Stereo headphone amplifier (4HP)
A stereo in, 6.35 mm out, low-noise amplifier that can drive low-impedance inputs such as headphones. How else are you going to listen to your synth?
Using the specified resistor values will give 'correct' VU readings on the panel, but +0 dB signals are already quite hot for feeding directly into headphones. Consider reducing the 51K resistors to make the meter more sensitive. The first PCB version has the trimmers implemented rather poorly, so they cannot be used for this purpose.
When using the resistor placeholders to convert a linear taper pot to log-like, a steep parallel decrease seems most pleasing (something like 12-15% of the potentiometer's value).