As a seasonal hobbyist, I have decided to make a multichannel 5.1 amplifier (6 channels).
Upon successfully making everything, a bad hum, not too loud but noticeable hum welcomed me.
Google told it was a ground loop, but it was not, everything was silent when no inputs were connected, but the hum started as soon I connect RCAs to anything, even battery powered devices.
This is a surprisingly common issue and just doing a search for "groundloop hum" will show you how whole world is facing this frustration.
Step 1: IDENTIFICATION
After 2 failed attempts (12 channels to be precise) and lot of head banging on internet, it turned out to be not ground loop (that's caused by earth connections, between devices) as its filled on internet and audio forums, but inter-channel ground loop. yup, its different, it happens when multiple channels input return electrons starts to wander here and there thus causing the looping humm.
Step 2: SOLUTION
Ironically, this seemingly complex problem has very simple and cheap solution, its called Hum Breaking Resistor. yup a single resistor to save all the hassles.
Images shows my amplifier based on TDA7294 ic using Hum Breaking resistor (highlighted in red).
This knowledge is alarmingly scarce and audio forums are filled with people disappointed by humming sound after they DIYed their amps. Needless to mention I have a silent amplifier. Shared in hopes of spreading knowledge for good purposes.