A feedback looper (FBL) is a simple device used to feed audio signal output from an guitar FX pedal, back into itself.
Features of this FBL:
- True bypass switching for any pedal
- Indicator LED to show whether effect is in use or bypassed.
- Momentary pushbutton OR "latched" operation of feedback loop, and switching between the two modes.
- Indicator LED to show whether FBL is in latched or momentary mode.
- Momentary pushbutton switching between adjustable "hi/lo" feedback levels.
- Two feedback level pots
- Output volume control
- an enclosure: some sort of box to mount all the following components in.
- 4 audio jacks, mono, 1/4 inch
- 1 switch 3pdt
- 1 switch dpdt
- 2 pushbutton, momentary "on"
- 2 resistors 1k
- 2 LEDs, any colour
- 2 potentiometers b500k
- 1 volume potentiometer a200k
- 1 battery clip, or power jack, or dead rabbit
- a bunch of wires, and some solder, and a soldering iron, and probably a drill, screwdriver, pliers, nail polish, etc.
Step 1: Step 1: Drill Some Holes!
Look at your enclosure (box). Look at all the components you're going to put into it.
Y'know what? go grasp a sharpie marker.
Arrange all your bits in the box, wherever the crap you think they should go, make sure you have room to solder wires between them (as per the circuit diagram), and then use the marker to mark where you'll need the holes.
Figure out what size drill bits you'll need for each part. Good rule of thumb here: normally all these components will come with both a nut and a washer. Make sure your drill bit is too big to fit through the nut, but small enough to fit through the washer.
Double check how you want everything to fit in the box, make sure your markey marks are all in the right places.
Drill some holes.
Step 2: Solder Some Crap
You've got all your holes drilled, now mount all your parts in the box. Put all those fine components in the box, and screw the nuts on them. Tight is good, and wrenches help, but too damn tight tends to break shit. (you'll see)
Got all your stuff in the box? everything fit okay? No terminals touching other components, or sides of the box? Good, now solder that shit together. Pay careful attention to the circuit diagram.
Oh, also, this diagram is arranged as if looking at your new FBL from the bottom (like you were soldering it's guts)
So keep in mind when you are soldering toggle switches, they work the opposite way round of what you see from the bottom. If you want "toggle up" to be "on" then "down terminals" is where you solder for that. For instance, if the bypass switch as shown here was a toggle, "toggle up" would be bypassed. But I'm assuming you use a stomp switch for that. The dpdt "mode" switch, as shown here, would be in momentary only position when the toggle is down. Also, when you flip this pedal right side up, the input jack will be on the left side (as they usually are).
Note: the LED resistor might vary a bit, depending on what size LED you're using. If your LEDs are too bright or too dim, try a different value resistor. A good range to experiment with is 300 ohms to 3k. Keep in mind that you probably don't want your indicator lights blinding you.
Step 3: Step 3: the Deluxe Model
Touch controls are stupid easy to add.
As you can see here, just wire and solder a couple of screws to the tips of your send and return jacks, and you have a touch control that works when you touch BOTH screws. Just make sure those screws are screwed into something non-conductive! If you are using an aluminum enclosure, and your touch screws are drilled into that aluminum, then they are going straight to ground! This means you'll likely get no audible signal at all! However you mount your touch controls, you want to make sure that they are insulated from the metal casing that your audio jacks are mounted in.
You'll notice that this version also includes a photoresistor. These are alot of fun. In this case we are using the photoresistor to augment the output volume control. when you shine a light on it, the volume drops. Adjusting the volume knob will affect the effectiveness of this light control. Shine a flashing light on it to achieve tremolo effects.
If you are using a dead rabbit as your power supply jack, remember that only Glenn Close can empower you.