Carvin DCM2000 trips GFI

[The Dude]

I've got 2 Carvin DCM2000 amps in the shop. Both work fine and both pass the AC leakage test on my variac with safety analyzer. I'm told by the customer that these amps, when connected to their mixer will trip a GFI circuit- not a circuit breaker, but GFI. Their band has several other amps and those do not create GFI problems. Reading around the web, I see that others have had the same problem with Carvin power amps only, so I believe it's a design problem causing nuisance tripping. While I've seen posts about the problem, I have yet to find a solution. I'm posting the schematic to see if anyone can spot something that might cause this symptom. The easy solution is to use circuits without GFI outlets, but the customer is determined to figure out "the why".

DCM2000_rev_M.pdf

[glebert]

I have an old Carvin tube amp that trips GFI outlets but only when I have the phase reversal switch set to certain positions, can't recall which one(s) right now. There is a whole bunch of "stuff" in that power switch circuit on the DCM2000, wonder if there is enough to delay the current between hot and neutral enough to trip the GFI.

Does it trip when turning the amp on or off? Mine only trips turning off.

[J M Fahey]

It does have a mechanical slow turn-on circuit, power resistors R44/45 are in series with primary, and shorted after "500ms" by relay contacts.

If such contacts get soldered by arcing, slow turn on does not work any more and magnetizing current will trip anything, it´s a beast of a transformer and large capacitor bank.

Confirm it relay works properly. (opens/closes)

[The Dude]

OK. The customer was in today, so I have more info. He has 2 Carvin DCM2000 amps and a Carvin C1644 mixer. If you plug any 2 of them in, no problems. If you plug in all 3 units, the GFI trips- even if all 3 are powered off. I verified this in my shop. The only thing I see connected with the units powered off is the EMI caps on the AC line. I'm going to try unsoldering them temporarily to see if the problem is still there. Still open to other thoughts and thanks for chiming in.

[nosaj]

Are there XY safety caps?
nosaj

[The Dude]

I will have to check to see if they are X or Y caps. The customer initially brought in one of the amps. I did some other repairs and kicked it out the door working fine. It's back again with the other two pieces and I have yet to open anything up. I'll add that this problem existed before my initial amp repairs, so it's nothing to do with those repairs. What's odd is that any two of the units work together in any combination. Only when you add a 3rd Carvin piece does the problem come up. The customer can also use any of the three pieces in another system and they work fine. It's f'n wierd.

[Enzo]

Id be checking the power cords were properly wired

[The Dude]

Yep. That's the first thing I did on all 3 units. It's also what I found wrong with the amp that came into the shop initially. It was miswired, but that has been corrected and the problem is still there.

[The Dude]

Just to put a bow on this one: I replaced the .047uf X2 EMI caps with .01uf X2 caps on the AC line and that took care of the problem. IMO, that should still provide plenty of filtering and gets rid of the GFI circuit nuisance popping problem.