Headphone Amplifier Using IRF510 MOSFET/12AU7 Tube

Overview

The project is known as NP-100v12 which refers to a simple headphone amplifier built around the 12AU7 vacuum tube.

Details

The 12AU7 is also known as ECC82 in Europe that is popular in the audio world since it is a twin triode vacuum tube that can be operated at low voltages while having rugged design. They are even used in older vacuum tube voltmeters and vintage amplifiers & organs since their life spans can reach into decades. The 12AU7 tube is used in a common cathode configuration and the incoming signal is amplified by approximately 10dB for the purpose of the NP-100v12.

There are two stages that comprise the circuit including the common cathode tube volt amp stage and the MOSFET source follower for current gain. MOSFETs are often more stable with temperature and current shifts although a Bipolar Junction Transistor can be used in place of the MOSFET. Through a coupling capacitor, the signal enters the grid and leaves the anode amplified and out of phase by 180°. It is then directly coupled to the gate of the MOSFET and leaves the source. An electrolytic capacitor couples the signal to the headphones.