Boosting the output signal – Erica Synths EDU DIY Dual VCA Eurorack Module Kit User Manual
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BOOSTING THE OUTPUT SIGNAL
To fix this, we can simply use a bit of our subtractor op amp’s gain. Because right now,
we are really only using it to subtract our two signals – not to amplify the result. How do
we change that?
By making the output work harder to equalize the two input
voltages
. And in order to make it work harder, we have to change the relations between
the resistors around the op amp.
If we make the two left hand ones smaller than the ones on the right, we’re essentially
creating two e
ff
ects that’ll synergize. First, the voltage swing at the non-inverting input will
get bigger. Because where before, the 50% voltage divider was e
ff
ectively halving the
signal’s amplitude, now, we’re only cutting it down by a relatively small margin. And
second, the op amp’s output will have to push and pull a lot harder through the feedback
resistor to match the bigger swing at the non-inverting input.
The resistor values I’ve chosen here will actually give us a slightly louder output for a 12 V
CV input than what we were aiming for. I did that because in a eurorack system, modules
like envelopes or LFOs won’t be pushing out voltages bigger than 10 V, tops.
With these
resistor values, we’ll get a 10 V peak-to-peak output for a 10 V CV input
.
Ensuring
that we can actually reach the maximum output volume when controlling the circuit
with another module
.
Speaking of connecting to other modules:
in order to be able to do that,
we’ll have to add
a CV input- and a signal output socket.
Also, we’ll keep the manual CV control in the
You can try this chapter’s circuit in a simulator. I’ve already set it up for you right her
you can change all values by double clicking on components.
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