DIY Proximity Wah

Because I’m getting so many questions about my “DIY Proximity Wah” video on YouTube, I will use this post to write about it in some more detail.

First of all this is obviously a DIY “interpretation” of the impressive Zvex Wah Probe, so all the idea and mental work comes from Zvex Effects…

The effect unit is basically a simple twin-t wah filter (like the inductorless Colorsound Wah for example). This type of wah circuit is controlled by only one variable resistor. This resistor can be easily replaced by a photoresistor which then allows you to modulate your guitar signal by altering the incidence of light to this photoresistor. There are some solutions out there which just take that photoresistor and lead it out of the enclosure, so the environment-light is your source light and the incidence of light is controlled by the shadow of your foot, however this is not the case on this pedal and it is very likely more unstable because it depends on environment-light sources (e.g. club-stages can be dark or light-shows will influence the resistor) and the response of the filter won’t be that smooth. So on this pedal the photo-resistor is controlled by an LED. This LED is hooked up to a simple theremin-like circuit which alters the intensity of the LED with the use of an antenna that senses your body (just like your foot for example). This solution is way more stable, though it has its limitations too… The antenna reacts with everything that is on ground-potential! That is an important fact that you should keep in mind when your trying to find a suitable enclosure for this circuit. Every grounded part should be kept as far away from the antenna as possible, especially grounded areas that could be in parallel with the antenna plate. That’s why it is not possible to simply put the antenna plate isolated on your common metal enclosures for example!

So here is what I did:

I took a standard B-type enclosure, put all the circuitry in it so it is shielded from RF, mounted an angled plastic enclosure (which I found here) with two screws to the metal enclosure, traced the antenna-lead through a hole to the plastic enclosure and attached a 7.5cm x 10cm (about 3inch x 4inch) PCB-board antenna-plate to it. This way it works pretty nicely…



Here is a video I took while building this circuitry which shows the LED controlled by the theremin-circuit. For testing purposes I used the bottom of a Hammond B type enclosure as the antenna:



The final pedal in action (through the 12AX7, ECC99 MiniAmp):




HERE you can find the schematic for the theremin part I used to drive the LED and HERE you can find the schematic for the modified colorsound inductorless wah I used (the 22nF must be a mistake it should be 2.2nF like in the original CS Wah I would guess).

Finally here are my perfboard layouts and some pictures:

Btw. HERE you can find an interesting forum thread about this topic, which also includes a PCB layout.


126 Responses to “DIY Proximity Wah”

  1. Hello! It’s very interesting! What is the material necessary for this?

    • I think it’s all in this post: the enclosures, the antenna PCB, resistors, capacitors, transistors, IC and the standard guitar effect parts like jacks and a footswitch etc. or what do you mean?

      • Hey was just wondering you just ran the wire to a copper plate? Also was just wondering whats the glue like stuff you have to boards stuck to in the enclosure.

      • Yes, the antenna wire is just soldered to a copper plate. The glue is hot glue which holds the circuit-boards in place and the boards are isolated with cardboard. Not the nicest way to do it, but easy and effective.

  2. Hey man sorry but is there another layout for the theremin part of the circuit?
    I have trouble reading PCB layouts and that schematic is a little hard to see. sorry was just wondering if there was a breadboard or vero schem out there? thanks it’s a great pedal and i would love to get it started.

    • My layout is a breadboard layout… Have you tried to click on the layout to enlarge it?

      • well not really a bread board layout for example C4 does not coeect to pin 12 on that line. or am i reading it wrong and it is supposed to?

      • Well, I think this a translation problem, sorry. I’m from germany and what I mean is called “Lochrasterplatine” in german, wich means “hole grit board” translated word by word. I thought this is called “breadboard” in english and my translator tells me the same. What you are refering to is a board with a striped copper back, right? I thought this called a veroboard or stripboard in english, sorry. Is there a proper word for a “hole grit board” in english?

  3. well your is kind of a PCB layout like a computer layout. But yes vero board is with copper strips but a breadboard is for expirementing with circuits.
    Just google breadboard images you’ll see what i mean.

    • No, I did not design this for PCB! Though you could use it that way too. What I meant is a perfboard! I think this is the correct name in english…

  4. Thanks so much! just wondering, can you use a 4069 instead of the 4093?

    • No not directly, the 4093 is a quad 2-input schmitt trigger and the 4069 consists of six inverters, you would have to use a different circuitry to get it to work.

  5. Hey, guys.
    Im sorta a newbie at electronics and im having a bit of trouble with the proximity control layout. I was wondering what kind of parts were VR2 and VR2, are they just resistors. Apart from that im kool with everything else. This is a great idea btw

    • VR1 and VR2 are trimpots, variable resistors and yes, the idea is great, search for the “Zvex Wah Probe” to see where it came from.

  6. will 3k3 work in place of 3k9? I don’t have any 3k9 on hand.

  7. Ben Laing Says:

    Hey there, cool build-
    Sorry if this is a dumb question-
    I was wondering if it’s possible to mount the antenna as a pickplate on the lower bout of a guitar.
    Would the RF signal just bleed into the magnetic pickups do you think?
    And would the grounding issue you discovered be caused by the strings being in close proximity and themselves being connected to ground the guitar? Or is proximity not an issue? If it is an issue, can it be shielded?
    Also, does the photo-resistor have a value?

    Cheers- Ben

    • Thx, I never tried this myself, so I can’t really say what the difficulties are. But I’ve seen it done on guitars. I think you should avoid putting the antenna under/parallel to the strings, it would be better to put it somewhere beside the strings on the body. Here is a nice approach on youtube:

      I used a LDR with a light resistance of 4-11K and a dark resistance of app. 100K


      • Ben Laing Says:

        Well, that’s cool- That’s about what I wanted to do, and it obviously can be done-
        ~thanks for the info & the link

  8. Hey man i built this and it’s great but. I’m having trouble using it when I’m wearing shoes? I see in your video that you have shoes on but i cant get mine to work.
    Do you know of a way to boost the antenna strength?

    I have tried different shoes and different plate sizes with no change works great with my hand and foot with no shoe but not with shoes.

    • Hi, when you’re using it without shoes, is there enough space for the sole of a shoe between your foot and the antenna-plate? I’m wearing socks in my video, but you can see that there is enough space between my foot and the plate for a shoe sole. You can try to put an additional resistor in series with the sensitivity pot to ground to get a better response something between 50k-100k.

  9. doncoxon Says:

    Hi, i’m a little nubie right here…
    can I ask you which cable will connect PROXIMITY CONTROL with MODIFIED COLOURSOUND WAH??

    I mean the proximity control is controlling potentio from MCS WAH isn’t?
    so basicly the PROXIMITY CONTROL can control any potentio on any type of fx.. i a right?

    • The “connection” between the proximity circuit and the wah circuit is the LED which illuminates the LDR of the wah-circuit. And no, this circuit can only replace a potentiometer that is wired to be a single variable resistor. Most potentiometers are wired to be a voltage-divider, but you can find approaches to control voltage dividers by an antenna circuit on the internet, too.

  10. Miika Pakkala Says:

    For what price would you build me a proximity wah?:D

    • What price would you pay? 😀 No serious… I’m sorry, but I don’t sell pedals, you can buy a pretty similar unit from Zvex Effects. It’s called the Zvex Wah Probe.

  11. This is great ! i have made my own based on your layout. But i think i have a problem with the Theremin circuit, the LED will only light up when i touch the antenna. How can i fix this ?

    • Are you using a battery to test it? The circuits needs to be grounded porperly to work right. If you were using it with a battery in a normal effectsbox scenario it would be grounded through the amp. To test it with only a battery attached you need to touch the battery with the other hand or use a wall-wart. If this is not the case you have to adjust the trimpots or look for mistakes in the wiring.

  12. Hello, i got few questions.
    1. Is D1 (LED) in your prefboard layout the LED that gets brighter when getting closer to antenna?
    2. What are VR1 and VR2, some kind of variable ressistors?
    3. Can the GRound for modified colorsound and for proximity control be the same?
    4. Does the copper plate antenna have to be exact thickness?
    5. Where -9V goes?

    Thank you in advance!

    • Hi Alex,
      1. Yes.
      2. Yes, you can use trimmers here.
      3. Yes.
      4. No not exactly, for testing I used the back of a hammond B-type enclosure and in the final build a PCB-board, which are of different size, thickness and material and both worked fine.
      5. I think you’re referring to the minus pole of a 9V battery for example? The minus pole is connected to ground.


  13. Thank you very much for quick response, I’ll try to make wah like this!

  14. In modified colorsound schematic, for R7 resistor, it says “LDR’. What’s that???

  15. And, i forgot, how to connect colorsound wah with antenna?

    • “The “connection” between the proximity circuit and the wah circuit is the LED which illuminates the LDR of the wah-circuit.” That was already answered in the comments before. 🙂

      • Aaaaa, now i get it! 😀
        But how do i install the LED which shows me amount of proximity, like on Zvex Wah Probe? Is that the same LED? And, should the LED be pointed directly on LDR? What’s the distance between?
        P.S. Sorry for bad english.

      • I think there is no LED that shows you the amount of proximity outside of the enclosure of the Probe. You just put the LED and LDR directly pointing at each other in a heat shrinked tube on the circuit board and you’ve got your “connection”.

  16. I’m sorry, one more question. Did you put a pot in place of variable ressistor to control the sensitivity of antenna? And what does those two VRs do?

  17. I’m very confused about LDR, can you help me to choose the right one here:

  18. oh, i thought inverted. Ok, i think i won’t bother you anymore. 😀
    I will order parts, and tell you if i make it working. Thank you very much for everything! I’m your debtor!
    P.S. We’re neighbors, i’m from Serbia. 🙂

  19. Can I use TTL IC 74LS132 (Quadruple 2-Input Positive-NAND Schmitt Triggers) instead of 4093N ?

    • No not directly, the 74LS132 has a different pinout and if I remember correctly reading in different forums, some people had even problems with different types of the 4093, so I would recommend you to stay with the 4093, though the 74LS132 does the same operations.

  20. M0zhe3z Says:

    Hi! i think it’s very cool effect.. can i use 4011 (Quad 2-input NAND) instead of 4093? it seems different because the 4093 is Quad 2-input NAND schmitt trigger.
    I’m from Indonesia

    • Hi, you are right, they are different, so just use a 4093. 🙂

      • m0zhe3z Says:

        thanks..! I’ve already bought the 4011 because the 4093 runs out from my favourite store 😦

        Maybe I will try to make ‘auto-wah’ using 555 astable first.

  21. Sry, me again. How to connect the DPDT switch?

    • M0zhe3z Says:

      i’ve using a switch as like this:
      (maybe it’s work…)

      Not connected–|o o|—output
      +9(To circuit) —|o o|—input_source
      +9v_Source—–|o o|—input(to circuit)

      • It is not common to switch the powersupply on/off while bypassing the circuit because it could cause excessive popping noises.

    • For true-bypass you have to wire it like this:
      Effect Input -|o o|- Effect Output
      Input Jack -|o o|- Output Jack
      Both pins… |o-o| …connected together

  22. Where is + and where – for electrolytic capacitors C8 and C4 on wah and proximity control?

  23. I made the proximity circuit and i’m 99,9% sure i did it correctly, but, when i attach +9V to adapter and ground to adapter’s negative, led is working all the time. Should i maybe use battery instead of 9V adapter, and where to connect the ground? I know that on your proximity test video, u touch the battery negative, but where the ground cable from circuit goes?

    • Ground goes to the negative pole of your power supply, that is correct. Have you tried to adjust the pots? Are the pins of the transistor connected the right way?

  24. I’ve tried to adjust the pots, it does nothing at all. Pins of transistors are connected the right way, but, on which side the 4093 circuit should be turned, it’s not shown in the layout? I only see that as a potential problem.

  25. m0zhe3z Says:

    By the way, is there any alternative way for the enclosure? hammond B is quite expensive for me. (I’m only a student of high school)
    Is aluminium plate will be useful for the enclosure?

    • You can use what ever you like, there are some inexpensive similar enclosures to the original hammond B on the market, too. But if you use any non-conductive material you should isolate the circuit from RF-noises by shielding it somehow.

  26. m0zhe3z Says:

    I’ve created the wah. It’s work good… Thanks for the layout etc.
    And, i think it’s better if the wah have 2 mode, manual (using proximity) and auto (using 555 adjustable timer).

    • Yes, I thought of this too. Seems like a nice modification/extension! Could you perhaps post a link to the NE555 circuit you used? I think there might be some others interested here… 😉

  27. m0zhe3z Says:

    Hi again, i have a problem with the proximity control, the intensity of LED only increased slightly. well, I use alternative transistors, BC546 and BC557.
    Can you tell me your configuration for the pots? or, maybe i should use the LDR with more range like 8k/300k…

    • VR1 should be adjusted so that when you’re not near the antenna the LED is right before lightning up. And then VR2 should set the range in which the antenna reacts, for the largest range this should be set right before the LED lights up, too. If you’ve got the wah attached, you can set this by hearing when the frequency-sweep begins to start from dark to bright.

  28. fakcior Says:

    I’ve made proximity sensor with your layout, but i have a problem. LED lights only when I touch battery and plate in the same time. When they’re untouched LED is completely dark. I’ve checked it witch many trimpots settings. I’ve double-checked layout and componenents. I use HCF4093BE, 7,5V zener (tried also with 5,1V and without zener at all – same effect), 2N3904, 2N3906, ceramic 1nF and 47pF caps. Plate is copper PCB (9x12cm). When I touch pin 11 of IC circuit starts working properly (range ca. 8cm, reacts for trimpots adjustments). What could be the reason? Please help. I can provide pics of the circuit.

    • I’ll send you an e-mail.

      • Hi!
        I have the same problem, however, I use 4093 and 5,1 zener. The probe circuit works propertly only when I touch pin 11, otherwise it has a range of about 0,5 cm. Please help me.
        Best regards.

      • If it works when you’re touching the battery, this should be fine when the pedal is finished and connected to an amplifier. If not you can increase the resistance at VR2 to make the antenna more sensible.

      • I’ve changed the VR2 to 500k and connected the circuit to the ampifier’s ground. Now it works like a charm. Thank you very much for your help.

  29. Hi there….I’m trying to build your project….but have a problem in the proximity control section…..while testing the led….to tune the trimpots….VR1 just goes from more bright to a bit less bright….instead VR2 goes from LED on to LED off….no changes at all when I get closer to the antenna and totally no reaction as I’ve seen in your testing proximity control video.
    What do you think is wrong in the circuit?
    I checked the circuit and seems everything right!
    THanks in advance for your answer.

    • Hi, try to set the trimpots to where the LED doesn’t light. Then adjust VR1 just right there where the LED begins to light up without being near the antenna. You should now be able to control the distance/range in which the antenna reacts with VR2. If you’re using a battery for testing the circuit you should touch the outside of the battery with one hand while you go near the antenna with the other one. (the final circuit will be grounded through the amp)
      If you can’t get any good range out of your antenna, try to put a resitor with something between 250k to 500k in series with VR2. That’s a way to adjust the circuit to your antenna.

  30. FrAnZiScOoo Says:

    Hi, what antenna have you used for the proximity control?

  31. Hi, thanks for the layout, just built one and it works well. I have found that it is much louder when switched on than in bypass mode. Have I made a mistake or is there somewhere I could add a resister or pot for volume control?

    • I didn’t notice any significant volume change with this pedal, did you use the values given in the layout or the ones from the schematic? If you’re really not having any mistakes, you could try to slightly increase R2 to lower the volume.

  32. smokin_ogre_audio Says:

    Hi, this is a really great project. Thanks very much for posting this.

    I wanted to give some feedback on what I’ve experienced with this build so far.

    I’m still in the experimental stages. VR1 really didn’t do anything for me until I put a 100k resistor in series with VR2. I tried a 270k resistor to start, but I could never get the LED to turn completely off. I used the values on your perfboard layout, so I figure that the difference is in the tolerances of the components used.

    My main issue right now is that the proximity circuit seems to light the LED sporadically when its just turning on. I can hold my foot over the antenna and the wah effect will jump around very similar to a Zvex Seekwah. I know that the issue is in my proximity circuit build because I see the LED flash randomly.

    I’ve done some troubleshooting on this problem and I think it maybe an issue with the antenna position or size. I currently have it mounted at an angle to a wooden block. I can lift it off the floor and the LED seems to stop its random flashing. I’m using a copper clad circuitboard for the antenna and have cut it down slowly to about 4″x4″. The size of the antenna doesn’t seem to make a huge difference except you have to put more foot on it the smaller you make it.

    Sorry for the long-winded post. I am curious if anyone else has experienced the unstable LED issue with the proximity circuit.

    • I never experienced this unstable LED issue, you should check your wiring again.

      For different antenna sizes it can be necessary to increase VR2 or to put a resistor in series, as you did. You could even try a higher value like 500k in series to get a better response.

      Are you using a battery or an adapter?

  33. Hi there-
    Thanks so much for all your work on this. Would you use audio or linear pots for VR1 and VR2?

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  35. HI,

    which photoresistor did you choose? some LED/LDR mashup or a vactrol?

  36. trumpet1 Says:

    Hi there, Thanks for putting these circuits up its been a great project so far. I have a problem with the wah circuit in that the output is very quiet, and the brightness of the LED doesn’t alter the photoresistor at all. I used ceramic capacitors on my board in place of all but c8. is this ok?

    • That capacitors are ok, there seems to be something wrong with the wah circuit wiring I would guess, have you double checked it? 🙂

      • trumpet1 Says:

        yep the wiring is ok, just wondering if some of the components are easily overheated?

      • No, there is no special part that can be easily overheated. I’ll sent you a PM…

  37. trumpet1 Says:

    Hi again, ive picked the project up again from a rest and playing with the sound with the ldr. I now have the problem with the theramin circuit to fix. I used linear pots. is this ok? the LED is constantly not in. the +9v and ground are connected to the same as the other circuit so they are effectively in parralel. Does anyone know the common problems people have had with this circuit?

    • trumpet1 Says:

      I have now completely rebuilt the led circuit and i know all the components are correct and soldering is fine.On my 4093 i have a notch in the middle at the top between the top two opposite pins. Is this pin 1? I have assumed it is.The LED is constantly lit when the circuit is powered on. the proximity of my hand doesnt alter its intensity nor either of the pots.(they are both linear pots arent they?) Im using a 9v wall adapter and its obviosly grounded through that. any ideas?..

      • Most of the time people are having problems with the controller part, they need to increase the resistance of VR2 by putting a resistor in series with VR2 to compensate different antenna sizes and other times it is simply a wiring issue. 🙂 I’ll send you an email for further details…

  38. Hi, I’m thinking about building this circuit. However, there are only three kinds of LDR that I can buy locally: 8k/300k, 2k/20k, 28k/500k. Which of them would be the best for this project?

  39. trumpet1 Says:

    Hi there FcKw, just built a 3rd proximity circuit and its riddled with the same problem; the LED is fully on all the time. The IC im using is a 4093B, is this ok? i notice in the schematic you say a 4093N. When i remove the IC from its holder on my circuit the LED goes out.

  40. tapedeck90 Says:

    I am having a similar problem to Rasta3, in that I believe I have everything wired up correctly, and VR1 simply controls the brightness of the LED, but VR2 changes the LED from on to off. I have tried several different values for VR2 (250k, 500k, and adding some resistors in series), but I cannot get any proximity response. I have everything grounded (testing with a battery) and am touching the battery with my other hand, but the LED wont respond to proximity at all (save lighting up a little more when I touch it, but even that is not much)

    • What are you using as antenna?

      • tapedeck90 Says:

        I am using a thin copper plate I found at a craft store. I just have a single wire connected to the center of it (approx 3 in by 4 in rectangle) and wired into the schematic

      • what happens if you touch the copper plate?

      • tapedeck90 Says:

        If I touch the plate either nothing happens or else the light increases slightly depending on how the variable resistors are set. However it doesnt increase by much and that is only when making contact, not when I am near

      • That doesn’t sound to bad, I think it’s just a tweaking issue from there, I’ll send you a mail so we can discuss further details…

  41. Hi, I followed everything as close as possible but the plate is only sensitive to my hand when it is very close, almost touching. I have very little control, unlike you in your video. Also, no 4093n was available so I used 4093b. Is this alright.

  42. Thanks for you contribution, i have a doubt about the potenciometers, wich one is mounted in the box? and why you used a 200k trimpot if the schematic has 250ka & 10ka ?

    • I used an external pot in series with the 200k trim pot to have the option to adjust the proximity wahs sensitivity from the outside.

  43. hi FcKw. thanks for this awesome works. i have an old proel wah2 pedal. as we know that the plastic holder for this babe is easily broken, and yes, mine did. so i detach the circuit, omit the pots and change it to an LDR. i make a proxi control as you did, but i have a problem here. the LED is sometimes working and sometimes not. when i touch the antenna, sometimes it’s getting brighter, but sometimes not. can you explain me what actually happened?. i’m a newbie in electronics so i have no idea in what condition i am. thanks a lot. 🙂

  44. De Java Says:

    THANKYOU (danke 🙂

  45. Raphiole21 Says:

    Hello ! Thankyou for this great DIY proximity wah ! Sorry for my very bad English… I have a question about the value of R11 on the Colorsound circuit. It is written 470R. Is it not rather to 470K? Thank you for your reply.

  46. Hi, this is a great projct. I tried it myself but i also have a problem here: The Circuit works only wehen i’m touching the battery or any ground connection with one hand. what could be the problem? thx for help….

    • Hi, this is normal. The final pedal will be proper grounded through the amp and should then work like if you’re now touching a ground connection.

      • Thank you very much. The proxi-control works perfectly (As it obviously did before but i thought it was a problem). Anyway, my biggest problem right now is not the proxi but the wah circuitry. It is distorted. The sound is more like a swelling fuzz then a clean wah. ever noticed something before? Are my guitar pickups (Ibanez Gio) to powerful?

      • I haven’t noticed anything like that, does it get better if you turn down the volume of your guitar? I would recommend to recheck the wiring of the wah circuit.

  47. hello, I’m wanting to do this project. But the Zvex Fuzz Probe. Can I use the same scheme ProximityControl? I’ll make a Fuzz Factory Clone, and I think in using ProximityControlLayout?
    Will it work? I wonder where to put the LDR.
    Sorry for my english.
    I’m brazillian?

    • Yes, that should work. As I understand the fuzz probe, the proximity sensor effects the stab control. So I’d guess you would have to replace the stab potentiometer in the fuzz factory circuit with the LDR or put it in parallel with it when the proximity circuit is enabled.

  48. age2pierre Says:

    Hi there!
    I was wondering if you could explain some theory about your proximity control?
    I know you can make an oscillator with a schmitt trigger, a capa and a resistor. But here, it’s a little more complicated… :/
    To be more precise it’s the PNP and two first triggers that are beyond my understanding.
    With regards from France.

  49. vytautas Says:


    Just found your project while googling and would like to do the same project also. Before would like to ask:
    1. What are dimensions of aliuminum box, plastic box and antena plate?
    2. What potenciometer model you used?

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