Crybaby circuit with digital potentiometer?

[ianmgull]

Hey guys,

I'm thinking about how I might go about building a crybaby in a standard 125-B sized pedal enclosure, controlled by a control voltage.

I've got a pedalboard that uses a Boss ES-8 switching system. I also have a single expression pedal. The switcher allows me to program what the expression pedal does for a given preset. I'd like to build a crybaby circuit that takes a control voltage input.

Does anyone have any experience with something like this? I've never used a digital potentiometer in a build, so I'm not sure what to look for. Do they typically accept CV input, or is additional circuitry required. How does calibration work?

Any input would be appreciated.

Thanks!

[ianmgull]

Also reading up on vactrols. Wondering if that makes more sense and would require less overhead.

[iainpunk]

they generally have I²C control inputs. you need a computer or micro-controller.
no calibration is required
they have FET switches inside which switch between 1024 individual resistors internally, like this drawing, but modern ones have more than 100 switches.


vactrols are way easier, especially when staying analog

cheers

[R.G.]

As mentioned, digital pots take ... digital... inputs. You want CV with a digi pot, you'll need to sense the CV, and convert that to a digital command to the digi pot. And deal with the digital steps that they take, which commonly comes out as "zipper noise".

The effects world really, really wants a good, linear voltage-controlled resistor. Those only exist with special restrictions and such, sadly. The effects world makes do with LED/LDRs or some other workaround.

The classic wah circuit operates with the pot as a gain control. Anything that changes the gain of the feedback loop instead of the pot can be tinkered to work. The Technology of Wah Pedals would be a good place for you to do some reading on the topic, including the Anderton remote wah mod. Here: http://geofex.com/Article_Folders/wahpedl/wahped.htm