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A Fender-Tone Tube Headphone Amplifier

A Fender-Tone Tube Headphone Amplifier

This project grew from several conversations that I had with John Broskie of the TubeCAD Journal. I was looking for a good headphone amp and John and I discussed some of the advantages and disadvantages of several of his published circuits.
I must say that for someone who creates so much good material, he is also very generous with his time. One particular discussion led me to a White cathode follower design that seemed elegantly simple, that could easily drive 300ohm headphones, and might do respectable duty driving 32ohm phones. The original circuit appeared in the April-May 2001 issue of TubeCAD Journal.

The more I looked at the circuit, the more I liked it. Naturally, because it was so simple, I decided to make it more complex. An issue for me at the start of the project was that I didn’t have any test and measurement equipment (except my ears), so I needed to find a design that I was pretty sure would work before I committed to building it. I spent many hours simulating various topologies with OrCAD PSpice using triode models from Norman Koren’s Vacuum Tube Audio Page that I modified for better accuracy. I also created a new 5687 model and added it to the library. The more designs I simulated the more I liked the simple White cathode output stage.

While Chu Moy and I were discussing the design for this article, he asked me how closely related Broskie’s amp was to the Morgan Jones amp featured in the HeadWize projects. Thus began a long conversation between us that resulted in the update to the MJ article with the new designs, the OrCAD PSpice circuit simulations and the tube libraries. For Bruce Bender’s 6N1P OTL amplifier, I suggested new values for some of the amplifier resistors and a higher voltage power supply, which Bruce generously agreed to try and was able to get much better results.

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