OT- Telephone as a vocal mic

[ianmgull]

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?

[candidate]

You're going for 'lo-fi'?

[Processaurus]

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

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!

[sean k]

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.

[mikemaddux]

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...

[Boogdish]

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

[PRR]

> Might be an ol' carbon mic in which case its alike



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.



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.

[ianmgull]

Thanks for all the info guys, time to dig in...

[Nitefly182]

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.

[chi_boy]

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.

[mikemaddux]

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...

[ianmgull]

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.

[doug deeper]

japanther uses the speaker part of the phone as a mic.

[mikemaddux]

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

[birt]

i've used both these setups for carbon mics:

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.