Erica Synths EDU DIY Wavefolder Eurorack Module Kit - Manual (Page 24)

INPUT STAGE
Great! But since using our existing attenuator feels pretty clunky and imprecise, we
should come up with a slightly more elaborate solution.
For that, it makes sense to restrict the input volume’s range somewhat. If the intensity
knob is dialed all the way down, you’d expect the input signal to just pass through the
circuit una
ff ected instead of going completely silent.
Also, it would be great if the output volume stayed the same, no matter the set intensity.
We can achieve this if we make sure that the signal always fits nicely between the two
folding thresholds.
This means that the minimum input volume should be just shy of
crossing the thresholds, while the maximum should be just shy of crossing them a
second time
. Ideally, we would use a fixed 100k input resistance, followed by a 10k
potentiometer and a 4k7 baseline resistance to ground here. 18
Given a 10 V peak-to-peak input, this outputs a range of 0,4 to 1,2 V peak-to-peak, which
fits between the two thresholds nicely. Before sending the result into our wavefolding
stage, we have to bu
ff er it with an op amp to avoid loading e ff ects. 19
Unfortunately, your kit doesn’t contain extra 100k and 4k7 resistors – so we’ll have to skip this 18
step on the breadboard right now. Feel free to set it up yourself if you have those values in your
stash.
You can try this chapter’s circuit in a simulator. I’ve already set it up for you right here: https:// 19
tinyurl.com/2j563omv – you can change all values by double clicking on components.
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