Turntable grounding question....

Vader · 03-01-2005, 09:41 AM

Last night, I found that I was getting a minor hum coming from the phono connection on my Denon AVR-2105. At first, I thought it was a splice to the grounding wire (the wire would not reach), so I started to troubleshoot by disconnecting it from the Denon. Note that both the Denon and the turntable is turned off (well, the Denon was in ‘standby’). When I turned the Denon back on, I was surprised to find a much louder hum. Next, I hooked-up an outboard phono pre-amp, undid the splice and ran the grounding to the pre-amp, and went in one of the 2105’s line-level inputs. I had done this for years on my old Marantz SR580 (no phono input) with no trouble. I got the same results (small hum with grounding wire hooked up, loud when disconnected). In all cases, the turntable itself was off, and was not sending any signal. How does the 2105 know whether the grounding wire is connected in this case (if the turntable is off)? I can understand when using the phono input (the amp knows that a ground should be hooked up?), but when using the outboard pre-amp and coming in one of the other inputs, the 2105 should not be able to tell, right? I mean, the phono pre-amp just boosts the phono to line-level (same as any other line-level source), right?

Finally, do any of the experts out there have any suggestions as to how to eliminate the soft hum?

Thanx!

John S · 03-01-2005, 11:08 AM

Try running a ground to both the pre-amp and the Denon AVR???

Ground loop problems can be tough to figure out for sure, no matter what components / connections are having the issues with it.

Vader · 03-01-2005, 11:18 AM

John, since I had the same quiet hum with both configurations, I returned to the direct connection to the Denon, so the pre-amp is now out of the equation. I figure that the pre-amp is just another chance for signal degradation, so if it does not solve the hum why use it? Besides, the pre-amp is a Rat Shack model, and I suspect that the Denon's onboard one is better. The problem is MUCH worse if the ground is disconnected, as the hum gets a lot louder (as it is - with the ground connected - I have to stand next to the speaker to hear it). I just don't understand why I got any hum at all when the turntable was off (and why connecting/disconnecting the ground made any difference)....?

John S · 03-01-2005, 11:58 AM

This usually means, the grounds are for whatever reason not at the same potential. You cna usually see it on a VOM even. This is not that uncommon, and is usually produced even when the offending device / connection is turned off.

There are Isolation / power conditioners that can solve it sometimes. Not on a turntable, but lifting a ground can solve it sometimes as well. (not really reccomended, but hey sometimes it comes down to whatever works / solves it)....

The turntable and AVR are fed from the same power source I take it????

Vader · 03-01-2005, 12:03 PM

Actually, the turntable is plugged into one of the switched outlets on the AVR, and the AVR is plugged into a Monster power center. I had not thought about it until you asked, but could that (theoretically) be a problem? I ran this same config with the Marantz, but could they react differently?

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John S · 03-01-2005, 12:34 PM

yes, I would certainly try plugging it in at the source, and every combo you can think of to try to get rid of it.

Vader · 03-02-2005, 09:58 AM

Well, last night I tried plugging the turntable into the source, as opposed to the switched outlet on the Denon..... made no difference. At this point, I'm starting to doubt it has anything to do with the grounding (mainly 'cause I can't think of anything else to try), and starting to suspect that it is simply a background hiss that I will have to live with.... shazzbot. Thanx, John...:-)



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