Boss Poly Octave OC-20G Owner's Manual page 13

Application Examples
Using in Combination with the GR-33
fig.12
Guitar with GK-2A
or other
GK-compatible guitar
AC Adaptor
PSA-series
(sold separately)
RETURN
GK IN
MIX OUT
GK
guitar amp simulator: ON
US-20
GR-33
Power Amp + Speaker
13