[sdiy] Verniers for Patch Recording

[Ian Fritz]

At 10:15 AM 9/30/2003, Czech Martin wrote:
>That's why some analog computers have 10 turn pots.
>Together with the counter knobs this will cost
>20$ per dial, ouch!
>
>OTOH, for critical applications it is the only way:
>Concentric dual pots would be cool, but they are not available.
>Old measurement gear has often a coarse pot/switch plus
>a "vernier" pot.
>I used a 12 step switch "coarse" with 1% resistors
>plus vernier pot for some purpose. The steps are not equal,
>to my dismay.
>
>
>Another source of error: some people have a couple
>of modules of the same type. Resistors have 1%,
>but the usual pots have a loose correlation between
>angle and resistance. A 1/10 ratio could mean 1.0
>on one module, but maybe 1.2 on the other.
>
>So, not only the type of module and all dials
>have to be noted, but also the actual "number"
>of the module that was used.

I think most people could manage this without too much trouble.

>But you are right, this unacuracy is the reason why
>finding an old patch is near to impossible.

I think that 7-bit resolution on all your controls (except pitch) would 
make it possible.  But it doesn't sound like anybody really cares.

   Ian





>m.c.
>
>
>
> > -----Original Message-----
> > From: Ian Fritz [mailto:ijfritz at earthlink.net]
> > Sent: Dienstag, 30. September 2003 15:52
> > To: Czech Martin; synth-diy at dropmix.xs4all.nl
> > Subject: RE: [sdiy] Verniers for Patch Recording
> >
> >
> > Hi Martin --
> >
> > At 05:21 AM 9/30/2003, Czech Martin wrote:
> >
> > >Depends on how good your eyes are.
> >
> > True.  Mine are just so-so. It also depends on how large the
> > knob is.  I
> > made a linear vernier about 5 cm long (corresponding to a
> > typical small
> > synth knob) and I can easily set and read the vernier at my
> > normal reading
> > distance.  It has a much coarser scale than I've seen on the
> > old radio
> > verniers. I did it that way to make it fairly easy to
> > construct.  You could
> > copy the image I posted into a graphics program and reduce it
> > to different
> > sizes to see how it works for your eyes.
> >
> > >I guess some control voltage pathes are more
> > >sensitive than others.
> >
> > Right.  But I think If you have a complex patch you may still
> > want to get
> > all the parameters quite accurately to avoid accumulated error.
> >
> > >What about a range switch together with the pot?
> > >This will virtually increase the resolution of the pot.
> > >It can be a 2 position, a 3 postion, or the usual
> > >12 position switches depending on application.
> >
> > Well, I did mention that at the end of the post.  Myself, I wouldn't
> > consider that practical for every single control, but for
> > some controls it
> > would probably be necessary.  For example if you need to
> > reproduce an FM
> > patch, the frequency ratio needs to be very accurate.  The modulation
> > amplitude I'm not sure about.  That could get tricky.
> >
> >    Ian
> >
> >