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Measuring A Capacitor

I have a preamp (NAD 1155) that has a hum problem. It started when I got a new turntable, so I thought it was a TT grounding problem. But no... The preamp's phono section hums every time it is selected. Even if there is no phono present. All the other inputs are dead quiet.

Anyway, a fellow 'goner thought it is a capacitor that's going 'round the bend. I'm willing to take my volt/ohm meter, and find the offending component, and replace it. All I know about capacitors is that they are measured in picofarads, and they discharge their energy in bursts, when it's requested.

Any help in this regard is much appreciated. I have a mountain of vinyl waiting to be played.

TIA

Lee
licoricepizza

Showing 1 response by metralla

metralla
945 posts
 
You can buy an instrument that measures capacitance - I think I paid about $70 for mine.

Otherwise, you need a bit of AC theory - send a signal of a known amperage and frequency and measure the voltage drop. You can easily find the formula on the Web.

http://www.pupman.com/listarchives/1998/April/msg00625.html

Now, where to find a signal generator - actually I found one in a dumpster at work. ;-)

Regards,
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