Strymon Tech Corner #1 – Anatomy of an expression pedal

Welcome to the first post of our new Strymon Tech Corner series! I will be posting technical articles on music electronics as part of our blog at least once a month. Pete, Dave and Gregg from our team may also write an article here and there when they can get time away from their PCB layout programs and DSP emulators. Hopefully you’ll find these posts helpful and informative.

In this first edition I’ll be going through the inner workings of the common expression pedal. Once we know how one works, then comes the fun stuff … tearing them apart, modding, etc, etc. But that will be left to next month’s article 🙂

expression pedal from moog

We knew from day 1 that we wanted some of our pedals to feature expression pedal inputs. So, the question was “what’s the standard?” That is, do all manufacturers make their expression pedals the same way? Luckily the answer is yes … mostly.

Expression pedals work by feeding a control voltage to a device, such as a guitar pedal or synthesizer. The voltage is read by the device and then used to change some type of parameter. The voltage range depends on the design of the pedal or synth. Our Strymon pedals, for example, read control voltages from 0 to 5 volts DC. Turns out that this is a fairly common voltage range, especially in music electronics where MIDI (a 5V system) is still popular and widely used after over 25 years. The expression pedal itself, however has nothing to do with the voltage range. It’s only function is to manipulate that range and control the control voltage. The way almost every expression pedal out there works is that it takes a reference voltage from the device it’s connected to, divides that voltage down by a certain amount and then feeds it back to the device. In electronic terms, this is most commonly accomplished with a TRS (tip / ring / sleeve) 1/4″ cable where the reference voltage is on the “ring,” the control voltage is fed back to the device on the “tip” and the “sleeve” is ground.

Here  is what a standard 1/4″ TRS plug looks like:

As you can see from this 1907 diagram, TRS has been around for a long long time 😉

Here is the schematic for a typical expression pedal:

As you can see, the simplest and most common method is to use a passive potentiometer. A reference voltage from the device would enter the expression pedal jack on the ring. Then that voltage gets connected across a 10k load which is the resistive element of the potentiometer. When you move the expression treadle up and down there is a mechanical mechanism that physically turns the treadle potentiometer or “pot” as it’s commonly known. You can visualize the arrow at pin 1 of the treadle pot moving from pin 3 to pin 2 as one moves his/her foot back and forth on the pedal. This is what varies the voltage at pin 1. This is the control voltage which then travels out of the pedal on the tip of the jack. R2 is only present as a current limiter and not applicable to this discussion.

The Moog EP-2, Roland EV-5, and M-Audio EX-P all work in this manner, and therefore, work with our pedals. The nice thing about this standard design is that the control voltage is very stable and the value of the potentiometer in the expression pedal doesn’t matter so much. The Line6 EX1 is the only one we’ve see that works differently, with only a simple resistor divider and a mono cable. The nice thing about their solution is that it uses a mono cable. Two disadvantages are: 1. The expression pedal input circuit is highly dependent on the value of the potentiometer in the expression pedal.  2. Their products won’t work with other manufacturer’s expression pedals and vice versa.

Watch our video for more info and audio demos with our Brigadier delay and Orbit flanger.

I hope you’ve enjoyed this first edition of the Strymon Tech Corner. Tune in next time where we’ll make our own D.I.Y. expression pedal from a broken crybaby wah!

Happy shredding!

*All product names used in this article are trademarks of their respective owners, which are in no way associated or affiliated with Strymon.

Enjoy this article?

Subscribe to our newsletter to be the first to hear about new Strymon products, artist features, and behind the scenes content!

Related Articles

68 Responses

  1. I would love to build an expression pedal instead of buying a Line 6 ex 1.

    Have you any tips on building one of these please?


    1. It uses a mono jack. The guys at Mission engineering make a compatible pedal if you want an alternative to the EX-1.

  2. Hi, i have a doubt ’cause i see some schematics of expression pedal and appear two pot, one of 10k ohms and other of 50k ohms, what’s the function for pot of 50k ohms? thanks for reading. Greeting from Puebla, México.

  3. I wired a 25 Ohm pot with a 1k resister to a stereo jack and its not working, Is a 25 Ohm pot just not going to work?

  4. That’s a cool function for the delay time. To do this with a TimeLine would you program the delay time to HALF the original delay time for an octave down? I think that’s right…

    1. What I did was use the minimum volume pot on the side of the expression pedal and adjust it so that the delay time correlates to an octave in pitch change. The important thing is that you need a variable clock delay which is available with the Brigadier or the TimeLine’s dBucket delay type.

  5. I have wah pedal ( active) if I just disconnect the battery and connect special cable (trs) will this work as expression ped …or will I definitely have to drop the circuit board it is a
    DanWah pedal ( danolectro)

  6. hey, this is great. I’m about to do it right now. do you know how to turn a hammond pedal into a volumen guitar pedal? thanks!

  7. Hi Terry, could you tell me how the Line6 EX! is made?
    It should be a 10k linear pot soldered with a mono TS jack.
    Is there a resistance somewhere?
    Thanks, Stef

  8. hi , i have a roland ev5 expression pedal , i plug into the strymon timeline , but doesn t work . you can help me?

  9. Hi everyone, I´ve been thinking about how to use my old Zoom FP01 expression pedal with my two Strymon pedals.

    So, I´ve bought a Stereo 1/4 inch “Y” splitter adapter to two 1/4 stereo jacks, this:

    Then, I connected the stereo plug into the expresion pedal input, and use two stereo (or trs cables) to connect my pedals into the two stereo jacks of the adapter.

    I´m not sure if I may damage my Flint and El Capistan on the long run, but they´re working fine by now, can someone tell me if i´m doing something very stupid or kind of clever?


  10. Hi,

    I have a vintage synth guitar (Ibanez IMG2010) which I converted the signal to fit a new Roland VG-99, passing from 24 to 13 pins cable.

    But the BALANCE (synth/guitar) button on the guitar remains unused and I would like to get it’s signal to work as an expression pedal that I would be able to plug into the VG-99.

    Since this signal is ACTIVE, how could I do that?
    It should work as a regular expression pedal like the Roland EV-5.
    Somebody has a clue?

  11. Hi Nicolas, I just replied to the email you sent us at our support address. Take a look when you get a chance and get back to me if you have any other questions. Thanks!

  12. Hi, I’m trying to build an expression pedal from broken Vox wah pedal (v847) and so far I have a question – do I need to use stereo cable (with stereo TRS jack) and a stereo jack socket?
    I used a mono cable and no luck at all)

  13. Hi,

    I just have bought a Line 6 EX-1 to use it with my Moog MF-Drive but I noticed it didn’t work. Then I found in this website that you explain that it won’t work with products from different brands other than Line 6. So, I wonder, is there any way to make it work or Am I simply forced to look for another expression pedal?

    Thank for your time and for your answer, I’ll be waiting for it :).
    Best regards

  14. @Juan, you could try switching the jack out of the EX-1 to be a TRS jack and see if that would work. I’ve never tried it so I can’t guarantee it though.

  15. Wondering if I can use my expression pedal (same as Roland) to A/B between two signals? I have an A/B footswitch and want to replace the hard switch with a TRS jack, and plug the expression pedal into that so I can “fade” between two line signals. Is this as easy as I am imagining?

    1. @Dave – I’m not too clear on what you are trying to set up here from your description. Can you send an email to [email protected] with further details on exactly what you are trying to control?

  16. I can not for the life of me get my strymon to operate with my M-Audio EX-P. I have read the manual, I understand the instructions.

    Somehow it is not saving the heel/toe parameters, I believe.

    When I edit the heel and toe parameters, the indicator light does not yellow. Has it not registered the change?

    I’m probably missing something silly, but I am very troubled about this.

    1. Sorry for the trouble with using that expression pedal. Try the suggestion I provided you through our support email by turning down the knob on the left side of the EX-P all the way down (counter-clockwise). Turn this knob down before using EP SET and saving the preset and let me know if you still have trouble through our [email protected] email.

  17. So it sounds like most devices use the tip to ground voltage, i.e. approx 0V with pedal at heel and sleeve voltage when pedal’s fully depressed? And don’t care about the ring to tip voltage?

    Got one device that adjusts slowly at first, then bunches up near the expression pedal toe, so I’m trying to picture what pot/voltage divider curve would work better.

    1. @Dimitri – We have not tested that particular expression pedal, but we have tested other pedals with 25kOhm resistance and those have worked well for us.

  18. I can’t for the life of me get an EV-5 to work properly with the Mobius. I want the speed setting in a Rotary patch to go from lowest to highest speed but when I set it, it will only get down to 225 bpm and up to 500. Am I doing something wrong or is this the best it will do. If so? What value pot would I need to make it work as it should. Or is there a way to calibrate the pedal to the Mobius (which would be possible with virtually every other decent equipment I’ve ever seen)

    1. @Peter – Sorry to hear you are having trouble. There is actually no way to control the Rotary machine to go from the slowest speed to the fastest speed with an expression pedal. On the Mobius’ ROTARY machine, the SPEED knob controls the fast rotor speed of the effect. As there are Fast and Slow speed settings, the expression pedal is only controlling the Fast speed which is why the range does not go down as you like. You still need to toggle between the fast and slow settings to access the slow speeds.

  19. Cool. I have a “Puke Green” Snarling dogs wonder-wah and im going to take my uni-bit and drill a hole next to the output jack and using your schematics add a stereo jack “have a switchcraft” in my bag of tricks. Then solder jumpers to the onboard pot with the 1k resistor. It shouldn’t effect the pedal because it will not turn on until you plug your guitar into the input jack….. Easy Thanks.

  20. Hey guys,

    Late to the party, but I haven’t seen mention of the Yamaha FC-7 around these parts, which struck me as odd since the FC-7 seems to be so prolific. Will it work with your guys’ pedals as an expression pedal? Thanks!


    1. @Dustin – Thanks for checking out the blog! Since the FC-7 has a mono TS cable connection, we do not recommend using it as an expression pedal with our gear since they require a TRS stereo cable connection from an expression pedal.

    2. FC7 is highly regarded among professional keyboard players. Hugo is mistaken: it definitely has a TRS plug and works using a voltage divider as described above. However,the polarity is opposite of many other keyboard manufacturers, so you have to either rewire the plug (exchange Tip and Ring), or get an adapter cable. The adapter cable can be found as a “expression pedal polarity reverse” or “stereo reversing” adapter.

      The adapter cable is best if you have keyboards with different polarity, or if you’re not handy with a soldering iron. But it’s such an easy job, if you have a friend who is handy with wires, this is a 1-beer job. Always best to bring the whole 6-pack, though!

  21. Hello

    Can a TRS cable/Plug harm my strymon pedal’S input/output or the board?

    I am instaling a DPC looper switch and I am runing out of path cables. I have a bunch of TRS cable that i normally use with the expresion pedals. Can this harm something in /Mobius/TimeLine/BigSky ?

    1. @Julio – Thanks for supporting Strymon! 🙂 You can use a TRS cable without damaging the pedal as only the TIP and SLEEVE of the pedal will be used with that connection.

  22. Hi,

    I bought the Strymon Big Sky and also, the expression pedal Moog EP-3. With this expression pedal, i just want to enable or disable the Strymon so i can use the effects once in a while during a song.
    I can i make it work? I plugged the EP-3 with the cable that came with it to the Strymon EXP slot but it didn’t make nothing.

    Can you please give me a help with this? Thanks!

    1. @Carlos Filipe – Thanks for supporting Strymon! 🙂 You can use the expression pedal to control parameters on the BigSky, but not the bypass function. If you assign the expression pedal to control the reverb MIX, you can fade the amount of the reverb effect in with the expression pedal. Please see the following video on how to assign an expression pedal to control a parameter:
      Just make sure to turn the BigSky’s MIX knob to control that parameter when going through the steps. If you have further questions, please email [email protected].

  23. hallo
    i have a ehx micro synth modded so the stop freq can be moved by a expression pedal. this works all right if i use a 100kpot in my pedal…
    i also have a expressionator by mission engenering. if i use the expressionator to control an other pedal (randys revenge ring mod) and the micro synth at the same time it does not work… why is this? the micro synth alone does work somehow with the expressionator but not al right. any ideas for a solution?

    and do you have a schematic or better an instruction to make a cv control with vactrols?

    1. @elias – It sounds like you may have trouble with the connections from the expressionator. It is possible that some of these pedals may require mono TS or stereo TRS connections. I would check to verify if you are using the correct cables with your setup. If this does not help, I would get in touch with Mission Engineering to verify if there is trouble with your expression ate,

  24. Hi,

    I’m using the expression pedal Roland EV-5 to control the Mix parameter of my Strymon Timeline. Is it possible to control in “Dual” Mode all the 2 Mix parameters at the same with the pedal?


    1. @Marco – Hi there, you can actually only control the knobs on the face of the pedal with an expression pedal. As there is no way to assign MIX2 to any of the knobs, you cannot control this parameter via Expression Control. You can, however, control these parameters via MIDI CC#’s 14 (MIX knob) and 33 (MIX 2).

  25. Hi Hugo, regarding this topic we talked few months ago, can you tell me please how Andy Timmons controls the Mix parameter of the Dual Delay preset on his timeline strymon with the expression pedal?

    Here the YouTube Link

    It seems that all the 2 delays are turned down.

    Thanks for your help.
    Best regarda

    1. @Marco – I could not find the exact part in that 4o minute video where it was shown, however, he does have a cable plugged into the EXP jack of the pedal so he must have the MIX2 parameter set to TRACK so that it is also controlled by the MIX knob which can be assigned to the expression pedal.

      1. Hi Hugo,

        14:57 you can listen the delay preset
        19:43 you can see he use the Dual mode
        36:25 you can listen how he use his Dunlop volume pedal as an expression pedal to control his mix level on the Strymon Dual channel delay

        So you think he has the 2nd delay set to Track so he control the entire mix level whith the Mix knob in front of the pedal?

        I cannot really reach the timing repetition he use on 14:57. he said he use a dotted eight note repetition, i tryed by ear on the timeline the 4/3 option on Time2.

        Also by reading the manual it is not very clear for me how to program the repetitions. If i have to set a specific bpm on timeline because for example i play with my band over a midi sequence how can i do?

        Thanks for help.

        1. @Marco – Yes, he has the 2nd delay set to TRACK to control the overall delay MIX with the expression pedal. Here are the recommended settings for the Andy Timmons delay:

          TYPE – DUAL
          TIME – 500ms
          TIME2 – 3/4 (500ms x 3/4 = 375ms)
          REPEATS – 11 o’clock
          REPEATS2 – TRACK (same as REPEATS knob)
          MIX – 11 o’clock
          MIX2 – TRACK
          CONFIG – SERIES
          FILTER – 10 o’clock
          GRIT – OFF
          SPEED- 9 o’clock
          DEPTH – 12 o’clock
          HIPASS – OFF
          TAPDIV – Quarter

          And to assign the expression pedal to control the MIX, go into the PARAMS menu of the preset and first set EP to ON. Then, go to EP SET and press the VALUE encoder once. The display will show HEEL; turn the MIX knob to 0%. Then, turn the VALUE encoder for the display to show TOE; turn the MIX knob to about 11 o’clock. Press TYPE to exit the menu and now save the preset with this setting. Also, make sure that EXP MD is set to PEDAL in the GLOBLS menu of the pedal.

          1. Ok perfect thanks!

            Yes my exp pedal was already setted, now i’m using an easy roland ev-5.

            I would like to ask you also If i have to set a specific bpm on timeline because for example i play with my band over a midi sequence how can i do?

          2. @Marco – On the TimeLine, you can use the TIME knob to adjust the delay time and the VALUE encoder to fine tune the delay time after you first move the TIME knob.

  26. Hi, I am trying to use an M-Audio EXP pedal to push the repeats of my El Capistan all the way up to infinite repeat but it only goes up until aproximetly 3 o’clock (Infinite repeat would be 5 o’clock on the Knob).
    Is it a limitation of the exp function of the El Capistan, a M-Audio exp problem, a setup problem or a user limitation of my brain function euhhhhh!?!?!?
    Thanks for your help

    1. @Marc Letendre – this behavior is likely due to the internal pot of the M-Audio EXP is not reaching the extent of the REPEATS parameter. We recommend using a different expression pedal like the Moog EP-2/3 or the Mission Engineering EP-25k.

  27. Could you help – I see strymon can use 10k or 25k for expression pedals. Does a 25k give more range than 10k? Does a 25k sweep values slower/wider than the 10k? Also, has anyone tested the Dunlop DVP4 Volume X Mini? Thanks.

    1. @Jeremiah – We recommend using 25k pot as it provides a slightly wider sweep to access the full knob range on our pedals. Unfortunately, we do not have any info on using the DVP4 Volume X Mini.

        1. @Martin – 10k is a bit low, but it will mostly work, but 250k may be a bit too high. We recommend something around 25-50k for best results. In your case, you should use with the TRS 10k expression jack.

          1. Dear Hugo,
            What’s the difference between Dunlop DVP4 and Roland EV-5? As far as I know the Roland is 10k linear, and it is recommended at the Strymon website. I’m looking for a small expression pedal for my Timeline. Thanks in advance!

  28. Hi,
    I use a Strymon Flint with a Moog EP-3 expression pedal to control the speed of the tremolo. It works very well, but I would like not have to press the footswitch of the Flint to start the Tremolo and use the expression pedal directly.
    Is there a possibility that the effect cannot be heard when the expression pedal is all the way down ?
    If not, is there an expression/switch pedal who could on/off the tremolo at the same time?
    If yes, do you think the Mission Engineering SP-1 will works ?

    Thank you in advance!


    1. Hello,

      This is not possible as by controlling the speed, even at minimum, the depth of the effect is still whatever you have it set to, so you would just get a very slow tremolo that is still heard.

      Sorry about that, let us know if you have more questions!

  29. Hello!

    I just bought the fantastic Strymon Riverside. My dream is to control its drive/gain/distorsion/purgatory-heat-level with my expression pedal (Zoom FP02M) from A (cleanish) to B (full-blown-solo-distorsion). This works in principle, but in practice the change from A to B happens in a very small segment of the pedal, close to heel position, i.e., it doesn’t morph smoothly through various in-between states. What should I do? Could I add, say, a resistor in the control cable to widen the sweep?

    1. You might need to use something with a larger resistance for this. This is an old article, but we currently recommend using an expression pedal with at least a 25k ohm resistance for the best results. Feel free to email us at [email protected] if you have more questions!

  30. Thank you Gohan for your kind response! For anyone having this issue, I’ve tested to add an extra resistance to the expression pedal’s cable with satisfying results! It seems that ZOOM FP02M has a nominal max resistance of R=100k ( but when measured, it seems to have a non-linear saturation point close to heel position, reaching only up to R=80k. By adding a resistor of R=50k, I was able to transform the sweep into the linear range of the Strymon Riverside and now the tones change smoothly.

Leave a Reply

Your email address will not be published. Required fields are marked *