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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

Showing 6 responses by maril555

maril555 OP
619 posts
 
Shadorne- amps are VAC PA 90C,four chassis mono blocks.
WWShull- the "quiet" one can only be heard with the ear to the driver, but the other one is significantly louder.
Zenblaster- good point:
I forgot to mention, when I took the amps to my technician- they are both dead quiet.
I moved "humming" amp to another floor, effectively different circuit in my own home- quiet.
Tvad- L and R amps were connected with the same power cord to the same outlet.
I simply physically moved "humming" R amp. to the L speaker and hum dissapeared,without changing anything else, but when the same power cord reconnected to the L amp. and the same L speaker, the L amp began to hum.
It hummed BEFORE and AFTER I swapped the tubes, and hummed again after tubes were in the original position, in other words, tubes swapping didn't affect the hum.
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.
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.
maril555 OP
619 posts
 
Hum was gradually decreased after lifting the grounds, unplugging projector and finally was gone after d/c DVI cable.
I havent's restored the ground on power amps yet, will do it today.
There is no cable or sat. connected to projector, just a DVD player.
Two new lines are dedicated lines, also they installed
new deducated subpanel and all five(two existing dedicated lines plus two new ones and one for the projector) are connected to the subpanel on the same leg, and grounded at the same panel, connected to a deicated ground rod, separate from the house ground.
Again, I'm going to restore grounding with the DVI disconnected.
I understand, that dedicated lines are not necessarily a cure for the ground loop.
I have Granite Audio Ground Zero, that I'm going to use soon. I just have to make ground cables long enough to connect mono blocks.
maril555 OP
619 posts
 
Tvad,
Thanks for the info on CATV.
I have nothing, but a DVD connected to projector, but I do have a computer with the the cable internet connection and also a wireless router in the same room, not on the same AC circuit though.
Would that be a potential source of hum?, and how do I deal with it? CATV have some cable filters, are they needed in my case?
maril555 OP
619 posts
 
Jea48,
Maybe I wasn't clear- new ground rod is connected to the house ground as well
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