PMA CFA - current feedback power amplifier

This project has started in the beginning of 2016 for the reason that I was interested in a current feedback topology behavior. The current feedback concept is well described in Intersil company application notes. For those who are interested, I recommend to download the AN that I linked. I could hardly add anything more to it.

Amplifier schematics is as follows. The circuit is complete, the only missing parts are a DC servo and 15V stabilizers for the input transistors.

Output devices are robust OnSemi MJL21194/93. Drivers are MJE15030/03. Similarly as in case of my PA4 amplifier, the rugged and reliable amplifier was my goal.

The amplifier is strictly dual-mono, channels do not share any common ground point, so no ground loops are created.

Output DC protection is made with 94A IRFP90N20D MOSFETs, driven through opto-couplers. This was chosen after bad experience with mechanical relay at this position.

Photos of the amplifier

Basic specifications

Distortion measurement

Frequency spectrum at 50Hz/72W/4ohm


THD vs. frequency at 100W and 4ohm load


Pavel Macura 09/2017, 02/2020