BBD modulation & large caps in power filters

[POTL]

Hello
I studied the modulation scheme and noticed that, in contrast to the delay / distortion / compression, large capacitors are installed in the modulation
for an example I will give a BOSS CE-2

we have the following meanings
C18 & C20 - 47uf
C30 - 220uf
is there any reason to set these values ​​or can I set standard (and more compact) 10uf and 100uf respectively?
in flangers, I often see the 470uf value of the capacitor in the power filter?
Is there a reason to set such a huge value or will 100uf work the same way?

[R.G.]

is there any reason to set these values ​​or can I set standard (and more compact) 10uf and 100uf respectively?
in flangers, I often see the 470uf value of the capacitor in the power filter?
Is there a reason to set such a huge value or will 100uf work the same way?

There is always a reason for a large-company design engineer to put a certain value of cap in a design. Large company engineers, especially Japanese engineers, are trained very well, and will have a good grasp of the electronic theory behind what value of capacitance is "enough" and will also apply to that a good grasp of what is affordable and what is manufacturable. This is distinctly not how amateur pedal makers and just-appeared-recently commercial pedals are designed. I have dealt with Japanese engineers from large companies, and they have earned my respect. This is by the way not always true of American engineers.

However, it may be difficult to figure out what that reason is. From where the caps sit in the circuit, two of them are filtering bias voltages. This application means that they were chosen to be (1) enough capacitance to do the job acceptably well to the testers' listening tests (2) small enough to fit on the PCBs as designed and manufacturable, (3) easily available without long procurement times (4) cheap enough (5) maybe already in stock in large quantities and the company wants to get rid of them - the list goes on. Notice that only a few of the reasons have to do with the electronics theory behind them.

So the answer is - yes, smaller values will work the same way, but perhaps not as well. They may not hold the voltages steady enough. Or they may. There is only one way to answer whether smaller values will work just as well, and that is to try it and see.
Fact is, a good search engine may well turn up high value caps in quite small packages. The larger capacitor makers have the same value in different "flavors", optimized for different applications. Panasonic, for instance, has miniaturized versions of their capacitor line. So unless you're otherwise constrained, you might solve your problem by simply looking for a smaller version of the cap in the same values. If you're constrained to only get parts one or two places, that's a different problem.

[thermionix]

I just finished a Madbean Pork Barrel (CE-2 clone) build, they specify 47uF for the "C30" position, and I can confirm that it works fine.  Sounds good and no noise issues even with my crappy switching wall wart.  I did notice the discrepency when I was building it, but the only 220uFs I have are 10v, so I went with the 47uF.

[Elektrojänis]

The larger value caps in power suply filtering in modulation effects might have something to do with the LFO on board. it may take a bit of extra effort to keep the low frquency signal that LFO is generating out of your signal path... Filtering out lower frequencies from your power supply lines (and bias voltage lines) usually mean larger value caps.

So... The large manufacturer seeks for the most cost effective solution available te get a performance that is good enough for the customer. For DIY I would preferably use a bit larger values in those spots... For just that bit of extra diy allows me... and perhaps to tame the voltages a bit better to counteract the limitations of my own layouts that may not be up to par with the commercial versions.

[anotherjim]

Time has moved things on since those classic designs. Electro cap production has evolved such that a 220u/10v then is now a 220u/16v or better voltage in the same size package.
To me, and I'm by no means a highly trained engineer, a 10v rated cap (C30) on a 9v supply seems a bit marginal, and I don't think I'd bother buying in any 6.3v caps such as that C20. In a 9v pedal, there's probably no advantage for the part size in stocking anything less than 16v rating caps.

C20 is the LFO reference supply AC bypass. At 1Hz, that 47u is worth 3k3 ohm. That might seem a bit marginal, but the paths it is referencing use little current so it gets away with it.

[POTL]

Thanks Everyone