ADDAC 308 Light to CV (2018–Present)

Turn sunlight, shadows, or a flickering candle into living control voltage - with quirks that make it feel like a secret instrument.

Overview

The ADDAC 308 Light to CV doesn't make sound. It listens to light. It turns shifts in illumination into evolving voltages that can liven up a static patch. A dimming room can slowly lower the cutoff of a filter. A hand waving over a sensor can modulate pitch in real time. A strobe light can trigger rhythmic gate-like pulses without a single clock in sight.

The 308 is part of ADDAC's 300 Series, dubbed "Expressive Controls". It's a niche, tactile modulation source for Eurorack. At its core it's a light-dependent resistor (LDR) interface. An external sensor picks up changes in light intensity, and the module converts that analog resistance shift into two bipolar control voltages, one normal and one inverted. One output rises with brightness while the other falls, so you can get opposing movements in filters, panners, or LFO rates without additional inversion. The module ships without the sensor by default - it's sold separately for around €5 - but the jack-mounted design means you can plug it into any standard 1/4" cable and dangle it from a stand, tape it to a wall, or hide it under a lampshade.

It's not the first light-to-CV module ever made, but it's among the most thoughtfully implemented in the modern Eurorack era. Unlike crude DIY builds that crackle or drift, the 308 has dedicated gain, sensitivity, and offset controls for both outputs, so you can tune the response for anything between moonlight and stage LEDs. The response time switch offers fast, medium, and slow slew. It smooths abrupt light changes into gliding swells. In slow mode, waving your hand over the sensor feels like playing a theremin with shadows. In fast mode, it can track strobes or video flicker with surprising precision.

This isn't a precision timing tool. It's slow, organic, and unstable. The LDR's response isn't linear, and it ages over time, gradually losing sensitivity. Temperature affects it. Dust on the sensor window throws it off. Owners report that a well-aged sensor develops a kind of "personality", responding more dramatically to subtle shifts. If you want a reliable, repeatable CV source for clock division or quantized modulation, look elsewhere. The 308 suits experimental patches, generative setups, and live performance where unpredictability is the point.

It's also simple. No menus, no firmware, no MIDI. Just knobs, a switch, and two outputs. At 4HP it's compact, and the black front panel (with optional custom colors like bronze or silver gray) blends into any system. It draws a modest ±50mA, and its 4.5cm depth clears all but the tightest cases. For tinkerers, ADDAC offers a full DIY kit for €77 (excl. VAT), with a detailed assembly guide.

Specifications

Manufacturer	ADDAC System
Production Years	2018–Present
Original Price	140€ (assembled), 77€ (DIY kit)
Format	Eurorack
HP Size	4
Power Consumption	±50mA
Depth	4.5 cm
Inputs	1 x Light Sensor (LDR) via 1/4" jack
Outputs	1 x CV Output, 1 x Inverted CV Output
Controls	Sensitivity, Gain, Response (Fast/Medium/Slow), Offset (CV), Inverted Offset
Response Time Settings	3 fixed slew rates (fast, medium, slow)
Output Type	Bipolar CV
Sensor Availability	Sold separately (5€ each)
DIY Option	Yes, full kit available
Custom Panel Option	Yes (Red, Green, Blue, White, Silver Gray, Yellowed Silver, Dark/Light Bronze)
Manual	Available online (PDF)
Assembly Guide	Available online (PDF for DIY kit)
Series	ADDAC300 Series – Expressive Controls

Key Features

A Sensor You Can Place Anywhere

The 308's sensor plugs in via a standard 1/4" cable instead of sitting on the front panel. That lets you put it anywhere - on a music stand, taped to a window, or inside a custom enclosure. One performer reportedly mounted the sensor inside a translucent sculpture, so audience movement around it modulated a drone in real time. Another used it to track sunrise in a 24-hour generative patch. The sensor itself is basic, a CdS cell in a small plastic housing. It's fragile (don't crush it under a cable), and the window can cloud over time, but replacements are cheap and plentiful.

Response Slew as an Expressive Tool

The three-way response switch works as a performance control. In fast mode, the module tracks light changes almost instantly, which suits rhythmic modulation from flickering sources. Medium smooths it into a gentle glide, useful for slow filter sweeps. Slow adds a lazy, breath-like lag that turns hand gestures into swelling textures. Unlike a standard slew limiter, this is baked into the signal path with fixed time constants, so it's consistent and predictable. There's no fine-tuning, but the three options cover most expressive needs. Some users report slight crosstalk between response settings when pushed to extremes, but it's rare and usually inaudible in a mix.

Dual Offset for Precision Patching

The normal and inverted outputs each have an independent offset control. You can bias each CV stream into a specific voltage range - say, 0-5V for a VCO while the inverted output runs -2 to +3V for a waveshaper. That matters when modules respond differently to positive and negative voltages. The gain knob affects both outputs equally. That keeps things simple, but you can't scale them independently. Gain, sensitivity, and offset together give enough range for most lighting conditions, including dim studio corners and sunlit windowsills.

Historical Context

Light-controlled synthesis has roots in the 1930s, with instruments like the Optophonic Piano and later the Theremin's light-controlled variants. In the modular revival of the 2010s, light sensors reappeared as boutique curiosities, often DIY kits or limited-run modules from small builders. ADDAC's entry in 2018 was notable not for inventing the concept, but for refining it into a reliable, production-ready Eurorack module with professional build quality and thoughtful ergonomics. Many utility modules at the time were becoming software-defined or multi-function. The 308 did one thing, converting light to CV, and did it well.

It arrived alongside a wave of "expressive control" modules - pressure pads, touch plates, and motion sensors - aimed at making modular synthesis feel more physical and immediate. Competitors like Intellijel's Touché or Make Noise's Pressure Points offered more direct interaction, but the 308 carved its niche by being passive, ambient, and environmental. It wasn't about touch, but about presence. In that sense it shared more with experimental systems like Buchla's touch plates or Serge's random voltage sources than with traditional CV generators. Its closest analog might be the now-discontinued Lich Module, which used a similar LDR approach but lacked offset controls and independent outputs.

ADDAC is a Portuguese boutique known for blending industrial design with experimental function. It positioned the 308 as part of a larger philosophy: giving modular users tools that respond to the world outside the rack. That ethos extended to other 300 Series modules like the 306 Touch Controller and 307 Distance to CV, a family of sensors that turn physical interaction into voltage. The 308 remains the most accessible and widely adopted of the bunch, partly because light is everywhere, and partly because its behavior is inherently musical.

Collectibility & Value

As of 2026, the ADDAC 308 is still in production, so it's not a "vintage" item in the traditional sense. It is gaining collector interest, especially in custom panel variants. The standard black version sells new for €140, and the DIY kit for €77, which makes it a mid-tier utility module. On the used market, assembled units typically go for $100-$140 depending on condition and whether the sensor is included. Listings without the sensor often drop to $80-$100, which can trap newcomers who don't realize it's sold separately.

Condition is straightforward. The PCB is solid, and there are no moving parts aside from the knobs and switch. The most common failure point is the input jack. If the sensor cable is frequently plugged and unplugged, the solder joints can weaken over time. The LDR itself can degrade with prolonged exposure to bright light, leading to sluggish response or drift, but replacement is simple for anyone comfortable with basic soldering. The module runs cool, so heat-related damage is rare.

For buyers, reliability isn't the real question. Intent is. The 308 is useless if you don't plan to use the sensor. Too many end up buried in racks, unused, because owners didn't realize it needs external placement and creative patching. It's not a "set and forget" modulator. It also doesn't play well with digital systems - there's no MIDI or USB, and the CV output isn't quantized or clocked. It's an analog improviser's tool, not a sequencer's sidekick.

Custom panel versions, especially bronze or colored prints, fetch premiums on the secondary market, sometimes reaching $180-$200. The difference is largely aesthetic, but ADDAC's limited-run panels have become minor status symbols in certain circles. The DIY kit remains a solid value for builders, with clean, well-documented analog sensor circuits. The kit doesn't include the sensor, so add an extra €5 if you're building from scratch.