Universal Audio Ox Box Mod
April 2026
Here is an interesting mod we installed on a Universal Audio Ox Box. This unit is basically a speaker soak, whose primary function is to reduce power output of a guitar amplifier going to its speaker, but it has other functions as well.
UA OxBox
From the Universal Audio web site: "OX is a premium reactive load box and guitar recording system, giving you perfectly studio-miked amp sounds from your favorite tube amp. OX lets you play and record your amp in its sweet spots - from huge clean tones and edge-of-breakup to fully cranked - at any volume level, and with mic, room, and speaker cabinet emulations at the turn of a knob."
The customer had found out about a mod to these units that adds a line input. The mod is fairly straight forward (though is does void your warranty, if it is still in effect!), as there is already an internal RCA jack line input on the main board that isn't connected to anything externally. The mod involves drilling a hole in the back panel for a 1/4" jack, and wiring it with a short piece of audio coax wire to a RCA plug that is then plugged into the existing jack.
The first step involves removing 25 screws from the top cover, and removing it, which took some effort, as it is a fairly tight fit. It is a very solidly built unit.
Top case cover removed
The hole for the 1/4" jack will be drilled through the back panel. We prepped for the drilling by adding some tape, sticky side up, inside the area where the hole is to be drilled, to catch any metal fragments that will be produced by the drill. This is to prevent any metal chips from later shorting out anything on the main board.
Sticky tape to capture metal fragments
After drilling the hole, and cleaning up any burs on the inside, we wired up the short cable. The cable and solderless RCA plug came from the 3 Monkeys Solderless web site. We had a 1/4" jack and insulating washers in stock. After testing the wire with the plug and jack attached, we mounted them in the chassis, and plugged the RCA plug in to the existing RCA jack on the main board. The 1/4" jack is grounded via the shielded coax cable, and is isolated from the chassis by using insulated fiber washers to reduce the chance of any ground loops.
Short cable assembly mounted and plugged in
1/4" jack mounted on the back of the chassis
The back of the OxBox showing the finished mod:
1/4" jack mounted on the back of the chassis
This was a pretty straight forward mod. The trickiest part was drilling the hole in the back for the 1/4" jack. We first drilled a 1/8" pilot hole, followed by a multi diameter drill bit, which does a cleaner and smoother job than trying to use a large diameter regular drill bit. The sticky tape did a good job of collecting all of the metal fragments, and the result was a nice clean hole the proper size for the fiber insulating washers.