Substituting Capacitors?

[Ortiz]

This is probably a dumb question, but:

I'm looking to build the Tube Screamer from GGG and I was ordering the parts from Small Bear. I noticed the 51pF capacitor (C4 here) wasn't in stock. There are, however, 47pf and a 68pf capacitors. I was wondering if it would be possible to substitute it for one of these? If so, how would it affect the sound? If not, what do you suggest?

Like I said, this is probably a dumb question, but I know very little about electronics and I'm eager to get started.

[Pedal love]

A 47pf and 51pf capacitor have slight differences, but not really anything that would cause any problems.pl

[Ortiz]

That's just what I wanted to hear. Thanks!

However I will wait a while in case there are different opinions.

[Fret Wire]

What Pedal Love said, 47pf will be just fine, you won't hear the difference between the 47pf and 51pf.

[Mark Hammer]

Memorize this formula - Freq = 1 / [2*pi*R*C] - and you will be able to answer many questions like the one you asked.

When the Gain pot is turned up full on the TS9, you will have 500k + 51k = 551k of resistance in parallel with 51pf of capacitance.  This will provide a high end rolloff at around 1/[2*3.1416*.551*.000051] = 5663hz.  If the Gain pot is at min resistance, then the rolloff starts around 61khz. 
With a 47pf cap, those rolloffs change to 6145hz and 66.4khz. 
With a 56pf cap, they change to 5157hz and 55.7khz.
With 68pf they change to 4247hz and 45.9khz.

The bottom line is that you can go upwards or downwards from 51pf quite a bit and have no impact on the tone at min gain settings.  If you tend to max out your gain however, you will notice tonal differences when you start to diverge more than 10% in either direction.  Values smaller than 51pf will tend to keep more treble when the gain is set high, and values larger will tend to roll off more treble when the gain is set high.  Increases in treble can be compensated for with the tone control, however cranking the tone up to compensate for treble loss resulting from cap choice (or lack thereof) will tend to increase hiss a bit.

So, both directions of change in cap value will "work", but one may be more to your liking and needs thanthe other.

[Ortiz]

Thanks for the info!

[jimbob]

 I had this same issue a long time ago. I found that I socketed it and tried all different values and I really didnt hear ANY difference. But, maybe you have great ears for such minute differences.

[Pedal love]

In some circuits it might be an issue. As far as I'm concerned in this case, 4 picofarads less=0.pl

[gaussmarkov]

i think someone pointed out in a similar previous thread another relevant point:  a cap rated 51pf could well be a 47pf cap and vice versa.  the nominal values aren't the actual values and tolerances are apparently big enough to allow that kind of variance.

[fusionid]

what is the variability of ceramic capacitors for say a 47pf?

[Barcode80]

generally, the tolerance is between 5 and 10% depending on the marking on the outside. most i've seen are 5%. that means that you can likely substitute within 5% of the total value and still possibly end up with the same value in actuality.

do a google search for capacitor tolerance and you should be able to turn up a chart listing letter codes for tolerance, though some caps don't have these markings.

[fusionid]

well, it is K +/- 10%
thats wooping but should do the trick. Like in is thread I need a 51 but only have a 47pf

[gaussmarkov]

fwiw, standard (or "preferred") capacitor values come in particular series values (as do resistors).  two common series for capacitors are E6 (1.0, 1.5, 2.2, 3.3, 4.7, 6. and E12 (1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2).  notice that 4.7 is in both of these series and 5.1 does not appear.  the full range of available values are these values times powers of 10.  so when you see power supply filter caps, they are values like 10, 15, 22, 33, 47, ..., 100, 150, 220, and 330uF.

google "standard OR preferred capacitor values" for some web links.

all the best, gm