Erica Synths EDU DIY EG Eurorack Module Kit - Manual (Page 33)

OP AMP BUFFERS/AMPLIFIERS
Bu ff ering, in the world of electronics, means that we provide a perfect copy of a voltage
without interfering with that voltage in the process. With an op amp-based bu ff er, the
bu ff ering process itself works like this. We use the non-inverting input to probe a voltage,
while the inverting input connects straight to the op amp’s output. This creates what we
call a negative feedback loop . Think of it this way. We apply a specific voltage level to
the non-inverting input – let’s say 5 V.
Before the op amp starts processing the voltages at its
inputs, the output will be switched o
ff . This means that
output and inverting input sit at 0 V at first . So then,
the op amp will subtract 0 from 5 and multiply the result
by its gain. Finally, it will try and increase its output
voltage to match the calculation’s outcome.
But as it’s pushing up that output voltage, the voltage
at the inverting input will be raised simultaneously .
So the di ff erence between the two inputs is shrinking
down. Initially, this doesn’t matter much because the
gain is so large. As the voltage at the inverting input
gets closer to 5 V though, the di
ff erence will shrink so
much that in relation, the gain suddenly isn’t so large
anymore.
Then, the output will stabilize at a voltage level that is
a tiny bit below 5 V , so that the di ff erence between the
two inputs multiplied by the huge gain gives us exactly
that voltage slightly below 5 V. And this process simply
loops forever, keeping everything stable through
negative feedback. Now if the voltage at the non-
inverting input changes, that feedback loop would
ensure that the output voltage is always following. So
that’s why this configuration works as a bu
ff er: the
output is simply following the input .
How about amplifying a signal though? To do that, we’ll
have to turn our bu
ff er into a proper non-inverting
amplifier. We can do that by replacing the straight
connection between inverting input and output with a
voltage divider, forcing the op amp to work harder.
Here’s how that works. Say we feed our non-inverting
input a voltage of 5 V. Now,
the output needs to push
out 10 V in order to get the voltage at the inverting
input up to 5 V
. We call this setup a non-inverting
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