I recently purchesed a Noble potmeter that is more than 10 years old but never used. It's at the input of a diy preamp.
After a couple of months it has started making scrathing noises
in the loudspeakers when turned up/down. More noise when turned fast, less when turned slowly or pressed inwards during turning.
The retailer claims it is because I have connected a DC coupled source without DC blocking cap in the output, a Noble MUST NEVER have DC at the input, he says
.
The source in question is a NAD C542 CDP which by factory default has no signal cap at the output from the OPA2134 output buffer opamps. And I can not measure any DC offset from it.
In another setup a Marantz CD7300 which measures 1.1mV DC offset feeds a similar pre with a Noble pot and has done so for nearly 2 years without problems.
Are NAD CDPs killing
all Noble pots all over the world or what may be the troulbe here? 
After a couple of months it has started making scrathing noises
in the loudspeakers when turned up/down. More noise when turned fast, less when turned slowly or pressed inwards during turning.The retailer claims it is because I have connected a DC coupled source without DC blocking cap in the output, a Noble MUST NEVER have DC at the input, he says
.The source in question is a NAD C542 CDP which by factory default has no signal cap at the output from the OPA2134 output buffer opamps. And I can not measure any DC offset from it.
In another setup a Marantz CD7300 which measures 1.1mV DC offset feeds a similar pre with a Noble pot and has done so for nearly 2 years without problems.
Are NAD CDPs killing
all Noble pots all over the world or what may be the troulbe here?