[sdiy] ARP VCO PNP-NPN exponential pair matching

[Dave Leith]

Thanks for all the help.

I'm also in the process of building 4027-1 modules to replace
defective 4027 modules in current synths. The 4027 modules are
completely encapsulated in epoxy and can't be repaired.

I've added a couple of simple modifications to the circuit. (Sync in and out)

Coming back (almost) to topic about the exponential generator I wonder
how easy it would be to add linear FM to the basic ARP VCO core? That
would be great!

I'm working from the 4027-1 from
http://www.till.com/arptech/modmain.htm and a combination of Arp
Odessey and Axxe circuits



On 6/8/08, Ian Fritz <ijfritz at comcast.net> wrote:
> At 11:05 PM 6/7/2008, Paul Schreiber wrote:
>
> > If you want to track 1V/Oct accurately, then yes.
> >
>
>  Remember that in an expo converter one transistor provides the expo
> response and the other is for temperature compensation.
>
>  The purpose of transistor matching is to ensure that the exponential
> prefactors cancel, in order to avoid temperature drift from this potential
> source.  It has nothing to do with tracking, which depends on the
> characteristics (log conformance)  of the anti-logging transistor.
>
>  Ian
>