I just built a power amplifier module based on the Trimodal Power Amplifier by Douglas Self. This is part of building a complete integrated amplifier. I'm now working on the preamplifier, power supply, PHONO preamp, input switching, speaker protection and maybe remote control unit.
For those not familiar with the trimodal concept by D. Self, this is a power amplifier that can be switched between two modes of operation. Class A operation with a fixed quiescent current (1A in my case) and a class AB/B mode with a much lower quiescent current of 50mA. The amplifier was build after reading his books (highly recommended). I also measured the THD with my QuantAsylum QA401 analyzer and have to say that the class A performance is very good as it can be seen in the images below. In class B I was a bit baffled by the high-ish 2nd order harmonics. It is still good performance by my standards but there might be something with my prototypes. This is still work in progress. The modules I've built have double output devices and the measurements were performed with an 8OHM load at an output of 5W. With 1A quiescent current in class A it can deliver about 12W before going into class AB. In class B it can deliver around 80W of output power with the +/-28Vdc rails. The measurements you see below were performed with a lab power supply and not on the actual power supply I will be using. I will come back with the same measurements performed with the actual unregulated power supply that will be implemented in the final amplifier. I'm expecting some mains frequency components (and their harmonics) but not too much as the design has a very good PSRR.
For those not familiar with the trimodal concept by D. Self, this is a power amplifier that can be switched between two modes of operation. Class A operation with a fixed quiescent current (1A in my case) and a class AB/B mode with a much lower quiescent current of 50mA. The amplifier was build after reading his books (highly recommended). I also measured the THD with my QuantAsylum QA401 analyzer and have to say that the class A performance is very good as it can be seen in the images below. In class B I was a bit baffled by the high-ish 2nd order harmonics. It is still good performance by my standards but there might be something with my prototypes. This is still work in progress. The modules I've built have double output devices and the measurements were performed with an 8OHM load at an output of 5W. With 1A quiescent current in class A it can deliver about 12W before going into class AB. In class B it can deliver around 80W of output power with the +/-28Vdc rails. The measurements you see below were performed with a lab power supply and not on the actual power supply I will be using. I will come back with the same measurements performed with the actual unregulated power supply that will be implemented in the final amplifier. I'm expecting some mains frequency components (and their harmonics) but not too much as the design has a very good PSRR.