Can someone explain "pots" to me?

[Harper]

This is something I had never given thought to until recently, but what's a layman's explanation of the differences between pots in electronics? I've seen 250 and 500k mentioned quite a lot. I'm assuming one provides a more modern sound than the other. What is the "standard"?

[fleabee]

250k would be pretty standard{warmer}
500k would be brighter

[Harper]

So I'm assuming most American Fenders would have 250k pots?

[Saxn]

Those numbers are just describing the "resistance" that the pots have to electricity... the higher the number, the greater the resistance. In the example you gave, a 250 would be 250 Ohms of resistance, whereas the 500k would indicate 500,000 Ohms (500 Kilohms), and would therefore have a much higher resistance to an electrical current. Now, those numbers are not the only information that fully describes potentiometer (pot) characteristics, but since the signal levels in your guitar are so low volt/amp, it is the most important one in this application.

Sorry if that made no sense. I'm not the world's best explainer.

EDIT: I see that my not being a guitar tech bit me here... I guess it's 250K and 500K pots we're talking about... but the gist is the same.

[fleabee]

Originally Posted by Harper

So I'm assuming most American Fenders would have 250k pots?

correct

[line6man]

250 (k?) and 500k are in reference to the pot's resistance range, as measured in Ohms.

The value across the outer terminals of a pot is equal to it's rating, plus or minus variations in manufacturing tolerance.

The resistance from the wiper terminal to either side is determined by the physical position of the pot, as the wiper sweeps from one side to the other.

In terms of volume controls, the higher the value, the less resistive loading is placed parallel to the signal when the volume is all the way up. A higher value will give you more output/treble than a lower value.

As far as tone controls, a higher value pot will be identical to a lower value pot from 0 Ohms up to the rating of that lower value pot, but from there on up, less signal will be fed to the capacitor, and thus, less treble will be cut when the tone is turned up.

There is no "standard" pot value, per se. The value you need is determined first by the impedance of the signal.
If you have a low impedance signal from active pickups or a preamp, you will want to use a relatively lower pot value like 25k, 50k or 100k, because if the value is too high, the pot will behave like an on/off switch. Conversely, if you are controlling a high impedance signal, like from passive pickups, you will want a higher value, like 250k or 500k, because if the value of the pot is too low, the resistance parallel to the signal is going to load the pickups down and kill too much output/treble.

There are standards for different types of setups.
25K pots are often used in low impedance active setups, while 250K and 500K are the most common values in passive basses.
It is by no means the rule, but the general practice that people go by is to use 250k pots in basses with single coils, to tame out their brightness, and 500k pots in basses with humbuckers, to preserve the treble and keep a hot output.

[fenderphil]

line6man rules.

[JohnMCA72]

"Pot" is shorthand for "potentiometer", which is basically a variable resistor network. Controlling resistance in a circuit allows you to do useful things like control volume, tone, etc.

Potentiometer - Wikipedia, the free encyclopedia

[colcifer]

Originally Posted by fenderphil

line6man rules.

QFT!

[Testing_123]

Everything you might want to know (and more) about potentiometers, including explanation of linear, log, and reverse log tapers, using as variable resistors vs. voltage dividers, what's inside pots and ways to refurbish them, and so forth:

The Secret Life of Pots

[bassbenj]

Originally Posted by JohnMCA72

"Pot" is shorthand for "potentiometer", which is basically a variable resistor network. Controlling resistance in a circuit allows you to do useful things like control volume, tone, etc.

Potentiometer - Wikipedia, the free encyclopedia

Gather round kiddies and I'll give you a little electrical history. The name "pot" which is short of "potentiometer" is actually a misnomer. It's a hold over from the VERY early days when people didn't have much of a clue about what electricity was and 19th century guys were fooling around with the Cells of Volta etc.

A "potentiometer" is actually not the variable resistor itself but the ENTIRE instrument that was used in those days to measure voltages. The way it worked was the variable resistor was wired as a voltage divider so it could put out a voltage set by the knob setting on the resistor. That output was connected to the point you wished to measure. If the instrument output was too low current would flow into it. If too high, out of it. But when the "potentials" (voltages) were exactly matched NO current flowed and that was the reading. Nobody does this anymore, but the name "potentiometer" stuck to variable resistors. These old "pots" in those potentiometers were usually about 6" or so in diameter!

Another name you may hear is "rheostat". This refers to the use of a variable resistor to adjust current into some device (was typically a radio) The pot was large, wire-wound, low Ohms and could take a lot of heat. (a battery was usually driving it) You don't hear the term much anymore even in power circuits.

Generally speaking, the pot circuits we use have little to do with electrical "potential" and the "pot" is simply used by us as a convenient way to have a resistance that can be easily changed by turning a knob.

[Saxn]

I thought rheostats had two terminals and were used to adjust voltage, while potentiometers had three terminals and were used to adjust current flow (and can be wired to adjust voltage)?

[SevenJacks]

Could someone dumb this down a little more for me and tell me what 'pots' actually mean?

[tjh]

Originally Posted by SevenJacks

Could someone dumb this down a little more for me and tell me what 'pots' actually mean?

... the more you turn the volume knob up, the louder it gets ...

... the more your turn the tone knob up, the more treble you will notice in your tone .. the more you turn it down, the less treble you will notice in your tone ...

... IF it sounds good to you, you are ... GOOD TO GO ...

... JMHO

[MonsterBass101]

Originally Posted by Saxn

I thought rheostats had two terminals and were used to adjust voltage, while potentiometers had three terminals and were used to adjust current flow (and can be wired to adjust voltage)?

You are correct.

[bassbenj]

Originally Posted by Saxn

I thought rheostats had two terminals and were used to adjust voltage, while potentiometers had three terminals and were used to adjust current flow (and can be wired to adjust voltage)?

You are correct in that some rheostats have only two terminals. Which is just like using only two terminals (center and one end) on a pot. Some rheostats, however, do have three terminals are are basically low Ohms pots.

Both pots and rheostats are just variable resistors. For that reason you can't really say if they are adjusting voltage or current without knowing how they are hooked up. In the old days rheostats were often placed in series with batteries to reduce the current draw (or voltage too) the circuit in question. The idea being that the current draw of the circuit creates a voltage drop across the rheostat proportional to it's resistance which you can set with a knob. Since the battery voltage must equal the circuit voltage plus the drop in the rheostat and the battery voltage is fixed, The rheostat therefore controls the voltage to the circuit. Standard thing in old days was controlling filaments in battery radios.

But obviously none of this historical stuff has anything to do with the pots in modern basses!

[Saxn]

I seeeeee... gotta admit my 'parts history' is not really up to snuff. It was explained to me going through electronics classes that 'if it does this, it's a that, and vice versa'. Thanks for the background.

[madmatt]

Dave Grohl of the Foo Fighters likes fresh pots of coffee. He is one coffee drinking SOB.

[SevenJacks]

Originally Posted by tjh

... the more you turn the volume knob up, the louder it gets ...

... the more your turn the tone knob up, the more treble you will notice in your tone .. the more you turn it down, the less treble you will notice in your tone ...

... IF it sounds good to you, you are ... GOOD TO GO ...

... JMHO

Heh thanks TJH, but I was more referring to what the word 'pots' meant, or where it came from, not necessarily what they do

[tjh]

yup ... sorry if that came off 'sarcastic', but when the talk gets technical to the point that the technicians begin to debate, I tend to revert to the K I S for S method ... and that would be referring to me, not you ...