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Intermittent hum

J

jmills

New Member
I'm sure you guys get a lot of these questions from newbies, so I hope you don't mind one more.

I recently moved. I'm using the same stereo setup I had at my old place, which includes DVR, Blu-Ray, TV, and turntable. The turntable is a Technics 1200-MK2 I got from kabusa a few years ago. It goes into a TC-750 preamp. The problem is a hum. It doesn't happen at all hours, but when it starts it goes on for a few hours. It's regular, with 37 seconds of hum and 43 seconds of not-hum. Even the sound of the hum is predictable, with a little crackle in one channel a few seconds in.

The ground wire is good (even tried replacing it). I replaced the RCA cables today with new ones. Tried different outlets on different circuits, but no help. The hum only occurs when the turntable is selected (although it does not have to be on). The hum goes away if I disconnect the RCA cables from the preamp.

I finally used the flowchart I found on your site, which suggested checking the location of the turntable within hum fields. I moved it to the other side of the stereo cabinet maybe 12 feet from it's original location, and while the hum didn't completely go away, it is much quieter.

Anyway to eliminate the cause of the hum? Or to find a way to shield my system from it? Or do I have to experiment until I find a spot that doesn't pick it up? I really hope you can help; I'm at my wits end.
 
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First of all I would want to be sure of where the hum is coming from. You are using an external preamp, right? Try connecting the preamp to a different line input. Did the hum move or is it gone? If you still have the hum that would point to the preamp/ turntable. If the hum is gone the input you were using has the problem. Let's assume the hum appeared with the new input. Can you remove the preamp and connect the turntable to a phono input? No phono input, you can still make the hookup because we're listening for hum and we're not concerned with listening to music. No hum? The preamp is the likely culprit . Still hum, then the turntable is the suspect. Try removing the cartridge and reseating it. By this point you will have a very good idea of what is the hummer.

By the way, I have had intermittent hum problems with older gear with corrosion in the RCA jacks. Usually a good detoxing and exercising of the Jack cleared the problem up. Good luck!
 
Thanks so much for your response. I've been waiting all day for the hum to come back so I can try your method, but it haven't heard since yesterday. So maybe moving the turntable did the trick after all.
 
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