FM on one of my lm3886 based amp's channels

[Nate805]

I have a gainclone that i built on protoboards with a 260VA toroid and have it enclosed in a hammond aluminum chasiss with a bottom piece. I noticed that when everything got quiet, i had very faint FM radio on one of my channels (99.9 mhz I believe). This of course bugs the hell out of me, and essentially has led to the dissolution / death of my amp. I have hacked it apart to bare-bones to try and get the fm to stop (thinking it must be coming from some input wires acting as antennea. Well anyways, i have removed all input wiring (just the pin of the chip is left), tried different speakers, different speaker cable lengths, different input wire, different sources when i still had the wires hooked up, and still nothing. I have used mostly proper technique for construction, the power supply is external, there is star grounding for days, and (before i hacked apart my amp) the inputs were all shielded. One other thing to note, the amp functioned perfectly besides this wierd issue. It sounded amazing, but if you had the volume super super low or off, u could lean in and hear some radio which is unacceptable to me. Please, and ideas?

[Juergen Knoop]

look for shield/grounding on that 'radio' channel.
Some RCA connections are slightly incompatible and don't give good ground contact.
Most RCA plugs can be bent for better, firm ground connection.
This would be the first issue to look after and it could push the radio thing beyond listening threshold.
regards

[jaycee]

Solder a 220pF capacitor between the + and - pins of the chip (pins 9 and 10 on an LM3886) and that should stop the problem.

[AndrewT]

Originally posted by jaycee
Solder a 220pF capacitor between the + and - pins of the chip (pins 9 and 10 on an LM3886) and that should stop the problem.

Yes, you must bandlimit the input of the power amp.

[BWRX]

Originally posted by Nate805
It sounded amazing, but if you had the volume super super low or off, u could lean in and hear some radio which is unacceptable to me. Please, and ideas?

Did you see if you could hear the FM station when then amp's inputs were shorted? Were you using a potentiometer at the input of the amp? If so, was it grounded? Did the FM station go away when you touched the knob?