PIMETA Headphone Amplifier

It’s a PPA-Inspired META42 successor. It’s about the same size as the META42 board, but the topology is closer to that of the PPA.

Features of the PIMETA design:

Small board size: 3.0" × 2.4" (76mm × 61mm)
The board should work with most FET-input op-amps in DIP-8 and SOIC-8 packages.
Burr-Brown BUF634 buffers on the outputs.
PPA-like 3-channel setup so return currents from the headphones don’t disturb the signal ground.
Reverse power supply voltage protection
With low-voltage op-amps, minimum supply voltage is 5 V on a minimal feature set.
The op-amps can be biased into class A.
The buffers’ bandwidth can be scaled to balance current draw with sound quality.
The board will accept either the small and cheap Panasonic EVJ or ALPS RK097/RK098 potentiometers or the nice, big and expensive ALPS RK27 series potentiometer (a.k.a. “Blue Velvet”).
All resistors are on 0.100" × 0.300" spacing so you can put a DIP socket in their place and socket the resistors for easy experimentation. Similarly, many other holes are placed on 0.100" centers to allow the use of socket strips.
It strikes a careful balance between spaciousness for things like large, premium capacitors, while still keeping the board small enough to fit in small, portable cases like the Serpac H-65.
The board’s layout is optimized for minimum trace length and no vias.