linear vs. audio resistors

[ron mccann]

First post. I am working through a Heathkit power/wave generator. There
are two rheostats both labeled 100k. One is supposed to be linear the other
an audio resistor. They seem to act the same with a basic digital vom. Does
anyone know what these two terms are referring to? I'll try there support
line on monday, but I'd rather be soldering today.
thanks for any thoughts.
rkm

 

[John Popelish]

First post. I am working through a Heathkit power/wave generator. There
are two rheostats both labeled 100k. One is supposed to be linear the other
an audio resistor. They seem to act the same with a basic digital vom. Does
anyone know what these two terms are referring to? I'll try there support
line on monday, but I'd rather be soldering today.
thanks for any thoughts.

The adjectives refer to how the resistance changes with wiper
position. Try setting them both at about middle position, and compare
the resistance from each end to the wiper.

Since your ear is sensitive to small energies, and becomes
progressively less sensitive to increases as the energy gets larger,
pots designed to vary volume sneak the signal up slowly near the fully
counter clockwise direction (when they are connected as a tapped
voltage divider) and increase the signal much faster near the fully
clockwise end of rotation, so you perceive a fairly smooth increase in
volume for both quiet and loud sounds.
See:
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

 

[Pooh Bear]

First post. I am working through a Heathkit power/wave generator. There
are two rheostats both labeled 100k. One is supposed to be linear the other
an audio resistor. They seem to act the same with a basic digital vom. Does
anyone know what these two terms are referring to? I'll try there support
line on monday, but I'd rather be soldering today.
thanks for any thoughts.

The term refers to the so-called taper or change in resistance with rotyation.

A linear taper is simply a linear relationship with rotation and an audio taper
is an approximation to a 'logarithmic' chage with rotation to suit the ear's
similar sensitivity to volume.

If you set both potentiometers at mid position, the linear type will have equal
resistance from the wiper to either end terminal and the audio one will be quite
different, around 10-15x the resistance in one direction vs the other.

Graham

 

[DecaturTxCowboy]

First post. I am working through a Heathkit power/wave generator. There
are two rheostats both labeled 100k. One is supposed to be linear the other
an audio resistor. They seem to act the same with a basic digital vom. Does
anyone know what these two terms are referring to?

No, they won't measure the same way with an ohmmeter.

One is an linear taper and the other is an audio (non-linear or
logarithmic) taper.

At the full left position, both the linear pot and
the audio pot will show almost zero Ohms.

At the one fourth position, the linear pot will show 25K Ohms and
the audio pot will show about 100 Ohms.

At the half position, the linear pot will show 5K Ohms and
the audio pot will show about 1,000 Ohms.

At the three fourths position, the linear pot will show 75K Ohms and the
audio pot will show about 10,000 Ohms.

At the full right position, both the linear pot and
the audio pot will show 100K Ohms.

 

[Phil Allison]

"Poopie Bear"

and the audio one will be quite
different, around 10-15x the resistance in one direction vs the other.

** Expect to see a ratio of 5 or 6 to 1 for audio taper.

With " Log " taper it is about 10:1.




........ Phil

 

[Phil Allison]

"DecaturTxCowboy


** This cowboy has fallen of his horse onto his head one too many times.

No, they won't measure the same way with an ohmmeter.

One is an linear taper and the other is an audio (non-linear or
logarithmic) taper.

At the full left position, both the linear pot and
the audio pot will show almost zero Ohms.

At the one fourth position, the linear pot will show 25K Ohms and
the audio pot will show about 100 Ohms.

** Nonsense, re the audio one.

At the half position, the linear pot will show 5K Ohms and
the audio pot will show about 1,000 Ohms.

** More like 50 kohms and 15 kohms.

At the three fourths position, the linear pot will show 75K Ohms and the
audio pot will show about 10,000 Ohms.

** Try 75 kohms and 50 Kohms.




....... Phil

 

[Pooh Bear]

"Poopie Bear"


** Expect to see a ratio of 5 or 6 to 1 for audio taper.

With " Log " taper it is about 10:1.

Mea Culpa - I did the sums wrong in my head.

JIS A ( audio ) taper is 15%. Typical British log pots ( when they were
still made here ) were ~ 10 %. So yes I should have said around 6-10 x .

Graham

 

[DecaturTxCowboy]

"DecaturTxCowboy


** This cowboy has fallen of his horse onto his head one too many times.

Oppps...I started my post then went to bed. Might have missed something.
But as for the ACTUAL values, I used something that might be typically
expected and more so to illustrate the non-linear scale, Lemme go back
to see what I posted.