# Where can I purchase a w25k pot?



## Causefarley (May 15, 2021)

Anybody know where to get these?


----------



## Barry (May 15, 2021)

stompboxparts.com carries a 20K W taper, probably as close as you get


----------



## Causefarley (May 16, 2021)

Barry said:


> thank you!
> 
> stompboxparts.com carries a 20K W taper, probably as close as you get


----------



## Barry (May 16, 2021)

You could also use a 50K pot and solder a 50K resistor across it to get 25k


----------



## fig (May 16, 2021)

Barry said:


> You could also use a 50K pot and solder a 50K resistor across it to get 25k


A homegrown pot is the best. I started buying only 1MΩ and reducing. Makes ordering MUCH easier.


----------



## music6000 (May 16, 2021)

20K OHM W-Taper W20K Tone Control Potentiometer PCB Mount Round Shaft Dia: 6.35mm
					

ALPHA - Get It Fast - Same Day Shipping




					www.taydaelectronics.com


----------



## finebyfine (May 16, 2021)

fig said:


> A homegrown pot is the best. I started buying only 1MΩ and reducing. Makes ordering MUCH easier.



Just to make sure I'm getting it right b/c it sounds genius: doing that w/ 1MΩ is just calculating the missing parallel resistor value between 1MΩ and the target pot resistance right and then connecting it to pin 1 and pin 3?

edit: well I guess any value but man the math is easy for 1mΩ


----------



## fig (May 16, 2021)

finebyfine said:


> Just to make sure I'm getting it right b/c it sounds genius: doing that w/ 1MΩ is just calculating the missing parallel resistor value between 1MΩ and the target pot resistance right and then connecting it to pin 1 and pin 3?
> 
> edit: well I guess any value but man the math is easy for 1mΩ


Right. I use 1M because they are typically the highest values used. The resulting resistance will always be a bit lower than the lower value resistor used (except when 2 of the same value are used).


----------



## finebyfine (May 16, 2021)

fig said:


> Right. I use 1M because they are typically the highest values used. The resulting resistance will always be a bit lower than the lower value resistor used (except when 2 of the same value are used).


🙇‍♂️🙇‍♂️🙇‍♂️🙇‍♂️


----------



## fig (May 16, 2021)

Google "parallel resistance calculator".


----------



## finebyfine (May 16, 2021)

fig said:


> Google "parallel resistance calculator".



One of the few concepts I remember from high school physics sections on electricity


----------



## Chuck D. Bones (May 16, 2021)

fig said:


> A homegrown pot is the best. I started buying only 1MΩ and reducing. Makes ordering MUCH easier.


HA HA HA HA HA HA HA


----------



## Chuck D. Bones (May 16, 2021)

Barry said:


> You could also use a 50K pot and solder a 50K resistor across it to get 25k


Bad idea.  It messes up the taper.  Pedals that use W taper usually need the W taper.


----------



## fig (May 16, 2021)

Chuck D. Bones said:


> Bad idea.  It messes up the taper.  Pedals that use W taper usually need the W taper.


Isn't the taper decided by the thickness of the carbon layer at the position of the wiper?

( the same way linear and normal / reverse taper function )


----------



## Chuck D. Bones (May 16, 2021)

Yes, for a bare pot.  Adding resistors in series and/or parallel changes all that.  You have to look at the bigger picture and consider how the pot's impedance varies with rotation and how that affects the rest of the circuit.


----------



## music6000 (May 16, 2021)

Unless your Resistors have a taper, you can't recreate number *5 ''W'' *taper!


----------



## fig (May 16, 2021)

Chuck D. Bones said:


> Yes, for a bare pot.  Adding resistors in series and/or parallel changes all that.  You have to look at the bigger picture and consider how the pot's impedance varies with rotation and how that affects the rest of the circuit.


Does parallel resistance have a different effect on a circuit than linear resistance?


----------



## fig (May 16, 2021)

music6000 said:


> Unless your Resistors have a taper, you can't recreate number *5 ''W'' *taper!
> 
> View attachment 11917


As I understand it, the taper is determined by the thickness of the carbon trail along the path of the wiper. The thicker (wider) the larger % of the whole is seen durinng rotation, and visa-versa.


----------



## fig (May 16, 2021)

btw, I appreciate the time you both are taking. I feel a learning moment coming my way.


----------



## music6000 (May 16, 2021)

fig said:


> As I understand it, the taper is determined by the thickness of the carbon trail along the path of the wiper. The thicker (wider) the larger % of the whole is seen durinng rotation, and visa-versa.


How is a Resistor going to change  the thickness of the carbon trail along the path of the W wiper?
You can get close with Potentiometers that start out with the Same taper!


----------



## fig (May 16, 2021)

music6000 said:


> How is a Resistor going to change  the thickness of the carbon trail along the path of the W wiper?
> You can get close with Potentiometers that start out with the Same taper!


It wouldn't, which is the point. The only thing that would change would be the total resistance of the pot. The carbon trail would still "taper" in the same manner...distributing the total resistance as dictated by the thickness..at 9:00 the % would be the same with or without the resistor, right?


----------



## fig (May 17, 2021)

After reading back though this, I think I see the issue. I was not suggesting you can transform the taper of a pot (my apologies for any lack of clarity). I am stating that you can change a pot of the same taper to a different value.

A 1MΩ *linear *(or "A") - solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *linear* taper pot.
A 1MΩ *tapered* (or "B") -  solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *tapered* taper pot.
A 1MΩ *reverse-tapered *(or "C") - solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *reverse-tapered* taper pot.
A 1MΩ *wide-tapered *(or "W") - solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *wide-tapered* taper pot.


----------



## zgrav (May 17, 2021)

I could have sworn that Chuck was laughing at the reference to homegrown pot for other reasons.....


----------



## Feral Feline (May 17, 2021)

smoke 'm if you got 'm...

The pots I mean. 


I seem to recall in the Secret Life of Pots, Mr Keen described how adding a resistor across 1 & 3 changes the taper somewhat...


Still, I'm really likin' the idea of bulk ordering some B1M pots...


----------



## zgrav (May 17, 2021)

I'm not sure these replicate some of the standard tapers, but so what.  Seems like there are some options to make some new tapers along the way, especially if you want to use different value resistors between terminals 1-2 and 2-3.


----------



## fig (May 17, 2021)

Feral Feline said:


> smoke 'm if you got 'm...
> 
> The pots I mean.
> 
> ...


I just re-read that, thanks. Actually, he was discussing modifying the taper between wiper and lug. Apples to Oranges as they say. In the extremely limited bonehead caveman tests I did, the tapers remained pretty darned constant when using a resistor from lug 1 to 3  (*NOT* a taper resistor between wiper and lug). Again, I am an uneducated hack so I'll just retract my statement. I certainly don't want to mislead anyone.

yeah...homegrown 🤣


----------



## finebyfine (May 17, 2021)

Feral Feline said:


> I seem to recall in the Secret Life of Pots, Mr Keen described how adding a resistor across 1 & 3 changes the taper somewhat...



This is that article for anyone else who might have trouble finding it like I did. I never know what pages stuff's gonna be on there ...


----------



## Feral Feline (May 18, 2021)

BAH, wrote the following yesterday or whenever... but didn't hit "Post reply"🤪


"Well it seems I'm due for a re-reading of Mr Keen's horticulture tome for DIYers, I'll pay more attention this time to the taper-resistors and the non-taper 1—3 combo."

Right you are Fig, it was the Taper-resistors between outer lug and wiper I was recalling through my foggy memory.

@finebyfine ‚ thanks for the link. I usually will link stuff like that, but I'm getting lazier the older I get, I guess. Also, it is tough to find, that particular link/page. Sometimes I find it easily, but mostly I have to hunt for it.


----------



## fig (May 18, 2021)

finebyfine said:


> This is that article for anyone else who might have trouble finding it like I did. I never know what pages stuff's gonna be on there ...


Duh, I should have posted the link. Thanks Mr. Fine!


----------



## fig (May 18, 2021)

Feral Feline said:


> BAH, wrote the following yesterday or whenever... but didn't hit "Post reply"🤪
> 
> 
> "Well it seems I'm due for a re-reading of Mr Keen's horticulture tome for DIYers, I'll pay more attention this time to the taper-resistors and the non-taper 1—3 combo."
> ...


🤣 It were a whimsical notion at best I suppose. Better I tink dat I stick to da schtick 🤪


----------



## Chuck D. Bones (May 18, 2021)

fig said:


> After reading back though this, I think I see the issue. I was not suggesting you can transform the taper of a pot (my apologies for any lack of clarity). I am stating that you can change a pot of the same taper to a different value.
> 
> A 1MΩ *linear *(or "A") - solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *linear* taper pot.
> A 1MΩ *tapered* (or "B") -  solder 1MΩ resistor from lug 1 to 3. It will now be a 500KΩ *tapered* taper pot.
> ...


Plenty has been written by others on this topic, so I won't repeat any of that stuff about pot construction or paralleling resistors.  It is clear from the literature that when you put a 1MΩ resistor in parallel with a 1MΩ pot, whatever the taper, you will end up with a different taper.  Whether that matters to the circuit depends entirely on the circuit, what the designer intends to achieve and whether the designer knows that they are doing.  Paralleling a W-taper pot is particularly problematic, so I will discuss that one.

W-taper pots are common in TS pedals.  First, let's examine why the designers at Ibanez selected a W-taper pot in the first place.  Consider the LGSM below.  Rather than bore you with the math, I'll demonstrate the effect of taper and paralleling a pot by running some simulations in LTSpice.





I'm simulating just the stuff between IC1 pin 1 and C7.

Here is the family of curves for the circuit as-designed.  Each curve represents the frequency response at the dial settings 0, 1, 2, 3... on up to 10.  The green curve on the bottom is with the TONE pot at 0.  Look at what's going on at 2KHz.  From 0 to 3, the curves are pretty evenly spaced.  Curves 3, 4 , 5 & 6 are bunched up together.  From 7 on up to 10 the curves are spaced fairly far apart.  You will notice when turning the TONE knob on a TS that it's pretty sensitive to rotation near 0 and 10, particularly near 10, and there's not much change near the center of rotation.





Here's the same set of curves with a B20K pot.  Notice how all of the curves except the top and bottom curve are bunched up in the middle.  This is why no one (well almost no one) uses a B-taper TONE pot in a TS. 





OK, now let's look at what happens if we don't have a W20K pot and we try to make one by paralleling a resistor.
This is the curve for a W50K pot with a 33K resistor from pin 1 to pin 3. It now measures 20K from pin 1 to 3, but look at the curve spacings. The top and bottom curves are more separated from rest and the middle curves are more bunched up.




This is the curve for a W100K pot with a 25K resistor from pin 1 to pin 3.  It measures 20K from pin 1 to 3, but look at the curve spacings.  The top and bottom curves are even more separated from rest and the middle curves are more bunched up.  Looks a lot like the B20K curves, doesn't it?





We get a similar effect if we use two parallel resistors, one from pin 1 to pin 2 and one from pin 2 to pin 3.


----------



## fig (May 18, 2021)

..and that should put to rest any ridiculous notions any of you might have about modifying pots.

Thank you Mr. Bones.


----------



## Barry (May 18, 2021)

Talking up electronics with Chuck is like taking that lick you think you've owned to a jam, only to have the other guitarist play it who really owns it


----------



## music6000 (May 19, 2021)

Barry said:


> Talking up electronics with Chuck is like taking that lick you think you've owned to a jam, only to have the other guitarist play it who really owns it


And he has probably forgotten more than we may ever learn!


----------



## fig (May 19, 2021)

music6000 said:


> And he has probably forgotten more than we may ever learn!


Yes, that seems likely at least in _my_ case given what I've read. You are extremely knowledgeable as well and I applaud you both (and others sharing their wisdom). 👋👋👋


----------



## Feral Feline (May 19, 2021)

Edification has been set on "stun" ever since I joined this forum and started reading CDB's posts.


----------



## fig (May 20, 2021)

Feral Feline said:


> Edification has been set on "stun" ever since I joined this forum and started reading CDB's posts.


Well, I know getting blasted by CDB's LTSpice Weasel added certain piquancy to my education. I'm now studying Kurhcoff's junction rule.


----------



## Feral Feline (May 20, 2021)

BAM! And that's how you sauté a Neptunian slug. 
Warp Speed!

Aye aye Captain Kurchhoff!


----------



## fig (May 20, 2021)

Feral Feline said:


> BAM! And that's how you sauté a Neptunian slug.
> Warp Speed!
> 
> Aye aye Captain Kurchhoff!


Pretty simple rule. According to Kirk, however many Klingons into the transporter, the same number must re-materialize on the other side. The fun part is applying that principle to the circuit as a whole (or black hole in this case).


----------



## Chuck D. Bones (May 20, 2021)

It's "Kirchhoff's Law" and you do it one node at a time.  Computers make it much, much easier.

I noticed Fig has a new sig, taken from "Werewolves of London."  Anyone ever heard the spoof tune "Big Hairs of Lynwood" by Bob Rivers?


----------



## fig (May 20, 2021)

Chuck D. Bones said:


> It's "Kirchhoff's Law" and you do it one node at a time.  Computers make it much, much easier.
> 
> I noticed Fig has a new sig, taken from "Werewolves of London."  Anyone ever heard the spoof tune "Big Hairs of Lynwood" by Bob Rivers?


Whoops, My apologies to Mr. Kirchoff (guess I should study his name first eh?)

I love Bob Rivers!


----------



## Feral Feline (May 20, 2021)

Nope, not familiar with Bob Rivers, will check on it.


I like David Lindley's "Werewolves of London" best, so many lyrics websites get his version wrongemboyo...

"_...
I saw Jack Nicholson drinking a pina colada at Trader Vic's
His hair was perfect
I was sitting in the booth right across from him,
dressed in my finest polyester.
I had just ordered some nachos marquez
and my hair was..... well,
(very very greasy)... very very greasy
(very very greasy)... very greasy indeed
(very greasy indeed).. kinda like - shellac
(way too greasy)_"


----------

