UTILITY: Test Box

When you're diving into breadboarding or building circuits, one thing becomes clear—you need a test box.  It can be used with a breadboard or a completed circuit, before you spend time boxing it up in a finished enclosure.

Testing using an enclosure that is known to work eliminates one area of trouble shooting, which often stumps new builders - and that is of course off-board wiring.  If you don't have a firm understanding of off-board wiring, you really need to spend some time on this, as it's crucial to building a working pedal.  

It's also handy that the test box can plug into a regular pedal power supply, battery or bench top power supply - basically treat it like a regular pedal, with a few extra benefits.   Before I had a full workshop set-up, my test box was mounted on a piece of plywood with a breadboard next to it, so I could carry it from the dinning room table to my amp to test (it didn't take long for the wife to suggest an alternative workspace).

I’m still using the very first one I ever built, which looks a right mess, but it works. 

TEST BOX WIRING DIAGRAM

It's fairly simple - it's just normal off-board wiring.  Use whatever switch wiring you prefer; the wiring below is probably the most common and easiest to understand, which is why I used it in the diagram.  It's not what I use in my pedals these days, but is it what's in my test box.  I prefer a wiring scheme with the circuit input grounded when bypassed.

Here's how to build your own:

REPURPOSE

Find a failed project or an old pedal casing you no longer need.  Remove the original circuit, but leave the rest of the components intact.  This gives you a good starting point.

MAKE SURE IT WORKS

Before anything else, test the existing stomp switch and make sure it works.  Reliability is key for your test box, so it's important to verify this first.

TERMINALS
On the top of the enclosure, mount the test sockets.  Personally I like the banana binding sockets as they're really designed for this kind of thing.  You can plug into the top, and/or secure wires with the screw down connection at the bottom.  

Some people use speaker terminal connections - while they work, you have less options for connections.

You will need the following connections:

• Circuit input
• Circuit output
• 9V power
• Ground

SWITCH 
Solder the input and output terminals to the corresponding contacts on the switch (where the old circuit was attached).   Stomp switches are easy to damage with a hot iron, when recycling an old enclosure, do as little as possible and do it fast.

JACKS 

I moved the input and output jacks to the top of the enclosure, as I found it easier to work with on a bench.  

POWER & GROUND

Solder the 9V and ground connections from the old, removed circuit to the newly mounted terminals.

DC / BATTERY CONNECTION

There's no battery connection, as I prefer to test circuits using a generic pedal power supply.  Why?  The cheap power supply should highlight any issues you have with circuit noise - if you plan on selling the pedal, it's good to know that it sounds fine on a terrible power supply.   

I do attach a battery to the terminals or breadboard at times to test vintage style circuits, as I don't always include the option for a DC connection on the vintage style pedals that I make.  I think a battery is the best possible supply of DC power, as it's isolated and ripple free.  That being said, I've never had an issue with my Voodoo Labs power supply using vintage style positive ground circuits with next to no power filtering or protection.