quick questions: pots

[ruger9]

OK- I know the pot designations, and what the differences are, yada yada.  I have a pedal with 3 pots in it (drive, level, tone)- all are alpha pots. ONE (drive) is stamped "A500K" the others are not stamped at all.  ALL have "a" with a circle around it.  

Are these AUDIO pots? Is that what the "a" means? Or is just the one with "A500K" an audio?

Also, I'm assuming they are all 500K- can I use a multimeter to find out?

My plan is, the tone pot has a bad taper- the highs all pile on in one spot. If this is an audio pot, I was going to try a linear in it's place, to even out the taper.  Any other suggestions are welcome.

I've read "the secret life of pots", I just want to be sure what I'm dealing with before I go tearing into a $210 pedal..

Thanks!

[Paul Marossy]

The A with a circle around it is probably the Alpha trademark. The one marked A500K would be a 500K audio. On the other two, break out your DMM and measure the two outside lugs on the pot. If you measure close to a standard pot value (25K, 50K, 100K, 250K, 500K, 1M) then it will most likely be that size pot. In other words, if you measure 989K, then you have a 1M pot. (they can be off a bit from the nominal value)

As to determining if they are audio or linear, that's pretty simple. Turn the knob so it's at 12 o'clock. If it measures half of the pot value, then it's a linear pot. If not, then it's some other kind of taper - most likely an audio taper, but not necessarily.

[guitarhacknoise]

hello,
I think that the circle a has nothing to do with it.
I think A100k = 100k audio pot
I think B100k = 100k log

Test the pot
measure it all the way up, then round up.
turn it to half way.
If it measures half of the previous measurement, Log.
if it some other (lower than half) it's more likely a lin.

Could be wrong!
Usually am.
-matthias
EDIT:
CRAP!
Sorry paul,
Well at least I know I got this right!
-matthias

[ruger9]

OK. The drive pot (marked A500K) measures .515M   so I guess this means 500K?  ...wait- there's only 2 lugs being used on this pot, the outer and the middle.  Does this affect the measuring method?

The level pot measures 101.6K - a 100K

The tone pot measures 18.1K - a 20K I guess, maybe a 25K

The drive pot seems weird- a POINT 500 M


As for the taper, with the pots turned 1/2 way up (not at 12 o'clock- literally halfway thru their travel) the readings on the outside lugs is the same as above.  Measureing the outside lugs to the INSIDE lugs, I get readings of:
.43M  and  88.6K  (drive)
19K and 84K  (level)
10K and 8K (tone)

SO-  am I correct in assuming the tone pot seems to be a 20K or 25K linear pot?

And both the drive and level pots are audio?  (And even if that's correct- what's the deal with the readings on the drive pot?  .43M )

Thanks again for the help.  I've done simple soldering/repairs on my guitars- this is my first foray into DIY pedal mods.

[Khas Evets]

.5M = 500K, so .43M + .0886M = .5186M or 430K + 88.6K = 518.6K

I'm not clear what you mean by

with the pots turned 1/2 way up (not at 12 o'clock- literally halfway thru their travel)

I would think that 12 o'clock is half way through their travel.

Anyway, if your measurements are with the pot turned to it's physical mid point, then drive and level are audio pots and tone is a linear pot.

[ruger9]

Thanks for the confirmation.  With the pot sweep, I mean that the way the pots were installed, 12 o'clock is NOT 50%.  The "off" position is about 8 o'clock, and the full-on position is about 6 o'clock, so the 1/2 way point is about 2 o'clock- not 12.

SO- this 25K linear tone pot I've got:  here's my dilemma:  there's very little tone change in the first 75% or so of the pot's rotation- the sound isn't muddy, but highs are added very gradually. Then when the pot gets to 75%-80%, ALL of the highs seem to be dumped on very quickly.  It makes it very difficult to find the "sweet spot", and very easy to kick the knob with a foot when activating the pedal, knocking the tone WAY out of wack.  I'd like to improve the taper of this pot.  

Is there a simple resistor fix to help with the taper? Or maybe put in a higher value pot? (I assume that a higher value pot = tone would get brighter quicker, therefore I wouldn't have to even USE the last 25% of rotation... I'd just be using the first 50% or so, which seems to have a nice smooth taper.) ?

[Khas Evets]

Without a schematic I can't say for certain, but putting a parallel 20K resistor across the outside lugs of the pot would reduce the pot to ~ 10K. Then adding a 10K resistor in series would make the pot only active between 10K and 20K, which I'm guessing is the range of the top half of your current pot.

[ruger9]

Thanks- I'll try just alligator clipping them to see what I get...  when I connect the 10K in series, in series with what? All 3 lugs on the tone pot are wired up.  Unfortunately, I don't have a schematic and because it's  a board construction, there's no hope in this relative newbie figuring it out.  PTP I could probably "de-code"...

(the pot isn't mounted on the board, just all the circuits)

[Paul Marossy]

I would think that 12 o'clock is half way through their travel.

That's what I meant - 50% through their travel.  :wink:

[dosmun]

I think A100k = 100k audio pot
I think B100k = 100k log

Audio and Log are the same.

The B usually stands for Linear taper

[Paul Marossy]

Audio and Log are the same.

The B usually stands for Linear taper

Yep, this is correct. I missed that. Thanks for pointing that out.  

[guitarhacknoise]

Yeah, Sorry about that.
:oops:
I already know I cannot talk on the phone and drive at the same time.
My post shows me two ( actually three if you include the fact that it took 10 min.!) reasons why I Probably should'nt talk on the phone and type at the same time!
-matthias