[sdiy] Voltage Feedback Resistors and Circuit Stability

[tpuefke]

>100k shows up a lot in eurorack circuits since it's the defacto input impedance.

Could it be that a lot of (more recent) Eurorack circuits are heavily inspired by Ray Wilson? ;-)

As to the context and design intention behind my question, in this case it's less specific, general curiosity. I'm just trying to weigh the options, for example for small circuits, or like Mattias mentioned in low-noise signal paths.

I was suspecting that input impedance plays into this, but for op-amp stages other than inputs there would be no obvious reason to use values as high as 100k unless to conserve power.

thanks,
Tom

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Friday, 13. November 2020 22:48, ben gebhardt via Synth-diy <synth-diy at synth-diy.org> wrote:

> (first time poster!)
>
> Hi Ian,
>
> Usually in my experience one would scale down resistors around an opamp to generally lower the johnson noise contribution. Additionally there is something to be said for high impedance nodes and coupling in radiated noise from external sources but usually that's only problematic over 1M.
>
> As to why it's commonplace, I'm not sure which schematics you are referring to, but as mentioned, 100k shows up a lot in eurorack circuits since it's the defacto input impedance.
>
> There are a ton of other factors in the decision of this resistor, it's hard to generalize rationale w/o the context of the circuit and design intentions. Happy to comment on something more specific.
>
> Ben.
>
> On Friday, November 13, 2020, 04:16:17 PM EST, Mattias Rickardsson <mr at analogue.org> wrote:
>
> Mattias Rickardsson <mr at analogue.org> skrev:
>
>> And perhaps 10k-22k for TL06x.
>
> I should have written 22k-47k.
>
> /mr
>
>>
>
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