2hp Turing Machine (2015–)

Name: 2hp Turing Machine
Brand: 2hp

A small module that seems alive until you realize you're the one being toyed with.

Overview

Patch up the 2hp Turing Machine and at some point the sequence it just made sounds too good to be random. It's a shift register with a probabilistic brain, cycling through 1 to 32 steps of random voltage, nudged by your touch or a CV input. The melody breathes and the rhythm swings, but that's the register doing its job. It feels like collaboration. You aren't programming it, you're negotiating with it. Sometimes it wins.

It comes from the open-source Music Thing Modular Turing Machine, and the 2hp version strips the idea down hard. No blinking LEDs, no dedicated gate outputs, no front-panel scale quantizer. What's left is analog randomness with memory. It lets you freeze a sequence you like, tweak its randomness on the fly, or let it drift somewhere new. The "lock" function is the key trick. Dial in a sequence you like, hit lock, and it repeats as a phrase. Then nudge the "random" knob and it starts mutating, note by note.

It is 2HP wide and 42mm deep. It does less than its bigger siblings, yet it earns its spot in a crowded rack. The catch is the lack of visual feedback. There are no step indicators and no blinking lights, so you learn its moods by ear. A certain patch will make your bassline lurch in a way you didn't expect.

It’s not a sequencer. It’s not a noise source. It’s a co-writer with commitment issues.

Specifications

Manufacturer	2hp
Production Years	2015–
Original Price	$120
Format	Eurorack
Width	2 HP
Depth	42 mm
Current Draw +12V	30 mA
Current Draw -12V	15 mA
Step Range	1–32 steps
Randomness Control	Manual knob with CV input
Step Length Control	Manual knob with CV input
Lock Function	Manual button
Outputs	CV Out, Gate Out (derived)
Inputs	Clock In, Reset In, Random CV In, Step Length CV In
Power Connector	4-pin Eurorack power header
Weight	35 g

Key Features

The Art of Controlled Chaos

The Turing Machine doesn't generate randomness the way a dice roll does. At one end of the "random" knob, you get a fresh, unpredictable sequence every time. At the other, it locks into a single voltage that never changes. In between is a sliding scale of mutation. Turn it up during a performance and your clean melody starts sprouting dissonant neighbors, one note at a time. The CV control over randomness means you can modulate the mutation rate with an envelope, an LFO, or even another Turing Machine (yes, people do that). Pair it with a quantizer and the drifting voltages snap into key.

Size as a Feature

Eurorack modules keep getting wider and deeper, and the 2hp TM goes the other way. It fits in the gaps, the 2HP spaces left behind by logic modules, attenuators, or blank panels. The size has trade-offs. The knobs are tiny, the labels are easy to misread, and with no visual feedback you rely entirely on your ears. Some users report patching errors because the "step length" knob looks too much like the "random" knob. It isn't ergonomic. But in a skiff or a travel case, where every millimeter counts, the small footprint is the selling point.

The Gate Conundrum

Unlike the original Music Thing Modular version, the 2hp TM doesn't have a dedicated gate output per step. Instead, it generates a gate signal derived from the CV output, a pulse that triggers when the voltage changes significantly. This works for many applications, but it's not foolproof. In quiet sequences, where voltages shift subtly, the gate might not fire. For percussion, this can be a dealbreaker. Some users chain it into a comparator or use an external clock divider to get reliable triggers. It's a compromise born of space constraints, not design philosophy. If you need rock-solid gates, you'll need to patch around it. For modulating filters, pitch, or panning, where the CV is the star, the gate is just a bonus.

Historical Context

The 2hp Turing Machine arrived in 2015, as Eurorack was shifting from boutique curiosity to mainstream synth culture. At the time, random voltage sources were still niche, and most composers relied on sequencers or LFOs for variation. The original Music Thing Modular Turing Machine, released in 2011, had already proven that probabilistic sequencing could be musically compelling, but it was a DIY kit, 16HP wide, and visually busy. 2hp saw an opportunity: distill the concept into something that could live in the cracks of any system. They weren't the first to miniaturize. Mutable Instruments' Braids and STG Soundlabs' Matchstick were already pushing density. But the TM was minimal. No extras, no compromises on the core idea. It arrived alongside a wave of small utility modules, like the Intellijel Metropolis or the ALM Busy Circuits series, that proved small modules could be generative, not just functional.

It also rode the "generative music" trend, fueled by Brian Eno's legacy and the rise of algorithmic composition in digital audio workstations. Software solutions could feel clinical, while the 2hp TM felt imperfect and unpredictable. It wasn't trying to replace the composer. It was trying to surprise them. Competitors like Noise Engineering's Mimetic Digitalis or Grayscale's Permutation offered more features, including multiple sequences, built-in quantizers and scale memory, but they were wider, pricier, and often more complex. The 2hp TM didn't compete on specs.

Collectibility & Value

The 2hp Turing Machine has never been rare. Production has been steady since 2015. Used units sell for $80 - $110, depending on condition, while new ones hover around $120. Unlike vintage synths, its value isn't rising, it's stabilizing. It's still in production and still being used in new systems. There's no collector's premium, just utility value.

It does have issues. The most common complaint is mechanical: the step length knob is a continuous pot with no click stops. In a live set, it's easy to misjudge the setting. You think you're at 16 steps and you're actually at 22. There's no visual indicator and no tactile feedback. Some users add nail polish marks or tiny stickers to the knob. Others avoid live knob tweaks entirely and rely on CV control instead.

Another quirk: the module can "lock up" in a zero state, where all bits in the shift register are off and the output sits at a flat 0V. This isn't a failure, it's a mathematical inevitability. It can be jarring mid-performance. The fix is a reset pulse or a quick clock burst. Some users patch a momentary switch to the reset input for emergencies.

Maintenance is minimal. No moving parts, no displays, no firmware. The PCB is simple, the components are standard, and 2hp's build quality is consistent. If it fails, it's usually a power issue, so check the ribbon cable or the bus board. There's no "recapping" culture around it like with vintage synths. It either works or it doesn't.

When buying, test the knobs. Make sure they turn smoothly and respond to CV. Check for cold solder joints if buying used. They're rare, but possible. If you're pairing it with a quantizer, test the combo, since some users report slight voltage drift that can push notes out of key. Otherwise, it's about as low-risk as Eurorack gets.