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James Lehmann

Joined: 17/05/05
Posts: 2011
Loc: Europe
LA Audio SPX2 Stereo Source Selector
      #236498 - 14/01/06 06:32 AM


1) You want a convenient way of controlling the level of your active monitors

2) You need more mixer inputs
Most of us hardly need reminding of the number one problem facing users of compact mixers - running out of inputs. A couple of synths, sampler, soundcard and you've already eaten up most of your inputs before even attempting to hook up a DAT, CD and cassette deck into your system.

3) You would like a Headphone pot that isn't hardwired to Control Room out
The lack of a discreet headphone level control is also a frustrating limitation. More often than not on many budget mixers headphone level is hard-wired to the Control Room output meaning that if, like me, you switch frequently between listening on cans and monitors you have to have keep messing with the gains on your power amp - not ideal.

4) You need a mono switch
Many budget desks lack a mono switch.

5) You want to connect two pairs of monitors and switch effortlessly between them
Hook up your nice new PMC's as well as your trusty NS10's or other grotboxes for checking radio mixes and go back and forth between them at the flick of a switch.


If any or all of the above limitations drive you nuts on a daily basis and eat into your creative time by forcing you to figure out unsatisfactory workarounds, read on! I recently sprang the cash for a very neat, relatively low-cost solution that eliminates all of the above problems and does a whole lot more besides - the LA Audio SPX2 Stereo Source Selector. This little unit is so convenient and flexible, and saves you so much time and routing headaches in all project studios! Here's why...


It's possible think of the SPX2 a bit like the (pre)amplifier component of a home-stereo system - 6 buttons select between six stereo input sources and 2 more select two different (or both) pairs of speakers. But of course the SPX2 is designed for a professional recording set-up not for a home-stereo so the ergonomics and connection options are very different. The SPX2 is housed in a 1U rack unit with a business-like cream and grey finish: the XLRs are industry standard Neutrik so I would imagine all the jacks are too (I didn't open up the box). The pots and switches are easy to operate with a reassuringly firm action, and the busy jackfield on the rear of the unit feels very solid when plugging stuff in and out.

IN & OUT & IN & OUT &...

Input 1 accepts XLRs at the rear panel or balanced 1/4" jacks on the front (which cut the XLR signal if both are left connected): a front panel centre-detented pot provides +/-10dB of gain. Inputs 2 & 3 accept 1/4" balanced jacks at the rear and a recessed front panel screw provides -6dB to +10dB of gain. Inputs 4, 5 & 6 accept unbalanced phono plugs at the rear and a recessed front panel screw provides -6dB to +10dB of gain. All inputs are stereo and are selected by momentary action buttons indicated by amber LEDs on the front panel; significantly these buttons allow more than one to be selected at once meaning the SPX2 can indeed function as a 12-input line mixer. The two pairs of outputs are on 1/4" balanced jacks, selection is by locking button indicated by green LEDs, and knobs control output level from 1 to 10 (disappointing for Spinal Tap fans then).

Rounding off the feature set at the front are a centre-detented balance control, a mono switch, a locking attenuation switch that reduces all outputs by 20dB, and the all-important discreet level pot and front-panel output jack for headphones. Completing the back panel tour we find a Record output on phonos, and Mains power which is via a standard IEC connector - thankfully not a(nother) wall wart. There's no dedicated power switch but power is indicated by a single green LED at the extreme right of the front panel. There's also no signal present or overload LEDs but I can't honestly think why you would need them unless you are an distortion freak who likes overdriving things just for the hell of it (these people do exist you know); in any case LED indicators won't help you - try a doctor. Output relay switching is delayed at power-on to prevent potentially dangerous thumps and clicks reaching your monitors. This last feature seems typical of the SPX2's design - hardly attention grabbing, but thoroughly well thought-out and valuable to have, in this case saving your monitors a trip to the repair shop after one too many crunching power-ons.


So much for the feature list - in practice how does the SPX2 earn it's keep? I think this is best illustrated with a 'real-world' application, so here's how mine is wired up:

Input 1 - Mixer, Control Room Out
Input 2 - VCR Out
Input 3 - CD Player Out
Input 4 - DAT Out
Input 5 - Mac Out
Input 6 - Cassette Deck Out

Output 1 - Main Monitor system PMC TB2's (Power amp, monitors) In
Output 2 - Secondary Monitor system NS10's (Power amp, monitors) In

Rec Out - Cassette Deck In

Headphones - Hmm, tricky one this, er... Headphones

(If you're wondering, my DAT takes its input direct from the Main Outs of my desk)

So there you go, or there I go, rather. I'm sure you can see at a glance the convenience of this kind of instant switching. I can flip easily between all my sources, and I have a discreet headphone output meaning I can finally pack my power amp away in a corner and forget about it. I can check mono compatibility, I can check my mix on 2 different monitoring systems, and if I want to jam along to a CD or play Tomb Raider whilst listening to a cassette I can do this without tying up precious desk inputs or repatching. I can route any individual or combination of inputs to a 2-track recording medium, and on one (desperate) occasion I disconnected the everything and used the SPX2 as a sub-mixer to bus an 8-track recording into my stereo mix! Previously all these ins and outs had to be fed through my mixer, necessitating a patchbay, a ton of extra cables and a great deal of time and hassle whenever I needed to switch between sources, not to mention taking up valuable input channels on the desk and causing level matching upsets. Audio quality is first class (the usual quoted 20 to 20) - if there is difference between direct monitoring and monitoring through the SPX2 I haven't noticed it, and it therefore seems hardly worth doing an extensive A/B.

WISH LIST (All these are very minor)

Calibrated knobs for all inputs, not recessed screws. Although in an ideal world you only need to set the trims once, the reality is that these will need adjusting from time to time as you add/subtract bits of gear from your rig. The current configuration necessitates keeping a tiny screwdriver within easy reach of the unit at all times for adjusting input trims 2-6, and there's no centre detente or calibrations on these to help you do this either.

On/Off switch for headphone out. With switches for everything else, it's a shame the designers didn't extend this concept to the phones output. A switch would make it just that bit more convenient to flip between cans and monitors, as well as reducing wear on the pot as you mess about trying to reset it at the level it was before you zeroed it. In the control room it is usually necessary to cut the headphone level completely when listening to the monitors because if the cans are in close proximity you'll likely still hear 'em jangling away distractingly.

Some folks might berate the absence of a dedicated power switch, but most people power-on their gear from a single mains switch anyway (the SPX2 helps here too by defeating those damaging thuds), and if you don't you can simply leave the unit on all the time (my solution).


The SPX2 was clearly designed by someone who has run into the kind of compact mixer limitations that folks like you and I come up against every day. You could spend the same amount of money on a patchbay, tons of cables and a speaker switching unit and you still wouldn't have anything like the convenience and flexibility the SPX2 gives you (take it from me - I tried this route previously!). I have outlined above how the SPX2 fits into my system, but this is just one way of making use of the SPX2's capabilities; another suggested method involves hooking the SPX2 into the 2-track return of your mixer as a line-in sub-mixer. You will undoubtedly find your own way of using the SPX2 that will eliminate any number of routing headaches from your set-up once and for all. The bottom line is that this is one of the simplest and most useful pieces kit I have ever purchased - one of those "how-did-I-manage-without-it" bits of gear that starts earning its keep and saving you time from the minute you hook it into your system.


A totally indispensable piece of kit for anyone with a pair of active monitors and/or a compact mixer (ie half the planet?), who needs a passive volume control, multiple speaker switching, multiple stereo source mixing, mono checking and a dedicated headphone amp.


LA Audio SXP20


The views expressed here are those of the author alone. The author has no connection with LA Audio, or any of its distributors. The technical information given here is correct to the best of my knowledge. Feel free to copy or quote all or part of this - I'd appreciate hearing from you if you do.


Since I wrote the original review (for v1 of the SOS Forum way back in 1999!) LA Audio have given the SPX2 a cool new green'n'black facelift to fit in with their new product lines, and a new name - the SPX20, but to the best of my knowledge the hardware specs remain unchanged. I suspect the price may have gone up though.

I have also updated this review to reflect more of today's needs - ie the SPX20 as an excellent passive volume controller for feeding active monitors straight from a DAW.

I used to be a rocker, but now I've gone off it and just sit in one. (JL)

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