Solid State Logic PureDrive Octo

SSL’s PureDrive preamps bring the sound of their Origin console to a new audience.

When the world turned away from giant mixing consoles in the ’90s and ’00s, Solid State Logic were quick to adapt. Over the last 20 years or so, they’ve introduced lots of novel products targeted at home and project studios, while high‑end mixers like the Duality and AWS Delta have incorporated advanced digital features to keep them relevant in the DAW age. So when SSL announced the Origin in 2019, it looked at first glance like an anachronism. Who would want to buy a new, all‑analogue, large‑format console with no automation or DAW control, when you could pick up vintage equivalents for pennies on the pound?

Quite a few people, it turns out — and a second glance at the Origin makes clear that it’s not at all equivalent to the analogue mixers of old. It incorporates some of SSL’s greatest hits, such as the parametric EQ from their E Series consoles, and the famous bus compressor, but there’s also plenty of innovation on display, including a clever new approach to routing and bussing, and a modular centre section that allows rackmounting processors, fader surfaces or screens to be built directly into the mixer. And, perhaps acknowledging the fact that vintage SSL preamp designs were never revered in the same way as their dynamics or EQ, the Origin features an all‑new mic preamp circuit dubbed PureDrive.

From The Origin

The Origin has proved a deserved success, but not everyone has the space, budget or need for a large‑format console. Consequently, the PureDrive preamp design has now been made available in two 19‑inch rack units: the four‑channel Quad and eight‑channel Octo. And, in typical SSL fashion, both units add on a ton of additional functionality. The Octo was supplied for review; the Quad is described briefly in the boxout.

The core function of the PureDrive units is to preamplify signals from mics, DI’ed instruments and line‑level sources. But both units also offer built‑in A‑D conversion, allowing their outputs to be disgorged in ADAT Lightpipe and/or AES3 digital formats. And if doing so frees up the analogue outputs, you can then use these as insert sends, with a dedicated set of insert returns available in addition to the line inputs. The icing on the cake is the addition of a USB Type‑C socket, which allows the PureDrive preamps to be used as class‑compliant audio interfaces.

There are also plenty of juicy plums within the cake itself. By my calculations, the preamps offer a colossal 90dB gain range on the mic inputs, and as well as the expected high‑pass filters, polarity and phantom power switches, there are also input impedance and Drive options, which we’ll come to presently.

Colour Ways

Unsurprisingly, SSL have chosen not to cram all these features in a 1U chassis, but they’ve managed to present everything very clearly and neatly in a 2U front panel. The flip side of this is that on the Octo, most of the controls have multiple functions, with coloured LEDs used to provide visual feedback on settings. Each channel has a stepped gain control, spanning +5 to +65 dB in 6dB steps for mic signals or 0 to 30 dB in 3dB steps for line‑level inputs. The first four channels also have high‑impedance inputs, which are automatically selected when something is plugged into the relevant front‑panel jack sockets, and offer 11 to 41 dB gain in 3dB steps. The trim control then adds a further ‑15 to +15 dB gain, in 1dB steps. Stepped potentiometers don’t always offer the precision of rotary switches but, remarkably, SSL claim that gain values across channels are matched to less than 0.08dB at all settings. For reference, this is an order of magnitude tighter than most mic manufacturers’ tolerances for pair matching.

Both the gain and trim controls also have multiple push actions. A short push on the gain knob engages the polarity reversal, whilst a long press switches phantom power on or off. The same actions on the trim knob engage the high‑pass filter and swap between mic and line inputs, respectively. In the default arrangement, it’s quite easy to accidentally flip polarity or introduce the filter when changing gain settings, but thoughtfully, SSL have added an optional Safe mode in which pushes of less than about a second aren’t registered as inputs. I quickly gravitated to having this active all the time.

If the specs are anything to go by, the PureDrive design should be a world‑beater. I’ve already mentioned the huge gain range and outstanding gain matching between channels...

Each channel on the Octo also has two square push buttons with integrated multi‑colour LEDs, and again, both have secondary functions. The ZΩ button cycles through four input impedance settings: 12kΩ (green), 1.2kΩ (not illuminated), 600Ω (amber) and 400Ω (red). These are available only on the XLR inputs, so it’s not possible to vary the 1MΩ impedance that a DI’ed instrument sees, which is perhaps a shame. The Drive button toggles the selected Drive mode on and off, with a longer press switching between Classic Drive (amber) and Asymmetric Drive (green). The former introduces predominantly odd‑harmonic distortion, in the same way as the Drive feature on the Origin console, while the latter is a new mode that brings in more even‑harmonic saturation. Unlike the variable impedance, Drive can be applied to all input types.

The secondary function of the ZΩ button is to switch the routing so that the A‑D converter for a given channel is fed from the insert return rather than the preamp output. However, this isn’t activated by a long press; instead, a global Insert button lurks to the right of the front panel. Holding this causes all the ZΩ buttons to flash, whereupon you can switch the insert return for each input in or out. A down side of this approach is that although the Insert button lights up to indicate that at least one insert return is active, you can’t see at a glance which channels have inserts enabled unless you press it to check — the PureDrive Quad, by contrast, has dedicated LEDs on each channel.

Also on the right‑hand side of the front panel are buttons for selecting clock source and sample rate, a slightly oddly shaped display housing six‑segment LED meters for each input, and a soft ‘standby’ power button. This is a nice touch, since the main on/off switch is on the back of the unit and thus inaccessible when rackmounted.

As you’d expect given that it’s so well featured, the rear panel of the PureDrive Octo is pretty busy. The eight XLR mic inputs are arranged in two rows of four, while the line inputs, insert returns and analogue outputs are all on DB25 connectors. Four more XLRs carry the AES3 outputs in pairs, and there are two optical outputs, allowing full eight‑channel ADAT operation at sample rates up to 96kHz thanks to the wonders of sample multiplexing. Higher sample rates are also supported, but the ADAT channel count drops to four at 176.4 and 192 kHz. Two BNC connectors offer word clock in and out, with a switchable 75Ω termination button. Mains power arrives on a standard IEC connector and the PureDrive automatically adapts to the local voltage and frequency.

DB25 connectors are used to carry the eight line ins and outs, along with eight insert returns that can be substituted for the line ins on a per‑channel basis.

See You Later, Aggregator

Connect a USB‑C cable to your macOS or Windows machine, and the PureDrive Octo will present itself as a class‑compliant audio interface; on Windows, you’ll need to install an ASIO driver to use it with most DAW software. As it contains no D‑A conversion and has no monitoring capabilities, it defaults to showing up as an eight‑in, zero‑out device. However, it’s possible to repurpose either or both of the AES3 and ADAT outs to carry DAW outputs rather than the signals from the PureDrive’s own A‑D converters. At base sample rates, this could give you a total of 24 digital outputs from your DAW, which might be handy for example if you like to work with a digital mixer in the studio. For most purposes, though, it means that the PureDrive’s USB interfacing is mainly useful as part of an aggregate device in Core Audio, or in conjunction with something like Audiomovers’ Inject or Omnibus. It’s likely to be less useful on Windows, since ASIO does not readily support aggregate devices or the use of different input and output devices simultaneously.

SSL describe the PureDrive Octo as a 32‑bit interface, but it does not offer the same ‘unclippable’ floating‑point conversion you find on some Sound Devices recorders, for example, so in practice there’s no advantage to recording at 32‑bit.

Like Safe mode and various other global configuration settings, digital routing is switched within a special Settings mode. This is accessed by holding down the CLK (clock) button during power‑up, and requires an actual power cycle, not just the use of the front‑panel standby button, so could be harder to enter if the unit is rackmounted. It’s also worth noting that switching either the AES3 or the ADAT out to USB mode causes all 24 outputs to appear to your DAW, even if the other one is left in the default setting; this is so that the I/O numbering and labelling remains consistent in the DAW. Other settings options include button and meter brightness, an optional auto‑sleep mode that can put the unit into standby if no control or signal input is made for a specified length of time, and even the choice of whether relays should click audibly or not when buttons are pressed.

Pure & Simple

If the specs are anything to go by, the PureDrive design should be a world‑beater. I’ve already mentioned the huge gain range and outstanding gain matching between channels, and the rest of the published measurements are equally impressive. Equivalent input noise is ‑130dBu (A‑weighted), THD+noise is below 0.0025% with Drive disabled, and crosstalk is below ‑108dB at 50Hz, ‑105dB at 1kHz and ‑81dB at 10kHz. Maximum signal levels that can be accepted are +21.5dBu for the mic input and +26.5dBu for the line input. The A‑D converter, meanwhile, boasts a dynamic range of 119dB.

In short, if you keep the input impedance in one of the higher settings and don’t enable Drive, the PureDrive very much lives up to the first part of its name. It’s an exceptionally clean, quiet preamp that is enormously versatile. The high‑pass filter introduces an 18dB per octave bass cut turning over at 75Hz, which seems a good choice for attenuating unwanted rumbles and thumps without affecting the main body of the signal. And, unlike the high‑pass filters on many preamp‑cum‑audio‑interface designs, it operates in the analogue domain, meaning that those noises won’t rob you of converter headroom. (The filter is an area where the four‑channel Quad actually improves on the Octo, as explained in the box.)

The manual states that the variable impedance settings shouldn’t have any effect with capacitor mics, but I found that wasn’t quite the case, at least with vintage transformer‑balanced models. With a Neumann KM84, for example, the input signal was about 3dB quieter at the 400Ω setting compared with the 12kΩ setting, and very slightly fuller in the midrange. I’m not sure I could claim the tonal difference was audible, but it was just about measurable with pink noise as a source. With dynamic and ribbon mics the impedance setting makes more of a difference; using a beyerdynamic M160, I measured a 4dB overall level difference between the 12kΩ and 400Ω settings, with the latter also introducing a 2‑3 dB dip at around 150Hz.

The Drive circuits, meanwhile, are commendably gradual in their onset. You don’t suddenly go from clean‑clean‑clean to fuzzbox, as can be the case with some preamp designs; rather, there’s a gentle coloration that creeps in as you crank the gain knob. If you want to maximise the saturation, the trick is to use more gain and then back off the trim, but even so, it only gets super‑hairy if you really want it to. And, as ever, it’s quite source‑dependent, and likely to be most noticeable on something like a DI’ed bass. The new Asymmetric Drive mode is more assertive and thicker‑sounding than the Classic Drive setting. Having initially been sceptical about the idea of artificially introducing the sort of artefacts usually associated with transformer or valve‑based designs, I’m definitely a convert.

If there’s one PureDrive feature I didn’t find much use for during the review period, it’s the USB interfacing. I’d want to be very confident of the robustness of any aggregate setup before using it on a real‑world session, and as long as one has a spare ADAT input, it’s simpler and easier to take that approach. But there are certainly times when one doesn’t have a spare ADAT input, and I can imagine it being a valuable option at a pinch.

It’s a little surprising to find that the PureDrive preamps face no obvious competition at their price levels.

Eight Way Fight

It’s a little surprising to find that the PureDrive preamps face no obvious competition at their price levels. For half the price or less, you can pick up something like Audient’sASP880 or the FocusriteClarett+ OctoPre; both are very capable units, but there’s an understandable gap in terms of specifications and capabilities, and neither comes close to offering the same massive gain range, for example. If you’re looking for something with a similar feature set, the obvious choices are Focusrite’s ISA428 and ISA828, and in many ways the similarities are uncanny. The ISA preamps likewise offer a huge gain range, impressive specs, variable impedance, switched or stepped gain controls, and so on. Even the panel layout is rather similar, with the ISA828 having separate gain and trim knobs, and a bank of four instrument inputs down the left‑hand side, while the analogue routing and connectivity is almost identical in both cases. In sonic terms, the main difference is perhaps that the ISA units have transformer‑balanced inputs. And from the ergonomic perspective, the ISA offers a dedicated knob or button for every parameter, with no secondary functions.

The PureDrive is at heart a more contemporary take on the ISA concept, and if they were the same price, I’d struggle to choose between them. In the end, I suspect that the ISA’s more immediate control set, line inputs on quarter‑inch jacks and optional Dante connectivity would just about tip the balance against the Octo’s Drive options and USB interfacing. But, here’s the rub, they are not the same price. The ISA828 is nearly 50 percent more than the PureDrive Octo, and its digital board is a pricey cost option on top of that. I don’t think the ISA828 is overpriced at all: mine has done sterling service for 15 years or more, and I’d recommend it to anyone in a heartbeat. Rather, the PureDrive Octo is a total bargain — and unless I get a sudden injection of willpower from somewhere, the review unit will soon be teaming up with the ISA in my setup. It’s just the latest in a string of surprisingly affordable, over‑achieving analogue processors from SSL, and I hope they’re making enough margin on it to give their designers a pay rise!