Audio Systems: Amp problemm, crossover distortion, bias network

Question
Hello,
 I currently own both a pre-amp and amp combo by Kinergetics research model Chiro C500/c800.  It is the 5.1 thx amp.  I play it thru a Sony 9000ES CD player
My problem is all of a sudden i had a bad connection today when I was using my Chiro Preamp and a loud hum came thru my speakers.  I think I have a bad RCA jack in the preamp. Anyway,  I shut everything down and then connected my amp to my passive pre which I use for music only.  However when I now use my amp there is a grainy or static type of noise in the music, like something is fried in the amp.   The vocals is where it is the worst.  My speakers are fine as I tested them with my other receiver.   Normally when i had this type of issue in the past I replaced a fuse in the amp and it worked.  But I checked all the fuses and none are blown. I also tried other outputs on the amp but all had the same sound issue.  Do you know what could have happened?  Thanks for the help

Answer
Do this test in order to identify if the problem is crossover distortion. I cannot tell from your description of the sound if it is crossover or something else.  But, it must be something that has not shut the system down  and crossover is about the only thing that runs through my  mind at this moment.

Turn the sound level down to very low level, just barely above audibility.  The sound should be very grainy or distorted.  Increase the sound level slowly.  As you do so the sound quality should become better and better as the level goes up.  If that is happening then you have a crossover distortion problem which has to do with the biasing of the output stage of the power amp.  Some amps have a separate supply line to the output stage to keep it biased up for lowest distortion whilst some of them have the bias network built into the output circuitry and merely drop down voltages from the main rails.  Therefore, some troubleshooting would be required to determine the cause - and the cure.

But, maybe this will help you identify what is going on.  Then let me know more if you need further discussion.  Let me know for example, if the grainy sound is in all channels of the amp or just one or two of them.

Finally, often a fuse will fail internally from age and looks good physically but is open internally. Only way to know for sure is to test it on ohmmeter or replace the suspected one.

Good Luck.