Pots. Determining taper via a schematic. "B" designation- created 04-24-2008
Wybierala, Mark - 04/24/2008.12:08:10
Full Time Instrument Tech
Does a "B" designation on a schematic indicate the type of taper for the pot? The example I'm looking at designates the pots as B50K or B100K
Generally, it does. The B indicates a linear taper.
http://sound.westhost.com/pots.htm#taper
In my experience "A" is clockwise log taper and "C" is CCW log taper. There are other specialized taper designations but they aren't universal
I've seen both A/C for blend pots, and M/N. I'm not sure what the M and N stands for though
Blend /pan pots are special cases because the the resistive traces start at the 1/2 way point (the other half of the trace is conductive) and one element will be reverse log (or antilog) while the other is log. The values are also halved so a 250K blend actually only measures 125k per element. That's why I always start with 500k blend pots which are 250k each element
I would say (not from hands on experience though) MN taper is like the blend pot David K described, with zero resistance traces starting at midpoint, but the resistive traces are both linear instead of log and antilog.
BTW, David K, do you happen to have a blend pot like you just described, not mounted in a guitar, at the moment? May I ask you to do some (5) simple resistance measurements if so?
Luc,
For the record, there are literally dozens of tapers available for potentiometers. We used to have some catalogs from the manufacturers that had page after page of taper charts to choose from. This was high-volume ordering, of course
Calculating already made cross connections out will be no problem, neither will be the brand of pot. It would go like this :
One ohmmeter probe connected to a wiper lug, the other probe to an outside lug (don't matter which one) of the same deck.
Resistance measurements would be with the wiper :
1. completely turned to one side (don't matter which one)
The wiper positions don't have to be set extremely accurate.
That would give me useful data for the feasibility of a little project I have in mind without having to order this type of pot from somewhere first.
If you have no time for this right now that's all right David so no further reaction is quite ok. It's not like I'm urgently waiting and I'm sure other occasions will come.
I know that the blend pots Stew-Mac sell aren't made right. They are both A taper. So at middle detent, one side is like 200K to ground, and the other side is 25K! (for the 250K pot). It works better than I would expect, and I have noticed that I did get hum cancelation on a Jazz bass style instrument that I installed one in at center, but it has to be messing with the tone of one of the pickups
Hi Lucas.
Low deck: (connected to outside right lug and wiper lug, rotation from left to right)
Upper deck: (connected to outside right lug and wiper lug,rotation from left to right)
Jairo, thanks for the reminder, I'll get those measurements together on my pots too
¡ Arriba
About MN taper again...
I would say (not from hands on experience though) MN taper is like the blend pot David K described, with zero resistance traces starting at midpoint, but the resistive traces are both linear instead of log and antilog.
My assumption in post #6 was not right.
If found a diagram with various special tapers and redrew the M-taper curve from it. It looks linear over a large part, but at the extremities it's bent.
I didn't find N-taper but it would seem logical to me that it's an M-curve mirrored.
Anyway, from this curve I'm also inclined to conclude that the M-designation only tells how the resistance "tapers" - not (completely) linear - and basically tells nothing about a non-resistive track being present or not, like in an MN tapered blend pot.