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GK MB500 problems

#42
GroovinOnFunk said:
The fan does work... It was really hot on stage, but it's only ever done this with this cabinet (though I've never run this amp at 4 ohms before getting this cab).

I'm not sure how I could reproduce that problem... I've plugged it in at home and never had that issue. But then again, if I turn up to "gig volume" in my apartment, I'll probably get evicted.

Again, I did have the -15db pad (or whatever it is... might be -12) to counteract the level of the preamp, and it's not like I was cranking all my EQs up to 11. I gave the mids and trebl just a slight slight boost and that was it. (especially once the amp started crapping out on me)
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Check the DC resistance of the cab. It should be about 3 ohms across the terminals. It may be that the cab has some kind of defect that lowers its impedance, causing your amp to thermal out.
 
#43
There may be reactive energy storage in an LC tank circuit (due to disconnected or blown tweeter) that is triggering the protection circuit on the power amp module. This is due to an interaction with the now defective crossover (which must have a tweeter present to damp the LC tank) and the residual PWM carrier. Any products using this power amp module will do the same thing (better than failing IMO)
 
#45
agedhorse said:
There may be reactive energy storage in an LC tank circuit (due to disconnected or blown tweeter) that is triggering the protection circuit on the power amp module. This is due to an interaction with the now defective crossover (which must have a tweeter present to damp the LC tank) and the residual PWM carrier. Any products using this power amp module will do the same thing (better than failing IMO)
Click to expand...

Not that I've ever had the OP's problem myself (I also have an MB500), but to your point about the tweeter being disconnected- are you saying that to avoid nuisance triggering of the protection circuit, one should NOT defeat the tweeter because it's an integral part of the 'LC tank circuit?'

I have a GK neo 2x12 cab and I always run it with the tweeter defeated just because I like the tone better that way. Would you recommend, for reliability's sake, that I get my tone through the EQ on the head rather than simply defeating the tweeter on the cab?
 
#46
Correct. Some crossover implementations, especially those that attempt to use zobel impedance correction networks, can present an illegal load in the presence of residual PWM carrier. In these cases (hopefully) the tweeter provides the needed damping to prevent energy buildup.

Most cabinets do not use these methods but some do, that's why I commented.
 
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#47
agedhorse said:
There may be reactive energy storage in an LC tank circuit (due to disconnected or blown tweeter) that is triggering the protection circuit on the power amp module. This is due to an interaction with the now defective crossover (which must have a tweeter present to damp the LC tank) and the residual PWM carrier. Any products using this power amp module will do the same thing (better than failing IMO)
Click to expand...
That's exactly what I was saying in simpler terms.
 
#48
Did a gig last night and when I got there I found out that we were having to use a generator for power and my amp went into protect mode. I tried it today and it seemed okay then randomly went into protect mode again briefly a couple of times. I usually use the channel with the overdrive and I tried using the other channel and did not yet replicate the problem.
 

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