Hello everyone.

I've been having troubles with amp and 990 hum and have assumed it's a ground loop issue. I took a look and saw that there isn't even a ground wire on the 990, although I assume it's still possible to have a bad power source.

I'm writing to ask if anyone here has had issues with their 990 humming and, if so, what was the cause and solution?

thanks,

John

Mine has never exhibited any ground loops. It's been a very quiet unit for me. Obviously that doesn't rule out a hardware problem in an individual unit, but as you mention the most common culprit is related to ground loops or other electrical "junk" (cable TV grounding problems, lighting dimmers) or wire routing issues.

Hi,

I had a serious hum issue with with my 970 and both of my subs in two different systems. I discovered the culprit by disconnecting source gear from the 970 one at a time until the hum went away.

In my case the culprit was the cable feed entering my home. when I disconnected the coax from my cable box, the hum disappeared. I had an electrician check it out and it was not grounded at all at the point of entry. When he tied the cable POE ground to same ground as the rest of the house wiring it helped some but there was still some noise. What took me the rest of the way was a ground loop isolation transformer. I have two installed, one on my HT (Jensen JEN-VRD1FF)and one in my bedroom (Dayton VIT-1), where I have cable boxes. No more hum.

Short story long, discovering the source of hum is a process; you need to be methodical and only change one thing at a time to be sure to get to the source. Once you've found the source, there may be another process waiting for you to figure out the fix. I hope it's as simple for you as it was for me. Google is your friend.

Best of luck,
Tony.

Can you perhaps hum a few bars to illustrate what exactly you are hearing. Sometimes the sub can be quite melodic.

Thanks.

Gonk and Palmer,

thanks for your responses. Gonk, I think I probably have issues with each point you site. And, Palmer, thanks for the filter recommendation; I think I will buy one of these units.

I've also been told that local transformers can introduce this kind of hum and given I'm fifth from the transformer, I'm wondering if it isn't at issue, also, given the changeable state of the problem.

While I've been out of this game for the past ten years, the new and higher level of transparency introduces also more complexity and the need for care ... a double edge sword.

Anyway, again, thanks for the responses.

John

I just purchased a 990/7500 combination about a week ago and have been experiencing a buzz. It has about a 60 Hz fundamental. Some experimentation shows that:
1. It comes and goes when the light engine in the television powers up/down. (Samsung HL-T6187S, rear projection LED light source 61").
2. Disconnecting various cables between the 990 and the TV make no difference in the hum
3. Powering the Samsung from an extension cord from another room gets rid of the hum.

The question now is whether I can filter the power sufficiently to eliminate the hum or I will have to run another power circuit.

Any other possible solutions appreciated.

Steve Mahan

Outlaw 990/7500/LFM1+
Adcom 555 II (in reserve)
Comcast digital Hi-Def cable DVR
Kef 107 (down for woofer surrounds)
Kef XQ-2c center (waiting for arrival)
generic CD and DVD players
still seeking surround speakers... (suggestions appreciated)

Steve:
If you've not run balanced you might want to try it.
I eliminated hum between 990-7700 with balanced cables. I just used some mic cables. Hum gone.

Suggestion for surrounds: Look for another set of 107s. Or if not 107s you might consider other s like 105s. Paul can help you. He helped me.

I"m not using balanced yet. The 107's with Kube will not allow balanced lines on their amplifier inputs. I plan on going to balanced cables for the center channel and the surrounds (assuming they don't require outboard equalization). Changing to a different outlet and using an extension cord for the display makes the system quiet enough that I can't hear anything with my ear against the speaker. The disk drive in the Comcast box is noisier than the audio system.

Steve
The Outlaw gear is definitely quieter than the Yamaha/Adcom preamp/amp that it replaces.

Oooooops
Sorry I forgot about the KUBEs.
Still as we discussed previously:if using a sub (and possibly the SMS-1 you probably won't require a Kube.

The hum in my system came from my Comcast Cable feed. As soon as it's disconnected from the cable box, the hum goes away.

I tried a Jensen ground loop isolator a long time ago, and it got rid of the hum, but it also knocked out some of the hi-def channels. Then, on a whim, I routed the cable coax through my Monster HTS3500MKII and it got rid of the hum and didn't affect the hi-def channels (or anything else). I couldn't believe it - I always thought of the Monster as a glorified power strip. FYI, I bought the Monster unit for $160 from buy.com about a year ago.

Good luck.