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Axial or Extractor Fans for Cooling SS Class A Amps

R

ryder

pfm Member
Can anybody advise if it's better to have mini fans blowing cool air across the top of the amp as shown in the image below, or extractor fans pulling hot air produced by the amp in the opposite direction?

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I am more inclined to go with the former, mini fans blowing cool air across the top of the amp but was curious to hear some opinions.
 
hifi-dog said:
If the rack is open then surely either way makes no difference?
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Some Class A amps emit a lot of heat. If the space at the top of the amp is limited, the air circulation may be compromised even though the rack is open as the heat is collected in that space, causing further build up of heat inside the amp. The mini fans may help the air circulation by accelerating the hot air removal that's collected at the top of air vents of the amp.

Not much of an issue with class AB amps which run cool.
 
The fan that you will be using will be an axial fan - you appearing to be asking which way round you fix it - suck or blow.

There's a very simple way to find out which is most efficient - measure the temperature of the case surface in a few places with the fans operating in each direction. You'll need a thermocouple. My guess would be best to blow over the case.
 
You don't want smooth airflow you want turbulence for greater mixing of the hot and cooler air, I'd lift the amp an inch or two and use a fan either side blowing onto it. Turbulence generates more noise tho'.
 
Appreciate the post. Similarly I feel that blowing over the case is more practical than extraction/suction. It is a cheaper solution as well due to the availability of these mini fans.

Having said that, I have found a company which actually manufactures cooling fan systems for hifi components based on extraction. The slimline component is placed on top of the amplifier to extract heat from the top of the air vents. Must be quite costly.

https://www.acinfinity.com/receiver-amp-cooling-fans/

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cooky1257 said:
You don't want smooth airflow you want turbulence for greater mixing of the hot and cooler air, I'd lift the amp an inch or two and use a fan either side blowing onto it. Turbulence generates more noise tho'.
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I'm not sure if I understand this. Presuming the heat is mostly dissipated through the air vents at the top of the amp, the fan(s) should be just blowing right at the top of the amp to get the hot air out?
 
ryder said:
I'm not sure if I understand this. Presuming the heat is mostly dissipated through the air vents at the top of the amp, the fan(s) should be just blowing right at the top of the amp to get the hot air out?
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That's why you need to experiment but really you need to get the amp up off the shelf first. Blowing from either side is a start. In the pro world fans are enclosed in the case and blow outwards over the output devices/ heatsinking so creating the inward draught through the case vents and expelling out the rear usually. Ideally if your amp has bottom vents then that's where I'd start to blow through. Put simply if you want to cool off on a hot day where is the best place to stand, in front or behind your desk fan?
 
My rack arrangements mean that one of my NAP 250s has to be stacked directly on top of another 250. I have bought 4 rubber doorstops and placed them loose between the amps. The resulting arrangement is stable and allows better airflow round both amps.
 
ryder said:
Some Class A amps emit a lot of heat. If the space at the top of the amp is limited, the air circulation may be compromised even though the rack is open as the heat is collected in that space, causing further build up of heat inside the amp. The mini fans may help the air circulation by accelerating the hot air removal that's collected at the top of air vents of the amp.

Not much of an issue with class AB amps which run cool.
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Yep but as your rack has loads of space above and has open sides and the fans mounted one side then surely big they are either sucking or blowing then the air is still moving vac cross the amp, just in different directions
I’ve run class a sugden with less space above and it was fine
 
cctaylor said:
My rack arrangements mean that one of my NAP 250s has to be stacked directly on top of another 250. I have bought 4 rubber doorstops and placed them loose between the amps. The resulting arrangement is stable and allows better airflow round both amps.
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There is no issue with Naim amps. They can actually be stacked on top of each other without any separation as they run cool, but it's not recommended due to sound quality aspects. :D

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I use wood blocks to separate components for better heat dissipation. The Sonneteer amp runs quite cool (no air vent at the top of the case). However, it is a completely different story with few Class A amps.

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hifi-dog said:
Yep but as your rack has loads of space above and has open sides and the fans mounted one side then surely big they are either sucking or blowing then the air is still moving vac cross the amp, just in different directions
I’ve run class a sugden with less space above and it was fine
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Thanks for the post. In my case, the protection circuit of my Luxman was occasionally trigerred as the amp automatically shut off by itself as the temperature got too high. It rarely happens but I am now beginning to take extra precaution, not only to prevent the amp from going into protection mode but to prolong the life of the amp as excessive heat will shorten the life span of parts and components inside the amp.

On a good day I listen more than 10 hours a day but am now starting to limit the sessions. The amp is hot to touch when in operation.
 
Use a squirrel cage blower rather than axial fans - if you hunt you can find very long, slimeline versions. Also very quiet.

The occasional tripping of the thermal cutout is telling you one of two things, or both, your listening level is too high for you amp, and/or, you speakers are too inefficient for the power of your amp (or vice versa).

I changed my amplification. You are, in effect, trying to polish a turd.
 
We have a largish, steel, wall rack/box that contains cctv, telecoms and ADSL main equipment for the biz. It, in turn, is in a small, under stairs cupboard.

On taking ownership this had two desktop style fans at the top, set to suck air in from the bottom. We very soon experienced a couple of component failures due to heat so I swapped the fans out for a single 8" fan blowing in from the bottom. Four years later and no problems.
Obviously noise is not a concern in this situation.
 
This reminds me of the challenges presented by a production manager who wanted to use a PIGI film projector in a control room to light the stage.

These are designed to light buildings and are supposed to be outside use only.

We had to calculate the required volume of air required to cool the space and source fans that would provide this. Blinking noisy, but created some amazing visuals.
 
ryder said:
Can anybody advise if it's better to have mini fans blowing cool air across the top of the amp as shown in the image below, or extractor fans pulling hot air produced by the amp in the opposite direction?

Screenshot-20210529-111817.jpg


I am more inclined to go with the former, mini fans blowing cool air across the top of the amp but was curious to hear some opinions.
Click to expand...

Blowing over is better, like with PC intake fans, but the best arrangement in this case would be mounting the fans horizontally as exhaust on top of the amps.
 
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