Understanding Potentiometers

[DeadAirMD]

Can someone help me understand Potentiometers better?

I see people doing mods, which I have also done myself, by replacing existing pots with those of different values to achieve different effects. What does that actually mean?

For example, what does replacing a 100k pot with a 500k/25k, higher vs lower value pot do for sound/tone/volume etc.? Maybe in reference to Gain, so I can understand at least something about it and then apply it to other potentiometer uses.

 

[gonzo]

Can someone help me understand Potentiometers better?

I see people doing mods, which I have also done myself, by replacing existing pots with those of different values to achieve different effects. What does that actually mean?

For example, what does replacing a 100k pot with a 500k/25k, higher vs lower value pot do for sound/tone/volume etc.? Maybe in reference to Gain, so I can understand at least something about it and then apply it to other potentiometer uses.

In most circuits a higher value gives you a wider control over something. But sometimes a high value might only work at the very last part, so people might narrow the value down to have a more usable sweep. Also the type of pot varies the type of sweep curve, line, audio, etc..in passive guitar wiring it effects the tone even when fulling open. Maybe someone else can explain this better.

 

[szukalski]

A pot is a variable resistor. Often with outputs, it lets you adjust how much signal goes to ground. Ie. the max resistance of the pot is how much resistance there is against the signal going to ground. Make it a bigger pot, more resistance and less signal goes to ground. This same thing applies to other parts of the circuit.

 

[DeadAirMD]

So decreasing a pot gives me tighter more refined control over a circuit? Or am I getting this totally backwards?

 

[Passinwind]

Can someone help me understand Potentiometers better?

I see people doing mods, which I have also done myself, by replacing existing pots with those of different values to achieve different effects. What does that actually mean?

For example, what does replacing a 100k pot with a 500k/25k, higher vs lower value pot do for sound/tone/volume etc.? Maybe in reference to Gain, so I can understand at least something about it and then apply it to other potentiometer uses.

It's entirely circuit dependent. Used in the feedback loop of a simple opamp gain stage it might redefine max/min gain available, with higher value = higher gain, used in series on the input it might work completely backwards to that.

 

[Aentons]

If wired as a voltage divider like an volume control, the value does not really matter.

If wired as a variable resistor like a gain control in a feedback loop, higher value equals more gain.

If a variable resistor is not in a feedback loop, a higher value equals less signal to that part of the circuit.

 

[DeadAirMD]

If wired as a voltage divider like an volume control, the value does not really matter.

If wired as a variable resistor like a gain control in a feedback loop, higher value equals more gain.

Awesome! That's totally making more sense now.

 

[Passinwind]

Awesome! That's totally making more sense now.

In the voltage divider scenario a value change can still affect bass or treble rolloff, or broadband level, depending on source and load impedances. If you're ever experimented with 250K vs 500K pots in a guitar you may have experienced that, for instance.

And then there's pot taper. Not uncommon for many amps to stop getting louder past the noon position, or conversely to only starting to get usefully loud at noon or higher. Swapping in a pot with a different taper can mitigate these effects, or make it worse, depending.

 

[Feral Feline]

A pot is a variable resistor. Often with outputs, it lets you adjust how much signal goes to ground. Ie. the max resistance of the pot is how much resistance there is against the signal going to ground. Make it a bigger pot, more resistance and less signal goes to ground. This same thing applies to other parts of the circuit.

What if the pot isn't going to ground in any way? "This same thing applies to other parts of the circuit that may not be going to ground."

If wired as a voltage divider like an volume control, the value does not really matter.

Except that wired as a Voltage Divider for a Volume control at the very end of a circuit may affect the output impedence?
Size matters, might push unity to a different part of the dial?
Sometimes "Volume" comes before the very tail end of the circuit with tone shaping resistor/cap combos.

@DeadAirMD So, you can see from all the answers that "it depends", a screwdriver can also be a hammer depending on how you use it.

A pot wired as a variable resistor, with either lug 3 or lug 1 tied to lug 2, can be also called a "rheostat".

Here's a stock Dist+ where the GAIN is wired as a rheostat going to ground:

Increases in Gain affect the bass response of the circuit, which may not be to your liking if you want a gain increase without the EQ swing. Brian Wampler has a mod for that, moving the GAIN control to where R4 is for a less obvious EQ change:

Read more about his above mods in his Premier Guitarticle.



I'm surprised nobody's yet mentioned RG KEEN's "THE SECRET LIFE OF POTS", so I just did.

It won't answer all your specific questions, like "if I wire this pot in this part of the circuit which way direction will the rotation affect it in what way?" – BUT it's still recommended reading if you haven't read it yet. I'm still referencing and re-reading it du temps en temps.

PS: I've quoted people above that are FAR more learned than I am about this stuff. My post is as much about clarifying in my own mind things/ideas/infos that are still fuzzy to me, as it might hopefully help others like me.

 

[DeadAirMD]

I read the Life of Pots within the 1st week of getting into pedal building, almost 2 years ago.....and read it again.....and again haha. I appreciate any and all information.

Learning on the internet is hard for me. I'm better doing it in person, because I always end up with so many questions and it's beyond easier to do that in person, apposed to chasing every rabbit into a hole with endless internet searches.

 

[coltonius]

Here's a helpful visual on different sweeps (A = Log/Audio; B = Linear; C = Anti-Log or Inverse Log, apparentlly)

Several builders like to use linear pots for Volume, which makes a pedal ear splittingly loud at 9 o'clock on the sweep. An audio pot helps with that by giving more control over the lower range of the sweep!