You either have a bad ground from the outlet (not really ground) or there is something wrong with your wiring. 115VAC is enough to kill you if there is enough current available.

I recommend disconnecting your power and figuring this out before you use the amp any more.

Any chance you could send pictures of your mains wiring?

Edited by user Wednesday, June 27, 2007 4:19:46 AM(UTC)  | Reason: Not specified

It sounds as though the mains wiring in your building is bad. 115V is what we use for mains voltage in the US, if that is any indication of the severity of the problem.

Are all the components connected to the same wall outlet? If not, try that to see if the problem goes away.

I think you need an electrician to examine your building wiring.

Hi,

I'm not a circuit drawer. so please excuse for the rude symbols. hope this part is enough:

I have to carry the amp to my neigbour to take pictures. my only worry is, if he insists on trying it out, he'll keep it. ;)

best, ullus

Edited by user Monday, March 30, 2009 3:03:26 AM(UTC)  | Reason: Not specified

Yes the output GND should be at identical potential if you are using a single center tapped transformer.

> Which trafo are you using?

a toroid with 2 secondaries, 4 wires.

I did the measurement as explained in the other thread, but is it possible that I formed such a CT?

p.s.: I have a 2nd toroid with 4 secondary wires, all black and no labelling. I'll try it out now, if using a DMM there are two possibilities to form a phase-right CT.

Edited by user Wednesday, June 27, 2007 6:56:28 AM(UTC)  | Reason: Not specified

It is a BSAB toroid; I have to reopen the case to see the type label since it is not mentioned in the auction; here is a picture; recently the same seller sold another one: transformer (link to an ended auction)

Edited by user Wednesday, June 27, 2007 7:06:27 AM(UTC)  | Reason: Not specified

just checked the 4 black wire secondaries' toroid: using the DMM-test procedure mentioned, there are two ways to form a two wire CT, - exactly as outlined above.

I checked again: both toroids are unlabeled what concerns their secondary phases; I unsuccessfully web-searched to find BSAB Elektronik toroid wiring specs. If you believe it might help, I could interchange the wires to form the 2nd CT possibility and see if the strange potential disappears.

Edited by user Wednesday, June 27, 2007 7:51:45 AM(UTC)  | Reason: Not specified

> Worth a shot

ok, changed the CT.

good news: the amp still runs. (I measured 54V~ between the ACx; so phases are ok.)
bad news: it has no effect on the potential; there's still about 120V~.

according to an application note "To earth or not to earth" on the hypex website, when using unbalanced input which is what I do, I found, quote:

"I can't recommend separating the audio ground from the chassis ground, because that's a recipe for making a radio receiver.
...
"the fact that tying chassis and audio grounds together is the only correct solution implies that earthing the chassis creates ground loops.
...
"If you want to use RCA inputs, disconnect the mains earth and employ double insulated construction techniques."

[they use frames; to read the full article, on hypex.nl click on applications, then on application notes]

disconnecting the earth and connecting the signal ground to chassis should solve my problem of the hazard to the fingers, - only I didn't use double insulation on the 220V part. so I can't disconnect the earth.

I hope to find another solution to avoid the potential, although the above word "only" deeply troubles me; it sounds exclusive.

in my case ground loops should not be a problem. so why not earth the signal-ground?

p.s.: just measured two old amps which are in original condition:
- accuphase E-204: both, earth and signal-ground (RCA) are on chassis.
- accuphase E-205: no earth at all; signal-ground (RCA) on chassis.
- my RevC: earth on chassis; signal-ground insulated.
so what does that tell us? in politics they make decisions according to the largest numbers (i.e., democracy). we'll see how it'll end.

Edited by user Wednesday, June 27, 2007 9:36:12 AM(UTC)  | Reason: Not specified

> What I don't understand is why there is an DC potential.

sorry, DC? I measured the 120V potential with DMM set at AC!

the primary is wound in the inner, the secondaries are wound outer side of the toroid. so where should the 220V primary leak to? to the secondaries? but no problem, I'll measure secondaries to chassis, with and w/o amps connected.

I'll also check the 12V toroid voltages against chassis.

could also easily replace temporarily the 300VAC toroid with a 600VAC (220V/2*24V) toroid and see if that changes anything.

if it is a leak, shorting chassis and signal-ground would not be a good idea.

I'll come back with the research results tomorrow.

thank you for your kind assistance!

best,
ullus

for the time being, I've connected signal-ground to earthed chassis; it works as before but potential is gone; maybe I'll do some research later.

posting pictures of my first DIY amp in a new thread.

Edited by user Thursday, June 28, 2007 6:45:48 AM(UTC)  | Reason: Not specified