[sdiy] Buffered question

Roman Sowa modular at go2.pl
Wed Dec 30 09:02:34 CET 2020

If you need opamp buffer or not depends on the answer to simple question 
- is any expected load connected to that output able to affect the 
signal significantly? And by "significatnly" I mean "to the level you 
care", for example 10% for audio or, say,  0.1% for control voltage.
To put it in simple terms, maybe even call it a rule of thumb - if load 
impedance is 100 times bigger than last stage's output impedance, you 
don't need a buffer.
So if you're making photodiode light detector and expected load is only 
very high impedance ADC you don't really need a buffer. Likewise if 
you're making opamp based summing amplifier that is expected to drive a 
speaker, then you need a buffer.


W dniu 2020-12-29 o 15:41, Kristian Blåsol pisze:
> Hello,
> 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
> -- 
> ---
> Kristian Blåsol
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