I learned a lot when I was trying to get a Source Audio HH3 express a Pigtronix EP-2, here's what I learned.
I wasn't able to get the HH3 to fully sweep the EP-2, and for a good reason, it never will. What I learned during that whole debacle is that the value of the potentiometer you are "Expressing" on your pedal needs to the same or lower than that of the "Expresser". So in the case of the EP-2/HH3 combo, the EP's pot value is 25k and the HH is a digital 10k.
What this means is that the HH will only express about 40% of the EP. It is probably the most overlooked issue when it comes to the typical "What's the best expression pedal?"-type questions. The answer has everything to do with what your are expressing.
All an expression pedal does is take the designated parameter that can be controlled by a pot or envelope and and sends it through the expression pedal's pot and now you can essentially turn a parameter's pot with your foot. These pots regulate the amount of voltage going to the effect.
So let's take a standard LFO/Expression pedal combo and let's say they're both 10k resistance pots. The TRS cable (Tip, Ring, Sleeve) is really only working as a two-way conductor. So let's say the pot for controlling the LFO frequency goes to the tip of the cable and that tip is then one side of the pot in the expression pedal. Then the signal goes through the pot on the expression pedal and back to the Ring part of the cable and back to the LFO telling it a specific value based on the position of the pot in the expression pedal, or, your foot.
The reason it was never going to work between the HH3 and Pigtronix EP-2 is because the EP needs at LEAST a 25k resistance pot in order for the full range of the circuit to be recognized. The REAL reason the Moog EP2s are so popular isn't just due to price, it's because the pot on the Moog is adjustable from 50k all the way down to 5k or lower.
So in a nutshell, the HH3 will only fully express FX and pedals that use a 10k pot or smaller. Obviously all the Source Audio pedals, as well as BOSS, and EHX use 10k pots for all their pedals. From what I understand, most of the Pigtronix use 25k.
Now if I haven't lost you yet, hang on, there's more. There are also two types of pots, linear and logarithmic. If you could picture a basic graph, the linear pot does what it sounds like, it goes in a straight line. We'll use volume pedal pots for this explanation. With a linear pot, you move it a little bit, the volume comes up a little bit or move it a lot the volume jumps a lot, it is directionally proportional to your movement like an equal power fade in a DAW. A logarithmic pot works a little bit differently. The movement of your foot is not proportional to the pot voltage. In other words, you can move your foot quite a bit and only get a little bit of response in volume, but once you are almost in toe position on the pedal, the volume moves up very fast.
Now in the real world, almost all volume pedals are linear, most. But that was just an example on how they work and I'll tell you why I'm telling that in a minute too. If you happen to be somewhat savvy with combustion engines, linear pots are like 4-stroke engines and logarithmic pots are like 2-stroke engines. The reason you can use volume pedals as expression pedals is that you have a TRS jack split into two TS jack in which one goes in the input and one in the output which allows you to use the pot of the volume pedal the same way as an expression pedal
After giving up on the HH3 with my EP-2, I bought the Mission Engineering Pigtronix Dual Expression pedal, which is a dual, 25k, linear pot expression pedal. Once I hooked it up to the EP-2, I was almost instantly disappointed. The reason why is because I *think*, but I'm not sure, that the pot on the EP-2 is a 25k logarithmic pot. The reason I think that is because I'd be in heel position and once I started to move my foot, the phaser would almost instantly kick on which is usually the case when pairing a linear expression pedal with logarithmic control on a pedal. A logarithmic pot on an expression pedal would provide much more smooth transition FROM the heel position. I got rid of my EP-2 (WAY too powerful for post rock) before trying it with a logarithmic expression pedal in which I think would be a perfect match, but that's speculation.
I'm telling you all this because I'm sure none of your equipment is defective, it's just that they aren't a match. Not every expression pedal works on every pedal. You have to know the value of the pot in the FX pedal and whether it is linear or logarithmic and choose your expression pedal from there.
Pedal Breeders' BIG Board Club #13