amps hums with only AC source input, help

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I have hifimediy amp, T1 with pot built in similar to here: Hifimediy T1 ALPS vol pot TK2050 STA510 MUNDORF CAP

I installed the 3.5mm audio input jack, with power on-off switch, and using 32V, 3Amp DC power supply, the sound is very good when connected to my iphone and nano, both battery operated. When I connect my CD player or PC, it develops hum which gets louder when the potentiometer is turned up about the half way. I am a novice in electronics but can someone help me out?. My case is wooden, I tried to change my DC adapter from 3 prongs to 2 pronges without any success. I have asked from help with hifimediy and also waiting for their answer.

thanks,

gychang
 
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