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Author Topic: Hum in reverb circuit  (Read 2404 times)

JHow

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Hum in reverb circuit
« on: November 19, 2011, 07:47:59 PM »
Okay.  So I have this Earth Sound Research transistor amp.  I got it up and running by replacing all electrolytic caps and the output devices (I used 2n3055 from mouser).   I don't have a schematic, but it looks very similar to peavey pacer in jack darr's book p. 263.

My issue is hum in the reverb section.  Amp is fairly quiet and normal with reverb on 1, if you turn it up to 10, it reverbs, but with hum.  I tried replacing the reverb wires and soldering to the inside of the rca jacks.  This helped a bit.  Oddly, when the pan is not bolted in, with chassis on my bench, it has less hum than when bolted in the amp.  The pan is not in  a bag, but is screwed to the chassis through rubber grommets.  It doesn't touch the chassis, but it is close to the transformer and everything else.  What else should i be thinking about?  I want to sell this amp and I want it to be quieter before i do.

J M Fahey

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Re: Hum in reverb circuit
« Reply #1 on: November 19, 2011, 08:18:45 PM »
Probably you can´t do much, I guess the magnetic pickup head is picking some transformer magnetic field.
Just to check unscrew it and move it around.
Usually you can get a hum free position .... just it´s unmountable inside the head  :(

JHow

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Re: Hum in reverb circuit
« Reply #2 on: November 19, 2011, 10:00:25 PM »
I think you are right.  The position it sounds best in is sitting on a cardboard box outside the cabinet.  If I flip the output side away from the transformer it substantially helps the noise.  I guess I could make longer leads and but it in a bag at the bottom of the cabinet.