2005-01-19 by James R. Coplin
I can try a little. At first, removing the resistor completely made the osc
much more receptive to resets, super hard sync with no effort. Any kind of
an edge would be enough to reset the osc. However, *anything* would also go
directly into the core via the reset circuit: DC, noise, the evil eye, etc.
It was fairly easy to get "odd" behavior besides the desired reset. It was
just too sensitive, any positive short voltage would reset the core, often
when you didn't want it to.
This is why Ken recommended putting at least a small value resistor to
provide protection for signals leeching in that were not intended to reset
and provide sync. This worked better at removing the oddness in having the
wire and provided a degree of input protection for the core.
Going on the "if a little is good, more is better approach", I started
increasing the value of the resistor to see what the largest resistor (ie,
closer to the osc. design spec) that would work and provide hard sync
behavior would be. 3k seems to be about the largest value that still lets
the core get reset by strong edges while providing an adequate buffer
against the external world. It is enough to block nearly all the DC, misc
noise, etc. that could impact the stability of the osc. So far so good...
However, a lot of this is personal preference. The 3k resistor is not super
hard sync. It is kind of a medium-hard sync. You could use a lower value if
you want the reset touchier. All of this being said, it is not perfect.
There are noticeable humps when the two osc are close together. The sync
circuit was not designed for hard sync, so you are getting part of the
behavior (enough to satisfy me at least) but not perfect behavior. I find
that you need to offset the freq of the slave osc to stop the humps and keep
the modulations from ending near the next freq crossover. Within these
ranges, it works lovely.
Again though, this works fine for me (I've converted all of mine and don't
have any problems) but it is not a STS sanctioned, blessed, or recommended
mod. It does change the circuit (although slightly) and has not gone through
the rigorous bench testing that a STS sanctioned change would have to go
through.
Bottom line, if you really want hard sync (and I did) this is probably the
only option you have as a STS change in the osc to accommodate hard sync is
unlikely. Later!
James R. Coplin
***************
If anyone asks of my whereabouts,
simply tell them i've gone out the window
for a spot of tea and am not
expected back any time soon.
***************
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> -----Original Message-----
> From: metafoetus2002 [mailto:jan-hinnerk.helms@...]
> Sent: Tuesday, January 18, 2005 7:38 PM
> To: SergeModular@yahoogroups.com
> Subject: [SergeModular] Serge Sync
>
>
>
> Hi,
>
> last December we saw some posts regarding modification of the Serge [PCO]s
> and [NTO]s
> from Soft Sync to Hard Sync.
>
> James R. Coplin suggested to replace the 22k Ohm resistor on the Sync
> input with a blank
> wire.
> Then Ken Stone suggested to replace the 22k Ohm with a 220 Ohm for circuit
> protection.
> One month later James suggested to replace the 22k Ohm with a 3k Ohm for
> "best sound
> and minimal (note I didn't say none) core effects".
>
> I am very thankful and excited about this possibility to get hard sync on
> my Serge. Now I
> wonder if someone of the more electronically knowledgeable guys on this
> list could be so
> kind and explain
> - the possible core effects
> - what's the trade-off between circuit safety and hard sync sound
> - why the difference between soft and hard sync is just changing a
> resistor
>
> Thanks much in advance,
> best regards,
> Jan-Hinnerk
>
>
>
>
>
>
> Keep on Patchin'!
>
> Yahoo! Groups Links
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