PAIA 9206 Headphone Amplifier - anyone build one?

I finished 6 of these but I have same problem with all of them.
It shuts down in many ways. If input sound is lowered or if many
pots are lowered also. At some point it starts to work like a noise gate :shock:

Anyone has a clue what is going on here? Seems like a bad design to me.

SCHEMS

With all pots fully CW the input sees 1.6k, or 800 Ohm in mono-mode. Can your source handle that?

Do you use 5532s, as stated in the schematic, or other op-amps? Are the op-amps socketed?

Are the pots scratchy?

What is the impedance of the headphones you're using?

What are you using to power this? The supply splitter is ... minimalistic, to say the least.

Have you contacted Paia?

I would expect more problems with this circuit for high in/out levels than for low ones.

JDB.

I built a four channel version of that back in the bad old days when I didn't really know what I was doing. I've still got it, but it was bloody awful. Distorts really easily, probably due to the poor old opamps going into current-limiting while driving low-impedance headphones. No blocking caps on the pots, so they were scratchy as hell. Don't remember it ever shutting down or cutting out at any point though, even when working hard to deliver four headphone feeds into a loud rehearsal room. It was just...bad... :sad:

I would check to make sure you didn't tie the "-" side of the 12V power input to the actual circuit ground ("G" at splitter output)...

With all pots fully CW the input sees 1.6k, or 800 Ohm in mono-mode. Can your source handle that?

Not sure. I bought cheap hong kong wireless microphone systems to feed the boxes.
But when I tried them I sent signal from my mixboard and it still doesn't work right.

Do you use 5532s, as stated in the schematic, or other op-amps? Are the op-amps socketed?

Just what they sent, 5532s. They were soldered directly by a friend. Is there any chance to use better ones here?

Are the pots scratchy?

Nope.

What is the impedance of the headphones you're using?

32ohm

What are you using to power this? The supply splitter is ... minimalistic, to say the least.

A socket PSU plug 1200mA. This should be enough for one unit.

Have you contacted Paia?

Yes, but no satisfying answers came from them yet.

I would expect more problems with this circuit for high in/out levels than for low ones.

I noticed, they distort very quickly :?
The bad thing is I organized 6 units which costed 600€ at our end I got
crappy headphone distribution amplifiers. Is there any chance to MOD
these to work better. I feel really embarrassed and desperate now :sad:

[quote author="Crusty2"]I would check to make sure you didn't tie the "-" side of the 12V power input to the actual circuit ground ("G" at splitter output)...[/quote]

I think it's wired OK, + goes to + and - goes to - .

If you have tied the circuit board ground to the chassis anywhere (output jack gnds, for example), and your 12v input jack is not an isolating type, then you are shorting out your V- rail, which may explain the strange behaviour...
Easy enough to check: measure that you have both your power rails.

[quote author="Crusty2"]If you have tied the circuit board ground to the chassis anywhere (output jack gnds, for example), and your 12v input jack is not an isolating type, then you are shorting out your V- rail, which may explain the strange behaviour...
Easy enough to check: measure that you have both your power rails.[/quote]

I just soldered the wires directly to the board, no input 12V sockets used here.

I checked the voltages and across the middle cap I have 12V and on the two side caps around 6V, so this looks OK, right?

Yeah, that's actually a perfect split. But it's still only +-6 volts, which is a really low rail and is the reason it distorts easily.

If the three rail-splitter caps are rated high enough, you can try a higher voltage supply, like 24V. Or better yet, you can remove the 470 ohm resistors and hook a +-15V supply up to it.

I just found out that after a few seconds when it craps out
one side cap goes down to 0V and the other side cap sees 12V.

Any idea why?

[quote author="Crusty2"]Yeah, that's actually a perfect split. But it's still only +-6 volts, which is a really low rail and is the reason it distorts easily.

If the three rail-splitter caps are rated high enough, you can try a higher voltage supply, like 24V. Or better yet, you can remove the 470 ohm resistors and hook a +-15V supply up to it.[/quote]

Caps are 25V only. Probably would need to use 63V, right?

Problem solved!!!

3 resistors were wrong cause my friend didn't check the values before he soldered them onto the board. :?

Sounds fine now and I don't see any problem with distortion at all.
I take back all my bad feelings about PAIA :thumb:

Hooray! :thumb: :thumb:
Sorry I coudn't help you, but glad you got it going on your own - even better and a great feeling isn't it? I know you were under some pressure to get it running.

All the boards had the same mistakes? I assemble boards for my uncle, usually in batches of 10. And if I make a mistake, it's usually the same on all the boards...

If you ever use these headphone boxes for music recording, you can always up the supply voltage too.

Thanks for the tips :thumb: :thumb: :thumb: