Adding a simple thermal switch for noisy bass amp fan

[bassboy]

New member, and novice solderer. My solid state bass amp has a noisy fan (2 wire). I read a post by JM Fahey, on this forum, about adding a simple C switch 75 degrees Celsius in Series with one of the wires from the fan. I searched and found the right switch?? https://www.amazon.com/Auxiliary-Fan.../dp/B009GJ3U4Y Is this what I need? Also, I would appreciate a dumbed down description of how to wire the switch? Would a Series wiring involve me cutting the red and black wires, soldering the red wire onto one side of the C switch, the black wire onto the other side of the C switch, and then soldering the loose red and black wires to their corresponding wires now attached to the C switch? Thanks, Keith I probably need a picture drawn to do this--lol

[TomCarlos]

Welcome Keith....

Before you decide to install a thermal fuse, please tell us what type of amplifier you have.

Many (if not most) amps already have a thermal circuit built in - so the fan would only turn on when the amp gets hot. Does your fan work the same way?

And can you tell us, are there any part numbers on the fan? Maybe a fan replacement is all you need.

Tom

[bassboy]

Hi Tom, It's a non-class D Hiwatt Bulldog 400. The amp is new, on the cheaper side, and the fan is noisy from the factory; I'm sure I'll get the same noisy fan if I order another fan--lol. The fan is always on, hot or cold, with this cheaper model. I've unplugged the fan from the circuit board. It doesn't seem to ever run hot. I was going to just add a switch for when I use the amp at a gig. I unplugged the fan because at home it's loud. I though the therm switch mod might be a possibility. Keith

[TomCarlos]

I too would probably go with the option of adding a small switch on the back of the amp.... but be careful. The amp has a fan for a reason - it was designed into the circuit. So be careful when disconnecting it. Hot devices without cooling may lead to failure.

If you're at home and playing at low volumes, the amp probably does not heat up significantly. If you are out and playing a gig (where it is already loud, room noise, etc), no one will ever notice the fan - so you switch it "on."

The thing with the thermal switch is that you would need to mount it to something - and in most cases, that is the heat sink for the output devices. So unless you get the right one, you are stuck with the preset of 75 degrees. And hopefully, that heat setting (trigger point) is just right for this amp.

I have a QSC power amp and did notice the fan was a bit loud. So I experimented with different fans. The more air it pushes, the louder they can get. You can look at the DB spec. But even then, there is no guarantee that replacing a fan significantly reduces the fan noise.

[bassboy]

Hi Tom, Here is what JM Fahey said "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".

How would I do this? would I just snip the fans black/neg wire in two, and then wire the switch in between the cut wires?
Here's a 100 degree unit https://www.hawkusa.com/manufacturer...MaAp6mEALw_wcB

[TomCarlos]

N.O. means "normally open." So when the device is cool, there is no connection point between the device terminals. When that devices heats up, there is an internal switch (it's mechanical) so you have a short across the device terminals. Think of it in the same way you use a light switch in the room. The only difference is that this devices has it's own internal means of "opening" (when cool) and "shorting" when hot.

Yes, you would cut the black wire from the fan, put one end on the device, and the other end of the device goes to the other part of the black wire that goes to ground.

But you cannot let this device just fly in free air. You need to mount it somewhere. And the best place for that is usually in the output device heatsink. After all, that is the one place that will get "hot" when the amp really starts to work hard.

[Enzo]

There are other sources of fans besides Hiwatt. Meanwhile your part appears to be an automotive sensor, designed to screw into an engine block. Difficult to mount on your heat sink.

Search for THERMOSTAT. Here is an example of close at 75C from Mouser, and it can screw right to your heat sink.

67F075 AIRPAX | Mouser

Here are some from Digikey

Sensors, Transducers | Temperature Sensors - Thermostats - Mechanical | DigiKey

[Enzo]

The fan has two wires, it doesn't matter which one we chose to insert our thermostat.


The circuit is simple, it is the same as a table lamp. Think of a table lamp but replace the bulb with the fan.

[bassboy]

Thanks guys!

[J M Fahey]

Liked that TO220 case type you show, must work fine, I never used one, but the *classic* one used since forever is this "fried egg" type:

https://www.mouser.com/new/sensata/s...t-thermostats/


or:

https://www.mouser.com/new/sensata/s...3-thermostats/


same thing, only with different bent legs.

They are bolted to heat sink where you have some free space, 1 inch square, so they are at the same temperature.

You cut *one* fan wire, solder each free end to one switch terminal.

Switch is "normally open" so fan will be OFF while heat sink is cold or warm, will self turn on when it reaches 65C to 75C, (point where it becomes unbearable to touch) , choose 65C for safety, in any case at that point you will be playing quite loud so fan noise will be hidden.

Plastic/rectangular/TO220 case will work the same, just I never used them.

Peavey are great users of thermal switches, probably part of their famous reliability, here some examples.

They are such fanatics that they even bolt one directly on top of a transistor case, or use 3 (three) of them in the same amp
Ampeg too.

[Enzo]

On some amps Peavey used both types, normally closed and normally open. The normally opens would close to speed up the fan (by shorting across a series resistor) And the normally closed would open to remove power from the circuit. And clever boys, the fan was wired "outside" the break switch for power, so the amp went off to cool down, but the fan continued.

JM, the TO220 looks compact and convenient, but it was the one available at the (arbitrary) 75 degree mark. I was actually looking for the classic type you linked, but they came in other nearby temperatures.

[Chuck H]

How about a quieter fan?!?! Some fans are, indeed, noisy while others hardly make a sound. Maybe there's a quieter fan option that won't require much retrofitting.

[Enzo]

And sometimes all a noisy fan needs is to peel the little label off the hub and add a drop of light oil to th shaft.

[J M Fahey]

it was the one available at the (arbitrary) 75 degree mark. I was actually looking for the classic type you linked, but they came in other nearby temperatures.

I never demanded 75C but suggested 65C to 75C *range*

[Enzo]

Aware of that. I arbitrarily used 75 as my search target and found those right away.. The other type didn't have specifically 75 but had plenty other temps. ANY of which would be fine.