Fans on Amps.

[benjaturner]

I've tried putting a basic, domestic fan behind my amp to cool it down and hopefully stop it over-heating. It works, but it makes the amp sound horrible. A really nasty modulation type sound. My dad thought it was probably because of the 240v motor (in the fan) giving off a signal that was interfering with the amp, or something. Do you think this is the most likely reason?

What can I do about it? I've thought about modding the amp with an internal fan. I'd just need to get a 12v fan and a step-down transformer, right? Is there anything else I should know before going ahead with this?

Thank you,
-Benja

[The Golden Boy]

Re: Fans on Amps.

I installed a fan onto my bass rig rack.

It might be more prudent think of why your amp is overheating, rather than covering up the symptom of overheating. Pay attention to what the amp's operating tolerances are. If you're running your amp at 2 ohms when it wants to see 16... or something like that.

In my case- a 900w amp passively draws air in from the back, blows the air through the heat sink towards a grate on the side of the amp. It's not the most efficient method. The hot air either doesn't exit the amp or it stays in the rack to get recylcled back into the amp.

[RW James]

Re: Fans on Amps.

I won't discount what your father is saying... and it may not be a bad idea to get a power conditioner for your rig anyway...

But the moving blades of the fan will reflect the sound back with a kind of doppler effect that can make it sound like you're playing underwater. It can be an interesting effect - but obviously not something you want all the time. You may be able to fix this by moving the fan around so it doesn't catch the sound from your speaker.

Or a smaller 12v cabinet fan just may be the answer.

Good luck,
Rick

[DesertRose]

Re: Fans on Amps.

small fan like those computer CPU cooling fans are alright.
I had a heat sink installed on my EL84 tubes. I don't know whether it works but I hope it does, so far its doing ok even after 3 hrs of long playing. thats nothing actually

[Jeff_H]

Re: Fans on Amps.

I've used just a very small desk fan, and even a battery operated fan....just to generate air flow. You don't need to generate that much flow to effectively cool what you need to cool.

I'd start with buying the smallest plug in fan (mine is actually a small clip on...no base) with 2 speeds and set it on low. I'll bet that would solve your problems.

[marvar]

Re: Fans on Amps.

I'd say that using a 240 volt fan will cause lots of noise. Are you in the US?
I use a small desk fan for both my Marshall combo, and my little class A amp to keep things cool.

[benjaturner]

Re: Fans on Amps.

I'd say that using a 240 volt fan will cause lots of noise. Are you in the US?

Nope. Sorry, I should have explained. I'm in the U.K. I'm sure you're aware that 240v (infact, anything between 250v and 220v) is the standard mains supply over here.

I

t might be more prudent think of why your amp is overheating, rather than covering up the symptom of overheating. Pay attention to what the amp's operating tolerances are. If you're running your amp at 2 ohms when it wants to see 16... or something like that.

It's a design fault with the amp. It's a Marshall JTM60. Everything you've heard is true, it overheats, bad! To avoid using a fan would basically require a complete re-design of the amp. The problem is simply that the valves are situated too close to the cheap, thin, weak PCB board.

Thanks for all your tips. It sounds like the best way to go is to install a 12v computer fan. I'm guessing the best bet is to take some jump leads from the power circuit to a step-down transformer. Does this sound right?

Should I aim the fan in the direction of the power amp valves? Or is there something else which needs the cool air more?

Thanks again,
-Benja

[Scott_F]

Re: Fans on Amps.

sell the amp and start over.

[larry_emder]

Re: Fans on Amps.

I had the same problem with my mesa boogie .22+ combo. The tubes were always over heating ,causing sound dropouts. So i just screwed a little fan into the back and now it works fine (except it mucks up the reverb)

[The Golden Boy]

Re: Fans on Amps.

Should I aim the fan in the direction of the power amp valves? Or is there something else which needs the cool air more?

Think of air flow. I would draw the hot air out of the amp rather than forcing cool air in. You probably don't want a large, fast and loud fan, as you don't need to be blowing a lot of air, especially if you can move the air from point A- into the unit, point B- across the unit, to point C- out of the unit.

If you do it sort of like mine, make sure to have some sort of vibratory insulative material between the fan and the chassis or cabinet, wherever you mount it.