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

[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.

[analogix]

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.

Thanks. Sorry for repeating my questions, but I'm just trying to make sense of all this, and also learn something for later.

Is the oversimplification (i.e. "1980s capacitor type X = 2024/2025 capacitor type Y") due to the fact that today's capacitors are differently made and behave slightly differently from those in the 80's?
So.... unless I have a time machine (unfortunately I don't), and actually go back to 1980 to buy the exact capacitor types and values asked for in the ETI magazine article's Vocoder parts list I will now in 2025 have to individually understand each capacitor's role in the circuit and take an informed decision of type from that?

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

Yes. I got the huge main board etched several years ago and it's more or less fully populated with components I bought back then.
The smaller boards were redesigned (from the exact same schematics) in CAD software by a kind individual who also wanted to build the same vocoder. Those boards are partly populated, so I need to order the missing components (among them many of the mentioned capacitors).

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.

Good point! Yes, these are through-hole boards. I'll keep that in mind when ordering as the newer boards I have are more compact than the original PCB layouts.

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.

Thank you. Fortunately the vocoder is built in several smaller parts (i.e. individual boards for the input amplifiers, output amplifier, internal excitation, slew rate, LED ppm meters etc.) so it'll be easier to troubleshoot than just a huge, single PCB!
Wiring on the other hand is a project on its own, but one step at a time.

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.

That's true. I don't have another one to compare with, and even if I did it's like you said that aging won't let it be the reference it should be anyway.
i'm pretty sure it'll sound awesome no matter what, and with individual filter controls and external input a lot can be done to shape the sound. I also have plans for several modifications, so I'm not really stuck on having it to sound exactly like a newly assembled one back in 1980 sounded, but rather building an analog vocoder.