Capacitors for SDIY

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AST
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Post by AST » Sat Apr 09, 2016 3:36 am

High precision or temperature stable application, such as timing reference in VCO core: Polystyrene, or NP0/C0G multilayer ceramic (may be hard to find the latter in a large enough value, though)
Is the % important for the timing cap of a vco? Does it matter if I use a 1% or a 5% as a timing cap?
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Post by PWM » Sat Apr 09, 2016 3:44 am

It's important that the cap is stable. I use polystyrene caps for VCO timing.
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Post by ringstone » Sat Apr 16, 2016 12:30 am

AST wrote:
High precision or temperature stable application, such as timing reference in VCO core: Polystyrene, or NP0/C0G multilayer ceramic (may be hard to find the latter in a large enough value, though)
Is the % important for the timing cap of a vco? Does it matter if I use a 1% or a 5% as a timing cap?
There should be absolutely no difference as long as the circuit allows enough variation in trimming to compensate for any variation from nominated value of the capacitor you use. I can't think of any offhand that wouldn't :)

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lcf
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Post by lcf » Sun Apr 17, 2016 9:36 am

Thanks guys!! This thread is really usefull.

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Zealot Vague
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Post by Zealot Vague » Fri Apr 22, 2016 5:58 am

Hello, dumb newbie question time. When a schematic gives a cap value as, say, ".068", without specifying whether it's zepto or mega, what magnitude and material is assumed?

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Post by kassu » Fri Apr 22, 2016 6:13 am

Probably 0.068uF = 68nF.

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Post by DJMaytag » Mon Apr 25, 2016 9:00 am

ringstone wrote:Large bypass caps, typically between 10uF->100uF (such as next to power headers on PCBs) - Electrolytic
Does this value really matter what size you use in that scenario, so long as its at least as big as what's called for? If a board calls for a pair of 10uF's, would 22uF's work just fine?
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Post by AlanP » Tue Apr 26, 2016 2:37 am

Probably. It's amazing what DIY will let you get away with (with the caveat, if you have trouble, be prepared to go back and fix all those bodges and altered values!)

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Post by CMOSCrash » Wed Dec 21, 2016 11:39 am

My problem is telling the difference between polyester, polystyrene, mylar, and polypropylene capacitors.

I'm in a bit over my head with a couple of my projects, namely a couple CGS Serge boards, and the J Haible String Filter. I try to source my components from Tayda as much as possible and they don't have a great selection of high-end caps.

I just need to know when to use polyester box caps vs. those green Mylar polyester blobs vs. something special like a Wima or Siemens metalized film cap.

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Post by memes_33 » Tue Dec 27, 2016 4:23 pm

ringstone wrote:Next, voltage rating - a voltage rating of 35V is pretty much going to cover any requirements, whether you are working with +/-12 or 15V. Once you start getting over around 100V, you'll find the physical size of the capacitor usually increases, so let's stick with that as a maximum. Once again using the CTRL or SHIFT key, select everything within 35V->100V (most likely values are going to be 63V and 100V, but let's see what we get)
i'm working on a 257r buchla clone right now, and a lot of the ceramic caps that are in the original BOM are listed as "obsolete" on mouser. i'm using their "show similar" button/feature to find a suitable replacement, checking boxes for "value" "tolerance" "dialectic" and "lead spacing", but the only items that come up in my search are rated at 2000V - much more than the 50V spec on the original BOM capacitors. this does't seem like it would be an issue (other than larger size), but am i missing anything here? would the rated max voltage affect performance in any way for the module i'm building?

there are plenty of other options, but most are 20% tolerance rather than 5%.

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egilegilegil
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Post by egilegilegil » Tue Dec 27, 2016 6:02 pm

Very informative thread, I'm learning a lot! Thanks!

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Post by cygmu » Tue Dec 27, 2016 6:07 pm

CMOSCrash wrote:My problem is telling the difference between polyester, polystyrene, mylar, and polypropylene capacitors.

I'm in a bit over my head with a couple of my projects, namely a couple CGS Serge boards, and the J Haible String Filter. I try to source my components from Tayda as much as possible and they don't have a great selection of high-end caps.

I just need to know when to use polyester box caps vs. those green Mylar polyester blobs vs. something special like a Wima or Siemens metalized film cap.
Ken Stone has a Parts FAQ on his site (http://www.cgs.synth.net/modules/parts_faq.html ) which answers this from his perspective, as follows:
Capacitors. I'm afraid I'm very untechnical in my choice of capacitors. Sure, sometimes you need a really high quality one for a specific application, but generally almost anything will do, as any degradation in performance is usually unnoticeable to the ear. Mostly I use what I have to hand, and that is MKT, greencap or some other brand's variant of mylar (red, yellow, whatever). If I have nothing else to hand I will use ceramic. I prefer MKT or Wima for larger values (100n and above) simply because they are physically smaller. My PCBs reflect this. For decoupling capacitors, little monoblocks (monolithic ceramic) are fine. That is what they are meant for after all.
A quick guide to quality of ceramics, courtesy of Harry and other SDIY members:-
The good stuff is at the top of the list. The stuff at the bottom are really only any good for decoupling power rails. "Low-k" versus "High-k" are referring to "K" (dielectric constant). Really, capacitors should be chosen for accuracy and stability, rather than just a very general reference to their dielectric constant.

Small cap values in any size package are usually "low-k" as in C0G or NP0 dielectrics

X7R is not too bad but its not good for critical or stable timing

Z5U is getting pretty bad... it's "high-k" and good for decoupling

Larger cap values in small packages are getting toward "high-k". 100n monoblocks are a prime example of this (about 3mm by 4mm or even smaller).
Ken's BOMs will tell you if he recommends a high spec capacitor (polystyrene in some cases, for instance) but otherwise, all the various film types you mention are likely to be ok, and C0G ceramics work in most cases too.

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Post by memes_33 » Wed Dec 28, 2016 4:52 pm

i was told on FB that my 2000V-ready blue capacitors shouldn't yield different results than the 50V BOM parts, so i'm forging ahead. godspeed

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Post by CMOSCrash » Wed Dec 28, 2016 5:59 pm

memes_33 wrote:i was told on FB that my 2000V-ready blue capacitors shouldn't yield different results than the 50V BOM parts, so i'm forging ahead. godspeed
I have read that caps will degrade due to under-voltage. I think I read that in Ray Wilson's "Make" book, but I don't remember if that was specifically electrolytic capacitors or not. Just putting that out there.

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Post by fuzzbass » Wed Dec 28, 2016 7:10 pm

CMOSCrash wrote:
memes_33 wrote:i was told on FB that my 2000V-ready blue capacitors shouldn't yield different results than the 50V BOM parts, so i'm forging ahead. godspeed
I have read that caps will degrade due to under-voltage. I think I read that in Ray Wilson's "Make" book, but I don't remember if that was specifically electrolytic capacitors or not. Just putting that out there.
You always need to pay attention to voltage ratings. Also, if a cap is gonna sit next to something that cooks, like a TO220 1A regulator, you should get ones rated for long life at 105C.

I have made all kinds of selection mistakes, overshooting on temp stability, undershooting, etc. I was still happy with the results, but I have old ears, and the stuff I built is still young. :hihi: On some things I build in 2014 and 2015, I think some of my selections were influenced by how cool it looked on the PCB, or whether there was enough color variety among the MKTs. :zombie: I'm all better now.

Resistors are very simple, but caps are not. My resistors sort out into a drawer set for standard values, and one Sterilite tub for all the unusual values. My capacitor inventory is spread out into four tubs: 1 for Y5G, X7R and C0G/NP0, one for various film types, and two for Electrolytics. The more you learn about this, the less simple it gets, but you will be more confident in your selections and possibly start saving money too.
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memes_33
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Post by memes_33 » Wed Dec 28, 2016 7:15 pm

CMOSCrash wrote:
memes_33 wrote:i was told on FB that my 2000V-ready blue capacitors shouldn't yield different results than the 50V BOM parts, so i'm forging ahead. godspeed
I have read that caps will degrade due to under-voltage. I think I read that in Ray Wilson's "Make" book, but I don't remember if that was specifically electrolytic capacitors or not. Just putting that out there.
well, dang, guess i'll have to go searching again for something that fits the bill better.
fuzzbass wrote:I think some of my selections were influenced by how cool it looked on the PCB
well, to be honest, i did really want the little tan caps as they look more "authentic" as a clone. pretty dumb, but actually motivated me to spend another hour searching!

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balbibou
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Post by balbibou » Sun Jan 08, 2017 4:28 pm

Wow I learn great things from this post. Thanks!

I just found "MKP" capacitors from dutch webshop suggested by PWM muff member. Is it just about the material ?

:doh: Found my answer from wikipedia, it's about the dielectric made of Polypropylene...

From wiki "In addition, PP film capacitors have the lowest dielectric absorption, which makes them suitable for applications such as VCO timing capacitors, sample-and-hold applications, and audio circuits. They are available for these precision applications in very narrow capacitance tolerances." Ok then

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Post by CMOSCrash » Wed Jan 11, 2017 7:07 pm

memes_33 wrote:
CMOSCrash wrote:
memes_33 wrote:i was told on FB that my 2000V-ready blue capacitors shouldn't yield different results than the 50V BOM parts, so i'm forging ahead. godspeed
I have read that caps will degrade due to under-voltage. I think I read that in Ray Wilson's "Make" book, but I don't remember if that was specifically electrolytic capacitors or not. Just putting that out there.
well, dang, guess i'll have to go searching again for something that fits the bill better.
fuzzbass wrote:I think some of my selections were influenced by how cool it looked on the PCB
well, to be honest, i did really want the little tan caps as they look more "authentic" as a clone. pretty dumb, but actually motivated me to spend another hour searching!
Yeah, I gave you possibly bad advice here. It's just electrolytic caps that suffer due to under-voltage.

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Re: Capacitors for SDIY

Post by khladomysl » Tue Jan 26, 2021 5:30 pm

Can someone please suggest some test filter circuit where one can hear the difference between capacitors? Something with feedback maybe? I've got some old capacitors which I want to test but not sure about the proper test for it.

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Re: Capacitors for SDIY

Post by Kunstbanause » Wed Apr 07, 2021 3:25 am

Hey guys, I am building the befaco rampage and had a small accident. I melted a tiny bit of a capacitors plastic hull. Is this worth replacing? Is it still safe to turn on and see what happens or will it definitely explode?
8C2C8ACE-AF26-4D6B-B8E9-00223E1E5808.jpeg
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khakifridge
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Re: Capacitors for SDIY

Post by khakifridge » Wed Apr 07, 2021 3:27 am

It'll be fine. No one will die. ;)

Kunstbanause
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Re: Capacitors for SDIY

Post by Kunstbanause » Wed Apr 07, 2021 3:31 am

😅 Thanks for your advice. It‘s my first build and a big one at that.

Edit: It worked!! Thanks again, after building for ~15hours, a little confidence is what I needed.

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