connect telephone microphone to guitar pedal

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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 microphone.

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 s**te and amplification would make you sound louder but you would still be s**te and, by the way, why don't you just f*ck off and stop coming down the pub to inflict your s**te 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 anymore.

DNA

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?

Cheers,

Ben

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 chamber.

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! Rich

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

Any ideas for a circuit then?

Cheers,

Ben

They also rattle.

Graham

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! Rich

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

Cheers,

Ben

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 fiddleforum.org.

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 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!

Cheers,

Ben

...

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. ;-)

Cheers! Rich