Here is the finished amplifier.
Don`t judge for wires stripped from mains cord (from and to psu), it`s a budged project, spent only 20eur so far on it
I will use CPU cooler with thermal switch for fan.
At what temperature should fan kick in?
I was thinking at 40°C with thermal switch placed 1cm away from the chip on heatsink.
I tried it on my 150w subwoofer and it plays pretty loud and deep.
Now I must came up with the chassis. I`m thinking of reusing chassis of old tape deck, but it`s a bit big, so I will see if I can figure something better.
Don`t judge for wires stripped from mains cord (from and to psu), it`s a budged project, spent only 20eur so far on it
I will use CPU cooler with thermal switch for fan.
At what temperature should fan kick in?
I was thinking at 40°C with thermal switch placed 1cm away from the chip on heatsink.
I tried it on my 150w subwoofer and it plays pretty loud and deep.
Now I must came up with the chassis. I`m thinking of reusing chassis of old tape deck, but it`s a bit big, so I will see if I can figure something better.
Yes, If you build amplifiers, touching the heatsink whilst operating is inevitable and 70C is unnecessarily painful. Even 60 is above the pain threshhold after about 10 seconds contact with your skin. Make it safer and less stress on you and also the components, PCB and wiring by choosing a typical compromise between efficiency and safety at around 55-60C.
Heatsink (Ts) at 50 to 60degreesC is OK for normal working.
Using a 70degreesC switch to turn off the amplifier is also OK.
Ts=55degreesC probably gives a Tc~60degreesC for a ClassAB power Amplifier.
This reduces the transistor power capability to:
De-rating Factor = (150-60)/(150-25) = 90/125 = 0.72
This leaves 144W of capability for each 200W device.
Using a 70degreesC switch to turn off the amplifier is also OK.
Ts=55degreesC probably gives a Tc~60degreesC for a ClassAB power Amplifier.
This reduces the transistor power capability to:
De-rating Factor = (150-60)/(150-25) = 90/125 = 0.72
This leaves 144W of capability for each 200W device.
No, lower power means less heat, except it's not that straight forward, have a look at this graph as an example, it's from the LM3886 datasheet https://www.neurochrome.com/wp-content/uploads/2017/07/PowerDissipation_vs_OutputPower_4R.png
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