A current feedback power amplifier

Introduction


This amplifier was designed to be good sounding. Its power rating is about 20-30 Watts depending on the speaker impedance. The components are ubiquotious and cheap. In contrast to some other CF amps (like the original Alexander amplifier) it does not need any operational amplifier, which is a big saving. The only difficulty is setting the zero DC output voltage by P2. The DC output voltage proved to be stable enough during long operation, but it is recommended to check it every once in a while. The bias can be set to 150mA using P1 after the 20 minutes of operation. There were 4 copies built with success. One of them is used as a guitar amplifier.

All the resistors are of 1% tolerance and 0.6W especially R2, R3, R5, R6 and those in the current mirror: R8, R9, R10 and R11. R16 and R17 are 5W power resistors. The output FETs can be replaced by their N versions or by other FETs e.g. the 2SJ162/2SK1058 pair, but those are more expensive.

Schematic

[Note]
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Foil (mirrored image)

This can be printed on a PnP foil and ironed on the surface of the raw PCB. There are cheaper techniques, where you can use photo printing paper that has a very glossy surface. You print this mirrored image onto the glossy surface and use the iron to transfer the ink to the PCB. This worked well after a few tries. Fortunately you can remove the printer ink using aceton if the wiring did not go through properly and start it over.

[Note]
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Wiring side

This is just for your information you won't need this.

[Note]
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Components side

[Note]
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Copyright © 2006, 2007 Robert Szalai
cfamp