I recently built an amp kit called qk50 which uses LM1875 chips. Funny thing is that it makes a hum only when it's hooked up to a portable CD player. The CDP is powered by a DC walwart which is connected to the same AC mains outlet in a surge protector. All the grounds in the amp are star-grounded. Power supply is in a separate enclosure which is connected to the amp enclosure by 3-pin DIN cable (shielded). +/- rail voltages are connected to ground via 0.1 uF film capacitors. Could anybody let me know what I should do to remove this hum? Thanks.
JAZZ2250 said:
Quite likely a star ground that is not properly realized.
First of all see if there's hum with the CDP on batteries.
Second, try a cable that has two wires plus shield. Connect one wire + shield to ground on the CDP end and only that ground wire on the amp end.
If this doesn't work try to make a diagram on what's connected to what.
Carlos
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