We've all heard the sound countless times, I want to convert an old handset for my singer. There are two wires coming out of the mic so it's not a balanced connection. I'm just trying to figure out how to terminate the connection. Would a buffer be helpful for this sort of thing? I plan on building a stompbox that when engaged buffers the mic, and when "bypassed" simply mutes the mic (when he uses the normal mic). Any suggestions?
You're going for 'lo-fi'?
If it is an electret mic like most telephones it needs a couple of volts of power to run an internal FET.
http://www.epanorama.net/circuits/microphone_powering.html (http://www.epanorama.net/circuits/microphone_powering.html)
An opamp boost like the micro-amp would probably be fine, you might be able to get a little better noise performance if you precede it with a moderate, discrete gain stage.
Not sure what the ancient rotary type telephones use for a mic, or the preamplifier needs. Those probably sound the most telephoney, modern electret mics are more mid-fi. Of course you can always make them sound worse!
Might be an ol' carbon mic in which case its alike a piezo and wants to see a high impedance ( cause the style of mic sees a capacitance in parallel with the source so the roll-off of lows is built in with a normalish input impedance) to get the bass sounds but if you want telephoney and that vintage kinda intercom sound then unbuffer it and just join it to a 6mm plug and way you go.
I just wired up the speaker to a 1/4 inch jack and it works great as a lofi mic or as a really really quiet speaker (like you have to hold the phone up to your ear to hear the volume)
very cool 1 hour project...
http://www.instructables.com/id/Telephone-Handset-Microphone/
and if you're not sure if it's going to sound good, go listen to some Japanther, they've used phones as mics every time I've ever seen them.
http://www.youtube.com/watch?v=YRfF7A1whvw
> Might be an ol' carbon mic in which case its alike
(http://www-ece.rice.edu/~jdw/figs/carbon_mic1.jpg)
Carbon mikes are low impedance and floating.
They can be wired balanced; balanced lines were essential to telephone operation. No 3rd wire because they have no shield.
BUT carbon mikes require a source of power. And a lot more than an electret. And an interface to meld the DC power and the audio signal. This was traditionally done with a "repeat coil", a fancy name for a transformer. Resistor and capacitor is less efficient, but since you won't have 9,999 telephones in your district, efficiency is not too important.
At a glance, the Instructables link seems wrong. Impedances are way high. His thoughts about power are confused.
This seems right, to me, for classic telephone carbon mike to modern recording input.
(http://i48.tinypic.com/4lj1xc.jpg)
As mikemaddux says, the earphone is sometimes a dynamic transducer which works as a mike just fine. However you don't get the carbon-grit.
Thanks for all the info guys, time to dig in...
Quote from: ianmgull on December 22, 2009, 02:48:53 AM
Thanks for all the info guys, time to dig in...
You could also sacrifice a cheap microphone and install the passive element into a telephone handset for a simpler solution.
Could you use something like the Telephone / Noise pedal from R.G.? It's on his site somewhere. It's designed for guitar, but maybe it could be adapted to mic use.
Quote from: Nitefly182 on December 22, 2009, 03:21:45 AM
Quote from: ianmgull on December 22, 2009, 02:48:53 AM
Thanks for all the info guys, time to dig in...
You could also sacrifice a cheap microphone and install the passive element into a telephone handset for a simpler solution.
Thats exactly what I did...
Quote from: mikemaddux on December 22, 2009, 09:39:54 PM
Quote from: Nitefly182 on December 22, 2009, 03:21:45 AM
Quote from: ianmgull on December 22, 2009, 02:48:53 AM
Thanks for all the info guys, time to dig in...
You could also sacrifice a cheap microphone and install the passive element into a telephone handset for a simpler solution.
Thats exactly what I did...
Did it sound as muffled as you would expect from a telephone? I thought about RG's lofi pedal but part of the appeal of this is that it looks pretty awesome for your singer to shout into a telephone on stage.
japanther uses the speaker part of the phone as a mic.
Did it sound as muffled as you would expect from a telephone? I thought about RG's lofi pedal but part of the appeal of this is that it looks pretty awesome for your singer to shout into a telephone on stage.
[/quote]
Yep, very muffled and lofi....it was great
i've used both these setups for carbon mics:
(http://i119.photobucket.com/albums/o153/siceffects/carbonmic.png)
i have one that is just the handset. the earpiece has been removed so there is some space for a 3V lithium battery there. on/off switch in the middle of the handset, cable with mono jack as output. i used the resistor/cap setup because a transformer would take too much space.