Being used to two separate output volume dials in the Fractal FM3 I designed and built my own pedal expression dial 
I use the main output dial for one lane that goes to the PA and the expression dial that I assign to a different lane that goes to anything I would like to feed on stage. In most cases my own monitor and in the near future maybe in ear monitors.
The potentiometer is a dual gang (stereo) 50K linear type. One pot controls the expression function. This is totally passive and the lugs are directly connected to the TRS lugs on the output jack.
The other pot controls the LED dial as a visual reference. On stage you will always see if your second lane is up or not. When the volume is completey closed, the red LED at the bottom will light up, showing you that the unit has power. Once you turn the dial and the first volume indicator LED lights up, the red LED turns off. Then the volume LEDs are your power indicator. The LEDs are powered by two mirco controllers… The pedal is 9V battery or 9V DC powered and the jack will accept any Boss type power supply (negative tip). The circuit has reverse polarity protection. It also has a battery on/off switch. If you use battery only, you can switch the power off so the battery does not drain. The DC jack is switching, so the battery will be disconnected when a plug is inserted.
To be clear - this is a passive expression control and it will always work. The power is used only for the indicator LEDs 
This unit is a prototype. The Hammond case is rattle can finished and I polished the front a little too long. You can see the metal of the case is shining through on the third last LED. It will be up for sale in Germany soon.
Here is a short video: https://youtu.be/YE7-OUY_Rmk
I am currently working on a pedal VU-Meter to help level the volume of presets. I will post this here too.
A dedicated 230V properly filtered power supply with a 12V 3A output for the QC and three additional 9V outputs for pedals totalling 1,2A is also almost ready and I will post info on this gadget soon too.
Cheers, Todde
5 Likes
This is absolutely stellar work. I will absolutely buy that unit from you if you’d be prepared to make a second, or if not I’d love a look at the guts of it to see how you wired it up! What a brilliant solution mate.
I will definitely buy that power supply as well if you do indeed build it, or build my own if you release plans. Are the outputs isolated?
~ignore the following ramble if so desired~
Hoping I can get enough juice to run a Behringer Flow 8 (5v 2A 10W) Boss RC-202 (9v 400mA 3.6W) and MC-101 (5v 500mA 2.5W)
Total 16.1W max draw… 9v x 1.2A = 10.8W… any way to beef it up a little without significant unnecessary complication? Seems unlikely that the mixer is using all of that 10W and will probably be fine on… one sec… the remaining 940mA @9v… but I don’t know much about headroom in power supplies and the drop down converters I’d need, only the basic math for wattage etc and handy with a soldering iron.
1 Like
Hi there,
thanks for the kind words. Making this expression pedal involved quite a lot of work from the very first idea to the actual finished and working device. It involves CAD drawing the LED circle with the through hole for the pot. Then using CAM software to make the actual machine file and then CNC-machining a Hammond 1590 case. Then inserting all the LEDs with a specially CNC-machined stencil, hooking them up to the two required controllers, writing the programm that actually turns the LEDs on and off at desired potentiometer positions, installing and hooking up all the rest and then finishing the case. I consider this a fully working prototype that has a minor finish flaw. I will be making two further versions (different colored LEDS and case colors) and would be happy to sell you my prototype if you live in the European Community. Send me a pm with your email address.
I am almost finished with the power supply. More info in the next post. I am currently working on a normal sized 20 LED and a smaller footprint 10 LED VU-Meter-Pedal in order to be able to match the volumes of different presets. Another detail the QC does not have.
Here’s a gut shot of the expression pedal. The output jack and the switch are not installed yet. I had just finished programming the controllers.
Cheers, Todde
Power supply on it’s way. I still need to reposition the 12v to 9v voltage regulator. Since this one involves high voltage I am giving this to a friend of mine who is a certified technician for the final wiring. The properly filtered 12v from the transformer goes directly to the QC. The 9v outlets are not isolated, but they are only for powering my “nifty gadgets”
The reverse polarity protection is nothing special. It’s just a 1N4007 Shottky Diode wired in series with the hot wire to the boards. The controllers that control the LEDs do not like voltage peaks and reverse polarity at all - it kills them. And replacing them is a bitch. 44 pins hand wired to two pcb boards in a tight space…
I’m late to the conversation, but I’m following. Great pedal ExAxe!
The power supply is still in the works at a friend of mine. In the meantime I updated the design of the expression pedal and made a new one. It now has a proper rocker switch on top that is not so prone to damage. It runs on a 9V block battery or 6-12V DC via a power supply with a standard Boss like 2,1mm barrel plug. Polarity is not an issue anymore. Plug in negative tip OR positive tip, as you like. As long as you are within the voltage limits it will always work. Reversing the polarity of the battery (touching the connectors in reverse order) will have no effect either, it’s fully protected. Undervoltage is not a problem, it simply won’t light up. Overvoltage is not protected and will kill the micro controllers. Again, the expression function works all the time - even when the unit is not powered. It’s analog and totally separate from the indicating lights. The indicators are just a fancy feature.
I still need to find a way to clean up the internal wiring a little bit. It’s kind of a tight fit, a lot of wires to be connected …
Currently I have two further pedals on the bench. Both silver with a red status indicator and green LEDs - much like the early Kemper units … 
1 Like
