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
How old are the amps - were the amps everin storage - could it be electrolytic caps aging?
What kind of amp do you have. Clean your tube sockets and
check the fit of the pins in the sockets. Also clean the
tube pins. This May be why it shows up in both units and then goes away. Be carefull when tighting pin sockets.
if you can only hear it with your ear to the driver i would not worry about it. i have the same problem and it used to drive me crazy and i have spent days and hours trying to figure it out. i have been told by my stereo person with 20 plus years of experience that it does not hurt the sound and not to worry aobut it. i have finally taken his advice and now just enjoy my systme
Try an outlet on a different circuit (not just another outlet))
You don't mention if you moved the L amp to the R speaker, but I suppose you did.

Do you have a halogen lamp nearby? It's possible a lamp transformer is interacting with one of the amps, but not with the other.

Do the L and R amps use two different AC outlets, or do they share one outlet?

It looks like you swapped power cords, yes? Maybe the ground is disconnected on one of them?

Tubes may be the problem, but each tube needs to be swapped one at a time rather than the whole set at once. Just in case you didn't do this. I did notice that in your sequence, the hum shifted from the R amp to the L amp (number 5 in the list) AFTER you switched the tubes from L to R. Did you swap the tubes back to their original amps before observing number 5 on your list? If not, I'd say it could be a tube...and probably a power tube.

My system in the past has had a hum with nothing connected except the amps, but then the hum went away when ICs were connected. Especially in the case of phono ICs not being connected.

Hum is a PITA to track down. Good luck.
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.
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 (System | Threads | Answers)

Understood. Good luck.

FWIW...when I have had a hum in one tube amp and not in the other, it was because either a power tube required re-biasing, or a power tube was bad.
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. Any electronics store should sell a simple outlet tester for less than $10 that will instantly tell you if the outlet is properly grounded and wired correctly...
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.
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.
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?

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.
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?
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?
Scroll down on this page for CATV hum filters and other hum filter options.
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.
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?
connected to a dedicated ground rod, separate from the house ground.
I thought you said you hired a Licensed Electrician??
Danger Will Robinson!
.
Maril555, I'm afraid I don't have any answers to your questions about your computer, cable or modem. Sorry.
Jea48,
Maybe I wasn't clear- new ground rod is connected to the house ground as well