Wiring up the off-board components, particularly a 3PDT switch, can be confusing. There are many good explanations of how to do it (see for example geofex.com, tonepad.com, and generalguitargadgets.com) and this one adds to the pile by breaking down the logic of one of the more elegant layouts with a series of detailed figures. I walk through the case where the audio jacks are not insulated from a metal enclosure, there is an LED to show when the circuit is on, and when the circuit is off there is simple by-passing with the circuit input grounded.

It seems simplest to start with the wiring for so-called true by-pass, a straight connection from the input jack to the output jack. The input jack is on the left and the output jack is on the right. They will be reversed to the usual placement when the stompbox is closed up and turned over.

The input jack pictured here is a stereo Switchcraft jack called the 12B. The output jack is a mono Switchcraft called the 11. You can read a post about these jacks in 1/4″ Phone Jacks and Plugs. The switch is a 3PDT Taiwan Blue. The picture shows

1. a white wire from the tip lug of the stereo jack (on the right, for input) to the switch;
2. in one switch position, this will connect to the white wire that goes across the bottom of the face of the switch;
3. which will then connect to the white wire that runs from the switch to the tip lug of the mono jack (on the left, for output).

So we have a simple connection from one tip lug to the other: true by-pass.

In the other switch position, we want to connect the input lug to the input of the circuit and the output lug to the output of the circuit. These are added in the following image:

The blue wire should be connected to the input pad of the circuit board. The yellow wire should be connected to the output pad of the circuit board, or to the middle lug of a level pot if one completes the circuit. I am leaving the board out of these pictures for simplicity. Any unconnected wires in this tutorial are supposed to connect somewhere on a circuit board.

As it stands, we do not need the 3PDT switch because we are only using 2 poles, one for input switching and one for output switching. The third (middle) pole can do the switching for an LED that lights up when the circuit is engaged (or not by-passed). For that we will also need a power supply, which we will get from a DC voltage supply.

This image shows the LED wiring from another vantage point, with the wires for the guitar signal removed for clarity. The LED switching opens and closes the ground connection for the LED circuit. The ground for the circuit is the sleeve lug of the output jack.

• The DC jack has a direct wire to that lug: the green wire that runs all the way across the middle of the picture.
• The LED also connects to that grounded lug through a resistor (2.2K for limiting current) and two green wires, one that goes from the LED to the switch and another that goes from the switch to the lug. Note that these two wires are connected when the switch is in the “not by-passed” position.

Also note that in this particular setup, the sleeve lugs of both jacks are connected through the aluminum enclosure that holds them. The entire stompbox is grounded through the output cable. So the input sleeve lug is grounded by its connection to the output sleeve lug through the enclosure.

In setups with insulated jacks, one must make these connections with wiring. You should still ground the enclosure in those cases because this improves the ability of the enclosure to shield the circuit from outside radio frequency (RF) signals.

Here is a close-up view of the DC jack connections:

The top lug is the positive power supply connection and the angled lower lug is the ground connection. We will use the third middle lug later when we hook up a 9V battery as an alternative power supply.

The red wire is the positive power supply. This colour is consistent with the leads found on most 9V battery snaps: red is positive and black is negative (or ground). In these pictures, I am using green for ground because it shows up better.

I prefer to use the DC jacks that are fastened with a nut on the outside of the enclosure and that is what is pictured in these figures. DC jacks also come configured with the nut on the inside of the enclosure. I find this inconvenient because it requires me to install the jack in the enclosure before I solder the wires to it. As a result, if I want to remove the circuit from the enclosure then I must unsolder these wires. The input and output jacks, the 3PDT switch, and any pots all have their nuts on the outside. If the DC jack does also, then one can remove the nuts and the whole circuit lifts out of the enclosure completely connected.

Here is a close-up view of the output sleeve lug for ground connections:

At this point, two wires are supposed to soldered to this lug. One wire is coming from the DC jack (not shown) above. The other wire is “flying in” from the switch.

Here is an image of the switch wiring with all of the wires in place: input, output, and ground connections:

Note that there is an additional green wire. This is the short wire that connects the first (input) pole of the switch to the middle (ground) pole of the switch.

• When the switch is in the by-pass position, this short green wire connects the input of the PCB to ground.
• When the switch is in the engaged position, this short green wire does not connect to anything.

This additional wire feeds the stompbox circuit a quiet input signal when the circuit is by-passed. That is the trickiest part of the switch wiring, making a nice use of that otherwise unused lug on the switch.

Now we are ready for the circuit board. Besides the input and output connections, the board needs the positive and ground connections which come from the same places as for the LED circuit: the positive lug of the DC jack and the sleeve lug of the mono output jack.

Wires for those connections appear in the figure above. Generally, it is good to run your positive supply lines next to ground lines. This is true of PCB traces as well. So I am showing the positive board supply wire running next to the ground wire for the DC jack.

I am not quite finished. I still need to add the wiring for the battery. It will take a while to make a figure for that, but in the mean time it is easy to describe. The red battery snap wire connnects to the remaining free lug on the DC jack. The black battery snap wire connects to the ring lug of the (stereo) input jack. That’s the obvious one facing up to the right of the tip connector. This battery snap hookup accomplishes two things:

1. The battery negative terminal will be connected to ground only when there is a mono plug inserted into the input jack. In that event, the ring connector is in contact with the sleeve of the mono plug and a ground connection is made through the ground lug of the input jack.
2. The battery positive terminal will be disconnected to the LED and the board when there is DC plug inserted into the DC jack.

Because of these properties, the battery will supply power when there is no alternative DC power supply and there is an input for the stompbox. Otherwise, the battery is preserved.

The basic issue that motivates concern about input and output impedances is that circuits (and individual components) generally interact when they are connected. In other words, the signal at their junction, where the output of one circuit connects to the input of another, depends on both circuits—not just on the output.

It is tempting to think of a sequence of guitar stompbox effects as a sequence of unfolding events so that the first effect “happens” and is completed, then the second effect “happens” taking the first effect’s outcome as a given. This way of thinking isn’t necessarily correct and sometimes it is quite misleading. Instead, you might think of guitar effects as sensitive communicators that not only respond to what they hear but also respond to how they are heard.

Here’s an example. Suppose that you plug a Fender Stratocaster into a fuzz face pedal. Viewed sequentially, the clean Strat signal goes into the fuzz face which adds distortion and puts out the fuzzed signal into whatever comes next in the effects chain. That seems reasonable. But if you exchange the fuzz face pedal for a tube screamer and compare the clean Strat signal in both setups, you will find that they do not sound the same. So there really isn’t one initial, clean Strat signal. Actually, the Stratocaster is a sensitive communicator and its measured output responds to differences in the way fuzz faces and tube screamers “hear.” In other words, the Strat’s output impedance interacts with the the stompbox’s input impedance.

When Impedance Equals Resistance

The simplest analogy for explaining output and input impedances is to treat the output (or source) as a perfect AC voltage source in series with a resistor and to treat the input (or load) as a resistor connected to ground. Certainly stompboxes and guitars are more complicated devices than these, but this approximation can be useful. When this output circuit is connected to this input circuit, their junction is the junction of a voltage divider. So it is possible to explain impedance within the framework of a (resistive) voltage divider, where we focus on the signal at the junction.

Here is a schematic representation. Admittedly, stompbox signal chains usually go in the other direction. as in right-to-left.

Photo credit: Gladmarr

R1 is the source (or output) resistance and R2 is the load (or input) resistance. We are concerned with the signal at the junction denoted by the red line.

First, consider two extremes. If we make the load (or input resistance) infinite, it is as though we remove that resistor altogether and leave an open circuit. In that case, the signal at the junction is exactly the output signal. On the other hand, if we make the load trivial so that the input resistor is just a wire (or a short), then the input signal goes straight to ground and there is no signal at the junction at all. In the first case, we have an input impedance that is high relative to the output impedance and the AC signal is preserved. In the second case, the input impedance is low relative to the output impedance and the AC signal is said to be loaded down.

Similar conclusions follow from extreme values for the output resistor. If the output resistor has no resistance, then the signal at the junction is exactly the output signal. On the other hand, if the output resistance is infinite then no signal reaches the junction of the voltage divider. As before, a relatively low input impedance (or relatively high output impedance) kills the signal and a relatively high input impedance (or relatively low output impedance) preserves the signal.

In between the extremes, we have a basic resistive voltage divider. In such voltage dividers, all that matters for voltage at the junction is the relative values of the resistors. The fraction of the original signal that appears at the junction is R2/(R1 + R2), as explained in Resistors in Series. If the input and output resistances are equal then the signal amplitude is cut in half by the interaction of the input and output resistances. The higher the input resistance R2, the greater the fraction of signal that appears at the junction. This formula gives precision to the basic lesson that low output and high input impedances are desirable.

More Generally . . .

Beyond the special case of a resistive voltage divider, the interaction of output and input depends on the particular AC signal. It’s really that complicated. To make the analysis tractable, electronic theory focuses on AC sine waves. In that case, there are only three characteristics of the signal to consider: amplitude, frequency, and phase. Impedance is a mathematical concept that is related to phasors, an algebraic device for solving a particular family of differential equations. If the input of a circuit does not preserve the sinusoidal character of a signal when connected to an ideal AC source in series with a resistor, then the input impedance is not even defined.

So what is the meaning of “impedance” in discussions about stompboxes? Often impedance refers to resistance that depends on frequency. An example is the behaviour of a capacitor, which actually fits into the sinusoidal electronic theory. An AC sine wave with frequency f through a capacitor with capacitance C has a resistance equal to 1/(2πfC), where resistance is the ratio of the amplitude of voltage to the amplitude of current. If you want to pursue the details, try reading Capacitors: Math.

More Practically . . .

A practical way to deal with the complications introduced by impedance is to ignore phase shifts, forget about sine waves, choose a frequency for calculations and measurement, and focus on resistance again. Later, you can always change the frequency and recalculate or remeasure to see how sensitive your results are to the frequency.

Zachary Vex gave a nice practical (as in observable) description of impedance in a post on Aron’s diystompboxes forum. The basic idea is that when R1 equals R2 in a voltage divider the voltage at the junction is half the voltage at the source. As a result, you can measure one resistor using a potentiometer (as a variable resistor) in place of the other and finding the setting that produces half the source voltage at the junction.

So let’s say you want to measure the input impedance of your effect pedal.

1. Create an AC source and connect that in series with a 1M variable resistor and the pedal.
2. Use a DMM to measure the frequency and amplitude of the source at the junction between the source and the variable resistor. Suppose you read 500Hz and 100mV rms
3. Start measuring ACV rms at the junction between the variable resistor and the pedal’s input.
4. Adjust the variable resistor until the ACV reading is 50mV at the junction.
5. Now disconnect everything and use your DMM to measure the resistance in ohms of the variable resistor.

That resistance is a practical version of impedance at 500Hz. For comparison, repeat the measurement for lower and higher frequencies.

Measuring output impedance is similar.

1. Create an AC source with a known frequency, say 500Hz, and connect that to the input of your pedal.
2. Connect the the variable resistor to the pedal’s output and to ground.
3. Use a DMM to measure the frequency and amplitude of the output of the pedal, say 500Hz and 100mV rms.
4. Start measuring ACV rms at the junction between the variable resistor and the pedal’s output.
5. Adjust the variable resistor until the ACV reading is 50mV at the junction.
6. Now disconnect everything and use your DMM to measure the resistance in ohms of the variable resistor.

In this case, it is unlikely that your pedal will put out a sine wave even if you send one into its input. So remember that we are forgetting about sine waves. All we need is a steady AC source. Don’t have one? Guess what? You probably have the parts to build one.

An alternative, but similar approach is to replace the variable resistor with a fixed resistor (R) and measure the AC voltage across the resistor (V_R) and across the source (V_S). Then calculate the impedance as (V_S−V_R)×R/V_R.

I admit it–this isn’t specifically about stompboxes. But people who need stompboxes also need amp stands. I needed several and it occurred to me that PVC pipe would be a good building material. Scouting around on the net, I found one example: PVC guitar amplifier stand. This gave me some good ideas but I decided to try something simpler. This figure above shows an exploded view of what I settled on.

The colour coding shows how I glued mine up, putting together the green, pink, and blue sections separately first and then assembling these three sections together at the end.

There are several kinds of PVC pipe and fittings out there. I chose to use 1 inch diameter Sch 40 water pipe from the hardware store. There are just two kinds of fittings, right angle and T, and that dictates what kind of angles you can make.

The principle design thought was that a tilted amp has most of the weight on the bottom. Imagine balancing an amp on one bottom edge. Then there would be no stress on the back struts at all. So some of the bracing that you might think is necessary really isn’t. Another feature of this design is that several stands are stackable.

I used one 10 foot length of pipe and had about a foot left over. I cut all of the pieces with a hack saw and did not worry much about getting the ends square.

Dry fit the whole thing together first. I was pretty casual about measurements and everything came out square enough. You can be as anal compulsive as you like though. I did take measurements of all my parts before assembling so that I could list them here … but now I cannot find that piece of paper. So custom fit yours for your equipment.

I found gluing straightforward. It’s true that you cannot take your sweet time when you glue two pieces together, but there seems to be plenty of time to line things up properly. I used the floor to make sure that T fittings lined up properly before letting something set. One thing to watch out for is some bumps on the fittings left over from manufacturing. Make sure those bumps are not facing the floor so that you get even contact.

The results are great. Here is a photo of one build, after I spray painted it black.

Stompbox circuits are not protected by copyright and they are rarely, if ever, protected by patents. Images and trade names are protected by copyright. As noted in the Wikipedia article Copyright,

Copyright does not cover ideas and information themselves, only the form or manner in which they are expressed.

Copying other manufacturer’s stompbox circuits has been standard practice in the industry since the beginning. A leading example is the many copies of the Tubescreamer by Ibanez. The copies are not labelled with either “Tubescreamer” or “Ibanez” but in other respects the copies are very similar, if not exact.

Jack Orman gives an explanation in his article Is It Okay to Clone?

Patents protect the circuit designs – copyrights on schematics do not. If there is no patent it is okay to clone, but do not use the name or trademarks of the original on your pedal. If you mention the original pedal name or company as a means of explaining that your pedal is a clone or based on its design, it would be good to include a disclaimer stating that you did not manufacture the original so that it cannot be claimed that you are trying to confuse the consumer or steal their business.

So a circuit design without a patent is in the public domain. Authors’ attempts to impose conditions for use are not binding. Demanding to be paid for application of such circuit ideas is naive. As described in the Wikipedia article Public Domain,

Public domain comprises the body of knowledge and innovation (especially creative works such as writing, art, music, and inventions) in relation to which no person or other legal entity can establish or maintain proprietary interests within a particular legal jurisdiction. …

If an item (“work”) is not in the public domain, it may be the result of a proprietary interest such as a copyright, patent, or other sui generis right. The extent to which members of the public may use or exploit the work is limited to the extent of the proprietary interests in the relevant legal jurisdiction.

Reverse engineering circuits is a form of reading about a circuit idea. In effect, producing and marketing stompbox circuits puts the associated circuit ideas in the public domain.

Manufacturers can certainly discourage attempts to reverse engineer their stompboxes. Various approaches are described by R. G. Keen in his article Dirty Tricks. R. G. concludes

In the end, [dirty tricks do] not protect a manufacturer from someone who will take the time to measure and think, and who also has the background to decide the circuit does or does not make sense from the parts that aren’t faked. … My own personal conclusion is that obscuring the contents of an effect is a costly exercise in doubtful security. I suspect that is why most makers do not use these.

Inventors do not always benefit from their ideas. Some ideas are difficult to exploit for profit even though the ideas are valuable. Claims of being exploited after placing a circuit in the public domain are mistaken. Clearly some people have been hurt and, just as clearly, they are also responsible.

If you design a circuit that might be a successful product then consider selling it to an established manufacturer. Most of the business seems to be marketing, not circuit design.

If you want your circuit ideas to be for your exclusive use then you must find a way to keep them secret. One way is to tell no one. If you want to control how your circuit ideas are used by others, then do not put them in the public domain.