Analogue Solutions Polymath - Manual (Page 36)

Polymath
36 Circuits – Main PANEL | Analogue Solutions
A mono headphone pre-amp. Normally you would patch the output from the VCA to the
headphone amp.
Although this is a monosynth (that is monoaurial!), you must use stereo headphones, that is
use a stereo jack, since a mono jack will cut out the signal -if mono headphones exist 
The top minijack is the input. Feed the output of the VCA into here. The bottom jack is for
your stereo headphones.
ADAPTOR
This is used to convert a mini-jack to a big jack (either way!)
Normally used when you want to send, or receive, audio from/to and external device such as
a mixing desk.