[sdiy] Pro One CEM3340 Sync magic

[Simon Brouwer]

Op 18-4-2010 12:08, Colin f schreef:
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of MTG
>> Sent: 18 April 2010 02:04
>> To: Synth-diy at dropmix.xs4all.nl
>> Subject: [sdiy] Pro One CEM3340 Sync magic
>>      
>    
>> Low and behold they used
>> a rather clever method of squashing the triangle wave of the
>> 3340 which resets the LFO. This seems to be somewhat
>> undocumented since the part has other pins for sync.
>>      
> Actually, it's documented as "Conventional Hard Sync", figure 5 in the
> Curtis CEM3340 data sheet.
>    

Can somebody explain how this should work? Note that a sync pulse pulls 
the triangle buffer *output* down. After the pulse,
the voltage on the integrator capacitor will not be reset but will be 
roughly the same value as before it (if the free running period is large 
compared to the sync pulse). See 
http://pdf1.alldatasheet.com/datasheet-pdf/view/87887/ETC/CEM3340.html
By the way, in this use the function of pin 11 appears to be reduced to 
a 1/3 Vcc supply as the decoupling capacitor on it will filter out 
practically all of the sync pulse.

In the Jupiter 6, the hard sync appears to be implemented differently, 
here the integrator capitor voltage is reset (to ground??).
See http://www.wiseguysynth.com/larry/schematics/jp6/jp6-page10.pdf

-- 
Vriendelijke groet,
Simon Brouwer.