Synch on the Digisound VCDO

[Grant Richter]

Look at Kevins mods on the synthfool site. He has implemented the hard 
reset. I think there is an extra section or two in the CD40106 you can use
to process the external signal? Just put a 100pf in series with the input
and run the output to the reset pin. Also a 10K or 100K to ground. You don't
want to hold the counter in reset, just bang it on the edges of the synch
signal. You may need to use a second section if the polarity of the reset
signal is wrong.

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>From: keithw at cix.compulink.co.uk (Keith Winstanley)
>To: synth-diy at node12b53.a2000.nl
>Cc: keithw at cix.compulink.co.uk
>Subject: Synch on the Digisound VCDO
>Date: Tue, Nov 7, 2000, 7:00 PM
>

> 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
>
>