[sdiy] Clarification on Breath Controller Q

[Tom May]

gmuir at sympatico.ca writes:

> Hi all,
> 
> To those of you who have replied, thanks much! 
> 
> I did want to clarify my original question a bit. I realize that you
> can simply feed a BC-1 or BC-2 signal through a DX and run that MIDI
> CC through a MIDI to CV converter, but what I am looking to do is
> keep the signal from the BC in the ANALOG domain (a la CS-01) to
> avoid unnecessary quantization of the control voltage during the
> conversion process(as many have described in their experiments).
> 
> My guess is that one of the pins on the BC plug takes a voltage from
> one of the rails, which powers the internal circuitry, and that
> another pin feeds the synthesizer with a steady CV (which in the
> case of a DX gets sampled into the digital domain and integrated
> with the outgoing MIDI data).

BC-2 is active, it uses a Hall effect sensor and some opamps, sleeve =
ground, ring = +rail, tip = CV out.  The output comes from an opamp so
it doesn't need to be buffered.  If the schematic I traced out a while
back is correct there is diode on the output:

   |\
---|-\___|/|_____ out
---|+/   |\|
   |/

Hmm.  That doesn't make sense.  I probably have it backwards.  I have
to guess it's for protection when it's being plugged in and the tip
hits the +rail contact.

The BC-2 has gain and offset trimmers which may or may not give you
the CV range you want.  Certainly if you want negative CVs you'll need
to tweak the output.  But, negative CVs from a breath controller
probably aren't terribly useful.

fTom.