fan for heat sink

[jamal]

hi, I intend to install fan on my amplifier heat sink. in fact the fan come with the heat sink. it was an AMD CPU cooling system fan. But I will power the fan with a separate 5V switching power suppy form the main AC. it sound silly, I know. But the switching power supply will cost me $3 only. it is rated 5V 500mA. will it effect the amplifier in any way.......thanks

[jackand08]

The SMPS may introduce some HF noise onto the primary of the amplifier transformer which may be transferred to the secondary (very little of it though because of the different core type). The main problem that I expect may be with radiated noise. This is due to the operating frequency of the SMPS and would be greater than the noise coming from the mains. To counteract this, I would put some kind of shielding around the SMPS in the form of copper clad board connected to mains earth. this would get rid of most radiated noise.

In any case, he noise won't be massive but if you are sensitive to it, then it may well be noticeable.

[Minion]

Also , most CPU fans run off of 12v DC so your Fan is going to run pretty damn slow ......

[jackand08]

Running it off 5V does have its advantages for an amplifier, mainly less noise.

[jamal]

I thought the SMPS is operating above audio frequency. does it still effect.
if I am not wrong the CPU fan operate in 5V ....thanks

[AndrewT]

Hi,
running any motor from ~42% of rated supply voltage is very likely to result in serious starting reliability.

This will get worse as the motor ages.

[jackand08]

Although the SMPS does operate above audio frequency, it will still introduce noise and an RF hash onto the mains and will radiate some noise (depending on the quality of the supply design).

[epitaxial]

Can you fit a bigger heat sink instead? I've been contemplating a huge 1 inch plate of aluminum to mount my amp on, and even as far as water or fluid cooling (silicone compund similar to heat sink compound).

Actually for a fan to work, there needs to be more fins for absorption, air trapping, and heat conduction. Air actually has to "hang around" or move through slowly to absorb the heat. There was quite a difference in design between wind tunnel heat sinks and regular heat sinks. When you use a fan, be sure some of the breeze cools the capacitors. Most chips have good thermal protection, but capacitors are defenseless to heat. Most amplifiers that use fans today have variable speeds or thermal cuttoffs/control.

And of course dust, noise, and acoustic noise will leave its mark.

[jamal]

how about putting the SMPS inside a metal cage. does it help.......thanks

[wwenze]

Originally Posted by jamal

if I am not wrong the CPU fan operate in 5V ....thanks

12V, and the motherboard uses PWM to reduce the speed.

Yes a grounded metal cage helps.