The Mother Of All Switchers, or switching multiple inputs between multiple outputs

 

My latest purchases, which I will review once the instrument in question is back from the luthier, exposed a small problem for which I could not find a ready-made solution on the market and instead had to make my own.

The Problem™

I have 2 amps. Both of them have an effects loop. I am lazy and I don't want to play "plug-unplug" whenever I want to switch between both amps. I could not find a 2-channel switcher let alone a 3-channel one. Since what I need is not sold, I had to make one.

The Solution™

Behold, The MOAS (Mother Of All Switchers)!

The circuit itself is super simple. It is entirely passive and does not require any power to function. The LEDs are purely for aesthetic reasons and do nothing except be shiny.

The commons of the 4PDT toggle will receive the +9V from the DC jack (through a current-limitting resistor), the input from the instrument, the pedalboard in, and the pedalboard out. Each side of the 4PDT is connected to its own LED and respective jacks for the instrument input, effects send and effects return. These are in turn plugged into the amp's input, effects send, and effects return jacks.

Flipping the toggle will send the signals to different jacks connected to different amps. Easy as pie.

Bill of materials

To assemble the MOAS, you'll need:

• 1x 4PDT toggle
• 9x ¼-inch jacks
• 2x LED (different colors), 5mm
• 2x LED bezel, 5mm
• 1x 1.8k-5k current-limitting resistor for the LEDs
• 1x 2.1mm DC jack
• Wire. Lots of it.
• Enclosure big enough to fit all these jacks.

Optional stuff:

• 2-wire headers assemblies for the LEDs
• Piece of stripboard/veroboard/PCB cut to size for the ground rail, and insulating material
• Optional: wire wheel to buff out the enclosure and give it that brushed aluminium finish. Drill the holes first, then wire wheel the enclosure.

Notes:

• 4PDT footswitches are a tad harder to come by, but you should find the toggle switches in any good electronics store.
• If you do not need or care about the LEDs, use a 3PDT toggle switch or footswitch instead, and do not install the DC jack (obviously).
• I prefer the NYS229 ¼-inch jack. Smaller than most of its similar counterparts and much more sturdy.
• The 2-wire header assembly makes swapping the LEDs simple if you want/need to later on.
• CLR resistor: I used 1.8k, but anything between 1.8-5k should do. You could get fancy and use a trimpot to adjust the brightness instead. 
• About the enclosure...
• Any enclosure that is at least 1½ inch deep with sides long enough should do. Make sure you leave enough space between each jack, and between the jacks and the top and bottom of the enclosure. A short would not be good.
• A 1590BB is big enough but depth might be a problem.
• A1590T is deep enough, and you can arrange the jacks in a nice triangular configuration. You could try to put all the jacks on the top face where the LEDs and switch are (3 on top, 3 on the left, and 3 on the right). That would use the entire depth of that style of enclosure.

Assembly instructions

Assembly is pretty straightforward. First, cut your lengths of wire, preferably all the same length. You'll need 24 wires in total (18 for the ¼-inch jacks, 2 for the DC jack, 4 for the LEDs). Next, solder the wires to the jacks. Now the fun part begins.

Start soldering the 4PDT switch from the common pins (i.e. the center ones). I did this in the following order:

1. CLR resistor , to which the +9V from the DC jack is soldered.
2. Instrument IN (tip)
3. Effects Send (tip)
4. Effects Return (tip)

Give some time for the switch to cool down a bit, then solder one side at a time in, of course, the same order:

1. LED anode or wire from the 2-wire assembly
2. Instrument IN (tip)
3. Effects Send (tip)
4. Effects Return (tip)

For the ground rail, I recommend using a piece of stripboard/PCB cut to size. Solder all the sleeves wires, the LED cathodes, and the -9V together. When fitting the ground rail in the enclosure, make sure it doesn't short against the sides, the switch, or the jacks. An anti-static bag should work fine for that purpose. 

The assembled circuit looks like an horribly deformed squid, but it works.

With a 1590BB, the inside layout will look like this. The inputs (from the instrument and the input/output of the pedalboard) should be top-mounted (on the right side in the picture), and the switchable outputs side-mounted.

With a 1590T, it will look like this (just picture the jacks arranged in a triangle to use the full 2½ inches depth of the enclosure). Same orientation as the previous picture; top is on the right side:

I ultimately went with the 1590BB, but it's a little cramped inside... Yes, I know, A and B are swapped. I had already labeled the jacks with the enclosure upside down and I decided to just go with it...

I used an anti-static bag cut to size to make sure the ground rail doesn't short anywhere

Since the toggle will be inverted compared to the side that is toggled, I flipped the toggle 180°. Flipping the LEDs would have made them match with the toggle, but not with which side is actually toggled.

The finished product looks great and is absolutely noiseless. The toggle I used is quite good and doesn't cause the amps to "pop" when the inputs are switched. All in all, a pretty simple and fun build to do that is actually useful.

Header image: FreeImages.