As a hobbyist DIYer, I have decided to make a multichannel 5.1 amplifier (6 channels to be precise). Upon successfully making everything, a humming sound welcomed me. It wasn’t too loud but a noticeable hum. A little research on the internet revealed that it’s a common issue and called ground loop.
Everything is silent when no inputs are connected, but the hum started as soon I connect RCAs to anything, even battery-powered devices. This is a surprisingly common issue and just searching for “ground loop hum” will show you how the whole world is facing this frustration.
After several failed attempts and a lot of headbanging on the internet, it turned out not to be a ground loop (that’s caused by earth connections, between devices). The culprit was an inter-channel ground loop. Yup, it’s different, it happens when multiple channels input return electrons start to wander here and there thus causing the looping hum. Read the great document on wiring from hifisonix here
What is inter channel loop? It’s the loop or unwanted path for signals created between audio channels of the amplifier. This is more pronounced if you go beyond 2 channels i.e., 6 channels for 5.1 surround sound.
Simple solution to Inter Channel Loop
This seemingly complex problem has a very simple and cheap solution, it’s called Hum Breaking Resistor. That’s it a single resistor to save all the irritation. You can increase the value from 10 ohms to 20 ohms if the hum is more prominent in your case. Apart from this trick do try to learn the dark art of eliminating ground loops.
Images shows my amplifier based on TDA7294 ic using Hum Breaking resistor (highlighted in red).
This knowledge is alarmingly scarce in the audio forums. This makes the DIY community disappointed by humming sound from amplifiers. A large number of so-called gurus suggest the issue is in the ground loop and no one talks about Inter Channel Loop. This was my observation during writing this article. Needless to mention I have a silent amplifier now. I’m sharing this in hopes of spreading knowledge for good purposes.