FM radio for a wireless surround
You can save some effort by wiring the active decoder right into the
FM transmitter. Power is derived from the transmitter's power supply (a
9 Volt battery if the transmitter is not modified). The RCA connectors
and the ground generator are eliminated, reducing the circuit to the four
components actually needed for the differential amplifier. The stereo/surround
switch could also be added to the transmitter.
Figure 10: Decoder to add to Ramsey FM-10 stereo transmitter
Since I am unfamiliar with the newer versions of the FM-10x transmitters
I cannot give a wiring diagram. You will have to cut the circuit board
traces where the signals enter the transmitter and wire the decoder in
there. Pin 11 of the BA1404 IC acts as an artificial ground and is where
the GND connection of the decoder goes.
One More Thing
One unadvertised thing a surround sound decoder will do is reduce the
volume of the lead vocal in most popular music. Reduce the volume in the
front speakers and you have an instant karaoki machine.