An OTL Tube Headphone Amplifier

The tube headphone amplifier is a high current mu follower, with a 12AU7 cathode follower driven by a 6CG7. Both sections of each tube are paralleled to minimize noise.

Both sections of each tube are paralleled to minimize noise. It's a zero global feedback, OTL design of pretty high quality. I use it and like it for Grado, Sennheiser, and Sony headphones. The maximum gain is about 25 dB with the 6CG7, so it pays to watch the attenuator level. R5 and R6 total 20K ohms as a stepped attenuator. A log pot of 20K to 100K ohms would be a good substitute. This design can be used as a line preamp as well.