Which capacitors to use? (polyester, polycarbonate, ceramic, tantalum, electr.)

[analogix]

I'm building an DIY audio project from 1980 (ETI vocoder) and I'm a little confused about the capacitors it lists in the parts lists.
Obviously a lot has changed in the past 44 years, so when they list the following, which types should I order as listed and which ones should I replace with something else today?

• Polycarbonate
• Polyester
• Ceramic
• Tantalum
• Electrolytic

From what I've been told, tantalum capacitors can be dangerous when used in power supplying situations as they can fail and short circuit the entire rest of the circuitry, so these should be replaced with electrolytic capacitors as far as I've been told.

[Konkedout]

The answer is a bit complicated.  Best to show a schematic diagram.  The capacitors generally need to be considered individually based on application.  A polycarbonate or polypropylene type might be used for audio coupling, and an electrolytic for power supply filtering.  Do not swap them!  (Also would not be practical to have 220 uF in a polycarbonate or polypropylene.

1) Are you planning to use through hole or surface mount?
2) Ceramic is complicated because there are different ceramic dielectric types.  Generally you do not want to replace a stable ceramic dielectric with a "High K" or semi-stable one.  If functionality is your only concern, you could probably replace all capacitors with NP0 ceramic.  But if you wanted to get microfarads in NP0 ceramic, it would be huge and expensive.
3) I think you could probably replace polyester and polycarbonate with polycarbonate.  But I do not think of plastic film capacitors as being very common in surface mount form.
4) I once had a design in which I replaced a common aluminum electrolytic capacitor with a low ESR (Equivalent Series Resistance) one.  Low ESR would generally be considered "better".  But that change did not work and I needed to undo it!!!

Anyway, best to present as much detail as you have about the design.

[golden_labels]

That tantalum one (C9) seems to only be used to filter power rails. I suppose they wanted a small capacitor. On the schematic it appears to be 5 mm diameter. But nowdays normal aluminium electrolytic capacitors offer the same parameters in an equally small package, and they cost single to a dozen cents.

As for the risk: all eletrolytic capacitors may fail in a violent manner. Tantalum ones got a bad rap, because they are more vulnerable to overvoltage than their brothers. If this happens, their demise tends to be more spectacular too. But don’t look at them as walking bombs. In this design I would switch to aluminium one, because it’s a bit cheaper.

There rest of capacitors seems to be chosen for their stability or just being a jellybean component.

As for wrapping your head around all the types, Wikimedia Commons has two nice diagrams you may use as a general map:

• Capacitors applications
• Capacity vs rated voltage

[Ian.M]

Tantalums really didn't like high dV/dt when operating at a significant fraction of their nominal rated voltage - the problem was high dV/dt causes high transient currents through the capacitor, which concentrate at weak spots in its dielectric, causing hot-spotting and possible thermal runaway failure.  See https://www.kyocera-avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf

Generally, modern low ESR aluminium 'wet' electrolytic capacitors have comparable performance characteristics to tantalums at a far lower price point, but greatly inferior life to a properly derated tantalum capacitor.   However aluminium solid polymer electrolytics are nowadays readily available and have superior characteristics to tantalums, comparable life, and aren't little incendiary bombs waiting to trigger, don't contain conflict minerals, and are at a comparable or lower price point.   

A bigger issue is the change in commonly available film capacitor dielectrics.    The favoured high quality low loss dielectric back in the '80s was polycarbonate, and for low leakage, polystyrene but the last factories manufacturing capacitor grade polycarbonate and polystyrene films closed circa Y2K, so both types of film capacitor are only available as $expen$ive$ N.O.S. of dubious quality due to possible degradation in improper storage.

As the ETI design is full of complex analog filters, capacitor stability and precision are the main factors that will drive your choice of replacements for the original polycarbonate film capacitors.

[brucehoult]

Damn! That's an ambitious project! A lot of duplicated circuits, a lot of knobs, and lot of chips too -- including 4000-series CMOS XOR gates and shift registers and analogue switches.

I see the 4030 XOR at Mouser, even in DIP. I didn't see the 4006 shift registers.

I think you may be in for some redesign. I'd find a fast microcontroller with a good ADC and redo everything DSP-style. But good luck!

[analogix]

1) Are you planning to use through hole or surface mount?

All through hole components.

Anyway, best to present as much detail as you have about the design.

Sure. Apart from posting the PDF with the schematics I don't have much to add (mostly due to ignorance on my part).
A lot of the vocoder is already done such as the main ("analysis/synthesis" or "filter") board. I used the components listed in the DIY article for that.
Then there's a bunch of smaller boards that are halfway done (LED PPM meter boards, input amp boards, slew rate board, output amp board, internal excitation board), and I'm missing some components for those, including capacitors of various types.

So, as I understand it from the replies here: there's no "one type for all" even in this design.
I'm looking at Farnell's website as I'm creating an order there, and I don't see any entries for either polyester nor polycarbonate capacitors, and I understand why, from Ian.M's reply stating that they are no longer produced.

Generally, modern low ESR aluminium 'wet' electrolytic capacitors have comparable performance characteristics to tantalums at a far lower price point, but greatly inferior life to a properly derated tantalum capacitor.

You mean a tantalum that has say a 50V rating and used for circuitry using only 12V will likely perform much better (and have lower risk of failing) than say one that is rated at 16V in the same circuit?

However aluminium solid polymer electrolytics are nowadays readily available and have superior characteristics to tantalums, comparable life, and aren't little incendiary bombs waiting to trigger, don't contain conflict minerals, and are at a comparable or lower price point.

Are those spceialized electrolytic capacitors? Should I look for "solid polymer aluminium electrolytic capacitor", or are you referring to commonly available modern electrolytic capacitors in general?

   

A bigger issue is the change in commonly available film capacitor dielectrics.    The favoured high quality low loss dielectric back in the '80s was polycarbonate, and for low leakage, polystyrene but the last factories manufacturing capacitor grade polycarbonate and polystyrene films closed circa Y2K, so both types of film capacitor are only available as $expen$ive$ N.O.S. of dubious quality due to possible degradation in improper storage.

No wonder I couldn't find any at Farnell.
Should I look for "film capacitors" wherever the DIY article states any of these?
 

As the ETI design is full of complex analog filters, capacitor stability and precision are the main factors that will drive your choice of replacements for the original polycarbonate film capacitors.

True. The more precise values/stability I can get the better the audio results.
I'm aiming for a good as possible result within a reasonable cost of course. I'm guessing this also means that I should order the components I'm missing (mostly resistors and capacitors now) from reputable dealers (Farnell, Mouser, Digikey etc.) and stay away from low cost sites such as Tayda etc. even though there's probably a considerable saving involved.

[TimFox]

The common through-hole "film capacitors" now are PE (polyester, formerly called Mylar^TM) and PP (polypropylene)
The former are mediocre, with mediocre loss (dissipation) and dielectric absorption (hysteresis).
The latter are much better, with excellent loss and dielectric absorption, but physically larger for the same capacitance and voltage.

Ceramic capacitors have an unwarranted bad reputation in audio, since older disc capacitors in larger values were crummy dielectrics (X7R and Y5V).
Leaded MLCC capacitors in the good dielectric (C0G or NP0) are now available in larger values, but limited voltage spec for large capacitance.

[Kleinstein]

For most of the supply decoupling / filtering low ESR Al electrolytics can replace old tantalum caps. With small values like 1 or 2.2 µF  also X7R ceramic can work OK. The 7912 regulator still wants a real electrolytic at the output and may not work with the low ESR of X7R. The main real need for tantalum is at low temperature and if physical size matters.

The polycarbonate caps can usually be replaced with polyester or PP (usually still THT) and for the smaller ones also with C0G ceramics (SMD).
AFAIR polycarbonate has a slightly lower temperature effect than polyester or PP. C0G gets a bit expensive for larger size, like > 10 nF, but is otherwise good with even lower TC. SMD film capacitors are rare and often a bit more expensive.

The real issue with tantalum caps is not that they can fail short - other capacitors can do that as well. The point is that if they fail short and the supply / circuit can deliver a high current / power this can be enough to ignite the capacitor from the inside and they can burn violently, a bit like a signal flare or thermite. With the 7812/7912 regulators one is likely OK in this respect.

[Haenk]

The common through-hole "film capacitors" now are PE (polyester, formerly called Mylar^TM) and PP (polypropylene)

Or use EVOX SMR series - those are PPS, which I would rate close to the then used PC. However they don't come with a wide range of capacity/voltage, which is a huge downside. Not cheap, either...

[Terry Bites]

An analog vocoder uses a lot of filters.
The filter cap can actually be any film type, drift over temp doesn’t matter much, the filters are not that narrow. I doubt that polycarbonate caps are absolutely needed.
Nothing critical in the envelope followers or VCA's either.

"Polycarbonate film capacitors are preferred to polypropylene capacitors when available because they have a very balanced, musical sound with very little coloration"... Yeah, and I'm the rightful king of Ireland.

I built an elektor vocoder one back in the dark ages (1981). It specified all MTK caps throughout. It looked great, worked well and left me bankrupt- Schrack attack!
I lost it and the pile of invoices. But see attched for schematics.

Dump the tants, they are bound to fail at some point in the future.
Upgrading some opamps in the audio chain might be worth looking into. It goes without saying that any 741's bring shame on your pcbs.

[analogix]

Thanks for all the replies.
I understand the choice of capacitor type depends on its application in addition to physical size limitations, so here are the various parts of the vocoder where I've also added the types of capacitors listed in the parts list.

First, here's the analysis/filter board with its 14 channels.
I've already completed this board several years ago (using the component types listed), but have a feeling I might need to replace the two tantalum ones (C13, C14) of channel 1.
However, I'm not sure if I should do that since they appear to be in the audio signal path and electrolytics might have an undesired change to the sound....


Here's a more complete schematic of the above and all filter channels. I've written (in red) the known filter types. As for the other ones (see the list to the bottom-left), I can't see from the magazine article which types they are, and can't remember how I chose them when building the board. I'll have to dig out the board to visually inspect, which I can do if necessary. But like I said, the board has already been assembled.


Here are the input amps. There are three tantalums, but surprisingly there are electrolytics in what I understand is the power-supply path (which is good). Do the tantalums need replacing here?


Here are the LED PPM boards. There's one tantalum, which I wonder why they've used that instead of an electrolytic.


Next up is the output amp board. From what I understand, tantalums are used here in the power supply section. Should I replace them with electrolytics?


Here's the slew-rate board. Two electrolytics in the power-supply path like I understand it should be done.


Finally, here's the internal excitation board with just one tantalum.

[TimFox]

The tantalums in the signal path were probably chosen for low DC leakage current, which current would shift the bias voltage of the following stage.
If you have polycarbonate capacitors to replace original polycarbonate units, go for it.
If building it from scratch, I would use polypropylene for those values.  Both are better than polyester (Mylar^TM).  Polycarbonate seems be almost extinct, however.

[Kleinstein]

The tantalums in the signal path are for AC coupling the signal. If at all the capacitors would cause distortion below the normal audio range. For the normal audio the voltage at the capacitor is small and thus no issue. The main issue with the electrolytic capacitors would be if they get always the right polarity.

There is no real need for PP capacitors, PE (MKS) should be good enough. This difference is rather small and additional loss at the capacitors would only give a minute change in the filter characteristic - less than from the tolerances.  PP capacitors are usually physically larger, which could be an issue for the larger values. For the small ones, like < 10 nF C0G ceramic is a real alternative.

[schmitt trigger]

Wow! Good ol' analog audio processing. Love it. 

My two Yen; not related to your capacitor questions, but something most important: The OTA's availability.

Both the CA380 and the LM13600/13700 have been obsolete for eons. I wouldn't start investing too much money and effort on this project, unless I had already procured sufficient of these.

[Kleinstein]

The LM13700 is still available and not maked as EOL.

[schmitt trigger]

I stand corrected.

[analogix]

To summarize, let me see if I've got this right:

- 1980s Tantalum: replace with "low-ESR" electrolytics if used within power-rails.
Otherwise use "Aluminium solid" electrolytics for better performance replacements, or modern day tantalums for applications other than power rails.
- 1980s electrolytics: replace with modern day electrolytics
- 1980s ceramic: replace with "NP0" ceramics (for low values). Stay away from "High-K" or "Semi-stable" ceramics.

What confuses me are 1980s Polyester and Polycarbonate capacitors.
Having read further into the subject both these go within the group of "film capacitors",
and Polyester often under the abbreviation of "PET" or named "Mylar" while
Polycarbonate is abbreviated "PC".

There is no real need for PP capacitors, PE (MKS) should be good enough. This difference is rather small and additional loss at the capacitors would only give a minute change in the filter characteristic - less than from the tolerances.  PP capacitors are usually physically larger, which could be an issue for the larger values. For the small ones, like < 10 nF C0G ceramic is a real alternative.

I'm confused 
"PP" are Polypropylene capacitors, right? But they weren't mentioned in the ETI vocoder article.
Polyester and Polycarbonate on the other hand were, but is it correct to assume that these are both a type of "film capacitor" which are interchangeable with each other?
Or is there a specific modern-day film capacitor replacement for Polyester capacitors, and likewise a specific modern-day replacement capacitor type for 1980s Polycarbonate capacitors?

[TimFox]

PP = polypropylene may not have been popular at the time of that article.
The film dielectrics can be interchanged, but they have different properties.
Poyester film capacitors are still popular, being physically smaller and cheaper than other film capacitors, but with inferior electrical properties to modern polypropylene and obsolete polystyrene film capacitors.
Polycarbonate capacitors are not popular now, but are generally superior to polyester:  I would replace polycarbonate with polypropylene if good properties are required.
Mylar^TM is a registered trademark of DuPont for polyethylene terephthalate polyester polymer ("PET").  Therefore, "PE" is the usual term for modern capacitors.

[Kleinstein]

There are different film capacitors that sometimes can be exchanged. There are still differences between the types and all have there pros and cons. PS and PC are essentially no longer made.
PC can sometimes be replaced with PE, if the temperature effect is not critical.  The difference from PC to PE is not that large, but could still be relevant.
If low temperature drift is important C0G ceramics is a superior choice, but can be a bit expensive for large capacitance.
PS can often be replaces with PP, though the PS capacitors were more used for small size and may have less leakage.
If leakage is not critical, COG ceramics can also be a good alternative, especially for small size.

PP capacitor were not in the old design but were suggested as a possible alternative. There are usually good performance, but usually a little more expensive then PET and physical large, as they rarely come in a lower voltage version (can't make good very thin foils).


The high K ceramics are not all bad, they are great for power decoupling and can in some places also be used instead of tantalum, especial small capacitance like 1 µF. There is still a difference with lower ESR - some low drop LDOs need some ESR.

Of days ceramics was often C0G ceramics for low values (like < 1 nF) and high K (class 2) ceramics for large capacitance like >= 10 nF. It is usually ok to replace old high K ceramics with new one (especially X7R). It's a similar material, just today usually smaller form factor mulit layer.

[TimFox]

For some applications, the higher loss (ESR) of a PE capacitor compared with the very low loss of a PP capacitor may be important.
Also, dielectric absorption (hysteresis) of PE is worse than PP.
When comparing the different films, the temperature co-efficient is different.
This Wikipedia article contains a table comparing film dielectrics now in common use (about halfway through the article).
https://en.wikipedia.org/wiki/Film_capacitor
Note that lower "dissipation factor" and lower "dielectric absorption" are good.
The last line in the table shows that PET capacitors can be smaller than the others.

[analogix]

I'm the OP and I've been trying to compile a summary of all the information presented here, but am still utterly confused 
I think I may have worded my question a little too imprecise, because the replies appear to be more about finding the best type of capacitors today for a 1980s article, which of course requires understanding the circuit design thoroughly.

My question however is this:
The ETI magazine article (from 1980) has part lists with components no longer available today, so when they list something like "100 nF Polyester", "1 uF Polycarbonate" and "22 uF/16V tantalum" -what components should I look up and order (from Mouser.com for instance) with the requested values, today in 2024?

I just want to build the vocoder as in the article and not mess around with trying to find improvements to its design, which will just complicate things. I also want it to sound the same way as it was originally designed.
* The only exception to this is perhaps regarding tantalum capacitors (because of safety measures, hearing that they can explode/cause fires), but then again I understand there is disagreement if this is an issue as well, which futher complicates things.

[Dentelf]

I would choose electrolytic capacitors because they are reliable, widely available, and come in a wide range of capacities and voltages. They are safer than tantalum capacitors for power supply, and their modern low-ESR versions ensure stable operation even in difficult conditions.

[JohanH]

My question however is this:
The ETI magazine article (from 1980) has part lists with components no longer available today, so when they list something like "100 nF Polyester", "1 uF Polycarbonate" and "22 uF/16V tantalum" -what components should I look up and order (from Mouser.com for instance) with the requested values, today in 2024?

Here are some example search results from Mouser.

"100 nF Polyester"
https://www.mouser.com/c/passive-components/capacitors/film-capacitors/?capacitance=0.1%20uF&dielectric=Polyester&instock=y
Select Termination Style Axial or Radial. For radial, select lead spacing. Then select voltage rating. You can use same or higher voltage than the original.


"1 uF Polycarbonate"
I would select PP or PS:
https://www.mouser.com/c/passive-components/capacitors/film-capacitors/?capacitance=1%20uF&dielectric=Polypropylene%20%28PP%29~~Polystyrene%20%28PS%29&instock=y&rp=passive-components%2Fcapacitors%2Ffilm-capacitors%7C~Dielectric


"22 uF/16V tantalum"
Tantalum (you could use higher voltage):
https://www.mouser.com/c/passive-components/capacitors/tantalum-capacitors/?capacitance=22%20uF&termination%20style=Axial%7C~Radial&voltage%20rating%20dc=16%20VDC&instock=y

Or possibly replace with Aluminium polymere (much more reliable):
https://www.mouser.com/c/passive-components/capacitors/polymer-capacitors/?capacitance=22%20uF&termination%20style=Axial~~Radial&voltage%20rating%20dc=16%20VDC~~500%20VDC&instock=y&rp=passive-components%2Fcapacitors%2Fpolymer-capacitors%7C~Termination%20Style%7C~Capacitance%7C~Voltage%20Rating%20DC

[analogix]

Thanks for the links and suggestions.

Is it more or less correct to summarize the "1980 to 2024 capacitor equivalents" like this?:

[TimFox]

Polystyrene capacitors are great (except for their low maximum temperature), but they are no longer generally available.
When good dielectric properties are needed in a film capacitor, polypropylene has replaced them.

[srb1954]

Polystyrene capacitors are great (except for their low maximum temperature), but they are no longer generally available.
When good dielectric properties are needed in a film capacitor, polypropylene has replaced them.

Polyphenylene-sulphide PPS is also a fairly good substitute for polystyrene in many less critical applications.

It has good temperature withstanding characteristics and is available in SMT form factors. In critical applications where hi-K MLCC capacitors are not suitable due to their temperature drift, voltage dependency, etc PPS can often be a suitable substitute that is compatible with SMT manufacturing processes.

[CatalinaWOW]

Thanks for the links and suggestions.

Is it more or less correct to summarize the "1980 to 2024 capacitor equivalents" like this?:

(Attachment Link)

I think we all understand that you want to simplify the answer.  And most are cautious about doing that because there are cases where this oversimplification will bite you.  The simplest answer is to replace all electrolytics and tantalums with modern electrolytics.  Replace all film capacitors with polypropylene. 

I assume from your comments that you are using the original layout for the boards, and indeed may already have the PWBs at hand.

Prior to ordering parts use the photos/layouts of the boards to estimate the sizes of the capacitors in the original and see if the current models available are compatible with those sizes.  Remember that through hole is more flexible than surface mount in this area as you can elevate some components above the board slightly to give them more clearance.  It is OK to buy larger parts if you have a plan for how to make them fit.

There is some chance that this simplest substitution approach will cause you problems.  You can come back to this forum with descriptions of the problems encountered and find help in understanding and correcting the problem, though in all probability other things than the capacitors will be the problem.

Also understand that your ear may actually like the result, even if it doesn't match the original exactly.  Only you can answer that question.  You can only compare to the original if you have one, in new condition, to compare with.   After forty plus years of aging it is unlikely that you will actually find such a reference beast.