[sdiy] Newbie alert: opamp resistor values

[harrybissell at wowway.com]

In general, lower resistor values reduce noise (but the resistors are probably
not the dominant noise source anyway)... and higher values reduce circuit loading.

Most synth CV (and even signal) inputs are 100K... you could stack 10 of them
in parallel and still look like a 10K load to the driver.

1M would be better for inputs like a guitar pickup, etc

I use 49.9K as a good trade (imho) between low noise and high impedance. I'd
consider it 'medium impedance'   :^)

Some opamps like the NE5532 should probably not use input resistors above 1K,
if you need higher, use the TL07x series.

BTW I like the 4558 opamp for low noise and reasonably stable operation
(the TL07x can go unstable driving a capacitive load...)

H^) harry



On Thu, 08 Jan 2009 09:34:54 -0800, David G. Dixon wrote
> Here's another question from a relative newbie:
> 
> What are the basic guidelines for selecting absolute resistor values 
> for opamp circuits?  For example, say one needs a unity-gain 
> inverter or summer, and is using a generic FET-input opamp (TL07x, 
> say).  What determines whether one uses 10k, 100k, or 1M for the two 
> resistors, or something inbetween?  Now, what if input impedance is 
> not an issue (i.e., the incoming voltage is well buffered)?
> 
> David G. Dixon
> Professor
> Department of Materials Engineering
> University of British Columbia
> 309-6350 Stores Road
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Harry Bissell & Nora Abdullah 4eva