Hi,

I have audio power amplifier which is in metal chassis. Inside the metal cassis, I put AC220V driven relay to switch mains power on/off with switch. It works but if but if I close metal chassis, I hear hum of the relay (hum is not present in speakers). If metal chassis is opened there is no hum also if I disconnect relay from AC mains and power amplifier directly, there is no hum.

How can I eliminate hum?

Thanks for your answers

 

Hi,

I have audio power amplifier which is in metal chassis. Inside the metal cassis, I put AC220V driven relay to switch mains power on/off with switch. It works but if but if I close metal chassis, I hear hum of the relay (hum is not present in speakers). If metal chassis is opened there is no hum also if I disconnect relay from AC mains and power amplifier directly, there is no hum.

How can I eliminate hum?

Thanks for your answers

The hum is caused by the coil of the relay being powered by the 50Hz AC from the mains. You could switch to a DC relay which would not make the sound, or possibly to an external AC relay in a purpose built case that suppresses the noise.

Also possible is an SSR (Solid State Relay) which would be completely silent and could be run form the mains.

I should also add that the duty cycle rating of the relay you are currently using should be checked. If it is noisy I suspect it might not be intended to operate continuously and it might overheat.

 

Or, try mounting the relay using rubber grommets as "hum insulators".

 

The simplest solution is to remove the relay and switch the power to the amplifier directly through the switch.