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stereo encoder circuit schematic

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

14 Comments

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  • Ander Abhadh

    The circuit has deliberate errors. The corrections are:
    1. The pin 13 of IC2 connect to pin5 of IC1
    2. THe pin 13 of IC2 connect to an inverter gate. The output of inverter connect to pin 13 of IC1.
    3. Delete connection between Vcc and pin 13 of IC1
    I attach the right circuit, with an opamp in the output to boost the output.
    Best regards

  • girish p

    I made one FM stereo transmeter its working perfectly (20db L R audio supporting ) range up to 300 meter i am enjoing the dolby digital surround sound wirelessly from my home …..here is one circuit its not working wast of time. if you want fm stereo transmeter then contact me facebook @ Girish parameswaran

  • zero

    just finished fitting a 19k pilot filter. heres the results. fantastic separation.

  • zero

    heres a better snapshot. [i had calibrated the screen but i had the 10x switched o on one of the probes].

  • zero

    ps. heres a couple of screen-shots of the LEFT and RIGHT chnls on the scope. both chnls are working. a tone generator is putting out a 80% modulated audio tone at about 1k-ish. its a “generator app” on the laptop. [so it may not be perfect]

    the 2x pictures show the LEFT chnl being driven to 80% and then the RIGHT. [left ch shown in YELLOW .. RIGHT in BLUE. as you can see the separation is not bad. this is how it sounds too. i would say at best .. 50% down in each ch.

    PS. the radio used for this test is a Tecsun PL380 pocket portable! i have have a panasonic tuner here that responds well. low noise and good separation.

  • zero

    i built this circuit a while ago. i had problems with high levels of whistling. i shelved it. recently i got the pcb out again and had a good check. i found a vey tiny piece of copper track that was making contact. [ i had used that horrible stripboard ]. anyhow i removed the short and gave it a good check over and wired it up again. this does actually work for me. the separation really depends on the oscillator. this is the problem using a vfo. it only has to be a bit off and the output becomes mono .. even if the pilot is working. i guess its down to phase issues. [ i built one myself a few years ago using my own design. the problem was exactly the same. that osc.!! my one used ALL bc548c,s no chips. i used a wein bridge osc.

    back to this encoder. one big problem .. as it stands .. is the carrier sidebands. this needs some fitering to stop the harmonics. with no audio the carrier sounds like its being overdriven.
    driving with audio and the sidebands sound bad.
    i also tried modding the pilot level using a resistor network. on the scope i found the osc to be a touch jittery. this doesnt help trying to keep the stereo locked either. the 19k output has a reasonable sinewave. oh and the separation? its fair to poor depending again on the vfo setting.
    ive seen very similar circuits using the same switching technique with a 4066. modifying the vfo to a crystal controlled version would fix the stereo issue .. but some filtering needs to be added.

  • DJ Adam Eve

    SO BASICALLY P.MARIAN WE’RE ALL CALLING BS ON THIS! HAVE YOU GOT ANY CIRCUITS YOU DID YOURSELF? I WOULD LIKE TO SEE THEM! YOUR ‘LONG RANGE FM TRANSMITTER’ HAS A WORKING OSCILLATOR (ALTHOUGH WHY TWO BACK TO BACK VCD I DON’T KNOW) BUT YOUR BUFFER/AMP LOOKS QUESTIONABLE TO ME. IS THAT YOUR DESIGN? I WOULD LOVE SOME HELP WITH IT IF IT IS.

  • ZaYka

    Hi. As i can see from the schematic the L and R switches at 4066 are driven at the same time so…. how come can this encoder “encode” ??? I Think the logic signal to one of the switches should be inverted and then it might even work. Siemaneczko!

  • meme

    designed the pcb. put this together but found way too much pilot carrier and the audio was very low. couldnt bring any stereo from it? just whistles. heard the pilot tone and tweaked it HF out of the audio band. replaced the TC c11 with a 560p to raise the FQY still no joy ??
    has this circuit been tested?

    • P. Marian

      Actually this stereo encoder has been tested and is working pretty well. I used it with my fm transmitters and the stereo separation was good enough, but not as good as the professional encoders.

    • AlbertH

      Nonsense. The circuit CANNOT work as drawn (copied?).

      “P. Marian” doesn’t understand the circuits he’s copied on to this site. Some are DELIBERATELY wrong (they’re my drawings he’s copied) and he has the errors in them that I put in to confuse copying idiots.

    • Dj Adam Eve

      Really? Well not according to the unanswered comment above its not! How come you didn’t reply? Do u have any pictures of it on an Oscilloscope? That would be cool.. I have had trouble with a couple of other designs on here too, is it your site? Maybe you can help…

    • AlbertH

      He wouldn’t know an oscilloscope if it fell on his foot.

      He has just copied circuits from other sites. many of them have DELIBERATE errors to prevent idiots like him copying them. Some of the circuits are mine and were put on the net with mistakes to confuse the copiers with no understanding of what they’re copying!

    • DJ Adam Eve

      Of course it’s not tested. It’s probably someones half cocked idea that they couldn’t get to work either, so instead of asking for help they upload it in the hope of you fixing it for them! THERE’S A LOT of that on here!

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