Guitar pedal (stomp box) wiring explained

Discussion in 'The Pedalboard' started by irishstu, May 17, 2010.

    May 17, 2010
  1. irishstu really experienced

    OK, guys. Mark posted on another thread ( ) about a very simple pedal circuit that would be perfect for beginners. The only problem was that it doesn't deal with how to wire up a switch, DC-in, etc., etc.

    I thought it would maybe be helpful to try to explain the surrounding wiring the goes on in just about any DIY pedal, so here goes. Please feel free to ask any questions at all. I've tried to describe just about every aspect you need to understand as clearly as possible, but it is a lot for a total beginner to take in in one go. Maybe you want to just forget about a DC-in, for example. That's fine, just ask and I'll try my best to explain.

    OK, on with the show...

    Apart from the effects circuit itself, there are three things that have to be thought about when wiring up a stomp box, which are the stomp switch, the stereo input jack and the DC-in connector.

    I’ll be referring to this image throughout the explanation:


    1. The Switch

    You'll see if you look closely that I have numbered the pins on my switch. The switch you buy may not have numbers, or they may even be numbered differently. Note that these numbers refer to my picture only.

    In the OFF position, pin 4 is connected to pin 1, pin 5 is connected to pin 2, and pin 6 is connected to pin 3.

    To try to make this easy to follow, consider the left-hand column of the switch to be the input column, the middle column to be the output column, and the right-hand column to be the LED column. If for any reason you only have a 6-pin switch, you can just ignore the LED column.

    Looking at just the left and middle columns, the input comes in on the yellow wire to pin 4, is directed upwards to pin 1, which is shorted to pin 2 via the blue wire, then this is redirected down to pin 5 which is the output (brown) wire. In other words, a bypass is in operation. As the effects circuit itself is completely disconnected, it cannot influence the signal, so this is true bypass.

    As for the right-hand column, there is not much going on there. The earth is connected to pin 6 via the black wire, but it is not redirected anywhere, so nothing happens, and the LED does not light up.

    Now in the ON position, pin 4 is connected to pin 7, pin 5 is connected to pin 8 and pin 6 is connected to pin 9.

    Again, looking at just the left and middle columns, the input comes in on the yellow wire to pin 4, is directed downwards to pin 7, which then goes to the input of the effects circuit via the green wire. The output of the effects circuit goes to pin 8 via the purple wire, and this is redirected up to pin 5 which is the output (brown) wire.

    As for the right-hand column, the earth is connected to pin 6 via the black wire, which is redirected down to pin 9 and fed to the negative terminal of the LED, allowing it to light up.

    OK, that’s the switch explained, but there’s more going on here.

    2. The Stereo Input Jack

    You may be wondering why a stereo input jack is required, when you are only using a mono signal. Well, that’s because the third connector (pin 3) on the input jack is used to control the power supply to the circuit.

    Let’s assume for a moment that you are using a battery. Instead of the negative of the battery being connected straight to the negative of the effects circuit, which would mean the battery is in use ALWAYS (even when the circuit appears to be switched off), the negative of the battery is instead connected to the third connector (pin 3) of the stereo input jack. That way, when nothing is plugged into the stomp box, the third connector is not connected to anything and the battery is not being used. When you plug in a mono jack plug, it shorts the third connector to the shield connector (pin 1) of the socket, which in turn connects it to earth, powering the effects circuit.

    You may wonder why you don’t just power up the battery at the same time as switching on the effects circuit. Without going into too many details, this is because the sudden surge of power leads to a loud popping noise, which no-one wants to hear.

    3. The DC-in Connector

    Lastly, we have the DC-in connector. This also has three connectors and can sometimes cause confusion, since instead of having a positive inner (centre pin), it actually has a negative inner. I’ve numbered the pins in the diagram for clarity, as follows: pin 1 is the (negative) inner and is connected to the negative of the battery, pin 2 is the outer and is connected to the positive (+9v) of the effects circuit, and finally in a similar way to the stereo input jack, pin three is the 3rd, extra, pin and is connected to the positive terminal of the battery.

    (The difference between this and the input jack is that in this case, pins 2 and 3 are normally shorted UNTIL you plug in a power supply, at which time pin 3 becomes disconnected.)

    When nothing is plugged in, the positive terminal of the battery, which is connected to pin 3, is shorted to pin 2, and continues on its way to the positive of the effects circuit. When the power supply is plugged in, however, pin 3 (and therefore the positive of the battery) is disconnected, and the positive voltage from the power supply goes directly to the effects circuit via pin 2.

    One more thing to note is that since the DC-in socket has a positive outer, it should be one with a plastic surround, so that the outer does not make contact electrically with the enclosure (which is earthed).

    Something like this (below) is fine:


    Whereas something like this (below) is NOT suitable.


    OK, fire ahead with any questions or comments.
    Last edited: May 17, 2010
  2. May 17, 2010
  3. Mark Wein :mad:

    This is awesome. Since I just got done wiring up my BSIAB2 pedal today much of what you are talking about is fresh in my mind and now I;m understanding what it is I was doing this afternoon. :)
  4. May 17, 2010
  5. Mark Wein :mad:

    I just put a link to this thread in the "Basic Electronics" thread in this forum..would you mind if I also made it an article for the front page? It's really well written and easy to understand...
  6. May 17, 2010
  7. irishstu really experienced

    Ha. I totally understand. As long as you follow the instructions correctly (assuming the instructions are correct) you really don't NEED to understand what's going on, but it really is a bonus if you can see why things are wired up the way they are.

    Oh and I should add that there is more than one way to wire up a stomp box. The method shown above is simply a suggestion, although I feel that it is the easiest to understand and makes the most logical sense.
  8. May 17, 2010
  9. irishstu really experienced

    Wouldn't mind at all, and thanks for the compliment.
  10. May 17, 2010
  11. Mark Wein :mad:

    This is great though because I'm using these projects to gain a better understanding of basic electronics and also what makes each of these types of effects what they are...hopefully I'll be better at using them for their intended purposes, too :D
  12. May 17, 2010
  13. Mark Wein :mad:

  14. May 18, 2010
  15. Prages User Error

    Very good info. Yeah, if the instructions with the kit are good, then you don't really have to know what's going on, but having this info when it comes time to trouble shoot something is invaluable. :aok:
  16. May 20, 2010
  17. The Crusher The non chosen one!

    Awesome info on making the boost pedal with the DC jack, but what about adding an external pot to adjust your amount of boost? Is this something that you could add? I sure I could figure it out after a while, but would you use and audio taper or linear pot and what value 100k? Just some ideas :weebz:)
  18. May 21, 2010
  19. Mark Wein :mad:

    Actually, in the booster project I was planning on replacing the trimpot with an external pot to make it a usable pedal (and a DC in). I figured that once I got it built (just ordered it last night) I would experiment with a few things just for my own education but then make what I end up with part of the build...
  20. Dec 16, 2011
  21. Psychotronic Bored Silly

    One thing I don't get is where the grounds are supposed to go. They just trail off into space. Those of us who don't know, NEED to know where we're supposed to connect these grounds. AND, on many veroboard layouts, for example, there is only a single ground out -- are we to daisy chain them to the jacks? Which one first? What abouth those of us who don't want/need a battery snap, how do we omit that?
  22. Dec 18, 2011
  23. irishstu really experienced

    Good questions, Psychotronic.

    Firstly, there's no hard and fast rule about WHERE you should make a common ground, but there are a few things to keep in mind. Firstly, you should avoid a "ground loop", which is to say you should avoid joining all the grounds together, going from one to the next, until you've basically created a circle of grounding wires. This can cause a weird effect, where the ground loop kinda acts like a transmitter and, well, causes noise/interference. So, like you mentioned, you should have a common ground, which is to say that all the grounds join at one point. This is also known as a star ground. Where you make the central point is up to you, but usually some area that's easy to join a lot of wires to is best, such as the back of one of the pots.

    Remember, by the way, that if you are using metal jacks in a metal enclosure, and if you use the back of the pot as the common ground, then you have effectively already joined the grounds for both jacks, and the enclosure (yes, the enclosure should be grounded too). If you were to use plastic jacks, or the pot wasn't firmly fastened to the enclosure (metal touching metal), then you'd need to manually add a grounding wire there somehow.

    As for the "no battery clip" question, give me a moment and I'll draw up a new diagram.
  24. Dec 18, 2011
  25. Help!I'maRock! Radical Sandwich Anarchist

    how did i miss this thread?!
  26. Dec 18, 2011
  27. irishstu really experienced

    OK, I'm not sure if you can all see the original image, cos I can't (stupid Imageshack), so I'm reposting it here:


    If you don't want to put a battery clip in there, then you can go with something like this instead:

  28. Dec 18, 2011
  29. jaxn slim Your Worst Nightmare

    This is awesome. And timely. Well the bump is timely.

    I just got my Rat clone kit in the mail. Gonna get started on it sometime this week.
  30. Dec 19, 2011
  31. dodgechargerfan Kick Henry Jackassowski

    Never mind..... I looked again at my build and I'm wrong......

    My switches are wired a bit differently but the net of it is the same...
    Last edited: Dec 19, 2011
  32. Dec 19, 2011
  33. Psychotronic Bored Silly

    Ah, ok, so let me see if I got this straight. As long as I am using a metal enclosure/jacks/switch (which I am), then essentially the input and output jack grounds are, in effect, already grounded? If so, does that also mean that I only really need to send the switch and circuit board grounds to, say, the back of the pot or output jack?
  34. Dec 19, 2011
  35. irishstu really experienced

    Correct (if you go with the pot, make sure it is making good electrical contact with the enclosure).
  36. Dec 19, 2011
  37. El Borrachito Premier Staff

    Just get Jacob to explain it to you.
  38. Dec 19, 2011
  39. Mark Wein :mad:



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