ESD noise from finger and volume control

[elvischan917]

Hello~

I built some TDA7293, LM3886 and discrete but all of them suffer one same problem. Everytime I touch the volume control and turn it, I heard some glitch noise on my loudspeaker. I don't want to connect signal ground to the case to solve this problem as it may cause a ground loop. What should I do? Can I connect two diodes from the ground toward the power supply?

Can anyone help?

Thanks.
Alvis

[johnr66]

I always solder a jumper from the signal ground lug on the control pot to the case of the pot. No more glitch and buzz when touching the control. If the pot is already in contact with a metal chassis, there should not be a noise unless the case is not grounded. I'd ground it at least at one point.

[pacificblue]

If the pot case is not grounded, you get hum or buzz. If you follow johnr66's advice you won't create a ground loop.

If the pot is DC-coupled to the amp input, you can get crackling noises as you adjust the volume, due to the accompanying change of DC offset voltage. A coupling cap between pot and amp will help, but don't forget to add a resistor to ground after the cap.

In general you can have noises, when the pot is either cheap or old (or both), because the wiper loses and makes contact. You can cure that temporarily with contact spray or for longer by replacing the pot with a better one.

[portreathbeach]

elvischan917, I usually connect a 10 ohm (2 watt) resistor and two diodes (in opposite directions) in parallel, between protective ground (main earth) and power ground. And then I connect another two diodes and resistor from power ground to signal ground:

[AndrewT]

Originally Posted by elvischan917

.................I don't want to connect signal ground to the case to solve this problem as it may cause a ground loop. .............

The Signal Ground must be referenced to the Main Audio Ground (MAG), somewhere.

The MAG must be connected to Safety Earth, somewhere.

The Safety Earth must be connected to PE, somewhere.