Making a Mic from an Old Telephone (Wiring Advice Needed)

[Unknown_User]

I'm planning to try making a mic from the speaker of an old telephone.  I found some instructions here: https://www.instructables.com/id/Balanced-Microphone-from-Telephone-Headset-Speaker/

However the link in there to the wiring diagram for connecting the XLR socket to the transformer is no longer available and I can't find any other source for a diagram.  I notice that there's two terminals on the transformer, but obviously three on the XLR socket.  I think I'm short a ground lead?

Is there a way for me to wire this up such that I won't blow up the PA or make a sound man pass a brick when he sees it?

Cheers!

[obbm]

This takes me back to my very first home-made bass which used the moving-coil earphones from a German flying helmet.

Firstly I would use a male XLR not a socket.  As far as the connections go, connect the transformer to terminals 2 and 3 of the XLR. If you are mounting the the whole lot in a metal box then connect that to pin 1otherwise I would leave it unconnected

[Unknown_User]

Thanks, @obbm !

Can I ask why you would not use a socket?  I already have a socket and fear I would probably just knacker a lead if I tried to do it that way!

The flying helmet bass sounds like it would be amazing.

[obbm]

Virtually all mics have XLR males and mixer inputs have XLR females.  Most mic cables are female to male so the sound man will expect to see an XLR male on your mic.  It's not written in tablets of stone but it just makes life easier for everyone. Good luck with the project.

[Huge Hands]

17 minutes ago, Unknown_User said:

Thanks, @obbm !

Can I ask why you would not use a socket?  I already have a socket and fear I would probably just knacker a lead if I tried to do it that way!

I'm wondering if you're being a little confused by the terminology.  The original photo in your link shows the guy used a male XLR panel mount.  Female XLR panel mounts or leads tend to be known as sockets, whereas male pin panel mounts and leads are known as plugs.

Obbm is correctly advising you stick with a box mount "plug" like the original unit, not cut up a lead and have a tail hanging out of the box - although you may find that easier than cutting a hole in a box.

Sorry if I'm being patronising at any point, I just think the whole XLR world can get confusing when you have a female socket on a cable doing the plugging in action to a male plug in a panel....  

[Unknown_User]

5 minutes ago, Huge Hands said:

I'm wondering if you're being a little confused by the terminology.

This is almost certainly the case!  Thank you for explaining.  I think I understand what everyone means now.  Apologies for confusing everyone.

I have a panel mount XLR, with the three pins inside.  Like you would normally see on the back of a microphone.

[Huge Hands]

1 minute ago, Unknown_User said:

I have a panel mount XLR, with the three pins inside.  Like you would normally see on the back of a microphone.

That is the one - and (what obbm is saying) is not technically a socket, although most of us, myself included, would probably call it that.

Good luck if you go ahead with it.  I'm still wondering what @obbm's German helmet bass sounded like!

[Unknown_User]

Thanks to everyone for your advice.  It worked!  Now to try and work out a way to box it all up!

[Phil Starr]

from the looks of this you don't have a balanced line mic. You would need three wires; two out of phase and ground. You can do this with the right transformer and it would do some impedance matching for you too but to me it looks like the original guy has a simple isolating transformer and his isn't balanced either. It's hard to tell from the link exactly what he has done. It doesn't really matter though, you've made a mic from a speaker and it works. You don't have a balanced line to run 25m cables back to a mixer but does that matter?

It's fun doing this, I days gone by I've used a headphone as a mic, you just plug the jack into the mixer and speak into the cup. It sounds remarkably good and makes an OK drum mic if you aren't too fussy.