MyDEL MP 4128 modification
Not really home brew but this seems like the best place to put it.
The 20 Amp switch mode PSU is actually a very good supply with no discernible noise on the HF bands but it does suffer from generating a worse type of noise - fan noise!
The stock fan is a very powerful unit and is on full blast all the time, this makes it extremely noisy and almost unusable. I originally put a switch in series with the fan so I only put the fan on for high load periods but that was a short term fix that was not really workable - especially when I failed to switch the fan on one day and power tripped.
So the next phase was to drop the voltage to the fan and a series resistor seemed the way to go but it needed to be quite a chunk as the current draw of the original fan was quite high.
I opted for a quieter fan run from a voltage regulator and also decided to make the fan aperture a lot more air air-flow friendly as this is particularly poor. I tested the fan in situ with a variable PSU and found 8 Volts to be perfect so an 7808 regulator was used and this works perfectly.
So now the PSU has a permanent fan on with very low noise. I intend to make the air flow better soon but it is a lot better now.
This is the fan extract aperture - plenty of room for improvement...
The 7808 regulator mounted on a DC earth stud towards the front of the PSU, very handy mounting place...
The new fan in place, you can see where I have cut away the metal work, it still needs some more cutting but is much improved...