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Hum mystery to me

Calling all Hum guru solvers!

A while back, I started getting a hum out of my right speaker when playing a record on one of my 2 turntables. When I played the 2nd turntable, there was no hum.

On table 1, I am using an MC cartridge which runs into an Audio Valve phono pre-amp and from there into the system preamp.

Table 2 is plugged directly into the phono input on the system preamp.

 Since the tables have different phono pre-amps, I thought it was the Audio Valve phono pre-amp and took it to the shop for repair. After getting it repaired, I hooked it up and now I am getting a hum out of the right channel. So, I took it back to the shop. We hooked it up to a turntable, played and there was NO hum at the shop. I will say that they had a MM cartridge on their test turntable, but do not know if that makes a difference.

This is a mystery to me and if anyone has any suggestion to try, please chime in,

These are the trouble shooting tests I have done so far:

  1. I played a side on turntable 2. No hum. So that should rule out the amp or pre-amp.
  2. The table 1 phono pre is connected to a DVD input on the system preamp. I changed the input to another line level input on the system preamp. Hum continued to be produced. So, I concluded that the inputs on the system preamp are not the problem.
  3. I disconnected the ground wire on the tonearm—hum persisted.
  4. I hooked up a cheap NAD PP2 phone pre-amp to turntable one and there was NO hum.
  5. I tried a different interconnect from the Audio Valve phono pre-amp to the system pre-amp and the hum persisted. I conclude it is not the interconnect.
dmgrant1
jond's avatar
jond
5,678 posts
 

This is not clear did you ever run table 2 into the phono pre and then into your preamp? And if so did you get hum? If not you need to try this.

soix
8,765 posts
 

Did you try running table 2 through the phono pre if possible?  I’d try a cheater plug on the phono pre just to see if that eliminates the hum, and if it does maybe someone here smarter than me can help you troubleshoot for a more permanent solution.  Best of luck in finding a solution.

dmgrant1 OP
55 posts
 

Thanks Gents for the excellent suggestions.  Will give it a try and report back.

spenav
416 posts
 

@jond 

If the information you provided is correct, you are done troubleshooting. You said:

  1. I played a side on turntable 2. No hum. So that should rule out the amp or pre-amp.
  2. I hooked up a cheap NAD PP2 phone pre-amp to turntable one and there was NO hum.

Looks like the offending component is the phono preamp. Am I missing something?  Also when troubleshooting, eliminate one item at a time. You have to be patient. You might get false positives. Try to replicate the results consistently. You are lucky to have 2 tables, that will help you eliminate things faster. Don’t overlook loose connections. Good luck. 

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