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ullus  
#1 Posted : Wednesday, June 27, 2007 4:12:44 AM(UTC)
ullus

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Hi,

Finally the [metal] case with my newly constructed amp is closed; the first music was Steve Reich's "Drumming", then followed Anthony Braxton; it sounded so great that I instantly removed my old amp from the set. ;)

One problem remains which doesn't seem to be RevC specific, but maybe someone has a quick fix; there is a nasty potential between signal ground and case ground of about 115VAC, - not very strong but not pleasant for the fingers (with one hand on the case, the other on the metal shielded plug connector) when changing any RCA plug.

Here's my setup:

- main input 220V with filter integrated in the mains connector
- main earth connected to the case
- one toroid 2*26V with [two wire] centertap for the two RevC modules
- one toroid 2*12V with
- - 1st secondary for Joshua (and Darwin)
- - 2nd secondary for a vent (12VDC, 0.12A) which runs almost unaudible at 9V
- all signal grounds are isolated from case
- 5 sources are connected to the inputs
- 1 output channel connected to recorder
- all external devices are off or in stand-by mode; all have two wire main without earth.

is there anything to be grounded except main earth?

thanks for any help!

best,
ullus

Edited by user Wednesday, June 27, 2007 4:16:03 AM(UTC)  | Reason: Not specified

Brian Donegan  
#2 Posted : Wednesday, June 27, 2007 4:18:51 AM(UTC)
Brian Donegan

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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

ullus  
#3 Posted : Wednesday, June 27, 2007 4:54:17 AM(UTC)
ullus

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Hi,

it was not enough to kill me. ;) I felt it when I connected a plug while the amp was running. then I measured the voltage between chassis and signal ground. it happens only with plugs that have metal shielded connectors; with normal outer-plastic plugs, usually the hand holding the plug touches only the plastic of the connector.

what picture would you like, please?
a circuit diagram drawing?
or pictures taken from the amp with opened case?
(the latter will take longer to produce than the former since I don't have a digicam. I only have a scanner here.)

I reused a like-new chassis which already had mains connector with integrated filter and fuse (and vent) and I didn't touch the existing main earth to chassis connection.

when the amp and one input source is on, the potential is 120V~ instead of 115V~ with a DMM. I doubt that could light a bulb; just tried a 12V/20W car lamp and it didn't blow up; didn't even glow a bit.

unplugged all main connectors of all sources. the potential dropped to about 70V~. reconnecting one source after another to mains and the potential between amp signal ground to chassis goes up about 10V~ per source device even if power of sources is off (most of these sources do not have real power sitches; there are two digital SAT receivers, one dvd-player, one cd-player, one DAT-recorder.)

best
ullus

Edited by user Wednesday, June 27, 2007 5:29:25 AM(UTC)  | Reason: Not specified

Brian Donegan  
#4 Posted : Wednesday, June 27, 2007 6:06:30 AM(UTC)
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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.
Brian Donegan  
#5 Posted : Wednesday, June 27, 2007 6:07:24 AM(UTC)
Brian Donegan

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Both a diagram of your wiring and a photo of the actual wiring would be helpful. Diagram first I guess, as it is easier.
ullus  
#6 Posted : Wednesday, June 27, 2007 6:16:06 AM(UTC)
ullus

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Hi,

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

ullus  
#7 Posted : Wednesday, June 27, 2007 6:39:15 AM(UTC)
ullus

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> It sounds as though the mains wiring in your building is bad.

all is well isolated; I even reused cables with the isolated connector shoes.

115V is just a coincidence with the voltage over there.

> Are all the components connected to the same wall outlet?

yes, same outlet. no ground loops.

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

I suspect that there's nothing wrong.

to find out about, two questions please:

Q1: is the transformer's centertap connected to signal ground on the RevC PCB? if yes, why shouldn't there be any potential difference between earth and centertap?

Q2: to determine which two wires should be used for centertap, I used a DMM in the way you'd explained in another thread; in regards to the observed grounds potential, assuming I'd still get 26V between CT (PGND) and ACx each and 52V between ACx (I want to avoid to re-open the circuit just to try that out), - then there would be two ways to form a CT - would it make any difference if I used the two outer taps of my drawing as CT (PGND) and the two inner taps going to AC1 and AC2 respectively?

Edited by user Wednesday, June 27, 2007 6:42:24 AM(UTC)  | Reason: Not specified

Russ White  
#8 Posted : Wednesday, June 27, 2007 6:42:05 AM(UTC)
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Yes the output GND should be at identical potential if you are using a single center tapped transformer.
Russ White  
#9 Posted : Wednesday, June 27, 2007 6:43:03 AM(UTC)
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Which trafo are you using?
ullus  
#10 Posted : Wednesday, June 27, 2007 6:50:14 AM(UTC)
ullus

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> 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

ullus attached the following image(s):
CTim-possible.jpg (7kb) downloaded 474 time(s).

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Russ White  
#11 Posted : Wednesday, June 27, 2007 6:56:23 AM(UTC)
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Do you have a brand per chance? Anything I might lookup on the internet?

If you formed the tap like that I think it would still work, it just looks goofy... :)
ullus  
#12 Posted : Wednesday, June 27, 2007 7:03:27 AM(UTC)
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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

Russ White  
#13 Posted : Wednesday, June 27, 2007 7:11:45 AM(UTC)
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Sometimes a trafo will have the windings illustrated on the side so you can tell how to hookup the primaries and secondaries. Look for any indication of the wire colors and to which secondary tap they belong, from there you should be able to determine how to correctly get your center tap.

Cheers!
Russ
ullus  
#14 Posted : Wednesday, June 27, 2007 7:50:30 AM(UTC)
ullus

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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

Brian Donegan  
#15 Posted : Wednesday, June 27, 2007 8:06:42 AM(UTC)
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Worth a shot
ullus  
#16 Posted : Wednesday, June 27, 2007 9:15:11 AM(UTC)
ullus

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> 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

Russ White  
#17 Posted : Wednesday, June 27, 2007 10:51:34 AM(UTC)
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You actually may not get a GND loop if you connect chassis GND to Signal GND. What I don't understand is why there is an DC potential. There should not be. What that inplies is there there is a "leak" of sorts some place. Something is not well insulated. It could actually be a faulty transformer winding. I am not sure. What I can tell you is I have many amps with floating GND configuration and there is no DC potential on any of them to Mains GND.
ullus  
#18 Posted : Wednesday, June 27, 2007 11:28:49 AM(UTC)
ullus

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> 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
Russ White  
#19 Posted : Wednesday, June 27, 2007 11:33:40 AM(UTC)
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Ahh I am sorry I misread that part about it being AC. Having never experienced this I am not sure what to suggest next.
ullus  
#20 Posted : Thursday, June 28, 2007 5:45:41 AM(UTC)
ullus

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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

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