Feedback from my amplifier's phono setting?

March 14, 2006 8:10 PM

When I have my integrated amplifier set on "phono", I get an annoying 60 cycle hum buzzing out my speakers.

I have eliminated the amplifier, turntable, power strip, and TV. BUT, when I take the inputs from the DVD player and VCR out from the amp, the hum vanishes. So my question is, how do I get to run my VCR and DVD through my stereo sytem and not have this annoying hum.

posted by Ber to technology (7 comments total)

Probably a ground loop - you might try picking up a ground loop isolator from a place like Radio Shack.
posted by twiggy at 8:14 PM on March 14, 2006

Ground. . the turntable will have a ground cord. . .or you'll have to improvise one. .asing at Radio Shack is a good idea.
posted by Danf at 8:44 PM on March 14, 2006

I don't remember what it is, but the phone input always does something specific to accomadate an actual phone signal. My understanding is you should just never plug anything but a phono into a phono-labelled input.
posted by btosch at 9:30 PM on March 14, 2006

Yep, sounds absolutely like ground/earthing. Does the amp have a ground terminal?
posted by holgate at 9:46 PM on March 14, 2006

btosch - the phono input has an additional amplifier as the signal from a turntable is considerably weaker than that from other sources.
posted by The_Partridge_Family at 12:04 AM on March 15, 2006

(To aid the slight derail) - it's not just amplification which is applied at the phono input, but also a standard equalisation curve. Vinyl doesn't have a great deal of bandwidth and in order to maximise what it had, the RIAA (yup, them, before they go into banging up mothers for downloading a copy of "Olivia Newton-John's Greatest Hits") developed a standard for vinyl production which removed a great deal of the bass and mid-range (which takes up vinyl bandwidth) and replacing it at play-time by a phono amplifier...

To the problem in hand though - definitely a ground loop. Are all of the components being powered from the same socket? (If not, it may help if they are.) And yes, the record deck should be grounded to the amp, and should have a wire with a lug on it to do just that...
posted by benzo8 at 2:29 AM on March 15, 2006

The turntable has a ground wire running to the terminal on the amplifier. In fact, when we took the amp and table into the store where we got it, the hum was totally absent. That clued us in that some other components were causing the problem. So I guess I'll have to find a ground loop isolator for the video components now. Thanks for all the great answers.
posted by Ber at 10:49 AM on March 15, 2006