Fan makes noise in the audio signal

[renepela]

Today I finished my MB6582. It works great and I want to thank TK and Wilba for their great work.

Unfortunately I have a small problem which hopefully can be solved.

I have attached a 5V fan to J3. The fan works but I can hear the fan in the audio signal. Quite strange.

It's present as a constant humm in the audio signal. When I put the fan to 12V I also hear it in the audio signal only at a higher pitch. It's related to the speed of the fan.

What is causing this and is there a way to fix this?

I'm afraid I have to buy a new fan. Is there any thing I have to look at to prevent I buy a noisy fan again?

Knd regards,

Rene

[lylehaze]

Based on what you describe, the noise is moving through the power supply.

There are a few different approaches you might try to fix this.

A capacitor across the fan power connections will help. It will reduce the noise, it will NOT eliminate it.

Depending on how the fan is made, it MIGHT be dumping back EMF back onto the power. I usually add a diode across the power leads as close to the fan as possible..with the cathode(stripe) to + and the anode to -.

That's just a guess, but adding the diode temporarily will tell you if that is part of the problem.

Moving the fan to unregulated DC (before the regulator) will lend some isolation as well, if the voltage is within an acceptable range.

Just a few things to try. Good Luck!

LyleHaze

[frailn]

I think you can just skip the fan if it's too noisy. I think Wilba mentions on the wiki that you don't have to use a fan, if you don't want to. Otherwise, you may need to experiment with a different speed. There's some notes in the wiki you can check out.

Now, if she shows up at your place with beer and asks to hear your MIDIbox,  you might need to plug in that fan!

[lylehaze]

I like Frailn's answer better.

LyleHaze