Rogers has put together a very simple hybrid headphone amplifier for use with 32 ohm Grado SR125 headphones. His hybrid head amp uses a vacuum tube voltage gain stage which feeds a MOSFET follower output stage. The tube is a the 12AU7 (ECC82) and the MOSFET is an inexpensive IRF612. The IRF612 is configured in a typical single-ended class A circuit using a passive constant current source (CCS).
What's best about this project is the power supply. Both the 12AU7 tube and IRF612 MOSFET are set up to operate at low voltage (~12-13V). Power for this project is supplied via an external switch mode power supply (SMPS). All of the project parts are readily available and one can easily put together one about $40. Rogers has reported very good results from this very simple project. For full project details, see the 12AU7 Tube / IRF612 MOSFET Hybrid Headphone Amplifier Project.
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