Focusrite Octopre LE

8-channel Mic Preamp

Published in SOS July 2005
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Reviews : Preamp

Photos: Mike Cameron

Paul White

Focusrite have a well-deserved reputation for building analogue outboard studio equipment, and their Platinum range is well established in the UK project-studio market due to its low cost and good audio quality. However, it is no secret that much of the analogue market is being hit hard by the relentless rise of software plug-ins, so for mass-market analogue gear to survive in the project studio world where the computer is king, it has to be designed to integrate easily into the computer environment. Focusrite's new Platinum-series Octopre LE has been designed with that consideration very much in mind, although the 24-bit digital I/O is available as an option rather than being fitted as standard, in order to save on cost.

As the name implies, this 1U rack unit comprises eight channels of mic/line preamplifier, using Class-A op amp design, but the secret to its integration into the DAW world is in its input/output options, which offer ADAT digital I/O as well as balanced analogue outputs. Having an 'ADAT to analogue line level' output stage enables the Octopre to be used for feeding, for example, a mixer or surround monitoring system. Without the digital card, you simply have eight mic/line preamps feeding eight balanced line outputs, which is ideal for feeding multi-channel audio interface cards that have only line-level inputs, or for feeding multitrack recorders without the need for a mixer.

The preamp circuitry features the same high bandwidth (-3dB at 200kHz) as for other Platinum designs, in order to preserve transients and prevent phase degradation at high frequencies. A gain range of +14dB to +60dB is available. The first two channels also boast high-impedance DI jack inputs for the easy connection of instruments. The THD is quoted as 0.003 percent for a 0dBu input (maximum gain) with a signal-to-noise ratio of 124dBA. When the digital option card is fitted, the dynamic range is 110dBA.

The eight line-level inputs and outputs are balanced, where the line inputs are on the front panel, the XLR mic inputs on the rear panel, and the analogue line output jacks are also on the rear panel. Rear-panel digital connections comprise a pair of ADAT optical ports (input and output) plus word-clock inputs and outputs on standard BNC connectors, though these are only available when the digital card is fitted. Power comes from an external supply coupled via a locking connector.

A front-panel stepper button with corresponding status LEDs allows the sample rate to be set to 44.1kHz, 48kHz, ADAT sync, or word-clock sync. Unlike the more professional (and more expensive) Octopre, there is no high-sample-rate option and no built-in dynamics processing. A further source option accommodates 256x clock for use with Pro Tools systems, and in all cases a red Lock LED shows that sync has been achieved. The unit has eight line-level jack sockets that can output the analogue mic-channel signals or monitor an ADAT digital input from a DAW or other source — a pair of rear-panel DAC To Line Out switches configure the outputs in two blocks of four.

Front Panel

The front panel is divided into three main sections, the first housing the eight line-input jacks, the first two channels of which have a high-impedance mode to suit instruments with passive magnetic pickups, such as guitars and basses. All eight mic inputs have gain controls, low-cut switches (operating 12dB/octave two-pole high-pass filters turning over at 120Hz), and overload LEDs, but there's no individual channel level metering. Instead, a small, circular moving-coil meter designed for peak reading monitors the output level of any selected mic channel (selected using the Source button). The overload LED doubles as an indication of which channel is selected for metering, but seems to be defeated for whichever channel is assigned to the moving-coil meter. There's a global 48V phantom-power switch just to the left of the first mic channel.

Compared to the rest of the channels, the first channel has additional Low Z and Phase buttons, while the second channel has just the additional Low Z button. Having variable input impedance is currently fashionable, as it allows mics to be more accurately matched to the preamps into which they are connected. To save on cost, this concept has been simplified to a switch offering one lower impedance setting, but, as always, the setting that sounds right is right! As a rule, the low impedance settings work best with ribbon mics — they just make capacitor mics sound quieter. The first two channels also have switchable instrument settings affecting the line inputs, so they can be used as regular line inputs as well as for instruments. Despite the Octopre LE's modest UK cost, the mic circuitry turns in a very pleasing performance, balancing clarity with weight.

Testing

Perhaps the most popular uses for the Octopre LE are expanding the I/O capability of a digital mixer with one or more ADAT I/O ports, or giving your DAW audio interface more I/O. Many DAW interfaces have ADAT ports, so expanding the channel count this way makes a lot of sense. I tested the Octopre LE by connecting it to the ADAT port of a MOTU 828 MkII interface. I selected ADAT sync and it worked right off with no fuss. I connected the unit via both input and output ADAT lightpipes so that it could be slaved to the MOTU 828 MkII. However, depending on which unit in your system has the best clock, you could also opt to use the Octopre LE as the master and slave your interface to that.

To my ears, the mic preamps sound similar, if not identical, to those used in other Platinum products, and operation of the Octopre LE is very straightforward. Having the option to split the outputs into two groups (ADAT or mic/line channel) adds to the flexibility. I don't think the Low Z option is particularly important unless you have ribbon microphones, but as more affordable ribbon models are starting to appear on the market it's nice to know it's there if you need it. Recording via the high-impedance instrument inputs provides a clean, uncoloured DI feed, and, overall, if you're familiar with the audio quality of a regular Platinum box, there should be no surprises. My personal preference would have been for a bar-graph meter rather than the small moving coil provided, but I understand that concessions have to be made to fashion occasionally.

Final Judgement

The Octopre LE sits comfortably between budget units like the Behringer ADA8000 (around £160 with ADAT I/O as standard) and the more costly, more professional Focusrite and RME solutions. Fitting the converter card adds to the cost, but the complete package is still very attractive if you need to expand your system's number of mic/line inputs and line outputs. Where corners have been cut to meet a price, it has been done thoughtfully. There are no high sample rates, but then there's very little reason for the majority of project-studio users to be concerned with these anyway, especially where the end result is going to be a 44.1kHz CD. The metering is a compromise, with a shared meter and individual overload LEDs, but it's a practical enough solution. You can't output all eight mic channels as analogue at the same time as using the ADAT-to-analogue output option, but then why would you need to?

Overall the Octopre LE is a nicely presented, straightforward rack box that delivers Platinum quality to the DAW owner with ADAT connectivity, but it is equally at home as a stand-alone rack of eight analogue preamps if you don't need the digital I/O option. The build quality and styling matches that of the rest of the Platinum range, right down to the style of switches and knobs, so if you have used a Focusrite Platinum preamp before, you'll know exactly what you're getting. Platinum may not be quite esoteric, but you do get extremely good preamps for your money.