Stereo FM transmitter using BA1404

admin February 17, 2011 41 Comments

Stereo FM transmitter circuit using BA1404.

A high quality stereo FM transmitter circuit is shown here. The circuit is based on the IC BA1404 from ROHM Semiconductors. BA1404 is a monolithic FM stereo modulator that has built in stereo modulator, FM modulator, RF amplifier circuitries. The FM modulator can be operated from 76 to 108MHz and power supply for the circuit can be anything between 1.25 to 3 volts.
In the circuit R7, C16, C14 and R6, C15, C13 forms the pre-emphasis network for the right and left channels respectively. This is done for matching the frequency response of the FM transmitter with the FM receiver. Inductor L1 and capacitor C5 is used to set the oscillator frequency. Network C9,C10, R4,R5 improves the channel separation. 38kHz crystal X1 is connected between pins 5 and 6 of the IC. Composite stereo signal is created by the stereo modulator circuit using the 38kHz quartz controlled frequency.
Circuit diagram.

stereo fm transmitter

Stereo FM transmitter circuit


  • Assemble the circuit on a good quality PCB.
  • Powering the circuit from a battery will reduce noise.
  • Use an 80 cm copper wire as antenna.
  • For L1 make 3 turns of 0.5mm dia enamelled copper wire on a 5mm dia ferrite core.

  • nemanja
    May 6, 2015

    Hello, I wonder can instead of 38 kHz crystal resonator to put strong such as 500 kHz to 1 MHz (Sorry if i have errors my english is bad i’m from serbia ) 🙂

  • Esmond Pitt
    September 8, 2014

    C13 and C14 are just coupling capacitors, nothing to do with pre-emphasis. The pre-emphasis circuit consists of C15/R6 and C16/R7 respectively, simple 1st-order high-pass filters. These ones give a time constant of about 50uS which is correct for UK, Australia, NZ, etc. For US/Canada change C15 and C16 to 1.5nF.

  • Darren
    February 26, 2014

    Correct me if I’m wrong but left and right Line In are wired at the same point looks like it would combine the two rather than having an independent left and right speaker(stereo)

    • Darren
      February 26, 2014

      …Ok my error I just see it properly the inside dot is + and the outer circle for line in is – so the only this it’s connected to is the ground between the two line ins

  • Abani
    February 19, 2014

    I need a BA 1404 IC. Is it available in India ? Please give me the address. I’m ready to pay in terms of Indian currency.

    • May 20, 2014

      i purchased it from e-bay

      • Jayakrishnan
        February 11, 2015

        i too want to buy ic ba 1404. from e bay i cudnt get a seller for order 2 IC or less.. kindly give me a link. and how many days dd it take to ship the part to you?
        thanks in advance.


  • Navneet raj
    February 7, 2014

    can i use it with my fm receiver??

  • Steeven
    January 27, 2014

    how can I variate the output frequency?

  • EVE Alain
    January 14, 2014

    I am a professor of electronics in France, and I would like to work with my students on a stereo encoder.
    For that I would like two copies of 38 kHz quartz please.
    Can you send me.
    Thank you in advance.

  • abhay
    November 13, 2012

    i found quality circuit at the same time i want all the component alogh with the pcb for Stereo FM transmitter using BA1404
    where should i purchase all the require component plz help

  • charles
    July 12, 2012

    i want 2 have back room radio station , can you please me more about transmitters, especially how to built them to broadcast for a long distance.

    Can it be possible to make a radio mp3 broadcast a long distance without buying an external boaster?

  • jojo
    March 28, 2012


    Start your learning by trying out simple circuits like – lighting an LED

  • frednand francis
    March 27, 2012


  • ninzibarrientos
    October 3, 2011

    sir how about monophonic transmission? is there any suitable or prefered circuit configuration?..thanks

  • ninzibarrientos
    September 29, 2011

    how much is the inductance range /value of L1? can i replace it with different type but with the same value?

  • ninzibarrientos
    September 23, 2011

    the freq comutation will still be equal to the computation for resonance freq of LC connected in paarallel? like fr=(2pi*sqrt(LC)^-1? how about some loading capacitance? do i still need to connect additional capacitor ? thanks

  • ninzibarrientos
    September 23, 2011

    i thought if we’re using LC as osc. it is in parallel connection? so you mean if i replaced the xtal with LC the Lc will be in series connection? from 5-LC-6 and vice versa? or i do still need to connect the LC(as the osc)into the gnd/ground? can yo please send me the details on the connection? plz? and what if i use external osc? like for instance a 555 timer ic configured as osc.with 38khz oscillating frequency output…how or what will be the connection from pin 3 of 555 timer ic to the BA1404 pins for osc? thanks

  • seetharaman
    September 23, 2011

    Hi Nin you can use series LC tuned circuit between Pins 5 and 6.

  • ninzibarrientos
    September 22, 2011

    hmmm i see.. if i utilized the LC as the alternative component for crystal , does it will follow the same connection? like for instance the crystal is connected across pin 5 and 6 and in series with the capacitor as its loading capacitance..if i replace it with LC will i connect it similar to the crystal? with LC both in parallel to each other,in series with a capacitor and connected across pin 5 and 6?..thanks..pls reply me immediately

  • seetharaman
    September 19, 2011

    Hi Nin you can try LC network than RC, but tuning is critical without proper test instruments. But the 38KHz crstal will be best.

  • ninzibarrientos
    September 18, 2011

    i encountering a hard time looking for 38khz oscillator..can i utilized RC osc. instead? as an alternative or replacement for the said crystal oscillator?

  • seetharaman
    July 19, 2011

    With the above transmitter and 1/2 wavelength antenna you can get the signal within the house. say within 50 feet or so. if you want higher range you have to feed the output of this IC to a 5watt or better RF amplifier.

  • mhz
    July 18, 2011

    Left in and right in are audio inputs, of course.

    How’s the power and signal range with this transmitter? Could it be made for >1 km?

  • Venkatesh
    July 17, 2011

    What is left in and right in

  • Newton
    February 25, 2011

    am a researcher, a student studing electrical engineering networking and telecoms is my field.

  • pankaj
    February 20, 2011

    it is very intresting circuit but i am unable to find 38khz cristal in agra please tell me any shop’s name in agra or delhi

  • sreejith kerala
    February 19, 2011

    From where can I get BA1404 it is not available in our area(kerala, TN). can any one suggest a shop (with address) in south india !

    • saiyathu ibrahim
      February 25, 2014

      hai sreejith ba1404 have in shop
      sunrise electronics

      “where can i get 38kHz crystal oscillator please tell me.

  • February 17, 2011

    Any information about L1 ??

    • admin
      February 17, 2011

      see notes

      • April 29, 2014

        I have a problem with this coil. I can’t make it properly at home.
        Is a ready-coil available in market? Plz…. .. help me.. .. I have the all listed parts include the IC without this coil & Xtal

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