Home Audio Hum Help

[Muff_Diver]

Sorry if this isn't the appropriate forum for this, but it seems fitting.

So a buddy of mine has a Technics SL-220 turntable and a Harman Kardon 330b reciever. When the two are hooked up to one another, there's a mild hum that's only really noticeable on quieter parts, but still very annoying. The hum does not exist when the receiver is set to the aux input or the radio.

For trouble shooting, we tried;
plugging my turntable into his receiver-no hum
plugging his turntable into my receiver- no hum
But once we plugged his table into his receiver, the hum was there (my setup has no issues).

Now I know embarrassingly little about electronics, but i fail to see how its possible that if his turntable works with my receiver, and my turntable works with his receiver, how his table and his receiver would create a hum that wasn't present with any of the other combinations.

[DRodriguez]

Is the turntable grounded? There should be a single wire coming out with and that should go into a silver hand screw on the back of the receiver.

[lordgalvar]

Some of those old technics had a third ground wire to attach to the reciever via fork and screw. You could attach it to the ground too. Might help? I don't know if yours has it or not (mine does SL-1600).

You could try isolating the turntable from the receiver too and see if that helps (if the motor is adding the hum).

Is your turntable more modern? Is it grounded? (That could be the difference).

DRod beat me by a second.

[Muff_Diver]

Is the turntable grounded? There should be a single wire coming out with and that should go into a silver hand screw on the back of the receiver.

It is and touching the grounding screw affects the hum.
Any clue as to why the same issue would not exist with the same (his) turntable on my receiver? Or why my turntable had no such issue with his receiver?

Lordg:
My turntable is an older unit as well, requiring the ground cable to receiver. We tried isolating the turntable from the receiver with no luck.
When the ground is "grounded" to the receiver it cuts the hum by half.
When you say a third ground wire, do you mean in addition to the RCA output (being the other two), or that there are multiple ground wires?

[lordgalvar]

Like, three prong power cable vs two prong (one is grounded, one is not). The RCA cables are grounded for themselves, but that thin wire is another ground (my technics has it, a few others I had did not).

I would just try to isolate the turn table (put it on another plug) and see if that helps. Check with chankgeez to see what's working with his power issues. It is more than likely the motor on the Technics creating some hum with the AC and the amp on the reciever (which is amplifying the hum). If you put it on another circuit, it might help.

Or, your reciever is amplying somekind of problem with the needle on the technics (ie, the preamps are different)...I don't know. I would try isolating it, then maybe trying your cartridge on the other turntable (could just be something weird like that)?

[Muff_Diver]

Ahhhh, then yes, it does have the third wire.
I will relay your suggestions onto him-hopefully one of them solves it.
Thanks a ton for chiming in-this is quite a dull topic to contribute to so its much appreciated.

[voerking]

these are super cheap: http://www.amazon.com/gp/product/B0009O ... ge_o00_s00