ASM-1 osc.sync issue

[Tom May]

Magnus Danielson <cfmd at swipnet.se> writes:

> From: e <edgarfov at zahav.net.il>
> Subject: ASM-1 osc.sync issue
> Date: Tue, 22 Feb 2000 00:06:51 +0200
> 
> > Hi all
> 
> Hi!
> 
> > i have tested the asm1 oscilators sync in's
> > And i'v found out it aint working
> > 
> > The schematics shows:     sync in-----> 100pf cap ---> so on.
> > i overide the cap to see what happends and the sync worked somehow
> > Maybe the results are abit extreme. saw tooth shown to be without
> > its tooth.
> > 
> > |``\  (example of single cycle with this kind of sync_without100pf cap)
> > 
> > In the asm text was written that 100pf cap was tested and worked fine
> > Any insight about this situation is welcome!
> 
> The time constant of that RC filter is
> 
> tc = R*C = (20k//10k) * 100p = 667 ns

And then there's the impedance of the driving source which may be driving
through 1K resistors.

> Maybe this timeconstant is a bit too low, so that slow slope waveforms will
> not make it thru this 1-pole highpass filter. I'd try stomping in a higher
> capacitance - maybe even go to the extent of 1 nF or so ;)
> 
> After all, the sync input isn't exactly the high precission part of that VCO.
> 
> Any opinions guys?

A larger capacitor will take the corners right off the driving wave.

IMO, the ASM-1 sync is weak, glitchy, too dependent on the impedance
of the driving source and the steepness of the driving wave, and loads
the driving source unnecessarily.  I did a replacement circuit for
glitch-free hard sync:

http://www.you-bastards.com/asm-1/vcosync.gif (pdf version too).

This finally motivated me to get off my butt and post the asm-1 web page
I started back in November . . . of 1998.  Just what the world needs,
another asm-1 page.  Check out the tri-to-sine converter if nothing
else.  It's a variation on an old theme, but I've never seen one
quite like it.

http://www.you-bastards.com/asm-1/

fTom.