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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
newbee
4,767 posts
 
Disconnect and unplug everything. Now working backward from your amp, one component at a time, connect RCA from pre-amp to amp, turn it on - any hum? If yes, try a cheater plug on the pre-amp to see if the hum goes away.

Assuming not, now connect a source, etc to the preamp. Any hum - same drill as above. Sooner or later this process will lead you to the hum's source and help you determine if floating the ground is a solution.. Don't overlook the antenna as a source of the hum - that is very common. Don't overlook the possibility of a hum occuring because of cable's being too close to transformers in your components (very common source) or other electrical sources. Don't just turn off components, actually unplug them and disconnect all of the connecting cables.

This may not solve the hum problem but you will have at least identified the source and then be able to figure out how to solve it.
boomzilla's avatar
boomzilla OP
13 posts
 
Very good advice, @newbee  - My gut feeling is that the chassis ground from the Yaqin is the source.  When that is unplugged (despite all the interconnects being hooked up), there's no hum.  Therefore, my next move will be to use the cheater cable on the Yaqin.  If that doesn't get it, then your "full court press" solution is next!

boomzilla's avatar
boomzilla OP
13 posts
 
SUCCESS - Cut off the grounding plug for the Yaqin and now the whole system's quieter than a bought-off witness!

:D
newbee
4,767 posts
 
I'm not surprised that that worked for you, however the actual source of the grounding problem might still be in a source  ahead of the Yaqin. I'm not against the idea of lopping off the ground on the Yaqin's PC to solve the problem like a lot of folks are, IE's included if not principally, however on some boring/rainy day you might need something to break up the tedium and my suggestion will give you something to do. FWIW, in an almost identical situation I sourced a hum to one of my CDP's. I used a cheater on it and the hum went away.
boomzilla's avatar
boomzilla OP
13 posts
 
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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