How important are pot and cap tolerances

[Frequent Fog]

If you have a fuzz sounding good on the breadboard, and you're ready to build it, do you use those exact pots and electrolytic caps to keep it sounding the same, or can you just sub ones with the same nominal value?

E.G. if the the actual value of the fuzz pot is 980 ohms and you sub one that's 1.1K ohms is it going to affect the tone?

[Mark Hammer]

In the case of pots, unlikely, although it could alter the range of adjustment in the example, such that the minimum gain could be a little lower if the actual pot value were larger.  The maximum gain would be unaltered, though.

Variations in cap values tend to be more consequential IMO.

[Rob Strand]

It also depends on how fussy you are about it being the same as before. In most cases there is an acceptable change in the sense that nobody will know except you .

In a circuit not all parts have equal effect.  In some places 10% could be significant and in others 50% might not be significant.  Knowing which ones are important is a next level design skill.

In an average circuit:
- the effect of tolerances on volume pots and gain controls can be ignored.  Unless
  the pot is also used for high-pass filtering, see below
- the effect of tolerances simple tone controls which change the resistance can be ignored.
  For Baxandall tone control it is more like the following two cases.
- When caps and resistors are used for significant filtering in the audio band: 10% tolerance can produce a noticeable effect but it's difficult to detect unless you do an A/B comparison.
  20% tolerance is noticeable as a difference but not perhaps as being way off or "bad".
- When the resistance of the pot directly affects biasing of transistors then it's probably wise to make some tweaks to other parts in the circuit to restore the bias voltages to the desired values.  Many things parts affect the bias point, for example the transistors, and having a resistance which tweaks the bias voltage can be a catch-all for all the part variations.

A trick used in test instrument design is to put resistors in parallel with pots to swamp the tolerance and temperature drift of pots.  There's only a few specific cases when this can be used in audio.

[mozz]

Many pots and electrolytic capacitors are 20% tolerance. That being said, most fuzzes i build i just stick a 1k resistor in there and control the fuzz with the guitar volume.