Author Topic: Help with a madbean stutr  (Read 466 times)

plain guitarist

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Help with a madbean stutr
« on: June 13, 2020, 04:34:29 PM »
Hi all.

I would like to build the madbean stutr. However, I would like to add an exp out to the rate knob (like the EQD hummingbird). I thought it was simple, but I got to talking to some guys on discord and they mentioned a few things.

1. Apparently, the rate knob works off voltage, while the exp works off resistance. So I would need to somehow translate the voltage. I was thinking an led to ldr, but I dont know how to go about it.

2. Even if it didn't work off voltage, the rate is 1mc, while the expression pot is 10k (a, I think?). Would I need to change the pot on the expression pedal?

The following was my original plan, but it fell apart:

Any advice would be greatly appreciated.

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Re: Help with a madbean stutr
« Reply #1 on: June 25, 2020, 07:29:06 PM »
I think this circuit will do the trick.

In order to get a 10k exp. pedal to control a 1M variable resistor you need to employ an optical controller. So, the LDR acts in parallel with the Rate pot to control the effective resistance, and therefore the speed of the LFO.

In this circuit, when there is no exp. pedal plugged in the optical controller disengages and the LDR is fully dark. When the exp. pedal is plugged in the pot in the exp pedal acts as a voltage divider which powers up the transistor which drives the brightness of the LED in the optical device. T1 is a trimmer which allows you to fine tune the range of the exp. pedal so you can get the right transition from slow to fast speeds. The EXP IN jack should be a Marshall style jack.

This might be more complicated than what you are willing to deal with, but I believe it will work.