Synch on the Digisound VCDO

[Keith Winstanley]

Hi All

I have been messing about with a Digisound VCDO which someone had
'appeared' to have modded for sync. There is a little op amp board
TL081 with a 3 position switch sending inputs to pin 9
of the CEM 3340 (the soft synch input) presumably to try for +- synch?

I haven't really managed to get much joy out of this arrangement or out of the
similar mod I did on my clone. With more understanding of this circuit I fail to see
how this arrangement could work as the pulse output on pin 4 of the 3340 is
attenuated and processed by a schmitt trigger before going through a frequency
doubler and clocking the lower addresses in the 2716.

I have heard talk that the way to get a hard synch on the VCDO is to send
an external input to the address counter's reset line, (pin 2 IC4 4024).
(Paul Maddox??)
Can this be a direct signal patched from another oscillator or is there
additional circuitry required?

Anyone know anything that could help? I would greatly appreciate their input.
Anyone tried the signal to the address counter method??

TIA

Keith

http://home.freeuk.net/lowpass