Fan causing noise in audio circuit

[Charles Linquis]

Brushless fans DO generate a fair amount of noise. They might not have brushes, but they do switch the coils via FETs. Since the fan probably draws less than 200mA @ 12V, I would put a 10 ohm 1W resistor in series with the fan, and a 100uF + .1uf across the fan leads. You should put the resistor and cap close to the fan (not at the end of 10" leads!). The fan will run a bit slower than normal, but I assume you can tolerate that. Cheaper and smaller than an inductor, and (for this purpose) probably just as effective.

Also be aware that your fan not only has switching coils, it has rotating magnets. Any nearby conductor (less than 3" or so). will have induced voltages.

I can't imagine getting much noise if you use the filter I described and have the fan well away from your circuit.

And I'm with Mister_e. Breadboards are no good for low noise - or high frequencies..

[The Master]

Thanks for all of your advice. I decided to go with bigger heatsinks and lose the fan completely.

Moving the fan etc didn't seem to have any effect. I will test the full circuit out with the volume right up and check that the heat is ok. I can always add the fan later if I really need it