PPA v2 Amplifier Board

PPAv2 is similar to PPAv1 except with a custom discrete output stage, plus a few other enhancements.

The pre-made boards are no longer available, but the design files are published below if you want to go and make your own.

Specs:

6.3 in. × 3.925 in. board size (Eurocard size, 160mm × 100mm)
Isolated power rails reduce rail-modulated crosstalk.
Differential-drive topology gives the simplicities of virtual ground without the crosstalk problems that normally go with that.
The signal channels use the Jung multiloop topology for low distortion.
Compatible with most FET-input op-amps.
Discrete diamond buffer output stage, with adjustable bias, to let you trade portability for sound quality.
Room for thousands of microfarads of rail capacitance, even with low-density audiophile caps. At the same time, differential drive means the qualities of the rail capacitor bank don’t affect the sound of the amp as much as in other topologies.
Reverse power supply voltage protection.
Quiescent power draw ranges from about 40mA on a minimal feature set to about 120mA when maxed out.
Enhanced JFET cascodes for biasing the op-amps into class A.
Optional bass boost.
Board-mounted ALPS RK27 (a.k.a. "Blue Velvet") potentiometers for volume control and bass boost adjustment.
Resistors on 0.100" × 0.300" spacing allow the board to be set up for easy experimentation.
A companion NiMH battery board allows for portable amplifiers.
Optional power LED turn-off circuit for indicating that the batteries need to be recharged.