[sdiy] 8038 XR2206

[Tim Parkhurst]

On 7/11/07, dj hohum <djhohum at gmail.com> wrote:
(snip)
> > >http://electro-music.com/forum/phpbb-files/schem2_161.jpg
> > >
> > >It seems that there's no positive power connection? Is this correct?
> >
> > Yes! The chip runs in reverse. ;-)  Seriously, the power connections
> > are Ground and V- instead of V+ and Ground. Thomas credits this
> > discovery to John Simonton (originally with the 566, I think).
>
> So are the outputs centered across zero? Or, are they negative going?
>
> tnx,
> Daryl

Hey DJ,

Thomas runs the chip on a negative supply to get the CV response going
in the correct polarity (higher CV = higher frequency). After that, he
uses coupling caps and op-amp buffers to get the outputs centered
around 0V. This trick works very well with the 566, and he's used it
on several others with great success. If you're running the chips at
LFO frequencies, then skip the coupling cap and add an offset voltage
into the output summer/buffer (a few more components, but works at
very low frequencies).

Shameless plug time: Don't forget that Magic Smoke (www.magsmoke.com)
has Thomas' 566 book for sale. Okay, I'm done. ;-)


Tim (stick a fork in me, I'm done) Servo
-- 
"Imagination is more important than knowledge." - Albert Einstein