More capacitor questions! Voltage rating...does it matter in a stompbox and why?

[skiraly017]

I can't get all the values I need in 100v rated caps and I can find some of the caps I need in a 63v rating. Does it really matter in stompbox? Thanks.

[calpolyengineer]

As long as the voltage rating is greater than any voltage that will occur in the circuit, there will be no problem. 63V caps would work just as well as 100V caps.

-Joe

[skiraly017]

Thanks.

Can I assume for the most part that since I'm building 9v powered circuits that 9v is the max the caps will be hit with?

[Peter Snowberg]

You don't need 100V caps in a stompbox.

Some commercial pedals use 10V caps and that is pushing it because most 9V wall warts will put out more than 10V when under less than rated loads.

Use 16V as a minimum for 9V effects and you'll be just fine. Use 25V or 35V for 18V pedals.

[Skreddy]

You may possibly prefer the sound of higher voltage caps for signal coupling in situations where you'd like to hear a fatter tone.  (edit: except in the case of electrolytic caps, where you want to keep the rating close to the actual forward DC and AC voltage being applied; it keeps them formed better)

[Mark Hammer]

The working voltage rating will depend on the function of the cap, and it is common practice to use a value 20% or more higher than the anticipated voltage, or next standard value up (e.g., 16v rating for 9v circuits). 

It will be EXTREMELY rare that any cap in the signal path (e.g., at the input or just ahead of the output volume pot) will be expected to pass more than maybe a couple of volts of signal, if that, so you could stick a 3v-rated electrolytic in front of that volume pot...if you could find one. 

Any caps used for decoupling the reference/bias voltage (called Vref or Vbias, and derived by dividing the supply voltage in half with a pair of equal-value resistors) won't have to contend with anything more than half of the supply voltage (generally 4.5v), so 6.3v ratings are often perfectly acceptable.

The highest voltage ratings for battery operated circuits will naturally be those caps expected to smooth and stabilize the power supply for the whole circuit.  If it's going to see a 9v battery across it (which could actually be as much as 10v), then it needs to be able to handle at least 12v safely, and the next standard value is 16v.

In general, 16v rated electrolytic caps will do for just about any battery-operated circuit you can name here, with the possible exception of those things like the Ibanez flanger where the circuit uses a pair of 9v batteries and regulates 18vdc down to 12.  There, you will want a 25v rated component.  These days, a bag of 16v or 25v rated caps will do you nicely for just about anything in a stompbox, unless it is high voltage.  While you can often do with less (as noted above) you won't benefit much in terms of size, and you'll probably get a volume discount buying a bunch of the same voltage rating anyways.

[Also Wik]

The norm i think is 16v or 35v. Anything higher is overkill, and anything lower isn't wise at all. Don't use 6v caps!

[skiraly017]

This question was brought on by my desire to change over to the small AVX box caps. I could find most of the values I use in the 100v range, but found all the ones I need in the 63v range.

Now, one more question. I layout I use calls for a .05 cap. The AVX's come in .047 and .056. Which one do I go with and will there be any issues if I substitute either value for the .05? Thanks.

[Pushtone]

Now, one more question. I layout I use calls for a .05 cap. The AVX's come in .047 and .056. Which one do I go with and will there be any issues if I substitute either value for the .05? Thanks.

Either one, or the cheaper one. Of course it depends on where it is in the circuit but I don't think you would be able to hear the difference between those values.

[brett]

Hi.
Except for precision caps, normal variation will be 10% or more, so the difference between 0.047 and 0.05 uF is meaningless. 

If in a few circuits (not very many), there are critical capacitors.  An example of a critical cap is the input cap in the Rangemaster, which determines the amount of treble boost (because it cuts bass).  For critical caps it is worthwhile trying smaller and larger values.  Typically  25% more and 20% less.  For example, instead of a 0.047uF, try a 0.068 and a 0.033 uF. 

There is usually some discussion in the forum archives about components that really affect pedal tone, so do a search before building any pedal to see what the popular mods are.
cheers

[Satch12879]

You may possibly prefer the sound of higher voltage caps for signal coupling in situations where you'd like to hear a fatter tone.  (edit: except in the case of electrolytic caps, where you want to keep the rating close to the actual forward DC and AC voltage being applied; it keeps them formed better)

What?!?!

[Connoisseur of Distortion]

he speaks true, satch. higher voltage caps will retain more frequencies. a TINY bit more...

tiny!

don't start building stompboxes with 1kV caps because you want better tone. if there's something lacking, use a filter and save yourself the trouble.

[R.G.]

I'm always very protective to what newbies are being told, so forgive me if I seem prickly. It's not personal, really.

You may possibly prefer the sound of higher voltage caps for signal coupling in situations where you'd like to hear a fatter tone.

What, exactly, is this "fatter tone"?

I think I know where this particular belief comes from. It's an article of faith among the hifi tweako crowd that higher voltage caps are "clearer" somehow that can't be measured. And the belief seems to have made the crossover to adverts in the "more tone!" school of guitar amps where people are looking for any way to stand out, so "more tone" is a rallying cry there these days. I suspect the amp guys don't want to talk about the hifi theory of better caps making for "an air of inner clarity, a space between the notes that is almost etched...".

Whenever I hear someone saying that changing a component makes something more better in an unmeasurable way, my puffspeak detector goes off.

Likewise this:

higher voltage caps will retain more frequencies. a TINY bit more...

makes me wonder - exactly what frequencies will it retain more of? Will I have to change the calculations I use in filters? Can I measure this? Will it be the same frequencies it retains more of? (and that's a disaster in a filter you've sweated blood in the design of) Or will it vary with cap value? And if so how??

Don't give in to the tweako dark side! Use Mother Nature's Rules, Luke!

However, in redemption we have:

don't start building stompboxes with 1kV caps because you want better tone. if there's something lacking, use a filter and save yourself the trouble.

And Mother Herself could not have said it better.

More truth:

(edit: except in the case of electrolytic caps, where you want to keep the rating close to the actual forward DC and AC voltage being applied; it keeps them formed better)

This is provably and measurably true. Right on, brother! Measurable!!

The bottom line on caps:

-There are two kinds of caps: electrolytic and others.
-Others are better in general if you can get the right value and you can fit it in side your box.
-Electrolytic is used where you can't get what you need otherwise.
-Tolerance bites you. Tolerance for non-electros is usually 10% or better. Tolerance for electros is often +80%-20%. 
-There exist measurable differences in electro signal passage versus non electros. Between non-electros the differences are tiny and difficult to measure.
-Use a voltage rating greater than the voltage the cap will encounter. This is almost a certainty in non-electros because they have trouble getting below 50 to 100V. Use what is most cost effective and which fits your board best until you can prove you need something different.
-For non-electros, use any voltage bigger than the circuit uses or generates.
-Electros need to be biased with DC to over half their rated voltage, and they last longest if that's 80%.
-Never, ever reverse an electro, even momentarily with a big signal.

[Connoisseur of Distortion]

i cannot recall where, but i am certain i read that higher voltage capacitors retain a bit more treble...

[rockgardenlove]

^I prefer little caps though, just because they're way smaller.

[Skreddy]

You may possibly prefer the sound of higher voltage caps for signal coupling in situations where you'd like to hear a fatter tone.

may
Used to indicate a certain measure of likelihood or possibility: "It may rain this afternoon."

possibly
adv 1: by chance; "perhaps she will call tomorrow"; "we may possibly run into them at the concert"; "it may peradventure be thought that there never was such a time" [syn: perchance, perhaps, maybe, mayhap, peradventure] 2: with a possibility of becoming actual; "introducing possibly dangerous innovations"; "he is potentially dangerous"; "potentially useful" [syn: potentially] 3: in a manner or to a degree possible of conceiving; "is it possibly true?" [ant: impossibly] 4: to a degree possible of achievement or by possible means; "they can't possibly get here in time for the funeral?" [ant: impossibly]

prefer
1. To choose or be in the habit of choosing as more desirable or as having more value: "prefers coffee to tea."

What, exactly, is this "fatter tone"?

There are applications in which I prefer overrated caps.  Subjectively, I perceive them as sounding punchier, clearer, fuller, having more dynamic range.  Sometimes, space constraints override my preference for bigger caps, and in most applications, it doesn't seem to matter.

Is it math?  No.  Is is science?  No.  Is it even an argument?  No.  Is it misleading?  How can it be?  I'm only stating my personal preference and subjective opinion.  Your mileage my vary.   

I think I know where this particular belief comes from. It's an article of faith among the hifi tweako crowd...

No; I was just sharing my personal experience.  I like fresh-ground coffee.  I don't like Folger's.  That doesn't make me a member of the Starbuck's Coffee Cult.

[Connoisseur of Distortion]

funny thing, as i have taken it as a given and i much prefer 25v caps. 450v is nice for amps, and they are also a real pleasure to handle (amp builders will agree, stompbox parts feel fake after making amps...)