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LA Audio SPX2

Source Switcher By Paul White
Published September 1998

LA Audio SPX2

Paul White switches on to a box which provides a dash of extra source for the smaller mixing desk.

The studio world is generally divided into 'must have' cutting‑edge products and those boring but essential tools that make recording possible — patchbays, cables... that kind of thing. LA Audio's SPX2 definitely falls into the 'that kind of thing' category, but its usefulness is so obvious that I'm surprised nobody has done it before.

Large consoles have comprehensive source select sections so that you can choose whether to hear the stereo mix or the output from, say, one of your DAT machines, a cassette deck or a CD player. However, if you have a smaller mixer, you generally can't do this without repatching all your leads.

That's where the SPX2 comes in. This rather neat 1U, mains‑powered, rack‑mounting processor provides the means to connect up to six stereo sources and then route them to two pairs of switchable outputs, each of which has a separate level control. Even if your desk has no source selection at all, by connecting this box between your mixer out and one or two monitor amplifiers, you get all the monitoring flexibility of a big desk.

If that's all the SPX2 did, it would be useful, though not exactly scintillating. However — and pay attention because this is the almost exciting bit — each input has its own gain trim control that can accommodate anything from ‑10dBV to +4dBu, and if two or more sources are selected at the same time, they are mixed together. Moreover, the first input has its connection and level control on the front panel, making it easy to patch visiting bits of gear into your system. In addition to the two Level controls and On switches, the output section has a Balance control, a Mono button and a Dim button, just like a large console. Because the two outputs are independently switchable, the SPX2 makes it possible to feed two separate monitoring systems — for example, a main monitor amp and a smaller nearfield system. Switch‑on clicks are prevented by muting relays and the input connectors come in various types to suit the equipment most likely to be connected. There's even a headphone output with its own level control.

The two main stereo outputs from the unit are on balanced TRS jacks, but there's also a pair of phonos wired as tape outs so that the selected source can be recorded pre the Dim, Mono, Level and Pan controls. Only three of the inputs are balanced. Input one is on XLRs, inputs two and three are on TRS balanced jacks, and the remaining three are on phonos (and therefore unbalanced). Signal levels of up to 20dB can be handled without clipping, with the gains of channels two to six adjustable via trim pots accessible by screwdriver on the front panel. Input one features two additional balanced jack inputs on the front panel complete with a ‑10dB to +10dB Gain knob.

Each of the inputs is activated by a non‑latching button with accompanying amber status LED. To select more than one input, it's necessary to hold down all the buttons of the relevant inputs at the same time. Pressing any other button cancels the previous selection.

That's about is as far as the SPX2's functions go. However, because it has the ability to mix multiple stereo inputs, it can function as a very basic mixer as well as a monitor source selector. For example, if you have a small digital desk, such as Yamaha's 03D, that has only one stereo input in addition to the main input channels, you could use the SPX2 as an effects return submixer to combine the stereo outputs from up to three balanced and three unbalanced effects units. The preset gain trims would only need to be set once since, from that point on, the effect level would normally be adjusted by setting the appropriate send level.


A simple but functional product, the SPX2 does a pretty good impression of a Swiss army knife — even though it doesn't have a tool for taking stones out of drummers' hooves! It fills a genuine need, it has a clean signal path, and it's flexible enough to have a number of uses in the typical small studio or production suite. My only criticism is the selection procedure for multiple sources — having to hold down several buttons at once is a little awkward. Latching switches or the facility to select multiple buttons one at a time while holding down the first one might have been better. Try as I might, I can't find a way to justify the SPX2's cost, especially as you can buy a complete mini mixer for less. The reality is that most users are reluctant to spend any significant amount of money on anything that doesn't make an interesting noise, so unless LA Audio can find a way to make this product cheaper, I don't feel it will enjoy the success that it deserves.


  • Useful and versatile source selector/mixer.
  • Clean signal path.
  • Integral headphone amplifier.


  • Expensive.
  • Select switch logic could be more logical (captain)!
  • Some users would no doubt prefer all balanced inputs.


Though relatively costly, the SPX2 does provide full scale monitor selection, complete with a headphone outlet, as well as having basic mixing capability.