Been there many times before but just in case anyone has any ideas. Large multichannel Phonic band mixer, no integral power amp. Owner reported a crackle at sound check and then it disappeared. Crackle returned near end of gig on both channels, confirmed neither of the powered heads causing problem. As affecting both monoised outputs I'm assuming at this stage problem with ps. It hadn't been used for a few days, when I powered up there was crackle on both channels on phones, random frequent discharge noise rather than lose connection crackle, disappeared after a few minutes. Unfortunately I would say a low voltage rustle sort of crackle rather than high voltage discharges in main capacitors. Of course since removing the casing and monitoring, no crackles of any sort with freezing, heating or knocking components. Other than replacing all ps caps
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