[sdiy] basic inverting op amp question 101

Tom Wiltshire tom at electricdruid.net
Mon Dec 30 15:03:34 CET 2019

At the simplest level, it’s a trade-off between current and noise. Lower value resistors generate less noise, but use more current (and provide lower input impedance) and higher value resistors do the reverse. So you tend to see “compromise” values around 10K-100K. 1Meg is getting “big” and 1K or less is getting “small”.

Years ago I had the same question and since the internet didn’t exist yet, I did some experiments on my breadboard with a 741 and discovered that 1M upwards was noticeably noisier, but that anything between a few K and a few hundred K didn’t really seem to make much odds.


       Electric Druid
Synth & Stompbox DIY

> On 30 Dec 2019, at 13:17, bbob <fluxmonk at gmail.com> wrote:
> (please excuse the noobiness).... 
> in a basic inverting op-amp circuit, where the input and feedback resistors are equal, the gain will be -1... but what are the pros/cons that determine the choice resistor value?  i commonly see/have used 1k, 10k, 47k, 100k in synth circuits, but what design considerations drive those choices of values?   my immediate application is basic output buffers on a LFO, and 1k seems to be working fine, but it got me to thinking (uh oh).
> thx, b
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