This is the socket for the external control input.
It is probably a switching connector.

TD

--- In Doepfer_a100@yahoogroups.com , <yahoo@...> wrote:
>
> > Thanks Dieter.
> >
> > I have yet to locate any in small quantities for sale in the US.
> >
> > I wonder whether one can make a temporary substitute with a standard
> > jack socket or does one need all 4 contacts.
> >
> > TD
>
> That depends upon the module and the in/output in question. In ~90%
of all
> cases only two terminals are actually used (GND and tip). But if
the socket
> has a switching contact the terminal of the switched tip has to be wired
> too.
>
> Best wishes
> Dieter Doepfer
>