Any ideas for a temperature controlled fan for Bass amp

[mikeydee77]

I recently bought a Hartke amp that I am very happy with sounds wise although the fans (24v) are a bit noisy. I cleaned them up which helped but in the end replaced them which made quite an improvement. I don't mind it being noisy when it is used in a live situation as you can't hear the noise then, but when I am just at home quietly playing I would like to reduce it significantly.

So I was wondering if it would make sense to have a temperature controlled fan. perhaps there is a schematic from another brand I could look at for ideas - or is it a bad idea for some reason?

Any ideas guys?

[tedmich]

its possible to use an NTC thermistor to vary fan speed, here is a 12v (PC based) design:
Simple temperature regulated FAN speed controller
sometimes just halving the fans voltage at a low temp, or adding it to the setpoint voltage divider resistors of a variable voltage regulator.
You can also use a snap action on/off White Rodgers (WR) "close on rise" type for about $8, although they are big and unwieldy. The key is getting the sensor (little NTC or big pad on WR) directly on the sensitive thermal component, usually the amps heatsink. Good heat transfer using silicon/metal oxide type thermal paste and secure attachment is a MUST. A sensor wagging in the air (or on the wrong component) will happily stay OFF while things melt.

[überfuzz]

Excuse my ignorance regarding this kind of amplifier, but is it a head or combo? Combos have fan like thingy called speaker. :-)

[tedmich]

speakers are "fan like" ?? I admit I don't get it but its morning and no coffee yet
My old PV Bravo with 3 x 12AX7s and 2 X EL84s all internal on their sides has a (24v?)fan header and space for a tiny fan. There are a MILLION fan choices at ultra low RPM, feathered blades, hydrodynamic / mag lev bearings etc etc to keep the PC guys ultra low noise, check Newegg. Most of these are 12v, but 2 in series work fine at 24v, you can even siamese two ultra thin 12v as a single (fatter) 24v unit. Cheap fans are often sleeve bearings and at ~4k rpm they can SCREAM

[diydidi]

Built this one yesterday Works a charm!!
http://www.google.co.za/url?sa=t&rct...80642063,d.ZGU

[Jazz P Bass]

A bit off topic:
I have seen temperature controller circuits from the factory that make no sense.
Ampeg has well over three versions on there bass amp.

Recently I had a Hartke LH amp where the fan came on when the heat sink was at 160 F!
Whoa Nelly.
Basically, it never came on.
Basically they ran a 12 volt powered 100K thermistor through a voltage divider, to a schmidt trigger ic, which turned a transitor on for the fan voltage.
I replaced the thermistor but it was the same.
By juggling the divider resistors I was able to get a 125 F On & a 110F OFF spread.

[überfuzz]

speakers are "fan like" ?? I admit I don't get it but its morning and no coffee yet

Lets just say the purpose of a speaker is to move air, back and forth. :-)

[g1]

That circuit has about 20 components, yet the text says it's a "real simple" circuit .
I was thinking simple more like a single thermal switch to turn the fan on and off, like the switches they used to use for overheat shutdown.

[J M Fahey]

^^^^^^^^^^^^
Get a N.O. one, 65 to 75 deg C switch, and put it in series with one of the fan wires.

If you use it to ground negative, you can save 1 wire.

Add a .047uF in parallel with switch legs to reduce click noise somewhat.

Although in home use it will never turn on and in band use it does not matter.

[tedmich]

g-one and JMF swoop in for all the glory when I covered snap action thermostats in post #2, jeeze there's no justice
:.(...

[The Dude]

g-one and JMF swoop in for all the glory when I covered snap action thermostats in post #2, jeeze there's no justice
:.(...

Think of it as your brilliance being confirmed.

[J M Fahey]

g-one and JMF swoop in for all the glory when I covered snap action thermostats in post #2, jeeze there's no justice
:.(...

Of course, you are absolutely right.

It's just that:

[mikeydee77]

Thanks for the inspiration. I had forgotten about those temperature switches. You see them on Peavey amps all the time and quite often they control the fans to be two speed so that is definitely a good option. In my case the HARTKE heatsink is pretty squeezed in so it might be a struggle to find a good mounting point.

In my research I found out that the GK amps have a LM35 based controller. This is more realistic to build as a module and bolt onto the heatsink as it is a TO220 package.

[diydidi]

Here is Rod's circuit from ESP. I built it on a small board. See my first post for link.

[J M Fahey]

Can I post this?
Don't want to lose a friend

To loop the loop, some Fender amps (BXR 300?) have a straight 110VAC fan, no messing with "girly" 12 or 24VDC ones, and 2, count'em TWO thermal switches .

The first one powers the fan through a resistor (say 100 ohms 10W or whatever is needed) so it spins at low speed; the second one shorts the resistor at higher temperature.

Brilliant.