely separate and use separate power rails.

 The HA5002 needs either input or output resistors or parts matching, otherwise they would fight each other and get too hot when paralleled. The BUF634 can be stacked, but does not sound as good.

 R1 is part of the standard Jung multiloop configuration. R1 = R3+R5, R2 = R6, so both opamp inputs have the same impedance. Gain = 1+(R4/R3). You can read about this on many past threads and on many websites.


----------



## dta116

Okay, I'll leave you alone now.....

 I have learned more in the past hour about amps, than the last 2 months fiddling with these things....

 Thanks a bunch..


----------



## aos

4 per channel really looks like overkill. 16 buffers per amp? Most suppliers only have that much in stock, what's the chance people will be able to actually buy these chips and use them? Not to mention the cost. I suppose one is free to only solder one or two so the rest is for fanatics, which is fine, but then there's the issue of space that's wasted if you don't use them. I mean don't get me wrong, overkill is fine, I do it myself often, but it only makes sense if you do all out overkill, on all issues. For example, those high speed buffers could really use some film bypass caps in addition to electrolytics, as electrolytics are not much good over a MHz or two. Also, to take advantage of low impedance you get by parallelling all those buffers, certain traces should probably be made wider to lower trace resistance also. And last but not the least, a regulator before the virtual ground split (regulating the difference between + and - rails) would help a lot in keeping noise dow, ripple down (if using AC, and many will) and keeping channel crosstalk even lower. Amps that have these regulators also have great sounding bass. From tangent's measurements PPE already looks good, and adding buffers will help cut THD down when using very low impedance loads (for high impedance 2 is quite enough) but to get extra dB in other measurements you'll have to go overkill on those other fronts too.


----------



## morsel

Hi aos,

 I thought it has been well established that 4x buffers sound better than 2x, unless you are lucky enough to have some discontinued EL2009 buffers left over, in which case you only need 1 per channel. BTW, it's 12 per amp, not 16, and sure, you could omit some to save money.

 The buffers do have film caps next to them, one for each channel. Wima MKS2 50V 1 to 6.8µF can be used. Voltage regulation will take place in the power supply, which is not being worked on at the moment.


----------



## aos

Damn, I can't even multply any more. 3 x 4 =12, not 16.

 From measurements - tangent's and mine - even a single buffer is enough for high impedance phones, two is great and even for low impedance you still get what 0.03%, and at volumes you are certainly not going to listen at. So even 3 buffers would be overkill except maybe for low impedance cans. 3 might make sense, 4 is one too much. You know the drill, first extra gives you 100% improvement in output impedance, second 50%, third 33%. This doesn't translate linearly into lower THD (because you get THD 10X better when going from 1 to 2 buffers) but the trend is diminishing. It's not a big deal because you don't have to use them but if you do run out of space it's something to be rid of.

 Film caps you are mentioning are between rails, not between rail and ground so I don't think they constitute an actual chip bypass. I think I've read somewhere that this isn't the same. Unless I'm not seeing right again.


----------



## tangent

Quote:


 Most suppliers only have that much in stock 
 

Newark's got 800 in stock, and I may be supplying them as well.

  Quote:


 Not to mention the cost. 
 

5002s are less expensive than the EL2002, almost as cheap as the EL2001. It's only going to be about $45 in buffers if you max it out, and as you say, many people will choose not to max it out. And on the other side of the coin, there are META42s out there with more than $45 in buffers in them.

  Quote:


 Film caps you are mentioning are between rails, not between rail and ground 
 

There are two "ground"s in the PPA, and you wouldn't want to bypass from the high-current rails to either of them. We'd have to change the design to get a ground we could bypass to.

  Quote:


 certain traces should probably be made wider to lower trace resistance also. 
 

The power traces are already 50 mils wide. That's sufficient for about 2 amps continuously according to ExpressPCB. From memory, impedance is under an ohm per inch for that wide a trace.


----------



## morsel

Aos, you see correctly, C2 film caps span rail to rail, but they are supposed to. The buffer outputs are referenced to each other, not to signal ground, so it would defeat the purpose and principle of the PPA's differential output to bypass the buffer rails to signal ground. I realize there is some controversy on this point.


----------



## aos

Somebody with more industrial experience should chime in here but from what I heard, you do need to bypass chip's rails to ground. Bypassing between rails might either have no effect or even do harm.

 And 1Ohm per inch sounds quite high if your four buffers achieve similar value. That's why I suggested widening traces. Ah, the goodness of gooey, thick copper....


----------



## tangent

I said _under_ 1 ohm per inch. Turns out that that's way conservative. I did some research and a 50 mil wide trace of 1.25 oz. copper (ExpressPCB's standard weight) is about 80 milliohms per inch. I don't know if this counts inductive impedance or not. Probably not, since frequency wasn't a factor requested by the program I used to calculate this.

 By the way, can anyone tell me what an "Ohm-cm" is? It's related to this concept of resistance per unit length, but I should have thought that it would be Ohm-cm^2, since you have to take into account the cross-sectional area of the conductor. So, is this implicitly cm squared, or what?


----------



## ppl

Bypassing the Buffres rail to rail was done hear to keep high current spikes off the system ground that is the input ground. On the opamps bypassing to ground is ok because of ultra-low Currents. on the output stage currents can get high quick.

 My complaint is that the one Bypass cap there is is located to far away to be effective. I am in agrement with aos hear if deliting one buffer results in the ability to put that bypass cap close to the Buffer proper supply rail fiols the by all means do it that way. As it is the previous versions had fewer buffers but alot better high frequency performance due to the bypass cap being located close to the supply pins


----------



## Arzela

Quote:


 By the way, can anyone tell me what an "Ohm-cm" is? 
 

One formula for resistance is

 R= p L/A,

 where A is cross sectional area, L is
 length, and p is the "resistivity' of the material, it has units Ohm X length...


----------



## Voodoochile

That is what I was referring to in my last PS tweak thread, where I moved an adjust resistor closer to the adjust pin, and moved the diode further away. The datasheets refer to the resistance of the trace and component leads themselves as having undesirable effects, and that you ideally solder the adjust resistor directly to the reg lead. Certainly it should be the first component on the trace, not the second. The schematic remained the same, electrically, either way.

 Not that this little sidebar is directly related to this project, but rather the concept of Ohm-Cm comes into play in the example. I do not profess to fully grasp the gymnastics of the formula, but rather it was a very simple tweak that made a measurable improvement in regulation. Not calcualted beforehand, though.


----------



## morsel

PPL says:  Quote:


 As it is the previous versions had fewer buffers but alot better high frequency performance due to the bypass cap being located close to the supply pins 
 

 How can you say this when you have not even TRIED it yet? You agreed to test this when we spoke yesterday. Unless you pulled an all nighter and didn't tell the rest of the team about it, this is a rash and unsubstantiated conclusion.

 If there are no instability issues there is no reason to sacrifice other functionality to get C2 1/2 inch closer to the buffers. Go do your tests, let us know, and we will continue discussing bypassing alternatives such as SMT PPS caps.


----------



## erix

Quote:


 _Originally posted by morsel _
*PPL says: How can you say this when you have not even TRIED it yet? You agreed to test this when we spoke yesterday. Unless you pulled an all nighter and didn't tell the rest of the team about it, this is a rash and unsubstantiated conclusion.

 If there are no instability issues there is no reason to sacrifice other functionality to get C2 1/2 inch closer to the buffers. Go do your tests, let us know, and we will continue discussing bypassing alternatives such as SMT PPS caps. * 
 

Uh Oh. 

 I smell trouble at the factory...

 entertained,
 erix


----------



## ppl

I decided the concept of locating the bypass caps so far away is not in agrement with most of the Electronic comunity. I decided not to waist my time and test such an abserd concept, of removing the bypass caps However You or tangent can feal free to do it since 

 Moreover speaking of not informing the team i was never informed by the team you were evean considering this untill the board was reliced and it was locked in stone so no i do not approve of the board as it is and feal no reason to jump off a clif with no shoot since operating a wideband chip with out a for of bypass is a rediculus concept i do not indorce and i am sure the DIY comunity hear is in agrement with this


----------



## morsel

PPL, nothing is locked in stone. You OKed moving C2 and then changed your mind after it was done. Let's take this offline.


----------



## jamont

I'm starting to enjoy this...


----------



## tangent

Thanks for that formula, Arzela. It's now clear to me why the resistivity isn't given in square units.

 It was helpful in another way: I re-ran the numbers using info from a reference data book and came up with the same value, except that I misstated it above by an order of magnitude. It's 8 mOhms per inch for a 50 mil trace in 1.25oz copper, or 10 mOhms for 1 oz. copper, assuming resistivity of 1.7241 uOhm-cms. (1 oz. of copper is 1.4 mils thick.)


----------



## aos

Compare that to 15mOhm you can get from some capacitors, and probably less from pure film caps/ceramic caps, and you'll see why widening the traces is good. It might be impractical for PPE though as I see you route them between DIP pins so that limits their size. However you can still widen them in parts that are away and between chips.

 Some of these things look irrelevant when running on batteries and away from EMI sources, but try to add a digital device feeding off same power rails and sending spikes down, have some digital signals withing few inches, and have it all run off your $5 wallwart and you'll see how quickly noise goes up.

 It can be hard changing something you made but to quote an old friend, a good writer dares to take a piece of his work and throw it away and rewrite if necessary. It can be heartbreaking but it has to be done sometimes. Until one gains experience, a lot of trial and error will happen.


----------



## jcx

Why should # channel buffers = # ground buffers? Low frequencies (which will have the highest amplitudes) will normally be correlated, both L/R channel amps will be pulling the ground buffers the same direction, resulting in 2X current in ground vs each channel; 4 ground buffers are required to match 2 buffers per each L/R channel – not that I see any need to rip up the “extra” buffer patterns; just consider it a stuffing option, some people might use 1:2, 2:3 or 2:4 channel:ground buffers

 Bypass controversy can be addressed by several means; adding second “C2” between buffers and R9-11 row (shorting the open ends of the power distribution fingers also reduces supply trace inductance), additional thru-hole bypass cap patterns can be placed inside some of the buffer outlines for those who choose not to stuff all the buffer positions, and back side SMT cap patterns can be located under each buffer – hand soldering 1206 or even 0805 size components is not that difficult – 1-10 nF size caps are better for high frequency bypass and allow using NP0 ceramics (which overlap Polyproplylene caps in DA quality by Pease’ measurements, are recommended by Cyril Bates’ Electronics World “Capacitor Sound” articles and exceed the linearity and DA properties of BK7/X7R ceramics by orders of magnitude, Thorsten Loesch of Thunderstone Audio (a notoriously particular “subjectivist” audio designer who couples solid engineering and good writing skills) considers BK7/X7R ceramics OK for power supply bypass – there is absolutely no reason to consider NP0 ceramics inadequate or inferior to film caps in this application – the reduced inductance of the SMT parts greatly increases the bypass effectiveness in the MHz range)

 Given that you expect extensive component substitution and already have the SMT op amp pattern option I can’t understand the apparent resistance to providing SMT bypass cap patterns as an option for those who chose to use them


----------



## morsel

We are in the process of looking at various capacitor options, including some .1uF polyester film 100x300mil box caps sandwiched between the buffer rows. We will probably bring up the subject of NPO ceramics again as well, but ceramics have a really bad name in audiophile circles. As for SMT caps, if we can get small leaded caps that fit they should be good enough and are easier to solder.

 There are a couple of reasons why we might want as many buffers for the signal channel as for the ground channel. We are not typically demanding the max current the buffers are capable of putting out, it is a matter of lowering output impedance for better control over the drivers, and then there is the appealing benefit of having the high max total current of 4 buffers in parallel which solves the output protection problem.


----------



## ppl

Jcx Prought up most of the points i raised on this issue yes SMT bypass cap locations can be easy to acomidate within this layout. morsel has all ready made a revised version that adresses the bypass cap issue ti my satisfaction.

 Regarding the use of NPO ceramics while thay are orders of magnatude better than the standard versions most importently tempature stability. this is why thay are so well recomended for Both RF and High frequency use. due to there small size and low cost alot of Audio companies are using these caps. IMHO these NPO types are still ceramics and thus have alot of change with voltage and suffer the Piezo effect making them somewhat microphonic. (See Jnug and marsh Picking capacitors)

 The Item jcx Brought up that is exactly on point hear, is the actual number of Buffers Required. if two are used on the gain channels and both channels are driven at once by an in phase waveform such as testing then the ground will have twice as much current flowing as the buffers in eather channel because of the shaired load of the ground channel buffers. I presently use two on each gain channel and 4 on the ground channel. i hand matched 4 buffers in order to stack with out a separate resistor. this works althought thay do get hotter than just a pair did.


----------



## aos

Ceramics caps are microphonic - some datasheets for ultralow noise devices show the effect of tapping a ceramic noise reduction capacitor with a pencil - it creates far more noise than the regulator itself. For bypass of a typical amplifier that shouldn't matter, but if you must use something else, get the PPS film capacitors in SMD. It shouldn't be hard to find some space for a SMD pattern.

 Actually NPO ceramics are NOT cheap. In low pF values yes, but in larger they can get quite expensive. CDN $1.94 each in quantity of 10 for 8.2nF NPO cap. Also, they are very hard to find in sizes over 10nF. You have to use X7R instead.


----------



## mekanoplastik

can a pair of rca connectors be added as line out so the amp can be also used as preamp? 

 m.


----------



## morsel

Actually, not easily. It would be dicey to connect the differential output to anything but headphones as it would likely be shorted to signal ground under those conditions. Probably the best course of action would be to tap the opamp outputs.


----------



## Squalish

What exactly are the differences between a headphone amp and preamp?


----------



## Nisbeth

A headamp (usually) has higher gain and is able to drive lower impedance loads. Otherwise no difference that I'm aware of.


 /U.


----------



## tangent

The gain differences between heaphone amps and preamps aren't really that great, all things considered. 6 to 12dB is common for preamps, but realize that they're dealing with line-level signals. Headphone amps often go for gains of 20dB or so, but that's because they're often used with portable sources that have less than line level output voltages. (My Panasonic PCDP's "line out" is something like 300mV as I recall, but true line level is 1 to 2V.) If you're making a headphone amp designed for being driven from a true line-level source, a gain of 6 to 12dB will be fine with most headphones.

 Output current is indeed given more attention in headphone amps, since preamps don't have to drive low-impedance sources. However, having high output drive on a preamp can't hurt, and it can help a lot with some power amps.

 But the biggest single difference is that most preamps have multiple inputs and one or two line level outputs plus a headphone output.

 Bottom line, it's not too hard to convert most headphone amp circuits into a preamp. It's mostly a physical issue: a larger case for holding all those extra jacks and switches and such.

 Morsel's point is that the differential drive circuit in the PPA is optimized for headphones. While it should _work_ if you plug the PPA's output into a power amp, the ground channel is likely to be useless in that kind of setup because the ground channel is either tied to earth ground or is some kind of active ground. Headphones' ground channels are totally passive, connected to nothing external. That allows the PPA's rule of the ground channel to be absolute.


----------



## ppl

Yes as stated above I would not use the PPA as a preamp or connected in a tape monitor Loop as tangent pointed out this will put the ground channel and the input ground at the same point. now considering the ground channel has Open loop Voltage gain and this is reduced by Negitive feedback. connecting the output ground and the input ground at the same point is connecting the input to the output of the Ground channel. This is a great way to create an oscillator.


----------



## Jupiter

What about using the signal after the pot? That way you could use the PPA as a passive preamp.

 I don't have a use for a passive preamp, but someone else might.


----------



## morsel

Layout v0020 is up for viewing. I did not make a v0020 schematic to go with it since the only changes are some .1uF bypass caps and heavy duty DIP8 parts with fatter pads and traces for the buffers.

http://elvencraft.com/ppa/


----------



## guzzler

not really about the PPA, but Chu Moy just posted an article on a passive preamp at Headwize

www.headwize.com for those not in the know

 g


----------



## morsel

Judging by the quiet reception of v0020 it sounds like most of the major issues have been addressed.

 Squawk now or hold your peace, as we will be having a second set of prototypes made soon.


----------



## ck42

Bump.

 Updates?


----------



## tophu

Quote:


 _Originally posted by morsel _
*Squawk now or hold your peace, as we will be having a second set of prototypes made soon. * 
 

My only comment is that there are a lot of places where traces could be made bigger without any problems. 

 Possible candidates for fatter traces would be the rows of caps along the left, the input signal traces to and from the pot, power rails to the opamps (especially the bits around the transistors, which are really skinny), etc, etc.

 Is there any reason not to have wider traces?


----------



## tophu

I guess that wasn't my only comment.

 It seems like there would be room to add an input protection section on the right. If you chose not to use it you'd just have to jumper it, while still allowing the board to be used with outputs that have DC on them.

 Also, from a purely aesthetic point of view, has anyone considered putting the pot dead center rather than off to the side? I think a pot in the middle with a jack on one side and a LED on the other has a nice symmetry to it.


----------



## tangent

Quote:


 Updates? 
 

The second prototype is being finalized now.

  Quote:


 My only comment is that there are a lot of places where traces could be made bigger without any problems. 
 

I guess along the power rails would be helpful, but larger traces don't seem to make sense anywhere else. Keep in mind, we've segregated the high-current sections of the amp from the low-current sections, and the circuit paths are all quite short. Also, fatter traces aren't without cost: space between traces can be as helpful as thick traces.

  Quote:


 the bits around the transistors, which are really skinny 
 

These are low-current paths that are nearly static -- only microamps flow here.

  Quote:


 It seems like there would be room to add an input protection section on the right. 
 

The PPA is not a general-purpose amp. It's for higher-end systems, which are assumed to have their DC offset situation under control already. Therefore, the cap is of no help, and of some disadvantage.

 My other thought on this is, if you want a cap, you can certainly put it in between the input jack and the input pads if you have to have it. The main downside of this is that it will have to be quite a large cap since the pot that follows it will be ~50K. That's not a big enough issue to justify trying to stick the input cap in after the pot, since that would require giving up precious space in the actual amp section.

  Quote:


 I think a pot in the middle with a jack on one side and a LED on the other has a nice symmetry to it. 
 

Not when the jack is a Neutrik NJ3FP6C jack, which is seriously being considered due to the buffer protection issues we're facing.


----------



## morsel

No news atm. I need to synch up the v0021 layout and schematic and make some modifications for prototype testing. I've been preoccupied lately but will try to get to it soon. After the new prototypes are ordered we will turn our attention to the power supply, probably in a new thread.

 I did widen the power traces to the output buffers. The other traces are probably wide enough that changing them is not going to improve anything. The pot is not going dead center, sorry. Air wire it if you want it centered. Given the limited space, having the pot and input leads against the edge of the board keeps noise and hum to a minimum.


----------



## tophu

Quote:


 _Originally posted by tangent _*Not when the jack is a Neutrik NJ3FP6C jack, which is seriously being considered due to the buffer protection issues we're facing. * 
 

You're right. I didn't consider the size of that jack. 

 Thanks for the comments from both of you. This is shaping up to be a very sweet-looking amp. I've been thinking about doing a better one than what I've got, but I might just hold off until this is ready...


----------



## eric343

Quote:


 _Originally posted by tangent _
*That's not a big enough issue to justify trying to stick the input cap in after the pot, since that would require giving up precious space in the actual amp section.* 
 

Put two holes in the input trace, and if someone needs/wants a cap, they can solder the leads into the holes and cut the trace between them...


----------



## morsel

v0022 (with SMT bypass caps) is up for viewing at http://www.elvencraft.com/ppa/

 v0023eng has been submitted as a prototype candidate. If it passes muster tonight we can order it in the morning.


----------



## daniel422

This is a really cool design. I'm not sure if this was addressed previously (and I'm to lazy to wade through the last 12 pgs), but have you guys verified the power dissipation for the ICs is capable of delivering the type of power you want? I know that the type of "differential" output (I'm pretty sure this is called OCL -- Output Capacitorless -- there are several IC manufacturers doing this for headphone amp ICs) also increases the power dissipation by a factor of 4 (just like full diff).
 Probably not an issue with the power this would typically be required to deliver (10mW), but I'm just curious because I've had parts go into thermal shutdown from exactly that.
	

	
	
		
		

		
			





 Not having output coupling caps gives GREAT bass response. I look forward to hearing one of these in the future.

 Otherwise you've got me hooked! Keep up the good work and I look forward to more.


----------



## morsel

We are pretty happy with the output current but the new prototype should clear up lingering questions regarding 4 .vs. 2 buffers per channel. Differential does not equate to OCL although the PPA is OCL. Very few solid state amps use output capacitors. You can read a brief description of differential output on the PPA website.


----------



## tangent

If the number of ground channel buffers is 2x that of the signal channel buffers, and you're running mono material (both channels identical and in phase) through the amp, then the amp should be capable of putting out something on the order of the theoretical maximum of the buffers. There may be graphs in the HA-5002 datasheet showing output current vs. various parameters like temperature, supply voltage, and signal voltage.

 In real life, none of that will really happen. Most of the time the two channels will be running somewhat out of phase, which cancels currents at the ground channel. Also, in real life you won't be asking anywhere near the max output power from the buffers.

 In testing, I've seen v0.012eng give expected output power with no surprises. I've also accidentally run my board past its theoretical limits a few times, and it will go into massive oscillation, but it recovers if the duration of the fault is short. You can do this with a high signal voltage and a low-resistance dummy load: 7V into 10 ohms, for example, asking for 700mA per channel from a pair of 5002s. If you let it sit and oscillate into a low impedance long enough, the buffers will burn up. That's a known risk with this design; in practice, the main risk is unplugging the headphones with a high signal voltage (read: "loud music") going. In some ways, this amp should be treated like a small power amp: most power amp manuals caution you against fiddling with your speaker wires while the amp is running full bore.

 An interesting question might be to find out what happens with highly inefficient headphones like the Sony F2s, the AKG K1000s, and various electrostatic phones. Does the PPA have the oomph reserves to drive these headphones safely?


----------



## daniel422

Ah! You're using parallel output buffers for your virtual ground -- yeah, I wouldn't think you'd have a problem with power dissipation until you got to rediculously high output power levels (for headphones). My experience came from running a single IC in OCL with both channels in phase (test condition). It died at about 80mW (into 16 ohms), but that was from a 5V supply. I had forgotten that output power stays the same for OCL (vs single-ended), but power dissipation increases by 4 (just like BTL). More amps in parallel for the buffer is a simple solution I don't often have the luxury of in my line of work. 






 One more thing: did you guys ever give any thought to a switch to change the virtual ground to (actual) ground? The outputs could be used as a line out at that point (assuming cap coupled inputs like most amps have). Maybe that's too much. Nah -- just keep it simple. I could see problems running into transformer coupled inputs (like a lot of crappy external PC speakers have).


----------



## tangent

Quote:


 did you guys ever give any thought to a switch to change the virtual ground to (actual) ground? 
 

Battery operation is an important use-case for this amp. Very low vground impedance is also an important goal. Thus all the hoo-hah with the ground channel.

 Even if this were primarily a wall-powered amp, I'm not sure it would be worth abandoning diff-drive. It's a very interesting circuit, I think. Step outside the mold.


----------



## morsel

Thanks to Tangent, the second prototype boards were ordered this morning. Yay! 
	

	
	
		
		

		
		
	


	



 We will get back to you after we have assembled and tested them.


----------



## eric343

Quote:


 _Originally posted by tangent _
*An interesting question might be to find out what happens with highly inefficient headphones like the Sony F2s, the AKG K1000s, and various electrostatic phones. Does the PPA have the oomph reserves to drive these headphones safely? * 
 

I was unaware that the PPA was capable of running off the +/-350V or so supply requried to drive electrostatic headphones well... heck, I didn't know it could run off even +/-100V!

 On the other hand, if you meant using it to drive an electrostatic output stage, such as the Blue Hawaii... you'd have to ask Kevin Gilmore about that.


----------



## tangent

I had no idea electrostatics had such high voltage requirements. Ouch.


----------



## kevin gilmore

quote
 I had no idea electrostatics had such high voltage requirements. Ouch.

 You have no idea. 
	

	
	
		
		

		
		
	


	




 Beveridge speakers run on +/-3500 volts.
 Quad ESL's run with a 2500 volt bias.
 koss electrostatic headphones run on +/-650

 The ppl amp is not even suitable as a driver for the
 blue hawaii because it's output would have to be referenced
 to -400 volts.

 Please don't try and run a ppl amp on +/- 400. Someone
 will get hurt


----------



## yejun

is it possible to use output trasformer to raise voltage that high?


----------



## kevin gilmore

quote

 is it possible to use output trasformer to raise voltage that high?


 Depends on how lousy you want it to sound after you are
 done. Decent transformers for this task by definition are
 large. Then there is the bias issue.

 You can put 10 buffer chips in parallel and you won't have
 enough power to drive a decent transformer.


----------



## ppl

It is not impossible to make the PPA or any other op-amp swing at that kind of voltages. However modifications would be needed and add a lot of complexity. one is to use high voltage op-amps but expect to pay about $300 or so USD for an Apex device. another is to cascode the existing op-amps and buffers with high voltage transistors or even tubes. anything is possible if you put enough effort into it.

 I don't know about anyone else but for me the PPA is for Dynamic headphones. if electrostatic cans are required then other alternatives are available like kevins amp for electrostatic cans as eric343 is building. Stax also has a tube Amp for electrostatic cans. so why reinvent the wheel. at least at this time. Heck I still use My Koss ESP-9B with the transformer based box that comes with them. however I seldom use them.

 for speakers see http://www.soundlab-speakers.com/


----------



## MERTON

HOW MUCH WILL IT WEIGH AND HOW MCUH WILL IT COST AND WHEN WILl it be finished.


----------



## guzzler

Quote:


 _Originally posted by MERTON _
*HOW MUCH WILL IT WEIGH AND HOW MCUH WILL IT COST AND WHEN WILl it be finished. * 
 

i think this has been perfectly well answered many times in this thread if you bothered to read it...

 g


----------



## AIM9x

agreed.... and STOP YELLING!!!!


----------



## mekanoplastik

what should be the minimum rated voltage and minimun/recomemded capacitance for C1 caps?


 also, is the "retirement" of the tle2426 going to affect the design of the board?


 m.


----------



## ppl

The Value of these capacitors is dependent upon what value your favorite types come in that are no more than 30 MM tall Max. regarding the ability of this Amp to drive low impedance headphones> I have used the 12 ohm Sony MDR-f1 and found the amp to have plenty of drive for these. The great sound stage of this amp really do the F1's proud.


----------



## Voodoochile

30mm seems plenty tall for the caps I like... but why the height restriction? Is it for stacking allowance of PCB to battery pack board?

 Just curious.


----------



## ppl

Yes. on my prototype with the Amp board placed so as to allow the battery board to slide into the slot below the Amp board. the 12.5mm Dia X 30mm H Nichcon Low ESR caps i used just fit. these are 1000uF/35 Volt and work fine.


----------



## Voodoochile

Got it. Nichicon is my fave cap, coincidentally, so even better.

Thanks, PPL!


----------



## morsel

According to Tangent, the max height limit is about 28mm. 1000uF 35WVDC 12.5x25mm Panasonic FC series are the recommended parts.

 As for the TLE2426CLP (TO92 package), I am talking with both TI and Digikey, as there seems to be a lot of confusion regarding the true status of this part. I hope it is a mistake, but if it truely goes away then yes, we will have to redesign the PPA as there is no room for DIP TLEs on the board.


----------



## Voodoochile

What about SOIC in the event that the TO92 is indeed gone?
 The footprint is a bit bigger than the TO92, but much smaller than the PDIP.


----------



## aos

Actually, I don't know why I haven't said this before, I'd DEFINITELY reccomend you change the board to use TLE2426 with noise reduction pin. There is no sense in spending money on high end parts and then infusing them with noise. META42 was a very compact amp and it was appropriate there, but this is a high end design. Furthermore, you're adding this noise after all the voltage regulation so even the best regulator in front of amp will not be able to eliminate the noise you're now putting straight into the rails of high end low noise opamps. So this obsoletion of TO-92 case is a blessing in disguise.


----------



## morsel

According to the pdf, noise is 120µV without Cnr, 30µV with Cnr. Has anyone actually tried measuring and/or listening to a DIP TLE with and without Cnr?

 Losing the TO92 TLE is not a blessing. There isn't room for 3 DIP TLEs on the PPA. Tangent will not be happy if we have to redesign the board right after ordering the second round of prototypes. It also screws the META42, MINT, and other smaller amps.

 I'm still waiting for TI to figure out the facts. Hopefully they will get back to me early next week.


----------



## guzzler

a small adaptor could probably be made, but that would just add complication to the design...

 i know its not my place, but theres no point in developing with a component whose future is in doubt, and you should just live with parts that are available to you... yes, its a pain to redesign, but much less of a pain than having your PCBs obsolete (and therefore unsellable) as soon as you make them!

 and aos's point is a good one!!

 g


----------



## Voodoochile

What about SOIC in the event that the TO92 is indeed gone?
 The footprint is a bit bigger than the TO92, but much smaller than the PDIP.

 Wait a minute...

 I do realize it's big compared to the TO92, but it's also small compared to the DIP. No way to wiggle them in without a total redo??


----------



## ppl

My thinking is to use regulators Like aos dose in his PDac. Then we could still retain separate op amp rails on each channel. Since these IC's are SMT type and would replace the present jfets and tle's with one master TLE splitter serving the 6 regulators. this should be able to be acomidated within our present layout without imparting upon any exsisting components. In addition this would also resolve any lingering issues as to the jfets operating in the ohmic rather than constant current range.


----------



## aos

>>According to the pdf, noise is 120µV without Cnr, 30µV with Cnr.

 This is a common occurence with voltage regulators (which TLE2426 is). Occasionally there are types with or without noise reduction pin, in order to add some extra features they squeeze out the pin. This pin typically allows you to bypass the voltage reference which is usually noisy. 120µV is not terrible but it
 invalidates any effort for making the power supply any better than a standard 3-pin regulator or two. This will affect the noise floor of the amplifier and that is audible through loss of resolution/detail. Whether this will be audible on 16/44 PCM or only on SACD or DVD-A material, is impossible to say before measuring the final product. It is a valid decision to live with it, as long as the rest of design reflects it (i.e. no point in using fancy-shmancy power supplies, expensive Black Gate or OS-CON bypass caps etc. because it doesn't make engineering sense). If there were an extra layer of regulation after the rail splitter then it'd be ok. I am not sure what effect does the current source have on noise, if they were after the rail splitter instead of in front they might attenuate the noise generated by it.

 I hate to say it, but I spent over a year and went through 5 prototypes, often working 30+ hours a week on (mostly) redesigning PCB in order to squeeze all I wanted onto my PCB, and many parts have been changed to something else, added or removed in the meantime. Perphas I was crazy to spend so much time but if you expect to get maximum out of the design you may have to do major revisions - and more than once. And then after the "final" one is built, you measure it and see that there are problems you couldn't foresee during design so you make another revision to fix it. Anyhow, I believe there's enough free space on the PPA board for this change. Decision is of course yours but I still say that this is blessing in disguise and that you'll benefit from it in the end even if you see it only as a major annoyance at the time. Besides, I thought META42 has also been obsoleted by the manufacturer 
	

	
	
		
		

		
			





.


----------



## aos

ppl, there is one big problem in that approach - a practical problem. You don't want to use the regulators that I used. SOT-23 are so small that they are hard to solder even for me. While I believe they are a great contribution to the wonderful sound, and they enabled me to pack incredible amount of stuff in small space, it takes just too much work to solder them, at least if you also use SMD bypass caps as I did. I would not reccomend anything this size in a wide-appeal project. Not to mention that those JFETs in series with rails are somewhat of a signature of your original pocket amp.

 One thing that can be considered is to use two-pin socket in place of those JFETs and then allow a small vertical board to be plugged in. Then you can either plug JFETs directly or add something more elaborate, delegating tough SMD work to someone else (the same idea as with SOIC to PDIP adapter sockets) or bypassing it completely. This also saves space, at least in the two board dimensions. It adds a lot of flexibility but would require extra work and consideration outside of the board itself so is probably not practical.


----------



## ppl

aos thanks for your input. I have been thinking real hard about making an adaptor board to try different alternatives like a cap multiplier and or regulator to test in the proto type. since the rail foils are easy to get at in the prersent version just by removing the FEts this could happen. still separate TLe's per channel as this would be alot harder to impliment a rail splitter in another location. however you are correct the JFETs on rails are as you say a signature of my amps.


 BTW the TLE is not classed as a voltage regulator if you dig through Ti's site thay list it as an op amp. this is what i belived it to be all along. look at the Spice model and you will see what i am refering to.


----------



## morsel

How would people feel about replacing the TLEs with resistive dividers? Using 12K or greater resistors for a current of 1mA or less would more than cover the miniscule input signal level. The resistors are cheap, quiet, and would fit in the existing layout without having to sacrifice the separate isolated rails for each channel. We will be testing this.

 (Morsel puts up a frail umbrella as protection from the incoming bunker buster bombs.)


----------



## Dreamslacker

Well... I've experimented with using resistive dividers instead of TLE2426CLP/P on my A47 variant, Proto42 & META42 amps. I can safely say that for me, I get a more open sound with the resistors than with the TI part. No idea why that's the case though.


----------



## ppl

I am adamantly against resistive Dividers. The isolation effect caused by the voltage divider effect of the Jfets and the Low output impedance of the TLE's. the isolation could go down to 10dB vs the 100 Plus we now get. other alternativs are available hear and these include keeping the present arrangement however implemented in another package


----------



## AIM9x

I wish i had some more audio circuit knowledge so I could better help you guys out.

 4 weeks into an electronics course and i'm starting to understand more about what's going on. This week, we're going to do amplifier configurations and I think i'll have a heavy understanding of what's going on here, 
	

	
	
		
		

		
			





.


----------



## eric343

Quote:


 _Originally posted by morsel _
*How would people feel about replacing the TLEs with resistive dividers? Using 12K or greater resistors for a current of 1mA or less would more than cover the miniscule input signal level. The resistors are cheap, quiet, and would fit in the existing layout without having to sacrifice the separate isolated rails for each channel. We will be testing this.

 (Morsel puts up a frail umbrella as protection from the incoming bunker buster bombs.) * 
 

/me hops in a B-52 and heads down to California...

 Weren't you the person who was adamantly defending the use of the TLE2426 in the M/ETA42?

 And unless you tombstone the resistors, wouldn't the SOIC package of the TLE2426 be the same size as two resistors side by side?

 Incidentally, isn't the TLE2426 availible as bare silicon? Now THAT's small 
	

	
	
		
		

		
		
	


	




 (we'd have to get aos to solder them... 
	

	
	
		
		

		
		
	


	







)


----------



## guzzler

a bog standard resistive divider sounds like a non sense in an amp that is supposed to be as high end as solid state is going to be. It is far easy, and more space effective, to use a TLE in another package, and the matching of +/- rails is going to be far more effect with a precision trimmed TLE, than 1% matched resistors... Don't cut corners when you don't have to!

 I've never heard it, but I would think that the more "open sound" dreamslacker speaks of is purely a placebo effect!

 g


----------



## morsel

This is a contingency if the part is really discontinued. There is not space for 3 DIP or SOIC TLEs on the PPA. If we lose the TLE we will resort to plan B, which is still being hashed out.


----------



## mekanoplastik

edit...

 never mind ..i just saw a thread discussing my question... (about Tangent stocking 2426's as he did with meta buffers)



 m.


----------



## morsel

Mek, it's a nice thought, but we are not going to design the PPA around a discontinued part. Hopefully TI will get back to me within the next couple of days so we will know for sure what is going on.


----------



## morsel

Errata: I posted the wrong C1 capacitor dimensions on 4/29 which I have just corrected.

 According to Tangent, the max height limit is about 28mm. 1000uF 35WVDC 12.5x25mm Panasonic FC series are the recommended parts.


----------



## yejun

if using a real ground, is the ground channel still necessary?
 another question is if using multi-battery, can i just put half of batteries to v+ another half to v-?


----------



## ppl

No you can't split the Batteries in half. unlike conventional Battery Amps that use a Virtual ground driver in the Primarry power supply the PPA uses a Virtual ground driver on each Channel in the Low current only section powering the opamps.

 If you delete the Ground channel you will defeat one of the real nice features of the PPA and if that is the direction you wish to go perhapps a more conventional Amp such as the META42 is what you want.


----------



## morsel

PPA v0027 layout and schematics are up for viewing at http://elvencraft.com/ppa/

 Changes include a fatter power bus, added RLED to save time jumpering the Zener and putting a resistor in the CRD spot for those who will not be using a current source for the LED, added no fly zone circles around the screw holes, and landing pads for the ALPs pot prongs.

 These prongs are little "feet" near the pot pins and are electrically connected to the pins. The pot actually sits on these prongs. They were shorting out against the ground plane on the prototype. There are now square landing pads where the prongs touch down. Under each silkscreen landing pad for the left and right channel prongs the ground plane is removed, so even if the prongs cut through the silkscreen and solder mask layers they will not short out. Ground plane remains under the pads for the ground prongs. It is important to make sure the pot pins are straight and perpendicular to the pot body for proper alignment of the landing pads.

 These prongs are probably only an issue for the prototypes, which have no solder mask or silkscreen layers, but better safe than sorry. I would hate to have to make everyone lay down electrical tape, rubber, or cardboard to protect the board from the pot prongs.

 Note that the square holes in the ground plane are not visible in a gif of the layout as the silkscreen covers them up.

 Kurt and I have been busy lately. Testing will likely take many more weeks.


----------



## Tim

Looking good team ppa!


----------



## yejun

oops.
 I think the ground channel's current should 1.4 times the right or left channel under the condition random L and R.

 Ig=Ir+Il
 <Ig^2>=<Ir^2>+<Il^2> the cross term will be zero if random.
 RMS(Ig)=sqrt(2)RMS(Ir) if Ir=Il

 so on random case, the ground channel current will 1.4 times individual channel.
 At high frequency the current can be assumed as random, but at low frequency the R and L channel is correlated, then the ground current is twice the individual one.

 So I suggest at least use 1.5 buffers at ground channel.


----------



## jasonhanjk

GREAT JOB!!!
	

	
	
		
		

		
			





 Currently still building another PPA in Singapore, only capacitor is complete...
	

	
	
		
		

		
		
	


	




 May change to this latest version!!!


----------



## rjones

morsel,

 I just looked over some of this thread today. very nice. I'm also happy to see you are not using the BUF634, I too find the sound not quite right.

 As for the 10R to isolate signal ground from power supply ground, I agree completely. I've used this technique for some time in power amps and preamps and it works exceedingly well.

 The other two suggestions to consider are:

 1. place ferrite bead (FB in SMT) in series with the power supplies to all devices to further lower noise.

 2. de-couple the power supply of the HA5002. that is, have a FB going to V2+/- after the FB, have a 100R in series with this point and V1+ and another from the (-) supply to V1-. place a 100 uF cap from V1+/- to ground, obviously observing proper polarity.

 The HA5002 is unique in allowing this sort of PS de-coupling of the input stage from the output. While such de-coupling is sometimes frowned upon as old-fashioned, it works amazing well at lower input noise. Check it out on a 'scope and see.

 Regards, Robert

 PS You might even consider a FB SMT on the input signal leads too to limit EMI getting in from that direction. I like adding a large one around the input AC wires inside my chassis too.


----------



## morsel

Thanks for your suggestions, Robert.


----------



## morsel

Mekanoplastik asked, "can a pair of rca connectors be added as line out so the amp can be also used as preamp?"

 I have a new answer for you. Wire the RCA jacks to the left and right channel outputs and the signal ground input. This does not buffer line out from headphone out as my first suggestion of tapping the opamp outputs, but it does not require the opamps to drive the line out jacks. In either case, signal ground should be used rather than the output of the ground channel or ground channel opamp to prevent shorting it to signal ground.


----------



## eric343

Just heard one of the prototypes (see my minireview over in the Amps forum, "Whoa. All hail the PPA!"). You guys (Ppl especially) did good...


----------



## jasonhanjk

YUP!!!


----------



## MERTON

can i be a reviewer of one of your prototypes? i promise i'll send it back.


----------



## jasonhanjk

Some question...

 The ground signal for the AD8610 comes from the TLE2426. If I have an ground channel, would it be the same if use FET isolate the ground to replace the rail splitter? Same like FET Isolated Power Rails?

 That's it. After I increase the rail voltage, the opamp and buffer are slightly hotter.


----------



## guzzler

is there any plans to include mounting holes for tangents crossfeed board ??

 g


----------



## tangent

Quote:


 would it be the same if use FET isolate the ground to replace the rail splitter? Same like FET Isolated Power Rails? 
 

No, that wouldn't be a good idea at all. A TLE2426 is a lot mroe complicated than a JFET. Some of the bad effects that would be caused by implementing your idea:

 - You'd need more board space: at minimum, you need some resistors to divide down the supply voltage, or to set the JFET's gain so that output stays at V+/2.

 - It is likely that you would get voltage fluctuations that depend on the load on the circuit. This would mean the voltage would rise and fall as current rose and fell -- voila, the load is now modulating the ground. Bad juju. We can get away with this on the power rails since the op-amps' current draw doesn't change very much in operation, especially if you bias it into class A. The same does not apply to the buffers or the ground channel, so they cannot get away with a simple isolating JFET.

  Quote:


 is there any plans to include mounting holes for tangents crossfeed board ?? 
 

There are plans to allow some kind of crossfeed daughterboard, but we don't expect to support the META42 crossfeed board, since that's space-compromsed due to META42 limitations. The PPA will allow us to use more space on the board for bigger caps and a nicer mounting scheme. This is all way up in the air at the moment, since the crossfeed doesn't drive the design of the amp; it's tacked on after the fact, so we're putting decisions about this off on purpose.


----------



## jasonhanjk

I think you misunderstood me. I better give you more details...
	

	
	
		
		

		
		
	


	




 I uses DC-DC converter with the output of +12V, -12V and 0V.
 TEN 3-0522
http://www.tracopower.com/products/ten3.htm 
 With the load regulation at 2% and 50mV pk-pk ripple.

 My question.
 Can I use JFET to isolate the 0V from my DC-DC?

 Thanks!!!


----------



## tangent

Quote:


 Can I use JFET to isolate the 0V from my DC-DC? 
 

Oh, and here I thought you were talking about the PPA project in the PPA project thread. 
	

	
	
		
		

		
		
	


	




 Please start a new thread about it. Give more details, like what measurements you're seeing that lead you to believe you should try this.


----------



## jasonhanjk

It is the clone PPA that I am working on. Try to cut down on the batteries to 4 or 6 instead of 18. 
	

	
	
		
		

		
		
	


	













 Let me try a new thread since US is awake. Now I am seeing about 2am with no dog howling!!!


----------



## morsel

I am mostly done moving to the new apartment. DSL is up. The kitchen is still a disaster. I'm on page 650 of 900 reading Harry Potter and the Order of the Phoenix aloud with a friend in the evening. It's slow going, but more fun that way. Work on the PPA continues.

 Kurt's measurements indicate there is no benefit to adding more buffers to the ground channel but not the left and right channels. So, for example, we could not detect any difference between 2-4-2 and 2-2-2. In order from best to worst, here is our ranking of buffer configurations:

 4-4-4 > 3-4-3, 3-3-3 > 2-4-2, 2-3-2, 2-2-2

 More buffers mean lower output impedance, tighter bass, and less distortion. As a result, we have no plans to eliminate the 4 buffer per channel configuration in favor of lesser configurations, a possibility which was discussed previously.

 We could not tell the difference between 2000uF and 8000uF of filter capacitance, nor between Elna Cerafine and Panasonic FC. Using 8 220uF Cerafine or 2 1000uF FC should be fine.

 There was almost no difference between using a cheap unregulated wallwart, a regulated Elpac WM080 wallwart, and an LM317 based regulated supply. Despite these results we have not given up on the capacitive multiplier power supply yet, as it may come in handy for powering the battery board or other amps, and it should please the uberanal.

 Using a single set of FET isolated power rails to power all 3 opamps instead of 3 sets of rails, one per opamp, Kurt and I were unable to either measure a difference using RMAA or hear any difference after about 30 minutes of listening. While we acknowledge your ears may be better than ours, we will include jumpers so that the PPA can optionally be wired for a single set of opamp rails. If nothing else, it will be interesting to see if anyone else (besides PPL) can hear a difference.

 We are currently working on resolving some battery board and power flow integration issues. A new layout and updated documentation will follow.


----------



## guzzler

thanks for the update!

 g


----------



## jamont

Quote:


 _Originally posted by morsel _
 There was almost no difference between using a cheap unregulated wallwart, a regulated Elpac WM080 wallwart, and an LM317 based regulated supply. 
 

Can you say a little more about this? Were there differences between the Elpac and the LM317 PS? Thanks and welcome back!


----------



## asdfeproiu9

ot, but: meta42 v3 ... what new features are there left to incorporate? will that be more expensive and/or sound even better than the ppa?


----------



## was ist los?

i think i remember the meta42 v3 will have buf634s instead of the El200xs.


----------



## asdfeproiu9

hm, i did a bit of reading, and the meta42 v3 would not be better-sounding than the ppa ... so never mind about that part. any other changes? ie, if i were to have a maxed-out mint (heh) at the moment, would it be good for me to upgrade to a ppa, or a meta42? my sources aren't great anyway, but i do plan to get much better headphones.


----------



## morsel

The difference between the Elpac and the LM317 supplies on PPA noise was small enough that I didn't bother to take notes. I'm guessing it might have been a couple db difference at around -110db down. Perhaps Kurt recalls the specifics.


----------



## ppl

The JFET isolated rails and separate VGD for the Opamp rails, as used in my Pocket Amp, in concert with the Ground channel are incorperated in the PPA to improve the Amps Power supply rejection Ratio and prevent unwanted feedback of Load current noise to both the sensitive opamp rails in addition to not contaminating the Signal ground. this also has the advantage of almost removing the quality of the DC power supply from affecting Both Performance and most importently Sound quality.

 BTW the sonic advantage I heard using Three vs one Op Amp rail is an inprovement in sound stage. this was noticable on my Sony MDR-V6/7506 Phones. These sonys are not Knowen for soundstage and with just one Isolated Op Amp supply the image was confined Between the ears but with Three Isolated Op amp rails the image extended to about 1 inch from the outside of the ear cups, Moreover the Image also had depth and extended to the back and lower base of the Neck vs just between ears within Head. Outside sounds also seemlessly blended with the Music. Nice.


----------



## jeffreyj

Quote:


 _Originally posted by ppl _
*The JFET isolated rails and separate VGD for the Opamp rails, as used in my Pocket Amp, in concert with the Ground channel are incorperated in the PPA to improve the Amps Power supply rejection Ratio and prevent unwanted feedback of Load current noise to both the sensitive opamp rails in addition to not contaminating the Signal ground. this also has the advantage of almost removing the quality of the DC power supply from affecting Both Performance and most importently Sound quality.
 ....* 
 

I am very curious how many more dB of PSRR this technique can produce. Any results on this?


----------



## tangent

Quote:


 I am very curious how many more dB of PSRR this technique can produce. Any results on this? 
 

I just did some informal testing with a signal generator injecting ripple on top of one rail with a 10V supply. I increased the ripple signal until I got at least 2mV on the other side of the JFETs, then measured the ripple voltage. (This was to ensure that I wasn't straining the lower limits of my millivoltmeter.)

 The rejection across the JFETs is frequency dependent. At 120 Hz, the ripple is attenuated by about 15dB, at 1 kHz it's 32 dB, and at 10 kHz it's 29 dB. This suggests a ramp upward towards a plateau, which is a neat complement to an op-amp's declining PSRR curve.


----------



## ppl

Quote:


 _Originally posted by tangent _
*I just did some informal testing with a signal generator injecting ripple on top of one rail with a 10V supply. I increased the ripple signal until I got at least 2mV on the other side of the JFETs, then measured the ripple voltage. (This was to ensure that I wasn't straining the lower limits of my millivoltmeter.)

 The rejection across the JFETs is frequency dependent. At 120 Hz, the ripple is attenuated by about 15dB, at 1 kHz it's 32 dB, and at 10 kHz it's 29 dB. This suggests a ramp upward towards a plateau, which is a neat complement to an op-amp's declining PSRR curve. * 
 

This was the Intent of using this topology. If a lower Idss FETs were used the rejection would be even better. The PN4392 is a rather stiff device for the AD-8610 However is good if Higher Icq op amps are used like the AD-843. I like to use the 2n5486 with the AD-8610. Let us also not forget the Psrr of the Buffer on the Ground channel. had more room been available on the PPA board i would have used the capacitor Multiplier like i did on my older Portable Amps. The jfet only was used in my Pocket Amp because of lack of room on the Pocket Amps board as is the case with the PPA also. I may play with the PPA board and see if i can incorperate the additional cap multiplier's on the rails with out upsetting other Requirements.


----------



## KTpG

This may have been addressed before on one of the previous 16 pages but I really don't feel like reading all 16 pages... perhaps you can understand. 
	

	
	
		
		

		
			





 How hard/easy is it to adapt the PPA board for home use ONLY with a true dual PS? It seems as though a lot would have to be done to the PS section to change it. Is it as simple as wiring it up, or a tad more complicated, requiring parts changes, etc.?


----------



## ppl

Due to the Highly intergrated nature of the PPA's internal power supply a single External Supply such as a qualty wall wart or a regulated Conventional supply on a singel rail (Positive & ground) will preduce as good of results as using a split rail supply. the PPA is designed to be a portable that has the sonics of the Better Home only units. this required an aproach to power supply design that is Highly optimized for this Amp.

 so if one were to do as KTpG Sugested then three Regulatedl ow current dual rail supplies are required one for each op amp Channel. then another singel polarity supply just for the output stage. In no way should an attempt be made to tie any supply connected to the output stages to ground.

 While the PPA is a DIY Amp the amount of custom user changes are kept to a min. as jeffreyj pointed out in another Post I would not want someone to undoo all the effort put into this Highle Optimized Amp and thus create a less than Ideal Performer.


 Wher are those "No user servicable parts labels at Hee.. hee..


----------



## tangent

You could configure a PPA with just one set of op-amp rails, remove all the TLEs, jumper the TLE-G position, tie PS ground to the ground plane and the PS V+ and V- to the appropriate places. That should work. But, to what end? I doubt it'd perform as well, and the premium for the dual supply is likely more than what you saved by removing the TLEs.


----------



## jeffreyj

Quote:


 _Originally posted by tangent _
*....
 The rejection across the JFETs is frequency dependent. At 120 Hz, the ripple is attenuated by about 15dB, at 1 kHz it's 32 dB, and at 10 kHz it's 29 dB. This suggests a ramp upward towards a plateau, which is a neat complement to an op-amp's declining PSRR curve. * 
 

Coss is starting to come into play around 10kHz, then, but the suppresion is still impressive at this frequency and seems to be very much worth the additional components. Nice!


----------



## dokebi

Any estimate on when the boards will be available?


----------



## Jupiter

Was a discrete buffer ever considered for the PPA? Or would that just take up too much space to fit in a portable amp? 

Borbely Super Buffer


----------



## Whitebread

Quote:


 _Originally posted by dokebi _
*Any estimate on when the boards will be available? 
	

	
	
		
		

		
			



* 
 

I was just about to ask that. Just give me a board, parts list and instructions.


----------



## guzzler

you could make an array of those buffers and attach them to the relevant pads on the PPA board if space allows, remembering however that the PPA is optimised for the HA200x buffers

 g


----------



## ppl

Quote:


 _Originally posted by tangent _
*You could configure a PPA with just one set of op-amp rails, remove all the TLEs, jumper the TLE-G position, tie PS ground to the ground plane and the PS V+ and V- to the appropriate places. That should work. But, to what end? I doubt it'd perform as well, and the premium for the dual supply is likely more than what you saved by removing the TLEs. * 
 

Yes Tangent I agree. this would create more problems than it would solve by having all those power supply wires running all around in side the Amp. These is nothing Wrong with the Power supply I used in this Amp.. I would however as stated before would have liked to add cap multipliers on each rail this would add another 30 dB of isolation

 Jupiter> I have been working on a discreet buffer that will Plug into the 4 Buffer sockets on each channel. I will prototype sometime next week using Quad Complimentry transistor arrays in the 16 pin dip. these are based upon the now discontinued MPQ-7551. this contains two match pairs of NPN/PNP transistors. I do not like Mosfets or jfets as an output stage since the BJT is a current device domain device and drive low impedance loads real well without the stability problems or high dropout voltages of Mosfets. I am open to sugestions as to the Actual device types so make any sugestions hear. BJT only

 it appears that this firm is second sourcing these. this is good as i have used these alot as buffer transistors and thay work great. only 50 MHz. Ft and Hfe of 25 not alot of gain or bandwidth however bandwidth is ok for the AD-8610 multilooped and by using a Dimond buffer the gain will go up. These transistor arrays were intended to drive the Old TTL logic. thay are well matched and sound god if Biased corectly. http://www.centralsemi.com/quads/index.html


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## guzzler

would it perhaps be possible to use the Walt Jung discrete buffer as this is a simple design consisting of commonly available parts??

 g


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## ppl

Have not tried it in the PPA however it sould work fine as long as you can confirm the Buffers bandwidth at at least 70 MHz with the AD-8610 opamp with your intended load


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## morsel

We discussed discrete buffers, but are sticking with the HA5002 for the PPA. Discrete class A buffers tend to use a lot of space and power.

 There is no ETA on boards. We will let you know when we know.

 Read http://elvencraft.com/ppa/ for a basic summary of the PPA.


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## ppl

if i get my discreet component buffer to the point that it sounds to me better than a 5002 it will be a plug in module that will fit the 4 5002 sockets so as i can listen to differences and make corrections in addition to finding a way to offer this to Builders of the PPA through tangent if he is interested


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## morsel

PPA v0030 layout and schematics are up for viewing at http://elvencraft.com/ppa/

 Changes:

 Caps are renumbered. C1-->C1, C2-->C2, C3-->C4, C4-->C5, C5-->C7, C6-->C3, new ground channel feedback cap = C6. Sorry for any confusion, but it makes more sense this way.

 added opamp rail jumpers for those who wish to use one TLE for all 3 opamps
 added wire passthrough slots
 moved Alps pot away from edge and mounting holes into corners
 removed extra LED current source
 moved LED current source to rear of board
 removed D2 as the battery board has diodes
 added Molex KK 3 pin power header
 replaced CRD with a pad that a CRD can be wired to along with an RLED pad to save space
 C4 electrolytics are larger in RL than specced, spread them apart so they seat properly
 replaced R6G with C6G to suppress a transient 1MHz ring on the ground channel during power on and off
 removed R5G
 deprecated R3G
 removed extra ground pads near the rear inputs as they would be confusing on a soldermasked board
 made C4 labels more legible

 We are now in polishing mode. Consider the light at the end of the tunnel to be in view. Comments, suggestions, and requests are still welcome.


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## Whitebread

*Scratches head in amasement* Excuse my ignorance, but the last time I check this thread, it had 2 pages!! Could some quickly give me a sumation of the advantages of this amp over the META42? And, about this battery board thing, I don't plan on taking any DIY headphone amp anyplace except my desk, so do I have to use the whole battery charger thingy??
	

	
	
		
		

		
		
	


	




 (I know what I'm talking about, lol)


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## morsel

The battery charger is not required, you can build the PPA as AC only. Advantages over the META42 include better buffers and differential output, which results in better sound. Read the PPA website and this thread for more details.


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## tangent

The battery board is indeed optional, but you may still choose to use the battery board for listening at your desk. A NiMH battery pack delivers exceptionally clean power compared to most wall power supplies.


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## Whitebread

That would require multiple cells (like you've said) and constant recharging. Even if I used the battery pack, would it be connected to the wall so the batteries would be constantly be recharging?


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## printed_jim

What kind of NiMH cells will the PPA be using? Will those be the gumsticks? And how many cells compose the battery pack?

 Any estimated battery life yet?


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## Whitebread

He said that the battery board was designed for AAA batteries and the charge rate was selected assuming you were using these size batteries. I guess you could mod the board so that it would charge C or even D cell battery packs as I believe he said it could put out over 100mah.

 Edit: I believe you can stuff as many as 18 cells in there.


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## tangent

Quote:


 Even if I used the battery pack, would it be connected to the wall so the batteries would be constantly be recharging? 
 

When the amp is plugged into the wall, the batteries are charging but the amp is running solely from the wall power. If you then unplug the wall supply, the amp runs from the batteries.

  Quote:


 What kind of NiMH cells will the PPA be using? 
 

AAA's or AA's.

  Quote:


 how many cells compose the battery pack? 
 

As many as you want, up to 18 AAA's or 10 AA's. (Or more if you chain battery boards together in an external battery pack.) This isn't the time to go into details, but suffice it to say that it will often make sense to go with fewer cells than the maximum the board will accept. The documentation will go into all the gory details to help you figure out what configuration makes the most sense.

  Quote:


 Any estimated battery life yet? 
 

Depends on the battery configuration and the amp configuration. As a very vague handwaving range, figure 7 to 45 hours, depending on many factors. Again, the docs will cover this when I get around to writing them.

  Quote:


 I guess you could mod the board so that it would charge C or even D cell battery packs as I believe he said it could put out over 100mah. 
 

I think you need a few more zeros in there....

 And no, you wouldn't want to try and mod the board to use large cells. It would be a waste because most of the board would be unused, but you'd still have to pay for it. Instead, a smaller standalone charger board that lets you hook up off-board battery holders would make more sense here. There are no plans to make such a thing at the moment.


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## binary_digit

PPL and myself have been listening to the PPA proto on any 9-32 volt AC wall wart we could find without any audible problems. The battery board is simply for those people who enjoy good tunes at the park, mountain, relatives, etc.

 I assure you a battery board is not needed but it will be a very nice accessory.


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## Whitebread

Ok, I don't think I'll need one. thanks!


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## printed_jim

Quote:


 _Originally posted by tangent _
* As a very vague handwaving range, figure 7 to 45 hours, depending on many factors. Again, the docs will cover this when I get around to writing them.* 
 

Thanks Tangent. 30 to 40 hours of battery life in an awesome sounding amp that has the capability to be a transportable is totally awesome. That's all I wanted to hear. It wouldn't matter for some people to use the maximum amount of cells the board can take if they'd be travelling and want to bring the best sound they can grab on to.

 Two thumbs up!!!


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## tangent

Quote:


 30 to 40 hours of battery life in an awesome sounding amp that has the capability to be a transportable is totally awesome. 
 

Fair disclosure: you'd have to go with AAs to get that kind of lifetime, or an external battery pack. Going with AAA's lets things lay out better inside the amp, and lets you get a higher supply voltage at the expense of run time. With a simple AAA battery setup inside the amp, lifetime is more like 7 to 15 hours.


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## guzzler

still enough for a full days usage even with AAA batteries, awesome!

 g


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## Whitebread

Any updates?


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## tangent

Soon, yes. Patience.


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## Whitebread

Sweet!


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## guzzler

hey, is there space on the board for a shunt resistor after the pot so people could use a linear pot with potentially better tracking?? just a thought...

 g


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## morsel

Hi Guzzler. Sorry, we are not going to add onboard shunt resistors. Shunting a linear pot presents a variable impedance to the source. The Alps Blue is a good pot. If you want better, use a stepped attenuator.

 Sometime later today I will start a new thread to announce the PPA final candidate and issue a last call for comments, suggestions, and requests.


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