50th Anniversary Edition
Issue 61

SM Pro Audio 500 Series Modules & JuiceRack8


June 12, 2014


SM Pro Audio has more than embraced the 500 series concept of flexibility, it’s taken it to heart.

Review: Brad Watts

During the last decade the 500 series format has made quite a resurgence, with dozens of top-shelf and budget units available. The initial concept was birthed by API. The company’s mixing consoles were modular, allowing preamp, EQ, or dynamics modules to be swapped in and out according to the operator’s taste and needs. Over time, audio engineers expressed the desire to carry a few of their favourite 500 series modules between studios or for field use, and the 500 series ‘lunchbox’ was created, capable of housing four modules. While there’s nothing utterly earth shattering about the idea (no doubt API lifted the concept from vintage German modular designs such as those from TAB and Siemens), API’s pseudo standardisation of the system has allowed dozens of manufacturers to piggyback on the platform and release tools to readily slip into 500 series specification power racks.

Joining the 500 series fray is Australian manufacturer, SM Pro Audio. Quite the innovative development team, SM Pro offers a wealth of affordable audio products. Sitting on my test bench is the company’s eight-slot 500 series JuiceRack8 — a ‘smart’ rack power system capable of accepting eight 500 series modules. While the JuiceRack8 is, of course, capable of housing any 500 series module, the unit has come loaded with three modules made by SM Pro itself, and these I’ll get to shortly.

I should note, the price of the JuiceRack8 is not that dissimilar to typical pricing for most eight-slot 500 series power racks; around $100 per slot is the going rate for units of this capacity (lesser numbered units such as four and two-slot units raise that figure to around $150 per slot). What does set the JuiceRack8 apart from other manufacturer’s offerings is the additional features.

Firstly, the 500 series spec calls for a minimum of 130mA for each slot. The JuiceRack8 provides 350mA per slot so you’re assured of supplying enough power to your modules — even those red herrings that require more power than the spec defines (and yes, there are a number that do require more). Build-wise the JuiceRack8 is very solid. It’s all plate steel construction and seems as sturdy and serviceable as any other power rack I’ve used.

Secondly, and this is the very cool part of the JuiceRack8, is the digitally controlled audio matrix built into the unit. From the front panel you can choose to send the audio output of one module into another, split a single balanced input and send it to multiple modules simultaneously, or split a single unbalanced input and send it to multiple modules simultaneously. That’s quite impressive in 500 series land as you can set up some complex channel strip-style setups with your modules without requiring any repatching of cables. Plus, your setup is stored in memory and will survive power cycling. Very, very cool. The patching procedure can be a little cryptic, but once you run through it with the manual in hand you’ll get the hang of it. The rear of the JuiceRack8 features both balanced XLR I/O and unbalanced jack I/O for each module slot. Again, not all 500 series racks even offer a choice of connection for I/O, so, another handy inclusion.


Of course it’d be remiss of SM Pro to release a rack without offering its own processing units, and the company has a number of devices ready to go. Supplied was the single slot TubeBox, a mic preamp and optical compressor, a dual slot PEQ505 parametric mono EQ, and a dual slot, multi-band compressor, predictably dubbed the MBC502. All units are finished with a red anodised aluminium face with knobs reminiscent of the Focusrite Red series. The knobbage is all tightly packed in and can get very fiddly, but this is true of pretty much all 500 series designs from any manufacturer as there’s not a great deal of ergonomic real estate available. The control pots are also oil-dampened so they feel pretty schmick.

TubeBox Preamp

My initial tinker was with the TubeBox. This is a transformerless Class A mic pre design with a 12AX7 tube circuit and LME 49720 low distortion/low noise op amps. Input gain and output level controls are available, as are 48V power and a phase reversal switch. There’s a -20dB pad switch and low cut filter — all the necessities of a completely equipped mic preamp. One small caveat is you’ll need an adaptor cable to plug a mic straight into the front of the unit as this is a TRS jack input — hey, space is at a premium with 500 series units.

The unit also features a well specified compressor with release, attack, and compression ratio controls which is quite a capable dynamics tool. Being an optical compressor it’s easy to pull an LA2A-style squash from it. Interestingly, in the good ol’ USA style, switches activate in their upward positions. When the compression circuit is switched in the extremely brightly backlit (perhaps terrawatt and nuclear powered) VU meter swaps from representing input level to gain reduction. But overall, it’s a smooth-sounding preamp and quite a tidy compressor. Very nice.


Next in line is the PEQ505 parametric equaliser. This unit takes up two slot spaces, no doubt so there’s enough front panel space to fit the controls. There are five bands of fully parametric EQ. Each band has its own bypass switch and there’s a global bypass. This is EQ I’d definitely put into the ‘Swiss Army knife’ category. The five bands all offer the same spectrum — from 100Hz through to 2kHz, with three-way multiplier switches for x10, x1 (i.e. what’s printed around the EQ control), and x0.1 for low end equalisation. Consequently you can create some huge overlaps between each band to basically eradicate a particular frequency, or you can set the bands up with more gentle curves for overall sweetening and closer to shelving-style EQ. The frequency bandwidth or ‘Q’ is adjustable from 0.03 through to two octaves. I’d actually just spent a week installing and using some API, SSL, JLM and Great River 500 series EQ units (all at least triple the price of the PEQ505) and while I can’t say the PEQ505 was as ‘sweet’ as these units, it does sound very good, keeping in mind the versatility it offers — there’s a bunch of EQ there for a minimal fiscal outlay. Harnessing the choices is a matter of studying other EQ devices and making appropriate adjustments to bandwidth. This will get you in the ballpark for setting up this EQ for countless equalisation duties, both broad and surgical.


Thirdly, included in the JuiceRack8 was the MBC502 multi-band compressor. Again a two-slot design so the knobbage has plenty of room. The MBC502 is a dual band optical compressor utilising the same LME 49720 super low distortion op amps employed in the TubeBox preamp. This is quite an interesting compressor with separate attack, release, and compression ratios for the two bands which are defined via a single 16-way notched pot. Master level is represented via a VU meter and gain reduction for each channel is shown via two five-segment LED meters. This is quite a fun unit. If you can imagine: two optical compressors with the ability to quickly alter the crossover point at which they each affect a signal, then screwing in the compression. Muting either compression circuit renders that channel as a filter only. It’s actually really fast and intuitive in use — a true ‘sound sculpting’ device, and again, very affordable.


Personally I can’t fault these 500 series units. In a perfect world we could all afford SSL and Neve processing, but these prices combined with the manufacturing quality are an outstanding combination. Plus the JuiceRack8 with its patching system is sheer brilliance — there isn’t another power supply unit on the market offering such a feature; until you start looking at power supply units offering built-in mixers and summing amps, and at that point the costs rise considerably. However, the beauty of this format is you can swap out units as you desire. You could for example, accrue dozens of 500 series processors and preamps and swap them in and out of a power rack with very little downtime — it’s almost like a studio engineer’s guitar pedal board.

The other attractive aspect is the easy upgrade path. Once your power rack is patched into your studio system, your upgrading options are left open to extract lessor favoured units and replace them with more upmarket or more suitable devices as deemed necessary — and all according to taste and budget. The other, perhaps more obvious advantage is you can fit a bunch of processing into an extremely small footprint. Eight processors in a 3RU space is efficient indeed, especially if your intention is to make your system transportable. I’d certainly recommend these as an ideal orientation to 500 series-ville.  


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50th Anniversary Edition
Issue 61