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RE: Odd hum issue - suggestions ??

Yes. My limited understand is that the signal ground (neutral) is best only connected to the ground in one spot. I gather to avoid ground loops, etc. There is an existing connection going from the neutral on the main board to a lug on the chassis at the rear of the amp. I removed it and then checked the resistance between the board neutral and chassis (ground) and it was infinite (no second connection).

As it turns out, the problem seems to have been fixed by connecting the signal ground (netural) at the big power caps to the chassis. I tried connecting the ground lug to the board neutral with a large jumper (assume the wire inadequate to handle the 'load'. No reduction of hum. Connected the main board netural lug directly to the ground lug at the front of the amp where the ground wire is attached - no improvement. Connecting the large cap neutrals to the chassis just eliminated the hum. The wires from the cap neutral lugs to the main board neutral are quite large, so it does not seem they are deficient and were causing the problem.

Hooked up a signal generator, and both sides seem to be working nicely, especially without the hum to get in the way. Just need to calibrate the amplifier boards, and hopefully will be ready to go.

Thanks very much for the tips and suggestions. A bit of support really helps when tackling a problem that seems to be somewhat obscure at times..

regards -- Roger

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