Using wrong size potentiometers?

[rbatts2000]

Hi there

Firstly, I must say that this forum is a great place to learn about the hobby/obsession of pedal making. 

I have tried using the 'Search' function but I simply cannot find suitable answers to my (hopefully) simple questions!   

1. Would using a potentiometer that has a slightly different value than the 'recommended' pot result in much difference to the overall sound/use of a pedal?  i.e. 22k pot instead of a 20k pot.

2. Same as above but with regards to using a 'lin' pot instead of a 'log' pot.

Many thanks

Rick

[Seljer]

1.
Yeah, for small differences like that it doesn't matter in 99% of occasions in pedals. I believe the tolarance for potentiometers is very high (10 to 20%) anyway so if you've got a pot that says 500k it can be anything from 400k to 600k when you actually measure it.



2. That depends on what you're doing, it will work but the sweep will be screwed up.
eg: using a linear pot instead of a log pot for a volume control means you get the area that would regulary be from 0-8, all bunched up on 0-3 or so, and then from 3-10 it'd do barely anything

[rbatts2000]

Many thanks for the quick reponse.  I think all this information is starting to slowly sink in. 

Thanks again, you've answered a couple of questions which have been bugging me for a few days now.

[Mark Hammer]

A great many component values simply don't exist anymore (e.g., can anyone in North America find .004uf caps for Big Muff tone controls?) or else exist, but in other countries.  So, what gets called 50k here gets called 47k somewhere else by another manufacturer.  Even though we call them 9v batteries all over the world, the fact is that the individual cells that provide 1.5v really provide a little more than that.  When Munky/Marcos from Brazil posted some projects from Brazilian magazines,  I was surprised to see all schematic indications of connection to the battery supply listed as "+10v", rather than +9v.  Clearly it wasn't some fancy regulated wall supply, and electro-chemical reactions don't work differently in South America (regardless of which way the toilet flushes), so it was just another "official" value for the same type of battery.  Of course, unless someone tells you this, you are only right to think that maybe a 470k and 500k pot are different or that a .02 and .022uf cap are different.

The rule of thumb for pot taper is this:
- if it is important in any way to know what the "middle" is, then you need a linear taper; so boost/cut tone pots need a linear taper to identify the point where there is no boost or cut.
- if the function of the pot is like a volume control function, you will want a log taper pot.

Most everything else is often a matter of your taste and needs.  Some circuits will want a fancy exotic taper, but that may only be to be able to have the full range of sounds equally easy to dial in as you rotate the pot.  If you are only interested in sounds at one extreme of that range, it can sometimes be that the "wrong" taper serves your needs better than the "right taper" (which is intended to serve everyone).

Either way, taper does not affect whether the circuit will work, merely whether it will be easy for the user to dial in the sounds they want in a repeatable manner.  If all the interesting variations in phaser speed happen to fall within a 5-degree arc of pot rotation, then clearly you won't be able to quickly set the control by eye because some very different speeds may be produced by a setting that is visually similar.  When pots are twitchy and settings are hard to nail like that, that signals a taper issue.

[KerryF]

I found this picture very helpful when explaining log and linear:


red- linear
yellow- log/audio