I get a lot of questions via email about variations on looper pedals, switchers, A-B boxes and the like. Such projects are fun and easy because they are typically passive designs, easy to create with basic components, and don't require power or circuit boards. And there are lots of variations on what people are looking for.
So it makes sense to have one big article that covers as many variations as I can think of, all in one convenient place. Here we go...
Let's start with the absolute simplest of switches: the Kill Switch. A kill switch simply kills the signal. Press the footswitch down and it mutes the signal. And its a good introduction to the basic parts and wiring of a lot of passive projects. Here are three variations using various switch types.
You can also see from this diagram the basic input and output jack arrangement. Ground is hard-wired between the two jacks, and the tip (signal) is intercepted by the switch.
A great source for the Momentary SPST NC switch is at Small Bear: http://www.smallbearelec.com/servlet/Detail?no=1222. Input/output jacks: http://www.smallbearelec.com/servlet/Detail?no=87
Let's say you want a foot-switchable volume attenuator. For example, you want to drop your signal by a bit at the stomp of a switch. Like the kill switch, this is phenomenally easy: two jacks, a potentiometer, and a switch.
Want to do the same thing in stereo? Simply add a few jacks, a second potentiometer, and a 4PDT switch.
This is a circuit that provides hardware true bypass capabilities to any pedal or outboard gear which lacks such bypass. For example, you have a Boss pedal that you love. But you don't love the buffer being in your signal chain all the time. So you want to add a true bypass switch around it. You could try to hack a big mechanical switch into your awesome Boss pedal, but that is rarely practical. So a true-bypass box would be ideal. Here's another place where a true bypass looper would be ideal: you have a rack-mount device and you want to incorporate it into your pedal board. a true-bypass looper makes this simple. To understand this circuit, check out the following diagram:
There are two basic versions of this device: with an indicator LED and without. First up, the True Bypass Looper with no LED indicator. This version uses a simple DPDT switch and four 1/4 mono jacks.
To add an LED indicator, you have to add a few parts. First, the DPDT switch is replaced with a 3PDT switch (the extra two lugs accommodate turning the LED on and off), and a power source. The power can either be a 9 volt battery or an AC adaptor. In the following diagram, we'll use a standard power jack so you don't have to worry about batteries.
Let's throw in one more variation: we'll add a volume control that makes it easy to attenuate the level of the signal returned from the loop. This is accomplished by splicing a 100K log pot in the signal line, configured as a voltage divider. Like this:
The A/B switch is dirt simple: it switches a single input between two outputs. A great example of this is when you want a switch that routes your signal to one of two amps:
First up is an A/B switcher using a DPDT switch and no LED indicator.
As with the true-bypass looper discussed above, adding an indicator involves just a few parts. For this one, we'll use two LEDs to show an indicator for A and an indicator for B.
Phaser before fuzz? Fuzz after delay? The order of effects can change the overall tone of your signal. So wouldn't it be nice to have a switcher that makes it easy to switch between pedal order? This circuit does just that.
Here's how it works:
Plug your guitar into the input
Plug your amp into the output
Plug Send A into the input of the first pedal
Plug Send B into the input of the second pedal
Plug Return A into the output of the first pedal
Plug Return B into the output of the second peal
Fire it all up: when you stomp on the switch, A will be in front of B in the signal chain. Stomp again and B will be in front of A. Great for A/B testing of pedal order.