Fans on amps.


Ive been checking out some posts about fans by amps but cannot find anything about them being good or bad for the amps. This is what I would like to know. Ok. I have a Krell Fpb 600 and I listen to my music about a 28-30 volume on my ARC Ref 6 which is pretty loud most of the time depending on recordings. Tonight I felt my amp like a lot of times and felt very hot like u could fry an egg on top. This is the normal with a few hrs of listening. Anyway I put a fan on the right side of amp and about a half hour later I checked the right side and was significantly cooler I mean like a night and day difference between the right and left top and heat sinks. I was wondering if adding 2 fans one on each side to cool the amp down would do more harm than good. Would I get more life out of the amp with fans ? Or are amps designed like that without using fans and just heat sinks to get rid of the heat. Btw my amp has plenty of ventilation as it is on the floor. Thanks. 
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I agree, that it has no effect on life of semiconductors while it has some small effect on their performance (Mosfet transistors getting slower while bipolars getting faster).  Electrolytic capacitors are affected by temperature.  They simply dry-out.  Each 10degC temperature increase cuts their life by 2.  In addition, increase in temperature increases ESR.  Cooling fan is beneficial, IMHO, as long as it is not noisy (audible and electrical noise). 
i would think that an amp would not need a fan if it was designed properly.
Not opining on fan or no fan, but I just discovered that there is a company that makes fans for amps and racks if you end up wanting one:

https://www.acinfinity.com/
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I'll go with Elizabeth on this one. The only problem with fans is the noise and perhaps the added complexity. Heat sinks are big, heavy and expensive. Commercial amps virtually always use fans for all the above reasons. Krell used fans for quite a while. A cool amp will always last longer. Temperature cycling is no good for anything. Electrical conductivity decreases with temperature which is why the fastest computers do crazy things like run in refrigerated freon baths. They do all kinds of stuff to keep superconductors cold. I have no idea how all this pertains to the performance of relatively mundane devices like audio amplifiers but I use a fan cooling system on my amps. I run a 12 volt power supply off a switched AC outlet. The switch is right next to my equipment cabinet. The supply triggers all the amps and runs #4 6" fans one for each side of the two main amps. I put a 100 ohm linear pot in series with the + side of the fans so I can control the speed (noise). It all works brilliantly. Whenever I turn the amps on the fans light up automatically. The whole mess is mounted on a shelf directly under the speakers in the basement. I hooked up the pots as an afterthought. I could hear the fans running full tilt under the floor! Backing them off a bit worked fine. 
Oh, and if you put your amps on the floor make darn sure they are not on carpet, any type of carpet. Hard surfaces only. Any carpet will interfere with the flow of air over the heat sinks. I set up this fellows system years back. About a year later he called me up all bent out of shape because his amp died.  The genius had his room redecorated and he put the amp back down on carpet. He did not know that it would take some time for it to reset itself and thought it has died permanently. An amp stand solved that problem. 
Fans can accelerate internal dust build up.
Unsound-  Dust build up is what gives that vintage sound and smell.  Some would say that it is a benefit.  
Way back in the day when the party was rocking and the Phase Linear was getting hot like that I went out on the deck scooped up some snow put in in a bag put the bag between the heat sinks. Well I figure anything helps it run cooler is better. Worked like a charm. 

Couple years later up in Lynnwood ran into Bob Carver asked the man himself about it. Bob Carver said anything helps it run cooler is better.

So there you go.
I’ve got a very nice fan unit off of Amazon specifically made for audio or video equipment.  It’s a AC Infinity AIRCOM T8, Quiet Cooling Blower Fan System 17" Rear-Exhaust for Receivers, Amps, DVR, AV Cabinet Components.  It keeps my AVR very cool and is virtually silent.
I use a Bryston, in the 4B series at 300 w/c. It sits on the lower shelf of an antique Chinese piece of furniture. The rest of the gear is above it on a second shelf. Not much room for convection air circulation. What I did was utilize a pair of 4" computer case fans (Antec btw). They are 12v and dead quiet. I did some minor insulation on the fan frame so it does not make direct contact to the wood shelf. I was able to power the fans from my Bryston Pre Amp power supply. The pre amp turns on the amp using the Bryston trigger feature and when it does the fans come on as well. Even slight air movement will aid most amp cooling. My point is that there are many computer grade quiet fans available and most can run off any run of the mill wall wart ps. I recommend looking at them as a solution for air movement. Oh ya their costs are very low as well.
I cool my vintage fisher CA 880 (have not replaced the heatsink jet) with a laptop fan. I elevated the amp with rubber feet and the fan is placed underneath and blows air through the holes at the bottom. Fan is almost noiseless and only to hear right at the amp. The fan got some resistors to run at lower speed and a switch to turn it on and off.Works flawless!  
AC Infinity makes thermostatic controlled fan units. They had a side mount and a top mount at the time I purchased mine. You could also add additional fans to the unit. I used one to cool a Krell FPB 300. I had the thermostat set at 90 degrees. I used to monitor the temperature with a laser thermometer. Without the fan unit the amp would easily get over 160 degrees. You could smell things cooking inside the amp. The fan does make a little noise but is about as quiet as fans can be. It can be programmed to do what you want it to do. I bought mine at Audio Advisor. Hope this is helpful.
                               Frank
  1. fans should pull air AWAY from the amp
  2. use inherently low noise fans with sub 30db ratings
  3. use 12v DC fans on a variable AC/DC adapter
  4. adjust the DC level so the fans run slightly above the stall point

Each installation requires its own design.

On a tube amp with cage, fans mounted atop the cage will keep the whole amp comfortable. For a PrimaLuna with 4 power tubes in line, two fans. http://ielogical.com/assets/Audio/PrimaLunaAmpFans.jpg These fans have been running for about 3 years and have zero dust build up.

For a SS amp with external heatsinks either use a rack and mount fans to pull heat away from the amp or fabricate a stand to draw air away from the amp.

!!! NEVER BLOW AIR ON/INTO AN AMPLIFIER !!!

Keeping the amps at more constant operating temperature makes them sonically more consistent and prolongs their life. HEAT KILLS

I’ve been doing this for more than 40 years.

Power supply example: https://www.amazon.com/AUTOTOOLHOME-Adapter-Adjustable-Supply-Controller/dp/B01M3NL3NV
I see anotherbob already mentioned the AC Infinity fan unit. Must've been still asleep earlier this morning. I checked the Audio Advisor site and they are still selling them. T9 is the top mount version.
AC Infinity fan unit
One purchaser mentioned it is quite audible at anything above a 1.

This device will pull air through the amp and likely build up dust in the bottom vents.

What is desired is to pull a small amount of air around and away from the amp. The airflow should be incapable of moving dust or holding a piece of cellophane against a vent.

Avoid any unit that cycles and does not provide CONSTANT air flow. Inconsistent airflow over grilles can be distracting.

Size fans for the device so they can run at minimum speed.
I have the AC T9, seems very quiet to me. I have 80's NAD amps and never ran any cooling on them and they lasted quite well. But I did notice that I was losing some bass. I took it in and had all new capacitors and learned that there are two types of temperature ratings for capacitors. 85 degrees and 110. On my amps, it had all 85 degree caps. They are rated to work at that temp for x amount of hours. Then they start to deteriorate. Anyway, putting in all new caps Really increased the bass and the overall sound. It did however take a full month of 24/7 playing to burn in the new components. Every service person I spoke with said "keep them cool!" Now, running the amps with the fan, the temp never exceeds 82 degrees. 

Just my two cents.
I have 80's NAD amps
Electrolytic capacitors have an industry rated life of about 15 years. Anything beyond that is borrowed time, running or not.

Capacitor temperature ratings are 65°C, 85°C, 105°C & 125°C

Caps are rated for about x000 hours @ the rating temperature. They start deteriorating from the instant they are made. For each 10°C decrease in temperature, double the life.

85°C caps rated for 2000h in an amp running @ 35°C [95°F] have an rated life of 8000h. Run a couple of hours a day, that's 4000d or more than 10 years. In well designed devices like NAD, caps a rarely likely to be much over warm.

Old electrolytic caps increase ESR and decrease in capacitance. Loss of bass indicates capacitor coupled [boohoo] stages.
Wow, excellent information. I was mistaken, I had 105's installed. Could you clarify your last sentence? Thanks!
@ieales. NEVER BLOW AIR ON / INTO AN AMPLIFIER.  I never knew that ! I thought I was doing something good for the amp. While I was listening to music the other night for a few hours or so I went to feel my amp like I do on many occasions and like always it was so hot u could not touch it for more than a sec. U literally u could of fried an egg on top of if. So I placed a fan right next to the right side of the amp for about a half hour or so and it significantly cooled down the right side of the heat sinks so much that they were only warm now. I didn’t know if that was a good idea or not so I took the fan away and decided to ask you guys for any suggestions about that. I was even tempted to buy another fan and place it on the left side like I did to the right side to have even cooling from both sides of the Krell Fpb 600. Thanks a lot for your advice. 
I run a fan on an amp at such a low rpm and airflow rate, that if it’s power supply is unplugged, it stalls out. It’s a small 12V fan running at approx 4.1V DC. When I plug it in, I have to touch one of the vanes to start it by hand. That is what you call the ’just above stalling’ voltage for the 12VDC fan. Each will be different.

It’s ’just enough’ air flow to move the air away from the heatsinks, and no more. The running temp drops by a good 20-30 degrees.

You can also buy a 12V fan speed controller from a computer shop. One that is all passive, just resistors and a few switches. That would have the least level of interference in your audio equipment.

Do not, I repeat, do not buy a PWM electronic controller of any sort. Buy a small unpowered passive one that uses resistors and is meant to go ’in line’ (in series) with the DC power line for the fan, and uses simple switched resistors to vary the loading or current/voltage that the fan has access to.

The problem is that the passive/resistive/switched fan speed controllers have all died away for the more expensive and ’egotistically more stroking’ expensive electronic ones with switches, big panels, tons of parts, LCD displays, lights, alarms, knobs, etc. This kind of poorly implemented (pulse power supplies, PWM voltage control, and electronic added noise) device is fine for computers (where the entire box is almost pure electrical and RFI noise) but absolutely terrible for high end audio.

You’ll have to search out a simple passive switched fan speed controller, that will have only a few speeds available to you, via the switches, and that’s usually slow, medium, and fast. they are difficult to find as ’passive’ type speed controllers are not cool and complex, and are considered passe and cheap. There is a good amount of them out there, but their specs and build are mostly hidden away from eyes, due to human perceptions about quality.

This kind of simple device:
https://www.newegg.com/p/376-0020-00007

Which is fine, if the cooling considerations you reach for... does not have an electrical system that does not destroy the sonic qualities you are trying to hold on to.

There are some that have simple amplifier circuits and are not PWM modulated, but this will take some discernment on the part of the buyer, to understand which is which.



Wow, excellent information. I was mistaken, I had 105’s installed. Could you clarify your last sentence? Thanks!
Installing 105°C caps is usually only a cost issue unless one takes the time to evaluate all parameters.

Old electrolytic caps increase ESR and decrease in capacitance. Loss of bass indicates capacitor coupled [boohoo] stages.
A high pass filter is a cap in series with a resistor. Typical design would place the corner one or two magnitudes below the minimum frequency of interest. For 20Hz, corner range would be 2 to 0.2Hz. It also blocks DC [A/C coupled]. As caps age, capacitance decreases, raising the corner frequency. The caps were shot long before a loss of bass would be perceived. The ’boohoo’ is because everything is audible and electrolytic capacitors tend to smear the sound. All other things being equal, which they seldom are, direct coupled can sound better. Bottom line, NAD weighed the trade offs and made fine sounding equipment for reasonable prices.

I run a fan on an amp at such a low rpm and airflow rate, that if it’s power supply is unplugged, it stalls out. It’s a small 12V fan running at approx 4.1V DC. When I plug it in, I have to touch one of the vanes to start it by hand. That is what you call the ’just above stalling’ voltage for the 12VDC fan. Each will be different.
IMO, this is a bad idea. Line voltage varies all the time and unless one is using a well regulated supply, the fans will stall when the line voltage drops. Additionally, a fan may run when cool, but stall when it warms up.

You can also buy a 12V fan speed controller from a computer shop. One that is all passive, just resistors and a few switches. That would have the least level of interference in your audio equipment.
Not so. If running multiple fans, resistors and switches are a PITA. The adjustable supply is a small transformer and an adjustable voltage regulator. The transformer is several feet away and injects ZERO noise. I know, I measured. Most 12v fans will run within about 0.5v of one another. If one fan is overly fast, add a diode [1N914 or 1N4001] in series to drop the voltage slightly.

For added flexibility, a small control panel http://ielogical.com/assets/Audio/FanCtrl.jpg

I do it my way, you do it yours.

My particular 12VDC fan with the 4.1vdc power supply has been running for over 12 years. 24/7.

Yes, is a fine example, not an outlier. But the power supply and fan were decided upon --together. Tested. Those numbers will not fit all situations.

I’m using it in a situation where no fan is actually needed, not in a situation where a fan is required to not fail. That would be like ..uhm..a closed cabinet with no visual access to the fans to check on them--combined with an amplifier that is likely to die if left in a hotbox like a sealed cabinet. In that scenario the fan is ultra critical. Not a good idea to make the life of the amp dependent on a $5-$20 fan and given power supply for said fan...

As for the rest, we can do it ourselves and arrive anywhere we want or with as much engineering rigor we may desire.

Most folks (95% plus, as a guess) want pre-fab solutions, so that is the reasoning behind indicating commercially available devices and critiquing commercially available devices.


85°C caps rated for 2000h in an amp running @ 35°C [95°F] have an rated life of 8000h.
Oops. 2^5 = 32. 2000h rated are 64,000h @ 35°C. 32k days @ 2h/d ≈ 88y.

However other factors limit the life other than temperature, so 15y is a safe limit.
I used to own an Ampzilla which had a fan...never quiet enough
Ya shoulda PM'd me back in the 70's. Mine was dead quiet ;-)
Fans on power amps are rarely quiet enough for listening to acoustic music. 

One friend had a fan cooled power amp and when we tried to listen to solo violin it was like attending a concert with a DC-6 winding up for take off in the room. Had we been listening to loud rock it probably wouldn't have mattered.

You can get away without fans if you have proper heat sinks, but that is expensive. Take a look at the pics of these Classe Class A amps:

https://www.aussieaudiomart.com/details/649274239-pair-of-classe-dr3-vhc/images/1228060/

The amps put out into the hundreds of watts of heat just sitting there (a bit less if they are converting some of the current into sound.

Another friend had some fan cooled Crown (commercial) amps - I couldn't listen to them with the fans going beside us.
The amps mentioned sound like PA amps which are not designed for HiFi home use.

Any system that is audible when not playing isn't HiFi.

There are many sound apps available for smart phones. Broadband, ambient noise should be below 40db or below 30db 1/6octave. If there is any delta between amp off and on at 1m, the fan is TOO LOUD!!
I put fans computers  big ones that are quite. If I would hear them I just turn it up more. I have had some dish unit shut down because it was too hot. Since the fans no shut downs.
I just turn it up more
For decades cognoscenti have played material at optimum level for the system and the material.

It's one reason recording studio control rooms are so well sound proofed.

Adjusting levels to compensate for ambient noise often compromises the sound quality.

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