I have built a 12 Volt amplifier and have installed a fan into the cover to circulate the air out the housing.

The amplifier makes a whinnying sound when I connect the fan I have earthed the heat sink and put a 4700Uf across the 12 volt supply but still I get the sound when the fan is running.

Please advise how I can stop this.

Thanks

Rodney

 

Remove the fan.

 

Remove the fan.

Mr Chips ha ha excellent solution BUT fear then the heat sink will get to hot. Would putting a capacitor across the supply of the fan work? I am not sure what else to do.

Thanks

Rod

 

Run the amplifier without the fan for about an hour and see how hot the heat sink gets.

 

Ok I will do that starting now. What is the cause of the sound?

 

Probably EMI (electro-magnetic interference).

 

It's a long shot but the first and easiest thing I would do is detach the fan from it's mounting and hand hold it in the same position - no contact with the chasis/cover etc. That's in case there is any microphony in the input stages.

Having rules that out try moving it around in that area to see if there is any change to the induced noise. This to test for magnetic interference into the circuit.
It sounds like an unusual problem, so look for an unusual cause..

 

Try a standard 1N series diode across the supply of the fan. Connect it in reverse biased. And use a 100nf ceramic to bypass the 12V supply.