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Hum in phono that comes and goes

I have a strange hum that I hear when I touch my tone arm, but not all the time. When I move it off of a record that I just played, it does not hum. If it sits for a while like before I get another record to play, it will hum when I touch the tone arm to place it in the lead in groove. If I repeatedly touch it the hum reduces and after several touches will go away, so this seems like some sort of capacitance issue.
Is this the cartridge, phono amp, or pre amp, and how do I track it down.
And just to add to the strangeness, if I touch the arm and the pre amp chassis (not phono amp), the hum will disappear.
mrvordo

Showing 3 responses by mrvordo

mrvordo's avatar
mrvordo OP
151 posts
 
I have checked the grounds, but I don't think that is what it is. I would think that a faulty ground would hum all the time, which this does not.
mrvordo's avatar
mrvordo OP
151 posts
 
Again, it doesn't act like ground loop or faulty ground hum. Since touching the tonearm repeatedly will cause it to diminish gradually until it's gone. It's like something is getting charged up sitting, and releases when you touch the arm, or the arm is playing.
I've changed outlets AND circuits, as well as power isolators, phono cable, and arm without any effect, I figure it has to be the cartridge or phono amp, with a slight chance of it being the pre. I'm going to change the input on the pre today to see if that has any effect.
mrvordo's avatar
mrvordo OP
151 posts
 
Al, I think you might be on to something. I know one of the traces in the phono had previously come loose and I had just soldered it back in place when I replaced the caps. I've been suspicious of that connection in particular. Maybe I got too much solder in the area and it is the problem. But I'll open them up and check everything like you suggest.
Thanks
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