[sdiy] Hard Sync mod for Serge Osc?

[Scott Gravenhorst]

If I may offer a small bit:  Listening can be a deceptive "test tool" because
there could be many things at work.  To see if the circuit is operating as it
should, watching both waveforms on an oscope is much more helpful.  Use dual
trace mode and display both the synched and the synch-er.  You should see a
reset in the hard synched signal for each normal reset of the oscillator
sending the synch signal.

I've had some strange things happen with VCO synch circuits.  I did it to a
FatMan, my first attempt was to capacitively couple the synching signal which
sort of worked, but failed under some conditions.  I found a much better way
(the FatMan VCOs are based on a 555 timer) by using the 555 pin 3 output (a
pulse which occurs during the saw reset) wired to the 555 pin 4 (Reset)
input.  This produce bona fide hard synch, where my other attempt was really
a form of enhanced soft synch using coupling.


"James R. Coplin" <moog at qwest.net> wrote:
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>Thanks! That almost fixed it. I pulled the resistor out completely and I
>definitely am getting hard sync type behavior now. It isn't as smooth as I
>would like but it works well enough to get by for the time being. I don't
>know that I want to monkey around with the circuit too much, at least not
>right now. ;)
> 
>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.
>***************
>  _____  
>
>From: mark verbos [mailto:mverbos at earthlink.net] 
>Sent: Sunday, December 05, 2004 3:06 PM
>To: James R. Coplin
>Subject: Re: [sdiy] Hard Sync mod for Serge Osc?
> 
>try making the 22k resistor on the sync in smaller. I think that's the only
>option.
>
>That signal goes through the 22k then through a 220p cap. That's connect,
>along with a 2.2k resistor to +4 volt reference, to the comparator's summing
>node. You could always replace that whole mess with what's on the ASM-1 VCO.
>That is the signal goes through a 100p cap and then connects to the summing
>node along with a 10k to ground and a 20k to +15.
>
>Though I think making the resistor smaller, or just eliminating it, will do
>the trick.
>
>Good luck!
>
>
>mark
>
>
>James R. Coplin wrote:
>
>
>Does anyone know if it is possible to modify the Serge oscillators (either
>the NTO or PCO) to use hard sync? The soft sync that is currently
>implemented on them has to be about the most useless thing I've ever heard.
>It doesn't sound like it does anything at all.  I was hoping to be able to
>change this to a more traditional hard sync behavior. Any ideas?
> 
>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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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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