[sdiy] Voltage Feedback Resistors and Circuit Stability

[David G Dixon]

After many years of building circuits, one acquires a basic sense of where stability caps may be required.  Often, I discover that an opamp circuit is ringing a bit when I go probing around with the scope.  I tend to lay out the pads for stability caps on most inverting opamp circuits, but often don't stuff them unless I find that I have to.  I keep a big stash of ceramic 101s for just that purpose.

  _____  

From: Chris McDowell [mailto:declareupdate at gmail.com] 
Sent: Saturday, November 14, 2020 8:44 PM
To: David G Dixon
Cc: Bernard Arthur Hutchins, Jr; synth-diy at synth-diy.org
Subject: Re: [sdiy] Voltage Feedback Resistors and Circuit Stability


[CAUTION: Non-UBC Email]I'm happy you said this. I had written out a post suggesting to build circuits before trying to optimize resistor noise performance. started sounding like the responses that miss the point and don't answer the op's question, so I deleted it hehe.  

yours didn't feel this way David, there was context and previous responses. I agree though, and I'm generally very happy when my hardware sounds "old" (usually jusy means noisey heh) I also use whatever value I have the most of on board, which often enough is 100k, with at least the option for caps in parallel with feedback resistors. 

Chris 


On Nov 14, 2020, at 7:13 PM, David G Dixon <dixon at mail.ubc.ca> wrote:



 
I've actually been accused of designing modules that sound "too clean" and I use lots of 100k resistors all over the place.  This is one of those problems that probably isn't really a problem.

  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Bernard Arthur Hutchins, Jr
Sent: Saturday, November 14, 2020 11:36 AM
To: synth-diy at synth-diy.org
Subject: [sdiy] Voltage Feedback Resistors and Circuit Stability


[CAUTION: Non-UBC Email] 

 AWKWARD Questions  



(1)   In a synthesizer with standard signal levels of +/- 5, has anyone even HEARD Johnson noises, let alone been able to attribute it to a particular resistance?    

  

(2)   Given a 100k resistor, how does one (specific circuit/methodology please) observe/hear its Johnson noise as compared to a 10k? 



-Bernie                             

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