NAD 3130 low level switch clicking when depressed/released

[poundy]

so the muting circuit is the issue.
I removed both of those 10m resistors and shorted the d/s of each FET and the click is gone

 

[Mooly]

so the muting circuit is the issue.

It would appear so. What you have done proves the point and that this is a design defect or characteristic if you prefer. Why not try and rearrange the circuit to be like the preamp version you showed. Turn the diodes around and alter the 10meg connections to suit.

 

[poundy]

yep thats what im going to do.

 

[poundy]

so i made the mod, and no clicks now.
the only thing is you have the buzz in there on start up, a bit like you get with the 3020A(where it has underated caps in the circuit), but that doesnt have a low level switch, so its a different set up.
so could this be because i havent changed the FETS to the other type?
but the click has def gone. Without the muting you just get a small thump as you would expect, so I'm not sure if it's better just like that

 

[poundy]

im going to put it back the way it was, as i have at least proved thats what it was, and dont want to ruin a perfectly good amplifier

good exercise though

 

[Mooly]

Fair enough. It's possible the hum is being introduced via the FET gates and whatever ripple/noise is present on the drive voltage to the gate from the muting part of the circuit.