[tangent]

Have you ruled out the source as the culprit? Noise from the source is "detail" that a better amp can reveal, which may be inaudible without the amp.

 

[jezz]

It's not the source; the hiss is present when I tie the inputs to ground. The source is a γ2 which is dead silent in my EHHA with a closed loop gain of 9 incidentally. Even then, the hiss is still present when the volume is turned to zero. Thanks though :-/

Given that the hiss is present equally in both channels, should I start assuming it's the ground channel? I was very careful with ESD-sensitive components when building it, but could I have blown the TLE2426?

 

[Spacehead]

Quote:

Originally Posted by jezz /img/forum/go_quote.gif It's not the source; the hiss is present when I tie the inputs to ground. The source is a γ2 which is dead silent in my EHHA with a closed loop gain of 9 incidentally. Even then, the hiss is still present when the volume is turned to zero. Thanks though :-/ Given that the hiss is present equally in both channels, should I start assuming it's the ground channel? I was very careful with ESD-sensitive components when building it, but could I have blown the TLE2426?

At gain of 3 and ADA4627-1 op amps on left and right
and AD8599 on ground I have no hiss if my source is quiet.

I have 10 pF compensation capacitor (C6G), multilayer ceramic on ground channel

What kind of C6G you have?

I think if you get non distorted sound from your PPAV2 you haven't blown anything.

It is easy to check if TLE is working correctly, measure +V and -V to input ground
If they are about the same tle is working.

Ground channel can easily give out hiss if configured differently. PPAv2 should be peacefully quiet if it is built with correct parts.

 

[jezz]

The C6G I used is this one, Mouser part 5982-15-500V10 from the BOM. It's a mica cap instead of a ceramic cap. I'll check later to see if I can replace it with a film cap, but I don't know if I have a 10pF lying around.

I don't get any distortion besides the hiss, and V+ and V- are just about perfect referenced to ground. However, I'm measuring with just a multimeter so I can't measure if there's any AC there. My understanding of the TLE is not so great, so I didn't know if they failed by arbitrarily oscillating or something.

Thanks all so far; hopefully it's an easy issue and I don't have to start going through the transistors.

Edit: In my bin, I've got one of these 33pF ceramic caps and one of these 100pF film caps. I'm fairly tired now, but if anyone has any input into which of these I should try first, let me know.

 

[Spacehead]

Quote:

Originally Posted by jezz /img/forum/go_quote.gif The C6G I used is this one, Mouser part 5982-15-500V10 from the BOM. It's a mica cap instead of a ceramic cap. I'll check later to see if I can replace it with a film cap, but I don't know if I have a 10pF lying around. I don't get any distortion besides the hiss, and V+ and V- are just about perfect referenced to ground. However, I'm measuring with just a multimeter so I can't measure if there's any AC there. My understanding of the TLE is not so great, so I didn't know if they failed by arbitrarily oscillating or something. Thanks all so far; hopefully it's an easy issue and I don't have to start going through the transistors. Edit: In my bin, I've got one of these 33pF ceramic caps and one of these 100pF film caps. I'm fairly tired now, but if anyone has any input into which of these I should try first, let me know.

Your C6G is fine I guess. Could you get a good picture of your PPAs upside and bottom?
Are your solder joints all shiny?

 

[jezz]

I'll check and reflow all the joints when I get the opportunity. This probably won't be the week for it though. I'll report back if I find anything. When I put it together I seem to recall checking everything fairly well.

I did notice something though; with no source connected, if I quickly turn the volume up, this hissing turns into a very distinct buzzing. I suspect that's real oscillation and only happens because I'm leaving the inputs floating, but maybe that's meaningful?

Also, is it worth reducing the bandwidth of the opamp by increasing my C6G to 100pF? Should I prioritize reflowing the joints or swapping out C6G?

Thanks everyone.

 

[Spacehead]

Quote:

Originally Posted by jezz /img/forum/go_quote.gif I'll check and reflow all the joints when I get the opportunity. This probably won't be the week for it though. I'll report back if I find anything. When I put it together I seem to recall checking everything fairly well. I did notice something though; with no source connected, if I quickly turn the volume up, this hissing turns into a very distinct buzzing. I suspect that's real oscillation and only happens because I'm leaving the inputs floating, but maybe that's meaningful? Also, is it worth reducing the bandwidth of the opamp by increasing my C6G to 100pF? Should I prioritize reflowing the joints or swapping out C6G? Thanks everyone.

You could try increasing C6G to 100 pF.

In my experience soldering job is usually good enough if there is no solder bridges. Solder joint needs to be pretty ugly so that it would cause whole amplifier wide hissing.

The hissing comes from both channels, doesn't it?

I would try different op amps. Some op amps hiss more , again in my own experience.

AD8610/AD8620 is very quiet op amp.

 

[jezz]

I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here (those links will die probably within the next 2 months).

I tried reflowing all of the joints but the hissing is still present. However, the right channel now has more hissing than the left. The left also has a very high pitched whining noise when I turn the volume up to maximum with the input pins tied together. I also tried changing out C6G for the 100pF cap I had but that didn't change anything.

I'm using OPA627's on all channels right now. Do you really think they could be the cause of the hissing? It was my understanding that they were up there in terms of opamp quality. While I'd be up for trying the AD8610, I don't have any lying around and would rather not spend $30 debugging this. I've been meaning to try some AD744's; would those be worth trying to reduce the hissing?

Because the hissing isn't present when I drive high impedance/low sensitivity headphones, would it be a logical assertion that the issue is isolated to the gain stage? I'm trying to figure out where to look while debugging. I don't hear any hissing (or anything, for that matter) when the opamps aren't in their sockets. It looks like that's a valid test because the input to the buffer is pulled to ground via the feedback loop, though it might not be because the output is also pulled to ground?

Edit: Has anyone tried the Audio-gd discrete opamps in the PPAv2? They have the requisite FET input stage and, while much larger, are cheaper than OPA627's.

 

[Spacehead]

Quote:

Originally Posted by jezz /img/forum/go_quote.gif I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here (those links will die probably within the next 2 months).

You need to jumper S2L and S2R! That is pretty common mistake

 

[jezz]

All times AM.
1:30, Email about subscribed thread.
1:31, Done reading, soldering iron heating up
1:32, Random resistor found, leads trimmed
1:33, Resistor in place, accidentally broke Molex
1:43, Fixed stupid mistakes from 1:33 to 1:43 while fixing Molex
1:44, Fixed Molex
1:45, Started searching for how to send beer to Finland
1:58, Found out I can't ship alcohol from Massachusetts
1:59, Failed at being witty instead
2:08, Gave up on figuring out how to ship alcohol to Finland
2:22, Had a few OCD issues

If you're ever in Boston, drop me a line and I'll buy you a beer.

That totally fixed it, which is unsurprising because running it without those jumpers basically leaves the buffers uncompensated. I'm humbled by your eyes sir.

For future reference to any folks who have been debugging hiss, gain of 3, 3x OPA627's, 3.3ohm output resistors, 110ohm R11's, and no bass boost when built properly has none of it to my ears with AKG K271's.

Things to try when debugging hiss:
- Double check your solder joints
- Check against the schematic
- Swap out R11 for a ~100ohm value
- Swap out the output resistors R24 and R34 for 3.3ohm or 4.7ohm equivalents
- Really check against the schematic

Thanks again. Smart people in these parts

 

[Spacehead]

Quote:

Originally Posted by jezz /img/forum/go_quote.gif Thanks again. Smart people in these parts

I am glad that you got your amplifier working!

BTW Pretty soon I got my PPA v2 working my ears fatigued pretty badly. Don't listen too long periods now, or you might get that pain too

 

[joe_cool]

I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here.

Nice work. I have two suggestions (this is DIY so that's part of the fun).
1) Clean the flux off your board with isopropyl alcohol or a commercial flux remover. It may not sound better but will look better.
2) A neat way to ground the potentiometer shaft is to install a ring lug between the front bushing and the front panel, and use this to attach the ground wire. Of course this only works if you attach the pot to the front panel using a nut. I generally use an internal-tooth lockwasher as well, it helps to prevent pot rotation when tightening the nut.

Let us know if the sound changes after training (burn-in).

 

[jezz]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif I am glad that you got your amplifier working! BTW Pretty soon I got my PPA v2 working my ears fatigued pretty badly. Don't listen too long periods now, or you might get that pain too

Thanks! I've never found the sound from the PPAv2 fatiguing; only a nice neutral frequency response, a lack of distortion, and a marked propensity towards revealing the sound signatures of the opamps used. I fervently avoid any headphones or configurations with sibilance though, which probably has something to do with it (OPA627's, AKG headphones, γ2 at the source).

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif Quote: Originally Posted by jezz /img/forum/go_quote.gif I've attached some OK pictures of the top and bottom of the board. I've also posted some higher quality versions of them here and here. Nice work. I have two suggestions (this is DIY so that's part of the fun). 1) Clean the flux off your board with isopropyl alcohol or a commercial flux remover. It may not sound better but will look better. 2) A neat way to ground the potentiometer shaft is to install a ring lug between the front bushing and the front panel, and use this to attach the ground wire. Of course this only works if you attach the pot to the front panel using a nut. I generally use an internal-tooth lockwasher as well, it helps to prevent pot rotation when tightening the nut. Let us know if the sound changes after training (burn-in).

Thanks for the tips! I do tend to clean the flux off using my trusty liter of 91% isopropyl (lasted me for over a year now, still 3/4 full). Those photos are from when I was still actively debugging the board so they're a bit messy. I think I personally like the look of the ground strap; I don't plan on removing the RK27 any time soon anyway.

I've actually run my amp for ~300 hours listening to my AKG K340's which have a low enough sensitivity that I didn't hear the hissing. Curiously I don't find there to be a difference in sound signature between PPAv2: the uncompensated buffered CMoy and PPAv2: the proper Jung multiloop. I'm sure there is one, but I don't hear it? Or I'm very odd; it's hard to say. The gain did seem a bit high though... Actually, looking at the schematic and how I had it configured, what the heck? I was running it at a gain of >100?

Well, for what it's worth, I didn't hear much difference in regard to burn in after about an hour anyway. I should say that I wasn't looking for the sound to change with burn in either, so it may have been the placebo effect.

 

[Spacehead]

I got tired of using input capacitors on my PPA v2 and to the fact that bipolar input op amps put out DC offset of their own.

I added my small DC servo to the circuit. It takes input from the amplifier output and injects DC corrected signal to other end of R4 (op amp feedback loop).
When the amplifier idles without phones the offset with AD8620 on the servo is 0.1 mV

When I connect the headphones, DC offset gets to 5-6 mV on both channels. I am using LME49860 on the ground channel, so that might be reason for slight shifting (should have JFET on ground too)

I have still so long cables that there is slight hiss when there is no signal. It doesn't bother me now, maybe later.

 

[nini_knoxville]

hi,
i found the PPAv2 diy headphoneamp project through google and i don't know if it is a good amp? i currently have the sennheiser hd590... but its getting kinda old.. maybe soon the hd650 or if i have enough money dhe hd800 (dreaming). i wanted to try a diy amp before i will buy (if needed) a mid/high end amp (lehmann linear or grace m902) just to really know.. how good my headphones can be/get. so... my question is.. is the ppav2 a good starting point? i have soldering skills, but i'm not a audio electronic freak, but a computer programmer and have some microcontroller experience (maybe i could add an display and controll the amp digitally or so)