No problems aside from noise.... Keep in mind you don't need the fan running full blast at 12v! A fan running at 5 to 7v will add airflow without making much noise, it only adds to the heatsink.
All my amplifiers (one 2xLM3886, another 2xLM1875+1xLM3886) run their heatsinks with fans at 5v off an LM317+heatsink. Plenty of airflow to make the most out of small heatsinks (Think stock AMD skt939 heatsinks) that would fail if used passively.
All my amplifiers (one 2xLM3886, another 2xLM1875+1xLM3886) run their heatsinks with fans at 5v off an LM317+heatsink. Plenty of airflow to make the most out of small heatsinks (Think stock AMD skt939 heatsinks) that would fail if used passively.
This makes me think of a cheap stereo I reverse engineered. It had TDA chips mounted on a small heatsink with a small fan bolted to it. The heatsink was three sides of a square, with the fan blowing through the center. The voltage to the fan was modulated by the output signal. I figured this out while I was poking around and the fan kicked on high when I made one channel oscillate.
I thought it was a cool idea, easy to implement yourself. It would only take a couple of transistors and supporting circuitry, which is all this unit had to modulate the fan.
There are heat sinks that are designed such that two of them go together to form a cooling tunnel of sorts. That's similar to the square extrusion you're describing, but has much larger surface area (= better cooling) than a flat aluminum surface. I'd go that route for fan cooling.
"A few years ago" (OK, 25-ish years ago), I implemented a fan controller for the fan in the power supply of my PC. I forget where I got the circuit from. Probably Elektor Electronics. There were quite a few of such controllers in the electronics magazines back then as PCs with noisy power supply fans were commonplace.
Implementing a temperature dependent control is pretty easy. An opamp with a temperature sensor of sorts can do that. However, keep in mind that to get the fan running at the lowest speed, you need to first overcome the stiction of the bearings. So have the fan turn on high for a second, then bring down the speed.
The temperature sensor does not need to be anything fancy. A diode or LED will do the trick. A regular silicon diode will have a temperature coefficient around -2 mV/ºC. Same for an old-fashioned GaAsP LED (think old school inefficient red ones). Of course, you can get fancy with something like an LM35 (10 mV/ºC) or an LM335 (10 mV/K), though that level of precision isn't really necessary.
Tom
"A few years ago" (OK, 25-ish years ago), I implemented a fan controller for the fan in the power supply of my PC. I forget where I got the circuit from. Probably Elektor Electronics. There were quite a few of such controllers in the electronics magazines back then as PCs with noisy power supply fans were commonplace.
Implementing a temperature dependent control is pretty easy. An opamp with a temperature sensor of sorts can do that. However, keep in mind that to get the fan running at the lowest speed, you need to first overcome the stiction of the bearings. So have the fan turn on high for a second, then bring down the speed.
The temperature sensor does not need to be anything fancy. A diode or LED will do the trick. A regular silicon diode will have a temperature coefficient around -2 mV/ºC. Same for an old-fashioned GaAsP LED (think old school inefficient red ones). Of course, you can get fancy with something like an LM35 (10 mV/ºC) or an LM335 (10 mV/K), though that level of precision isn't really necessary.
Tom
This has fins facing the inside. The board completes the square. It's a tunnel with fins. I still have it, but it's not quite big enough to use with a decent power supply. The unit delivered about 50 watts before clipping, but only 12 watts continuous, both channels driven. It's designed that way on purpose so that they could use a small heat sink. The amp sounded plenty powerful driving 8 ohm 90 dB/watt speakers. But that's not how we build amplifiers around here.
Thanks for the tip. I need to build a temperature controlled fan to sit on top of my amplifier. I might be able to work with that. I have spare parts out the wazoo and would like to build it from them.
A bipolar transistor can be used as a temperature sensor as well. Just short collector to base and you have a diode (B-E junction). Convenient if you want something in a TO-220 package that you can bolt to a heat sink.
Obviously, each device will be slightly different, so you'll need to calibrate it. No biggie for DIY where you're building only a few.
Tom
Obviously, each device will be slightly different, so you'll need to calibrate it. No biggie for DIY where you're building only a few.
Tom
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