Bass amps and fuzz pedals... OUCH

[lowell]

I've had at least 3 bass amps come in over a couple years that had PA issues, fried power transistors, fried screen resistors in tube PAs and the customer said they were using a bass fuzz pedal when it happened. I'm curious how the experts here on the forum feel about this. I wouldn't think a pedal could cause such a problem, but I don't know. My thoughts are that the amp will just clip when it can't provide any more power, but then again maybe a wave approaching that of a square-wave can cause some problems. thoughts?

[olddawg]

The clipped signal increases the duty cycle. Also most fuzzes are set up with a gain boost. All of that heats up speaker voice coils. If one shorts the amp fries. Also the amp will be drawing max current if cranked, clipped, and boosted. If something is going to fail it will.

[loudthud]

Big square waves really stress the power supply and the screen grids of the output tubes. The amount of stress depends on the load. Speakers have resonant impedance peaks and look like inductors above 400Hz. At frequencies where the impedance is low, the power supply gets the load. At frequencies where the impedance is high, the screen grids take the shot. With square waves you get a little of both all the time.

I would think power transistors would do ok unless a current limit circuit kicked in and caused them to over heat.

[Steve Conner]

I wouldn't be surprised if all of the above were true. Bass fuzz can be pretty vicious, square waves can stress an amp beyond its sine wave rating, and bass amps may well not be designed to be stressed that way, though guitar amps certainly are.

I've seen a few times at small club gigs, where the bassist is DI'd, and he stomps on a fuzzbox. It just made a deafening blast of noise from the PA, and the sound guy freaked out and leapt to turn it down.