Axiom Home Page Forums General Discussion Technical Questions Is this a ground loop hum?

As I have been sorting out my receiver/DVD player with regard to playing audio CD's and switching between the coax and analog outputs, I have suddenly noticed what I believe to be a ground loop hum. I hear it out of all five speakers, fortunately not just my new M22Ti's and VP150, but it is most noticeable from the front three. With the VP 150, the sound appears to be coming more from the right hand mid range drivers than the left while facing the speakers. The sound is pretty low frequency and rather than a continuous sound like a tone, it is almost like a low frequency vibration. I assume this is ground loop hum.

My receiver is an older HK AVR65 that was know for having ground loop hum issues, but I swear I have not heard it until tonight. It is loud enough that I can hear it from ten feet away. The only thing I have done since Saturday night when I didn't hear the hum was change speaker size from large to small for audio CD playback. I can't believe this would be the cause.

Lastly, with the receiver powered up but my DVD player off, I get no hum. Once I power up the DVD player I can hear it. I have since removed the analog connection between the DVD player and receiver but the hum is still present. Could the problem be with the DVD player and not the receiver? What would make it happen all the sudden? Is this the excuse I need to buy the new AVR335/435 that I want?

If someone can possibly confirm that what I am hearing is indeed a ground loop hum, that would be a big help. Gotta go and troubleshoot.

Greg

I have done some quick research and one potential solution is to make sure all equipment is plugged into the same power feed. I have my PJ, receiver and DVD player all plugged into the same surge protector but that hasn't helped. In fact, it has been that way all along yet this problem has still suddenly materialized.

Greg

Greg, if you mean that, for example, you could listen to an FM program through the receiver without the hum, that would indicate that the problem wasn't in the receiver. It's difficult to see, as you say, how simply changing to a "small" speaker assignment could have anything to do with a ground loop or anything else involving hum. Does it now hum on "large"? Possibly a defect just developed in the player.

It has gone from bad to worse . . .

I have now unplugged everything from the back of my AVR65, except the speaker connections. There is no coax or analog connection, nothing from the X-Box or to the PJ. Just the receiver plugged into power. I have tried it both to the surge protector and straight to the wall. I can still hear hum!!!!

Whats worse is that if I toggle from DVD to CD on the front of the receiver it gets much louder. In DVD mode it is so loud that I can hear the center channels hum over the rear speaker's hum despite the fact that I am three feet from the rear and sixteen from the center.

I am now convinced it is my receiver but how do I know for sure? Also, do I want another HK? I am not happy tonight.

Greg

Greg, Have you tried to re-connect your cables and see if the hum would stop ? I know this sounds a bit far fetched but I wonder if you receiver was getting it's ground through one of the cables.You could also try a cheater plug and see if it gets rid of the ground.

Greg,

If you don't have a video connection to your H/K (from a cable feed or dish), which is often the source of ground loop hum, then it seems the H/K may have a problem in the power supply and needs service.

You could try plugging the H/K into a different wall outlet than the surge protector and see if that makes any difference. Also try reversing the AC plug if it's possible (it may be a 3-prong or polarized plug that does not let you do that).

I presume you do not have a powered sub connected by a coaxial link to the H/K (another possible ground loop hum source)?

You could try running a single piece of speaker wire (use any old stuff) from under a chassis screw on the back or bottom of the H/K to a cold-water metal pipe under your sink. If that doesn't eliminate the hum, then the problem is in the H/K.

Another ploy: if your H/K has a headphone jack, disconnect the speakers and see if you can hear the hum through the headphones. If you can, the problem is in the H/K.

Regards,

Thanks for all the ideas. I did not unplug the powered subwoofer from the receiver during testing, but I did unplug it from the electrical outlet and the hum remained. I have not tried another outlet so I'll do that tonight when I also try the headphones trick.

Repair centers want $125 US for labor plus parts to fix this receiver. If the receiver is at fault, I'll just buy a new HK AVR335 or Denon AVR 2106 and have a Merry Christmas with my new receiver.

Greg

Okay here is the latest.

1) I first tried the headphones WITH all other speakers connected. I couldn't hear the hum but Alan recommended to disconnect the speakers first. I thought I would give it a try anyway.

2) I hooked up my old Pioneer VSX5300 receiver to my VP150 as a left speaker and one M22Ti as the right speaker. I ran the analog RCA connectors from the DVD player to the receiver. The pioneer receiver was plugged into the same powerstrip as the AVR65 and DVD player. I powered up the receiver but left the DVD player off. I heard zero hum coming from the VP150 or M22Ti. I did hear a very slight high pitched hiss but you had to be six inches from the speaker and I heard similar sounds with the AVR65 connected to my Atlantic Technology speakers so I'll call this normal. I then powered up the DVD player but still could get no hum.

Does anyone think I have isolated the problem to being the AVR65? I intend to order an AVR335 tomorrow on-line and I probably can't return it if it hums as that would indicate a line problem in the house. Local prices are $150 higher, but I could return it if necessary, so I hate to pay a premium if I am right because I think I am.

Any additional thoughts are appreciated. I just thought of something else, maybe the digital coaxial cable is the culprit? I can't connect that to my old Pioneer but I can try using analog RCA to the AVR65 and see if the problem persists . . .

Greg

It is not the digital coaxial connection. If I have only speakers connected to my AVR65 I can still hear hum if CD is selected on the front of the receiver. If I switch to DVD the hum goes away until I power up the DVD player. I hate to spend money on a new receiver if it is the DVD player but if it is the DVD player, why do I get hum at all if it is disconnected from the receiver?

Still searching . . .

Greg

Try a cheater plug on the receiver.