expression pedals sleeve to ground?

[Boner]

Is it normal for an expression pedal to NOT have sleeve connected to ground? Im building a small handful of pedals that have an expression input but I dont connect sleeve to ground, but instead a different reference. Its kind of got me worried.

I dont have an expression pedal to try out so Ive been improvising with a 50k pot and TRS jack and of course everything works fine on the bench, but in use Im wondering if this will be a terrible problem.

[MikeA]

Unfortunately, expression pedals come in many flavors and there is a lack of standardization.  Here's an overview I archived from the Mission Engineering website that's no longer posted (they make expression pedals).  Part 3 talks about the pots in the pedal and how the three lugs are connected to the jack.  Expression pedals are usually passive, with the battery and/or ground coming from the device (effect pedal).  Hope this helps, Mike
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1. Potentiometer resistance.
Many devices require an expression pedal potentiometer resistance of somewhere between 5k Ohm and 50K Ohm. Some equipment is quite forgiving and will work well with anything in this range, others may require a very specific resistance to work properly. Still more equipment needs specific resistances outside this range including 100K, 250K, even 500K. Using a pedal with an incompatible resistance for the device can result in limited range, jumping or notch like response or in some cases, the pedal just won't function at all.

2. Potentiometer taper.
The taper of a potentiometer describes how its electrical resistance changes proportional to it's mechanical movement. In a linear potentiometer, the electrical resistance changes at the same rate throughout the mechanical range of the pot. In most cases, although not all, linear taper works best for expression pedals. In a logarithmic taper potentiometer, the resistance changes more slowly as you first move the pot, becoming increasingly faster as you get near the end. Log, or near log pots are commonly used in volume controls but don't always work well for other effects. This is one of the reasons why trying to repurpose a volume pedal as an expression pedal often produces unsatisfactory results. Some wah pedals use pots approximating a reverse log taper. In most cases this will not work well for an expression pedal either, but there are at least two known cases where this is actually a requirement for an expression pedal.

3. Wiring.
Most potentiometers have three connectors; Clockwise, Counter-clockwise, and Wiper. Amazingly, there are actually several different ways these can be wired, all achieving largely the same result, which means yet more variations for expression pedals.

The most common expression pedal wiring is to connect the pot to a 1/4″ stereo (TRS) instrument jack as follows:
CW —— Sleeve
Wiper — Tip
CCW —– Ring

An alternative is with the tip and the ring reversed as follows:
CW —— Sleeve
Wiper — Ring
CCW —– Tip

Yet a third way is as follows:
CW —— Sleeve
Wiper — Tip
CCW —– Tip
In this last one, the wiper and CCW are bonded together and connected to the tip and the ring is unused. This requires the use of a mono (TS) cable such as a regular guitar cable, in place of the stereo (TRS) cable used in the other two.

An expression pedal with wiring polarity that matches the equipment specifications is required. Using a pedal with incompatible wiring can result in limited range, jumping or notch like response, or the pedal just won't function at all.

[DIY Bass]

My understanding is that an expression pedal is pretty much a fancy pot, and will sit at whatever potential you connect it to.  I would not be surprised if the sleeve connector usually has continuity with the case of the expression pedal (assuming a metal case) and the jack on the pedal end would probably have continuity with the pedal case as well unless you use an insulated jack socket.  The expression pedal sleeve connecting to the expression pedal case shouldn't affect operation though - it will just sit at whatever potential the electronics of the effect pedal sets for it.

[Mark Hammer]

It's going to depend on how the pedal is supposed to exert control.  So, for instance, if the means of control was to vary a resistance that would illuminate an LED modulating some LDRs, then it might make sense to only use tip and ring, and keep a ground connection out of the picture.

Line 6 uses a variable 0-10k to ground as their standard, requiring only tip and sleeve, but many use a pot to divide down either an externally-provided or internally-provided voltage, and feed that control voltage to OTAs or whatnot.