ChipAmp cooling

[Ivchikx]

Is it possible to feed amp's cooling fan from amp's transformer? If it is, then how? It's a 2xTDA7294 amp with 2x24V transformer. Fan 12V 80mm computer fan.

[abraxalito]

Certainly its possible but its not going to be very efficient with a 12V fan. You'll need to work out a value for a series resistor to drop around 24V at the fan's typical load current.

[pacificblue]

You need to drop 22 V, because a 24 V transformer will give you ~34 V DC.

[abraxalito]

The DC voltage will depend on the regulation - a typical 160VA transformer as might be used for a simple stereo chip amp like this has a figure around 11%. That'll give around 37VDC off load.

0160224 : 160VA 230V 2 x 24V toroidal transformer

[!]

Is the transformer potted? If not, I wonder if you could wrap another winding around it sufficient to power the fan.

[digits]

Dropping the voltage easy, preventing motor noise from fan entering amp, not so much.

[lnh]

If you took the power for the fan straight off the traffo before it went to the psu, and just used a resistor to drop the voltage, wouldn't that eliminate most of the noise? I wouldn't think the fan would need to go to the earth ground: a standard 12v computer fan will just stop working if anything goes wrong with it, and it can't provide enough of a surge to do any damage to any other components.

And to the OP: if you can fit it, get a 92mm or larger fan that has dual ball bearings with loise noise levels...they move the same amount of air as the smaller ones cause they run slower, but they're also quieter too so there's less background noise while running.

[Michael Bean]

Why not use a 12 volt regulator? A LM317T set for 12 volts would work well here.

Mike

[AndrewT]

ESP and a few others show a temperature switch/ speed controller for a fan motor.

But, be careful of injecting control pulses into the Audio signal circuits.
A separate transformer may be required.

I recently completed a remotely controlled integrated amp (my second integrated and first remote control)
The motor control to the motorised attenuator produces audible electrical noise to the speakers, even though the whole remote kit is powered from a separate small EI mains transformer. Could be the control pulses arriving at the motor are inducing interference into the attenuator audio track/s

[Ivchikx]

Well, free space in amp's case is limited. I also want to include tone control for my amp, that also could lead to another psu or transformer + psu.

Series resistor will heat up and burn, if it should dissipate in heat about 24V DC (34v-10v) to leave 10V for fan. I suppose regulator would do the same, e.g. dissipate excessive amount of heat. How about zenners or something? Looks like another small transformer will going to do...