noisy preamp channels

[traidma]

Oki, some time ago I posted here a problem with my Behringer UB1020. By now, it's 'dead' as part of my equipment for me.
But I'm still wondering what is wrong with it.. just in case i'll have that problem in future with other stuff.

Ok, I get this humm on my inputs. It only appears in the channels with the mic preamps. Stereo channels are 100% clear of noise.

The humm comes in after the channel gain and before the EQ (gain does not change the volume of it but eq does affect the tone of it). What might cause it? any idea?

[manning1]

could be a number of reasons.
bad mic cable.
mic gone bad.
mixer capacitor burnt out.
hooking mixer to a different house outlet than the pc thus getting a ground loop. you should come out of ONE wall socket to a series of power bars powering your pc and mixer and other gear !!
(by the way - smile - powertracks has a hum filter !)peace.
ps. try coming out a ub insert jack into the pc and tell me if hum goes away.

[traidma]

Cant be the mic cable and Mic as the hum appears even without anything plugged in...
And I already connected them all one wall socket..
And the capacitor... the humm on all 4 preamped channels with the same amount.

[manning1]

ok then...hers the clincher.
disconnect all inputs and outputs from ub.
plug phones into it. NOTHING ELSE CONNECTED.
play around with faders etc. if still hum. then sounds like a bad power
supply i would think in the ub.

[traidma]

yup, did it.. still hums.. but ONLY the four channels with preamps. All the stereo channels are clear..

[manning1]

you have a bad unit then.
get it repared asap under warranty.

[traidma]

it did work well until i used the 220>120V adapter...