Some help reducing hum from turntable for recording?

[keepitsimple]

Hello all I've been trying to convert LPs to CDs and Audacity's helped a lot but I'm getting some hum from my turntable/receiver set up.
It's a Technics SL-D303 direct drive TT from 1982 with Shure V15 Type IV cartridge hooked up to an Onkyo TX-904 Tuner-Amplifier (receiver) from 1992 with Phono input. I'm using the Tape 1 out to send the signal to my mac.
It works pretty well but I get some hum. It's not overpowering but you can clearly hear it if you turn the volume up on the receiver. Also, it gets better or worse depending on a few things.
For instance if I connect the ground wire from the TT to the receiver I get a little more higher pitched hum in the right channel. I thought the ground wire was supposed to get rid of hum but not in this case.
Also I get even more hum once I turn the on the power button of TT unless I reverse the power cord plug (it's not polarized). In that case there's more hum with the power off and it reduces with the power on.

I probably could live with that small amount of hum (with no ground wire and the TT plugged in that way), but when I connect any other device to the back of the Onkyo receiver I hear some more hum. No hum if I just connect cables to the receiver but as soon as the other device is connected then I get the hum.

I don't know if these hum problems have to do with the turntable, magnetic cartridge, receiver or what. Any suggestions would be appreciated. Thanks!

[kozikowski]

There's some alarm bells ringing.

Is the receiver connected to an FM antenna on the roof? What happens to the hum if you disconnect it?

Is your house wired properly? Do you have three prong power outlets?

http://peaceful.manufacturer.globalsour ... Tester.htm

You can invest in one of these things to check out your outlets. I've lived in two houses where at least one outlet was wired dangerously wrong.

Let's stop there and find out how much trouble we're in. The hum should vanish when you connect the turntable ground wire. You could have a shock hazard if it doesn't.

Koz

[keepitsimple]

Thanks for the reply Koz. No there's no antenna on the roof and yes my apt. building seems to have good (enough) wiring with 3 prong outlets.

I located the source of the hum yesterday: my beloved Technics SL-D303 turntable that I bought brand new in 1982 (or maybe the cartridge or the headshell wires).
A friend of mine has a Yamaha P-520 TT that I hooked up to the Onkyo receiver and no hum! I behaves like a TT should with lots of hum before connecting the ground wire and nada after connecting. I turned the volume all the way up with headphones on and didn't get the slightest wisp of hum.

I'm not sure what happened to the Technics but when I went to make sure the L/R wires were solidly connected to the receiver I got additional hum when I touched the connectors. Those and the ground wire are hard wired to the TT so I can't replace them. So much for that TT but it was great for years!

[kozikowski]

<<<Those and the ground wire are hard wired to the TT so I can't replace them.>>>

I'd be surprised if that was where the error is. I suspect the Turntable internal power supply is leaking some raw building power into the sound connections. That's why your whole system becomes unstable if you reverse the power plug or shift around the TT ground cable.

There is an engineering way out of this. You can by an isolation power transformer to separate city power from your sound system. That would probably cost more than replacing the turntable.

Congratulations. It usually takes days to find a problem like this.

Koz

[keepitsimple]

Koz I think you're right about the power leaking out because the orange strobe light doesn't work like it's supposed to, either.
In order to see the marks on the platter with the light it has to be at night with the lights out and it's still faint. The slightest adjustment to the speed adjust and it adjusts a lot, too much. Thanks again!