Building an FX Loop Footswitch

RECENTLY, I HAVE BECOME INTERESTED in modifying pedals. I modified my Vox Wah pedal by adding an LED and a true-bypass function. It came out great, and it made me want to give my TS-9 Tube Screamer a true bypass. I can’t seem to find any info on how to do this, though. Can you help me? —Anthony Muñoz

You are smart to go for true bypass in your pedals. Without true bypass, an effects pedal can muddy and/or drag down your signal when the effect is disengaged. There are several different types of switching designs used on stompboxes. Some, including your Vox’s, use mechanical switches. Adding a true bypass for an effect such as this is a simple modification. Other designs use IC switching triggered by a pulse. And still others, like the TS-9, use FETs (field effect transistors). To add a true bypass to such a pedal is a complicated undertaking. A much simpler solution would be to make a passive FX Loop Footswitch, which can be used with any pedal to give it instant true bypass. With this device, the “send” is connected with a short patch cable to the input of the effects pedal, and the output of the effects pedal is connected to the “return” of the footswitch. The effects pedal is permanently switched on, and is taken out of the signal path completely with the FX Loop Footswitch, thus giving you true bypass while eliminating the need to modify the pedal. If you have more than one effects pedal, you may prefer to make a Multi-FX Loop Footswitch, which can connect to several pedals to give them all a true bypass.

Parts for this project will cost $55 to $85, depending on whether you are making a single or multiple FX Loop Switcher. Here’s what you’ll need (the part numbers listed below can be found at Antique Electronic Supply, tubesandmore. com):

• One metal project box, such as a Hammond enclosure box (part #P-H1444-8). For a three-loop version use part #P-H1444-16.

• Four Switchcraft 1/4" phone jacks (part #W-SC-11). You’ll need eight jacks for a threeloop switcher.

• One Carling DPDT footswitch (part #PH497). Order three for a three-loop version.

• 20-gauge hookup wire (part #S-W804L-50).

• Rosin core solder (part #S-T9001).

Let’s start building. For a single FX loop device, look at Figure 1 (see page 192). This is a wiring diagram that shows the view looking inside the chassis enclosure. You will begin by drilling mounting holes in the enclosure box. Drill 3/8" holes for the input, output, send, and return jacks. You will also need to drill a 1/2" mounting hole for the actual DPDT footswitch, but I would wait and drill it after the jacks are installed so you can space it appropriately and make sure it clears the jacks. Notice there is a short jumper across two leads on one end of the switch, and there is a short hook-up wire going from the “hot” of each jack to a lead on the switch. Make all wire connections and solder each termination. After making a solder joint, it is best to let the switch cool completely before making the next solder joint to avoid overheating the switch. If you melt the innards of the switch, it will be history.

If you would like to build a Multi-FX loop switcher, look at Figure 2. You would build it basically the same way, except there are three stages instead of one. You could easily expand it to four or five or six stages just by adding more switches and send/return jacks. It is important to use an enclosure box made of a conductive material so that all the grounds on all the jacks are made properly, and to also provide shielding to reduce noise. Good luck. I think you’ll be pleased with the results. — Gerald Weber, Kendrick Amplifiers