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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
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almarg
9,670 posts
 
Outstanding! Phono hum is a very common problem, as others have noted above, so I'm sure the information brought out in this thread on the various possible approaches will prove useful to others in the future. Glad it worked out.

Regards,
-- Al
licoricepizza OP
48 posts
 
An update - This morning, the hum had returned, so I retraced my doings of the day. It turns out that the cause of the hum wasn't plug orientation, like I first thought. But rather, it was airborne RF interference caused by my amp. As long as there is a piece of foil between the amp and the cables going into my preamp, everything is fine.
danmyers
135 posts
 
Excellent! Make sure the foil is grounded and it will make an excellent EMI/RFI shield (or even a Farady cage if you're so inclined).
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