Stereo Encoder Circuit

This simple stereo encoder circuit schematic is build with 2 IC MMC4066E and MMC4047 and one transistor BC547B. On IC1 2 and 3 pins is the audio output which is amplified by T1 (current amplification). On IC2 pin 10 you can find 19kHz pilot tone frequency.

To adjust the frequency rotate R13 (multiturn) untill on IC2 pin 10 you measure 19kHz or the stereo led lights up on your stereo receiver. From R10 adjust the pilot tone signal and from R7 adjust the sound level.

Use metallic resistors and 100nF ceramic capacitor for low noise stereo signal.
If your audio source has dc voltage on audio output connect 2 x 0.47uF capacitor on the stereo encoder inputs. You can use a better T1 like BC549C if you want a higher sound amplification. Keep short circuits distances.

If you want the best from this mpx stereo encoder use metallic resistors, ceramic capacitor, shielded audio cables for input and MPX output and a good stabilized, filtered 5V power supply. I have worked with this stereo encoder in my youth and it’s pretty good because has a 70% stereo separation that is pretty good.

Stereo encoder components

R1 = R2 = 68K
R3 = R4 = 270K
R5 = 22K
R6 = 2.2K
R7 = 50K
R8 = R12 = R14 = 10K
R9 = 12K
R10 = 10K variable
R11 = 47K
R13 = 50K variable
C1 = C2 = C7 = C8 = 1nF
C3 = C4 = C5 = C9 = C10 = C12 = 100nF ceramic
C6 = 10uF
C11 = 620pF
IC1 = MMC4066E
IC2 = MMC4047
T1 = BC547B, BC549C

Stereo encoder circuit schematic

Stereo encoder circuit schematic

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