More thoughts on StudioLive crashes.....

Dick Rees

Dick Rees

Curmudgeonly Scandihoovian
Jan 11, 2011
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St Paul, MN
Edit:

Rambling post deleted.

Two brand new amps failed on stage and I'm wondering why. Fender "Cyber-twin" and an Ampeg bass amp, both with Class D switching power supplies. Got through sound check and one preperatory number, then both amps failed after the first song. Dead. Nothing else showed any sign of harm and the third amp on stage (an older Fender amp) was good for the rest of their time handling one guitar AND the bass guitar.

Power was from my Honda 3000ei which I have used for 5 years for such gigs with never a problem. In fact, I've used it with twice the system I was using that day. The difference from other years was:

Power to the two failed amps was taken off the same Furman AR1215 line regulator handling side-of-the-stage mix position. The older Fender was powered from a spare outlet on the front of the stage monitor power stringer, so it was not on the line regulator, nor was it a Class D amp.

None of my gear has switching power supplies and none of my gear sustained any damage. I have always run my consoles and processing off of the line regulator since losing a bunch of gear to bad power in my "learning the hard way" years. I have a MixWiz 14:4:2, Sabine GraphiQ, Shure auto-mixers and TCE IIIC multi-band comps in the rack along with a dual-CD "DJ" playback setup. It's all fully-functional.

Question is, why did the brand new amps fail? Why only them and why at the same time?

Thanks in advance for any help in understanding this.
 
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Re: Thread edit: Class D amp failures

There is a chance that it was merely coincidence that both died on you, but that's less likely. Without seeing the exact failure that happened inside the amps, it's hard to tell exactly what went wrong. However, I'd suspect some sort of high frequency oscillation got into the line and caused them to blow. Switching power supplies can be sensitive to that sort of thing, whereas standard linear systems don't mind it as much. This could actually have been caused by the Furman, if it got confused with what was being sent to it.
 
Re: Thread edit: Class D amp failures

Dick, as a service tech with over 40 years of professional electronic repair experience I can tell you with expert certainty that I don't know.

This probably doesn't make you feel better.

Yesterday I discovered a satellite receiver was constantly restarting itself. It and the entire rack room is protected by a 15,000 watt dual conversion UPS plus surge suppression on the main entrance and the sub panel. Its pretty easy to point the finger and say 'bad power' but finding the true culprit isn't so easy.

On one backup generator I experienced a great deal of trouble with voltage regulation. It turned out the load was non-linear (not reactive). The non-linear load then caused harmonic issues particularly the 5th and 7th harmonic to be reflected back to the regulator causing erratic behavior. Running the generator into a 60,000 watt resistive load worked just fine.

My conclusion was that although the gen was 2x the expected max load it still wasn't big enough. The gen is 130 kW. The next size up is cost prohibitive.
 
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