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Evaluating Electrolytic Capacitors Specified for Audio Use: A Comparative Analysis of Electrical Measure- ments and Capacitor Distortion Products in Line Level Interstage Coupling Applications

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This paper provides a number of comparative, quantitative evaluations of 10 different makes and models of electrolytic capacitors. Models range from expensive parts specified for use in audio circuits to low-cost general-purpose parts. The datasets comprise out-of-circuit electronic measurements, total harmonic distortion (THD) fast Fourier transform (FFT) sweeps, and cumulative distortion products resulting from 31-tone stimulus performed on the components in a circuit designed to emulate a typical line-level audio recording and mixing console. Results are examined in an effort to identify any measurable properties that may distinguish "audio capacitors" as outliers from their general-purpose counterparts.

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JAES Volume 68 Issue 7/8 pp. 559-567; July 2020
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Scott Dorsey
Scott Dorsey

Comment posted May 18, 2021 @ 15:32:44 UTC (Comment permalink)

What is most interesting about this paper is that it operates the capacitors over the zero-crossing region.  I was told by Marshall Leach when I was an undergraduate to always stay away from the zero-crossing with electrolytics as higher distortion will result, and to always make sure there was considerable DC bias on any electrolytics used for coupling.

On the other hand in a recent paper, Gaskell at McGill reports a higher measured distortion when both electrolytics and film capacitors are given substantial DC bias.  So what is the actual optimal regime?

Also the source impedance seen by the capacitors in this case seems rather high, meaning that there will be little ripple across them, and Doug Self claims that this is the key to reducing distortion in coupling capacitors.  It would be interesting to see if the differences between capacitors become more evident if either the values of the capacitors are reduced or the input impedance of the stages being driven are reduced.

So from my perspective this paper may answer some interesting questions but it opens up a whole larger set of questions that are just as interesting.

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AES - Audio Engineering Society