[sdiy] Verniers for Patch Recording

[Czech Martin]

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.

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

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
> 
>