duncan tone stack calculator

[qwixzh]

Hello guys,

Dont know if this is the right forum.

Just wanted to clarify what the potentiometer description on the Duncan tone stack calculator software.

log type A = audio taper??

log type B = reverse audio taper??

thanks Duncan Munro for an excellent software!

thanks in advance!
qwixzh

[Robert M. Martinelli]

AFAIK "A" stands for linear and "B" for audio ( logarithmic ), at least on this side of the ocean...

[Enzo]

And B for linear over here.

I have never seen B for reverse audio on either side of the pond, though I have learned never to rule things out.

But DUncan spells it out. LogA and LogB are both audio tapers, he describes them in the notes. Linear he calls.... "linear" One is more pronounced a taper than the other.

In the calculator, open the help menu and read about pot value adjustment.

[qwixzh]

I've attached the screen shot.

on actual parts, B is linear, A is audio and C is reverse audio.

But on this software, not sure what is the 'log type B'. It so happens that it has a better control of the tone compared to the 'linear' and 'log type a'.

I'll be using it for my diy tube amp.

thanks to those who replied.

qwixzh

[Enzo]

As I said, read through the help menu. from the potentiometers section:

Next set the potentiometer style. Linear uses a linear track where the resistance is in proportion to rotation of the potentiometer. Log A has 30% of the full value at half-way position, and Log B has 10% of the full value at half-way position.

[qwixzh]

sorry, missed that one on the bottom of your reply.

thanks again!
qwixzh

[Enzo]

Oh, the 188558s are fine, but most of us have moved on to the 188559s by now.

[kevtronic]

I've started playing around with the Duncan Tone Stack Calculator and understand the Log-A and Log-B difference as it pertains to the software. What I'm having an issue with is finding out what the audio taper is for the pots being made today. I generally use the Alpha log pots like these: https://www.tubesandmore.com/product...dio-38-bushing

Are they (and others made today) 10%, 30%, or ??? at the half way position? I'll be measuring some of my pots later today (maybe tomorrow) to see about what percentage they are at the halfway point.

I've been looking at baxandall in the tone stack generator and there is a big difference between Log-A and Log-B. I was wondering what pot selection (log-a/log-b) others are using in the Tone Stack Generator software for the Baxandall tone stack and what pots they are actually wiring up in their amps, etc?

UPDATE/EDIT
So, I measured four of my Alpha Log pots at center (well, I tried for center anyways) and got an average of about 13.99%. I got anywhere from about 10% to 17% trying for center, so not sure if these would be considered 10% (and I went a little too far on my shots for center) or if these are 15%. I'll try it one or two more times later on. These are all the same make/model pots that I am measuring. I can't seem to find any info on them, I may try reaching out to Alpha about them and see if they'd be kind enough to enlighten me on the taper percentage...

[Chuck H]

Alpha themselves are a little unclear IMHO about just what the standard "A" 24mm pot that Mouser sells is (since it's simply marked "A" without a number preceding). This page shows Alpha's letter designators for taper types, but doesn't specify what "A" on a pot means if it isn't preceded by a number.

Taper Curves for our Potentiometers

Carefully measuring all my Alpha 1M audio pots I find them to be 15%. I remember once upon a time when I thought that their standard "A" taper was different for 50k, 100k, 250k at 25% and 500k, 1M were at 15%. I don't have any of their audio pots in 100k or 250k to measure right now though. I've read that more recently all values simply marked as "A" are 15%.

[kevtronic]

I contacted Alpha about their log/audio taper, but still haven't heard back. If they get hold of me I'll pass on what they say. In the mean time, is there anyone using the the standard log pots from Alpha or CTS for the Baxandall tone stack?

[Dave H]

is there anyone using the the standard log pots from Alpha or CTS for the Baxandall tone stack?

Do you mean "James"? The Baxendall tone control uses linear pots.

[kevtronic]

Do you mean "James"? The Baxendall tone control uses linear pots.

I wasn't aware the Baxandall tone stacks specifically used linear pots, but if they do then I guess it'd be the "James" tone stack I mean
I've never really paid much attention to either until recently, so I am on a learning curve.
Thanks for the info/tip, it's what these threads are all about, know what I mean...

On another note, ALPHA hasn't responded yet, but CTS has twice and they sent me a PDF, so I figured I'd upload it for anyone else that ends up on the Baxandall/James learning curve too

CTS Element Curves.pdf

[Dave H]

I don't know much about the James stack but I know the Baxendall is an active virtual ground -ve feedback circuit because I have a pdf of the original paper published in Wireless World in 1952. All the tone circuits in the Tone Stack Calculator are passive. For the controls to have flat frequency response in the centre position the James would need 10% log pots and the Baxendall linear.

Baxandall.pdf

[Chuck H]

Mouser sells Bournes 10% log pots. They come in standard torque and "guitar" pots (very low torque) so you'll want to make sure you get the right one for an amp or it feels funny. Good pots. I like them. Obviously many manufacturers make 10% log pots also, but finding them for sale is the trick. The Bournes pots are easy to find.