[sdiy] TL07x as output stage?

[rsdio at audiobanshee.com]

Complaining about the open loop output impedance is rather strange, because I can't imagine any reason to design a line-level output stage with an open loop. The impedance will be controlled by the feedback, so it will be different. Am I missing something?


Thanks for the links, Olivier!

On Feb 25, 2016, at 2:14 PM, Olivier Gillet <ol.gillet at gmail.com> wrote:
> Not necessarily... You can alleviate the problem described above with:
> * A small resistor in series with the output (if you don't mind the
> slight voltage drop when driving low-ish impedances - it's very
> commonly done in Euroland for anything that doesn't require precision,
> unlike pitch CVs)
> * And/or a small cap between V- and Vo, and a resistor "in the loop".
> (In Euroland, you'll find this more commonly in circuits producing or
> manipulating pitch CVs, such as the output stage of a MIDI to CV
> interface).
> 
> This has the additional benefit of isolating the op-amp if another
> signal is patched there by mistake.
> 
> See:
> http://www.st.com/web/en/resource/technical/document/application_note/CD00176008.pdf
> http://www.analog.com/library/analogdialogue/archives/38-06/capacitive_loading.html?doc=CN0343.pdf
> (Figure 8, Figure 3)
> 
> On Thu, Feb 25, 2016 at 10:07 PM, neil harper <metadata at gmx.com> wrote:
>> Hey guys,
>> When referring to the final opamp stage of a line-level output - I recently
>> read: "any popular op-amp known to the author, except for the TL06x, TL07x,
>> or TL08x series (their high open loop output impedance
>> makes them unstable with capacitive loads such as cables"
>> 
>> I've always been a fan of TL07x's (since I have hundreds of them) and this
>> is my usual go-to op-amp for anything, including this final output stage.
>> Should I be looking for alternatives?