I don't see how it could harm it,but,it's better to set your fan up to pull heat from the unit.Just my opinion.
12 responses Add your response
Warm is normal, why the need for a fan, is the amp going into thermal shutdown? Typically, fans are used to exhaust the heat from the enclosure thus creating a more natural cooling convection. I know that designers of tube equipment frown on fans blowing directly on the tubes as it could excite the tube thus causing microphonics and noise. I am not aware of any amp in which the fan blows onto the electronic, most exhaust the heat.
Blowing air ONTO an amp may actually make it run warmer by inhibiting the convection of air from the top...sucking in cooler air from the bottom.
TPreaves is right....pull air out the top, rather than blow it in.
A small computer style box fan, on top aiding the natural airflow would help.
I have experimented with an old Intel CPU fan running off a 9v battery. Extremely quiet and moves a surprising amount of air.
That being said, the other posters here are right....and the amp is supposed to run warm. But not hot, depending on many factors, including class of operation and the amount of heatsink vs power. Lots of heatsink is needed for class 'a' amps while my 'd' amp has minimal heatsink, lots of RMS power, but a short time limit at those power levels.
Factors for any given amp, such as low sensitivity speakers run loudly in a larger room will (can) tax even the most robust amp making extra cooling or at least a well ventilated space a good idea.
I have built many of Nelson Pass's Aleph Class A Amplifiers as a member of DIYAudio.com. Amplifiers biased as class A have a maximum theoretical efficency of 50%. In the real world they are more like 15% to 20%. That means of all the power the amplifier can deliver, 80% to 85% of it is dissipated as heat, with maximum heat dissipation at idle. These amplifiers become giant space heaters. Such is the price we pay for no crossover distortion. Not having the proper heat sinks available when I need them has made me pull out the trusty fan to cool these bad boys down on more than one occasion. Other than the fan's audible background noise, it has produced no ill effects on the amplifier itself.
I have used those ultra quiet 120 mm PC fans to cool a number of power amps I own. I have cooled Parasound JC-1s and A21s by mounting the fan under the top cover plate, blowing out. These fans are so quiet you cannot hear them with your head right next to the amp. Took about 25C off the internal temp by doing this. They can be powered using the 12V turn on voltage supplied externally by the amps.
I don't care what anyone says, heat is the mortal enemy to long life of any electronic component. Particularly the electrolytic caps and solid state devices, whose lifetimes drop (and failure rate rises) exponentially with increases in temperature.
Authorized McIntosh Service Tech here, and I seem to recall that the MC7505 runs very cool like most recent McIntosh Solid State amps.
In my opinion your bias settings need to be looked at and I'd be willing to bet they are higher than the 13mV-15mV Factory setting. If I am right, you can then nix the fan once adjusted.
(I always reduce the bias by a schoshe [20%] to decrease heat/prolong component life).