B25k instead of A25K?

[joelorigo]

Building the Pharmacist and my A25k pot for the MIDS doesn't have a washer or nut. Don't know how that happened. I have a B25k, will that work? Is it just that the taper will be direct vs that curved line of the A pots?

 

[benny_profane]

Use the washer/nut from the B25k on the A25k?

 

[joelorigo]

Sorry, I also should have mentioned that the threads on this A25 pot is much wider in diameter than any other pot I’ve seen. I have a bag of random pot and switch related hardware, but no nut this big.

 

[Locrian99]

It'll work just fine. The taper will be different though. Depending on the circuit it could be that the last 50% of the turn has most of the variation so they don't want to use a b or linear taper they will use an A where the resistance climbs quickly so you have more control in the portion of the resistance where it matters most. Also since its an eq thing. its nice to have noon being noon for treble bass and mids since they will interact some. But it will function just fine..

 

[Locrian99]

Another thing you could do is if you have a 50k B taper pot run a 47k resistor between legs. It will alter the taper and give you paraellel resistor should be like 26k or something as well.

 

[music6000]

Do you have an A50K, put a 47k across legs 1 & 3, it would work better than a B25K
In saying that, you probably don't as you can't find a nut, Time for some spare pots!:
I have spare nuts & washers plenty as Tayda end up having extras than not in the order!

 

[joelorigo]

No A50k. Currently I have A5k and A1M in the A category. I also have a C25k.

 

[cdwillis]

The a50k with the 47k resistor on the outside legs will be close to 25k total resistance, but if I'm thinking right the taper will basically be reversed so it'll be close to c25k?

 

[DailyDovetails]

I use B taper pots in place of A tapers often. I have guitars that have A or B tapers for volume and tone I honestly don’t think I have a preference between the 2. I just turn the knobs until it sounds how I want it to.

The only time it really bothers me is when the output volume is controlled by a pot as a variable resistor and I need a setting close to the lowest setting and then I mess around with resistors between the terminals until I get the range closer to what I need.

 

[music6000]

The a50k with the 47k resistor on the outside legs will be close to 25k total resistance, but if I'm thinking right the taper will basically be reversed so it'll be close to c25k?

My experience is it ends up in between a Linear & Log taper, C taper comes on way ealier!?

 

[music6000]

As a very last resort, use the C25 & cut the 2 outside legs shorter & use the middle leg in PCB.
Run a fly wire from Leg 1 pot to pad 3 PCB, Leg 3 to Pad 1 PCB

 

[joelorigo]

As a very last resort, use the C25 & cut the 2 outside legs shorter & use the middle leg in PCB.
Run a fly wire from Leg 1 pot to pad 3 PCB, Leg 3 to Pad 1 PCB

Ah yes, I did this once before for...something...

Or I'll just make an order from Stompbox Parts, which ship pretty fast, and get the correct part.

Thanks guys!

 

[Bio77]

You can covert a B25k to an A25k by soldering a 4k7 resister between pin 2 and pin 1 (sometimes its pin 3) of the B25k pot. You have to take a look at the circuit to figure out if you want pin 2->3 or 2->1; one will change the taper to C, one will change it to A. I've done this loads of times, here is a reference:

The Secret Life of Pots

 

[joelorigo]

You can covert a B25k to an A25k by soldering a 4k7 resister between pin 2 and pin 1 (sometimes its pin 3) of the B25k pot. You have to take a look at the circuit to figure out if you want pin 2->3 or 2->1; one will change the taper to C, one will change it to A. I've done this loads of times, here is a reference:

The Secret Life of Pots

Oh wow, interesting

 

[temol]

You can covert a B25k to an A25k by soldering a 4k7 resister between pin 2 and pin 1 (sometimes its pin 3) of the B25k pot. You have to take a look at the circuit to figure out if you want pin 2->3 or 2->1; one will change the taper to C, one will change it to A. I've done this loads of times, here is a reference:

The Secret Life of Pots

A25k in Pharmacist is connected as a variable resistor (two terminals). It is not possible to change the linear characteristic of the potentiometer to logarithmic in such a case. No resistor will help. This trick works for the potentiometer wired as a voltage divider (three terminals).

You could use A50k with 47k between pins 1 and 3. Taper may be a little steeper but still log and the final value will be around 25k

 

[jimilee]

 

[The Gator]

What is it's function in the circuit? How is it used?
B25K maybe perfectly fine.
I have not built that circuit, so if you could screen shotvit in the schematic so we can all look at it.

 

[temol]

MIDS potentiometer.



Top set - A25k, bottom set B25k.


A25k (top) vs A50k (bottom). This requires slight modification of the tone stack mid adjustment component values (section between C3 and R11). Every R times 2 and C/2. Not exactly a match but quite close.

 

[The Gator]

So used as a variable resistor.
I would just put the B25K in and call it good for this application. You can always order the proper A25K later if it bothers you.

 

[joelorigo]

I appreciate all these replies, I'm always learning things here!

I ended up adding 2 A25k pots to an order of some things I need for upcoming builds from Stompbox Parts that I had been compiling. I decided I can wait on finishing this Pharmasicst build for a few days until it arrives. He ships fast, already got the status update that the order has changed to "shipped" and I put it in yesterday!