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Alternatives to Aluminium Electrolytic Capacitors

 

Hi all,
?
I've been using polarised aluminium electrolytic caps in my designs as per the advice of members here and also how they are used in schematics like the Alice, etc.
?
This has been going great, though I'm currently working on a pencil mic and to fit into the tiny space my circuit board (and also the mic body) has gotten very long, so I was hoping I might be able to shrink down some of my largest components — great big capacitors. I have already been following the guidelines for minimum component spacing from PCBWay, and this has helped, smaller component footprints would help further.
?
My understanding is that aluminium electrolytic caps are a great combo of cheap, able to reach large values, and stable in a large range of conditions. I briefly looked into MLCC's, but quickly found multiple sources saying that these are not stable enough to be suitable for precision audio circuits.
?
All of the evidence I've found so far tells me that the polarisation of electrolytic caps is a limitation rather than a useful design trait, but I wanted to double-check with you folks whether there is some secret usefulness to the polarisation when it comes to the subtleties of microphone building. If polarisation is required, that limits my choices.
?
In light of that, is there an alternative kind of cap I could be using in my designs that is more compact, perhaps with the trade-off of being more expensive? I only need a handful and I'm not mass-producing these, so components in the range of dollars instead of cents is not a big deal in this case — I'm much more concerned about making a smaller PCB. The only values for electrolytic caps that I'm using in this design are 47uF and 4.7uF, so even if there is an alternative for the smaller value that will help a little.
?
Cheers,
Zander.
 

I have been using 22uF and 47uF MLCC capacitors for coupling caps with no issues. The impedance?is far lower than Aluminum electrolytics. There is one catch -- the Capacitance goes down significantly?with voltage across?the?capacitor. See . If you take that into account you will be fine. I wound't use them for things that require precise capacitance?such as filters etc.?

Jules.

On Tue, Dec 17, 2024 at 8:51?PM Zander via <zanhulme=[email protected]> wrote:
Hi all,
?
I've been using polarised aluminium electrolytic caps in my designs as per the advice of members here and also how they are used in schematics like the Alice, etc.
?
This has been going great, though I'm currently working on a pencil mic and to fit into the tiny space my circuit board (and also the mic body) has gotten very long, so I was hoping I might be able to shrink down some of my largest components — great big capacitors. I have already been following the guidelines for minimum component spacing from PCBWay, and this has helped, smaller component footprints would help further.
?
My understanding is that aluminium electrolytic caps are a great combo of cheap, able to reach large values, and stable in a large range of conditions. I briefly looked into MLCC's, but quickly found multiple sources saying that these are not stable enough to be suitable for precision audio circuits.
?
All of the evidence I've found so far tells me that the polarisation of electrolytic caps is a limitation rather than a useful design trait, but I wanted to double-check with you folks whether there is some secret usefulness to the polarisation when it comes to the subtleties of microphone building. If polarisation is required, that limits my choices.
?
In light of that, is there an alternative kind of cap I could be using in my designs that is more compact, perhaps with the trade-off of being more expensive? I only need a handful and I'm not mass-producing these, so components in the range of dollars instead of cents is not a big deal in this case — I'm much more concerned about making a smaller PCB. The only values for electrolytic caps that I'm using in this design are 47uF and 4.7uF, so even if there is an alternative for the smaller value that will help a little.
?
Cheers,
Zander.



--
Best Regards,

Jules Ryckebusch

214 399 0931
 

开云体育

By "polarization", do you mean the fact that electrolytic capacitors are not bi-directional, or that they need to see a DC voltag eacross them?
There are "bipolar" electrolytic capacitors. they are generally considered capable of better performance than polarized ones. However they usually are bigger than polarized ones, because they are constituted of two polarized capacitors head-to-tail.

Polarization of electrolytic capacitors is not a "useful design trait", it's inherent in the formation of the dielectric, and it's only a limitation in the sense that they are not supposed to operate with reverse DC voltage across them, which is extremely simple to ensure in any half-decent design.

A frequent alternative to aluminium electrolytics is tantalum. They offer larger capacitance vs. bulk than AL types, but are not much loved because of their fragility vs. reverse voltage. They also are not considered sonically neutral.

As to using MLCC's for coupling, as Jules mentioned, their value is not particularly stable, but it's also the case with electrolytics.
The usual technique for minimizing the effects of non-linearity is to over-specify the value. The typical audio adage is to make capacitors 10 times bigger than required for LF extension, i.e. if you want to pass 20Hz nicely, you should calculate the -3dB LF turnover frequency at 2Hz. But for distortion reduction, this value should be divided by 5, for 0.4Hz.
Dielectrics used in large value MLCC's are very non-linear (more than electrolytics). The exception would be C0G/NP0 types but they don't offer the same density as the other types. The largest capacitance in C0G/NP0 MLCC's is 0.47 uF. It's a 1206 part (3.2x1.6x1.6mm).

I suggest you check Cyril Bateman's paper

Le 18/12/2024 à 03:51, Zander via groups.io a écrit?:

Hi all,
?
I've been using polarised aluminium electrolytic caps in my designs as per the advice of members here and also how they are used in schematics like the Alice, etc.
?
This has been going great, though I'm currently working on a pencil mic and to fit into the tiny space my circuit board (and also the mic body) has gotten very long, so I was hoping I might be able to shrink down some of my largest components — great big capacitors. I have already been following the guidelines for minimum component spacing from PCBWay, and this has helped, smaller component footprints would help further.
?
My understanding is that aluminium electrolytic caps are a great combo of cheap, able to reach large values, and stable in a large range of conditions. I briefly looked into MLCC's, but quickly found multiple sources saying that these are not stable enough to be suitable for precision audio circuits.
?
All of the evidence I've found so far tells me that the polarisation of electrolytic caps is a limitation rather than a useful design trait, but I wanted to double-check with you folks whether there is some secret usefulness to the polarisation when it comes to the subtleties of microphone building. If polarisation is required, that limits my choices.
?
In light of that, is there an alternative kind of cap I could be using in my designs that is more compact, perhaps with the trade-off of being more expensive? I only need a handful and I'm not mass-producing these, so components in the range of dollars instead of cents is not a big deal in this case — I'm much more concerned about making a smaller PCB. The only values for electrolytic caps that I'm using in this design are 47uF and 4.7uF, so even if there is an alternative for the smaller value that will help a little.
?
Cheers,
Zander.
 

Thanks heaps Jules and Jerry!
?
Great resources and info as always — you've given me everything I need to solve my problem and it's very much appreciated.
?
Cheers,
Zander.

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