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Hum- help needed

It's been very strange and I cannot think of a logical explanation.
It will require all your attention.
1. Two mono blocks plugged in. EVERYTING ELSE IS UNPLUGGED,
ICs disconnected- hum in the R channel (can be heard from
2-3 ft. away)
Hum in the L channel- order of magnitude lower, I would consider it "normal", can only be heard with the ear to the driver.
So I would think, it's not a ground loop (nothing else is plugged in, heard in R ch. only.
2. R Amp. moved to the L speaker (other amp unplugged altogether)- no hum.
L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
3. All tubes switched L to R- no difference.
4. R amp moved back to the R speaker (position, where it used to hum- no hum.
5. L amp (used to be quiet)- hums, no matter what.
To sum it-up:
I think it's not a ground loop (see #1),
It's not the amp.- (see # 2),
It's not a speaker- (see # 2),
It's not the tubes- (see # 3)

So, here is my question- what the hell is it?
maril555
maril555 OP
619 posts
 
Plato, Tvad- I agree with you, and also think, that the problem is with the outlet. Actually I have an electrician coming tomorrow to install two extra lines, and I will have him check the existing one, as well.
All that said and done, the most puzzling part to me is, that hum went from one amp to another. I can't even contemplate a reasonable explanation for this one.
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maril555 OP
619 posts
 
Here is an update.
Yesterday my electricians installed two new 20 A. lines for my mono blocks and fixed the two I already had- ground was not connected at all, plus the wiring was screwed up beyond belief.
Anyhow- connected the amps- strong ground loop noise.
Lifted grounds- much lower. Unplugged my front projector- lower yet. Physically disconnected DVI video cable from the DVD player- DEAD QUIET.
Bottom line is- as many of you, and myself thought, faulty line wiring was the culprit.
As a side note- the whole system now sounds unbelievably better- explosive dynamics, more natural tonal balance,
much more relaxed presentation with great frequency extension at the same time.
My new preamp, that I was not too impressed with initially-
it is fabulous now.
Deep inside I was always somewhat sceptical about potential benefits of the dedicated lines, now I understand how wrong I was. The best upgrade I've made.
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