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Hello all,In the very near future I will have to replace large 22000uF/50V electrolytics in my vintage amp. These are the beasts labelled C4-x in the picture. Problem is, the amp being more than 30 years old these caps have gained unobtainum status and to add insult to injury, the amp case has so low of a profile that I can't find modern replacements that would fit in there height-wise.
So I was thinking of designing a PCB that would have a round footprint to fit in place of the large caps, and fit multiple parallel caps on it to get to the required value.
Now I value this amp and don't want it to blow because of this mod, so would like to hear from inmates that have replaced large caps with multiple smaller ones. Are there any precautions to take, perhaps fit a current limiting resistor on the bank? A concern I have is that modern caps with lower ESR once paralleled could present too much a load for the transformers and bridge rectifiers upstream. Bridge rectifiers can be replaced yes but these transformers are also low profile and potentially hard to replace if they fail.
Potential advantages I see are multiple, first by having better technology and much lower total ESR than the original caps, the ability to use a combination of caps with different sound characteristics, e.g. for example a couple large ones of good quality for the bulk of the capacitance combined with smaller ones of superior quality, perhaps fit a low value film cap in the mix for a faster transient response.
Thanks in advance for any insights.
-Joris
Edits: 10/31/23Follow Ups:
I prefer multiple smaller caps in separate enclosures by using smaller multiple from electronic theory you lower the esr many early modifiers did this on dynaco amps it's really easy and sounds amazing on everything I have modified over 40 years. I even do my crossovers externa; modules.
I've done this on the low voltage PS in my Atma-sphere amps, replaced one huge can with a gaggle of much smaller, much lower ESR Panasonic TS-ED caps for higher total capacitance and yet better sound. (In the circlotron, the LV PS is in parallel with the output, so anything that lowers Z and improves performance in theory can be heard on the speakers.)So, IMO, it's a good idea. But sadly, I think the Panasonic TS-ED series has been discontinued. There may be similar from Panny or Nichicon.
Edits: 11/12/23
Large capacitors usually have a higher ripple current rating than small ones (both physical size and capacitance). Two 4,700µF caps will usually have a lower combined ripple current than a single 10,000µF cap, and will also show a lower ESR (equivalent series resistance). The combination will generally be cheaper as well - one of the very few instances where you really can get something for nothing. Using ten 1,000µF caps will generally give even better overall figures again, but the cost (in time and effort) of assembling them into a proper filter bank may not be felt worthwhile.
Below are some links for your reading pleasure.
https://www.diyaudio.com/community/threads/single-vs-parallel-capacitor.214869/#:~:text=Multiple%20smaller%20caps%20in%20parallel,parallel%20with%20a%20large%20electrolytic.
https://electronics.stackexchange.com/questions/239764/why-multiple-capacitors-in-parallel
Hello and thanks for your reply, interesting links in there.
I already stumbled upon the stack exchange one but not through the first link there's already very interesting points, in particular concerning the layout of an hypotetical pcb, which should use a star arrangement of traces going from one output terminal to each individual cap in the bank to avoid any possibility of ringing from parasitics, in lieu of a single large trace connecting all caps, that I would probably have done!
Good stuff, thanks!
I built a large external capacitor bank and used solid copper buss bar to connect all positive connectors in parallel and the same with negative. These were large value caps not like what you are proposing. What I would do is to get some 12awg Romex and strip out the copper wire and use that as your buss wire (don't use stranded). You layout your caps in straight line, "S" lines or whatever fits your space, then use the bare 12awg copper wire to run from the plus from cap to cap in your configuration and do the same for the negative. Don't try to get fancy with a "star" configuration as it will be more bother than it's worth. Running the 12awg from cap will work in circles, straight lines and "S"'s and in any combination. Figure what layout fits the best with the most caps and go for it. What you want is the positive and negative wire running in parallel from cap to cap. Make sure they are firmly in place...you don't want them shorting out to anything and remember once you've got them all wired together they aren't a little cap anymore but one very big one and depending on the values and how many you have they could be potentially lethal.
Edits: 11/08/23
I would look in the catalogues for what are the options-
Up in voltage (perhaps 60V) up /down in total capacitance-
You may not fid the exact Form Fit or specs - but you might find something that will work quite well...
Happy Listening
Thank you 6bq5 for your reply.
Believe me I have searched Mouser and Digikey throuh and through, no single can fits its size of 50 mm diam., height 44 mm, and 10mm lead pitch. That's why I look for a way to combine many which will be easier to find with a height of 40mm or lower, allowing 4mm for supporting pcb and pins underneath.
Just for good measure I will do another sweep of the main distributors, alternative sources recommendations most welcome.
Thanks,
Joris
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