This simple circuit mutes the audio out of the Accessory connector based on the squelch status.
The Accessory connector on the IC-7100 provides a fixed, line level audio output that is independent of the volume setting on the radio. This is ideal for feeding rig audio into a mixer, powered speakers or any other interface where a fixed audio level is important. Unfortunately, the audio signal is not connected through the squelch circuit. So, on FM in particular, there is constant static even when no signal is present.
Fortunately, the Accessory connector also includes the squelch signal. This can be used to mute the audio when no signal is present. The PDF below provides a simple, solid state mute circuit based on a P-channel JFET transistor. The circuit only requires 3 connections from the accessory connector: Audio, Squelch and Ground. The circuit does not require any separate power source. None of the components are critical. Anything close to the values in the schematic should work fine. Even the J175 JFET is not critical. Any general purpose P-Channel JFET should work.
The PDF below contains the schematic and description