Pass Labs Pays Tribute to Sony
As mentioned in our report from the 2013 Burning Amp Festival, the veteran designer showed his "simplest amp," created with “two transistors, a [Jensen] transformer and wirethe fewest parts he'd been able to use to make it work.” The transistors weren’t identified back then but it turned out that they were Sony Vertical Field Effect Transistors or VFETs (footnote 1), a device Sony had developed 1972 to mimic the transfer function of a 300B triode tube. Sony and Yamaha both made amplifiers using this unique device, but discontinued them in the early 1980s when lower-priced power MOSFETs became available soon after.
Nelson’s Burning Amp used two complementary VFETs, part numbers 2SK82 and 2SJ28, the only ones Nelson had to hand, but he then set to work finding more. Eventually, he uncovered a stash in Singapore and bought all of them, enough to make the single pair of “Sony VFET Amplifier 40 Year Commemorative Edition” amplifiers at CES. This uses 24 pairs of VFETs as complementary followers and front-end/driver circuitry based on a Pass Labs’ XP topology. Output power is specified as 250W into 8 ohmsit sounded like more!
1 To avoid confusion with MOSFETs, devices with a vertical rather than lateral structure are now called Static Induction Transistors or SITs.