Erica Synths EDU DIY Dual VCA Eurorack Module Kit - Manual (Page 39)

OP AMPS
Op amps might seem intimidating at first, but they’re actually quite easy to understand
and use. The basic concept is this: every op amp has two inputs and one output. Think of
those inputs like voltage sensors. You can attach them to any point in your circuit and
they will detect the voltage there without interfering.
No current flows into the op amps
inputs – that’s why we say their input impedance is very high . Near infinite, actually.
Okay, but why are there two of them?
The key here is that op amps are essentially di ff erential
amplifiers. This means that they only amplify the
di
ff erence between their two inputs - not each of them
individually. If that sounds confusing, let’s check out a
quick example. So we’ll imagine that one sensor –
called the non-inverting input – is reading 8 V from
somewhere. The other sensor – called the inverting
input – reads 5 V. Then as a first step, the op amp will
subtract the inverting input’s value from the non-
inverting input’s value. Leaving us with a result of 3.
(Because 8 minus 5 is 3.) This result then gets multiplied
by a very large number – called the op amp’s
gain .
Finally, the op amp will try to push out a voltage that
corresponds to that multiplication’s result.
But of course, the op amp is limited here by the voltages that we supply it with. If we give
it -12 V as a minimum, and +12 V as a maximum, the highest it can go will be +12 V. So in
our example, even though the result of that multiplication would be huge, the op amp will
simply push out 12 V here and call it a day.
The handy thing though about op amp outputs is that they draw their power directly from
the power source. This means that they can supply lots of current while keeping the
voltage stable.
That’s why we say an op amp has a very low output impedance .
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