[sdiy] VCO sync question

[megaohm]

M.A.,
  Though your suggestions didn't help to solve my problem, thanks for taking 
the time to respond.
After much component and value swapping with no improvement, I finally found 
a solution. I used the Elby Designs ASM-2 VCO sync circuit and now the sync 
works reliably with pulse waves ( why it mattered whether the pulse was 
inverted or not is still a mystery to me ). This circuit will sync to a 
master pulse, saw (falling ramp), and even sine (it dosen't do so well with 
triangle or riaing ramp). Whereas my CGS/EN VCO would only sync to rising 
ramp or inverted pulse (I don't know why). This was a problem because some 
of my VCOs don't have a rising ramp output (some don't have a saw either). 
 This is a nice sync design and I highly recommend everyone checking it out. 
Sorry no link but you can easily Goggle it out.
 peng

 On 9/5/05, Michael Ruberto <frankentron at hotmail.com> wrote: 
> 
> Check the pulse output for DC offset. In most VCO designs the pulse is
> generated from an op amp functioning as a comparator and invariably there 
> is
> no offset null trim. I've run into this sort of thing before. If this 
> turns
> out to be the case the solution is simple, AC couple the pulse through a 
> cap
> and the offset will be blocked.
> In VCOs where an actual comparator chip is used I usually find the output 
> of
> the comparator is not buffered and gets loaded down easily when connected 
> to
> other modules. Check for no signal or a tiny signal from your pulse output
> when connected to an input. If this is the prob, try using a diode in 
> series
> with the pulse output or using an op amp to buffer the signal. Use an op 
> amp
> with a fast slew rate like an LF353, or an AD712. If you have a positive
> only pulse you can also use a CA3130 which is single supply and has like
> 30V/uS slew and includes the + and - rails in it's output. It also has
> connections for offset nulling. It is a CMOS device though so take
> precautions on it's output.
> 
> M. A. Ruberto
> 
> 
> >From: megaohm <megaohm1 at gmail.com>
> >Reply-To: megaohm1 at gmail.com
> >To: synth-diy <synth-diy at dropmix.xs4all.nl>
> >Subject: [sdiy] VCO sync question
> >Date: Mon, 5 Sep 2005 01:31:20 -0500
> >
> >Hmmm... I'm scratching my head on this one.
> > The VCO I just built (EN/CGS/Blacet/etc. style) is working great.
> >But...the
> >sync input behavior is mysterious to me. It syncs fine to a master rising
> >ramp (no surprise) but it won't sync to a master pulse or square...unless 
> I
> >invert them first. Since the square is either +5v or -5v, why does
> >inverting
> >it make any difference?
> > peng
> 
> 
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20050905/9f40d261/attachment.htm>