Erica Synths EDU DIY Wavefolder Eurorack Module Kit - Manual (Page 18)

PNP WAVEFOLDER
Now that we’ve got a decent triangle wave, let’s get back to our wavefolder. The problem
with our design so far is that it only a
ff ects the bottom of the output waveform. In a
traditional wavefolder, you’d want to fold both the bottom and the top, though . To
get there, we’ll first check out an alternate version of our circuit that folds just the top of
the output waveform.
As you can see, the only real di ff erence here is in the type of transistor we’re using. I’ve
simply replaced the NPN with a PNP transistor. And since the PNP transistor is
basically just the NPN transistor’s bizarro twin brother, everything about it is
inverted
. Collector and emitter switch positions, and the current flowing through them
increases as the base voltage decreases.
So if we look at the relation between base- and collector voltage for this circuit with
another graph, we can see that the two regions are switched.
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