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Mixwave Coil Audio CA-70S

Mixwave Coil Audio CA-70S

Coil Audio’s CA‑70 valve preamp is based on classic Western Electric and RCA designs dating back as far as the 1930s. Unlike later preamp circuits, these used the valves as fixed‑gain elements and the overall gain was adjusted using attenuation on the front or back end. As the CA‑70 has two valve gain stages, it’s designed with two attenuators: a stepped input pad, and a variable control that adjusts the level passing from the first stage to the second. It also has tone‑shaping filters and a dial that sets the amount of negative feedback. Available in several physical formats, the CA‑70 has proved very popular since its launch a few years back, and has now inspired an official plug‑in emulation.

Mixwave’s CA‑70S faithfully replicates the rackmount version’s feature set, with a choice of input sensitivity settings, a five‑position Low switch that affects the tone of the bottom end, plus feedback and ‘output’ controls, the latter being in fact the inter‑stage gain control described above. On top of this, they’ve added controls to help it fit into a plug‑in context, including fully variable input and output trim, optional high‑ and low‑pass filters on both input and output, and a wet/dry mix knob.

Contrary to some people’s expectations, valve gear isn’t intrinsically colourful or distorted. When used within its intended operating range, it can be very clean, and that’s reflected in this plug‑in. If you operate it in ‘line’ mode, leave the negative feedback control in its default position and feed it a signal with a reasonable amount of headroom, you’re unlikely to hear significant changes. As you begin to play with the controls, you discover that it’s certainly possible to achieve crunchy drums and overdriven telephone‑style vocals, but what’s perhaps most impressive is the huge hinterland of ‘subtle warming’ treatments that lurks between these extremes. This definitely isn’t one of those saturation plug‑ins that jumps straight from “Is it on?” to “Too much!”

If what you’re looking for is rich, thick, controllable warmth that never gets harsh or brittle, this is definitely the plug‑in for you.

The effect of the Low control is rarely dramatic and, as you’d expect, it’s mainly useful on sources with a lot of low‑frequency content. In conjunction with the NF dial, it makes the CA‑70S plug‑in a brilliant tool for treating synths and electric basses. If what you’re looking for is rich, thick, controllable warmth that never gets harsh or brittle, this is definitely the plug‑in for you. On sources with more midrange and high‑frequency content, things can get a bit edgy at one end of the NF control’s travel, whilst turning the feedback all the way up delivers a muted, darker tone, but pretty much the entire range has the potential to be useful somewhere. Its relative restraint makes it usable on busses and entire mixes as well as on individual sources.

Mixwave have also sourced a preset collection from an impressive roll‑call of engineers and producers. Step through these and you’ll hear one or two that seem much more radical than the others. They typically make use of the input or output filters, which are the only controls really capable of extreme results; however, unless you click to expand their control panels, there’s no visual indication of whether they’re active, or what frequencies they’re set to. This could perhaps be improved in a future version. Other than that minor foible, this is a very classy software implementation of what seems a very classy piece of hardware — and, naturally, it’s an order of magnitude cheaper than the physical CA‑70 hardware.


£119.32 (discounted to £79.22 when going to press).

$149 (discounted to $99 when going to press).