Introduction: Balanced Microphone From Telephone Headset Speaker

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After putting together my first lo-fi microphone using an old rotary telephone carbon microphone
(Instructable Here), I wanted to see how the speaker part of the headset would sound.

The idea is that a speaker works the same way was a dynamic microphone, just in reverse. Initially I threw it together in an hour, and the sound was much better than I thought! So, I spent a bit more time to make the microphone look a little nicer and also convert it to a balanced signal for stage use.

Parts
-Old phone (rotary / vintage). Free if you're lucky, $5 to $40 flea market, used, etc
-600 ohm 1:1 audio transformer ($3 ebay + shipping)
-XLR jack ($6, local supply store)
-Some sort of case ($8, I used a Hammond 1591 case)

Some sound clips of the mic are on the final step.

Step 1: First Version of the Speaker Microphone

Initially I kind of threw this mic together mostly just to hear it. I created it simply by wiring the speaker part of the headset straight to a mono 1/4" jack.

I used some acrylic I had kicking around to mount the 1/4" jack. I realized ahead of time that the 1/4" jack wouldn't fit inside the phone headset, so I cut the acrylic bigger then needed on purpose. When I widened the headset end with a heat gun the acrylic was the right size.

This sounded better than I expected! So, on the next steps I'll show you how I re-did the mic to look a little better. Ok, maybe this version was bad ass, but I wanted a balanced signal and didn't feel like somehow getting a small transformer inside the headset.

Step 2: Making It a Balanced Microphone

First thing - to make it a balanced signal I wired the 1/4" jack directly to a 600:600 ohm audio signal transformer.  I followed exactly trusty RaneNote 110, scroll down to the section "The Next Best Thing"

http://www.rane.com/n110fig2.gif

The audio transformer came from eBay.

Step 3: Making It Look a Little Nicer

Step 4: Adding a Stand Attachment and Final Shots

I added a way to attach the mic to a mic stand. I used a cheap mic clip and a 90 degree metal bracket. Just bolted it on.

If you promise not to leave comments on my singing, here are some sound clips to compare this mic, and the microphone made out of the actual microphone part of the handset.

speaker mic AM test.mp3 is this microphone.

carbon mic AM test.mp3 is the sound from the microphone part / other instructable

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