[sdiy] discrete/no-OTA VCO

[harrybissell at wowway.com]

There is a triangle wave VCO that uses two opamps and one
transistor. The CV is input to the first opamp (an inverting
integrator) through two resistors, one to inverting and one to non-inverting.
A transistor shunts the non-inverting side to ground. Unequal
resistors make the ramps equal in time. The other opamp is a schmitt
trigger.

Classic circuit suffers from relatively small tuning range (maybe 10-20:1)
because eventually the control voltage must get really large to get the
current in.  Current controlled oscillators have much wider range.

I think this is in the National Semiconductor Linear Apps databook...
but I can't find it right now.

H^) harry



On Mon, 29 Dec 2008 08:45:02 -0500, DAF wrote
> thanks for all of the suggestions thus far - I am particularly 
> intrigued by the UJT voltage-controlled relaxation osc. especially 
> because of the low parts count, but I am wondering if the UJT is 
> also going the way of the dodo bird, and also is the control of 
> frequency linear over a wide enough range (I see it used in synths 
> that use octave divider schemes)?
> 
> In that Ray Wilson schematic, he says for a VCLFO, leave out the 
> parts in RED; are you to join the resulting gaps together on the 
> wires shown remaining?
> 
> Dave
> 
> ----- Original Message ----- 
> From: "Simon Brouwer" <simon.oo.o at xs4all.nl>
> To: "sdiy" <synth-diy at dropmix.xs4all.nl>
> Sent: Monday, December 29, 2008 3:13 AM
> Subject: Re: [sdiy] discrete/no-OTA VCO
> 
> > Here is one:
> >
> > http://www.elby-designs.com/asm-2/lfo/lfo1-asm2-cct.pdf
> >
> >
> > DAF schreef:
> >> Hello - can someone point me to a circuit for a  voltage-controlled
> >> lfo that uses discrete or other easy to source parts.  I have used an
> >> OTA-based design in the past, but I want to design around more generic
> >> parts.  I seem to remember a vco that used a discrete JFET?  I don't
> >> neet expo response or temp compensation.  I am looking for about a 2
> >> to 10 Hz response range.  I don't want to use any specialty chips or
> >> OTA's, just discrete transistors and op-amps.   Any help greatly
> >> appreciated.
> >>
> >> thanks,
> >> Dave
> >
> >
> > -- 
> > Vriendelijke groet,
> > Simon Brouwer.
> >
> > | http://nl.openoffice.org | http://www.opentaal.org |
> >
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Harry Bissell & Nora Abdullah 4eva