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Cut Sheet Exploded view Leg assemblies The box—upside down to show leg notches Stretcher assembly (PVC pipe, centering plug, threaded rod) Attaching the locking nut to the stretcher Attaching the leg assembly 
to the box All done! (Side view) All done! (Top view)
Cut Sheet
Exploded view
Leg assemblies
The box—upside down to show leg notches
Stretcher assembly (PVC pipe, centering plug, threaded rod)
Attaching the locking nut to the stretcher
Attaching the leg assembly to the box
All done! (Side view)
All done! (Top view)

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Caddy for Headphone Distribution Amp
On wheels—it goes where you need it to go
By Matt Seiler

Headphone distribution amps are wonderful tools. Problem is, we need to use them out where the performers do their thing, not in the control room space with the rest of the rack gear. So instead of being placed neatly in a rack, these units often end up piled onto a chair. That places them in the path of all sorts of harm.

The answer is something we’ve never seen available commercially: a compact roll-around caddy to house your headphone amp and several pairs of headphones.

Theory of construction

This project is essentially a vertical rack enclosure on some legs with casters. The caddy must be easy to reach from both standing and sitting positions. It’s going to be out where performers are wandering around, so it has to be sturdy. It needs to be just big enough to avoid getting stepped on, but small enough to stay out of the way. 

The unit is comprised of only three main parts: the box that houses the amp units, and two U-shaped leg assembly pieces that pass through the body of the box. 

Note that the long boards on each side of the box body have cutouts to accommodate the leg assemblies. Rather than having four separate legs that must somehow attach to the box, it’s structurally more sound to have two large pieces and let the box straddle them; the short ends of the box enclose the legs to give a more streamlined appearance and provide added strength.

Materials needed for this project include a plank of wood at least 54" long by 9" wide, 108 linear inches of thicker stock for the legs, four casters, two 24" lengths of 3/8" threaded rod with mating locking nuts, and about 36 inches of 2" diameter schedule-40 PVC pipe.

Tools required are a carpenter’s square, circular saw, jigsaw, coping saw, drill or drill press with a 3/8" drill bit and a 3/4" forstner drill bit (this is a special bit that’s used for drilling wide, shallow holes with an ordinary drill), two 1/2" sockets on socket wrenches, and a hacksaw. You’ll need some carpenter’s glue, four 2-1/2" screws, and a handful of 1-5/8" screws.

The type of wood you use for this project can be just about anything you want. Since very little lumber is required, it wouldn’t be cost-prohibitive if you wanted to build yours out of expensive exotic hardwoods. Be adventurous!

Building the box and legs

The box will be made from 3/4" stock. Once you’ve built it, it will be 21" long and 9" deep, with the width (shown as X in the cut sheet image) depending on how many units of rack space you want the caddy to hold. The width X should be 1-1/2" plus 1-3/4" for every unit of rack space you want to accommodate. (Adding a hair of extra width to make the rack units easier to slide in and out couldn’t hurt either.)

The prototype shown in the photos was made from a single poplar board that was 9" wide and 54" long. It was cut into two 19-1/2" boards for the sides and had enough left over for two 5" pieces for the ends of the box, letting it accommodate two 1U amps (1.5 + 1.75 + 1.75 = 5.0). If you want to enclose only one rack space’s worth of electronics, then your ends will be 3-1/4" wide (1.5 + 1.75 = 3.25).

If you want to hold more units (perhaps you’d like to put a rack reverb in there with your amps so the talent can have some ambience in their ’phones), you can widen to suit. Don’t get too wacky here, though—this caddy’s designed to hold up a few small headphone amps, not 20 spaces’ worth of PA or synth modules!

Cut out the four boards that will be the sides and the ends of your rackmount box. Cut about an inch off each end piece, so the sides are deeper than the ends—in other words, if your sides are the full 9" deep, the ends should be 8" deep. Set them aside for now. Save the leftover wood for some small parts you’ll need later, too.

My prototype’s legs are made from hard maple and are 2" wide by 1-1/4" thick. You could use the same 3/4" thick stock for the legs that you used for the box sides, but only if you glue pieces together double-thick. These legs are going to get some hard abuse from people kicking into them over time, so the added thickness is a real must!

Also, the casters need something substantial to tie into. Just leaving a single 3/4" inch board ain’t gonna cut it—you’ll blow a caster right off the bottom of a leg the first time you use it. Go with thicker stock or doubled-up 3/4" boards.

Each leg unit is made from three 18" lengths of wood, joined to form a large ‘U.’ Joinery for the legs is up to you; the prototype’s legs are joined with half lap joints that were just glued and clamped until dry, with no extra fasteners or dowels.

Whatever method you use should result in two U-shaped units that are at least 18" wide at the floor. The prototype has them splayed outward, for a 27" span at the floor. That was done for aesthetics more than stability. If you choose to go with right-angle corners on your leg set just by screwing them together at the ends, and end up with an 18" span at the floor, you’ll be just fine. See Photo 1 for what the legs of my prototype look like (with the casters attached, something we’ll get to later).

Next, make the notch in the long sides of the box for it to straddle the leg sets. Use your jigsaw to cut out four notches, two on each of the long sides, as shown in Figure 2 (the exploded drawing) and Photo 2.

Now you get to benefit from a mistake I made while building the prototype. I thought it’d be slick to create the side pieces of the box by rabbeting (thinning) the sides of two pieces of 3/4" stock down to 1/4" in order to make everything fit together nicely. The prototype in the photos has thin-looking sides because of that design decision, which turned out to be a bad one; I’ve already cracked one side of the box with a careless kick to a leg because that wood is far too thin. The design you should use, which is shown in the cut sheet and which I’ll now explain, is much sturdier (and easier to build, too!).

From the leftover pieces of your big board cut out two cleats. The cleats as wide as the number of rack units you’re enclosing, and they serve as rack rails. Make each cleat an inch thick and several inches deep; they need to fit inside the box when it’s put together, glued to the side pieces.

Just clamp them in place for the moment. Now dry-fit the box together and measure the distance between the two cleats—it has to be at least 17-1/2", so you can fit regulation rack gear into the box. Having it a bit too wide is okay if you don’t mind a little rattling, but too tight and your headphone amp may not fit. If you want to really customize it for the amp you have, measure the amp and size the cleats for a snug fit. Glue and screw them to the inside faces of the box ends.

As you dry-fit the box together, notice how the long pieces stand about an inch taller than the sides? That’s deliberate; you’re providing a shield for the amp’s exposed knobs so that a careless swipe from a mic stand or other moving object doesn’t hurt them.

As long as you’re dry-fitting things, check the fit of the box onto the leg assemblies. Make sure that when complete the box ends will cover the legs snugly, and that everything comes out square.

Glue your box and set it aside to dry thoroughly. In the cut sheet I’ve also added four screws to each end piece in addition to the glue; these will help the glue set and add strength. (They aren’t in the photos of my prototype.) Be sure to drill a pilot hole for the screws so they’ll go in easily and their heads will fit flush to the wood.

Building the stretchers

The stretchers are two lengths of PVC pipe with wooden plugs cut to fit snugly in each end of each pipe. There’s a hole drilled into the center of each plug, and a threaded rod will pass through the holes. It’s kind of like making a weird looking rolling pin. The threaded rod will attach through holes drilled and countersunk into the legs, and we’ll attach them with nylon locking nuts.

These stretchers are to keep the legs from breaking if they get pushed/pulled out of alignment. Since we need them anyway, why not use them for headphone storage? The PVC tubing will give us that opportunity.

Stand the legs up and place the box across them where it will eventually live. The box will serve to hold the legs in place while you build the spreaders. 

Measure the distance between the inside faces of the legs roughly where you’re going to put the stretchers. Using a hacksaw, cut two lengths of PVC pipe to this measurement. Unless you’re going for the industrial look, you might want to sand or scrape the lettering and markings off the pipe at this point.

Now cut out an additional thin ‘donut’ piece of your PVC for use as a tracing template. Just half an inch will do. Set out another scrap piece of wood and trace the inside dimension of the PVC donut four times. Use a coping saw to cut out these four plugs, and then test fit them into your tracing donut. You want them to fit pretty snugly. Then drill holes through the centers of the plugs just a little bigger than your threaded rod—they’re intended as centering guides to hold the rods in position, but the threads shouldn’t bite into them.

Measure the legs again, this time to find the distance between their outside faces. Then deduct 1/8" from the measurement. Using a hacksaw, cut your two pieces of threaded rod to that length.

Insert a donut into one end of the pipe. Pass a rod through the hole in the wooden donut and out the other end of the PVC. Insert the other end of the rod into the hole in the other wooden donut and snug it into the other end of the PVC pipe, as shown in Photo 3. You should now have something resembling a rolling pin.

Mark a point on the outside face of each leg, centered across its width at least a foot above the flo or. Then, using a 3/4" forstner drill bit, drill into the face of each leg just deep enough to recess one of the locking nuts. Now switch to the 3/8" bit, center it into the recessed hole you just made with the forstner bit, and completely pass through the remaining thickness of each leg.

Take your two rolling pin assemblies and pass the threaded rods through the holes you just drilled in the legs, as shown in Photo 4. Tighten your locking nuts and see that they’re completely recessed into the countersink holes in each leg. Why are these little countersinks to hide the nuts so important? You’ll know the first time one of your players catches his headphone cord on an exposed nut and damages it, forcing an expensive repair or replacement.

Putting it all together

Turn the assembly over so the legs are in the air. Position your rack enclosure box where you want it on the legs. Predrill four holes through the bottom face of the legs and up into the body of the box. Insert the 2-1/2" screws into your pilot holes. Then follow with four more screws, two on each side, through the side panels and into the legs. See Photo 5 for a photo of all four screws on one side, partway in. While it’s upside down, attach the casters to each leg, following the manufacturer’s mounting instructions.

Flip the unit back over and test fit your headphone amp into the box. Make sure that you can reach the controls comfortably from a standing or sitting positions. Note that you don’t have to tap screw holes into the rack rails—gravity does the job nicely and the amp will sit happily under most uses. You can finish the job by smoothing the wood with 220-grit sandpaper and coating with 2 cans of spray lacquer before rolling it into your recording space.

This project, as photographed, really went easy on the wallet. The 54" board was a whopping $18, the casters were $6 each for sets of two. The maple boards for the legs came in at just over $20. The two cans of spray lacquer were a bank-breaking $4 each. So for under $50 I have a really cool and useful piece of studio furniture.

And nobody else has one—until you build yours! Best of luck with your project.

Matt Seiler has one foot in the audio world and one foot in the woodworking world. He’s wondering if there’d be any market for a cable TV series called ‘This Old Studio.’ He can be reached via talkback@recordingmag.com




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