Erica Synths EDU DIY Wavefolder Eurorack Module Kit User Manual
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This approach has two benefits. First: we undo the inversion that the wavefolding stage
applies to the input signal. So the output will be in phase with the input again.
And
second, the new 10k resistor gets to work double duty: it’s providing the extra
current for our two transistors – and it’s playing its role as input resistor for the
inverting bu
ff
er
.
This works because in an inverting bu
ff
er, the op amp’s inverting input is what we call a
virtual ground node: it behaves just like a path to ground without actually being one. So
connecting the collectors to the op amp’s inverting input through a 10k is functionally the
same as connecting them straight to ground here.
With this change, you can finally listen to the output. By adjusting the input volume, you
can again change the e
ff
ect’s intensity. If you check the output on the oscilloscope, you’ll
see how it crosses the folding thresholds a second time at maximum volume – but
doesn’t get folded. That’s because we’re just going deeper and deeper into saturation of
the same transistor.
You can try this chapter’s circuit in a simulator. I’ve already set it up for you right here:
you can change all values by double clicking on components.
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