Roland JC120

This project was 100% about reducing hiss, which is inherent in these amps.  To rule out noise sources one by one, I replaced all the electrolytic capacitors, then all the preamp JFETs (after measuring for Idss and sorting from 100's of other RF JFETS), then all the preamp BJTs.  This reduced the noise considerably, especially in the normal channel.  

After replacing almost all the preamp resistors with mil-spec metal film, the VIB channel was still just a little noisy.  With nothing else to try, and the obvious source of the remaining noise being the large value volume pot, I replaced it with a much lower value, and the necessary EQ compensations.  Because the signal is well buffered at that point in the preamp, there was no tone change - and the hiss all but disappeared! 

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