Left channel hum - rack + Speedball

[jj4001]

Ok. So that's the small board between the volume Pot and the output jack, is that correct?

And if I understand you correctly, the white wires at OA and OB would reverse places. Red wires at 1A and 1B would reverse places. And black wire would stay in BAB.  Do I have that right?

[Paul Birkeland]

Yes, that's all correct.

[jj4001]

Thank you for your help.

I will try this today or tomorrow and report back.

[jj4001]

I flipped the board, rewired, and the hum has stayed in the left channel.

[Paul Birkeland]

Now try doing the same thing with the big board (which is a bit easier.

[jj4001]

Ok. And should I leave the small board flipped, or put it back to normal?

[Paul Birkeland]

That won't really matter for this test.

[jj4001]

Ok. And for the bigger board do I exchange positions of the white wires with each other? And what about the black and red wires?

[Paul Birkeland]

The white wires switch, the red and black need to stay where they are. 

[jj4001]

Thanks again for your help!  After this switch the hum is still in the left channel.

[Paul Birkeland]

I think you may need to take the small PC board out and put the 22.1K resistors back and see if the issue goes away.  If it doesn't, tack in the 3K resistors and see if the noise goes away.  If it doesn't then something was disturbed while installing the Speedball that was present in the underlying build. 

[jj4001]

Anything that was taken out is long gone unfortunately. Are there any areas or solder joints i should look carefully at if you had to take a guess on what the issue might be?

[jj4001]

One interesting thing I just noticed. While I had the amp upside down, when I applied pressure (pressing down) in any area of the main chassis between the large tube and the transformer the hum greatly reduced.

When I flipped it upright and pushed down in the same area it didn't have the same result. It was only when pushing down on the under side while it was upside down.

[Paul Birkeland]

Tighten all your screws before doing anything else.

[jj4001]

Oddly, all screws were very tight from previous troubleshooting. Last night I tried experimenting with the tightness of the transformer screws while listening and loose or tight it didn't change the hum.