Unusual Amplifier

This is an integrated amp I use sometimes. It is likely the lowest distortion amp one could ever find. It is flat to DC and -.25 dB at 200 KHz. The circuit is pretty simple, JFET input and MOSFET output, and would be even simpler if so much protection had not been built in. Can you spot the reason why it is wise to include those features? Hint: component type. No need to analyze how the circuit works.

To avoid a red herring, double 3W resisters were used because they cost less than a 6W. That might matter because you could build this yourself and the components minus case and power supply would cost less than fifty dollars. It has been done for twenty if one had the usual stuff lying around already.

Attachment 88990

The obvious difference with the First Watt F5 is coupling capacitors. There are none. No need to fret over boutique caps when the amplifier section has no caps at all. The flat to DC specification was not hyperbole. While 25 watts into 8 ohms and 40 watts into 4 ohms will not power inefficient speakers to rock concert levels, having the most accurate amplifier yet designed has its rewards. The First Watt philosophy has been, from the beginning, "Who cares what the hundredth watt sounds like when the first watt sounds like shit?" Another point in its favor is that no First Watt amp has ever suffered a failure in the field. That and the ridiculously low build price of the F5 should seal the deal. Nelson has always designed First Watt amps to be owner build-able. His DIY forum often has circuit boards available, and sourcing stock parts from Parts Express is a go-to for his own builds.

https://www.firstwatt.com/pdf/art_le...2019_redux.pdf