D.I.Y A/B Box.

[DrNomis_44]

Hi Everyone,


As you probably know, I build my own FX pedals and amps, since I'm going to be organizing a pedal-board for my pedals, with the help from a good friend of mine, I found that I needed to build a device called an A/B Box in order for my pedal-board design signal-flow to work, so I bought all the parts I needed to build it yesterday from Jaycar Electronics and got to work on it today, I have just finished working on it and it seems to be working properly.

So, what is an A/B Box and what does it do?, an A/B Box is a device used to switch a signal from one signal path to another, it is particularly useful in making pedal-boards for guitars.


Say for example you've got two guitar amps, one excels at distortion sounds, the other excels at clean sounds, now supposing you want to use both amps as part of your stage setup when playing in a live band, you want to be able to use either of the sounds but you don't want to keep going through the routine of unplugging from one amp and plugging into the other, that's where an A/B Box comes in handy, you simply plug your guitar into the input, and then run an instrument lead from the A and B outputs to the two amps you're using, to switch amps simply stomp on the footswitch, the A/B Box I built is a very simple passive one, and I thought that seeing as it is such a simple design and easy to build that maybe some PBG forum members might like to build one for themselves, so here's a little D.I.Y project for those forum members interested in building one.


Here's a list of the parts I used to build mine which I bought from Jaycar Electronics, along with the Catalog numbers so you can find them:


* X1 Diecast Aluminium Box Cat. No. HB-5067

* X1 3-Pole Double-Throw Metallic Footswitch Cat. No. SP-0764

* X3 Stereo Switched 6.35mm Sockets Cat. No. PS-0195

* X1 Pkt of Adhesive Square Rubber Feet Cat. No. HP-0816

* X1 Roll of Tinned Copper Wire Cat. No. WW-4032

* Some pieces of stranded insulated wire, you can also use some vintage cloth-covered wire as used in wiring up guitar scratchplates.


I'll be uploading a couple of pics of my A/B Box build together with a wiring diagram and will also do a write-up of how I built mine, so stay tuned for more updates.


Update:


Here are the pics and the wiring diagram:










Note: The design of this A/B Box is not copyrighted so please feel free to use this design as you see fit, this is something I'm giving back to the PBG forum community for all the help I've received with my kit build....enjoy, and I hope it proves useful.

[DrNomis_44]

Here's how I built my D.I.Y. A/B Box:


1, First thing to do was to mark-out the positions of the three 6.35mm sockets and the 3PDT Metallic Footswitch, I used a metal ruler and a red CD marker pen, you can see in the pics I posted where I chose to position them, although the positions are not critical to the operation of the A/B Box you do need to make sure the soldered connections don't come into contact with the lid of the box, feel free to use the pics as a guide.

2, Once all the mounting holes have been drilled in the Diecast box, install the 6.35mm sockets and footswitches ensuring that all mounting nuts are tight.

3, Using some tinned copper-wire, I linked all the S lugs on the 6.35mm sockets together and soldered each of the lugs to the tinned copper wire as shown in the pic, the tinned copper-wire is the ground wire for all the sockets.

4, Referring to the pics, using some stranded-wire connect the T lug of the in socket to the centre solder-lugs of the footswitch, make sure you have the footswitch oriented as shown in the wiring diagram, I soldered the wire to all three centre solder-lugs but you don't necessarily have to.

5, The two outer solder-lugs of the footswitch were then connected to their respective T solder-lugs on the other two 6.35mm sockets using a couple more pieces of stranded-wire, again refer to the pics I uploaded.

6, Once the wiring-up was completed I put the lid back on the Diecast box using the 4 screws that came with the box.

7, Lastly I stuck one of the square rubber adhesive feet to the lid of the box next to each of the four holes for the screw that attaches the lid to the box.


That completes the assembly of the D.I.Y A/B Box.

[Andy40]

Doc, you are a dead set legend.

thanks for that. I've been meaning to ask if you could put up a tute on one of your stompboxes using Jaycar stuff. I don't suppose you could keep 'em coming say for an overdrive pedal, compression, delay or chorus.....no pressure....

[DrNomis_44]

Doc, you are a dead set legend.

thanks for that. I've been meaning to ask if you could put up a tute on one of your stompboxes using Jaycar stuff. I don't suppose you could keep 'em coming say for an overdrive pedal, compression, delay or chorus.....no pressure....

No worries at all mate, and I most certainly can and will keep them coming, Delays and Choruses might prove a bit difficult though as they need specialized ICs to build them, which are hard to find and are expensive when you can find them, but I will see what I can do.

[DrNomis_44]

Here's how to check if your newly-built D.I.Y. A/B Box is working as it's supposed to:


Using a Digital Multimeter set to a low Ohms range, touch the tip of the Black probe to the T lug on the input socket, then touch the Red probe to the T lug on each output socket, you should get a very low-ohms reading on one of them, note down which output socket gives the low-ohms reading, and an infinite ohms reading on the other, next press the metal actuator of the footswitch so that you hear a clicking sound and repeat the test with the Digital Multimeter, if your A/B Box is working correctly you should get a low-ohms reading for the opposite output socket to the one you noted down, if so, your new D.I.Y A/B Box is working correctly and is ready for use, if not you might have gotten the footswitch incorrectly orientated.


Hope that helps.

[Fretworn]

My DIY A/B box is dying, so I will have to build a new one soon. I'm thinking of building two back-to-back so I can switch between two inputs and two outputs.

[DrNomis_44]

My DIY A/B box is dying, so I will have to build a new one soon. I'm thinking of building two back-to-back so I can switch between two inputs and two outputs.

That sounds like a pretty cool project, I might present another little D.I.Y project about building a footswitch for a guitar amp based off the one I built for my Peavey Backstage Plus amp, so stay tuned.


I think my basic A/B Box design could be easily expanded to switch two inputs and outputs, I've got another design in my head for a pedal board that features a row of footswitches along the bottom of it, which I would like to try out at some stage.

[stan]

looks great Doc, how would you add some LEDs as a visible cue as to what you have switched in?

[DrNomis_44]

looks great Doc, how would you add some LEDs as a visible cue as to what you have switched in?

It would actually be very simple to add a couple of indicator LEDs to the basic design, the metal footswitch I used is actually three double-throw switches in one so what I would do is use one of the double-throw switches to switch the LEDs alternately on or off, you could power the LEDs using either a 9V battery through a couple of 22k current-limiting resistors, or substitute a 9V/100mA plugpack for the battery, I'll draw up a circuit-diagram for you and post a pic of it a bit later on if you want.

[stan]

yes that would be excellent thanks