A Very Simple MOSFET Amplifier

[steveu]

If you want simple, you should consider complimentary N+P MOS outputs. This avoids a lot of messy bias issues. The attached CMOS design uses bootstrapping, and a P-channel offset to achieve rail-to-rail output and about 0.001%THD into 4 Ohms. It also makes it possible to filter the VAS supply because the P-channel gate is offset below the VAS collector.

 

[jxdking]

Just asking, you don't have any working prototype yet, only simulations ?

No prototype yet.
I would go straight to layout PCB when I am free.

 

[jxdking]

You could replace Q2 with mosfet 7002 to have a higher open loop gain.
All the other bipolar transistors can be replaced by BC547 or 557. This will also give you 1 or 2 dB more open loop gain and a little lower noise.

This is the "Ultimate" version while keeping the same topology. Use mosfet in Q2 position to get high input impedance. Cascode the input stage to get high output impedance. They combine together to reach 106dB loop gain.
It doesn't improve 10KHz THD by much. At 10KHz, the NFB is limited by the slop of the gain anyway (see the bode plot below). However, the 1KHz THD improves by 20dB just because there is more loop gain available that previously is not.

PS: 1KHz -96dB THD @ 25W

 

[lineup]

It's a good amp.
I like your works with amplifiers 🙂