how far off can my caps be?

[liam012]

Hi i have put in an order for caps for a a few pedals and some of the values i can't get however i can get some within 4pf and some within 2uf of the original or specified value- will this tuin the sound and effect alltogether or will it be ok? linking up caps could be a problem due to trying to keep to a circuit board.
any info gratefully accepted!
thanks
liam

[liam012]

here are the caps in question with the values available in brackets behind them.

Metal Film caps

6x   .05 uf (47nF)
3x   .005 uf (4.7nF)
3x   .05uf (47nF)
3x   .0027uf (2.2nF or 3.3nF)

electrolytic

2x   25uf (22uF)


ceramic disc cap:

2x   51pf (47pF or 56pF)

silver mica

2x   51pf (47pF or 56pF)
2x   396pf (390pF)
2x   225pf (220pF)
2x   50pf (47pF)

[nelson]

Depends on which circuit and where the caps are within that circuit.

[Paul Marossy]

Those values all look close enough for your build(s). If you measure your caps with a capacitance meter, you'll find that they are all over the map anyway. Unless, of course, you have bought some really high quality caps with close tolerances...  

[Mark Hammer]

First off, ignore ALL differences between those values stated as "47" something and those stated as "5" something.  For all intents and purposes, .047 = .05, 47k = 50k, 47uf = 50uf, etc.

Second, as Nelson notes, it depends.

In many instances cap values are selected because those values are handy and "won't hurt".  In many cases, cap values are selected to provide more than enough bandwidth than one really needs, just to assure that an accumulation of "just enough bandwidth" components doesn't erode tone too much.  So, if EVERY input capacitor provided a rolloff of 3db down at 30hz, maybe one or two pedals would have little impact on guitar, but 6 or 7 certainly would, and 2 would certainly have an impact on bass guitar.  Using an input (or output) cap whose calculated low-end rolloff starts around 4hz obviously will provide precious little impact on bass even with a half dozen such pedals in a row.

In the case of decoupling caps (i.e., those straddling V+ and ground or Vref and gnd) one can often tolerate values below those indicated in the schem without problem, and certainly larger values do not hurt either.

In the case of small value caps, such as those in the <1000pf range, often the function of those caps in the circuit is such that you will want to stick as close to them as possible.  For instance, changing a 100pf for a 180pf cap in the clock circuit of a flanger can bump the delay range up into chorus territory and change the sound you were aiming for.  My advice would be to post queries about the function of specific caps, and ask about what sonic changes one might expect as a function of value.

Note that even if you have the "correct" value, that is no guarantee that it will sound fabulous to YOUR ears, and you may even find yourself changing values to taste.  Note as well that there is nothing preventing you (except for maybe space) from using parallel combinations of values should the precise value not be in your parts bin at the moment.

[Paul Marossy]

Good point about the flangers and stuff. I was thinking more in terms of the typical distortion circuit. And, as Mark said, you can always parallel caps to get the "right" value(s). All of those values were close enough that I would use them in a circuit without a second thought. The only ones that were a little far off is the 2.7uF cap - you'll probably want to find a parallel combo to get you close to that. But, if it's a power supply filter or something, you can usually go with the 3.3uF cap w/o any problems.

[Pedal love]

I wouldn't worry, the values listed will do the same thing.pl

[liam012]

wow- absolutely amazingly helpful replies
thank you very much indeed-
cheers
liam

[Manolo Dudes]

2x 51pf (47pF or 56pF)

First off, ignore ALL differences between those values stated as "47" something and those stated as "5" something.  For all intents and purposes, .047 = .05, 47k = 50k, 47uf = 50uf, etc.

ASMOF, every time I measure a ceramic 47pF capacitor with an LCR meter I get a reading of 51pF  :roll:

[Mark Hammer]

It works the other way, too.  Pick up a cap that has 51pf written on the side, and it could measure 48pf.  That's why modest diferences between typical cap values can be comfortably ignored - the tolerances aren't so tight that what is printed on the component will be exactly what you want OR too far of from what you need.