I have an Outlaw 950 preamp and have noticed a peculiar problem that I have not been able to correct. I have a passive subwoofer hooked up to an external crossover and amplifier. I have noticed a low frequency hum (on the subwoofer channel only ... other channels are clear) when I hook up the monitor video out (either S-video or composite) to my TV video input. If I leave the monitor out disconnected, no hum or audible problems. I tried reorienting all my power cables, equipment, removing the crossover from the audio chain, changing the interconnects, switching amps, etc. The hum sound only comes through the subwoofer channel when the video is connected to my TV video input. Something tells me it is a ground loop problem, but I have not been able to isolate it and I am open to any suggestions. I know the subwoofer, crossover, interconnects, and amps are good. Again, I get great sound from the 950 unit as long as none of the video inputs are connected from the 950 to my TV. I have other video preamps and have not had this problem, so I am baffled by this problem.

Try using a ground 'cheater' plug that lifts the ground connection of a 3 wire AC plug on your power amp. You can also try reversing the AC plug in the outlet and see if that helps. Try unplugging your video display and see if the hum goes away. You can also try the 'ground cheater' plug on your video display. If all else fails, unplug _everything_ except the 950, your sub and it's amp. Start plugging things in until the hum returns (assuming it went away with everything else unplugged). This will at least isolate the culprit. You can also try plugging the video display into another power outlet. Some power amps have external posts that can connect the chassis ground to the AC ground. If your amp has such a connection, play with that. Another alternative would be to try the 'component' video connection if your display supports that.

Hum can be a pain, but there is always a cure for it in there somewhere if you dig deep enough.

[This message has been edited by soundhound (edited December 01, 2002).]

Do you have any other interconnects between your TV and 950? Analog audio, anything like that? If not, then it is almost certainly a ground loop -- probably your sub amp and your TV are on different circuits, and the connection between them via the 950 is producing the hum. Is that a possibility?

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gonk -- Saloon Links | Pre/Pro Comparison Chart | 950 Review

If you have your TV hooked up to cable, try leaving your tv hooked up to the 950 and unplug the cable from the tv. This will tell you if your cable connection is your problem. If so, you need to isolate your system from the cable system's ground. Let us know. I'll look for a link that shows how to do this. Good luck.

I was able to eliminate the hum by disconnecting my cable connection (Knology) from the wall. Now the big question is how do I get rid of it permanently because I still want to watch cable TV. Does the local Radio Shack sell these ground isolators? What do they do and where are they installed? Never used one before.

BTW: Somebody suggested I try the component inputs on my TV ... no can do because my 40" Mitso Tube was made before component video inputs were available.

There are in-line ground isolation transformers available for just this problem, probably at RadioShack.

ememi-- You need a ground loop isolator or ground breaker such as this one
Scroll down to see the #63400 "Ground Breaker". I could not find one at Radio Shack- so bought one elsewhere. This is one source you might want to try. Best..

Just wanted to close the loop that a ground loop isolator eliminated the problem and to thank everyone for their suggestions. I could not locate one through Radio Shack, but used the link above and it works fine (is very cheap in price too).