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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
tvad
9,467 posts
 
10-07-07: Plato
If you changed the "bad humming" amp to a different circuit and it was quiet then I would suspect that the outlet you are using for your stereo may not be properly grounded or may be wired improperly.

Precisely. That's why I asked if the same outlet was used for all the swapping, or if two different outlets were used.

The tester Plato mentions is handy to have. It will also check for proper polarity.
maril555 OP
618 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.
jea48
2,944 posts
 
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)
Ics disconnected. Amp and speaker totally isolated from other Amp?
>>>>>>>>>>>>>

2. R Amp. moved to the L speaker (other amp unplugged altogether)- no hum
#2. Test, was L speaker cable still attached to L speaker and then R Amp connected to (L speaker cable and L speaker?) (L speaker cable/L speaker, a constant test control unit)
>>>>>>>>>>>>

L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
Was L speaker cable still connected to L speaker?
In other words for your tests did you always keeps the speaker cables mated to the speakers they were originally connected to?.......
>>>>>>>>>>>>>>

L amp. (used to be quiet), connected to the same L speaker, with the same power cord- hum.
>>>>>>>>>>
Just a shot in the dark, Could it possibly be a cable impedance problem? A problem with a Speaker cable?

maril555 OP
618 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.
tvad
9,467 posts
 
The hum existed after your rewire, and only after you disconnected the DVI video cable did the hum go away?

Seems to me this indicates the DVI cable was the problem, not the AC lines...despite the rewire. Many report hum caused by video cables in a mixed use AV system, particularly coaxial video cables from satellite and cable TV. There are some inexpensive filters mentioned in the threads that address this issue. I mention this only in the event you have satellite or cable connected to the system, and the DVI cable which you removed is simply sending the hum-producing video signal downstream, but is not the ultimate cause.

You shouldn't have to lift the grounds in the system to remove a hum, especially when the AC lines are all correctly installed.

Now that the DVI cable has been removed, have you restored the grounds?
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