[sdiy] Buffered question

David G Dixon dixon at mail.ubc.ca
Wed Dec 30 04:46:41 CET 2020

Most of the common opamp circuit configurations also act as buffers.  What
that means is that the opamp will supply as much current as is required to
maintain the desired voltage regardless of the downstream impedance.
However, if there is something like a diode inbetween the opamp's output and
the destination, then you have to be very careful.  For example, the classic
two-diode opamp rectifier does not buffer, and must be followed with a
buffer generally.  This is one of those areas where it is easy to make a
design mistake, and then when your design doesn't do exactly what it is
supposed to, you have a forehead-slapping moment when you realize that you
have inappropriately taken opamps for granted.

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of
Kristian Blåsol
Sent: Tuesday, December 29, 2020 6:41 AM
To: synth-diy mailing list
Subject: [sdiy] Buffered question

[CAUTION: Non-UBC Email] 

A question about opamp buffers or voltage followers. So one of those
circuits makes sure that whatever you plug in to the output of the buffer
wont affect whatever you have on the input of the buffer... right?

But there are so many different circuits you can make with an opamp, is
there any of those that in itself IS a buffer, or do ALL other opamp
circuits need buffering after it for the output to not affect the input?

For example: a comparator, isnt that already buffered in itself? Since the
output is either ground or +v?

And how about a mixer/summing amplifier, op-amp as an amplifier, high and
low pass filters.

Im thinking so I dont put a buffer on an already buffered signal... :)

Thanks in advance,


Kristian Blåsol

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