Before solid state amplifiers hit the scene in the ’60s and ’70s, audio was amplified using vacuum tubes. On paper, solid state amplifiers seemed better in just about every way: they were more compact, less expensive, more efficient, and less distorted. But for a subset of musicians and audiophiles, they just don’t sound as good as tube amplifiers. That’s likely due to the “warmth” that is introduced by the tubes, which is especially desirable for guitarists when the tubes are overdriven. Josh has always wanted to experience that for himself, so he built this beautiful tube headphone amplifier from scratch.
Josh’s design is a modified version of the 6CY7 valve amplifier created by Cascade Tubes. Josh chose that because he wanted a hybrid design that utilized modern PCBs and SMT (Surface-Mount Technology) components, but which didn’t have any semiconductors or negative feedback. This design is also ideal from an aesthetic perspective, because it negates the need for the old-school point-to-point wiring that is common in vintage tube amps. That wiring was the norm in the days before printed circuit boards, but results in an unappealing rats nest of wires.
This design also isolates the right and left channels, because each channel has its own tube and transformers. Josh didn’t want any distortion from the tubes, since this is intended for headphones and not a guitar. The cathode heater can handle up to 30VDC, and in testing the circuit remained silent even at 20VDC with full gain. In further testing, Josh did find that the amp does affect the harmonics of music, which is likely the cause of the “warmth” that people describe. So far he’s only being using the tube amp with bookshelf speakers, but he reports that he’s very happy with the sound quality so far.