Building a Pedal Test Rig
 

When I build a pedal circuit, I almost always test it before I load it into an enclosure and do the final soldering. I do this mainly because I make a mistake or two in every project, and it sucks to have to yank everything apart to diagnose and fix the problem. Also, there are times where I want to experiment with a working circuit before I finalize the build--for example, I want to decide if a trimpot should be taken off the board and turned into a knob, or if a particular value component sounds better.

To accomplish this "test before finalize" step, one typically uses a bunch of alligator clips and other nasty twisted bits of wire to connect to input and output jacks, power and a LED. Lots of things to wire wrong or short out with all the wires involved. Another problem is that pedal circuits use the metal enclosure itself for ground, so if you wire it up and test it out of an enclosure,  you have to wire in additional clips or bits of wire to make sure you have grounded things correctly.

After struggling through the debugging process of a particularly troublesome board, I realized that I was spending way too much time disconnecting and reconnecting all the wires. At the same time, wires that were soldered to the board were getting loose and sometimes falling off with all my heavy-handed testing. It was time for a change.

My idea was to take an unused pedal enclosure, put in and out jacks, a 9v wall wart adaptor and a standard LED and make it all easy to get to. So when I'm ready to test a circuit, I just hook it into this rig without alligator clips and I'm ready to go. I also threw in a SPST switch, and a Dying Battery Simulator so I could play around with voltage drops in any pedal.

Once I had everything wired into the Hammond enclosure, I ran the wires out through a hole and attached them to a 13-position barrier strip. (A barrier strip is a really simple piece of plastic with screw terminals, like this:)

Typical barrier strips

I then mounted the whole thing on a piece of thin plywood, added a 10 vDC meter for visual indication of the input voltage, and added rubber feet to the bottom so it wouldn't slide around on my workbench.

Finally, I printed small labels so I'd know what each position on the barrier strip was for. Now I simply use a screwdriver to hook the circuit wires into the front side of the barrier strip, plug in a 9v wall wart and I'm ready to go.

The completed test rig
(click on the picture for larger version)
 

Build Your Own

This was a very easy project to build and has saved me a lot of time and misery. You don't have to follow my design exactly--there are lots of things you can do. I've seen far better test rigs which include integrated breadboards, a row of various value pots, additional LEDs and other great prototype/testing gear. Let your imagination run wild...