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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
 
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?
jea48
2,944 posts
 
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,

Did you tell the electrician to make sure all the circuits were fed from the same Line, leg, of the electrical panel?

Did the electrician install 2 new dedicated lines, not separate lines? Two Separate lines often share a common neutral.... Not good for an audio system connected together by ics....

Anyhow- connected the amps- strong ground loop noise.
A ground loop problem more than likely would have existed before, it was not showing up at the time because as you said the electrician said the outlets were not grounded. Grounds were lifted.

As Tvad asked in his last post,
Now that the DVI cable has been removed, have you restored the grounds?
Tvad
Try restoring all the safety equipment grounds with the DVI removed from the system, do you still have a ground loop hum?
tvad
9,467 posts
 
Scroll down on this page for CATV hum filters and other hum filter options.
maril555 OP
618 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
618 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?
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