A15 Mk1 hum: please help!

Hi everybody,
I've just finished the A15 kit with the deluxe chassis and it gives the following problem:
it works BUT produces a strong hum (doesn't seem 50hz, but ground related) even with all volumes turned down, on both channels. Turning up the clean channel volume doesn't result in a louder hum, while turning full up the 2nd channel volume (even with gain at 0) makes the hum a 30% louder.

Checked everything (star ground, etc etc) and it's all right (the amp works, I can play it).

I've tried to put a cable in the send plug (or return one) to separate the pre stage from the final stage (it hums exactly the same way). The hum just disappears if I touch the star ground (or transformers screw or other grounded objects) with the inner part of this jack (the positive pole of the jack in the send/return plug).

Please can you suggest something to try?

Here is a sample of the hum with and without the above mentioned cable contact.

Re: A15 Mk1 hum: please help!

Zitat von david_djd

the place where you plug the amp into current have a ground wire?

Yes it has aground wire

Thanks for the reply

Mauro

Re: A15 Mk1 hum: please help!

Zitat von krusty

Have you removed some of the paint on the chassis (I mean on the back side where there is the earth wire and close to the ground star?
I have a15mk1 deluxe too! the chassis is painted also on the back side..insulating it...so..maybe this could be the cause.
Hope It helps.
Krusty.
P.S. I saw you are italian..I'm italian too if you want you can private message me in italian and we will exchange our opinions.

Yes, I've already removed the paint on both the earth screw and the star ground screw.

Thanks
Mauro