Minimum AND maximum volume circuit

[Fafnirsbana]

Hi y'all, first time poster.

I made this account specifically because I can't re-find a post that I'm fairly certain was a thread here.

The OP was asking for help adding minimum and maximum volume controls to a circuit. They first posted with an image of a wiring diagram with three pots, then another user replied with the assumed circuit diagram with the minimum and maximum pots wired as variable resistors.

THEN a comment states something like "this will work, however there will be problems if the minimum and maximum pots are set to overlap" and then provided a better alternative implementing (I think?) an IC.

If someone knows what I'm talking about, a link to that thread or just the diagrams would help me sleep at night again.

Thank you!

[Mark Hammer]

Not clear whether what is sought are switch-selected presets, or simply limits.

[Fafnirsbana]

Not clear whether what is sought are switch-selected presets, or simply limits.

Adjustable limits on either side of a primary pot. I'd be using these for treadle pedals that would control two or three parameters, eg. wet/dry min/max and expression or A/B loop mix min/max.

[Mark Hammer]

Well that's pretty easy.  Indeed, if one looks at enough circuits, you'll see it is often implemented.

Let's take the example of an output volume control, using a 100k log potentiometer.  The pot acts as a voltage divider, with the voltage coming off the wiper of the pot being a function of the ratio of the pot resistance between its input and the wiper, compared to the total pot resistance.  So if the pot "leg" between input and wiper was 33k (with the remainder making up 66k), 33/100 makes the output voltage 1/3 of whatever the input is.

Okay, let's expand this, and use a 50k pot with additional resistors on each end.  If there was a (mythical) 25k resistor on the input, and another 25k between the ground "leg" of the pot and ground, then our total voltage divider is 100k (25+50+25) but could NEVER go above 75% of whatever the signal level is, OR below 25% of the signal level.

A good example of this in action is the "Sustain" control on a Big Muff Pi.  You'll find they include fixed resistors from the pot to ground of 1K to 1.5K.  That control adjusts how much signal is fed to the gain/clipping stages. But the additional fixed resistor assures that it will NEVER be below 1% of what that signal is.

The punch line is that you can vary the values of added "input" and "ground leg" resistors to arrive at whatever maximum and minimum you wish.  Granted, that applies specifically to contexts where the pot is connected to ground, but that covers a LOT of applications.