ADDAC 201 (2023)

Name: ADDAC System 201
Brand: ADDAC System

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

Overview

Say the sequencer's output is positive but the filter needs a negative CV to open up. Or the LFO's slow rise is right, but it's going the wrong direction. That is where the ADDAC 201 comes in. It's not a sound generator and it's not a processor. It's a dual-channel voltage inverter, plain and simple. It also has an offset knob per channel and LEDs that show at a glance whether the output is positive or negative. That sounds trivial, but when you're knee-deep in cables and a gate won't trigger, a backwards polarity is a common culprit.

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.

The 201 sits in ADDAC's 200 series, which is dedicated to analog CV utilities. Its neighbors include attenuverters, summing circuits, and signal mappers. It's not the most complex module in the lineup. Other modules in the series offer scaling or quantization, while the 201 does one job and does it cleanly. It's 4 HP wide, so it fits into a corner of a case without much fuss.

Specifications

Manufacturer	ADDAC System
Production Years	2023–present
Original Price	€110 (module), €85 (kit)
Format	Eurorack
Width	4 HP
Depth	2.5 cm
Power Supply	±12V or ±15V
Max Current Draw	30mA
Bus Board Connector	8×2 IDC (Doepfer style)
CV Input Range	±10V
CV Output Range	±10V
Channels	2
Controls	Offset knob per channel
Indicators	2 LEDs per channel (positive/negative polarity)
Inputs	1 per channel
Outputs	1 per channel

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. That helps when a module expects one polarity and the source goes the other way. Unlike passive inverters or those buried in multi-function modules, the 201 gives you a dedicated 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 to keep signal integrity across the full ±10V range, so there's no unexpected clipping or offset drift at the limits.

Offset Knob for Voltage Shifting

The offset control on each channel is what sets the 201 apart from a simple inverter. After inversion, you might not want the signal centered at zero. Say a -2V to +8V envelope becomes a +2V to -8V sweep, but then needs to be shifted up by 3V to stay within a module's control range. The offset knob does that on the fly. It makes the 201 a flexible CV transformer rather than only a polarity flipper. It's especially useful with asymmetric modulation sources, or when matching the voltage requirements of vintage-style modules that expect specific control ranges. The knob is smooth and precise, with enough resolution for fine adjustments without overshooting.

Polarity LEDs for Instant Feedback

The 201 has two LEDs per channel, one for positive voltage and one for negative, so you can see the polarity of the output right away. That makes them a troubleshooting aid. If a filter isn't opening as expected, a glance at the LEDs shows whether the CV is negative when it should be positive. No multimeter, no guessing from the sound. The LEDs respond quickly and light up in real time as the CV changes, which helps with slow-moving LFOs or random voltage sources.

Historical Context

The ADDAC 201 is part of a broader trend in Eurorack toward specialized utility modules, small tools that solve specific problems in a patch. Early modular systems often bundled inversion and offset into larger modules. Modern Eurorack favors dedicated modules for inversion, attenuation, mixing, and logic. The 201 fits that approach. It's not a revival of an old circuit or a copy of a vintage piece of gear. It's a contemporary answer to a persistent patching problem. ADDAC is based in Lisbon and has a reputation for musician-first design. The 201 is reliable, well-built, and priced accessibly, especially in kit form, which appeals to DIY builders. Some utility modules in this ecosystem cost more than entire starter cases.

Collectibility & Value

The ADDAC 201 isn't a collectible in the traditional sense. It's not rare, it has no cult following, and it's not likely to appreciate in value. Its original price was €110 (or €85 as a kit), which makes it one of the more affordable modules in the ADDAC lineup. Used units typically sell for 60-80% of the original price, depending on condition and whether they're assembled or kit form. It's a passive utility module with no moving parts or complex circuitry, so failure rates are extremely low. The most common issue reported is LED burnout, which 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.