midiphy zetaSID Firmware 1.5 Adds 303-Style Bassline Engine

TL;DR: The midiphy zetaSID — a 4HP Eurorack module packing a SID chip emulation — just got firmware 1.5, adding a 303-style bassline engine with a built-in 16-step sequencer, eight patterns per channel, and per-step parameter control. It’s a free update for existing users, and it turns a single module into a surprisingly capable acid machine. Stack up to 12 for polyphony, or just let one burble away while your coffee brews.

• New bassline engine emulates a 303-style synth with a 16-step sequencer, eight patterns per channel, and per-step note, octave, gate, slide, accent, and one assignable parameter.
• Firmware 1.5 also adds individual instrument attenuation for the drum engine and 180° screen rotation for upside-down module mounting.
• Up to 12 zetaSIDs can stack via the phybus for polyphonic or unison operation; two modules enable true stereo bassline patching.
• Existing users can load their own MIDIbox SID lead and drum patches, though compatibility isn’t guaranteed for all.
• Available now for $199/199,98€; the nexusMIDI expander adds extra MIDI ports and frees CV inputs for modulation.

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The Bassline Engine Arrives

Let’s be honest: the SID chip is a legend, but it’s not exactly known for its acid basslines. The Commodore 64 could do a lot of things — loading games from tape, causing existential dread with its loading screens — but a 303 impersonation wasn’t high on its resume. Enter midiphy’s zetaSID, a 4HP Eurorack module that emulates the SID faithfully, and now, with firmware 1.5, it adds a bassline engine that channels the spirit of the Roland TB-303.

This isn’t a half-hearted addition. The engine includes a built-in 16-step sequencer with eight patterns per channel, per-step control over note, octave, gate, slide, accent, and one freely assignable parameter. You also get two LFOs and an additional envelope with curvature — because real acid needs to squelch, not just sit there. The module’s three CV inputs (SEQ step, SEQ reset, and SEQ pattern) let your modular drive the sequencer with clocks, resets, and pattern selects. If you own two zetaSIDs, you can chain them via the phybus for a true stereo bassline patch. That’s the kind of overkill we can get behind.

What Makes the zetaSID Tick

At its core, the zetaSID is a 4HP module that runs the MIDIbox SID synth engine — an emulation that midiphy claims is “state-of-the-art” and faithful to the original chip’s output, but without the noise and voltage headaches of actual 1980s silicon. It features six LFOs, dual envelopes with delay, quad-wave sequencers, three independent oscillator arpeggiators, eight modulation paths, algorithmic operations, and a 24×12 event trigger matrix. That’s a lot of firepower in a space smaller than your average coffee mug.

The single-knob interface might raise an eyebrow — we’ve all had nightmares about menu-diving with a Disting — but midiphy promises an intuitive graphical UI with fluid visualization of oscillator outputs and arpeggio patterns. If you’re using multiple zetaSIDs, the phybus expands the interface across all displays, turning a cluster of tiny modules into something that feels more like a proper instrument. Still, if you’re only buying one, be prepared to spend some time with the screen and encoder. It’s not a showstopper, but it’s worth noting.

Polyphony, Unison, and the Phybus Ecosystem

One of the zetaSID’s party tricks is its ability to stack. You can link up to 12 modules via the phybus backplane, creating a full polyphonic, MIDI-controllable synthesizer with up to six stereo voices. Alternatively, you can run them in unison for massive detuned leads that would make any monosynth blush. The phybus handles low-latency control messages, MIDI data, and CV/gate updates, plus virtual cords between modules to reduce cable clutter. Total recall is available via microSD, so you can save your patches without needing a second brain.

The nexusMIDI expander adds more MIDI ports and frees the zetaSID’s CV inputs for modulation sources from your system. This is the kind of modular thinking that makes the zetaSID more than just a novelty SID module — it’s a building block for a larger system. But let’s not pretend you’ll buy 12 of these on a whim. Start with one, see if you gel with the workflow, and then decide if you want to go full SID army.

Drum Engine and Firmware 1.5 Refinements

Beyond the bassline engine, firmware 1.5 also brings individual instrument attenuation for the drum engine. That’s a quality-of-life improvement that should make the 19 parametric drum algorithms — covering kicks, snares, claps, toms, and classic C64 effects — more usable in a mix. No more having a snare that buries everything else because you couldn’t dial it down.

There’s also 180° screen rotation support, letting you mount the module upside-down if your rack layout demands it. It’s a small thing, but in Eurorack, every millimeter and orientation counts. The update is free for existing users, which is always a good look. The module itself remains $199/199,98€, with the nexusMIDI at 189,98€. Considering you’re getting an entire SID-based synth voice — plus now a 303 engine — that’s solid value, provided you can live with the single-knob interface.

Who Is It For?

The zetaSID is for the modular user who wants something that doesn’t sound like every other VCO/VCF combo. It’s for the retro enthusiast who remembers the C64’s sound but doesn’t want to deal with actual vintage chips. It’s also for the acid-head who wants a 303-style voice that can integrate with a larger modular setup, without buying a dedicated clone.

If you’re the kind of person who enjoys deep menu systems and is willing to invest in multiple modules to unlock the full potential, the zetaSID rewards you with polyphony, unison, and a drum engine that can go from classic TR-style hits to weird C64 noise. If you just want a simple, knob-per-function voice, this might feel like a compromise. But then again, the Disting has a thriving user base. The zetaSID is at least more focused, with a clear identity and now two distinct sonic personalities: SID lead and 303 bass. That’s a lot of personality for 4HP.

I’ll be honest: I’m still a little wary of that single knob. But if the bassline engine sounds as good as the demos suggest, I might just forgive the menu-diving — especially if I can do it with a fresh pour-over in hand. Now if only the module could make coffee, we’d be set.