Taper of Potentiometers

I have always known pots to either have an audio or a linear taper.
I'm looking at a schematic which has numerous pots. Some say they are "W
taper", the others say they are "K Taper". I have not seen them listed
in this way, ever.

What do these letters mean?
Are there other letters used?

Anyone have a chart that shows and explains them?

Thanks

(This schematic is for an early 1990's era semiconductor preamp, using
op-amps, and transistors).

 

[Fox's Mercantile]

On 1/23/18 5:08 PM, oldschool@tubes.com wrote:
> Anyone have a chart that shows and explains them?

There aren't any.
Each manufacturer has their own idea of -suffix for what
kind of taper.

--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

 

[pfjw@aol.com]

On Tuesday, January 23, 2018 at 6:09:10 PM UTC-5, olds...@tubes.com wrote:

I have always known pots to either have an audio or a linear taper.
I'm looking at a schematic which has numerous pots. Some say they are "W
taper", the others say they are "K Taper". I have not seen them listed
in this way, ever.

What do these letters mean?
Are there other letters used?

Anyone have a chart that shows and explains them?

W-taper pots are center-detent (center-null), typically used for tone controls, where center is Null.

K-taper pots typically will show a number ahead of the K, meaning *number* K-ohms.

K-pots may be linear or audio. W-pots are typically linear.

Your questions are getting better and better!

Peter Wieck
Melrose Park, PA

 

On Tue, 23 Jan 2018 18:01:50 -0800 (PST), "pfjw@aol.com" <pfjw@aol.com>
wrote:

On Tuesday, January 23, 2018 at 6:09:10 PM UTC-5, olds...@tubes.com wrote:
I have always known pots to either have an audio or a linear taper.
I'm looking at a schematic which has numerous pots. Some say they are "W
taper", the others say they are "K Taper". I have not seen them listed
in this way, ever.

What do these letters mean?
Are there other letters used?

Anyone have a chart that shows and explains them?

W-taper pots are center-detent (center-null), typically used for tone controls, where center is Null.

K-taper pots typically will show a number ahead of the K, meaning *number* K-ohms.

K-pots may be linear or audio. W-pots are typically linear.

Your questions are getting better and better!

Peter Wieck
Melrose Park, PA

I know that K ohms means 1000 ohms. But this is written as follows
(directly from the schematic) (except they use the ohm symbol and have
the +/- symbol printed one on top of the other)

Pot, 20K (ohm symbol) +/- 20%, K-taper

The other ones are
Pot, 50K (ohm symbol) +/- 20%, W-taper


There are 4 of the W-taper. so that makes sense about the tone controls
(center null). Because there are two per channel.

But there are a shitload of the K-taper ones, and this is a preamp
mixer, so lots of volume control pots.

This is an Altec Lansing preamp/mixer. It has a broken shaft on one of
the volume pots, so I need to replace that pot. I found a schematic for
it on this Altec Lansing unofficial website.

http://alteclansingunofficial.nlenet.net/proelectronics/rackmixers/index.html

This is the model to download:
(It says Click to download the .ZIP file)
Altec Lansing 1692A Mixer Literature Sheets - All

The zipfile contains a bunch of .JPG images.
The parts list where these pots are listed, is 1692a-4s.jpg

 

[Phil Allison]

olds...@tubes.com wrote:

------------------------

I have always known pots to either have an audio or a linear taper.

** Tube radios and TVs using carbon track pots used either linear "lin" OR logarithmic "log" taper pots. The log pot would always be for volume.

Log pots had a very gradual rate of increase in resistance as you turned it clockwise.

Audio taper pots arrived with hi-fi amplifiers and gave a quicker rise in volume than a log type, so was preferred by many makers and also guitar amp makers.

The code letters used varied alarmingly, A originally meant linear and C =log. Pots coming from Asia used A = audio taper with B = linear and D = log.

The code letter "E" referred to a "reverse log" pot, useful in instrumentation where the actual gain of a amplification stage must be varied smoothly.

Strangely, I have not come across a reverse linear pot anywhere.


..... Phil

 

[N_Cook]

On 23/01/2018 23:08, oldschool@tubes.com wrote:

I have always known pots to either have an audio or a linear taper.
I'm looking at a schematic which has numerous pots. Some say they are "W
taper", the others say they are "K Taper". I have not seen them listed
in this way, ever.

What do these letters mean?
Are there other letters used?

Anyone have a chart that shows and explains them?

Thanks

(This schematic is for an early 1990's era semiconductor preamp, using
op-amps, and transistors).

I had a go at rewinding a wire-wound log pot one time, it survived a
year and then something went wrong.
3 sections of former, like a large saw blade with 3 teeth stretched out,
bent into a ring. Each section had a different gauge of wire.
The wiper ran around the non-toothed edge of the "saw".

 

>"Strangely, I have not come across a reverse linear pot anywhere. "

You probably have, in instrumentation somewhere. Just not marked as such. Like the intensity control of a scope or some shit like that. I could see there being applications like that. And some things just give you a part number and that's it.

I do bet they're rare though.

 

"I had a go at rewinding a wire-wound log pot one time, it survived a
year and then something went wrong. "

I repaired a variac a while back. Obviously it was linear. Luckily I caught it in time as it was rubbing the wiper over a winding that was popped out of place and it would have broken soon.

But don't confuse a variac with a pot, a variac actually works like a transformer. Now if one were to feed it DC it would be nothing but a pot, and likely burn up unless you kept the input voltage down.

But a little bit of glue took care of it, good thing too as it was one of the ones that go up to 150 VAC.

 

On Wednesday, 24 January 2018 09:59:25 UTC, jurb...@gmail.com wrote:

"Strangely, I have not come across a reverse linear pot anywhere. "

You probably have, in instrumentation somewhere. Just not marked as such. Like the intensity control of a scope or some shit like that. I could see there being applications like that. And some things just give you a part number and that's it.

I do bet they're rare though.

What you been smokin?

 

[Mike Coon]

In article <gvsf6d960l0o7p6cr1g90nkac4hdjo7auh@4ax.com>,
oldschool@tubes.com says...

I know that K ohms means 1000 ohms. But this is written as follows
(directly from the schematic) (except they use the ohm symbol and have
the +/- symbol printed one on top of the other)

Pot, 20K (ohm symbol) +/- 20%, K-taper

Multiples of 1000 are written "k" not "K". There is an erroneous belief
that capital multipliers are >1 and lower case means divisors. This rule
works OK except for 1000...

Mike.

 

[Terry Schwartz]

The log pot would always be for volume.

Log pots had a very gradual rate of increase in resistance as you turned it clockwise.

Logarithmic pots were typically used in volume controls for two reasons:

1) The log taper provided a finer control of listening volume at low levels, where users need that fine control, and

2) The log taper provides what is essentially a "dead band" at the low end of the pot, therefore accommodating the installation of an on/off switch on the back of the pot, without sacrificing low level volume control. The switch often requires a 15 or 20 degree rotation in order to activate -- using up part of the pot travel.

Interestingly, some of the aftermarket modular pot/switch manufacturers weren't that great about following those "rules" and when you installed such a replacement switch control into an old radio, the volume at switch activation was already too high for comfortable listening.

 

[pfjw@aol.com]

On Wednesday, January 24, 2018 at 7:21:20 AM UTC-5, Mike Coon wrote:

Multiples of 1000 are written "k" not "K". There is an erroneous belief
that capital multipliers are >1 and lower case means divisors. This rule
works OK except for 1000...

As already noted, there are almost as many codes as makers. In my (very) old Centerlab Catalog, I did find references to W-Taper pots, but nothing conclusive at all on K or k taper as a specific reference.

With the additional hint of this being a slider, further googling got me to drill bits, but nothing on pots, linear or rotary.

Peter Wieck
Melrose Park, PA

 

[Ralph Mowery]

In article <743d1aa8-fd64-414d-9ef5-3e93477a9043@googlegroups.com>,
tschw10117@aol.com says...

The log pot would always be for volume.

Log pots had a very gradual rate of increase in resistance as you turned it clockwise.


Logarithmic pots were typically used in volume controls for two reasons:

1) The log taper provided a finer control of listening volume at low levels, where users need that fine control, and

2) The log taper provides what is essentially a "dead band" at the low end of the pot, therefore accommodating the installation of an on/off switch on the back of the pot, without sacrificing low level volume control. The switch often requires a 15 or 20 degree rotation in order to activate -- using up part of the pot travel.

Interestingly, some of the aftermarket modular pot/switch manufacturers weren't that great about following those "rules" and when you installed such a replacement switch control into an old radio, the volume at switch activation was already too high for comfortable listening.

I always though the audio taaper was because the way the ear responds to
sound in sort of a log function.

 

[Mike Coon]

In article <MPG.34d26d73eaffe919896ec@news.east.earthlink.net>,
rmowery28146@earthlink.net says...

I always though the audio taaper was because the way the ear responds
to
sound in sort of a log function.

E.g. https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law

Mike.

 

[Terry Schwartz]

Yes -- I imagine that is true, hence the need for finer control at lower volume levels.

Terry

 

[Terry Schwartz]

On Wednesday, January 24, 2018 at 10:59:48 AM UTC-6, Terry Schwartz wrote:

Yes -- I imagine that is true, hence the need for finer control at lower volume levels.

Terry

Actually, I think the ear responds in an anti-log fashion. Small changes in audio source output levels are perceived as large changes at lower volume levels. Not so much at higher levels, where the ear essentially "saturates" and cant tell the difference between 90dB and 100dB (numbers pulled out of nowhere as examples) So the log curve on the pot compensates for this.

 

On Wednesday, 24 January 2018 17:03:50 UTC, Terry Schwartz wrote:

On Wednesday, January 24, 2018 at 10:59:48 AM UTC-6, Terry Schwartz wrote:

Yes -- I imagine that is true, hence the need for finer control at lower volume levels.

Terry

Actually, I think the ear responds in an anti-log fashion. Small changes in audio source output levels are perceived as large changes at lower volume levels. Not so much at higher levels, where the ear essentially "saturates" and cant tell the difference between 90dB and 100dB (numbers pulled out of nowhere as examples) So the log curve on the pot compensates for this.

AIUI log pots were never really log. They normally used 2 resistance zones to give a very crude approximtion of a log law. It was good enough for audio, where the aim was to avoid everything happening down the bottom end of travel.


NT

 

[Gareth Magennis]

wrote in message
news:aa7420bf-47db-4c33-a3f6-2bfd9cb05d88@googlegroups.com...

"I had a go at rewinding a wire-wound log pot one time, it survived a
year and then something went wrong. "

I repaired a variac a while back. Obviously it was linear. Luckily I caught
it in time as it was rubbing the wiper over a winding that was popped out of
place and it would have broken soon.

But don't confuse a variac with a pot, a variac actually works like a
transformer. Now if one were to feed it DC it would be nothing but a pot,
and likely burn up unless you kept the input voltage down.

But a little bit of glue took care of it, good thing too as it was one of
the ones that go up to 150 VAC.



*************************************



Pah, mine goes to over 260 VAC.



Gareth.

 

On Wed, 24 Jan 2018 06:02:37 -0800 (PST), "pfjw@aol.com" <pfjw@aol.com>
wrote:

On Wednesday, January 24, 2018 at 7:21:20 AM UTC-5, Mike Coon wrote:

Multiples of 1000 are written "k" not "K". There is an erroneous belief
that capital multipliers are >1 and lower case means divisors. This rule
works OK except for 1000...

As already noted, there are almost as many codes as makers. In my (very) old
Centerlab Catalog, I did find references to W-Taper pots, but nothing conclusive
at all on K or k taper as a specific reference.

With the additional hint of this being a slider, further googling got me to drill bits,
but nothing on pots, linear or rotary.

Peter Wieck
Melrose Park, PA

That's exactly what I found on the web. In other words, NOTHING
regarding the K-taper. But I did find the W-taper and it was explained
the same as you said. I found some forum where they were discussing pot
tapers and some mentioned even more letters, such as N, S, M, D, and a
few more. But not K. And yea, I managed to bring up drill bits too.
That forum is here:
http://www.diystompboxes.com/smfforum/index.php?topic=92918.0

This pot is R60, (master volume control). It's a unusual type of pot in
the sense it's mounted to the PCB and mounted backwards, meaning there
is a small piece of metal (ring) attached to it's rear, that is soldered
to the PCB and the three tabs are bent downward, where they are soldered
to the PCB.

I have not yet taken it off the board. The pot does work, but the shaft
is broken below the front panel surface. My first thought is to contact
Altec Lansing and see if I can get an exact replacement. If not, I may
try to saw off the remaining plastic shaft so it's flat, and make up a
"sleeve" for it, (a piece of metal tubing) and glue another shaft to it
with the tubing to reinforce it. This shaft should be about 1.5 inch
long, (before being broken) so I have room to work, since there is
still a half inch to work with. If none of that works, I'll have to
Mcgyver some other pot in there, and will choose an audio taper type.

With any luck, Altec will have a replacment part. That would be the
easiest fix.

A while back, I found out that Peavey electronics does have parts for
all their old stuff. I hope Altec Lansing does too.

For reference, there is a lot of useful info about pots on this website.
http://www.potentiometers.com/potcomFAQ.cfm?FAQID=29

 

[pfjw@aol.com]

On Wednesday, January 24, 2018 at 4:24:24 PM UTC-5, olds...@tubes.com wrote:

I have not yet taken it off the board. The pot does work, but the shaft
is broken below the front panel surface.

JB Weld is your best friend. Get a soda-straw or heat-shrink tubing about the same diameter as the shaft, either use the broken piece or a suitable bit of solid material to extend the shaft to the correct length. Mix up the *SLOW* JB Weld epoxy, and use the straw/tubing to hold the shebang together and vertical, but out of the pot, until the epoxy sets up. Let the epoxy fill any voids. The result will be stronger than the original.

Peter Wieck
Melrose Park, PA