2HP Filter (2013–2018)

Name: 2HP Filter
Brand: 2HP

A tiny titan of tone-shaping that proves big sound doesn’t need big real estate—just clever design and a fearless resonance knob.

Overview

Slap a signal into the 2HP Filter and twist the resonance past noon—you’re not just filtering, you’re summoning. That sudden burst of sine-wave squeal isn’t a glitch; it’s the module singing in self-oscillation, a party trick that doubles as a full-fledged VCO with legit 1V/oct tracking across four octaves. For a module that eats up only two horizontal pitch units in your Eurorack case, that’s borderline criminal. But 2HP never played fair when it came to density. The Filter—later renamed MMF to avoid confusion with other designs—was their answer to the eternal modular dilemma: how do you get a rich, expressive analog filter into the smallest possible footprint without turning it into a lifeless utility? The answer lies in its OTA-based, 12dB-per-octave architecture, a gentler slope than the steeper 24dB designs, but one that trades raw aggression for fluidity and versatility.

It’s not a bruiser like a Moog-style ladder, nor does it aim to be. Instead, the Filter carves out a space somewhere between surgical precision and warm musicality. Turn the cutoff wide open and it’s nearly transparent—perfect for subtle tonal sculpting. Wind it down with a touch of resonance and it gets creamy, the kind of low-pass warmth that makes basslines throb and pads breathe. Push resonance harder and it starts to snarl, capable of acid squelch when fed with a sharp transient or a well-timed envelope. But what really sets it apart are the simultaneous outputs: low-pass, high-pass, band-pass, and notch. Route all four to separate VCAs, modulate them independently, and you’ve got a spectral playground in 2HP of space. It’s the kind of module that makes you rethink what “multimode” really means—not just selectable outputs, but parallel universes of the same signal, all accessible at once.

Despite its compactness, the Filter doesn’t feel like a compromise. The controls are spaced just right, the knobs are sturdy, and the panel—available in both black and silver—has that minimalist 2HP aesthetic that’s more “lab instrument” than “guitar pedal.” It runs on standard Eurorack power, draws modest current, and at 45mm depth, it plays nice with skiff builds. But don’t mistake its size for simplicity. This is a deceptively deep module, one that rewards patching creativity. Want a metallic bell tone? Feed noise into the band-pass output and ping it with a short gate. Need a rhythmic filter sweep across a drone? Modulate cutoff with an LFO and route the high-pass output to a reverb. The notch output, often overlooked, can create hollow, phasey textures that sit perfectly in a mix without muddying the low end. It’s a utility in form, but a lead voice in spirit when pushed.

Specifications

Manufacturer	2HP
Production Years	2013–2018
Original Price	$99 USD
Module Type	Analog multimode voltage-controlled filter
Filter Slope	12 dB/octave
Filter Types	Low-pass, high-pass, band-pass, notch (simultaneous outputs)
Topology	OTA-based
Self-Oscillation	Yes, with 1V/oct tracking across four octaves
CV Input	Cutoff frequency CV, resonance CV
Audio Input	1 x normalized input
Audio Outputs	4 x simultaneous: LP, HP, BP, Notch
Power Requirements	+12V, -12V
Current Draw	+12V: 30 mA, -12V: 30 mA
Width	2 HP
Depth	45 mm
Panel Options	Black, Silver

Key Features

Parallel Filter Outputs Unlock Sonic Multiplicity

Most multimode filters force you to choose one flavor at a time—low-pass or band-pass, high-pass or notch. The 2HP Filter laughs at that limitation. All four filter types are available simultaneously, meaning you can split a single oscillator into four distinct timbral paths without daisy-chaining or switching. This isn’t just convenient; it’s transformative. Imagine sending the low-pass output to a distortion, the band-pass to a delay, the high-pass to a granular processor, and the notch to a spring reverb—all from one source, all in real time. The module becomes a spectral hub, a passive yet powerful node in a larger signal flow. It’s especially potent in generative patches, where independent modulation of each output creates evolving textures that feel alive. Even in simpler setups, having the high-pass output on tap means you can extract crisp, clicky transients from a plucked waveform without losing the body in the main low-pass signal.

Resonance as Instrument, Not Just Effect

The resonance control on the 2HP Filter doesn’t just emphasize frequencies—it becomes a sound source. Push it past the threshold and the filter begins to oscillate, producing a clean, stable sine wave that tracks accurately across four octaves with 1V/oct input. That’s rare in such a compact module. Most self-oscillating filters in the 2HP form factor either drift out of tune or require constant tweaking. This one stays locked, making it a legitimate substitute for a dedicated VCO in a pinch. But even when not fully self-oscillating, the resonance has character. It’s not harsh or brittle; it’s musical, with a rounded peak that enhances without piercing. CV control over resonance opens up dynamic timbral shifts—think of a snare hit that starts bright and collapses into a subby thud, or a pad that swells from silence into a resonant peak before fading. The resonance CV input accepts both unipolar and bipolar signals, so you can modulate it with envelopes, LFOs, or even audio-rate sources for FM-like effects.

OTA Topology with a 12dB Personality

The choice of a 12dB/octave OTA (Operational Transconductance Amplifier) design over the more common 24dB transistor-ladder approach defines the Filter’s sonic signature. It’s less aggressive, less “vintage synth,” and more “modern sculptor.” Where a 24dB filter might carve out deep notches or create dramatic sweeps, the 12dB slope is smoother, more gradual—better suited to subtle shaping than radical transformation. But that’s not a weakness. In dense patches, a gentler filter can sit in the mix without pulling focus. It’s also more forgiving with feedback loops and complex modulation, less likely to go unstable or distort unexpectedly. The OTA core gives it a slightly organic edge, a softness in the highs and a warmth in the mids that digital filters often struggle to replicate. It’s not trying to emulate anything—it’s its own thing, a compact analog voice with a quiet confidence.

Historical Context

When 2HP launched the Filter in 2013, Eurorack was still in its adolescence. Cases were getting bigger, modules were getting wider, and the “more is more” mentality dominated. In that climate, 2HP was a provocateur. Founded by engineer Tony Rolando—known for his work on the Buchla 200e and later the Make Noise 0-Coast—the brand was built on the idea that minimalism could be maximal in expression. The Filter was a statement piece: proof that a two-pitch module could do the work of four. At a time when multimode filters were typically 8HP or wider, this was radical. Competitors like Doepfer and Intellijel offered more features—morphing filters, drive circuits, multimode envelopes—but they came at a spatial cost. The 2HP Filter didn’t try to beat them at their own game. Instead, it redefined the rules, appealing to skiff builders, travel synth enthusiasts, and minimalists who valued elegance over excess.

The Filter also arrived as the DIY Eurorack scene was exploding. Builders were hungry for compact, reliable, well-designed modules they could integrate into custom cases. 2HP delivered that with precision-machined panels, clean layouts, and straightforward functionality. It wasn’t the first 2HP module—Rolando had already released the Dual Attenuator and Dual Switch—but it was the first to show that such a narrow form factor could host a full-featured analog circuit. Its success paved the way for later designs like the MMF (a refined version), the VCA, and the Dual Oscillator. While the original Filter was eventually rebranded as the MMF to distinguish it from the later Comb and LPF models, its legacy as a pioneer of dense analog design remains.

Collectibility & Value

The original 2HP Filter is no longer in production, having been succeeded by the MMF, but it remains a sought-after piece for collectors and minimalists alike. On the used market, prices typically range from $120 to $180, depending on condition, color, and whether it includes the original packaging. Silver panels tend to fetch slightly more than black, though both are common. Because the module is all-analog and built with high-quality components, failure rates are low—but not zero. The most common issues reported are intermittent connections at the power header or jack sockets, usually due to mechanical stress from frequent patching. These are repairable with basic soldering skills, but buyers should test all outputs and CV inputs before purchasing. The module has no user-serviceable parts inside, so opening the case voids any remaining warranty and risks damaging the PCB.

One thing to watch for: counterfeit or clone modules. Due to the popularity of 2HP’s designs, third-party manufacturers have released unlicensed versions that mimic the layout and functionality but use inferior components. These often lack the precise 1V/oct tracking and exhibit instability at high resonance. Authentic units have “2HP” laser-etched on the panel and a clean, tight fit between the PCB and front panel. The original manual is available online, and service technicians recommend checking for consistent tracking across octaves when testing self-oscillation. For those building a period-correct 2010s Eurorack system, the Filter is a genuine artifact of a pivotal moment in modular history—when size stopped being a limitation and started being a design philosophy.