I am new here and I realy need your help. For diplome at the end of my studying I am making the audio amplifier module (power amplifier, preamplifier, tone control, power supply, linear regulator) all in one. A have almost everythink work yust can solve noisy hum in preamplifier (TL082) that is caused by DC power supply ripple. I put pi filter CRCRC (1k Ohm, 20 uF) before linear regulator to filter DC voltage from power amplifier and get pretty good symetrical voltage, but with 100 Hz noise at both voltages. How can I get rid of that 100 Hz ripple?
I am using LM337 and LM317 to voltage drop from 40 V to 18 V and that ripple also copy to the output of the linear regulator and causes hum in sound. Just for information, the power amplifier work great alone and also preamplifier work great with external DC power supply from professional power supply device.