Capacitors for SDIY

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pre55ure
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Capacitors for SDIY

Post by pre55ure » Sun Apr 14, 2013 12:26 pm

Hi everyone, I've been building stuff (with lots of help from some really awesome people on this forum) for the better part of a year now. I've learned a great deal about electronics, schematics, audio etc...
One area where I still feel like I don't get it is capacitors. I understand that different types of capacitors are appropriate for different functions in a circuit, but I dont quite understand why... Also I know some capacitors are higher quality than others, but that doesn't seem to mean that you can just replace all low quality capacitors with high quality ones and be done with it... or does it? Or is that just a case of trying to keep costs down?

For example- can I always use a film box type of capacitor instead of a ceramic capacitor? Can I always use mylar capacitors instead of film box type? Or will I be negatively affecting something?

Is there any sort of quality scale? Like polystyrene->Mylar->Film->ceramic?

Also what are COG or NPO and other various designations?

And lastly I find hunting for capacitors to be the absolute worst part of filling BOM's at Mouser. Do you guys have any sort of "go to" capacitors that you commonly use for your builds (preferably with mouser part numbers :hihi: )

Thanks for any help you can offer. :tu:

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daverj
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Post by daverj » Sun Apr 14, 2013 5:21 pm

Last question first:

C0G and NP0 (those are zeros, "C" zero "G" and "N" "P" zero) are designations for ceramic capacitors with no (or very little) change in value as the temperature changes.

NP0 stands for "Negative Positive Zero", meaning the value doesn't go negative or positive as temperature changes. It's an industry term that means the same thing as C0G. C0G is a designation given by the EIA (Electronics Industry Association) for temperature drift on ceramic caps. There are two groups of temperature designators in EIA and C0G is the lowest you can get, which is +/-0.003% per degree C of change (so going up 10 degrees C might change the value 0.03%).

Other common ceramic temperature styles are X7R (+/-15%) and Y5V (+22%, -82%). There are lots of others too. If the first letter is A through U then it holds it's value very well with temperature. If the first letter is X, Y, or Z then it drifts a fair amount with temperature.

This tolerance to temperature drift is a separate issue than tolerance to initial value. For example a capacitor might have a value (at any temperature) that is +/-5% of the value it is sold as. But might maintain that value within 0.1% across the range of temperatures.

Now to the first question:

Capacitors are made up of conducting materials separated by insulating (dielectric) materials. Like most other passive electronic components they are never pure ideal components. The materials and the method of construction create a number of phantom components inside of them. Placing them in a circuit board adds a couple more phantom components.

What this means is that a capacitor, besides having capacitance, also has resistance and inductance. The equivalent circuit for a real world capacitor is usually modeled as a capacitor with a resistor in parallel with it plus another resistor and an inductor in series with the first two.

The resistor in parallel with the capacitor defines the "leakage" of the capacitor, or how much of the charge drains away on it's own. The resistor in series with it is known as the ESR or Equivalent Series Resistance. That resistance prevents the capacitor from charging or discharging as quickly as a theoretical capacitor would. Then there is also an inductor in series with that resistor known as ESL or Equivalent Series Inductance (inductance is represented by the letter L). That usually includes the leads that connect the capacitor to the real world, and that inductance can change the frequency characteristics of the capacitor. The inductance, resistance, and capacitance all form a sort of passive filter that effects how the capacitor works at various frequencies.

Even these equivalent circuits are generalizations, and the real world capacitor might have a much more complex equivalent circuit. But in general this model is used the most, and the specs for capacitors are created with this model in mind.

Different types of capacitors have different values for each of those phantom components. Those different values in turn make that particular type of capacitor work better in some types of circuits than in others.

At the same time, the type of materials used to make them, and the style of construction (flat layers vs rolled up layers, SMT vs through hole, etc...) also determine the range of values that are available for that type of capacitor. For example electrolytic capacitors are generally high values of capacitance while ceramic are generally small values. Film caps are generally in the mid range. All of those ranges overlap to some degree.

In general aluminum electrolytics are not so good at high frequencies, while ceramics are great for high frequencies. Aluminum and ceramic caps in general are not very accurate values and drift with temperature, except for NP0/C0G ceramics. Film capacitors generally have more accurate values, and in general have low drift with temperature. But then there are a lot of different types of film caps, and each has different characteristics.

The bottom line is that if a circuit designer specifies a specific type of capacitor, they did that for a reason and you should try to use that type. Sometimes they don't specify a type, but assume that a given type will be used because of the value or physical size in the board.

There are many cases where one type can be replaced with another and there won't be any changes in function. There are other times that will cause something about the circuit to work differently. Knowing what will happen when you substitute a part involves understanding exactly what the original part was doing in the circuit and how the new part will change that circuit. In many cases the characteristics that make different types different are not all that important in a circuit. In other cases they are very important.

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Post by ringstone » Sun Apr 14, 2013 10:47 pm

I can't really add any theory to Dave's excellent explanation there, but I will give you my rough guide to choosing caps as well as some typical applications you'll find and what are suitable.

Generally, values under 1nF: Ceramic
Values between 1nF->1uF: Metallised plastic Film, such as MKT (other plastic films such as Mylar are probably fine for most applications, but the MKT caps are generally a standard size).
Values over 1uF: Electrolytic

Large bypass caps, typically between 10uF->100uF (such as next to power headers on PCBs) - Electrolytic
Small bypass caps, typically 10nF, 100nF (near opamps and other chips for power decoupling) - Mid K Multilayer Ceramic (MLCC), such as X5R, X7R
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)
General timing application: (e.g. LFO) - film cap
Lower precision timing application (e.g. ADSR stage) - tantalum or even electrolytic (as these have improved so much in the last 20 years).
DC blocking cap on audio input - film cap, or audio-specific electrolytic if larger value required.

BTW Polystyrene caps are often found in projects that are re-creations of vintage circuits, as when the circuit was originally developed these may have been the only suitable capacitors for the job.

In some projects, there may be caps of the same value specified, but required for different purposes - e.g. I'm building some CGS Burst Generators at present, which require 3 x 100nF (0.1uF) caps - but two are for power bypass, and one is intended as a timing cap. So, always refer to the build notes/schematics if unsure - for example the CGS ASR will only work reliably with certain types of film caps. Looking at the PCB will sometimes also give a clue to the type of cap required - a rectangle for MKT, circle for electrolytic, oval for ceramic.

Since capacitor parts counts on most projects are relatively low, I would recommend you try and go with best quality (within a reasonable price) for each type. The price difference should be negligible.

For ceramics, NP0/C0G multilayer - good quality brands include Vishay, Kemet, Philips, TDK, Murata
For film caps, metalised Polyethylene/Polyester (MKT), brands such as WIMA, Epcos, Phillips, are generally considered good quality
For electrolytics, brands such as Nichicon, Elna, Panasonic

None of the caps found on Mouser should really be "poor quality" though, although of course some of them will be lower-spec intended for use in non sensitive applications.

So, yes, it can be confronting to try and find the right capacitor for your application when Mouser has 100's of different ones in the value you need! But the site also has very powerful search and filter tools that can make your search fairly easy - the trick is to narrow down to the subset that you want. For capacitors, the important criteria are: capacitance value, technology, voltage rating, price, size, and application specific (e.g. temp coefficient, low ESR, audio). So, let's take an example - I want to find a general purpose capacitor with a value of 5.6nF - sometimes you will also see this written as 5n6. As sometimes, values are specified in pF or uF in Mouser's value dropdown lists, you need to know:

1000pF = 1nF
1000nF = 1uF

So 5n6 could also be written as 5600pF or .0056uF

Capacitors are passive components, so we start there from the main page - then go to the capacitors heading.

Straight away we have the ability to narrow down to technology type, being 5n6 we would most likely be looking for a film capacitor, so choose that sub-group.

Now we have to start doing a bit of work:
First off, always click "Stocked" - otherwise you'll be sorting through obsolete and out of stock items as well.

For this value, it's actually listed as 5600pF, 5.6nF AND .0056uF - using the CTRL key to select individual values (if you're on a Mac you'll have to work out what the equivalent is :hihi:) or the SHIFT key to select a range, select all 3 of these values. You'll notice the number of selections is already starting to reduce significantly.

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).

Finally, most PCBs generally have a 5mm lead spacing for most film caps (CGS often have a number of holes, so you can use different sizes) but make sure you check, just in case! In this case it's 5mm (actually 5.08mm, so choose that if it's there as well as any other value close, like 5.1mm). I'm in Australia, so you US people will have to pick the equivalent value in inches (0.2in I believe!). Now click Show Products

I get 2 results at this point, so that makes the choice pretty easy! If you get no results, or not a wide enough range, you could try expanding the search range a bit - say go down to 25V min, 160V max - just watch you don't select any AC rated caps BTW - and see what you get. It's easy to knock a particular sort term out by unchecking it, then you can go back and respecify it later if you want.

If you lots of results, then click the sort button under pricing, to get the cheapest ones at the top. And just keep an eye on tolerance - generally you probably want around a 5% tolerance for film and ceramic (this will be higher for electrolytics) though 10% is probably ok for most applications.

Ok, I'll take you through a bit trickier one - let's look for some 0.1uF multilayer ceramic bypass caps:

Once again, Passive Components->Capacitors.
This time, Ceramic Capacitors. We have some further sub headings, choose Multilayer Ceramic (MLCC) - Leaded
Ok, now choose value 0.1uF
Voltage range between around 35-100V
Important in this one is temperature coefficient - Choose X5R and X7R
(this is where you would select C0G/NP0 for smaller values)
This is once again for a PCB with 5.08mm lead spacing, so choose any values close to that - we have 5mm, 5.08mm, 5.1mm and 0.2in (which is for you folks in the US!).
Click Show Products

Wow, so we still got quite a few hits - I count 194. Let's sort these by price ascending. Now, this is important - don't just pick the top one! With a product like this, you are probably going to be buying more than one. In fact I go through these like candy, so let's see what volume discounts we can get.

The top one has a price break at 500, down to .065, which is pretty good, but I reckon it'll be a while before you can use all of those. Let's keep going. Third one down is a Vishay cap, with price breaks at 50 and 100 - looks a bit better! Just scan down the first page or so, making sure you get the best deal. Done!

Most importantly, BTW - if you get stuck trying to work out what cap you need, or have trouble tracking down some esoteric value, ask in the build thread for that particular project.

Cheers
Blair

EDIT: Corrected a couple of minor errors!
Last edited by ringstone on Tue Apr 16, 2013 2:57 am, edited 2 times in total.

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pre55ure
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Post by pre55ure » Mon Apr 15, 2013 1:52 am

Awesome!
Great information guys, I really appreciate the time spent typing this stuff out.
:tu:

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Post by home_listening » Mon Apr 15, 2013 8:17 am

Thanks for this!

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Post by LED-man » Mon Apr 15, 2013 8:33 am

whats about MICA - GLIMMER or Styroflex ?
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Post by e-grad » Mon Apr 15, 2013 9:25 am

LED-man wrote:whats about MICA - GLIMMER or Styroflex ?
Glimmer is AFAIK 'silver mica' I've never seen them mentioned in any synth documentation. If a Mica is specified and I've none at hand I'd substitute it by any quality capacitor of the same value available. However, others might track down a Mica.

Styroflex is German for polystyrene, see ringstone's post on these kind of capacitors.

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Post by LED-man » Mon Apr 15, 2013 9:36 am

e-grad wrote:
LED-man wrote:whats about MICA - GLIMMER or Styroflex ?
Glimmer is AFAIK 'silver mica' I've never seen them mentioned in any synth documentation. If a Mica is specified and I've none at hand I'd substitute it by any quality capacitor of the same value available. However, others might track down a Mica.

Styroflex is German for polystyrene, see ringstone's post on these kind of capacitors.
thanks.
Silver Mica is very expensive each between 0,8USD (10P) - 4,5USD (10N), i have used this in my ARP Filter, because they have a linear temperature and high frequency spectrum.

Can you tell me more about Tantal ?
i have many of them here and don´t know, what i can do with them.
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Post by keninverse » Mon Apr 15, 2013 9:40 am

LED-man wrote: Can you tell me more about Tantal ?
i have many of them here and don´t know, what i can do with them.
I wouldn't ever use them in synth DIY applications. Major pros are that they're small and great ESR. Major downfall is when they faill they...they fail hard. Like take out everything next to it hard. Reverse the polarity and sparks fly. I've seen people use them in microwave circuits or in positions where it's near impossible to fit a large electrolytic.

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Post by Peake » Mon Apr 15, 2013 9:48 am

Polystyrene/polycarbonate (the latter seemingly obsolete) are sometimes found in the core of analog oscillators. The earliest Moog and IIRC EMS oscillators used film caps there. Buchla specified a polycarbonate timing cap from his first oscillator.

Regarding components and character... Ken MacBeth says on his MicroMac page:

"Once again- the most important parameter has been the final output- the sound quality."

"...to provide the best, most vintage sound available."

"Many of the parts- notably integrated circuits, transistors, and capacitors are the same types as found in the synthesizers of old- so the sound you are going to get is truly vintage!"

I note the presence of carbon film capacitors in the picture there alongside metal film. Ceramic disc caps as well. I happen to really like the sound of his gear and of the earliest synths so he might have something there. I'm personally not sure if the march away from whatever it is which results in "vintage sound" is a movement in the right direction. That would depend upon what you personally prefer, and always does.
This is not the place I'd imagined it to be.

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Post by daverj » Mon Apr 15, 2013 2:45 pm

For the most part silver mica has been replaced with NP0 ceramic. The only exception is if you need extremely high tolerance values in a through hole packages. You can still buy silver mica in leaded packages with 1% tolerance, and sometimes less. NP0 ceramics tighter than 5% are available in some common values as through hole (and all values as SMT), but it's harder to find certain values in through hole at tight tolerances.

30 or 40 years ago silver mica had some advantages in characteristics over ceramic disc. But in recent years the MLCC ceramic NP0 caps meet all the same specs.

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Post by 303monkey » Mon Apr 15, 2013 5:27 pm

Cool thread
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Post by negativspace » Mon Apr 15, 2013 5:48 pm

Micas pop up in old gear from time to time. Some Euro modules, too - I think the SEM20 has them in the core if memory serves? Same goes for tantalums, you'll find more of them in vintage gear but basically none in new circuits. I've only ever used both types in my Synthasystem DIY builds, and only because that's what was specced in the original and I felt like being faithful.

@the character argument - Depending on the circuit and the capacitor's job within it there can be quite a difference in sound with different types. I was a skeptic until a friend had me re-cap his ~20-year old Tubescreamer. I took out all of the electros and tantalums in the audio path and replaced them with polyester film and bipolar electrolytics and it was an entirely new pedal. Shockingly so, actually.

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Post by ejr27233 » Tue Apr 16, 2013 2:26 am

Superb thread. Many thanks to all the contributors

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Post by e-grad » Tue Apr 16, 2013 3:27 am

negativspace wrote:Micas pop up in old gear from time to time.
Some Blacet modules make use of mica caps.

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Post by Idzard » Tue Apr 16, 2013 3:40 am

Just what I was looking for! Thanks for the info!
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Post by roglok » Tue Apr 16, 2013 6:28 pm

e-grad wrote:
negativspace wrote:Micas pop up in old gear from time to time.
Some Blacet modules make use of mica caps.
Ray Wilson lists silver mica as an alternative to polystyrene for his MFOS VCO. A couple of these VCOs were the first modules I built and since I couldn't find any polystyrene caps at the time I built them with silver mica. I really like the two — they are a pair of reliable and stable workhorses.

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Post by Ayab » Thu Nov 05, 2015 7:27 am

Great information and impressive knowledge - thank you Daverj and Ringstone for sharing.

I am interested in the sound difference that Negativespace heard replacing tantalums and electrolytics in a 20 year old tube screamer. Was that sound difference more down to tolerance differences. Or would the temperature behaviour have a large influence.

I have been using super cheap capacitors but, especially for the power conditioning electrolytics, should I use good quality? Are there any reliable yet not expensive brands to look out for in this area?

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Post by cane creek » Thu Nov 05, 2015 7:38 am

My memory is terrible so i always refer to this little chart when shopping for capacitors

Image

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Post by raveboyy » Thu Nov 05, 2015 8:13 am

Thanks a lot for this lesson :)

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Post by keninverse » Thu Nov 05, 2015 9:22 am

Ayab wrote: I have been using super cheap capacitors but, especially for the power conditioning electrolytics, should I use good quality? Are there any reliable yet not expensive brands to look out for in this area?
I always used higher-reliability, lower leakage electrolytics for my builds simply because they are relatively cheap (~$0.10/ea in bulk) and I'm comfortable that they won't fail in the near future. For audio circuits where I worry about noise and the finer details I'll use something like elna silmic's. Do they sound better? Just barely. But I tend to operate under the philosophy of the sum of better parts = a better whole ergo the sum of better modules = better system. Having said all this I do think there's a point at which I won't buy into audiophiliac BS snake oil.
So in general, I buy Panasonic FMs for everything and if I can't find the values I need in FMs I go to Elna Silmic IIs for audio and Panasonic FCs for general duty bypassing.

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Post by qfactor » Thu Nov 05, 2015 9:29 am

Then are there any major differences between Ceramic disc caps and MultiLayer ceramic caps?
:hmm:

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Post by euromorcego » Thu Nov 05, 2015 10:35 am

negativspace wrote:[...] I took out all of the electros and tantalums in the audio path and replaced them with polyester film and bipolar electrolytics and it was an entirely new pedal. [...]
I am a bit puzzled by the bipolar electrolytics. Can the be substituted by polar electrolytics (in the right orientation, of course)?

I am trying to build Ken Stone's drum simulator (cgs18) which specifies 10uF bipolar electrolytics at the output. Is this because of audio quality? There do not seem too many uses for them in eurorack diy (judging from the BOMs I have seen so far, and I have seen most usual suspects).

Maybe someone who knows more about this stuff than I do can provide a clue ...

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Post by audiohawk » Thu Nov 05, 2015 11:16 am

Thank you all for your time sharing information with us noobs.
Much appreciated! :hail:

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Post by DabiDabDab » Thu Nov 05, 2015 11:19 am

qfactor wrote:Then are there any major differences between Ceramic disc caps and MultiLayer ceramic caps?
:hmm:
Im finding the disk type caps on Tayda have 20 % tolerance and Multilayer have 10%, not to mention the temperature coefficient. How critical this difference is is probably dependent on the function in the circuit.

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