What size heatsink is needed for Rod's 3A amp?

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Fairly big, but not excessively so. Rod recommends a 1deg/C heatsink - I used a 0.7deg/C heatsink with TO-3 outputs, and cut a hole in the back of my case so it could mount on the outside.

In hindsight, that's overkill - I could've used a smaller one, and mounted it inside the case. It gets warm, but doesn't heat up much more even running hard.
 
This amp is quite flexible in regards to power supply voltage and load, and the heatsink requirements will vary accordingly. I'm using a +/-25 VDC supply and am driving a 4-ohm load. It sounds like my heatsinks are about the same as ih's, and I mounted them on the outside as well. They barely get warm to the touch, but I don't run at significant power very often.
Later, I'll change to a +/-42VDC supply to run an 8-ohm speaker. My feeling was that this higher voltage was a bit too much for driving 4 ohms.
I'm very happy with this amp. I'd go with the biggest heatsinks that are reasonable for your budget and the case you select; reliability will increase if you keep the temperature down.
 
Dear kec,

I agree with PaulB:

"I'd go with the biggest heatsinks that are reasonable for your budget and the case you select; reliability will increase if you keep the temperature down."

If your heatsinks seems to be too small you can always add a fan
🙂

Best regards,

HB
 
I beleive Rod stated in the article that a 0.6 °C/W would work good for an stereo pair. I once found that kind of sinks for $20-25; if you get those prices, buying one for each would be a bit overkill, but if you have the $50 the amps would run really cool.

A friend of mine used a 1°C/W on his and the amp runned just warm.
 
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