Anyone know how to convert a battery-powered mic to phatom power?

[Yareek]

So I was digging through my boxes of junk, and I came across a headset-worn microphone (Audio-Technica AVM25 I think). I cleaned it up and tested it to put on eBay, but accidentally found that it sounds fantastic on snare (especially underneath). It is bright becuase it's a small-diaphragm condenser, has a low-rolloff switch, and it's incredibly directional.

Now I'm not expecting this thing to fetch more than about 20 - 40 bucks, and if I can use this thing for under the snare (instead of my Rode NT2, which I kind of worry about), I might be able to save some money. However, the thing takes batteries, which I really don't like.

Anybody know of a way to mod battery-powered microphones to use phantom power? I've got some electrical experience (and my dad's an engineer) so I wouldn't mind soldering some parts in.

I came across this page: http://www.jdbsound.com/art/art520.html
I don't know how much different these circuits are, but if any of you have done this, please let me know if it can be done, or if I should just dump the mic and get a real condenser.

Thanks!

- Jarick

 

[reshp1]

A simple resistive divider to divide the 48V down to 1.5V (or 9V or whatever the battery is) should work since I doubt there will be much current draw. Make sure you take into account the current limiting resistor inside the phantom power supply (usually a few kOhms) when working out your resistor ratios. Best bet is to "eyeball" the resistance values and use a potentiometer and dial in the exact voltage after you connect the resistor and pot. Saves accounting for current draw, leakage, etc. Of course you'll need to work out the power dissipation of the resistors to make sure they don't toast.

 

[paddyponchero]

On all the audio technica electrets I've seen the drain gate and source are accessible, I would suggest connecting up as a source follower ala the linkwitz mod.

This should be a very satisfactory circuit, phantom powered and balanced:

http://www.mp3forkidz.com/mic/phantxy.html

I'm not sure about the 12V zener, I've never seen an audio technica electret on more than 9V but it may be ok.

If I was you I'd try to get $30 for the mic and pick up an ATM35 used - you can get em cheap if your not worried about things like missing battery covers and duct tape residue. I picked up a couple of 'broken' ones for $20, cut 4 inches off the cable where it gets stressed (just like headphones) and hey presto working mics.

 

[dayvel]

What a cool website! (OK, it's mine.)
That circuit should work fine with a 9V zener instead of a 12V one. Might want to raise the 100kOhm resistors up to 130kOhm, though.

 

[paddyponchero]

What a cool website! (OK, it's mine.)
That circuit should work fine with a 9V zener instead of a 12V one. Might want to raise the 100kOhm resistors up to 130kOhm, though.

Good work

 

[reshp1]

What a cool website! (OK, it's mine.)
That circuit should work fine with a 9V zener instead of a 12V one. Might want to raise the 100kOhm resistors up to 130kOhm, though.

Yes, very sweet. Good work.