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Building an effects microphone out of an old telephone
Old 21st September 2007
  #1
Here for the gear
 

Building an effects microphone out of an old telephone

hello all,

I am wanting to build an effects microphone out of an old telephone receiver, circa 1970-1980. I would like to drive it off of phantom power since I believe that 48 VDC is comparable to line voltage of most (older) phones.

Here come the questions:

Since the microphone elements of these phones where a two wire system, can I simply tie one of the legs carrying the phantom power to the neutral pin through a significantly large resistor 100k?? 1M??

(I know this unbalances the system, but this is to achieve a low fi sound anyway.)


Next what would be the protocol for impedance matching. I dont have the thing on the bench so I am unsure of the impedance?

Would it need to be an more complex than a series resistor?
Would I need anything else?
Remember that simplicity is better in my opinion as long as I can be relatively sure that I would destroy my board or its phantom power.

Does anyone have any ideas?

Thanks

-E
Old 21st September 2007
  #2
Gear Addict
 

I'd post this in the "So much gear, so little time" forum. It's just s guess, but there might be more guys in there that could help you.
Old 21st September 2007
  #3


It depends on the telephone.

By the late 70's some phones were using condenser mics, but most were still using dynamics.




-tINY

Old 22nd September 2007
  #4
Gear Guru
 

I made a very nice effects mic using the earpiece of a standard telephone of that vintage (black, Ma Bell, regular old telephone from when there was only one phone company)

I put a 1/4" jack on it and I plug it into a DI box. It works great and gives you exactly that telephone sound. No phantom power needed, and the Direct Box seems to work perfectly for the impedance.

I left it in the handset. It looks a little weird when you use it because it is clearly upside down- but I suppose you could move the wire...
Old 22nd September 2007
  #5
Gear Head
 

I was thinking about this yesterday...
Recreating this effect in software just never sounds right.
Any schematics for this project, joeq?
Guess I'll Google around.
Old 22nd September 2007
  #6
Gear Guru
 

Quote:
Originally Posted by ramona View Post
I was thinking about this yesterday...
Recreating this effect in software just never sounds right.
Any schematics for this project, joeq?
Guess I'll Google around.
you don't really need a schematic- you don't even need a soldering iron.

if you unscrew the earpiece there is a round Army-green speaker about 1/2 thick with seven holes in the metal, behind which you can see a silvery metallic diaphragm. That is normally the speaker, but a transducer is a transducer.

If you pull this unit out of the handset and flip it over, there are two very obvious screw terminals. Wire those up to any guitar cable - you can strip one end and leave the 1/4" plug on the other. Then just plug it into a DI box. You're done. I am sure there are things you could do circuit-wise to improve it, but I don't know what they are and I can say that it works with just two wires.



It was a long time ago that I learned this trick, but I seem to recall the guy who showed it to me said that using the MIC as the microphone was a lot more work.

in addition to "phone" stuff, it is also good for 'robot voice' stuff and sometimes I even plug it into a guitar amp and mic the speaker.



Mounting it back inside the telephone handset is just for fun.

I am looking at mine right now - I used one of those coily guitar cords so it would look like a coily phone cord (only longer) I snaked my cable through the phone set's stress relief so it looks all 'official'

(except for the part where I have to talk into the "Ear" )

looking at it now, I bet I could have worked a little harder and either crammed the earpiece into the space meant for the mic, or flipped the handset over and drilled a new hole to make it look like the coil came out of the 'bottom'.
Old 23rd September 2007
  #7
Gear Head
 

Thanks, joeq.
I appreciate all the info. This is going to be a fun Sunday afternoon project.
Old 27th September 2007
  #8
Gear Head
 

to joeq

I was wondering if you could elaborate a little on your experiences with this microphone. What a great idea!

Have you used it on strictly vocal stuff or did you ever mic up a guitar cabinet with it? More input please....

It does seem like a logical way to go to achieve that 'telephone' sound...you seem to hear that everywhere these days.

Last edited by Jaymes G; 27th September 2007 at 03:51 PM.. Reason: spelling error
Old 27th September 2007
  #9
Gear Guru
 

Quote:
Originally Posted by Jaymes G View Post
I was wondering if you could elaborate a little on your experiences with this microphone. What a great idea!

Have you used it on strictly vocal stuff or did you ever mic up a guitar cabinet with it? More input please....

It does seem like a logical way to go to achieve that 'telephone' sound...you seem to hear that everywhere these days.
I never miced up a guitar cabinet or a drum set with it, just used it in some "silly" applications on vocals.

I have had rappers use it for skits, and this comedy writer I work with has used it on a couple of tunes.

I have plugged it into a guitar amp - I just plug it straight in, without the DI - and then miced up the speaker to get an even more filtered sound.

I suppose it would be worth a shot to try it in a wider variety of applications.

If it turns out to be TOO low-fi for you, you might be interested in the Copperphone mic. Judging from the posted samples, it has that same band-limited tone, but a nice clarity at the same time.
Old 6th November 2007
  #10
Here for the gear
 

I'm looking into doing this as well...

anyone got a pic of the innards on this? plus...guess I need to get a phone, so the wife dosen't yell at me for breaking ours. =P
Old 6th November 2007
  #11
Lives for gear
 

record with a 57/58 that has been through years of abuse, dont clean out the foam all that tobacco in there will help and a bit of rust on the grill can be good aswell, then beat someone with to get a bit of blood on the mic as it adds to the sound, and then crush it with Di-Fi/Low-Fi and enjoy the crappyness
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