Help with noisy fan

[artcarmo]

Hi gurues...i have this Legion900.(by madisound?),that i bougth recently,but besides the amp seem to work fine ,the fans is killing me with the noise trought the speakers ,not to mention the flow noise, but the most important to me is the one in the speakers.I check the PSU and everything is ok( hi lo ,v+,v-,ground osicll etc)i try increasing the capacitance in the -+20 power suply ( the fans feed from here trought a 12v+regulator) but the noise seems to increase more like a hum but still very "wasp's nest" or mosquito fly...so i decline this approach ,try a external supply for the fans and the noise change in to a very loud hum....any advice? thanks
Art

[Richard Ellis]

Turn the regulator down....If she is spec. for 14VDC, go for a nine VDC, if a twelve shoot for Seven...........you will get less flow but it will quiet down considerably.
__________________________________________________ Rick........

[AndrewT]

You must use a separate secondary winding to power the fan or better still a separate transformer.

Take care with using a low voltage to reduce audible fan noise. the fan needs a kick of both volts and amps to get it started.

If turned down too low, it may "jam" and not self start. This is a big concern as the fan gets older.

Find a circuit that gives it a self starting kick and then turns down the voltage to running level. Even better if the running voltage is proportional to heatsink temperature. Off when cold, slow when cool, faster when warm, full speed and warning light when hot.

[artcarmo]

Hi my friends,thanks for this answers,tomorrow i will get a transformer for build a sep.power for the fans,
and i like the idea of a heat variable speed,does anybody have a schematic of DIY temperature variable fan speed circuit?
This way i use both advices...

[artcarmo]

well my friends,thanks to your advices i took a closer look to the fans,and i realize that this ones have a termistor,actually shorted to set the max speed,so i go into the junk box,find a 12v transformer and set a source for the fans,take out the termistors of the fans and attach it to the output transistors...now with the new psu for the fans ,no more noise in the speakers,and with the termistors working,the fans run slowly so less flow noise,later i run the amp harder to test the increase in flow according to the temperature raise at the outputs transistor Thanks again.
Art

[artcarmo]

The termistor in place

[artcarmo]

The termistor ready to work

[artcarmo]

now for real