GK MB 500 whirring sound

[8stringfunk]

I've only had the MB 500 for a few days, but occasionally it will make a whirring sound much like the fan in a laptop, in fact I'm pretty sure it is the fan. It's kinda un-nerving when it happens as it's pretty loud for such a small unit. Is this considered "normal" operation?

[8stringfunk]

Ok I think it's normal. This is my first real bass amp so it's all a bit new to me!

[Wes Whitmore]

Its a small fan in there. You can hear it when it spins up and slows down more than a 3" PC fan that most amps have. As far as I know, it only comes on when you get the heatsink warm enough to come on, and shouldn't be coming on at Idle, but I'm not sure of the exact behavior of a properly working fan.
Wes

[8stringfunk]

Yeah I was practicing at a very low volume, hence why I could hear the fan so well when it kicked in. Then after that I had stopped playing all together, and it did it again.

I haven't got much experience with high power gear (this head is the most powerful thing I've ever had), like you said it's that it's doing it while idle that troubles me.

[craig.p]

This has me wondering whether my MB200's fan works at all. I don't think it's ever come on even when the amp case has gotten fairly warm.

[Wes Whitmore]

I don't know if mine has ever come on either.

[8stringfunk]

Hmm.. You guys saying that has me a little worried..

[8stringfunk]

I've joined the GK forums but I'm waiting to be accepted as a forum member, once I am I'll ask them what they think.

[HailCorduroy]

My GK Backline does that as well when it gets warm.

[Savage_Dreams]

i think i would be worried if mine never came on. if you can hear it though, just means you need to turn up!

[Sneakypete]

Small fans are in loads of things these days and mostly they are 'intelligent' meaning there's a little thermistor in series with the fan motor. This is usually fixed to the heatsink - if the heatsink is cold the thermistor is high resistance so the fan is slow but as the thermistor gets hotter it drops in resistance and gives more voltage to the fan which then speeds up. It might be spinning but too slowly to make a noticeable noise. The only way to really know is to look inside but DON'T do this unless you know how to work safely and NEVER with the power cable connected. Most fans - if you blow on them like you were blowing out a candle will spin - if it doesn't, try gently pushing it with a finger. You should be able to feel that it turns freely. I've replaced many fans in industrial computers - the usual problem is that the bearing has dried out and the fan is too stiff to be turned by the motor. Any electronics store should have a suitable replacement fan for not much money. On my own equipment I always take the thermistor out and let the fan go full speed all the time but you might not want to do that in a studio situation. If you replace one - make sure it blows the same direction the original did!

[Wes Whitmore]

You can see the entire fan from the side of a MB500.