![](https://www.audiotechnology.com/wp-content/uploads/2024/07/SSL-Pure-Drive-Quad_MAIN2-pichi.jpg)
Review: SSL Pure Drive Quad
Four channels of SSL’s Pure Drive microphone preamps with an integrated USB digital interface.
For decades now the name SSL has been synonymous with analogue mixing consoles of the highest quality. From the the legendary monster J and K consoles to the modern flagship Origin, Duality Fuse and TriniTy models, when we think SSL the next logical thought is ‘How many channels?’ and ‘Does it have the (also synonymous) mix-bus compressor?’. Less frequently discussed are the mic preamps in said consoles. You certainly don’t see vintage SSL pres discussed ad nauseam on audio forums, nor do you see them parted out, re-racked and sold on eBay for eye-watering sums of money. To remedy this situation SSL has gradually developed a re-designed preamp that aims to offer the best of their earlier clean, high-end fidelity designs while adding the option of harmonic colouration that was absent from its older offerings.
ORIGIN STORY
SSL’s Variable Harmonic Drive (VHD) preamps first appeared in 2006 in the first iteration of the Duality console. The idea was to give users a high-definition, low-noise, transparent preamp with a big trick up its sleeve – the ability to add harmonic ‘drive’ and distortion to taste via a variable input gain and output trim control set. Subsequent design upgrades landed in the sweet spot with the introduction of the large-format Origin console in 2019. The success of this design has led SSL to re-package the VHD preamps in a variety of rackmounted formats giving smaller studios and home recordists the opportunity to buy into the new SSL preamp sound. Latest among these offerings are the Pure Drive Octo and Quad which also integrate high-grade conversion and digital interfacing.
FORM FACTOR
The Pure Drive Quad is an interesting beast. The four VHD preamps are very much front and centre (more on them later) but a quick look at the back panel reveals a unit that is way more than just a four-channel mic preamplifier box. Firstly, the multi-function input sockets take both XLR microphone and balanced 1/4-inch jack inputs, meaning you can run line signals through the Pure Drive circuitry. Secondly, the unit can run as a fully functional USB audio interface at up to 32-bit/196k sample rates. The connectivity on the rear panel includes D-Sub for four insert returns and four dedicated line inputs, BNC wordclock in and out, AES and ADAT outputs and a ‘Link In’ socket for ADAT input as well as for cascading multiple Pure Drive units.
SSL allows the repurposing of the AES and ADAT digital connections as additional analogue outputs, so the unit can operate as a 12-in/12-out interface, but only at the lower sample rate of 44.1/48k. Like many interfaces of this type, the channel count drops as the sample rate gets higher, so at 88.2/96k you’re down to 8-in/8-out, and at 176.4/192k it’s six channels. The unit also lacks things like monitor and headphone outputs and master volume controls (not to mention dedicated software), so it is undoubtedly more suited as an expansion unit to an existing computer+Interface setup. Having said that, the build quality, cutting-edge conversion and versatility of the preamps make the Pure Drive Quad a formidable audio tool, and for the odd off-studio recording or live gig it can well and truly hold its own.
NEED TO KNOW
SSL Pure Drive Quad
Four-channel Mic Preamp
![QuadFront-pichi](https://www.audiotechnology.com/wp-content/uploads/2024/07/QuadFront-pichi.jpg)
![QuadRear-pichi](https://www.audiotechnology.com/wp-content/uploads/2024/07/QuadRear-pichi.jpg)
FRONTING UP
While there are limitations to the Pure Drive Quad’s abilities as a studio centrepiece, there’s no doubting the quality and utility of what’s on offer. The front panel gives precedence to the four preamp channels and allows for a modern-looking and spacious layout featuring dedicated controls for continuously-variable stepped preamp gain, trim and a high-pass filter.
A push of any channel’s gain knob enables the insert circuit making it ideal for effortless A/B’ing of EQ and/or dynamics processing chains. Similarly a push of the Trim button flips the channel’s phase. Both these options are elegantly signalled by small LED indicators.
At the bottom of each channel are dedicated pushbuttons for phantom power, line input, hi-Z input and Drive. The latter is bypassed when in clear white mode, but turns yellow with a push that enables the Classic Drive circuit found on the Origin console. This is a subtle colouration that introduces primarily odd harmonics into the sound and gently flavours things in a musical way. Holding the Drive button down turns the button from yellow to green and switches it into Asymmetric Drive mode. This is a new colouration that is a little more aggressive and makes the even harmonic content more dominant, providing additional thickness, colouration and softening of transients.
To the right of the channel controls are further pushbuttons for standby mode and wordclock setup, while a pair of 14-segment LEDs provide excellent visual feedback on input levels. In typically comprehensive SSL style, the brightness of the backlit buttons and other indicators can be adjusted, the meters have their own brightness adjustment settings and the ballistics and peak hold/release settings can also be tweaked to suit the user’s preferences. There’s also a safe mode that can be programmed in for polarity and send/return switch isolation. SSL really has put some serious thought into the detail of this unit and the look, sound and feel of it is reassuringly pro.
MAKING THE CONNECTION
Connecting to my existing rig was as easy as plugging into a spare USB-C port on my iMac and creating a new Aggregate Device that incorporated my existing UAD Apollo, RME converters as well as the 12 inputs and outputs of the Pure Drive Quad’s I/O. Once established, this setup automatically folds down at the higher sample rates mentioned above so there’s no need to re-allocate things when changing sample rate values.
My initial listening tests compared the conversion quality of the SSL with my other converters using program material run through at line level. The SSL analogue-to-digital conversion has a quoted dynamic range of 119dB and a frequency response of ±0.035dB down to 5Hz as well as extremely low distortion and crosstalk figures. With these typically high-end specs it was no surprise that the sound quality was excellent. Like its cousin, the Sigma, which I reviewed several years ago, the sound of these converters is smooth, musical yet accurate and delivers a satisfyingly wide and deep soundstage suited to a wide variety of music and sound applications. The sound of the Pure Drive Quad is top drawer and will hold its own against anything in the market at twice this unit’s price.
DRIVE TO SURVIVE
Turning my attention to the Pure Drive Quad’s preamps, I set up some tests with two identical mics strapped together, one running through Preamp 1 on the clean setting, the other toggled between the two Drive settings on Preamp 2. On acoustic guitar the differences between clean, Classic Drive and Asymmetric Drive were fairly restrained. The clean signal was beautiful and transparent while Classic Drive changed the tone only very subtly. Certain overtones started to ring out a little more in the upper registers and there was a nicely restrained ‘glow’ to the overall tone. In Asymmetric Drive mode these characteristics were a little more overt and some lower frequency bloom was introduced, but again the overall effect was quite restrained and added just a little intensity to the sound rather than turning it up to 11. On drums these effects were more noticeable and the range of drive tones was increased as there was more dynamic range to play with. Again a subtle sweetening and tonal shift in the upper frequencies was evident in Classic Drive mode, while Asymmetric Drive made a bolder statement and added an extra full-range harmonic thickness to the sounds. In both Drive modes there was only a small impact on overall dynamic range, even at the most robust settings. When pushed to its limits the Drive button flashed red to indicate peaking and the tone got crunchy but not in a nice way.
As a final test I ran some full-range program material through the line inputs and was able to really fine-tune the results. I got a fairly clean country rock track to thicken up nicely (especially in Asymmetric Drive mode), lending it a tougher wallop on the drums, more spark in the guitars and bigger attitude in the vocal. The tradeoff was in the bottom end where I had to be careful not to lose too much definition on the bass and kick drum. In this context the HPF was a handy feature but needed to be used judiciously. There’s definitely a tipping point where subtle thickness and harmonic enhancement give way to a slightly deadening, overloaded sound so it’s worth really playing with EQ on the incoming material and the input gain, trim control and filter to dial in the perfect amount of VHD goodness. As well as processing programs material, you could have a lot of fun re-processing individual tracks with the Pure Drive Quad where elements like synths, guitars and drums could really benefit from this kind of tonal enhancement. Having said all this, It’s important to note that the VHD processing is not an out ’n’ out distortion circuit: it adds weight and harmonic richness to sounds but it is calibrated for subtle colouration, not outrageous sledgehammer effects.
THE DIRTY FOUR
I’ve talked a lot about the VHD processing in this review but it shouldn’t be forgotten that the Pure Drive Quad can also be a transparent preamp box par excellence. In normal clean mode the preamps are whisper quiet, extremely high-fidelity and very musical. Add flexible analogue and digital connectivity and class-leading A/D conversion and you’ve got something pretty special going on here for a very reasonable outlay, even before you add the flexibility of controllable harmonic drive. With the caveat of reduced track counts at higher resolutions, the Pure Drive Quad offers a whole lotta bang for buck and can seamlessly slot into just about any studio or DAW environment. Lately, SSL has had a handy knack of releasing affordable yet high quality kit that ticks a lot of boxes for a lot of people, and this offering is no exception. If you’re in the market for a set of high-quality preamps with flexible flavour, high-end conversion and USB interfacing, the Pure Drive Quad (at just a tick over A$500 per channel), and its big sibling the Pure Drive Octo should definitely be on your short list.
![Clean.7a8d5b92e6979e4df3a30a1883c00927-pichi](https://www.audiotechnology.com/wp-content/uploads/2024/07/Clean.7a8d5b92e6979e4df3a30a1883c00927-pichi.jpg)
RESPONSES