Capacitors; is there a rule?

[Coda]

I am working on a new build (Muffin Fuzz, Triangle), and I decided that it was time to learn something about capacitors. I always struggle the most when picking out capacitors. Which ones to get? For example, this build calls for 4n capacitors. The PCB layout suggests that these should be electrolytic, but I can't seem to find any in that value.

Another question: does polarity always matter? I have seen non-polarized box capacitors used on PCBs that call for a polarized capacitor.

So is there a rule or trick to knowing which capacitors to get? Or is it one of those things that you just have to figure out?...

 

[mywmyw]

basically you may safely sub a non-polarized in place of polarized, but not the other way around. otherwise, check the voltage rating and value and youre good to go as long as it fits.

 

[Chas Grant]

I am working on a new build (Muffin Fuzz, Triangle), and I decided that it was time to learn something about capacitors. I always struggle the most when picking out capacitors. Which ones to get? For example, this build calls for 4n capacitors. The PCB layout suggests that these should be electrolytic, but I can't seem to find any in that value.

Another question: does polarity always matter? I have seen non-polarized box capacitors used on PCBs that call for a polarized capacitor.

So is there a rule or trick to knowing which capacitors to get? Or is it one of those things that you just have to figure out?...

I finished 2 Big Muff pedals a couple of weeks ago. A Violet Rams head and a Triangle. With the triangle variant, the only polarized cap is the 100uF (C14) in the power supply stage.

Caps are a funny breed. If you notice, with the pedal circuits they come in 3 flavors most of the time. Micro-farads (uF), nano-farads (nF) and pico-farads (pF). uF = .000001F, nF=.000000001F, and pF=.000000000001F. So say 47pF would equal .000000000047 Farads.

The pico=farads are the smallest values and normally come in ceramic disc or MLCC. MLCC are a better quality and last longer, ceramic disc are cheaper. Do yourself a favor and look for the MLCC first.

So next is nano-Farads, Higher value capacitance so the caps start getting bigger. 1nF to 1uF look for the box film caps. These have a lower noise level and caps this size are normally (but not always) in the signal path.

Now we come to uF. This is where the polarized caps come in. You'll notice that around 220nF the size of the box caps start to get bigger, for the same voltage rating. By the time you get to 1uF 100V the box caps are much bigger and toke up space. This is where they switch to polarized caps, which are quite small at 1uF 50V. Tantllums caps are also an option here these also also polarized. When using either of these you have to pay attention to the voltage polarity and ensure the + lead is connected to the higher DC value side in the circuit. Thais why you see the square pad on these. Which should take the longer lead, but always check your polarity on these caps to ensure they don't pop when applying power.

As for interchanging caps , yes you can. Just make sure the capacitance is the same for both caps, and if you are putting in a polarized cap for a film then make sure the polarity of the polarized cap is correct against the schematic..

There is overlap between the cap values and types, which is a good thing. For the triangle build there are 50nF caps (C5 and C8) used before the clipping diodes. 50nF is not a common value anymore. To get the 50nF I used 2 100nF MLCC caps and placed them in series, which is 50nF. Search for capacitance in series and parallel if you need to know more on this as its a lesson in it's self.

 

[Coda]

I finished 2 Big Muff pedals a couple of weeks ago. A Violet Rams head and a Triangle. With the triangle variant, the only polarized cap is the 100uF (C14) in the power supply stage.

Caps are a funny breed. If you notice, with the pedal circuits they come in 3 flavors most of the time. Micro-farads (uF), nano-farads (nF) and pico-farads (pF). uF = .000001F, nF=.000000001F, and pF=.000000000001F. So say 47pF would equal .000000000047 Farads.

The pico=farads are the smallest values and normally come in ceramic disc or MLCC. MLCC are a better quality and last longer, ceramic disc are cheaper. Do yourself a favor and look for the MLCC first.

So next is nano-Farads, Higher value capacitance so the caps start getting bigger. 1nF to 1uF look for the box film caps. These have a lower noise level and caps this size are normally (but not always) in the signal path.

Now we come to uF. This is where the polarized caps come in. You'll notice that around 220nF the size of the box caps start to get bigger, for the same voltage rating. By the time you get to 1uF 100V the box caps are much bigger and toke up space. This is where they switch to polarized caps, which are quite small at 1uF 50V. Tantllums caps are also an option here these also also polarized. When using either of these you have to pay attention to the voltage polarity and ensure the + lead is connected to the higher DC value side in the circuit. Thais why you see the square pad on these. Which should take the longer lead, but always check your polarity on these caps to ensure they don't pop when applying power.

As for interchanging caps , yes you can. Just make sure the capacitance is the same for both caps, and if you are putting in a polarized cap for a film then make sure the polarity of the polarized cap is correct against the schematic..

There is overlap between the cap values and types, which is a good thing. For the triangle build there are 50nF caps (C5 and C8) used before the clipping diodes. 50nF is not a common value anymore. To get the 50nF I used 2 100nF MLCC caps and placed them in series, which is 50nF. Search for capacitance in series and parallel if you need to know more on this as its a lesson in it's self.

Lots of very useful info there. So a safe full would be pF=ceramic, nF=film, and uF=electrolytic, right?

Also, a question about that 50n. I had planned on using a 47n as a substitute. Would this be a bad idea?

 

[lcipher3]

For example, this build calls for 4n capacitors. The PCB layout suggests that these should be electrolytic, but I can't seem to find any in that value.

You may want to check that "4n" value again - if it shows a round circle on the PCB (electrolytic) are you sure it's not 4u? (more commonly 4.7u or 4u7)
a "n" would mean nanofarad and I've never seen an electrolytic that small. 4u (4u7) is a common electrolytic value.

 

[Coda]

You may want to check that "4n" value again - if it shows a round circle on the PCB (electrolytic) are you sure it's not 4u? (more commonly 4.7u or 4u7)
a "n" would mean nanofarad and I've never seen an electrolytic that small. 4u (4u7) is a common electrolytic value.

C10=4nF. The layout is polarized.

 

[lcipher3]

C10=4nF. The layout is polarized.

That's odd - I'd suspect a typo - do you have a schematic? What is the 4"n" doing in the circuit?

 

[Coda]

That's odd - I'd suspect a typo - do you have a schematic? What is the 4"n" doing in the circuit?

The BOM is the Triangle.

 

[krsdrm]

I believe 4nf is the correct value for that era Big Muff. Also tolerances are something to keep in mind as well. MLCC and electrolitics are usually 20% tolerance and film or box caps are any where from 5 to 10% so in all likely hood 3.9nf would easily fit the bill and is way more common than 4nf. Which is why I'm guessing most of the other Big Muff schematics have either 3.9nf or 4.7nf in that position.

 

[Chas Grant]

Lots of very useful info there. So a safe full would be pF=ceramic, nF=film, and uF=electrolytic, right?

Also, a question about that 50n. I had planned on using a 47n as a substitute. Would this be a bad idea?

The pF=ceramic, nF=film and uF=electrolytic is not a hard and fast rule but will generally work. Nothing beats reading through the build docs and doing research on the circuit your planning to build. There are alot of cases where the the build doc will call for a 1uF and if you look at the pcb its designed for a box film cap. in this case go with the box film, its most likely in the signal path and film caps have less noise and beter tolerances, so they sound better. Be sure to look at the pcb in this case, a 1uF 100V film cap is twice as wide as a 1uF 50V film cap. If the pcb outline is the same size as the other film caps then get the 50V caps. If it bigger and more square then a 100V cap is fine. But trying to fit a 100V cap into a 50V cap space is not fun, I learned this lesson the hard way.

The 47n will slightly change the tone but not by much. For a true triangle it is 50n. get 2 100nF MLCC, solder one leg from each cap together, then the other 2 legs you didn't solder will go into the pcb, since the 2 caps are in series they will equal 50nF.

 

[Chas Grant]

krsdrm is correct on 4nF. That is the value that was used around 1970. They really don't make a 4nF caps suitable for audio use these days, so 3.9nF is the closest thing there is. If you want to know all about a Big Muff check out Kit Raes page on the Big Muff. It has everything including many vintage schematics. You'll see that they used many different caps in all parts of the circuit across the years. The build doc is correct on the values for each variant, so go with the build doc if possible. The schematic with the polarized caps is for the variants where the electrolytic are used. http://www.kitrae.net/music/music_big_muff.html

 

[Nostradoomus]

Lots of caps have a 10% tolerance as it is so even if you bought a 4n cap somewhere it could still read as 3.9nf. Same goes for 50n and 47n. EHX used whatever they could get their hands on.

 

[MondoJim]

I know this is an old thread but I ran across the same errors in the PedalPCB MuffinFuzz.pdf. The schematic shows polarized caps for values that don't exist, such as 50nF and 4nF written that way in the BOM and shown as polarized in the schematic.

Since there isn't such a thing and schematics of actual Big Muffs show unpolarized, I guess there's the answer but the documents supplied with the pedalpcb.com boards are not helpful in this regard still showing these same errors for years on end. Especially since the one for the MuffinFuzz ignores the ceramic/film/electrolytic pF/nF/uF convention.

 

[Nostradoomus]

The muffin board is highly tweakable and experiment worthy, it’s meant to show you the right polarity if you choose to use a polarized cap. Note the three legged cap footprints on the actual board. It isn’t a mistake!

 

[owlexifry]

documents supplied with the pedalpcb.com boards are not helpful in this regard still showing these same errors for years on end.

it's not an error.
the polar indicators are there for the person that wishes to use polarised caps.
you can also use non-polarized caps in these positions. it really doesn't matter and it's all up to personal preference.

the idea of the board is to support multiple big muff circuits, sometimes a certain cap (e.g. C12) will differ in value depending on the circuit.
whether or not that particular cap is "supposed to be" polarized or non-polarized is irrelevant, and it certainly doesn't mean the schematic is wrong or misleading

 

[MondoJim]

owlexifry, thank you for confirming. The back of my brain figured it out after I made that post, but it took a day to stew.
It dawned on me that yeah, the BoM is correct, the PCB is labelled for multiple iterations and the schematic only matches a few of the many many versions of a Big Muff. I didn't realize that there was a version of the Triangle Muff that used no polarized caps at all until I finally scrolled down far enough on the bigmuffpage. But now this all fits.

It just threw me because I've looked to the schematic as the main source of truth in the past, not the list of components, but in this case it's a different story.

Thanks again for pointing the way after my brain hiccuped and rebooted.

 

[Nostradoomus]

Happens to the best of us

 

[andrewsrea]

First rule of caps is voltage rating (never less than 1.25% of voltage used) and polarity for polarized caps. Next, electrolytics are typically high Farad values and slower than other types. Non-polarized are more expensive and typically used for A/C filtering and could be used in smoothing stages (like a power supply cap to ground) , but the polarized are better for that. You may see an electrolytic in parallel with a mylar, to which the mylar is faster and will handle transients until the (typically large) electrolytic catches up.

I don't recall seeing anything under 400nF in electrolytic. The crossover between mylar, poly, film, etc. and electrolytic, is around 1uF. For substituting polarized electrolytics for other types, you need to assess which side of the connection has the more positive voltage via the schematic. The 'negative' (cathode) will always go to the least positive or most negative and the 'positive' (anode) will always be connected to the most positive, least negative voltage.

Hope this helps