[cynan]

I'm encountering a feedback hum with my M901, similar to something you would observe with improperly grounded equipment. I sent an email to Virtue and hopefully, one of their techsperts will be able to provide me with a few clues as to the cause. In the mean time, I was advised to post this issue in case anyone else might be able to proffer any bright ideas.

Here is a breakdown of the issue as I have observed it.

When I first received the M901, I connected it to my digital music player without incident. I also connected the analog out on my AVR without incident.

Recently, I decided to try connecting the M901 to my computer's sound card. Low and behold, I get a low-level hum. Changing inputs on the M901 does not help.

I assume that perhaps there is something wrong with the connection between my sound card and the M901. However, attaching my digital music player to the same interconnect I used with the sound card produced NO hum. Must be the sound card.

I set up my Virtue TWO, and using the same interconnect, power supply (even with batteries) as the M901, I get NO discernable hum. This baffles me. Why the hum with the Sensation and not the TWO? 

So far, the only source that causes this hum with the M901 is my computer's sound card. Yet plugging this sound card into other amplifiers with the same speakers, cables and interconnects (and amplifier power supplies), all using the same wall outlets where applicable (as I sometimes use batteries for the Virtue amplifiers) results in no hum.

How could it be that the M901 is more sensitive to some kind of ground-loop or source of interference in my computer than the TWO?  (I also think I've tried plugging the sound card into my AVR (Denon AVR-2309) without any issue, though I will verify this).

Any ideas? Do I just give up on the computer as a source for the Sensation?

[jtsnead]

I would suggest unplugging each one of your other sources at a time to try to see which one might be interacting w/ the sound card causing a hum

[cynan]

I would suggest unplugging each one of your other sources at a time to try to see which one might be interacting w/ the sound card causing a hum

Well, how boring. (And now I have egg on my face  )

I thought I checked my other inputs. But sure enough, when I unplugged the analog out from my Denon AVR, the hum went away. Duh - That's why no hum on the TWO under identical conditions. And here I thought I had a really interesting issue...

Nevertheless, thanks jtsnead! It would have probably taken me a while longer to resolve this without your suggestion.

Now to figure out where the hum is coming from in the AVR...

Note: It's still peculiar that the AVR input was not interacting with my other source to cause a hum... jtsnead could you shed any light on why this might be the case?

[jtsnead]

Your welcome.
The reason I first went with a battery phono stage is because all the noise problems I had, which led to alot of plugging, unplugging and cheating.
The Virtue stuff uses a different type grounding scheme (I think, maybe Seth could chime in) and is more sensitive what is hooked up to it.
First I would put a two prong cheater on the AVR if it has a three prong ac cable. If that does not work do the same as you did w/ the Sensation start unplugging sources. If you cant get it build another room and seperate to video system LOL, I have my home theater system in the room next to my audio room

[OzarkTom]

I had the same issue with bad hum and the One.2 amp I was using. It turned out to be the HDMI cable from my Blu Ray player that I was using going into my HDTV.

[cynan]

Thanks for the suggestions.

My AVR comes with a cheater AC plug. Incidently, unplugging the AVR makes no difference - with the unit off and unplugged I still get the hum.

After unplugging all the inputs, the only one that makes any difference is one of the HDMI in (the one from my computer's video card). Except that unplugging this HDMI makes the hum about twice as loud! 

The only thing I haven't tried unplugging are the surround/center speakers.

Also, the hum is heard with any audio out from my AVR (zone 2, tape 2 monitor, etc)

And I was so sure that it would be my crappy digital cable box (which has been known to be sensitive to improperly grounded cable lines coming into the house...)

I think I'll just forgo the AVR/Sensation combo for now.

[virtue]

Dave - thanks for posting here and to all of you for responding.   

I'll never forget Michael's face as we fired up Sensation at RMAF one year and it was buzzing like a bee!  But since then, Ivan did a lot of working cleaning up the grounding on Sensation and it's pretty GOOD.  Not perfect... but good.

Sometimes and isolation transformer will help but we found that with power supplies, as with grounding, certain components just aren't going to work together.