Erica Synths EDU DIY Dual VCA Eurorack Module Kit - Manual (Page 27)

ELIMINATING TRANSISTOR
MISMATCH
Here’s how it works. Instead of connecting our second transistor’s base directly to
ground, we’ll give it a very small, constant, non-zero voltage via a precision trimmer set
up as a variable voltage divider.
By doing that, it’s as if we’re changing the 24
transistor’s natural gain level – a positive voltage simulates more gain, while a
negative one simulates less
. And it’s this natural gain level that would ideally be
identical between our two transistors. Because then, their collector voltage swings would
have the exact same DC o
ff set – and subtracting them from each other would give us our
precious properly centered output signal.
You can try this chapter’s circuit in a simulator. I’ve already set it up for you right here: https:// 24
tinyurl.com/y7kh5c72 – you can change all values by double clicking on components.
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