[sdiy] emulating bi-polar capacitors
mr at analogue.org
Tue Feb 15 21:30:54 CET 2022
Hej Danjel and others,
I don't recall seeing any hard facts about non-polarized electrolytics
performing better than ordinary polarized in audio circuits, but still they
occasionally turn up in designs. Would be interesting to hear why they
sometimes are preferred by audio designers, though! :-)
I searched for "non-polarized" in Douglas Self's reference book "Small
Signal Audio Design" and found a couple of applications where they actually
do make sense - but it's a practical reason rather than an audio
DC blocking in inputs & outputs, where it's possible that the connected
gear pulls the voltage way off ground level, and you never know in what
Douglas Self writes:
"C2 is a DC-blocking capacitor to prevent voltages from ill-conceived
source equipment getting into the circuitry. It is a non-polarized type as
voltages from the outside world are of unpredictable polarity, and it is
rated at not less than 35 V so that even if it gets connected to defective
direct-coupled equipment with an op-amp output jammed hard against one of
the supply rails, no harm will result."
Any other good reasons for using them?
And sorry, no - I don't have any better advice than what has already been
Den tis 15 feb. 2022 20:43Barry Klein via Synth-diy <synth-diy at synth-diy.org>
> I used one in a typical dual op amp triangle oscillator on the phaser in a
> Music Man amp design. It made a difference in extremely slow sweep symmetry
> and also I had a function where you pull the knob out and could fix the
> sweep wherever you wanted it. After I left the whole thing was redesigned.
> Maybe I didn’t know what I was doing…. 45 years ago… Self-taught by
> Electronotes. What a fun job before work politics F’d it all up.
> > On Feb 15, 2022, at 11:32 AM, Mike Bryant <mbryant at futurehorizons.com>
> >> I've never bothered, I've never noticed a difference in just using a
> 47μ instead of playing about with back-to-back capacitors even after the
> thick end of 40 years the earliest stuff I built that way still has
> capacitors that capacitate just fine.
> > --
> >> Gordonjcp
> > Agreed. Unless you actually have a reverse DC bias voltage (in which
> case rotate the capacitor) I've never understood any need for the
> non-polarised capacitors. Most mixing consoles are full of thousands of
> them either feeding the input or fed from the output of an opamp via a
> resistor to ground.
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