Gainclone noise

[tonitze]

I've just completed my NIGC 3875. The sound is surprisingly good despite only using 2x12vac 120va trafo which i had in hand for testing. The problem is, I had buzzing noise at the speaker if I put my ear real close to it. The problem went off if I disconnect my RCA connected to my CDP. Is the dc offset of about 25-45mv at the CDP output that may have cause the problem? There no cap at the output of my modified marantz 63 and also my NIGC.
Please help.

Toni.

[Nuuk]

Those DC offset figures are quite good and won't be the cause of the buzzing noise. The mostly likely cause is a bad joint/lose connection somewhere.

[GregGC]

Most likely has to do with the powerlines (220VAC) GND/earth loops. Connect the RCA's and unpug the CDP from the wall outlet. Is the noise there? Is this a new CDP to you or you used it before?


Greg

[Kadin2048]

Most hum problems in my experience have been caused by ground loops, which is basically when you have the audio signal ground connected to the earth ground in more than one place. Ideally in your entire audio system / chain, you only want the audio signal ground to be connected to the chassis / earth ground in ONE place. Where that place is, doesn't matter particularly. But you only want one.

If you have all homebuilt equipment, this shouldn't be a problem, because you should know where your grounds are; if you're using pro gear you can probably look in the manual and see whether it's grounded or floating (or look for a 'float' switch somewhere on it). But if it's a mix ... well then you have to play around.

An easy way to eliminate some problems is to make sure that all of your gear is plugged into the same electrical circuit. Even if this means running extension cables (good ones! not cruddy ones where the conductors are all mashed up and shot inside -- the more resistance in the cable, the bigger possible voltage difference you can develop across it) if your equipment is physically separated, at least you'll know that all of your components will have approximately the same ground.

If that doesn't solve anything, then you'll have to start delving deeper, and isolate what component is causing the issue. If you have an oscilloscope, it may be helpful in tracking down these things once you get into the equipment itself.

Good luck!