Small pF caps - when to use ceramic or other?

[motterpaul]

I didn't get a reply before so I thought I would re-word this.

Especially for smaller caps under 1n (in the pf range) - how do you know when a more rare/expensive mica or film cap might be better than a cheap little ceramic cap?

I can get the mica, or teflon or other more costly small caps but they are costly and I don't want to use them when they don't matter.

Should I look for caps in the audio portion of circuit only?

Any simple rules to make it easy to know when are appreciated - anyone have any rules.

Does anyone NEVER use ceramic caps here?

Does anyone always use them?

[Frank_NH]

The whole topic of capacitors in audio circuits is an interesting one, but also one that has been worked over to death by the audiophile community (you know, the people who pay $10 for a mojo capacitor ).  Those arguments are, in many/most cases, not applicable to guitar effects circuits, especially if those circuits are designed to make distorted sounds!

Nonetheless, my capacitor rules are as follows:

* ceramics for < 1 nF
* box (film) caps for 1 nf - 1 uF
* electrolytics for > 1 uF

I strive to get "J" tolerance box caps (5%).  Electros can be notoriously off (> 10%), but you can always measure them if necessary.  I'm not going to get worked up about power supply filter cap values, but anything directly in the audio path is well worth measuring.  This means:

* All coupling caps
* All caps in the tone circuit or other key filters in the design e.g. op amp feedback loops or jfet source bypass.

In particular, for coupling caps, often the circuit requires 1 uF and greater values.  You can get non-polar caps up to 10 uF.  In fact, I just ordered some from Smallbear Electronics and I'm going to try them out in an upcoming overdrive build.  I think these will provide less noise and better performance (although it may just me mojo on my part unless I can do an a-b comparison).

Finally, I've had some issue measuring capacitance on my DVM for very small value ceramic caps.  For example, a 47 pF cap may measure only 30 pF!  I wonder though if this is just a limitation with low end DVM.  If this is important (as it can be with filter circuits), then maybe more expensive caps would be warranted.

[motterpaul]

Thanks Frank - that helps a lot.

I know hi-fi quality audio is not major concern with guitar effects; but noise seems to be a factor including microphonics or hum. Especially a circuit like Sabra that makes noise when interfacing with a guitar.

I hear what you are saying about tolerances, the article I posted says ceramics can really drift in certain applications, and they can be microphonic. I have seen people here recommend a film or mica (something non-ceramic) in rare instances.

I do see a lot posts saying their builds are microphonic - which to me generally means they howl (feedback) and are sensitive to touch - like if you tap the IC you hear it. It has happened to me, but it is usually something wrong with the build.

[Beaker]

Paul, it looks to me as though you are doing it again - taking a couple of comments, and deciding that a disadvantage or two implies that something should be avoided at all costs.

Yes, ceramics can go microphonic - but it only generally becomes a problem with high values. And yes they can be noisy - "hiss".

That said I totally agree with Frank - anything in the pF range, and they are invariably the best choice. They are also the best choice anywhere where space is severely limited. They are also great in naturally noisy builds - Big Muffs are a great example. The originals use ceramics, 'cos Mike Mathews was a cheapskate, and Big Muffs are noisy, but eliminating that noise does not make them inherently "better" - it's all part of the big Muff character.

You can avoid larger ceramic values, and use MMC (monolithic multilayer ceramics), which are also very small, but are less noisy. Loads of us use them 'cos they are great - and cheap.

Personally, I would not use mica, tantalum or any other expensive caps, unless the build specifies it.

BTW, and as you point out, lots of components can go microphonic - including pots, and yes, when people (including me) complain of a microphonic howl, it is almost always a build error.

Ultimately though, some builds are noisy, not because of the component types used, but because of poor design. If this is the case - and the Sabra Cadabra has been criticised as badly designed, then you might be on a hiding to nothing.

As the old saying goes "You can't polish a turd, but you can roll it in glitter".

[motterpaul]

I know it - I hope I am not a pain, but sometimes asking the question is really the best way to find the answer. So thank you again.

Just so you know, I did google this and ran into the same "long conversations" that Frank mentioned by audiophiles. One guy said "mica has a 'glistening metal' effect on your tone, so what we really recommend is teflon" - geeze.

So - sorry to be a pain, but at least you are really helping someone learn. So kudos for that. I have many different kinds of caps already, MMCs included. I should use them more, but they are so damn hard to read.

[Beaker]

Then you need something like this:

https://www.buildcircuit.com.au/wp-content/uploads/2015/02/capacitor-color-code-chart.png


Just compare the number printed on the MMC cap to the chart, and it will tell you it's value.

EDIT: By the way, I would not worry too much about cap tolerances - particularly down to picofarad values. These tiny value caps  in tone circuits are ripe for substituting with higher or lower values to tune the tone to taste.

I never bother to measure them myself, just whack them in.

[motterpaul]

Heh heh... what I need are more like this....



But for finding codes I usually use:

http://www.electronics2000.co.uk/

You know, I was going to say I'm with you on the sound of a fuzz being what it is. I get it. But I have noticed a lot people (especially women) get pretty uptight when they hear an amp making noise - they are like "what's that noise?". And have you ever noticed at a club if a mic feeds back for even a second half the audience grabs their ears and whines? "Oh, my tender ears, ouch..."

My reaction is "shut up you crybabies, it was just a noise. Get over it." but that is what happens.

I'm in a band with a chick singer/sax player and she heard my amp humming just a little but last week (I didn't even notice it) so she said "If your amp knew the words it wouldn't have to hum." I wanted to tell her to "F*ck off" but I just didn't say anything.

Anyway - noise is something that some people make a big deal out of - and we all talk about making the best pedals we can, so if there is a way to make a pedal quieter without ruining the sound, it probably makes it more sellable, too. Bottom line, I think everything that makes a pedal better is good to know, even if there is a point of diminishing returns, but it also depends on who is using the pedal.

Edit - I realized I don't even have a cap setting on my DVM. I didn't know they made them when I bought it.

[Silver Blues]

I just tend to not like to use ceramic caps in my builds at all, sometimes I do for the sake of convenience and/or availability but in an ideal case I wouldn't use any.

[Beaker]

"Anyway - noise is something that some people make a big deal out of - and we all talk about making the best pedals we can, so if there is a way to make a pedal quieter without ruining the sound, it probably makes it more sellable, too. Bottom line, I think everything that makes a pedal better is good to know, even if there is a point of diminishing returns, but it also depends on who is using the pedal."

You are right there, and ultimately, it's all in the design of the original circuit,  some are way better designed than others.

However, and it's just my personal preference, but I would take any number of crude, primitve two knob 60's or 70's fuzzes, even with all their faults, (hell, even because of all their faults), than any modern ten knobbed monsters that promise to address every tonal "issue". I just find that designing out all the flaws also takes out all the character and "fun factor" of their ill-behaved Neanderthal ancestors. That and you seem to spend all your time twiddling knobs to get it sound right, instead of playing your guitar!

[motterpaul]

And there's nothing wrong with wanting the original design with all the flaws (I'll send some TGP missionaries your way)  -

Seriously, I think that's cool and have no problem with it. It's like the original Les Paul bridge - if you have a '52, you want the original tailpiece, even if the later stop tailpiece was considered an improvement.

So - Silver - what would you use instead of ceramics for anything under 1nF given an ideal world?

[rocket88]

"However, and it's just my personal preference, but I would take any number of crude, primitve two knob 60's or 70's fuzzes, even with all their faults, (hell, even because of all their faults), than any modern ten knobbed monsters that promise to address every tonal "issue". I just find that designing out all the flaws also takes out all the character and "fun factor" of their ill-behaved Neanderthal ancestors. That and you seem to spend all your time twiddling knobs to get it sound right, instead of playing your guitar! "

i actually agree with you beaker. i think that's part of the reason i have my obsession with Ge. they're finicky, ill tempered, pain in the ass to get right if the weather isn't what they want, but it's that quality that makes them great, IMHO. it's part of my issue when it comes to modifying and designing pedals now, as if there's too much tweakability then i feel like a lot of the effect is lost. believe it or not, i like my BMP to SOUND like a BMP, which is why i'm happy with the simple mids switch, you can change a bunch parts, like using LEDs or Ge diodes instead of Si, but it still will retain that muff character. i don't need 9million controls like the musket.

but, on the original topic at had i typically will use multilayer ceramics to save space, and i don't find them microphonic at all. i will use the traditional ceramics in a lot of old school builds to keep some of the flavor, and in some builds they just sound better then if you use film or multilayer ceramics.

to reiterate what's been said before, and by frank:

<1nF: ceramic
1nF-1uF: film (box, greenies, panasonic)
>1uF: electrolytic

note:
1 - i will use multilayer ceramic caps for everything from 1pF - 10uF if space is tight, or i don't need to worry about polarity >1uF although i only have 1uF, 2.2uF, 3.3uF, 4.7uF, and 10uF so it's limited but works.
2 - if space is really  and i have to span 2 rows and use an electrolytic i use SMD's that i remove the plastic bottom and use the short leads.
3 - i have use tantalum, and silver mica caps before when doing a mod for someone as they requested it. i compared it to my own that used more "traditional" caps and it didn't sound a damn bit different. the value of the cap effected the outcome, not the cap material. to me it's a waste of money.

[Silver Blues]

I'd use films. The mica caps are great and can be found for cheap, but aren't all that necessary in an effects circuit. One of their benefits is that they have tight tolerances and maintain their integrity at high frequencies; for example my dad uses them in RF amplifiers. My Poinsettia was a special build for me so I made a point of using the best parts I could get my hands on within reasonable price points - I have a polystyrene 47pF cap in there even though the 100pF is ceramic because it was all I had. Like I said it's not really all that big a deal, I will use them if I have to.

I agree as well, lots of knobs is sometimes good but I like simple, effective circuits.

[dbat69]

motterpaul wrote

I should use them more, but they are so damn hard to read.

Paul, I use a jewlers loupe as I struggle to see some of the numbers / letters on components.  They are cheap from China off evilbay.  This is one similar to what I use - it has a 40x magnification (30x is cheaper) and also an LED light
http://www.ebay.co.uk/itm/40X-25mm-POWER-JEWELER-LOUPE-LED-LOOP-MAGNIFIER-MAGNIFING-GLASS-LIGHTED-GT-/111482654406?pt=LH_DefaultDomain_3&hash=item19f4e24ec6

[motterpaul]

That is funny. I found a jewelers loupe in our house last week (setting up for a yard sale). They are like microscopes. But the numbers are that small.