Pot Terminal Numbering in Schematics

[Phend]

Hello:
Is there a rule of thumb for numbering pot terminals in schematics.?
I understand volume, where terminal 1 is ground (in most cases I guess) when turning CW the volume goes UP.
Now take the attached Orange Squeezer picture as an example.
There are Gain and Bright pots.
Suppose turning the Gain CW and wanting it to Increase, would terminal 1 be towards Gnd ?
And with Bright, assume turning it CW to increase the "Brightness" which terminal is which ?
Note that each of these pots have two terminals that are connected, is that a clue.?
Thanks for any help and education.

[aion]

This is one of the things that was very frustrating for me early on, and honestly it still throws me off once in awhile in an unfamiliar circuit. It's proper to number the pot terminals or at least mark the CW terminal (pin 3) in schematics, and generally for official schematics you'll see this, but not always in DIY redraws. In cases like this where it's omitted, you're just expected to know which is which based on the operation in the circuit.

Looking at this one, I can say that Level has input to pin 3 and pin 1 is grounded, just because that's how all volume controls work. Gain and Bright are variable resistors, meaning one outer pin is shorted to the middle pin. But which outer pin depends on whether you want the resistance to increase or decrease as you turn the pot up (clockwise).

In both of these cases, reducing the resistance will increase the named effect, so you'd get more gain and more brightness as the 10k resistors are lowered. This means you'd want pins 1 and 2 shorted for both of these controls.

In this application, when a pot is wired as a variable resistor, it doesn't matter which direction it goes, because a resistor is not polarized. So using Gain as an example, as long as pins 1 and 2 are shorted, then it doesn't matter whether R10 connects to pin 3 or to pins 1/2, the operation will be the same.

[antonis]

You can locate lugs numbering by identifying pot's role..

e.g. P1 is a Gain pot.. Gain increases in reverse with resistance (proportionally if it was in place of R9).. So, for gain increase when pot turned CW, lug 3 should be the one connected to C8/R9/pin2 node..

[Rob Strand]

Agree with everyone else it's just an annoyance.

If you already have a schematic then it's pretty easy to work out what the gain pot pins need to be.

The tone rotates can be wired two ways clockwise treble vs counterclockwise.  There's no correct
way to do it although most modern pedal go for Clockwise = treble.

Sometimes the real pedal is not logical, for example on some transistor based pedals one of the distortion related knobs seems to go the wrong way. It's always very tempting to make it normal.

Be aware not all schematics represent the real pedal.

Take P1 and P2 there's actually 4 ways to wire those pots and be functionally equivalent:
- Leave pins 1 (ccw) and 2 (w) connected together.  Then swap the positions of 1+2 with 3.
  Does the same thing. the pot still produces a low resistance in the clockwise position.
- Now suppose we don't connect pin 1 and just connect pin 3.  Still works.
  We have two cases pin 2, 3 and shown and then the case where we flip 3, 2.

So four connection with the same behaviour.   I have a preference for connecting 1 and 2 together
since it can crackle a bit when the pot gets old - especially when used as the feedback gain pot.

With log pots and antilog pots you have to use the correct pins, but there is still the option to
leave the one pin hanging.

Some examples:
- Boss SD1
  https://www.hobby-hour.com/electronics/s/sd1-super-overdrive.php
  Drive pot.
  Want high resistance when drive on full.
  That requires the pot to be at maximum resistance in the clockwise position.
  That requires pin 1 (ccw) and pin 2 (cw) are the main terminals with the option of connecting 2 to 3.

  Many pedal uses a log taper pot here but we still need to use the same pins.
  An anti log taper cannot be substituted unless you make clockwise = lowest gain, which makes no sense.

- MXR distortion +
  https://3.bp.blogspot.com/_1KIwZrxSy6A/S-ZcjF6uRaI/AAAAAAAAAeU/5k2LTErtfNE/s1600/mxr_distortion_plus.gif
  Distortion pot.
  Want low resistance when drive full
  That requires the pot to be at minimum resistance in the clockwise position.
  That requires pin 2 (ccw) and pin 3 (cw) are the main terminals with the option of connecting 1 to 2.

  Most pedal uses an antilog taper pot here but we still need to use the same pins.   
  A log taper cannot be substituted unless you make clockwise = lowest gain, which makes no sense.

- Frequency pots on filter more often than not an antilog will be more correct but you might
  see linear tapers due to availability. 
  https://aionfx.com/project/ivp-preamp/

  Want low resistance when at highest frequency setting clockwise/max.
  That requires the pot to be at minimum resistance in the clockwise position.
  That requires pin 2 (ccw) and pin 3 (cw) are the main terminals with the option of connecting 1 to 2.

- When a tone pot is wired as a variable low pass filter it the same as a frequency pot.
https://1.bp.blogspot.com/_YMwCptcbQ4w/SncGgswJZNI/AAAAAAAAAcs/OPnOwgXFNeg/w1200-h630-p-k-no-nu/boss_ch1_superchorus.jpg

- An alternative connection for a tone pot is a circuit like the OCD:
  https://tg-music.neocities.org/schem/ocd_schem.png

  If you want clockwise = treble then you want highest resistance at tone maximum/clockwise.
That requires pin 1 (ccw) and pin 2 (cw) are the main terminals with the option of connecting 2 to 3.

You could use a log pot here but again you also see linear.

Don't forget if you want the tone to work opposite to what I have mentioned you need to flip the taper.
The rat tone control is an example.  For the last case, on guitars you see log pots and the tone is high cut, so there you go.

I hope I haven't screwed up any of the examples.  It's easy to do.  So many cases.

[amptramp]

The schematic for the OCD above shows another means of identifying pot terminals:



The arrows beside each pot indicate the direction the slider of the pot goes when it is turned clockwise.  This has been used for ages in schematics and there are some for antique radios that show this rather than pot terminal numbering.

[bluelagoon]

That arrow for direction which indicates clockwise rotation in pin 3 direction is by far the best method to simplify orientation.

Brought the matter up the other day, with some further helpful tips.

https://www.diystompboxes.com/smfforum/index.php?topic=130894.msg1270709#msg1270709

[Phend]

Thanks all for the help, hope this will also help the needy someday.