Pot Values

[macfadyb]

Hey Guys,

Sorry if there's a post on this already somewhere... I've been digging around online and haven't been able to find any good info.

My question is about the value of pots and how changing that value changes the parameter.

For example I built the big muff board recently and wanted to try setting the sustain at a lower base (zero) level

Is there an easy rule to follow here? Higher pot value = MORE (vol/sust/intensity/treble/whatever)

Any help would be much appreciated!

[matmosphere]

As I understand it a pot is a variable resistor where the highest resistance is at the lowest setting. So with a volume knob, for example, the circuit would give the same volume with the knob at ten as it would not having a volume control at all. As the volume knob is lowered the resistance increases and the volume is decreased.

If you increased your sustain pot from, for example, a 100k to a 250k you wouldn't see a difference at the maximum setting but set to zero on the 250k pot you would have less sustain than would be possible with a 100k pot.

[midwayfair]

Not worth it. A different pot is $1 while a resistor is 1c. Look on the schematic. There is a 1K resistor hanging off of the bottom of the sustain pot. Make it 470R and you'll have half as much gain at minimum. Whether that will sound good is another matter entirely.

[RobA]

As I understand it a pot is a variable resistor where the highest resistance is at the lowest setting. So with a volume knob, for example, the circuit would give the same volume with the knob at ten as it would not having a volume control at all. As the volume knob is lowered the resistance increases and the volume is decreased.

If you increased your sustain pot from, for example, a 100k to a 250k you wouldn't see a difference at the maximum setting but set to zero on the 250k pot you would have less sustain than would be possible with a 100k pot.

The Sustain pot on the Big Muff is used as a variable voltage divider, not a variable resistor. It works in this circuit very much the same way a volume pot works on your guitar.  Changing the volume pot value on your guitar doesn't change the output level of your guitar, but it does change the tone because of the way the pot "loads" the pickups and the interaction with the passive characteristics of the pickup, output impedance, inductance, etc.

The impedance of the Sustain pot interacts with the output impedance of the Q1 amplifier, input impedance of the Q2 amplifier, and the input and output capacitors. As a general kind of thing, you'd want to match the value of the pot to output and input impedances as much as possible. You also need to look at what is happening with the coupling caps and what the filters look like that this sets up with the Sustain pot. If you want to play with gain on the Big Muff, you'll get more out of varying the resistors in the first amplifier stage. If you want to play with the frequency response, you are going to get more out of playing with the input, output and feedback caps of the first amplifier stage. And, these are just what the various Big Muff versions do modify.

As a general thing, changing the pot values can do a lot of different things and you really have to look at the individual cases and see how the pot interacts with the various components and elements in the circuit around it.

[matmosphere]

Wow, thanks Rob I wasn't 100% on that particular example. I still have a lot to learn.

[macfadyb]

thanks for the great replies guys

very informative!