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connect telephone microphone to guitar pedal

Discussion in 'Electronic Basics' started by amorphia, Feb 11, 2006.

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  1. amorphia

    amorphia Guest

    Hi all,

    In the 1960's the band Fairport Convention kick-started UK electric
    folk, and the fiddle player Dave Swarbrick is still a legend. His
    fiddle sound was extremely distinctive and I have read that back in the
    day, he used an accoustic fiddle amplified using a microphone from a

    In a bid to recreate his sound I bought an second hand old fashioned
    telephone and took the microphone out. It then occured to me that
    soldering the mike to a cable and plugging it into my mixing desk
    probably isn't going to cut the mustard!

    So I am wondering if anyone can recommend a circuit that would allow to
    use a telephone microphone and produce the same sort of signal that,
    for example, an electric guitar would, so that I could plug it through
    my guitar effects pedal into an amp or mixing desk. I'm really not
    bothered about excessive quality - the main point I suppose is to get
    the level right and not have a stupid amount of noise. Preferrably the
    minimum amount of components!

    Thanks a lot for any advice,

  2. Depending upon the vintage of the microphone, it may well be a carbon
    granule based unit. This means that it acts like a variable resistance
    when sound wave pressure is applied. This means you will need to pass a
    continuous current thru the microphone and then convert the varying
    current into a varying voltage. Tell us the resistance of the
  3. Genome

    Genome Guest

    I might be able to tell you how but I just got a phone call from the people
    down your local and they said that your folk band is shite and amplification
    would make you sound louder but you would still be shite and, by the way,
    why don't you just **** off and stop coming down the pub to inflict your
    shite upon us. We just tolerate you because Ted smiles a bit but, in case
    you haven't noticed, Ted is senile.... Oh, you wouldn't have noticed because
    you are as well. Anyway, we've bought Ted an MP3 player so you're not needed

  4. amorphia

    amorphia Guest

    Hi Anthony,

    thanks very much for the info. I measured the resistance of the
    microphone and it varies a lot, between I would say about 200KOhms min,
    and at max so high my metre thinks there is no connection. Does that
    sound like a carbon granule unit? I think if it isn't, there is no
    point in me trying this experiment because I'm pretty sure Swarbrick
    would have used one of those. I have looked on the telephone for
    markings which might reveal its age but I can't find much... it just
    looks like a classic 70s telephone. Any ideas for what next?


  5. Rich Grise

    Rich Grise Guest

    You can tell if it's a carbon element by inspection. Carbon elements
    are about the diameter of a quarter or half-dollar, and almost 1/4"
    thick. The front is domed, with fairly large holes, and on the back
    there's a center contact like a mongo "D-cell"-type contact, and a
    ring around it like a slip ring. If you shake it while holding it up
    to your ear, you can hear the carbon particles rattle around in the

    If it's a little tin cannister about the size of a pencil eraser, with two
    leads coming out of it, it's not a carbon mic, but probably easier to use. ;-)

    Hope This Helps!
  6. amorphia

    amorphia Guest

    It does help, Rich, it's definitely a carbone mike according to that...

    Any ideas for a circuit then?


  7. Pooh Bear

    Pooh Bear Guest

    They also rattle.

  8. Rich Grise

    Rich Grise Guest

    Well, a carbon mic needs a current going through it - the sound
    compresses and releases the carbon particles, so the resistance
    changes. I suppose you could take a 1.5V battery or wall wart,
    and pick some handy current - like, put about a 600 ohm resistor
    in series with it, with a 1K or so pot, and the mic., all in
    series with the battery.
    .. Batt + o-+- 1K pot --- 600R ---+---- CAP ----o Signal
    .. `----^ |
    .. MIC To Line In
    .. |
    .. Batt - o-----------------------+-------------o Gnd

    Try maybe a 10 uF cap, with the positive to the mic, and the
    negative to the input. The mic. shouldn't be polar, but just for
    the sake of style, I'd connect the ring to the negative and the
    center contact to the R/C junction.

    I don't know how long the battery will last with this setup,
    but a wall wart would last forever. ;-)

    I haven't built, simulated, or even tried this, so all of the
    standard disclaimers apply: you assume all risks, there are no
    guarantees, etc.

    Have Fun!
  9. amorphia

    amorphia Guest

    Thanks a lot Rich! I'll give it a go and report on the results...


  10. amorphia

    amorphia Guest

    Right, I tried it, and it worked! It sounds very distorted though. I
    don't think it is seriously useable as it is very feedback prone, but I
    had fun making it work.

    Here is a copy of the post I just made on

    Now I know I'm not the only one here who regards Dave Swarbrick as
    something of a hero... he seems to have starting the ball rolling when
    it comes to the amplified fiddle in english folk. Not only his playing
    but also his sound on the early Fairport Convention records has a
    certain something that I have always wondered what it was. I read in
    several places that he used a telephone microphone to amplify his
    fiddle back then.

    I decided seeing as I can't play like him but I can just about handle a
    soldering iron, I would try a little experiment. After a trip to the
    second hand shop for an antique telephone with a carbon granule mic,
    and a trip to usenet for some advice on a circuit to connect the thing
    to my mixer (, I produced this:

    I warn you it's not pretty. I can't decide if it sounds like anything
    other than a really distorted recording on a rubbish mike. It might be
    surprising if it did seeing as that's what it is... But, I don't know,
    something in me is almost saying there might be just a hint of that old
    Swarbrick sound. Just my imagination?

    Please no comments on the playing, after arsing around with making the
    circuit all evening I had a rushed minute left to actually record
    something before neighbour imposed curfew!


  11. Rich Grise

    Rich Grise Guest

    Aw, shucks! This is just a link to the _advice_! How about a link to
    the _mixer_! :)

    I produced this: And yeah - I haven't bothered to configure sound yet on this box, but
    again, I was hoping for a picture of your carbon mic duct-taped to
    your fiddle. ;-)

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