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Old 17th March 2007, 12:35 AM   #1
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Default Hum in phono circuit

I hooked up my turntable to my homemade power amp thru a small mixer that had a phono preamp. There is a slight hum when the phono pot on the mixer is turned up. All the other mixer inputs are dead silent with no signal. I never experienced hum when driving the amp directly with line level sources. The hum is very slight. Any normal music completely drowns it out. You only hear it between record cuts. The mixer is sitting on the left side of the power amp, directly over the amp's power transformer, an EI type. But I'm guessing magnetic interference would make all mixer inputs hum.
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Old 17th March 2007, 02:55 AM   #2
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Default Re: Hum in phono circuit

Quote:
Originally posted by Bama Slamma
...... The mixer is sitting on the left side of the power amp, directly over the amp's power transformer, an EI type. But I'm guessing magnetic interference would make all mixer inputs hum.
Hi,
The phono section is much more sensitive to interference since it is designed to work with lower signal levels. Can't you move the mixer to the other side away from the transformer?

Regards,
Martin.
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Old 17th March 2007, 03:25 AM   #3
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Default Moved mixer no improvement

I moved the mixer, but the hum was still there. I guess I have a ground loop somewhere. I plugged a mic into the mixer but it was quiet. The ground loop seems to only be on the phono input.
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