breath controller schematics?

[Haible_Juergen#Tel2743]

Hi!

I'd like to built an analogue interface for my Yamaha VL-7 that
shall replace the BC-2 original Breath Controller.
The reason is I don't want something stuck into my mouth while
I play, and it always gets in conflict with my headphones, too.
So I think of using a common microphone instead, plus a preamp
and envelope follower.
What I need is the voltage range / impedance etc. of the Breath
Controller interface. Ok, I could start some measurements, but
as the BC-2 was supported by previous (FM-) synths as well, I am
sure somebody has the schematics / information laying around.

Thanks in advance,

JH.