Dumb Question #1 - Stompbox Cookbook question...what is a "Static Point" pot?

[skiraly017]

In the Stompbox Cookbook, several projects have a Static Point control. I've never seen this anywhere esle and was wondering what it does. Thanks.

[smnm]

I've never heard it called this but it sounds like it might be a trimpot, a mini variable resitor mounted on your PCB that you use for biasing a transistor or whatever.
Once you set it to the optimum value you never need to touch it again, I think Craig Anderton calls it a 'set and forget' pot in the Electronic Projects book, IIRC.

[RickL]

I suspect you're refering to the tremolo projects. The static gain sets the mid point of the volume of the trem. Imagine a wave that moves up and down 1 volt around some set voltage. If the set voltage is 0 volts it will go from -1 volts to +1 volts. If you're listening to it all you will hear is the part where the voltage goes above 0 volts so you will hear half a wave of silence followed by half a wave of increasing, then decreasing volume.

Put the set (static) voltage at 1 volt and you will hear the volume start at 1 volt, decrease to 0 volts (silence), increase to 2 volts, then decrease to 1 volt. It will only be actually silent at the very bottom of the wave form.

Put the set voltage at 2 volts and it will never be silent (lowest volume will be at 1 volt).

Simply put, it sets the average volume that the volume changes of the tremolo swing around.

[skiraly017]

Based on Rick L's description, this sounds like a "set it and forget it" kind of thing and that instead of using a full size pot I could stick a trim pot on the board.

[RickL]

Nope, use a panel pot. The sound of tremolo that varies between no volume and lots of volume is very different from that which varies between no volume and some volume. I've built at least one of the Boscorelli trems and the pot is worth having as a panel mount control. Besides, it was intended to be a panel mount, as the parts placement diagram clearly shows.

[RickL]

A little further elaboration. This is directly fromThe Stompbox Cookbook by Nicholas Boscorelli. I hope I'm not breaking any copyright rules by posting it.

From the Use section of Project No. 5 Tremolo-Matic: Specific settings of depth and static gain let Tremolo-Matic provide three distinct types of tremolo. >With static gain centered and depth at ~40%, the control feed causes instrument volume to intensify on positive control peaks; to soften on negative ones.  >With static gain at maximum and depth at ~50%, instrument volume softens only during negative control peaks. Positive control peaks clip in IC2-b and cannot further effect volume.  >With static gain at minimum and depth at~60%, sound pulses from a background of silence, lending the effect a percussive air.

I've built it and can tell you from experience that these three variations, and the stuff in between, are noticably different and are all usable.

The Pan Tremolo-Matic (which I've also built), Tremolo-Matic II (I think I've built this too), Tremolo-Matic III, Tremolo-Matic IV, Vibrato-Matic and Tremolo-Matic V also have this control and it's always shown as a panel mount pot.