ALM Busy Circuits O/A/x2 (2016–Present)

A 4HP module that reshapes control voltages, with LEDs that show what the signals are doing.

Overview

The O/A/x2 doesn't generate sound, and it won't win any beauty contests. It solves real problems in a patch, though. Offset an LFO to swing a filter from -2V to +5V, invert another envelope's polarity, and it just works. ALM designed it as a dual-channel attenuverter with integrated bipolar offset and visual feedback. It's the kind of module you buy for one job and end up using for ten.

Each channel handles signal inversion, attenuation, and DC offset with independent controls. That makes it good for reshaping control voltages, like turning a symmetrical LFO into an envelope follower-style unipolar sweep, or flipping a sequencer's output to drive a VCA in reverse. It's just as useful in the audio path: subtle amplitude modulation, inverted waveforms for phase tricks, or offsetting audio-rate signals. The offset range spans ±8V, which gives plenty of headroom for extreme CV manipulation. The attenuverter knob sweeps from full negative gain (×-1) to full positive gain (×+1), with unity at center. It's an active shaping tool, not a passive attenuator.

Then there are the LEDs. They show both polarity and relative amplitude of the output signal. Red means positive voltage, green means negative, and brightness follows signal strength. That makes them diagnostic, not cosmetic. One glance tells you if your modulation is clipping, if an inverted signal is actually negative, or if your offset has pushed a CV out of range.

Specifications

Manufacturer	ALM Busy Circuits
Model	O/A/x2
Production Years	2016–Present
Original Price	£80 GBP / $100 USD
Width	4 HP
Depth	32 mm
Power Supply	±12V
Current Draw	+12V: 50 mA, –12V: 50 mA
Function	Dual Attenuverter with Bipolar Offset
Offset Range	±8V
Attenuation Range	×-1 to ×+1 per channel
Signal Monitoring	LEDs for polarity and level (red = positive, green = negative)
Mixing Function	Jumper-selectable mix mode (upper output mixed with lower)
Reverse Polarity Protection	Yes
Skiff-Friendly	Yes
Country of Origin	United Kingdom

Key Features

Two Channels of Surgical CV Control

Each side of the O/A/x2 is a complete signal conditioner: input, attenuverter knob, offset knob, output, and LED. The attenuverter actively inverts and scales the incoming signal across its full range. Turn it counterclockwise and you get inverted output, peaking at ×-1. Clockwise gives non-inverted gain up to ×+1. To flip a rising envelope into a falling one, turn the knob. To scale a 10V LFO down to ±2V for a subtle filter wobble, same thing. The offset control then injects a DC voltage from -8V to +8V, shifting any signal up or down in the CV realm. That is handy for setting modulation depth or lining up sequences with specific voltage ranges.

LEDs That Actually Tell You Something

Most modules give you no feedback. The O/A/x2 does. The dual-color LEDs (red/green) respond to the output signal's voltage: red for positive, green for negative, with brightness increasing with amplitude. This helps when patching complex modulation chains. Is your inverted LFO actually negative? Check the LED. Did your offset push the signal into clipping? The LED will be blazing. It also helps with slow, sub-audio signals that don't produce audible cues.

Jumper-Selectable Mix Mode

Under the panel is a tiny jumper that changes the module's behavior. When engaged, the upper output becomes a mix of both channels. That turns the O/A/x2 into a compact dual attenuverter with a summed output, useful for blending two CV sources with individual level and polarity control before sending them to a single destination. It's not a full mixer, but it works for light summing with CV shaping. Because it's a hardware jumper and not a front-panel switch, the panel stays clean and nobody changes modes by accident during a live set.

Historical Context

The O/A/x2 came out in 2016, when Eurorack was growing fast but still short on utility modules that combined flexibility with clarity. Many manufacturers focused on sound-generating modules like VCOs, filters and effects. ALM Busy Circuits, founded by Andrew Macpherson, went after the "plumbing" side of modular synthesis. The concept wasn't new, since attenuverters and offset generators had existed for decades. What the O/A/x2 did was put both functions in each channel, add visual feedback, and fit it all in 4HP.

It arrived alongside utility-focused designs from makers like Intellijel, Doepfer, and Mutable Instruments. It's built in the UK with reverse polarity protection, skiff-friendly depth, and a clean, functional layout. It wasn't built to be cute or minimal. It was built to be useful, repeatedly, under real conditions.

Collectibility & Value

The O/A/x2 isn't a "collector's item" in the traditional sense. It's not rare and not discontinued. Its value lies in ubiquity and reliability. New units typically sell for around $100 USD or £80 GBP, with little fluctuation. Used prices hover between $70 - $90, depending on condition and market availability. It's a passive utility module with no moving parts beyond the potentiometers, so failure rates are low. The most common issue reported by technicians is pot wear from heavy use, which can cause scratchy output or intermittent signal. Contact cleaner or pot replacement fixes it.

There are no known design flaws or batch issues. The reverse polarity protection means it's safe even in miswired racks, and the 32mm depth makes it compatible with nearly all cases, including skiffs. When buying used, check that both LEDs respond correctly to signal input and that the knobs turn smoothly without crackling. Units with clean PCBs and original hardware are common. The module is simple enough that most repairs succeed and don't require board swaps.

The O/A/x2 has become something of a staple. It's frequently bundled in "starter utility" recommendations and appears in modular setups from hobbyists to professionals. It's still in production and actively supported, with firmware and documentation available from ALM's site.