Which Capacitor Types Should I use

[brownj4]

Hi Everyone,

I'm finally moving on from BYOC kits and am trying to build some pedals using madbean PCBs and ordering all the components myself. 

I've searched these forums for a while and can't seem to find the answer to my question regarding capacitor types.

As an Engineer - though not an Electrical Engineer, hence the capacitor questions - I might be over analysing this one.  But in any case, I'm hoping someone can help lead me down the right path.

1. There are 3 "types" of capacitors I have seen on the madbean PCB layout drawings:  Circular, Rectangular, and Oval.  What does this represent in terms of the type of cap to use?  I haven't seen this info. anywhere.

2.  I am building a Bill Of Materials for a Runt, and have noticed that certain capacitor values span different types of caps.  For example, at Mammoth Electronics you can get a 0.0033uF cap as a 100V polyfilm cap, 630V polyfilm cap, and also as a 3300pF 50V ceramic cap.  In situations where there is overlap between 2 or 3 different types of capacitors, what should be used?  Or does it matter?

If this info. is already somewhere else, please feel free to just direct me there.

Thanks!

Jeremy

[DutchMF]

If somebody doesn't beat me to it, I'll get back to you after dinner!! It's actually really easy. What kind of engineering do you do? I'm in HVAC myself.

Paul

[alanp]

Circular is typically electrolytic or tantalum.

Box is typically a box film type cap. Sometimes "greenie" caps, sometimes high-value ceramic caps or multilayer ceramic caps.

Oval is normally a picofarad ceramic cap.

I'd go for the capacitor in the right value, in the smaller packaging, with enough voltage rating (25V for a 15V circuit, 16V for a 9V circuit. Most box caps are rated at 63V, IIRC.)

Some people say that the type makes a difference... I suspect most of that difference is at 600V in a valve amp. You're more likely to get a change if you change the value.

[jkokura]

Welcome to the forum! Glad you're asking questions before you start building, because that's the best way to learn. I'll try my best to answer you.

1. Yes, there are multiple types of capacitors. There are actually more types than you might think. I'll try and sum up what I can here.
a) Circles on your PCB usually indicate high value capacitor needs. In other words, usually a 1uF or higher capacitor (perhaps as high as 220uF). The most common type of capacitor used here is the electrolytic type, which come in circular 'can' type packages, generally radial with lead spacings of 2.5mm. The bodies are usually 5mm in diameter, but 6.3mm can be found as well. An alternative to electrolytic is the Tantalum capacitor. These are commonly found, but not typical to pedals because of their higher cost in comparison with Electrolytic.

b) Rectangular caps are middle value capacitors, and are the most common in many builds. These indicate a value between .001uF and 1uF generally. Another way to read .001uF is 1nF. To get nF from uF, you simply multiply by 1000, so 1nF = 0.001uF, 10nF = 0.01uF, and 100nF = 0.1uF. The most common type of capacitor here is the poly film box type of capacitor, hence the rectangles. These come in many different packages, but it is common to find them in 5mm spacing, with boxes that are about 6mm long by either 2.5, 3.5, 5 or 6mm wide. Generally, the higher the value, the large the box cap. Any value between 1nF and 100nF will be 2.5mm wide with 5mm pin spacing. These caps are a little bit more expensive than alternatives, but they have been proven to be quite good in building pedals and we often go for the added expense over some of the alternatives. While box caps have become popular and common, Panisonic film caps which look like 'chicklets' are also commonly used. They look like red pieces of gum with leads sticking out, hence 'chicklet'. Panasonic caps are being phased out of production - you can still get them, but they are becoming less common in DIY pedals. There are many other types of caps in this value range as well, like Green Poly film, and Multilayer Ceramic Caps (MLCC) which are found in builds as well.

c) Oval caps generally indicate small values less than 1nF/.001uF. Again we can multiply 1nF by 1000 and get 1000pF. Caps of the value between 1pF and 999pF are usually indicated by those small ovals. The most common values used are 47pF, 100pF, 220pF, and 470pF, though it may be that you'll see other values occaisionally. The most common type of cap found in the pF value range is the Ceramic Disc Cap, which looks like that small oval you see. There are also film chicklet style caps, and the MLCC type are also gaining popularity. Ceramic Caps get a bad rap because they are known to be 'noisy' in circuits, however they are also really cheap, and plentiful. A less common, more expensive, and larger sized cap for the pF value is Silver Mica, though they are becoming less common as I watch pedal build reports. Mica Caps are much more common in amplifier builds nowadays.

2. When you can find multiple caps of the same value from different types there are no hard and fast rules as to which one to pick, but there are some factors which you may want to consider in your choice:
a) Is it in the sound path? If the cap is in the sound path, you may want to choose a cap that is known for low noise (unwanted distortion). Poly Film is usually a good choice, but there are others.
b) What kind of space is available? If the board specifis a 2.5mm spaced set of pads with little to no room for the cap than the ceramic cap is a good choice. If the board specifies a 2.5mm pad spaced electrolytic, than it doesn't make sense to get a gigantic 630V 12mm spaced Film cap. Get a cap that fits the spot it's aimed for
c) What kind of voltage will it see? If the part is going to see 24V, or even 18V, than getting a 16V part isn't going to be good. Caps explode violently, and you don't want electrolytic burning through your retina. The reverse is generally true as well. You don't need 630V worth of protection, because the pedal is only going to see 9V or so. 25V, 50V, 63V, and 100V are common voltage ratings. When the voltage rating starts to get higher, the capacitor size starts to enlarge as well, so watch you don't get a mammoth sized cap by accident.
d) How much is the cap? Don't spend $3 on a part when there's an equally good part available for $.30 or even $.03.

In the end, cap choices come down to two things for me: quality sound at a reasonable price. There are expensive Wima cap snobs out there, and to them I say I can't hear the difference using my Topmay caps at 1/4 the price. But, I can hear the difference over the ceramic caps of the same value. So getting good sound for a good price is my primary goal.

Jacob

[brownj4]

WOW!  All the information I was looking for, and more!  Thank you all for helping me out.  Hopefully this will help others out as they get started as well. 

I'm ok when it comes to conversions from uF to nF or pF, but when there's several different types of caps with the same ratings, I start to question what to use.  This has definitely straightened things out for me.  Looking forward to showing off some successful builds!

Cheers,

j.


PS. Paul, my degree is in Chemical Engineering, but I work at a Nuclear Plant as a jack-of-all-trades Engineer that helps to keep everything running smoothly from day to day.  Lots to learn, and new challenges every day..... but building circuits that I can use on my pedalboard isn't something I really get to work on during the day 

[stevie1556]

I know it's been answered above, but the general rule I follow is:

pF - ceramic caps
nF - box/film caps
uF - electrolitic caps.

Sent from my thumbs using Tapatalk!

[Hangingmonkey]

Hey Jacob, thanks for the info on caps. Just a quick question, is the much difference in noise levels between box caps and panasonic film caps.

[jkokura]

Hey Jacob, thanks for the info on caps. Just a quick question, is the much difference in noise levels between box caps and panasonic film caps.

That's a bit of a redundant question, because the two types of caps are essentially the same in construction, the only difference between the two is the package form.

That being said, there is some evidence that not all film caps are created equally - some reports suggest that certain brands or types are 'better' than others, in regard to their performance. However, in te restraints of DIY pedal building, I doubt that anyone would be able to say that wima box caps out perform topmays, or Panasonic, or whatever - there's no audible difference. The only thing to watch for is noise, an they all perform the se in those respects.

Jacob

[Jabulani Jonny]

Can I carry this a step forward and ask when to use Tantalum caps versus Electrolytic?  I'm getting ready to build up a Bear Hug compressor and I see several builds using all Electrolytics, while Jon's build splits the difference between Electrolytic and Tants.  I've got the same values of both, but I'm just wondering when I should go with one over the other.  Thanks!

EDIT:  Hey Look What I Found!!  -  http://www.beavisaudio.com/techpages/Caps/

[aballen]

also, worth mentioning, the circles, which are usually electrolytic caps have a polarity, meaning the is a right way and a wrong way to put them in.  There are bi-polar electrolytic, but I have yet to see one in a pedal.

You probably saw this on the kits you already built.  So when you see a square 1uf, typically its film, a round 1uf, typically has a "+" indicating the polarity.

As far as audio quality, some will say film is better than ceramic, some will say it makes no difference, you will have to decide for yourself. 

A personal anectdoe though.  I recently built a Zero Point SDX.  I used mostly MLCCs, which are ceramic caps.  It was an easy build, but when I first tested it, I thought something was wrong and immediately questioned my choice in caps.  Oh, I shoulda used film, I thought.  We once it was boxed, I loved it.  It was just user error, without knobs I did not have a good grip what position the pots were in.... really it was just in my head....and I'l probably still use film wherever I can.