# B10K Pot Vs A10K Pot



## DrVon

Just wondering if there is an actual difference between the two. The Phase II PCB is calling for a A10K pot but all I could find on Tayda was a B10K. Is there actually a difference?


----------



## Robert

The difference is the taper. (How quickly the pot value changes as you turn the control up)

Tayda has them, they're listed as "Logarithmic Taper":






						Search results for: 'A10K'
					






					www.taydaelectronics.com


----------



## DrVon

Great thanks. Another question as I couldn't find an A25k pot. I know I can get a A50K pot and add a resistor of equal value on pin 1 and 3, and get the 25 I need. The only issue is I can only see a 51k resistor which brings me to 25.25k ohm. Would this be OK? Thanks for the help.


----------



## Robert

I don't think you'll get the results you want by adding a resistor across a pot where all three lugs are used, that's typically done when the pot is used as a variable resistor (two lugs used).

I _think_ I used B25K in mine, and it seems like I recall someone mentioning using a larger value (A50K maybe) for more control of the slower speeds....

Maybe someone else can chime in.


----------



## Jovi Bon Kenobi

Yeah A25k's are tough to find in PCB mount. You can also order a solder lug version and run discarded clipped leads from the lugs through the board. Something sturdy like the clipped 1n5817 leads are nice (I save mine), or just hook up wire.


----------



## DrVon

Robert said:


> I don't think you'll get the results you want by adding a resistor across a pot where all three lugs are used, that's typically done when the pot is used as a variable resistor (two lugs used).
> 
> I _think_ I used B25K in mine, and it seems like I recall someone mentioning using a larger value (A50K maybe) for more control of the slower speeds....
> 
> Maybe someone else can chime in.



  OK I ordered the B25K and see how it goes, Thanks again


----------



## bengarland

The part you want is Alpha RV16AF-41-15R1-X where X is the value of the pot, e.g. RV16AF-41-15R1-B25K

Also B = Linear, A = Audio. Linear trim is the same resistance all across the dial and generally used for signals which you don't hear. Audio trim is generally for signals which you will hear, and since our sense of hearing is logarithmic (i.e. dB) this type of knob compensates for that --- when you turn the A-type pot, the signal _sounds_ like it's being adjusted equally all the way across the dial even though electrically it isn't. If you use a Linear B-type pot for an audio signal, you only have a very small range at the lower end of the dial to actually adjust the loudness of the signal (so in essence an A-type pot is just more convenient to use).

Somewhat frustratingly, Tayda does not carry all of the pot values that you might find on a PedalPCB build.

But it seems like SmallBear Electronics does (for instance, B2K which I can't find anywhere else).









						Alpha Single-Gang 16mm Right-angle PC Mount
					

Small Bear Electronics DIY Parts




					smallbear-electronics.mybigcommerce.com
				




Just note that Smallbear apparently does not include "dust" covers for their pots (which really just keeps the bottom of the pot from touching the PCB when you mount it). They are a separate item but they're only like 10 cents each.


----------



## DrVon

Thanks for the feedback. I will order some through smallbear.


----------



## Cucurbitam0schata

I'm trying to build a Phase II, which requires an A25K pot. I'm trying to cash in on a sweet sale over at Tayda (ends tonight...). And there's no A25K (logarithmic / audio 25k) pots for PCB mount available on the site. Everything else is, to my chagrin!

Like @PedalPCB suggested above, has anyone else had success using an A50K instead? Or a A20K? Many thanks, pals!

Dan


----------



## DrVon

I ended up buying the one I needed from small bear. It worked out well. Just remember you will need to order a duct cover


----------



## Chuck D. Bones

Here's another way to look at it:
*A* taper spreads out the bottom end of the pot's rotation.  At noon, the pot has only covered 15% of the resistance.  As bengerland said, good for audio signals (usually).
*B* taper is linear; at noon the pot has covered 50% of the resistance.  Sometimes, B taper is actually better for Gain and Volume controls, more about that in a minute.
*C* taper spreads out the top end of rotation.  At noon, the pot has covered 85% of the resistance. C taper is good for certain kinds of Gain and Tone controls and for Speed controls on some modulation pedals.

All that being said, the circuit around the pot can alter it's effective taper.  Many fuzz pedals have a resistor at the bottom end of the Fuzz control because there is little use in dialing the signal all the way down to zero.  Let's use the Ungula (EQD Hoof) as an example.  The Fuzz pot is B50K, linear taper.  But there is a 2.2K resistor at the bottom.  That 2.2K resistor effectively makes this pot behave like an audio taper pot, at least at the bottom end of rotation. Without the 2.2K resistor, there would be a huge jump in gain from zero to 1 with a B taper pot.  with it, the gain change is only 9%, about 1dB.  In the case of the Ungula, and other BMP designs, the circuitry after the Fuzz pot loads the pot and affects the feel of the pot.  Because R7 is 8.2K, which is small compared to the 50K Fuzz pot, the pot will be less sensitive in the middle part of the rotation.  This is a good thing because that is usually the part of the rotation we use the most.  Well, some of us anyway.

Many OD and boost pedals are capable of outputting a large signal, which is great for overdriving the next pedal or an amp.  But we don't always want that.  For those pedals, A taper is preferred for the volume control because otherwise, unity would be around 1 or 2.  Other ODs output a modest signal, such as the Distortion 250 (DOD 250 Overdrive).  The max output signal is maybe 0.7Vp-p.  The Volume pot on those is A taper, but B taper would work better because unity can be up around 8 or 9 with humbuckers.


----------

