ADDAC813 Stereo Mixer+

At 8 HP wide, it tucks into tight Eurorack systems like a utility knife in a pocket — simple, sharp, and always ready.

Overview

The ADDAC813 Stereo Mixer+ is a compact 5-channel stereo mixer designed for Eurorack modular synthesizer systems. Built as part of the ADDAC800 Series by ADDAC System, it serves a straightforward role: combining multiple stereo signals without clutter or compromise. Its design philosophy leans into minimalism — described as a "straight forward stereo mixer" with no-nonsense functionality that prioritizes utility over flourish. For builders and performers working in dense, layered patches, the module offers a clean way to manage stereo sources while preserving headroom and clarity.

Four of the five stereo channels include individual gain knobs, allowing precise level control over incoming signals. The fifth channel accepts stereo input but lacks a gain knob, functioning instead as a fixed-level pass-through — ideal for sources already at optimal output or for cascading with other mixers. This configuration keeps the layout efficient and avoids unnecessary clutter on the front panel.

Despite its modest footprint, the ADDAC813 doesn't sacrifice versatility. It includes a dedicated mono send/return path, enabling parallel processing of any signal routed through the mixer. This feature transforms it from a passive summing device into an active part of the signal chain, allowing users to patch in reverb, delay, or distortion effects and blend them back in with precision. According to the manufacturer, the Return Gain operates in parallel with the Master Output, mimicking the wet/dry control found on traditional effects units — a subtle but meaningful touch that enhances its integration within complex systems.

The module is cascadable, meaning multiple units can be linked together to expand mixing capacity in larger racks. This flexibility makes it a practical choice for evolving setups, where scalability matters more than all-in-one solutions. At 8 HP wide, it occupies minimal space, a key advantage in Eurorack environments where every millimeter counts. While no detailed technical specs like frequency response, THD, or S/N ratio are documented in available sources, the emphasis on clean signal routing suggests a design focused on transparency rather than coloration.

Specifications

Manufacturer	ADDAC System
Product Type	Compact 5-channel stereo mixer with mono send and return for Eurorack
Channels	5 stereo channels
Channel Controls	Four channels with stereo input and gain knob. Fifth channel with stereo input without gain knob
Additional Path	Mono send/return path for parallel processing
Function	The Return Gain works in parallel with the Master Output, just like regular wet/dry mix on effects
Format	8 HP

Key Features

Four Gain-Controlled Stereo Channels with Fixed Fifth Channel

Four of the five stereo channels feature dedicated gain knobs, giving users control over input levels before summing. This allows balancing dynamic sources like stereo oscillators, dual filters, or stereo field recordings. The fifth channel accepts stereo input but has no gain adjustment, acting as a unity-gain pass-through. This design choice saves panel space and streamlines operation — the fixed channel works well for line-level sources or when integrating with downstream level controls.

Mono Send/Return Path for Parallel Processing

The inclusion of a mono send/return loop sets the ADDAC813 apart from basic stereo mixers. Users can route a mix or individual channel to external effects, then bring the processed signal back into the main output. The return signal’s level is controlled by a dedicated gain knob, which operates in parallel with the master output — effectively functioning as a wet/dry blend. According to available documentation, this mimics the behavior of traditional effects loops, allowing subtle texture or dramatic washes without losing the dry signal’s integrity. This feature makes the module particularly useful as an effect bus in larger systems.

8 HP Compact Eurorack Format

Measuring just 8 HP wide, the ADDAC813 fits easily into densely packed Eurorack cases. Its narrow profile makes it a go-to option for skiffs, travel systems, or utility rows where space is limited. The compact size doesn’t compromise connectivity — all five stereo inputs, master output, send/return jacks, and controls are arranged clearly on the front panel. No physical dimensions beyond HP width or weight are documented, but its footprint alone speaks to its role as a space-conscious solution. For system builders prioritizing modularity and expandability, the small size enables strategic placement without sacrificing functionality.

Cascadable Design for Expanded Mixing

The module is designed to be cascaded with additional mixers, allowing users to scale their mixing capabilities as needed. This approach aligns with the modular ethos of building systems incrementally. Instead of opting for a large, fixed-channel mixer, users can chain multiple ADDAC813 units to create custom configurations. This also allows for specialized signal routing — for example, dedicating one mixer to internal voices and another to external effects returns.

Collectibility & Value

The ADDAC813 Stereo Mixer+ had an original MSRP of 160€ according to the manufacturer's website, though ModularGrid lists it as $178 MSRP As of current listings, the module retails new for $247.57 It remains available through select vendors, including as a Complete DIY Kit from Synthcube, suggesting ongoing accessibility for builders. No data is available on common failures, maintenance issues, or spare parts, and production status — whether still in manufacture or discontinued — is not explicitly confirmed. Given its utility and compact design, it maintains steady interest among Eurorack users focused on efficient, high-density systems.