Apple Performa 6400/180 - Manual (Page 30)

Basics Sound - 28
Sound Input
One sound input port for stereo sound input supports the
Apple PlainTalk Microphone, and it supports non-Apple
microphones. It also supports a standard stereo (miniplug-
to-RCA) cable adapter for connecting stereo equipment to
the computer.
Note:
The sound input port does
not
support the Apple Omni
microphone (the round microphone shipped with some
earlier Macintosh models) or the attenuated RCA adapter
provided with some models of Macintosh.