The Cavalli-Jones Amplifier

The final step in the evolution of the amp was the realization that it could benefit from some amount of negative feedback. Headphones are a punishingly low impedance for an OTL tube topology. Negative feedback reduces the distortion and lowers the output impedance of the amplifier. But, as I began to study this problem, I realized that no single value of NFB would work equally well for low Z and high Z headphones. The simple solution was to add a variable feedback mechanism controlled using another potentiometer. The schematic for this change is:

The Cavalli-Jones Amplifer

The Cavalli-Jones is a simple amplifier that provides good performance and the ability to adjust its behavior depending on the headphones being used. Quite a few Cavalli-Jones amplifiers have been built since the optimizations were published, but this basic tube headphone amplifier has been replaced by better ones.