Erica Synths EDU DIY Dual VCA Eurorack Module Kit - Manual (Page 14)

peak-to-peak output. This is an impressive amount of gain! Because remember, the signal
we sent into the transistor’s base was just a measly 20 mV peak-to-peak. But what about
the distortion that our circuit introduces? Where’s that coming from?
Simple. If we take another close look at the relation between base voltage and
collector current, we can clearly see that the plot is not linear . It’s slightly bent .
That’s because it is part of an exponential curve. And so as our voltage is oscillating at a
constant pace – remember, we’re using a triangle wave here –
the current oscillation is
slightly speeding up and slowing down. And since this change in current is directly
translated into a voltage swing, that voltage swing will be slightly bent as well. Tough luck!
So what can we do about that?
There’s just one solution here, really: use a smaller
portion of our curve . Why does that help? Well, the thing about exponential curves is
that if you divide them into smaller and smaller chunks, these chunks begin to look more
and more linear. The zoomed-in graph above is already a lot straighter than the full curve.
But in order to minimize distortion, we’ll have to scale our oscillation down even further.
So here our signal is swinging only between 567.5 mV and 572.5 mV – netting us a tiny 5
mV peak-to-peak oscillation.
And as we can see, the resulting plot looks almost
linear! It’s not perfect, mind you, but still close enough in my books.
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