Audio Switchbox 3.0 – Part 1







I’ve always had the need to share my computer speakers with a computer and a portable CD player, laptop, or a MP3 player.  Years ago, I used a boombox with inputs that were RCA jacks.  I used the same style connector on the switchbox, and was able to switch between the computer and a Sony Car Discman.  That system worked for quite a while, until a set of proper computer speakers were purchased, the speakers I’m still using now:  Altec Lansing ATP3.  For a while, I did not need a switchbox, until I purchased a gaming laptop.  Then I needed to switch between the desktop and the laptop.  A couple years ago, I built this:  A 2 source switchbox.

Audio Switchbox 2.0 - Front Audio Switchbox 2.0 - Back

I liked the overall design, but there was a major problem.  Since the stereo jacks were mounted on aluminum, the ground was in common, which is bad when there are two devices such as a desktop and laptop connected.  There can be ground loop issues that resulted in a humming sound.  I replaced the metal in the back with a piece of plexiglass, and installed a new 2D3P switch the ground as well as the left and right channels.

My two sons have need for 4 devices to share a single set of speakers… this presents a good challenge because of the switch that will be required.  We’ll need a 4P3T, and finding one for less than $5 proved to be a huge challenge.  I finally settled on one from Talon Electronics, a T-MEC switch was new, originally used in Soundcraftsmen Mixers.  Bonus, it was designed for an audio application!  The switch is advertized as a 4P4T, but it is not, it’s a 4P3T (which is all that is needed anyway).  The knobs I purchased are not intended for the post on this switch, but I like how they look, so I’ll make them work.  The stereo jacks are a Radio Shack part.

Knob - Side Stereo Jack Knob - Top Rotary Switch, Jack and Knob Radio Shack 274-0249

The case material will be plywood again, 1/2″ birch.  The sides will be two pieces glued together for a final thickness of 1″.  The front and back panel will be plexiglass.  Here’s the design plan so far (it will probably change as I go along):

Switchbox Rev B Switchbox - Schematic


Started out by cutting all the plywood and plexi pieces, using a table saw for all operations.  Too bad the garage was 35 degrees!  Once cut, I dry fit the pieces and made any necessary adjustments.

Switchbox Parts Switchbox Dry Fit


The plywood is glued, no mechanical fasteners were used in the assembly.  Started with the sides, attached the sides to the bottom, then attached the top.  When attaching the sides to the bottom, position them using the plexiglass.

Glue Up - First Glue Up - Second Glue Up - Third Switchbox - Final Glue Up


Next, I did some test drilling and decided to undersize the hole for the switch just slightly, and then thread it into the plexi.  It was a snug fit that will not loosen.  A couple holes were placed on the outside edges, counter sunk for the flat-head screws that will be used.

Switch Mounted - Back Switch Mounted - Front Drill And Counter Sink



Here’s a gallery of all the images:

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