Yet another hum question (yes, I know - and I DID search the forums first)


I have a persistent hum problem from the main speakers.  First, I'd like to describe the system, then, I'd like to tell you what I've tried so far:

Dramatis Personae:

Samsung 65" TV (2 conductor cord)
Ethernet Switch (wall-wart transformer)
Cable box (2 conductor cord)
Oppo BDP-105 (grounded cord)
Yaqin SD-CD3 tube buffer (grounded cord)
Emotiva XPA-5 amplifier (grounded cord)
two PSA XV-15 subs (grounded cords)
Surge suppressor (power source for all but the PSA subs)

But note that ALL these items are grounded to each other via signal-cord grounds (via Ethernet, HDMI, or audio-signal cable grounds).  Also

What I've tried so far:

Unplugged the Oppo - still hums
Plugged the Yaqin into an isolation transformer with the Oppo unplugged - still hums
Plugged the Yaqin and the amp into the same isolation transformer (with the Oppo unplugged) - still hums
Plugged the TV into a (second) isolation transformer - still hums
Plugged the ethernet switch & the TV into a (second) isolation transformer - still hums
Unplugged the subs - still hums
Turned off the Yaqin - still hums
Unplugged the Yaqin - NO HUM

Something in the Yaqin's grounding is causing the hum (my conclusion - do you agree?).

How do I isolate the Yaqin's chassis from the power amp to stop this hum?  The signal grounds seem to be the (unavoidable) connection between the amp & the rest of the system, but isolating the Yaqin's chassis via an isolation transformer did nothing to stop the hum.

Could (should) I crop the grounding plug from the Yaqin's power wire?  That would essentially leave it as a floating ground but for the signal-wire grounding connections to the Oppo & the power amp.  Or, to ask the question another way, is it credible that the Yaqin's chassis is sufficiently above ground potential that I would damage other equipment if I removed the third ground pin of the Yaqin's power cord?

Thanks - Boomzilla



128x128boomzilla
There was no hum before the Yaqin arrived.  I'm relatively sure that it's the culprit.  There's not much directly in the signal path - Ethernet via DNLA to the Oppo - Oppo to the Yaqin - Yaqin to the power amp.
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Now there can be a number of things that can cause hums in a system, but the most common ground loop issue is from two or more components in a system that are different phases of the AC line and sharing a common ground.  Your home has 220v coming from the pole to your panel.  It is then split 110v to each side of your panel, but each side is 180 degrees out of phase.  So if you have equipment that are plugged into different outlets and any of the AC outlets are from different phases, AND your sharing a common ground you will get a ground hum.  

So you always want to have your equipment on the same phase, and that is important when running dedicated lines, and good idea to have 20 amp lines.  Now if that is not possible or you don't want to go to that extent, you can simply lift grounds.  I have done it for years, never ever heard of any issues, in fact many systems I have installed I lifted either all grounds or left just one connected typically the preamp.  Other issues can be dimmer switches, unshielded interconnects, power cords running parallel to speaker cables, refrigerators or appliances on the same circuit, just to name a few.