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
I have a Yaqin MS22B phono stage.  The factory, for some stupid reason tied the negative (grounds) of right and left channel inputs and the right and left channel outputs together.  It was a pretty easy fix.

Read post number 68.

http://www.diyaudio.com/forums/tubes-valves/216979-yaqin-ms-22b-phono-amp-7.html

I realize that you have a tube buffer, but maybe since it's the same company, they followed suit with other pieces of gear.


Hi @kenny928  - No, my speakers aren't shielded, but they aren't close to the TV either & I've never had the hum problem before.


Hi @mofimadness  - It's certainly possible - I'll look & see - thanks for the link!
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.
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!