3340 sync

[Fraser, Colin J]

> -----Original Message-----
> From: Haible Juergen [mailto:Juergen.Haible at nbgm.siemens.de]
> Sent: 08 January 1999 16:39
> To: Fraser, Colin J
> Cc: DIY
> Subject: AW: AW: AW: VCO-1C #2
> 
> 
> A (crappy (:->) ) drawing with several 3340 sync types can be found at
> http://www.synthfool.com/diy/hj2vco.gif
> I have a 6-position switch that selects separate sync modes. You
> can clearly see the external transistor for the P5 etc. style sync.
> I have *never* really understood how it works - note that the 
> transistor
> is *not* connected to the VCO's capacitor, but to the 
> buffered capacitor's
> voltage. Somehow it discharges the cap thru the buffer (?).
> 
> I think this sounds *similar* to ordinary hard sync at least. But then
> again I'm used to the sync sound of my OB-8 and Prophet 5 ...

I guess the 'buffer' in the 3340 is not really a buffer - otherwise it
shouldn't need another op-amp buffer on this output.
I used a voltage follower on this output - I haven't seen a summing node
used as in the schema above. Doesn't this load the cap ?

The E&MM Spectrum synth, which uses 3340s, uses an external FET which resets
the voltage on the timing cap directly.
See http://www.tellus.vallentuna.se/gymninfo/personal/anders/andersus.html
for the schematics.

I always meant to try this method out, maybe I will soon as I have a problem
with the octave position selector in a 3340 vco on the modular.

Colin f