I Don't See The Point

[James Stroker]

I thought the purpose of dual potentiometers was to change the
value of both pots by the same amount at the same time. But
every duo-pot that I've gotten is off between the pots;
sometimes a little, sometimes a lot. But so far I've never found
a dual pot where the values tracked each other. Why do they make
them if they don't track each other?

 

[Peter Meyer]

Hello,

"James Stroker" <stokerjames@hotmail.com> a écrit dans le message de
news:bp7k22$1l0o2g$1@ID-43450.news.uni-berlin.de...

I thought the purpose of dual potentiometers was to change the
value of both pots by the same amount at the same time. But
every duo-pot that I've gotten is off between the pots;
sometimes a little, sometimes a lot. But so far I've never found
a dual pot where the values tracked each other. Why do they make
them if they don't track each other?

Well, I think it is possible to get the two to track to any error one needs.
but this will be expensive...
I would suggest you use two small trim pots in series - but most of the time
it is not really necessary : for sound applications the tracking error in
"normal price" duals is most of the time not audible.
Peter

 

[JeffM]

I've never found a dual pot where the values tracked each other

The response in each is proportional.
Expecting exact matching in pots would
ignore the differences in the circuits in which they are connected,
which have their own differences.

 

[Jacobe Hazzard]

"Peter Meyer" <peo.meyer@free.fr> wrote in message
news:3fb75842$0$2776$626a54ce@news.free.fr

Hello,

"James Stroker" <stokerjames@hotmail.com> a écrit dans le
message de
news:bp7k22$1l0o2g$1@ID-43450.news.uni-berlin.de...
I thought the purpose of dual potentiometers was to
change the
value of both pots by the same amount at the same time.
But
every duo-pot that I've gotten is off between the pots;
sometimes a little, sometimes a lot. But so far I've
never found
a dual pot where the values tracked each other. Why do
they make
them if they don't track each other?

Well, I think it is possible to get the two to track to
any error one needs. but this will be expensive...
I would suggest you use two small trim pots in series -
but most of the time it is not really necessary : for
sound applications the tracking error in "normal price"
duals is most of the time not audible.
Peter

For audiophile work, one can buy multiple ganged 256 position rotary
switches with precision resistor networks built in. These track very well,
and indeed cost many $100's

jacobe

 

[James Stroker]

Ahh, but that's he point. Let's say I wanted to build a filter
where the frequency is dependent upon two resistor values. To
change the frequency response is to change both values equally.

The usual formulas for determining the frequency are never
accurate but are ballpark figures. If I had a dual pot that
changed by the same amount on each pot, I could easily use that
pot to check out the frequency response of that filter without
having to use two separate pots to be adjusted to the same
value.

I can see a lot of real-world reasons for having dual pots with
the same values tracking each other. But there doesn't seem to
be much of a point to me anyway, for having two different pots
that aren't ever going to be the same. And for that matter, I
would never know without doing measuring, what each value is at
any given time between the two extremes of "zero" and whatever
upper limit.



JeffM wrote in message ...

I've never found a dual pot where the values tracked each
other

The response in each is proportional.
Expecting exact matching in pots would
ignore the differences in the circuits in which they are
connected,
which have their own differences.