Old telephone mics wanted to use them as LOFI mics

Hi,

I found two old telephone mics (50K and 10K) and I want to know if there's a way to use them as LOFI mics to record audio or even Harmonica

is 50K or even 10K way to much for a mic pickup to record voice??

Telephone mics are properly referred to as transmitter elements, and can be either of two types, AFAIK, depending on vintage.

They might be dynamic elements, in which case the impedances should be fine for connecting to a guitar amp or other 'high' impedance line input, such as those found on domestic equipment (typically 100k or so) - but if the transmitters are of the carbon granule type, they act rather like condenser elements and require a potential across them in order to give any useful output (and likely a blocking cap of some sort before the following stage).

It would be a simple experiment to find out which type you have, if it works into a guitar amp as is, you're good to go. If not, maybe try a 9v or so battery across - or in series with - the element and see if that works. Just make sure that you block any power from the amp's input. 


Dan

EDIT: Doh! I just spotted this thread right below yours, which seems to have all the right answers.

so, this could be done with a 9V or 1,5V battery and a CAP to KILL the excesive current?

or how should I use the cap? like the image attached?

This circuit will never work, because the capacitor will not allow any current through the microphone capsule.
You need a resistor in series with the capsule and the battery. Then use a capacitor to get rid of the DC over the resistor and use this as the output.

Yes, here's another representation of the same idea.

Well, test results:

with the second picture, it sounds pretty decent for a telephone mic, has ENOUGH output, so the 100K pot was a good choise.
The sound is like an old telephone, add some distortion, and lofi sound...

sure will do some more experimentation with them as to try to record some demos of voice or guitar micking.

well after some test (with 1,5V cell and later with a 9V battery):



and a demo of the NOT SO COOL SOUNDING mic

http://www.mediafire.com/?mzktmjtyjxy

PS: clean amp was used

That is a great sound dude.... awesome! I want one... ;D ;D ;D ;D

J

GREAT JOB !!!!!