I am told what happened is they tried to switch amps to see how the other one sounded, when it was turned on the breaker in the panel tripped.

One is a Stagg. I forget the model but suffice it to say it is in the few hundred watt range, using a bridged configuration. I pop that and BOTH legs of the bridge are shorted. I had enough transistors for one leg and that's all it needs, but I ran out and haven't dry tested the other leg yet but I suspect it only needs outputs as well. How could one blow the other even if it shorted ? Ain't there current limniting or something ? It has double pairs of outputs on each leg.

(by dry test I mean cut the collector legs and see if you ast least get the DC centered)

The other amp is an Ampeg, I think a something someting 3500. It is a normal configuration with a triple set of MOSFETS. It has good outputs. The protection relay not only disconnects the outputs, but also shorts the speaker wire to ground. (I remember the discussion about the magnet on the relay, but that was a kilowatt rainge amp, this is only maybe 500 watts) Both NC and NO terminals were shorted causing the amp to run into ground.

Luckily it has current limiting but working into that short, it fooled me on the dim bulb test at first. Obviously it couldn't correct the DC offset at that low a voltage. The bulb was not completely lit. After a few tests I plugged it in directly and it did not emit any smoke. (one of these days I think I will put a meter across that bulb just to get another piece of information) Lifting the temrinal to ground got the amp working but I can't ship it that way of course.

Anyway, with this scenario, what kind of frigged up failure mode happened here ? The one thing I can tink of is that they connected the speaker to the next amp without disconnecting it from the first one. Well, they're musicians...

However they deny that. However, maybe more than one of them was doing this little hookup thing and they don't know what happened for sure.

Thing gets me is that one it blew the breaker. Two, BOTH legs of the Stagg are blown. If you short that out it would blow whatever side of the line got shorted, right ? It would not need all eight outputs.

So at this point I am wondering if we are dealing with some sort of ground fault deal. This happened at the shop which is a commercial building. You kinda think it would be wired right. (maybe I should chck ?)You know there are still those amps around that can shock you if the ground switch is set wrong. However neither of these amps have a ground switch at all.

Other thing is i have o idea what else was plugged in. These are bass amps, far as I know they were not going to record or anything so ther ewere not likely plugged into a mixing board or something like that.

Wrack your brain on that and have a beer. It is Friday.