30-05-2017, 08:48 AM
You are correct about the transfer characteristics of power FETs but the un-decoupled source resistor reduces this to a more manageable 5mA/Volt. For more gain split the source resistor into two and decouple one part only.
That has given me an idea. It should be possible to create a volume control to speaker amplifier in a single stage. Positive feedback due to the increased stage gain could be a problem but it is worth a try.
Most linear power supplies use valves or transistors as cathode or emitter followers for the output devices. I don's why power FETs couldn't quite easily be substituted. The rest of the circuitry would need to be redesigned to match the devices used.
Nick, yes I had read about Fetrons before. I believe what killed the use of these and transistors in receiver signal stages was the discovery that using power FETs gave the signal stages a much wider dynamic range due to the difficulty of driving them into non-linearity.
Al
That has given me an idea. It should be possible to create a volume control to speaker amplifier in a single stage. Positive feedback due to the increased stage gain could be a problem but it is worth a try.
Most linear power supplies use valves or transistors as cathode or emitter followers for the output devices. I don's why power FETs couldn't quite easily be substituted. The rest of the circuitry would need to be redesigned to match the devices used.
Nick, yes I had read about Fetrons before. I believe what killed the use of these and transistors in receiver signal stages was the discovery that using power FETs gave the signal stages a much wider dynamic range due to the difficulty of driving them into non-linearity.
Al
Tuned for maximum smoke . 
