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November 10, 2016

Balanced Audio Switchbox - Audiophile Quality

If you're an audio purist, it can be worrisome adding components in the signal path, even if it enhances convenience during your listening sessions. This is compounded even further if you are taking a delicate signal from a turntable to a phono pre. It doesn't make sense to to spend all that money on fancy interconnects if they are plugged into a switchbox with a low-quality switch, forcing the signal to travel across questionable metal contacts that may not be making a secure connection. That being said, everyone appreciates being able to change inputs and/or outputs at the turn of a knob. There's an easy solution, use the best materials available so the switchbox will be as transparent as possible.

A great client of mine, Todd, wanted a balanced switchbox that would fit conveniently on his rack and not harm the signal. Based on the sizing constraints, he chose a size that would match his Schiit Audio Mjolnir 2 headphone amplifier and fit conveniently underneath. We selected a Par-Metal 16" wide aluminum case (20-16123x) that matched the dimensions perfectly, anodized with alodine for EMI/RFI shielding, and black on the exterior.

Par Metal aluminum chassis 20-16123x

The unit would have a single pair of balanced XLR inputs, and four pair of balanced XLR outputs. I selected the Neutrik DLX series with heavy duty shielding. As Neutrik states on their page: "[the] all metal housing works in combination with a new duplex ground contact yielding the best RF protection and ground conductivity in a chassis mount XLR". Creating the holes in the back chassis panel simply requires using a ruler to plan out where the holes would be cut. Greenlee makes an excellent punch for D-size mounting dimensions. The D mount specification calls for a 23.80mm (0.9370") diameter hole, but a 15/16" hole is 0.9375" and works perfectly well. As you've likely seen in many of my other posts, I use these punches a lot. You drill a pilot hole, insert the bolt and tighten with a ratchet and you get a nice accurate punch every time.

Greenlee 15/16" Metal Punch

The XLR connectors can be inserted from the back for a clean mount. I chose to use pop-rivets to install the connectors as I like the look, however, a screw, nut and lock washer would also suffice. 

Aluminum pop-rivet

Installing the D mount XLRs on the back panel 

Below you'll note the D-mount XLRs installed. Despite being directly installed to the metal chassis, solid grounding is very important, so a bus wire is run across the chassis ground pin on each unit, and each unit is shorted to the metal surrounding the plug. You'll also note the mount for the switch has been installed a little past the halfway point on the chassis.

Bottoms up!

And here comes the fun part, wiring. I encourage labeling the chassis interior which won't be visible after completion so you don't get mixed up during the wiring process. In this case, one wafer (or level) on the switch is dedicated to the right signal (both positive and negative), and the other to the left (+ and -). At any given time, four connections are being made: L+, L-, R+, R-. The Elma switch selected is really nice quality, make before break, with Swiss movement, gold plated connectors, the works. Solid core UP-OCC in teflon wire is being used for all connections. The shaft extension rod is a general cut-to-size unit with lock-nuts and a brass fitting. 

Wiring up the Elma switch

I do like to tidy up the wiring after the fact with a few zip-ties, although this is not a necessary step. 

For a nice finishing touch, brass plates are engraved to fasten to the chassis.

The front art I created in Adobe Illustrator in EPS format so the engravers could use it. This was the design Todd and I collaborated on. The knob is knurled aluminum from Goldpoint and has a nice solid weight and feel. I added a bit of J.B. Weld to the connections on the shaft extension to ensure they wouldn't loosen up over time and annoy poor Todd.

Engraved brass plate

Goldpoint milled aluminum knob

And some final photos to see the finished product. The footers are EAR isolation feet.

Balanced Switchbox Front

Balanced Switchbox Back

The Fine Print:
The above steps detailing the creation of a switchbox are for entertainment purposes only are not intended to be instructional. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property.

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