Fans on amps.

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

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 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!

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

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.

Ya shoulda PM'd me back in the 70's. Mine was dead quiet ;-)

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 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.