Rod's instructions say "a 0.5°C/W heatsink for normal hi-fi use if the quiescent current is maintained at the minimum recommended of 20mA."
I don't know what to do with that.
This is the heatsink I was considering and I found this calculator, but I'm not sure what value to use for Ts (max).
I don't know what to do with that.
This is the heatsink I was considering and I found this calculator, but I'm not sure what value to use for Ts (max).
I have built two similar 2-pr output amplifiers. These hatsink fins are overkill, I have used the same length, same base thickness, but with 1" fins 3" tall (3U) and it worked great, never had any heating issues. That said this HS will be more than enough for the amp.
No such thing as a heatsink that is too big.
20 to 45ma is min idle/bias per device 120ma is ideal. I dont think the amp would benefit from 120ma, 30 to 45ma over the temp range would be fine.
Be more worried about DC offset, one of the outputs will ring like a bell if excessive. Forget if he used 100n across the VBE that helps too.
20 to 45ma is min idle/bias per device 120ma is ideal. I dont think the amp would benefit from 120ma, 30 to 45ma over the temp range would be fine.
Be more worried about DC offset, one of the outputs will ring like a bell if excessive. Forget if he used 100n across the VBE that helps too.
Height and base thickness are the main contributors to getting heat away from the output transistors - IMO, anything 3-1/2" or taller would be plenty for a single channel amplifier. I have run this same heatsink, with 2 channels of a 2-pr lateral mosfet amp on each heatsink 4-1/2" tall, +/-65Vdc without issues.
If you have space for taller HS and can afford it, it will always be better for reliability, also can be used later when you get the itch to build a different amplifier, which you will. Good luck!
If you have space for taller HS and can afford it, it will always be better for reliability, also can be used later when you get the itch to build a different amplifier, which you will. Good luck!
The calculator posted in post #1 is not really useful, since it only varies fin pitch.
Maybe try this one :
https://heatscapecal.com/natural
The heatsink supplier actually gave you a spec of approximately 0.80 °C/W for a 3" extrusion.
But you should study in detail what that figure means.
See :
https://linearaudio.net/design-considerations-class-enclosure
(Free download)
In case you might want to turn the P3A into P3B (exactly the same circuit) one day, you should consider getting a heatsink of 0.25°C/W.
https://sound-au.com/project3b.htm
You would be looking at something like 400x50x150mm minimum per channel, something like this :
www.alibaba.com/product-detail/High-Power-Amplifier-Heatsink-400-W_62390597411.html
(copy the link text and paste in your browser)
Patrick
Maybe try this one :
https://heatscapecal.com/natural
The heatsink supplier actually gave you a spec of approximately 0.80 °C/W for a 3" extrusion.
But you should study in detail what that figure means.
See :
https://linearaudio.net/design-considerations-class-enclosure
(Free download)
In case you might want to turn the P3A into P3B (exactly the same circuit) one day, you should consider getting a heatsink of 0.25°C/W.
https://sound-au.com/project3b.htm
You would be looking at something like 400x50x150mm minimum per channel, something like this :
www.alibaba.com/product-detail/High-Power-Amplifier-Heatsink-400-W_62390597411.html
(copy the link text and paste in your browser)
Patrick
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