Fan noise

[lilmike]

When I use the outputs from my MX630 to drive fans based on system temps (the primary reason I purchased the unit) I get a growling or cogging noise form the fan. I've searched the forum, others have noted this issue too, the solution I came across is to place a large capacitor in parallel with the fan, noting polarity, or try a different fan.

So since all the fans I have tried make this growling noise when run at significantly reduced speeds, I guess I need to try the capacitor solution - the only question I have as a non-electrical engineer - what exactly is a large value for a capacitor - 1000 microfarad? Larger? Smaller? Are there other concerns that this will cause - do I need to derate it in any way?

[Henry]

Also try changing the PWM frequency of the fan outputs, we have seem that seems to help in some situations.

[lilmike]

How would I do that? Is it software or hardware controlled?

I've not come across that setting yet, but I am not sure I've looked in the right place.

[lilmike]

Found it - seems to do exactly what I was after.

Is there any concern with using the higher frequencies for GPO PWM switching?

[invalidbuffalo]

Found it - seems to do exactly what I was after.

Is there any concern with using the higher frequencies for GPO PWM switching?

I found raising the frequency (4880Hz and above) eliminates audible noise coming from the fan's circuitry, but it also prevents the fans from running at low speeds, so it kind of defeats the purpose...

This may be of interest to you:
http://www.silentpcreview.com/forums/vi ... hp?t=36707