Author Topic: Potentiometer Values?  (Read 4977 times)

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Offline eruatTopic starter

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Potentiometer Values?
« on: October 20, 2014, 01:29:28 am »
Hi Forum!
So I've had some scratchy pots on my guitar amp. Decided to pull the board out and see what the situation is. Where I'm at, I can't see anywhere to squirt contact cleaning fluid.  :-/O
So, I've decided it's probably best to just solder in all new pots to increase the lifespan. Before I go out and buy some, just wanted to make sure I know what I'm getting.
So, stamped in the back of each of the 6 pots is the following;

   1            2               3              4               5              6
A10K      B20K      B2.2K      B20K      B200K      B10K


As I understand, A and B mean the same thing? Both mean linear pots.. but just confuses me that I have an A10K as well as a B10K..   :wtf:

So what do I need to know when buying new ones? What am I doing...?  :-//

Thanks heaps for any help!!!
 

Offline bills

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Re: Potentiometer Values?
« Reply #1 on: October 20, 2014, 01:35:24 am »
deoxit is your friend, clean them.
or in a pinch use wd 40. you can drill a small hole or spray it down the shaft.
regards
bill
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Offline eruatTopic starter

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Re: Potentiometer Values?
« Reply #2 on: October 20, 2014, 01:37:51 am »
drill a small hole

ha! tricky!

Thank you!
 

Offline bills

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Re: Potentiometer Values?
« Reply #3 on: October 20, 2014, 01:47:34 am »
To address your original post there are audio taper and liner taper pots among others.
regards
bill   
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Offline tautech

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Re: Potentiometer Values?
« Reply #4 on: October 20, 2014, 02:07:04 am »
A & B mean "Logarithmic" or "Linear"
http://en.wikipedia.org/wiki/Potentiometer
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Offline dentaku

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Re: Potentiometer Values?
« Reply #5 on: October 20, 2014, 02:16:55 am »
By the way, are they regular big round metal pots.
Those always seem to be wide open at the bottom like this
ttp://www.o-digital.com/uploads/2226/2230-1/Rotary_Potentiometer_WH0171_1_6246_909.jpg
I'm guessing your amp is more modern and has small completely enclosed pots if you say that you can't find anywhere to spray cleaner.
Deoxit is the best stuff I've found too.

If the pot that's labeled A10K is the volume then I would replace it with another pot of the same type. Volume knobs are usually logarithmic.
 

Offline Richard Crowley

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Re: Potentiometer Values?
« Reply #6 on: October 20, 2014, 04:07:44 am »
So I've had some scratchy pots on my guitar amp. Decided to pull the board out and see what the situation is. Where I'm at, I can't see anywhere to squirt contact cleaning fluid.  :-/O
It seems quite unlikely that they are sealed pots, so there is almost certainly at least one place to squirt fluid into the pots. Post some photos of the pots if you want help identifying where potential openings are.

Quote
So, I've decided it's probably best to just solder in all new pots
If they are standard 3/8 inch threaded panel-mount bushing pots, then you can probably find replacement pots as as long as they physically fit the space.
But if the pots are PC-board mounted or some other more modern physical configuration, finding replacements may prove impossible.

Quote
As I understand, A and B mean the same thing? Both mean linear pots..
Your understanding is incorrect.  "A" traditionally means "Audio" i.e. logarithmic, i.e "volume control".
"B" traditionally means Linear for most other circuit applications.
 

Offline vk6zgo

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Re: Potentiometer Values?
« Reply #7 on: October 20, 2014, 04:12:37 am »
In Oz,(& I'm pretty certain,the UK).back in the day,linear pots were called "A" curve,& log pots were "C" curve.
In the one of the silliest changes imaginable,now log is "A",& linear is "B".
If your equipment is quite old,you can't necessarily trust the markings.

Why the International community couldn't have come up with completely different alphabetical descriptions & avoided this confusion is beyond me! |O
 

Offline eruatTopic starter

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Re: Potentiometer Values?
« Reply #8 on: October 20, 2014, 04:15:52 am »
Those always seem to be wide open at the bottom like this

I see now.  :clap: Had only seen them on YouTube with the little hole seemingly designed to get sprayed into.
They are exactly like that; they are mounted perpendicular to the board so you can't see the gaps. But could probably fit a spray tube up into them.

Thank you very much, all! Case solved!
 

Offline eruatTopic starter

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Re: Potentiometer Values?
« Reply #9 on: October 20, 2014, 04:16:19 am »
In Oz,(& I'm pretty certain,the UK).back in the day,linear pots were called "A" curve,& log pots were "C" curve.
In the one of the silliest changes imaginable,now log is "A",& linear is "B".
If your equipment is quite old,you can't necessarily trust the markings.

Why the International community couldn't have come up with completely different alphabetical descriptions & avoided this confusion is beyond me! |O

Exactly what confused me!  |O
 

Offline Richard Crowley

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Re: Potentiometer Values?
« Reply #10 on: October 20, 2014, 04:47:00 am »
It is trivial to actually measure the pots to confirm whether they are linear or logarithmic. 
And measure the end-to-end resistance value as well.
So you don't need to trust the markings for value or law curve, either.
But replacement seems like a poor substitute for cleaning the existing pots.

Note also that noise could also be a result of DC current through the pot. 
From failure of a DC-blocking capacitor or two, for example.
 

Offline Mr 12

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Re: Potentiometer Values?
« Reply #11 on: October 20, 2014, 05:20:11 am »
I am a pedal steel picker and all you need do is soak them good with Deoxit.

Most times if you look close you will see an opening where the pins come out of the case.

Turn them upside down so you can load them with Deoxit inside the metal case then slosh it around a few seconds then drain out excess and let them dry out good.

Deoxit evaporates quickly so it will not take long, maybe three minutes tops.

I use a volume pedal so I took my pot apart and drilled a small hole in the back of the metal case so I can Deoxit them with a squirt of Deoxit with the little plastic spray tube on the can.
 

Offline G7PSK

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Re: Potentiometer Values?
« Reply #12 on: October 20, 2014, 02:28:14 pm »
In Oz,(& I'm pretty certain,the UK).back in the day,linear pots were called "A" curve,& log pots were "C" curve.
In the one of the silliest changes imaginable,now log is "A",& linear is "B".
If your equipment is quite old,you can't necessarily trust the markings.

Why the International community couldn't have come up with completely different alphabetical descriptions & avoided this confusion is beyond me! |O

Back in the day pots were marked Lin. or Log. there was no confusion. I still have a few lying around printed lin or log. Why the need for codes that then get changed every other day I don't know, god help us if the parts manufacturers ever get hold of an enigma machine, wait I think that they already have. :-DD
 

Offline Dave Turner

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Re: Potentiometer Values?
« Reply #13 on: October 22, 2014, 08:32:07 pm »
As Richard C stated it is relatively easy to measure the pot. Don't forget that in addition to log & lin pots  one used to be able to obtain log-log  and anti-log pots. Whether or not this is still true I haven't checked, but measuring them will determine what you need.
 


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