I'd suggest you don't use a thermostatically switched fan in audio, the sudden change from one speed to another is more noticeable than gradual changes. It's easy enough to build an infinitely variable thermal controller, using a thermistor as one of the voltage-setting resistors in an adjustable regulator.
Also PWM control, though efficient, tends to make more acoustic noise at low speeds than linear control due to the power pulse action "kicking" the fan bearing, and with a low-noise fan using under 2W efficiency is not an important factor.
Fan PWM control falls into two camps
On that yellow or sometimes white (speed) fan wire - it's typically an open-collector configuration switched low twice per rev, nothing to do with speed control per se, just an indicator signal.
Also PWM control, though efficient, tends to make more acoustic noise at low speeds than linear control due to the power pulse action "kicking" the fan bearing, and with a low-noise fan using under 2W efficiency is not an important factor.
Fan PWM control falls into two camps
- Low frequency, 30-120Hz, pulses applied directly to the fan motor. Suits any fan.
- High frequency, over 20kHz, pulses LC filtered to a DC level, typical of motherboard fan controllers. A given filter design only suits a narrow range of fan powers.
On that yellow or sometimes white (speed) fan wire - it's typically an open-collector configuration switched low twice per rev, nothing to do with speed control per se, just an indicator signal.
whats wrong with keeping it simple..
Dont control it with pwm, thats just overkill..
I would use some voltage regulator or resistor thing and bypass it with an electronic relay (or maybe mechanical) that gets reset by the tach pulse via some kind of filter maybe or something like that .. That couldnt take many components and it would probably be safe enough for many years.. or am i wrong.. tach pusle is for monitoring fan speed so it doesnt go slow or stop.. lets use it for that..
Dont control it with pwm, thats just overkill..
I would use some voltage regulator or resistor thing and bypass it with an electronic relay (or maybe mechanical) that gets reset by the tach pulse via some kind of filter maybe or something like that .. That couldnt take many components and it would probably be safe enough for many years.. or am i wrong.. tach pusle is for monitoring fan speed so it doesnt go slow or stop.. lets use it for that..
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