bzblues
Full Member level 1
Removing noise from the power supply should not and must not affect the sound being amplified.
If the capacitor across the DC jack does not help, then the hum is being picked up from air. First of all, you need to figure out whether the hum is 50 or 100 Hz. Compare with a pure tone generator like https://www.szynalski.com/tone-generator/. If the mains frequency is 60Hz, then listen for that.
while running on battery, if you bring the adapter (powered on but output not connected to the amplifier) power connector close to the signal input, do you get any hum pickup? If you touch the signal input with your finger, how much hum it picks up?
The capacitor didn't work. I must say that the noise or hum its much more higher than 100Hz. The sound is similar when you are not conected to ground.