Roll Music Systems: Vacbax 500 Series Tube EQ

There's something appealing about a two-band EQ. It implies a broad stroke – "just a bit of this and a pinch of that" – in a way that is optimistic, confident, and unfussy. Simple tools work particularly well in hybrid situations, like feeding Pro Tools sessions out to a console using hardware EQs to provide a gentle tilt to summed stereo groups, or on single sources after a surgical plug-in EQ that notches out any offending frequencies. At tracking, two-band EQ can be great for quick coloration and excitement with minimal opportunity for a misstep. One can, of course, do all this with any decent equalizer, but if we're choosing our tools, we may as well pick the ones that resonate with our workflow.

For me, a quick, simple interface with a degree of limitation reminds me to keep moving forward and focus on the essentials. Roll Music Systems' Vacbax is such a unit, featuring a switchable 8 or 16 kHz high band, a fixed 150 Hz low band, and a high-pass filter around 80 Hz. Being a Baxandall-style EQ, both bands work on gradual curves that reach far inwards from their noted frequency points, capable of ultra-smooth tone shaping that is more like the program Treble and Bass EQ controls on a home stereo than a console-style parametric EQ. While this style of equalizer has gained a following for its smoothness on mix bus and mastering processing, it's also a useful quick tracking tool. It's worth noting that the Vacbax isn't a 100% true Baxandall circuit, but rather a passive spin on the design to further facilitate big moves without distortion. The Vacbax's passive EQ circuit and 240 V vacuum tube output amplifier feature transformer inputs and outputs. Activating the Out button (bypass) removes the tone controls while leaving the filter, amplifier, and transformers in line. All this sounds like they should be turning your equipment rack into an oven, but nope – these units run no hotter than the standard solid state gear. There's a rudimentary meter by way of a color-changing signal/clip indicator LED that goes from green to yellow and then red. Regardless of its LED hue – the input transformer acts as a step-down to maximize headroom, while the output operates at a fixed gain to help keep the unit in its tonal sweet spot. Props also to Roll Music Systems for the clever low-waste/low-material use shipping boxes they use.

My first tracking session with the Vacbax was one where I didn't really expect to see a lot of use for it – the day was to be almost entirely electric guitars, and the lack of midrange control didn't point to it being a big part of that process. I decided to give it a shake nonetheless, and ran it behind an AEA R92 [Tape Op #56] ribbon mic plugged into a Retro 500PRE [#135] to record a Rickenbacker 330 electric guitar through a Fender Super Champ amplifier. Then came a (literal) moment of clarity – the guitarist was playing fingerstyle with a healthy dose of reverb and delay. Pushing the highs on the Vacbax brought out a welcome definition and high end texture to showcase the precision of the performance against the effects. This subtly enhanced the presence of each pluck without undoing the character of fingerstyle playing – if anything, it enhanced the distinction between finger and pick. This was notable in that there was no sense of adding a point of focus to a specific frequency, but rather registered as though the change was at the source itself. I first had that same feeling about an EQ when using Pultec EQP-1A3s at Avatar Studios years ago – not bad company to be in! Later that day, with guitars complete, we ran a pair of Vacbaxes between a stereo drum machine output and sampler input. Though the drum machine's kick drum had plenty of punch, its bottom was a little anemic. We were able to dial in huge low end without losing the focus and added in just a tiny bit of high end which kept the hi-hats crisp against the guitar tracks. Once again, the smoothness of the Vacbax curves made our adjustments sound natural and easy. It's a great tilt EQ to have on hand for tracking – especially if your preamps and mics don't have built-in high-pass filters. Regarding the curve shape, Justin Ulysses Morse [#84] from Roll Music Systems says, "it's not exactly a shelf. It's not exactly a bell. It's a Bax!"

In addition to some simple additive EQ moves, I love the flexibility you get when playing the low boost of the Vacbax against its high-pass filter but sometimes wished I could drop the band frequency to between 70 to100 Hz on many sources. Similarly, I ran into a few acoustic guitar and male vocal tracks in mixing where the high frequency boost selections just weren't landing right. With an API 550A or even a JLM Audio PEQ500, I could quickly find the slope I was looking for. To be fair – I'd applied EQ at the time of recording to these tracks, and they were perhaps past the "broad strokes" phase, being very close to where they needed to be in the mix already. While we're complaining, the bypass (Out) switch emits a scratchy static sound when pushed. It's not terribly loud, but I did hear back from Roll Music Systems that they have implemented a design change to minimize this, and that the pair I had for review may have predated this change. In all cases, the switches are self-cleaning. The noise did become less present over time.

While the Vacbax was less universally applicable than some other equalizers on individual tracks at mix time, it quickly proved handy on mix groups. Across a group of backing vocal tracks, stacked in a Beach Boys tonal harmony style, it sounded killer! With the filter engaged, a little low end bump for control and solidity, plus a nice boost to the high end, the vocals sounded exactly right – lots of presence, but smooth enough to not push their way out of place in the mix. Next, I put the Vacbaxes to use on drum groups: Both main and parallel drum buses. I found the 16 kHz band to be great for rolling off highs and softening cymbal harshness without making the drum kit feel dark or muffled. On parallel drums, in particular, I could dip the highs substantially while pushing a low boost against the high-pass filter to keep the heavily compressed drums focused where I wanted them, thanks again to that quality of being able to make substantial changes without leaving negative artifacts or compromises. That character came through a few other places, too. Though it had been a little hit-or-miss at mix time on the previously noted male vocals, we found the Vacbax to be absolutely perfect on the single female voice I had to work with (which, coincidentally, I hadn't EQ'd at all at tracking). Big boosts at either the high or low frequencies never got harsh, and, while you could certainly go too far, it never went outright bad. The 16 kHz setting gave air to the performance while 8 kHz (along with a slight low bump) gave the vocal an electric presence and closeness that sounded so good that I considered remixing the material we'd finished before the Vacbaxes arrived!

Across the mix bus, this EQ lived up to the Baxandall reputation. Small boosts to both bands gave a smooth and tasteful take on the addictive "smile-curve" profile that feels invisible until you disengage it (I pretty much always wanted to re-engage them). The knobs aren't stepped and do have a light feel, but I didn't find it difficult to keep balance when using the units over stereo groups. The high band really comes into its own on the full mix. The 16 kHz setting opens things up unobtrusively but appreciably, whereas the 8 kHz setting offers that top end sheen with an added extra snap and presence to midrange sources like electric guitars due to the long slope as you get into anything but the tiniest boosts. While I enjoyed using the Vacbaxes for cuts on subgroups, I couldn't get over how good they sounded for boosts across the full mix. If these weren't as beneficial during tracking, I could imagine leaving them wired to the outputs of the console!