Erica Synths EDU DIY Wavefolder Eurorack Module Kit - Manual (Page 13)

SAW-TO-TRIANGLE BASICS
If you’ve used a sawtooth wave as your input signal, you probably noticed that at
maximum volume, we almost fold it into a triangle! Since wavefolding generally sounds
really good when applied to triangle waves (and because the mki x es.edu VCO does not
have a triangle output), it makes sense to take a short detour here and talk about turning
our circuit into a proper sawtooth-to-triangle converter.
To do that the ideal way, we’d have to add a ~450 mV o ff set to the sawtooth to center it
around the folding threshold. This would give us a symmetrical, clean triangle at the
output. Unfortunately, there isn’t enough space on the module’s PCB to pull this o
ff , since
it would require us to add another op amp IC. So we’ll have to find an alternate approach
with a smaller footprint.
And the alternate approach with the smallest footprint is changing the relation
between the collector- and emitter resistors
. How does this work? Well, as we’ve seen
before, if that relation is 1:1 (meaning that the resistance values are equal), the relation
between base voltage and collector voltage is 1:1 (or 1:-1, depending on the region we’re
operating in) as well. Now, let’s say we drop the emitter resistance to 10k, shifting the
resistance relation to 1:2.
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