ASM-1 osc.sync issue

[Debby and Gene Stopp]

Hi all, sorry for the delay, been out of town again....

Regarding the sync issue - don't use the sawtooth output from one VCO to the
sync input of the other VCO, use the pulse output.

The sawtooth does not provide a good sync signal. The pulse wave is much
better and will give the classic hard sync sound.

The sawtooth as generated by the VCO core rises from 0v to +5v and then
resets to 0v. I add a level shifter afterwards which produces a sawtooth
between -5v and +5v , and the waveform is inverted in the process. The
output waveform really starts at +5v and ramps down to -5v, then resets to
+5v.

The sync input of the VCO allows an external signal to change the reset
threshold of the VCO comparator. A negative-going pulse is needed to lower
the threshold so that the VCO sawtooth resets sooner than it normally would,
forcing the edge alignment with the external signal which is also referred
to as "sync". A sawtooth going the "wrong way" will provide poor sync
behavior.

So, use the pulse wave. I discovered this after I had already created the
ASM-1 documentation. If I ever release a new revision of the documents, I
will include this advice.

Best Regards,

- Gene

----- Original Message -----
From: "e" <edgarfov at zahav.net.il>
To: <synth-diy at mailhost.bpa.nl>
Sent: Monday, February 21, 2000 2:06 PM
Subject: ASM-1 osc.sync issue


> Hi all
>
> 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!
> Tnx in advance
>
> ALn
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