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I have the dreaded hum

I have a humming that occurs on one channel only. It happens when TT is off or on. When you swap TT leads it stays on same channel. When you swap interconnects from pre-amp to amp it switches channels. Only occurs when pre-amp is on phono input and set to moving coil. If you disconnect TT leads it stops. Equipment and set-up is all new. I've moved the equip around, no change.
I sent the pre-amp back to the dealer a while back and he said it was ok.
Today I bought a diff phono stage and the hum went away.
Dealer still thinks the pre-amp is ok.
What else could it be?
Tube amp and pre-amp
dirtbag
swampwalker's avatar
swampwalker
5,138 posts
 
There is a problem in MC portion of the the internal phono stage. I'm not knowledgeable enough to tell you if its the MC switching or or the MC gain or step up, but there is no question that there is a problem in the internal phono stage. You know that the cart and arm wiring, and the phono interconnects are OK and you know the line and MM inputs are OK on the full function pre-amp. There's nothing else left.
champlainbass's avatar
champlainbass
4 posts
 
I had the same thing for a while, except mine was intermittent. I had to replace the Rca's. One had just worn out over the course of 25 years. I tried everything else first. Everything has been fine since. Good luck.
dirtbag OP
17 posts
 
I would be surprised if it was the RCA's since everything is brand new.
atmasphere's avatar
atmasphere
11,794 posts
 
Well, you've already tried other phono/arm cables. And they work with your outboard. So the problem is in the preamp, whether the dealer thinks so or not.
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