cooling fan controller for chipamp

oldfatbubba · 11th July 2007, 09:24 PM

Can anyone comment on using this fan control circuit in an audio environment? Will it introduce noise?

http://www.rason.org/Projects/fancont/fancont.htm

I brought a new amp LM3875 based amp into the world earlier this week, realized its sinks are whimpy and determined fans might help. Pics are below....

http://home.comcast.net/~eric.ericks...gainclone1.JPG

http://home.comcast.net/~eric.ericks...gainclone3.JPG

Nordic · 11th July 2007, 09:29 PM

It was realy pretty and I didn't want to say anything at the time...

Firstly I would rotate the sinks so the fins act as chimneys from bottom to top, to work with natural convection...

oldfatbubba · 11th July 2007, 09:32 PM

Quote:

Originally posted by Nordic
I would rotate the sinks so the fins act as chimneys from bottom to top, to work with natural convection...

I realized that will improve cooling, but they'll stick above the top of the chassis if mounted vertically.

SpittinLLama · 11th July 2007, 10:04 PM

Those heat sinks look to be plenty big for a LM3875, unless your supply voltage is too high or your speaker are too low impedance to cause a high power dissipation. Or maybe you case has no or very low venting for very low air flow. A fan would make a big difference. Even a small amount of air moving makes for much better cooling. The circut looks like it will work just fine but I only know what I read and saw on the link. In the past, I have used fans at lower voltage (say 15V for a 24V fan) so that fan wind noise was low and then a regulator or a separate supply to keep electrical noise low. I found that electrical noise came more from the fan and the wires if they run too close to inputs or outputs than from noise on the supply lines. On one build I used aluminum tape to quiet down the electrical noise.

-SL

I_Forgot · 11th July 2007, 11:23 PM

Heatsinks INSIDE the box? Where is the heat supposed to go?

If you use a fan, where will it go?

In past threads there was a fan control circuit that kicked up the fan speed based on the load current, not the heatsink temperature. When you use heatsink temp to control the fan, the heatsink has to get hot before the fan turns on/up. By using load current, the fan kicks up before the heatsink gets hot and maintains a lower temperature or at least reduces temperature swings.

I_F

Jonathan Bright · 11th July 2007, 11:43 PM

I think there is also a fan control circuit on Rod Elliot's ESP site in Sydney. It might be useful. Its project "42". and typing in ELLIOT SOUND PRODUCTS with Google will get you the site.

justblair · 12th July 2007, 12:24 AM

Maxim do IC's that handle PWM and Temperature measurements, I just cant find the one I am thinking of from their site that does what you want. I'm pretty sure its there, the site just got unresponsive on me... couldn't look anymore.

App Note

I have done a project before on the maxim 1668 temperature sensor (not quite what you are looking for)

the maxim chips though use a very common transistor for temperature monitoring, allowing you to make cheap accurate controllers.

(they also have a prety good sample program

)

TroelsM · 12th July 2007, 12:10 PM

With horizontal fins and a small fin-to-fin-spacing that sink wont dissipate much heat without a fan.

It looks to be designed to be used with a fan.

Even a very small fan at low speed will make the sink a LOT more efficient. With a bit of luck you'll only need a few holes in the case. You just need to get the heat transferred to the air in the case. The alu-case will transfer the heat to the surrounding air.

The above statement is off cause optimistic and will NOT work with any high-power amp.

Regards TroelsM

davidlzimmer · 13th July 2007, 03:43 AM

Yeah, if you remember, I was concerned about the sinks when you were asking about the plastic cover.

I think, if you still want to go with the clear top with a gap for ventilation, go ahead and mount a fan on each heat sink. (power supply...your problem...your solution)

You may find that from your listening position the noise to be very acceptable. My first clone had simular problems. My un-elegant solution was.... when I wanted to rock, I simply puuled the cover off and put a muffen fan on the heat sink. Believe me, no one heard the fan!

After that, I started designing from the heat sink down. This is my latest.
Overboard....maybe. I don't care.

oldfatbubba · 25th July 2007, 03:06 AM

Thanks, everyone. You've been great helps. I've ordered the fans fr. Mouser and have breadboarded a controller circuit.

It may be overkill since the speakers will have <1 watt running through them 99% of the time, but it's always nice to have the option.

Bubba

11th July 2007, 09:24 PM	#1
oldfatbubba Account disabled at member's request Join Date: Jun 2006	cooling fan controller for chipamp Can anyone comment on using this fan control circuit in an audio environment? Will it introduce noise? http://www.rason.org/Projects/fancont/fancont.htm I brought a new amp LM3875 based amp into the world earlier this week, realized its sinks are whimpy and determined fans might help. Pics are below.... http://home.comcast.net/~eric.ericks...gainclone1.JPG http://home.comcast.net/~eric.ericks...gainclone3.JPG

11th July 2007, 11:43 PM	#6
Jonathan Bright diyAudio Member Join Date: Feb 2004 Location: Queensland	I think there is also a fan control circuit on Rod Elliot's ESP site in Sydney. It might be useful. Its project "42". and typing in ELLIOT SOUND PRODUCTS with Google will get you the site. __________________ "It was the Spring time of the year when aunt calls to aunt like mastodons across the frozen waste." P.G. Wodehouse.

12th July 2007, 12:10 PM	#8
TroelsM diyAudio Member Join Date: May 2003 Location: AARHUS. DK	With horizontal fins and a small fin-to-fin-spacing that sink wont dissipate much heat without a fan. It looks to be designed to be used with a fan. Even a very small fan at low speed will make the sink a LOT more efficient. With a bit of luck you'll only need a few holes in the case. You just need to get the heat transferred to the air in the case. The alu-case will transfer the heat to the surrounding air. The above statement is off cause optimistic and will NOT work with any high-power amp. Regards TroelsM __________________ Need more time...

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11th July 2007, 09:29 PM	#2
Nordic diyAudio Member Join Date: Sep 2005	It was realy pretty and I didn't want to say anything at the time... Firstly I would rotate the sinks so the fins act as chimneys from bottom to top, to work with natural convection...

11th July 2007, 10:04 PM	#4
SpittinLLama diyAudio Member Join Date: Apr 2005 Location: In the Wild, Wild West	Those heat sinks look to be plenty big for a LM3875, unless your supply voltage is too high or your speaker are too low impedance to cause a high power dissipation. Or maybe you case has no or very low venting for very low air flow. A fan would make a big difference. Even a small amount of air moving makes for much better cooling. The circut looks like it will work just fine but I only know what I read and saw on the link. In the past, I have used fans at lower voltage (say 15V for a 24V fan) so that fan wind noise was low and then a regulator or a separate supply to keep electrical noise low. I found that electrical noise came more from the fan and the wires if they run too close to inputs or outputs than from noise on the supply lines. On one build I used aluminum tape to quiet down the electrical noise. -SL

11th July 2007, 11:23 PM	#5
I_Forgot diyAudio Member Join Date: Jan 2005 Location: Phoenix, Az.	Heatsinks INSIDE the box? Where is the heat supposed to go? If you use a fan, where will it go? In past threads there was a fan control circuit that kicked up the fan speed based on the load current, not the heatsink temperature. When you use heatsink temp to control the fan, the heatsink has to get hot before the fan turns on/up. By using load current, the fan kicks up before the heatsink gets hot and maintains a lower temperature or at least reduces temperature swings. I_F

12th July 2007, 12:24 AM	#7
justblair diyAudio Member Join Date: Jan 2007 Location: Glasgow, Scotland	Maxim do IC's that handle PWM and Temperature measurements, I just cant find the one I am thinking of from their site that does what you want. I'm pretty sure its there, the site just got unresponsive on me... couldn't look anymore. App Note I have done a project before on the maxim 1668 temperature sensor (not quite what you are looking for) the maxim chips though use a very common transistor for temperature monitoring, allowing you to make cheap accurate controllers. (they also have a prety good sample program )

25th July 2007, 03:06 AM	#10
oldfatbubba Account disabled at member's request Join Date: Jun 2006	Thanks, everyone. You've been great helps. I've ordered the fans fr. Mouser and have breadboarded a controller circuit. It may be overkill since the speakers will have <1 watt running through them 99% of the time, but it's always nice to have the option. Bubba

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