Perreaux 1150-b Distortion

[wolfman]

I have the oportuninty to buy a Perreault 1150-b with the matching pre-amp SA-2 for just $250.00 Canadian.. a good deal me thinks. Unfortunately the left channel has quite noticable distortion. I have done all of ther checks and it is definetaly the amp that is the problem. I have been advised that the odds are that it is an output transistor and I have checked and there apparently are substitutions available for the K135/ J50.

My question is this: Any other thoughts on the cause of the distortion ?

I have listened to ther amp as best I could and it sounds to be a quite fine sounding amp into my JBL S/3100 horn/reflex speaker. I am wondering if it will be worth persuing the amp and the subsequebt repair. Could I be getting ito more than I might be bargaining for or might this be something easily fixed ?

Any input would be much appreciated.

 

[djk]

Check the gate to source resistance on both the K and J outputs on both channels. It should be quite high, several thousand ohms. If low, then the FETs are shot and must be replaced as a group (all in one channel).

 

[Chris Daly]

Dear Wolfman

Check for any burnt resistors or blown fuses which would
indicate problem with output devices.

Distortion can arise from many locations - high on the
list would be feedback paths with open circuit resistor
or differential pair input transistors current source.

I have worked on one Perreaux monster amp and it
used an outrageous +120volt - and + Dc rail, so
precautions when working on such an amp. The
topology of this fet model was fairly straightforward.

I would try and source a schematic before going any
further. http://www.perreaux.com. I think repair
should be somewhat easier than if the amp wasnt
working at all. You can very convienently compare
one channel to the other with a multimeter- remember
to power down if probing around as occasionally the
internal resistance of the multimeter ( most multimeters
are designed so this wont occur ) can cause further
faults. With power off and voltage rails dissipated
you can compare a lot of junctions one channel to the
other and localise where the fault is coming from.


Hope this helps
Cheers / Chris

 

[wolfman]

Thanks for the quick reponse - as it turns out I had not noticed that one of the fusses was gone. I repalced it with another 4 volt slow blow and low and behold everything is A OK now ! I hope the blown fuse was just that and not an indicator of something more serious, but so far the amp has been running for 20 hours or so with no problems.

BTW, this is my first forray into a Mos fet amp and I am pleasantly surprised at how good it sounds. Up till now I have been running a Jadis DA30 PP tube amp. Wish me luck with this Perreaux !

Wolfman