Erica Synths EDU DIY Mixer Eurorack Module Kit - Manual (Page 7)

PASSIVE MIXER
To start out, we’ll first take a look at the simplest mixing circuit imaginable: two resistors,
connected together on one side. Send in your two input signals on the other side, and
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you’ve got a mix going. Here’s how it works. The two resistors, taken together, form a
voltage divider – which might sound somewhat confusing at first . 6
Usually, you see voltage dividers being set up like this:
with one resistor connected to a reference voltage and
the other connected to ground. If both resistors are of
the same value, you can pick up half of the reference
voltage in the middle between them.
In our setup above, confusingly, both resistors are
connected to reference voltages – which also change
over time, since we’re dealing with oscillations here.
Can we even call that a voltage divider, then?
Actually: yes! If we simply freeze time at any moment,
we will see something like this: two fixed input voltages
and a fixed output voltage. Now of course, either of
these input voltages may or may not sit at ground level.
But for a voltage divider, it’s mostly irrelevant what the
two input voltages are, exactly.
What matters is the
di ff erence between the two inputs – which is what
the divider is operating on .
Since both resistors in our divider are of the same value, that 4 V di ff erence will be
slashed in half – and the result gets added to the lower of the two input voltages. Giving
us a 3 V output. The „grounded“ voltage divider does exactly the same thing, if you think
about it: it slashes the di
ff erence between our reference voltage and ground in half – and
then adds it to the lower of the two input voltages.
Read more about resistors in the components & concepts appendix (page 21). 5
Read more about voltage dividers in the components & concepts appendix (page 24) 6
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