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)
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?
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.
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.
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.
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...
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.
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
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.
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