2HP ADSR (2010–2023)

Name: 2HP ADSR
Brand: 2HP

The tiniest envelope generator in Eurorack that somehow still feels generous to play.

Overview

You reach for the 2HP ADSR not because you want bells and whistles, but because you want to get on with it—patch, play, move. It’s the module that fits in the gap between two oscillators like it was always meant to be there, a sliver of control logic that refuses to hog space or demand attention. Yet despite its 2HP width—the absolute floor for usability in Eurorack—it doesn’t feel compromised. Attack, Decay, Sustain, Release: all four stages are fully manual, each with its own knob, and the response is linear, which gives it a certain clinical snap that cuts through lush pads or tightens up percussive hits. It won’t breathe like an analog envelope from the ’70s, but it will punch. The output swings a full ±10V, which means it can drive almost any filter or VCA in your rack without begging for help from an attenuverter.

And then there’s the range switch—up or down, normal or fast—tucked in like a secret. Flip it down, and the envelope tightens into snappy, plucky territory perfect for hats, clicks, and FM percussion. Flip it up, and you’re in lush, slow-swell territory, capable of evolving ambient swells that linger just long enough. It’s not CV over the stages—that’s a different module—but the range toggle does more heavy lifting than you’d expect. The trigger input is forgiving, responding to both short gates and longer triggers without hiccup, and the loop function, while not a dedicated LFO, can be coaxed into rhythmic cycling with a steady clock. It’s not flashy, but it’s smart.

This is the envelope generator you buy when you’re tired of dedicating 8HP or more to dual envelopes, or when you’re building a travel case and every millimeter counts. It’s also the one you keep when you realize you don’t actually need modulation matrices or curve shaping for 90% of what you do. It’s the synth equivalent of a well-balanced kitchen knife: not the slicer, not the cleaver, but the one you reach for every time.

Specifications

Manufacturer	2HP
Production Years	2010–2023
Width	2HP
Depth	42mm
Power Consumption +12V	24 mA
Power Consumption -12V	7 mA
Power Consumption +5V	0 mA
Polyphony	Monophonic
Oscillators	None
Envelope Type	ADSR
Envelope Shape	Linear
Output Voltage Range	±10V
Inputs	Gate/Trigger, Loop
Outputs	Envelope CV
MIDI	No
Keyboard Size	N/A
Effects	None
Weight	Approx. 40g
Color	Black anodized aluminum panel
Mounting	Eurorack 3U, 84HP standard case compatible

Key Features

A 2HP Miracle of Layout

Fitting four functional knobs, a toggle switch, and two jacks into 2HP should be impossible, but 2HP pulled it off with the kind of industrial design that makes other manufacturers wince. The knobs are low-profile but not fiddly, spaced just far enough apart to avoid accidental nudges, and the toggle switch for range selection is recessed just enough to prevent misfires during transport. The panel is black anodized aluminum—lightweight, durable, and heat-dissipating—so it doesn’t feel like a toy. Even the jack positions are optimized: inputs on the left, output on the right, so patch cables flow naturally across the module without kinking. There’s no wasted space, no unused features bloating the footprint. This is minimalism with intent.

Linear Response with Character

The envelope is strictly linear—no logarithmic or exponential curves here—which gives it a modern, precise feel. Attack isn’t soft; it’s immediate. Decay doesn’t trail off like smoke; it steps down like a metronome. That makes it less “vintage synth” and more “digital-era utility,” but in a good way. It excels at modulating digital oscillators, FM engines, or wavefolders where predictability matters. It’s also excellent for rhythmic modulation of filters or panning, where the straight-line response ensures timing accuracy. Some users report that the sustain level isn’t perfectly stable at extreme settings—there’s a slight voltage droop when held for long periods—but it’s rarely audible in practice unless you’re doing extreme slow-evolving drones.

Range Switch: Two Personalities in One

The single toggle switch on the front panel is the secret sauce. In the down position (“fast”), the timing ranges are compressed, making it ideal for percussive sounds: snappy plucks, tight bass, FM clicks. In the up position (“normal”), the envelope stretches out, allowing for long attack swells or drawn-out releases that can last several seconds. It’s not infinitely variable—there’s no CV control over time scaling—but the two ranges cover a surprising amount of ground. Users often patch a logic module or switch to flip the range dynamically, turning a single envelope into two distinct voices depending on context. It’s a simple feature, but it multiplies the module’s usefulness.

Historical Context

The 2HP ADSR arrived in 2010, right as Eurorack was shifting from boutique curiosity to full-blown modular renaissance. At the time, envelope generators were typically 4HP or wider, often with CV control, multiple outputs, or looping functions. 2HP, founded by engineer Tony Rolando, took the opposite approach: strip everything back to the essentials and make it tiny. The ADSR was one of the first modules to prove that ultra-compact didn’t mean underpowered. It was based on René Schmitz’s “Fastest Envelope in the West” open-source design, which emphasized speed and simplicity. By shrinking it to 2HP and refining the layout, 2HP created a module that became a staple in minimalist, travel, and 1U racks.

It wasn’t the first 2HP module—that honor goes to the company’s own Logic and VCA—but it was the first to show that even complex functions could be miniaturized without sacrificing usability. Competitors like Intellijel and MakeNoise were building feature-rich envelopes with multiple modes and CV options, but 2HP offered a counterpoint: sometimes you just need an envelope, and you need it now, and you don’t want to spend 8HP on it. The ADSR became a quiet standard, showing up in racks from Berlin to Brooklyn, often paired with other 2HP modules like the Noise or Mixer to form ultra-dense utility cores.

Collectibility & Value

The 2HP ADSR is no longer in production as of 2023, making it a sought-after module for minimalists and 1U builders. Used prices reflect that: expect to pay $120–$160 in good condition, with mint units sometimes reaching $180 if sold with original packaging. It’s not a “grail” module, but it’s close to irreplaceable for certain builds. There are DIY kits available—Pusherman and others sell PCBs and panels—but the original factory build has tighter tolerances and better long-term reliability.

Failures are rare but not unheard of. The most common issue is potentiometer wear, especially on the sustain knob, which gets the most use. Service technicians observe that the trimmers underneath the panel can loosen over time, leading to intermittent control response. A full recalibration isn’t common, but a simple pot cleaning or resoldering usually fixes most issues. The toggle switch is robust, but some early units had a tendency to short if debris got into the socket—keeping the panel clean helps prevent this.

When buying used, check that all four stages respond smoothly across their range and that the output hits a clean ±10V. A multimeter test is ideal. Also verify that the range switch clicks cleanly between positions and doesn’t cut out. Units with scratched panels or wobbly knobs are common but don’t affect function—this is a workhorse, not a showpiece. For those restoring a 2HP-based system, it’s worth noting that the company used consistent power draw and pinout standards, so replacement or substitution is straightforward.