Would you have a reference for that?
No, it is obvious, based on the operating principle of electrochemical capacitors.
It happens only at very high signal levels across the Capacitors, more than realistic. You need to be just exceeding the reverse voltage on one side, causing rectification effects to show up and at a specific fraction of the formation voltage.
If so, the two separate H2 dominant distortion mechanisms cause cancellation, that is an H2 and THD minimum.
As said, it is not something to be used in practical circuits to lower polar capacitors HD in audio circuits.
If DC coupling (and servo) idls not practical, if foil & film construction capacitors are not practical, if metalised film capacitors are not practical, the best choice are bipolar electrochemical capacitors, preferred two in series for line level DC bias or not.
Finally, if polar electrochemical capacitors must be used, use two in anti-series or anti-parallel and consider the biasing situation in the presence of large DC voltages to be blocked.
The circuit probably will have to be tested in the real world using an AP2 and priority should give to avoiding or minimising audible fidelity impairments, as opposed to signal fidelity (e.g. for HD do not use THD [signal fidelity] but psychoacoustic weighting of harmonics [audible fidelity].
I would think nobody picks an electrolytic signal cap other than for size or economic reasons.
Funny, this thread is full of posts asserting that these capacitors are the best ever, nothing is better and that there is never a need to use something better and somehow DC magically makes them better, instead of worse. Aging is never mentioned, so clearly it's "perfect sound forever (TM)".
Nobody said:
"I would have figured out a DC coupled scheme, or used film capacitors, but the beastly accountants didn't let me! It's all the accountants fault!"
It is, btw the accountants fault. I'm part qualified accountant, Assistant Director Financial Control in series Enterprises and CFO in a startup that now makes middle double digit turnover after a decade were my highest positions in that line of work. Sh!t work, excellent pay, better than most Merc's make (don't ask how I know).
So, if not blaming "the accountants", it is obvious that the global believe is that there is nothing better.
Bypassing said cap with a PP cap is also an option.
That is mainly another old wives tale.
I say mainly, because there are narrow cases where bypassing with a smaller value capacitor of different quality improves the situation, but usually the result is that the much larger capacitor dominates in the audio range and multiple resonant LC tanks at higher frequencies.
Again, I am absolutely guilty of having fallen for this old wives tale myself, for years if not decades. I eventually got to a point where I could do a lot of tests, with really horrorshow gear and large scale listening tests and rejected this as "BS".
Proof, imagine a (typical) 47uF polar elcap with 1R ESR. And an 0.1uF PP bypass. The frequency where the bypass capacitor carries ~ 30% of any signal current is ~ 1.6MHz. that's higher than my Heavy Metal Loving Cats can hear while playing 192k masters of Rush.
It also holds for RF bypassing, 3 x 1uF 0402 SMD is preferred to 1uF, 0.1uF and 0.01uF (classic old wives tale bypassing).
Even 3 x 1uF 0603 is preferred to 1uf 0603, 0.01uF 0402 and 0.01uF 0201. That surprised me, incidentally, I didn't expect that.
DC servo would be another option if a bipolar power supply is used.
This is kind of what I suggested, but to handle 48V phantom power with DC coupling the positive rail should be > 48V and the common mode range for the circuit's input must include 0V to + 48V.
But yes, in 2024 it is the the solution that falls under BFBFOTO.
In a post I nixed as it made the natives restless, I suggested that taking the folded cascode "enhanced Cohen" circuit from the THAT presentation on microphone preamplifiers could be used.
It would need to be flipped in polarity for a PNP input pair but would be trivial to be made to include -0.5V to 48.5V common mode range as long as we have at least 50V DC available or allow +46V phantom power (it is within IEC spec).
But there is no problem anyway and talking about polar electrolytic capacitors being a "potential trouble source" and in need of is very obviously a Red Cloth to many.
So PLEASE use the cheapest, physically smallest and cheapest Scheena made garbage 22uF...47uF polar caps in phantom powered microphone input coupling.
Follow the advise of all these big famous people who build the best consoles in the world and know everything and have nothing left to learn
I have nothing to add.
Back to "constuctrive threads" (pun intended) about making tube microphones, Tube and J-Fet preamplifier intentionally designed as "electronic crayons".
Over and out.
Thor
