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MFJ 618 convert to stereo input

Discussion in 'Home Brew' started by TBoyd, Mar 7, 2011.

  1. TBoyd

    TBoyd Member

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    I am getting a MFJ 618 speech enhancer, and want to be able to have separate stereo channels all the way through - hope to use it an an external hearing aid - and having dual mikes will help determine direction to the sound source.

    Has anyone attempted such a modification on this unit? Thanks.
    Boyd/KO4WK


     

  2. ve2ky

    ve2ky Member

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    MFJ-618 mod for stereo input...

    Hi Tom,
    I own one and I am also considering doing this modification.

    From the schematic (fig.9 page 14 of user manual), I would do the following:
    1- replace the volume potentiometer (R21) with a dual potentiometer (stereo)
    2- add a RCA jack for the second channel input on the back panel
    3- intercept the PBC trace going to pin 6 of doughter board connector (SV1)
    4- add a wire from this trace (after the cut) to the second potentiometer's wiper
    5- connect a wire from the added RCA jack to the high end of the second potentiometer

    This should do it...
    The only thing would be that the input select switch would operate on only one channel.
    If dual stereo input is required, then a second RCA jack may be added for the second channel of the alternate input.

    I hope this helps.
    73
    pierre ve2ky
     
  3. TBoyd

    TBoyd Member

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    Thanks, Pierre - that's very helpful if I ever do the conversion. Actually, at that time I was working on creating my own hearing aid, (with dual mics) thinking I could do better than the commercial hearing aids (although a little less compact :) ).

    But since then, I finally got new aids that are far superior than any previous ones, and they have bluetooth and a remote control, so I finally am able to hear even in crowds. Haven't tried the Ham band yet with them, but I know that I will be able to hear much better than before. The ones I got are by ReSound, sold by Costco.

    Boyd/KO4WK
     
: mfj-618

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