Doepfer

Can someone answer the question of how to make a pot scale more  
finely?  If you insert a resistor in the output path, does this divide  
the voltage and weaken the effect of the pot?  I don't know much about  
circuits.

--- In Doepfer_a100@yahoogroups.com, Monroe Eskew <monroe.eskew@...>
wrote:
>
> Can someone answer the question of how to make a pot scale more  
> finely?  If you insert a resistor in the output path, does this divide  
> the voltage and weaken the effect of the pot?  I don't know much about  
> circuits.
>
if you have a resistor of, say 100 ohms, you can connect another 100
ohm fixed resistance across its outside terminals (legs) and you will
now have a combined resistance of 50 ohms (they are said to be
connected "in parallel"). the pot will now sweep between zero and
fifty ohms, giving you only half the range but double the sensitivity.
using a smaller resistance will give you even more sensitivity.

if you're interested in the maths: combine two resistances a and b in
parallel to give resistance c

1/c = 1/a + 1/b

hope this helps,

stu

> Can someone answer the question of how to make a pot scale more  
> finely?  If you insert a resistor in the output path, does this 
divide  
> the voltage and weaken the effect of the pot?  I don't know much 
about  
> circuits.

The answer is not very straightforward, as it depends on how the pot is 
being used. Generally to have more control with a pot, i.e. so that 
larger movements have less effect, so you can finely position it to 
*just* where you want it to be, you have to reduce its value. But then 
depending on how the pot is being used, you will need to add one or 
more resistors to compensate for this lowering of value: if the pot is 
actually being used as a potential divider (that is how the 
name 'potentiometer' is derived), you will need to add resistors either 
side to bring the total back up to the original value, but how much 
each side will depend on where out of the total range, the now reduced 
pot is to have its effect; if it is being used as a variable resistor 
(the wiper connected to either end or one end left open), again another 
resistor will probably be needed, but you will only need one, and which 
side of the pot it goes will not matter.

If you have a particular pot in mind on a particular module, I might be 
able to make suggestions on exactly *what* values to use and *where* to 
add the resistors (depending on whether I have the circuit for that 
module of course!), but if it was a general question, then I'd suggest 
your best course of action would be to either look around on the web 
for some basics electronics sites (there will be tons out there!), or 
buy a beginners book (your local Maplins/Radio Shack/whatever will 
undoubtedly have something suitable), and then get studying! I'm afraid 
there is not substitute for you putting in some work in order to gain 
some understanding of how all this stuff works!

Tim

Hi Monroe,

> It is for a Plan B envelope generator (elf).  The time range of the
> A,D,R events is much too wide, making it so that only a small angle 
of
> turn contains useful settings.  So what would you recommend?

On the face of it it looks like decresing the pot values is what you 
need to do, *BUT*, because of the 'add on' module to give voltage-
control of everything, the circuitry in the main module will 
necessarily be more complicated, and so this might not be an obvious 
mod to do. My recommendation would be to ask Peter Granader directly, 
over on the Plan B group.

> I'm confused about what Stu said.  Increasing resistance increases 
the
> voltage throughput?

No it won't, but he didn't actually say that.

>  If you go to infinite resistance by breaking the
> path then no signal goes through.  If you add a resistor in a series
> circuit, the voltage across each other resistor drops.  Intuitively,
> resistors slow down current, so adding resistance in the current 
path
> should decrease the energy of the signal.  So shouldn't the effect 
be
> the opposite?

Most of what you say here is more or less right. Stu was talking 
about adding another resistor *in parallel* (so they are joined 
together at both ends), what you are talking about above is adding 
them *in series*, and there is a big difference. When added in 
parallel, a second resistor of the same size as the existing one will 
pass the same current as the first, so you now have twice the current 
flowing, which effectively looks like you have halved the resistance. 
(And for what it is worth, I think what Stu said will only work for 
the 'variable resistance' way of using pots, and not for 
the 'potential divider' way!)

Tim

It is for a Plan B envelope generator (elf).  The time range of the
A,D,R events is much too wide, making it so that only a small angle of
turn contains useful settings.  So what would you recommend?

I'm confused about what Stu said.  Increasing resistance increases the
voltage throughput?  If you go to infinite resistance by breaking the
path then no signal goes through.  If you add a resistor in a series
circuit, the voltage across each other resistor drops.  Intuitively,
resistors slow down current, so adding resistance in the current path
should decrease the energy of the signal.  So shouldn't the effect be
the opposite?

Thanks,
Monroe

On 8/10/08, Tim Stinchcombe <timothy@tstinchcombe.freeserve.co.uk> wrote:
>
>
>
>
>
> > Can someone answer the question of how to make a pot scale more
>  > finely? If you insert a resistor in the output path, does this
>  divide
>  > the voltage and weaken the effect of the pot? I don't know much
>  about
>  > circuits.
>
>  The answer is not very straightforward, as it depends on how the pot is
>  being used. Generally to have more control with a pot, i.e. so that
>  larger movements have less effect, so you can finely position it to
>  *just* where you want it to be, you have to reduce its value. But then
>  depending on how the pot is being used, you will need to add one or
>  more resistors to compensate for this lowering of value: if the pot is
>  actually being used as a potential divider (that is how the
>  name 'potentiometer' is derived), you will need to add resistors either
>  side to bring the total back up to the original value, but how much
>  each side will depend on where out of the total range, the now reduced
>  pot is to have its effect; if it is being used as a variable resistor
>  (the wiper connected to either end or one end left open), again another
>  resistor will probably be needed, but you will only need one, and which
>  side of the pot it goes will not matter.
>
>  If you have a particular pot in mind on a particular module, I might be
>  able to make suggestions on exactly *what* values to use and *where* to
>  add the resistors (depending on whether I have the circuit for that
>  module of course!), but if it was a general question, then I'd suggest
>  your best course of action would be to either look around on the web
>  for some basics electronics sites (there will be tons out there!), or
>  buy a beginners book (your local Maplins/Radio Shack/whatever will
>  undoubtedly have something suitable), and then get studying! I'm afraid
>  there is not substitute for you putting in some work in order to gain
>  some understanding of how all this stuff works!
>
>  Tim
>
>
>
>