PLAN B analog blog

You may be thinking of the 901A, the VCO controller.  Here's my
references:

In the 901-B VCO, Bob handled octave switching by changing the cap in
the integrator.  Go here:

http://moogarchives.com/901bs.jpg

It was the 901-A VCO Conttrller which had the switched resistors in
it's octave rotary, which I believe was recommended by Dave Lutz (sp?)
because precision resistors were easier to come by without matching. 
Go here:

http://moogarchives.com/901as.jpg

- P



--- In PLAN_B_analog_blog@yahoogroups.com, John Mahoney <jmahoney@...>
wrote:
>
> 
> >...
> >OK fine no harm done, no fowl, right?  The bottom line is my VCO will
> >not nail tracking perfectly...but none will.  Some will do better than
> >others (read: ours) and there are reasons for this, most of which have
> >to do with the incorporation of a Moog's octave switch which limits
> >the range of the VCO to within what's called the 'linear region' but
> >is able to offset that to higher or lower registers.  In this way, the
> >circuit is responsible for tracking a much smaller distance, but it
> >can move that gap higher and lower over the audio band.  If you want a
> >VCO which demands keyboard tracking, this is the type you should stick
> >to because this is the only config which will give you large-range
> >keyboard tracking.
> 
> Whoa, whoa... Say what? I certainly defer to your superior knowledge, 
> Peter, but this is contrary to my understanding of VCOs, so I'd love 
> a little clarification. (A brief reply would be more than enough.)
> 
> I have not studied Moog VCOs in much detail, but I thought that a 
> VCO's octave switch just adds different voltage offsets to the pitch 
> CV. All the VCO circuits that I know of use this technique. It's not 
> as though different capacitors are switched into the circuit for each 
> octave. Is the Moog different from the rest?
> 
> (Apologies for non-PlanB content, but I hope that it's relevant 
> enough for everyone.)
> 
> John
> 
> 
> -- 
> No virus found in this outgoing message.
> Checked by AVG Free Edition. 
> Version: 7.5.516 / Virus Database: 269.19.20/1260 - Release Date:
2/5/2008 9:44 AM
>