Plotting Potentiometer Curves

Big Monk

They call me Derek. Formerly EpiLP1985
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After a long hiatus, I am slowing getting back into the guitar game with a beater guitar and a practice amp. This is mostly driven by my 4 year old's budding interest in classic guitar music.

One thing I have long desired to do was acquire a range of cheap to boutique pots and determine their Taper ratios. Over the next few months i'll be testing quite a few. In addition to the pots in the screenshot below, I have a line of some Hamer pots as well as 2 vintage Centralabs.

Numbers below are either from the listed tech specs for the pots, or a placeholder to make all the graphed lines visible:

Pot Curves.PNG


I can't help but think this has been done before but since i'm doing it anyway, I thought it would be good to document.

[EDIT - I see there is a sticky here with similar information and sound files!]
 

spitfire

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Since you mentioned sound files, I think you might be expecting to hear something different. You won't. Only the resistance value of the pot itself will affect the sound. The taper has nothing to do with the tone. It only affects where you need to rotate the knob to get the same sound. So taper will affect the feel or sensitivity to knob position, but not the actual sound.

Something similar is true of make, model, and quality of the pot. None of these will affect the sound. Of course a worn out pot or extremely low quality could be scratchy or intermittent. And different pots have different feels. Higher quality do tend to rotate smoother and some are stiffer than others.

I can only guess as to what the image you posted is supposed to be. It is too small to make out any detail.

So I say go forth and measure. In the end, pots have pretty loose tolerances so actual measurements on the pots you have would likely be more useful, given you want that level of detail.
 

Big Monk

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Since you mentioned sound files, I think you might be expecting to hear something different. You won't. Only the resistance value of the pot itself will affect the sound. The taper has nothing to do with the tone. It only affects where you need to rotate the knob to get the same sound. So taper will affect the feel or sensitivity to knob position, but not the actual sound.

I get it. I'm an electrical engineer! ;) I was referring to the sticky where a member showed the volume increases from the audio files he recorded. The file shows the approximate volume increase as he rolled up the controls. I wasn't trying to say that the taper was a function of the actual sound.

I can only guess as to what the image you posted is supposed to be. It is too small to make out any detail.

It wasn't really meant to show anything other than the plotted curves. The cells to the left have user inputs for measured total resistance of the pot and the resistance measurements along the travel of the pot itself. It then calculates the percentage of total resistance at that point to show the user where the taper percentages are and plots out the curve.

So I say go forth and measure. In the end, pots have pretty loose tolerances so actual measurements on the pots you have would likely be more useful, given you want that level of detail.

Right. Could be a useful "at-a-glance" resource for people shopping for pots.
 

spitfire

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I get it. I'm an electrical engineer! ;) I was referring to the sticky where a member showed the volume increases from the audio files he recorded. The file shows the approximate volume increase as he rolled up the controls. I wasn't trying to say that the taper was a function of the actual sound.

I gotcha. I just wasn't too sure what you might be thinking. And I feel it never hurts to spell something out for the sake of others that might read it. There's just an awful lot of misunderstanding by those with little or no electronics understanding. Mostly attributing tone changes to things that just can't affect it.

Good luck in your endeavors characterizing pots.
 

cooljuk

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EpiLP1985, very cool of you to put in the work! Do you think you could post a larger / high resolution version of the image?

I can't read a single letter in that and there seems to be no option to zoom without further quality loss. ...I know you said it was only to show the plots, but I can't even read what color equates to what pot. All text is a total blur, even when downloaded and opened in external software.
 
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Big Monk

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EpiLP1985, very cool of you to put in the work! Do you think you could post a larger / high resolution version of the image?

I can't read a single letter in that and there seems to be no option to zoom without further quality loss. ...I know you said it was only to show the plots, but I can't even read what color equates to what pot. All text is a total blur, even when downloaded and opened in external software.

It's actually an Excel sheet. I'll post the link tomorrow. I just ordered some of the GFS XGP Alpha pots for my 4 year olds beginners guitar. Those will be the first with actual measurements. After contacting GFS, and in turn getting them to contact the manufacturer, it turns out that in addition to upgraded shafts and internals, they have a 60:40 ratio.

What you'll see in the spreadsheet as of now are either technical specifications or fudged numbers to differentiate the curves.

As I populate it I'll be plotting separate graphs for each pot as I test more.
G
EDIT: These are straight off my phone so they should be clear when you zoom:

IMG_5068.jpg
IMG_5069.jpg
 
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