Krell KSA80 crackle and pop sound

[lanchile]

Hi all,

An update -- I tried freeze spray and could not find conclusive evidence so I started poking around the board. When the popping started, the DC offset went from 1mV to 35mV. I measured all around the input stages and could not find a smoking gun in the input stages. When I got to the MOSFET differential stage, I touched the drain of one of the diff pair, the noise went away and the DC offset was able to be re-adjusted to 1mV. The noise has not returned after another hour or so. Question is -- should I replace the MOSFETs (VP210N5 and VN210N5) or was that just an indication of something else wrong in the circuit? Can they be sourced or substituted with better types? Thanks in advance!

Use the freeze spray on the mosfet that you touched as soon as the noise comes and see if the noise goes away.

 

[rss388]

Thanks lanchile. After the last time when my meter lead touched the MOSFET drain and the crackle and pop went away, I cycled and ran the amp many times and over hours at a stretch. I re-adjusted the offset and now there is no pop and crackle. I do not understand what happened. Anyone has any thoughts?