Do I really need a fan?

[Boomzilla]

So I've got this monster "pro" power amplifier - a Crown PSA-2:

The thing has a two-speed, 115vac, 150mm fan in it. The intent is that the fan idle at low speed until the amp gets hot, and then it kicks into high gear. At least, that's what the manual says - I've never heard it go to high speed. So - long story short - my fan is worn out. It whines like a banshee even at its low speed setting - it runs continuously (by design) when the amp is on and there's no way to turn it off.

Now keep in mind the following factoids (some of which may actually be pertinent):

1. The intended use for this amp was for rack mount while inside a closed travel case with either zero or minimum ventilation.
2. The intended use for this amp was for extremely high power output for extended periods of time (hours on end)
3. The intended use for this amp was for potentially low impedance loads (rated for continuous 2-ohm service)

In other words, not only is the amp intended to be used in far more hostile service than home audio, but also it is intended to (if necessary) run much hotter than a typical home audio amp. The amp is also festooned with an array of "self analyzing" functions that protect the amp should it be shorted or else get too hot. So even if the fan dies, the amp won't fry.

Now the question - The majority of fans that might function as replacements in this amp are out of stock (and probably won't be available for some time due to global shipping slowdowns). I'm thinking of just removing the existing fan and running the amp completely without a fan at all. I can do the following:

A - Initially monitor the amp temperature with a thermal gun
B - If the amp runs very warm, install an external fan that will pull air through the chassis

My gut feeling is that the external fan won't be needed at all - the amp has generous heat sinking and even without forced air cooling, should be adequately cooled. Also, the amp will reside in an open equipment rack (not in a rack mount that places it in close proximity to other heat-generating equipment). And finally, the amp will rarely be played at more than one watt of output, and even then into no load of less than 4 ohms.

Does this seem reasonable?

Boomzilla

[AudioHTIT]

Editorially I won’t have any fans in my system, that said, I think your plan to try running without it is sound (with silence in the quiet parts 🙂).

[ttocs]

Yes, so long as you "poke" around by aiming a laser temp gun at the innards to document which parts operate at what temperature, just to get an idea of what normal operating temps are under your usage scenario.

[KeithL]

That may not be a good idea....

If the amp is designed to run with continuous air flow over certain parts then it may not have any provision for convection cooling...

In other words, without a tiny bit of airflow in certain spots, certain components may heat up REAL FAST...

Think of it like an engine that suddenly "runs dry" of coolant.

Things that are intended to always have forced air cooling are often designed with relatively little "thermal mass" to even out temperature spikes.

I don't know if that's the case with this particular amp...

And, if that did happen, hopefully it would just shut down...

But, if it were me, I wouldn't take the chance.

They could have easily designed it so that the fans stayed off until it got warm... but they didn't.

You may also find out that it simply refuses to run if the fan stops or you disconnect it.

You could ask around... maybe someone knows for sure.

Apr 27, 2022 15:59:03 GMT -5 Boomzilla said:

So I've got this monster "pro" power amplifier - a Crown PSA-2:

The thing has a two-speed, 115vac, 150mm fan in it. The intent is that the fan idle at low speed until the amp gets hot, and then it kicks into high gear. At least, that's what the manual says - I've never heard it go to high speed. So - long story short - my fan is worn out. It whines like a banshee even at its low speed setting - it runs continuously (by design) when the amp is on and there's no way to turn it off.

Now keep in mind the following factoids (some of which may actually be pertinent):

1. The intended use for this amp was for rack mount while inside a closed travel case with either zero or minimum ventilation.
2. The intended use for this amp was for extremely high power output for extended periods of time (hours on end)
3. The intended use for this amp was for potentially low impedance loads (rated for continuous 2-ohm service)

In other words, not only is the amp intended to be used in far more hostile service than home audio, but also it is intended to (if necessary) run much hotter than a typical home audio amp. The amp is also festooned with an array of "self analyzing" functions that protect the amp should it be shorted or else get too hot. So even if the fan dies, the amp won't fry.

Now the question - The majority of fans that might function as replacements in this amp are out of stock (and probably won't be available for some time due to global shipping slowdowns). I'm thinking of just removing the existing fan and running the amp completely without a fan at all. I can do the following:

A - Initially monitor the amp temperature with a thermal gun
B - If the amp runs very warm, install an external fan that will pull air through the chassis

My gut feeling is that the external fan won't be needed at all - the amp has generous heat sinking and even without forced air cooling, should be adequately cooled. Also, the amp will reside in an open equipment rack (not in a rack mount that places it in close proximity to other heat-generating equipment). And finally, the amp will rarely be played at more than one watt of output, and even then into no load of less than 4 ohms.

Does this seem reasonable?

Boomzilla

[Boomzilla]

I tried it (for about 30 minutes). The amp seems to work normally, and the exterior remained cool. But as KeithL points out, the internal boards may have undetected hot spots. With the amp functioning with its bottom plate on, there’s no way for me to measure internal component temperatures…

[garbulky]

I know nothing of amp safety and if amps have thermal shut down protocols, but this sounds like a fire hazard?

[Priapulus]

The fans in my HTPC were noisy. I replaced them with some equivalent "silent" fans from Amazon. It is now inaudible.
/b

[Boomzilla]

Apr 28, 2022 8:49:12 GMT -5 garbulky said:

I know nothing of amp safety and if amps have thermal shut down protocols, but this sounds like a fire hazard?

I think probably not. This amp (designed for "pro" use) has not only high temperature trips, but also distortion monitors. Should the output signal differ from the input (via distortion or via DC on the outputs) the amp detects the issue and shuts itself down. The PSA designation in the amp's name stands for "Professional - Self-Analyzing." The amp self-checks these trips every time it starts up and ensures that they're working & on-line. If not, the amp won't transition to its normal function mode. Most "pro" amps have such features now because it is expected that they'll be required to function at low impedance - for long hours - and at maximum output regularly. The shutdowns are essentially redundant. If the fan(s) can't keep the amplifier cool, then the high-temperature trips shut the amp off. If the circuitry overheats and begins distorting, the distortion monitors shut the amp off. If capacitors fail in the amp (from high temperature or any other cause), the DC sensors on the outputs shut the amp off. The Crown PSA series was one of the first to offer all these safeguards, but virtually EVERY "pro" amp sold these days has them.

So I'm not really worried about fire hazards. The worst that can happen is that the amp will destroy itself, but the (far) more likely hazard is that the amp will shut itself off from high temperature. But more likely than either of these previous hazard scenarios is that the amp will run just fine for years more without any issue at all. Were I using the amp for its intended application (full power output while powering a stage show or a stadium), I'd need the fan. For home audio, not so much.

[Boomzilla]

Apr 28, 2022 10:29:42 GMT -5 Priapulus said:

The fans in my HTPC were noisy. I replaced them with some equivalent "silent" fans from Amazon. It is now inaudible.
/b

I did look on Amazon - The fans I need were out of stock & the suppliers said that they had no idea when they might have more due to the global shipping backup.

[housetech]

If I had some pix of the rear and the inside, fan specs, I might be able to "home brew" a fix if you don't care about the looks.
I would also consider what I suggested before- use a DC fan off a wall wort at half, 3/4 speed via the applied voltage. (6vdc, 9vdc, 12vdc) Mount over the panel exhaust area or on top. Put some round sticky cabinet stops on the fan to stop vibration noise.

[DYohn]

The answer is very simple. As Keith points out, it's not a good idea. Indeed, in my opinion is is never a good idea to mod a piece of electronics gear unless you have as much information as the designer had when they designed it, and it is an especially bad idea to mod thermal management systems. Unless, of course, you consider the gear to be disposable.

[405x5]

My go to solution, (although this does not help the OP now) is to run with amplifier designs that need no fan at all.
Of course, even the coolest running COULD be in trouble if it’s confined to a bottled up space, but passive ventilation has always been a top priority with my personal installations. I’ve never had a fan and I’ve never had a problem.
There’s another fan trick I don’t hear a lot of guys talking about. That is to go to a larger amp. Than what’s needed.
If the amp. is sitting there loafing, you can bet the farm it’s not gonna blow up.

[AudioHTIT]

Apr 28, 2022 16:02:34 GMT -5 405x5 said:

My …
There’s another fan trick I don’t hear a lot of guys talking about. That is to go to a larger amp. Than what’s needed.
If the amp. is sitting there loafing, you can bet the farm it’s not gonna blow up.

I would say with traditional A/B designs, it depends much more on the bias point than how hard you’re driving it, and in the case of pure Class A, would be the hottest just sitting there ‘loafing’. In the OP Boom already indicated the amp has much more power than he ever uses. In any case there are too many variables to make generalizations about power usage.

[novisnick]

I’m a firm believer in air flow. Heat kills. I’ve even rigged an AC fan to a plug for the wall. Placed in on top of my at the time AVR. It works to this day, 25+ years later. The fan wasn’t audible and did a great job.
Keep cool sir! 😁

[Dreamer]

AC Infinity Fans!

These are really great A/V rack/cabinet/rack fans!

I own several....they are fantastic! They cool down my equipment extending the life of the units! They are very quiet, programmable and come in lots of configurations!!