SV: Re: Re: [sdiy] Polyester or Polypropylene for VCO?

[karl dalen]

Here we go.

Now, if  we add a tiny DC voltage to Iref 
summing point we offset the VCO what if we
use the Expo CV voltage as the offset voltage?

Constant multiplication of a varying linear voltage! Ugh!
 
--- "JH." <jhaible at debitel.net> skrev:

> 
> > Why fuzz with two capps, more or less the same effect
> > are achived by applying a small DC voltage at the linear
> > input in the expo.
> 
> Because it's not the same.
> If that offset current is multiplied with your expo CV, it's not a constant
> value anymore.
> 
> JH.
> 
> 
> 
> >
> > Reg
> > KD
> >
> > --- "JH." <jhaible at debitel.net> skrev:
> >
> > > The original cap is replaced by a series connection of two capacitors.
> > > One being much bigger than the other, the total value is not much
> changed
> > > compared to the original circuit, so the VCO operates in a similar
> region as
> > > before.
> > > The tap between the caps is used to feed a dc current to offset the
> (linear)
> > > CCO core, bypassing the expo converter. So you can detune the VCO as
> > > if it were a linear (V/Hz) VCO. As the offset current is fed into the
> bigger
> > > cap only
> > > (i.e. the lower impedance part of a capacitive divider!), the offset is
> > > scaled down
> > > accordingly, allowing for more practical current values.
> > > Of course you cannot divide DC currents with a capacitive divider - thus
> the
> > > tap needs an extra discharge path to make the offset current dc-free
> > > over-all.
> > >
> > > The page contains a link to my former web site on synthf**l.
> > > This isn't valid anymore. Looks like from ancient times, hard to imagine
> > > now.
> > > The link should be
> > > http://home.debitel.net/user/jhaible/hj.html
> > > Or, more easy to memorize: http://www.jhaible.de/
> > >
> > > JH.
> > >
> > >
> > >
> > > ----- Original Message ----- 
> > > From: <simon.oo.o at xs4all.nl>
> > > To: <synth-diy at dropmix.xs4all.nl>
> > > Sent: Monday, August 01, 2005 10:34 AM
> > > Subject: Re: [sdiy] Polyester or Polypropylene for VCO?
> > >
> > >
> > > > Hi Harry,
> > > >
> > > > harrybissell zei:
> > > > > Simon Brouwer wrote:
> > > > >
> > > > >> In this circuit you have a capacitor of 150nF in series with one of
> > > > >> 1000pF.
> > > > >> The bigger capacitor hardly contributes to the combined
> capacitance, so
> > > > >> the
> > > > >> same is true for its tempco. So in this case it probably doesn't
> matter
> > > > >> much.
> > > > >
> > > > > Nope. These capacitors are NOT in series. There are two capacitors
> here.
> > > > > One
> > > > > is reset (?) by Q10, the other couples a sync pulse into the VCO.
> > > >
> > > > OK, strictly they are not in series, but as far as I understand, for
> the
> > > > purpose of determining the stability of VCO frequency they are.
> > > >
> > > > Referring to the component numbering used in
> > > > http://home.swbell.net/roy_tate/info/lindetun.html ,
> > > >
> > > > Q7 resets C3 and Q7a resets C3a at the same time.
> > > >
> > > > In theory, linear detuning could be implemented by a very small offset
> > > > current directly into C3. However, you would then need an absurdly
> high
> > > > value of Roffs.
> > > > Instead, a larger current is dropped into the bigger capacitor,
> resulting
> > > > in the same effect, while a practical resistor value can be used.
> > > > Because of the detuning current, C3a receives additional charge and
> for
> > > > this reason discharging by Q7a is needed. Except for this, Q7a has no
> > > > practical effect, so that the capacitors can be considered to be in
> > > > series.
> > > >
> > > > In any case, that's how I understand this circuit.
> > > >
> > > >
> > > > Vriendelijke groet,
> > > >
> > > > Simon Brouwer
> > > > --> nl.openoffice.org <--
> > > >
> > > >
> > >
> > >
> >
> >
> 
>