[sdiy] emulating bi-polar capacitors
David G Dixon
dixon at mail.ubc.ca
Wed Feb 16 03:00:23 CET 2022
I use back-to-back electrolytics to block DC in my four-quadrant multiplier circuits. I'm paying exactly $0.02 for 47uF electrolytic caps from Tayda, so it is an absolute no-brainer.
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Mattias Rickardsson
Sent: Tuesday, February 15, 2022 12:31 PM
To: Barry Klein
Cc: Synth DIY
Subject: Re: [sdiy] emulating bi-polar capacitors
[CAUTION: Non-UBC Email]
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 performance reason:
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 direction.
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 said. :-)
Den tis 15 feb. 2022 20:43Barry Klein via Synth-diy <synth-diy at synth-diy.org> skrev:
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> wrote:
>> 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.
> 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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