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 for Eurorack modular systems. It is part of the ADDAC800 Series from ADDAC System. The job is simple: combine multiple stereo signals. The design is minimal, described as a "straight forward stereo mixer" with no-nonsense functionality. In dense, layered patches, it manages stereo sources while preserving headroom and clarity.
Four of the five stereo channels have individual gain knobs for level control over incoming signals. The fifth channel accepts stereo input but has no gain knob. It works as a fixed-level pass-through, which suits sources already at the right output level or cascading with other mixers. That keeps the front panel layout efficient.
The ADDAC813 is small, but it still has a dedicated mono send/return path for parallel processing of any signal routed through the mixer. That makes it more than a passive summing device. You can patch in reverb, delay, or distortion and blend the result back in. According to the manufacturer, the Return Gain operates in parallel with the Master Output, mimicking the wet/dry control on traditional effects units.
The module is cascadable, so multiple units can be linked to expand mixing capacity in larger racks. That suits setups that grow over time. At 8 HP wide, it takes up minimal space, and in Eurorack every millimeter counts. 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 aimed at 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 have dedicated gain knobs, giving control over input levels before summing. That lets you balance sources like stereo oscillators, dual filters, or stereo field recordings. The fifth channel accepts stereo input but has no gain adjustment, so it acts as a unity-gain pass-through. This saves panel space. The fixed channel works well for line-level sources or when integrating with downstream level controls.
Mono Send/Return Path for Parallel Processing
The mono send/return loop sets the ADDAC813 apart from basic stereo mixers. You can route a mix or individual channel to external effects, then bring the processed signal back into the main output. The return level is controlled by a dedicated gain knob, which operates in parallel with the master output and works 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. It makes the module useful as an effect bus in larger systems.
8 HP Compact Eurorack Format
At just 8 HP wide, the ADDAC813 fits easily into densely packed Eurorack cases. Its narrow profile suits skiffs, travel systems, or utility rows where space is limited. All five stereo inputs, the master output, the send/return jacks, and the controls are arranged clearly on the front panel. No physical dimensions beyond HP width or weight are documented.
Cascadable Design for Expanded Mixing
The module is designed to be cascaded with additional mixers, so you can scale up as needed. Instead of buying a large, fixed-channel mixer, you can chain multiple ADDAC813 units into custom configurations. That also allows specialized 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. No data is available on common failures, maintenance issues, or spare parts. Production status, whether still in manufacture or discontinued, is not explicitly confirmed.
Similar items on eBay
No exact ADDAC System 813 listings are live right now — these searches show current ADDAC System and similar vintage synth gear on eBay:
As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.