[dhp]

Quote:

Originally Posted by Filburt Those two things seem to be connected on the PCB itself. I'll try to clean it up but I'm not sure it'll make a difference...

just clean up that one top right pin on the bottom opamp so it doesn't touch the board, just the pad

 

[Teerawit]

Quote:

Originally Posted by Filburt Yes, and one might note the diodes are in place to provide reverse supply protection, anyhow

Let me clarify:

one battery connector has the red lead going to B+, black lead to M-
the other battery connector has the red lead going to M+, black lead to B-

 

[Filburt]

Okay, I cleaned it up. It didn't make a difference. The pad for that pin is connected to that hole, which is connected to the pad for C8.

 

[Teerawit]

Quote:

Originally Posted by DieInAFire just clean up that one top right pin on the bottom opamp so it doesn't touch the board, just the pad

It's a via, shouldn't be a problem.

 

[Filburt]

Quote:

Originally Posted by Teerawit Let me clarify: one battery connector has the red lead going to B+, black lead to M- the other battery connector has the red lead going to M+, black lead to B-

Yes, that is how it is connected.

 

[cire]

Quote:

Originally Posted by DieInAFire C8+ appears shorted out to the opamp's top right pin on the bottom

C8 is the V+ bypass for the ground channel opamp. they are supposed to be connected.

 

[JDAPJ]

Your problem is probably due to oscillations.
I have had those problems too, and for me the solution was to increase the caps
at each op. 10uF standard electrolyte to the l/r amp and 1uF to the ground channel.
Now let's not get into a debate about that this doesn't make any difference because of this and that...all I know is that it worked for me and it's worth a try isn't it?

/jdapj

 

[kramer5150]

Maybe you could use your multi-meter and do continuity checks across different / adjacent solder pads. Refer to the schematic, and hopefully find a short ...? Maybe this would help show any pads that are NOT supposed to be connected to each other?

Garrett

 

[cire]

its possible the ground 8397 was damaged when you previously removed it. i would try sticking a new one on.

 

[Filburt]

It's possible that it was damaged, but the whole reason I rebuilt it was because it did this on the *other* board too. Same exact problem. I rebuilt it with fresh components other than the op-amps on a new board, and it still does it. I'm thinking maybe it's just a bad 8397 and it can't run unity gain stable. I don't have any spares, unfortunately. All I have is a couple of LM6172s.

I ordered some new stuff from tangent, but it hasn't arrived yet for whatever reason (I'm guessing USPS-related problems).

 

[Filburt]

Okay, I threw a 6172 on, and didn't experience the rapid heating up. Looks like that 8397 was bad.

 

[JDAPJ]

U didn't try my solution?
Or did u even bother to read it??

/jdapj

 

[cire]

your solution wouldn't have fixed a damaged opamp....

 

[Filburt]

Okay, new problem. I'm only getting some crackling sound out of the left channel, and all I have is hiss on the right channel. It's not a loud hiss, just some hiss. I have to turn up the volume pretty far to hear anything on either side. I checked my connections for the input/output, and can't see anything wrong.

The ground channel amp gets pretty hot when I have it turned up high enough to hear stuff.

Any ideas on what might be wrong? Oscillation again? I didn't leave out the ferrites, as you can see from the pictures, and my installation of the LM6172 was _very_ clean, even cleaner than the 8397 installation thanks to my trusty desoldering braid and very thin silver solder.

 

[tangent]

Quote:

Originally Posted by Filburt I'm only getting some crackling sound out of the left channel

Why are you testing first with headphones? I'll bet you find that DC offset is unacceptably high.

Quote:

Any ideas on what might be wrong? Oscillation again?

Yes, that's likely. Can you try some low value resistors (10-100) in place of the L1s? If that fixes it, the ferrites aren't the right sort for the problem you're having. One problem with the ferrite solution is that it requires careful tuning: the ferrite has to match the problem, it's not a guaranteed fix. I'm having second thoughts about recommending it as a default.