There are amplifier projects that are just a MOSFET and a Resistor. Thats it.
Factors that are involved in their popularity include:
- Cult status
- Lack of crossover distortion
- Excellent midrange performance
- Simplicity (minimalistic circuit design and minimalistic triode tubes)
I tried this approach - the resistor being 2x120V 200W incandescent light - but the sound was not very good at all. To fix it, I just turned it from common source into a source follower and built it a voltage gain stage with tubes. It's the only amplifier I have that's single ended - mainly because the entire amplifier cost me less to build than buying a pair of good SE transformers. 8WPC out from over 400W in from the wall though - I only use it in the winter but it sounds wonderful for what it is.
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It's usually an EL34 amp running UL (or something similar)