200w amp trouble (LM3886T) - one chip only wants to oscillate

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Hi,

I've built the 200W amp as shown in AN-1192, with each LM3886T chip on a separate pcb; so the output from JFET (U5) feeds four separate circuit boards.

When 2 or 3 of the circuit boards are wired together, there is no problem.
When I wire up the fourth circuit board, it only wants to oscillate.
I've double checked solder joints and looked for bridges and all seems fine.

Anyone have any suggestions?

cheers
 
Not a bad idea - bloody amp's ****ing me off a treat.
5-6 weeks work and it's still not quite there!!!

That said, I'd still stick with a single 200W amp rather than two separate amps for two subs; surely it will mean two volume controls?

Made a further discovery today - when I wire up all four boards, the DC offset is 42V, the + / - rail voltage. Yet it works fine when only two or three of the boards are wired together.
Anyone, any ideas???
 
Thinking about it, I probably won't destroy it yet.

All the chips are the non-isolated type and earlier they were connecting to the heat sink. I've fixed that though.

Now two of the chips just oscillate. If you look on the application note, it's the two non-inverting chips U1 and U2.
 
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