ADDAC 308 (2019–)

Turn sunlight, shadows, or a flickering candle into control voltage.

Overview

The ADDAC 308 doesn't generate notes or sequences. It turns ambient light into control voltage. Point a flashlight at its sensor, hang it near a window at dusk, or let stage lights wash over it during a performance, and your oscillators follow the light. The sensor is an external LDR (light-dependent resistor) in a 3.5mm jack housing. No proprietary connectors, no fragile wires. Plug it in, put it wherever light hits, and the light becomes voltage for shaping filters, modulating pitch, or stuttering gates.

ADDAC gave the 308 real control over how light becomes voltage. Sensitivity sets how reactive the sensor is. Turn it up for dim rooms, back it off under harsh stage lights. Gain sets the amplitude of the CV, so you can get subtle undulations or wide voltage swings. The response switch has three fixed slew rates - fast, medium, slow - that set how quickly the output reacts to changes in light. On slow, a passing shadow becomes a languid glide. On fast, a strobe light becomes a rapid-fire gate source. Each of the two outputs, normal and inverted, has its own offset control. That lets you bias the CV range to suit the module you're controlling, whether it's a VCO needing 0-5V or a filter that responds best to -2.5V to +2.5V.

What really sets the 308 apart is its duality. The main output increases voltage as light increases. The second output does the opposite—more light, lower voltage. This isn’t just a convenience; it opens up stereo modulation, push-pull filter sweeps, or complementary envelope shapes from a single light source. You could, for example, route the normal output to open a filter while the inverted output simultaneously lowers the pitch of a second oscillator—creating a call-and-response effect driven entirely by ambient light. It’s the kind of expressive, almost performative control that feels more like conducting than patching. And because the module is only 4HP wide, it slips into even the most crowded systems without a fight. It draws a modest ±50mA, and at 4.5cm deep, it won’t bump up against back-mounted cables or power supplies. This is Eurorack minimalism with maximal impact.

Specifications

Manufacturer	ADDAC System
Production Years	2019–
Original Price	140€
Format	Eurorack
Width	4HP
Depth	4.5cm
Current Draw +12V	+50mA
Current Draw -12V	-50mA
Function	Light to CV Modulation Source
Sensor Type	External LDR (Light-Dependent Resistor)
Sensor Connection	3.5mm Jack
Outputs	2x Bipolar CV (Normal and Inverted)
Controls	Sensitivity, Gain, Response (Fast/Medium/Slow), Offset (x2), Inverted Offset
Response Time Options	3 fixed settings via toggle switch
Offset Adjustment	Per output channel
DIY Availability	Yes, kit available for 77€ (excl. VAT)
Custom Panel Options	Red, Green, Blue, White, Silver Gray, Yellowed Silver, Dark/Light Bronze
Weight	Not specified

Key Features

External Light Sensor with Jack Interface

The ADDAC 308’s sensor isn’t hardwired—it’s a separate LDR housed in a standard 3.5mm plug, letting you place it anywhere. This isn’t just about convenience; it’s about performance. You can tape it to a window, mount it on a mic stand, or even embed it in a custom light-reactive installation. The jack connection means you can use any 3.5mm cable to extend its reach, and replacements are cheap and easy to source. Each sensor costs just 5€ from ADDAC, so losing one in a dark studio corner isn’t a tragedy. This modularity turns the 308 into more than a module—it’s a system for environmental interaction.

Dual Bipolar CV Outputs with Independent Offset

Having both normal and inverted outputs is useful, but giving each its own offset control is what makes the 308 genuinely flexible. You’re not stuck with a fixed voltage range—instead, you can shift the CV output to match the requirements of your destination module. Want to modulate a VCA that only opens above 2V? Offset the normal output to start there. Need the inverted output to swing between -3V and +3V for a waveshaper? Adjust the inverted offset accordingly. This level of fine-tuning means you’re not just reacting to light—you’re sculpting how that reaction behaves, turning raw environmental input into musically useful modulation.

Adjustable Response Time for Expressive Dynamics

The response switch is what turns the 308 from a simple light meter into a performance tool. The three fixed slew rates - fast, medium, slow - set how dramatically the module reacts to light changes. Fast can track rapid flickers, like a strobe or hand-waving gestures, and turn them into staccato gates or tremolo effects. Medium smooths things out for gentle swells, such as sunrise simulations or slow ambient shifts. Slow turns even abrupt changes into long voltage ramps, good for evolving drones or cinematic tension builds. Unlike a continuous slew control, these fixed settings can't be tweaked endlessly. You pick one.

Historical Context

The ADDAC 308 arrived in 2019 as part of the ADDAC300 series, dubbed "Expressive Controls" - a shift from traditional modular functions toward performance-driven, physical interaction. Eurorack at the time was flooded with complex digital sequencers and algorithmic generators, and ADDAC went for the tactile and unpredictable. The 308 sits alongside modules like the 307 Heart Sensing and 303 Muscle Sensing, all exploring bio-responsive and environmental control. It drew inspiration from early experimental music, such as David Tudor's homemade circuits and Alvin Lucier's use of physical space, but repackaged it for the modern rack. It also arrived as artists like Scanner (Robin Rimbaud) began incorporating light-based control into live sets. It wasn't the first light-to-CV module ever made. But its combination of simplicity, flexibility, and build quality made it a standout in a niche that had long been dominated by DIY kits or unreliable surplus parts.

Collectibility & Value

The ADDAC 308 isn't a rare module. Since its release, it has stayed available through ADDAC's direct sales and a global network of distributors. New units typically sell for around €140, with DIY kits at €77, which makes it one of the more affordable expressive control modules. On the secondhand market, prices hover between $100 and $140 depending on condition and whether the LDR sensor is included. Units missing the sensor often sell for less, so buyers should check that it's there. The module has no moving parts and minimal circuit complexity, so failure rates are extremely low. The most common issue is a damaged 3.5mm jack on the sensor plug from repeated plugging and unplugging. Replacements are inexpensive and easy to solder. The external LDR itself can degrade over time if exposed to extreme UV or moisture, but replacements are cheap too. There's no need for recalibration or firmware updates. Custom-colored panels (offered in red, blue, green, bronze, etc.) occasionally surface on the used market and may command a slight premium, especially in limited combinations.