Hello,
I made preamp circuit using PGA2311 (atmega8 MCU and MAX7219 led display driver)
BUT, when I connect input to pga2311 i get loud noise, obviosly from digital plane. And I can here PWM used for MAX7219 brightness in my speakers. When I disconect input, I stll can hear that noise but much, much, much weaker, almost not audible, but still present. and when I disconect pga2311 output from my power amp, then, nothing can be heard.
I think I separeted digital and analog ground plane. Here is my pbc output:
Digital power supply is done with small mobile phone charger connected to connector named POWER-DIGITAL, and analog power supply for pga2311 are done using power toroidal transformer which is also used for power amplifier, but in pga2311 case., it is regulated, first via transistors to lower voltage from 54V to 15V and then via LM317/LM337 to lower to +/-5V.
I am not sure why I get so much noise in analog input/output of pga2311. I can here how PWM pulse/pause changes(on display driver IC) like changing frequencies
Thank you.