Broken JBL 300.1 Amp. Help plz!

I have a JBL 300.1 car amp hooked up to some infinity ref. series and kicker comp 12" subs. I hooked the amplifier up a while ago, as i didn't have a subwoofer enclosure to finalize my system, but i got it now. i hooked everything up, the RCA cables to the head unit, the power remote, the ground, and the subs all to the amp. No sound came out of the subwoofers, but the amplifier did amp the car speakers. the amplifier made my car speakers sound really distorted and sound comes out of two thick wire coils inside the amp. it sounds like crackling/buzzing, and the crackling follows the beat of the bass in the song. nothing in the amp appears burnt. it's weird that no sound was going to the subs too. maybe it's the power supply to the amp?
Any help/suggestions/input is appreciated(even one-liners)

new to DIY audio, but i love it so far.
thanks
~crust
 

ocool_15

Member
2004-11-26 3:15 am
sk
Re: really distorted and sound comes out of two thick wire coils inside the amp
Im assuming your talking about the power transformer(s) and you had the amp operating with out the cover? I would expect then there is a problem with the power supply, if your getting resonable volume but distorted I would guess something to do with the pwm( pulse width modulator) myself. I've only once ever hear buzzing sounds out of a amp.
 
if you hear a buzzing from the power supply that follows the beat of the music, you most likely have a short somewhere, or other utput stage problems. as the "follows the beat" of the noise means that signal has to be getting into teh amp, and getting itself into the power stage somehow, which means that the preamp-stuff (most likely op-amps running on zener-derived +/1 15 volts) must be somewhat alive, and also the early stages of the amplifier (running usually straight from the rails, or slightly decoupled). this means that the power supply is working somewhat.

I would check the wiring of the speakers for shorts, and check the output stage/driver/bias system for shorted devices and other problems. scope the output (and directly look at the waveforms on the power devices, as zobels and series inductos might reduce HF oscilation on the output) looking for oscilation. Also measure the voltage drop accross the emiter or source resistors to see if there is eccessive draw.