ADDAC 201 (2023)

A tiny Eurorack workhorse that flips your control voltages like a pancake—and tells you which way is up.

Overview

You know that moment when your sequencer’s output is positive but your filter needs a negative CV to open up? Or when your LFO’s slow rise is perfect, but it’s going the wrong direction? That’s where the ADDAC 201 steps in—quietly, efficiently, and without drama. It’s not a sound generator, not a processor, not something that’ll make your patch explode with character. Instead, it’s the kind of module you don’t realize you need until you’re knee-deep in cables, cursing at a gate that won’t trigger, and suddenly—lightbulb—the polarity’s backwards. The 201 is the fix. It’s a dual-channel voltage inverter, plain and simple, but it’s also got an offset knob per channel and LEDs that tell you, at a glance, whether your output is positive or negative. That might sound trivial, but in the abstract, patch-driven world of modular, knowing your voltage’s direction is half the battle.

It’s not flashy. It doesn’t make noise. It doesn’t even have a knob labeled “magic.” But in a system full of chaos, the 201 is a grounding force. You can use it to invert modulation sources—turn a rising envelope into a falling one, flip a random voltage to explore the negative side of a parameter, or reverse the sweep of a filter cutoff. The offset control lets you shift the inverted signal into a usable range, which is critical when you’re dealing with asymmetric CV sources or trying to center a bipolar LFO around zero. And those dual LEDs per channel? They’re not just for show. They’re a diagnostic tool, a sanity check, a little flashlight in the dark when your sequencer’s output isn’t doing what the manual says it should.

Positioned in ADDAC’s 200 series—dedicated to analog CV utilities—the 201 sits alongside modules like attenuverters, summing circuits, and signal mappers. It’s not the most complex thing in the lineup, but it’s one of the most quietly essential. While other modules in the series offer scaling or quantization, the 201 does one job and does it cleanly. It’s not trying to be a Swiss Army knife; it’s a precision screwdriver. And at 4 HP wide, it doesn’t take up much real estate, which means you can tuck it into a corner of your case and forget about it—until the moment you absolutely need it.

Specifications

Key Features

Dual-Channel Voltage Inversion

The core function of the ADDAC 201 is straightforward: it inverts incoming control voltages. Feed it a +5V signal, and it outputs -5V. Feed it a -3V LFO, and it becomes +3V. This is invaluable when you’re working with modules that expect a specific voltage polarity but your source is going the opposite way. Unlike passive inverters or those buried in multi-function modules, the 201 gives you a dedicated, clean inversion path with no signal degradation. Each channel operates independently, so you can flip two different CV sources at once—say, an envelope and a sequencer step—without crosstalk or loading issues. The circuit is designed for precision, maintaining signal integrity across the full ±10V range, which means no unexpected clipping or offset drift when pushing the limits.

Offset Knob for Voltage Shifting

What elevates the 201 beyond a simple inverter is the offset control on each channel. After inversion, you might not want your signal centered at zero. Maybe you need a -2V to +8V envelope to become a +2V to -8V sweep, but then shifted up by 3V to stay within a module’s control range. The offset knob lets you do that on the fly. It’s a small addition, but it turns the 201 into a flexible CV transformer rather than just a polarity flipper. This is especially useful when dealing with asymmetric modulation sources or when you’re trying to match the voltage requirements of vintage-style modules that expect specific control ranges. The knob is smooth and precise, with enough resolution to make fine adjustments without overshooting.

Polarity LEDs for Instant Feedback

In a world where a single cable can make or break a patch, visual feedback is everything. The 201 includes two LEDs per channel—one for positive voltage, one for negative—so you can instantly see the polarity of your output. This isn’t just a convenience; it’s a troubleshooting lifeline. If your filter isn’t opening as expected, a glance at the 201’s LEDs can tell you whether the CV is actually negative when it should be positive. No need to patch in a multimeter or guess based on sound. The LEDs respond quickly and accurately, lighting up in real time as your CV changes, which is especially helpful when working with slow-moving LFOs or random voltage sources. It’s a small touch, but it speaks to ADDAC’s attention to the practical realities of modular patching.

Historical Context

The ADDAC 201 didn’t emerge from a vacuum. It’s part of a broader trend in Eurorack toward specialized utility modules—small, focused tools that solve specific problems in a patch. While early modular systems often bundled inversion and offset into larger modules, modern Eurorack encourages modularity within modularity: dedicated modules for inversion, attenuation, mixing, and logic. The 201 fits squarely into that philosophy. It’s not a revival of an old circuit or a homage to a vintage piece of gear. Instead, it’s a contemporary solution to a persistent patching challenge. ADDAC, based in Lisbon, has built a reputation for thoughtful, musician-first design, and the 201 reflects that. It’s not flashy, but it’s reliable, well-built, and priced accessibly—especially in kit form, which appeals to DIY enthusiasts. In an ecosystem where some utility modules cost more than entire starter cases, the 201 stands out for its no-nonsense approach.

Collectibility & Value

The ADDAC 201 isn’t a collectible in the traditional sense. It’s not rare, it doesn’t have a cult following, and it’s not likely to appreciate in value. But that doesn’t mean it’s not valuable—quite the opposite. At its original price of €110 (or €85 as a kit), it’s one of the more affordable modules in the ADDAC lineup, and it delivers consistent, reliable performance. Used units typically sell for 60–80% of the original price, depending on condition and whether they’re assembled or kit form. Since it’s a passive utility module with no moving parts or complex circuitry, failure rates are extremely low. The most common issue reported is LED burnout, but even that is rare and easily repairable. When buying used, check that both channels respond correctly to input signals and that the LEDs light up as expected. There are no known design flaws or batch issues, and ADDAC’s build quality is solid across the board. For collectors, the 201 is less about investment and more about utility—a module you buy because it makes your system more flexible, not because it might be worth more later.

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