Epson HX-20 - Manual (Page 60)

At each end of the cable you'll find three plugs, colored red, white,
and black. Take the three plugs at one end of the cassette cable and
plug them into the following sockets on the right side of the HX-20:
P l u g HX-20 Socket
WHITE EAR
R E D MIC
BLACK REM
Now take the three plugs at the other end of the cassette cable
and plug them into the corresponding sockets on your cassette
recorder:
P l u g
WHITE
R E D
BLACK
Cassette
Recorder Socket
EAR
MIC
REM
If you wish, you may use separate patch cords to connect your
cassette recorder to your HX-20: just connect REM to REM, MIC
to MIC, and EAR to EAR.
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