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AJH Synth/Tone Science Triple Cross

XFader Panner Eurorack Module By William Stokes
Published October 2023

It’s always a good day when I hear of a module created by an artist and a developer working together. This is usually because instead of an idea stemming from a designer scratching their head about which gap in the market they can fill with a new product, it’s arisen from an actual need expressed by those using the tools. Such is the case with the Triple Cross, a three‑channel stereo crossfader and panner with some rather powerful tricks up its sleeve. It began life as a joint venture between two stalwarts of the electronic music landscape: Allan J Hall of the eponymous AJH Synth and electronic composer Ian Boddy, owner of the venerable DiN Records and the modular‑focused sub‑label Tone Science. “Ian comes up with the ideas and we herd the electrons to make them real!” Enthuses Hall on the AJH Synth website.

The Triple Cross is what I like to think of as a ‘blank canvas module’: a design so open‑ended it has almost no ‘correct’ application in a patch. It can swing signals from one speaker to the other, it can have stereo channels swap places, it can act like a VCA or almost‑a‑mixer, it can blend modulation signals and exchange them between channels, and then some. Like many classic synth circuits — sample & hold, for example, or a slew limiter — it presents a relatively simple yet elegant concept and challenges you to be as creative as you can with your patching, to think laterally and tease out new behaviours from your system’s circuitry. The idea purportedly arose from Boddy’s work on his vintage Serge system, specifically a patch involving three separate crossfaders and “a sea of patch cables” to create undulating movement within a pool of source signals. The Triple Cross condenses that general idea down into a neat 14HP, and generously is DC‑coupled to work just as well with audio as it does with CV.

The module’s panel consists of three Fade knobs with accompanying CV inputs and attenuverters. Beneath these are three sets of stereo inputs and outputs with respective input pairs labelled A and B and outputs labelled L and R. On the surface it’s fairly simple, but there’s a lot to explore here. AJH Synth encourage us to think of the Triple Cross as having different ‘modes’, which helps to rationalise things a little.

At its most simple, in Mode 1, the Triple Cross can act as a good old‑fashioned three‑channel VCA. With one signal patched to any channel’s A input and its L output, and a voltage source patched to that channel’s CV input, the Fade knob acts as an offset. Being attenuverters, of course, the CV inputs can also open the VCA with negative voltages if desired, which is handy. Patch two inputs — audio or CV — to one output to crossfade between the two down a mono patch cable with the Fade knob, or automate it with CV. Taking two different waveforms from the same oscillator, for example, it’s a cinch to create a sound much more interesting than the sum of its parts — in fact with this simplest of patches it does something of a brilliant job of having that oscillator pretend to be a wavetable.

Patch one input to two outputs to pan it between the two channels — or fade a CV signal between two different destinations. Lastly (you may have seen this coming) is the ability to patch both inputs to both outputs on a channel. This is where the elegance of the Triple Cross really comes through, essentially allowing two channels to swap sides with each other according to either CV or manual control — or both. Of course, the CV input opens up some very interesting possibilities, not least the dizzyingly fun exercise of making two sounds swap speakers at audio rate for some bizarre, ghostly ring‑mod‑type sounds that seemed almost to project into the room beyond the stereo image. Experimenting with variable LFO frequency and waveform made for further excitement, and that’s just scraping the surface of what’s possible.

The Triple Cross’s channel 3 adds a few tricks to the equation. It has additional level attenuators, which is useful, and the left sides of channel 1 and channel 2’s outputs are also normalled to the A and B inputs of channel 3. In light of all of the above, in practice this means it’s possible to bus four different crossfading signals down a single stereo output with three different modulation sources at work, and still balance the levels of those constituent sounds internally. Clever.

Good thing the Triple Cross harks back to the old‑school — this has the makings of a classic.

I wondered at points if those aforementioned modes might even have been illustrated on the panel in some way, or at least the signal flow made a little clearer; just to speed up the inevitable mental maths that comes with a module like this, particularly one whose layout isn’t always the most intuitive. I had to keep reminding myself that the normalling does not mean the whole equation can mix down to channel 3. But this is a minor bugbear. It took no time at all to start teasing out some very interesting results, particularly since each channel can simultaneously be used in any one of the above modes. Apparently we can expect more modules from this collaboration, and for those I’ll be waiting eagerly. Good thing the Triple Cross harks back to the old‑school — this has the makings of a classic.