The fm10 audio front-end circuit was designed by G. Forrest Cook.
It contains an audio mixer, a condenser microphone preamp, and a stereo
test tone generator.  The circuit is intended to work with the Ramsey
FM10 stereo transmitter.

Note, the NE5532 is a high quality audio op-amp and may be a bit hard
to find, it is not really necessary in this circuit since the Ramsey
and other BA1404 based transmitters are way noisy to begin with.  
Other 8 pin dual op-amps should work, most have the same pinout as
the NE5532.  An LM1458N should work ok for this circuit.
Also, the 2N5089 transistor is not mandatory, you can probably
get by with another common 2N3904 but the gain will be reduced a bit.

The coil-capacitor filters shown may or may not be needed depending
on the RF power level around the circuit, coil values are not critical,
10 turns of #18 (stiff) wire wound over a pencil or 1/4" drill bit should
suffice, remove the pencil or drill bit after you wind the coil.

This circuit may be used and copied freely as long as credit is given to
the designer (G. Forrest Cook).  Commercial distribution is not permitted.

Enjoy.

P.S.  If you want to get into FM Stereo transmission seriously,
I highly recommend replacing your FM10 with a Free Radio Berkeley
PLL transmitter.  The FRB transmitter is mono, use this circuit:
http://www.solorb.com/elect/fmst/
to generate a stereo signal.