ADDAC System 804 (2013–)
A Eurorack module that connects iOS audio to a modular rig and turns app volume into control voltage.
Overview
The ADDAC 804 connects an iPhone to a modular synth. It's not a MIDI translator and not a USB interface. It's a dedicated audio bridge that treats the iOS device like any other source in the Eurorack. Route an app's output into your filter bank, or use its volume swings to trigger envelopes. It ships with the exact cable you need, which is rare in modular, where powering up often means a scavenger hunt.
It was designed in the early 2010s, when iOS music apps like AUM, Loopy, and GarageBand were gaining traction among experimental musicians. Modular users were asking how to get a tablet into the rack without a laptop. ADDAC kept the answer analog, direct, and simple. The 804 is a stereo audio interface with envelope followers built in, so you can pull control voltages from the amplitude of each channel. That means you can use an app's volume automation as a modulation source, trigger drums from a synth's crescendo, or feed a module's output into an effects app and return it, transformed, to the mix. Almost no other module does this so cleanly.
The 804 is compact and no-nonsense. It takes up 8 HP and is 1.5 cm deep, so it fits in even the tightest skiffs. It runs on either ±12V or ±15V and draws a modest 20mA, so it won't tax your power supply. Its real value is in workflow, not specs. You can run a modular sequence into a granular app, bounce it back with time-stretching, and use the resulting audio peaks to modulate a filter cutoff. It doesn't color the sound - no saturation, no EQ - just clean, bidirectional audio flow with CV extraction on the return path.
Specifications
| Manufacturer | ADDAC System |
| Production Years | 2013– |
| Original Price | $284 |
| Format | Eurorack |
| Width | 8 HP |
| Depth | 1.5 cm |
| Power Supply | ±12V or ±15V |
| Max Current Draw | 20mA |
| Bus Board Connector | 8×2 IDC (Doepfer style) |
| Inputs | 2 independent audio inputs from ADDAC804 to iOS device |
| Outputs | 2 independent audio outputs from iOS device to ADDAC804 |
| Volume Controls | 2 independent output volume knobs |
| Envelope Followers | 2 independent, with level and decay controls |
| Envelope Outputs | 2 CV outputs derived from audio amplitude |
| Compatibility | iOS devices (iPhone, iPad, iPod), MacBook (later models), Android devices with TRRS audio I/O |
| Accessories | Duplex iOS audio cable included |
| Series | ADDAC800 Series – Analog Sound Utilities |
Key Features
Duplex Audio Interface with No Latency Drama
The 804’s core function is bidirectional audio transfer: two channels out from your modular to your iOS device, two channels back in. This isn’t USB audio over MIDI, which can introduce latency and jitter—it’s direct analog audio in and out via a TRRS cable. That means you’re not relying on Core MIDI or app-specific routing; you’re patching audio like any other module. The included cable is the key—it’s a custom TRRS-to-dual-TRS solution that handles stereo output and stereo input simultaneously, something most headphone jacks aren’t wired for. Without it, the module wouldn’t work, and the fact that ADDAC includes it speaks volumes about their understanding of real-world usability.
Envelope Followers That Turn App Volume into Control Voltage
The 804 also has dual envelope followers. Each incoming audio channel from the iOS device is analyzed for amplitude, and that level is converted into a CV output with adjustable sensitivity and decay. You can use the volume envelope of a synth app, a loop's fade-in, or a vocal recording's dynamics to control filters, LFO rates, or sequencer triggers. The envelope knobs set the threshold, so quiet passages don't trigger and only the peaks you want get through. The decay sets how long the CV lingers after the audio drops. It's not a precision envelope generator like a Maths module, but it's responsive and musical for organic, performance-driven modulation.
Skiff-Friendly and Plug-and-Play Simplicity
Some modules demand firmware updates, USB configuration, or MIDI mapping. The 804 is entirely analog and needs no software. Plug in the cable, power the module, and you're routing audio. The front panel has two large knobs for sending audio out to the iOS device, two pairs of knobs for envelope threshold and decay on the return path, and clearly placed jacks. No menus, no modes, no hidden functions. It does what it says, and it does it reliably. That makes it a favorite for live performers who need things to just work, and for educators introducing modular synthesis to students already fluent in tablet music apps.
Historical Context
The ADDAC 804 emerged in 2013, as Eurorack was shedding its niche status and iOS was becoming a legitimate music-making platform. Apps like Koala Sampler, DM1, and Animoog offered powerful synthesis and sequencing, but connecting them to hardware was clunky and usually required a computer in the middle. ADDAC, a Portuguese company known for bridging analog and digital worlds, saw the gap. They weren't the first to suggest iOS-modular integration, but they were the first to deliver a dedicated, self-contained module that handled both audio and CV extraction without compromise.
At the time, the alternatives were DIY setups with TRRS adapters and external mixers, or high-end audio interfaces that cost far more and offered no CV features. The 804 is not a sound generator or a processor. It's a translator. It arrived alongside other hybrid-focused modules like the Expert Sleepers FH-2 and the Mutable Instruments Yarns, but those dealt with MIDI conversion, while the 804 stayed purely in the analog domain. It reflected a broader trend: modular users weren't rejecting digital tools, they wanted low-latency ways to bring them in. The 804 wasn't flashy, but it enabled workflows that are now commonplace, like using a phone to record and resample modular output in real time.
Collectibility & Value
The ADDAC 804 isn't a rare module, but it's not common either. It's still in production, so new units are available from ADDAC and dealers like Analogue Haven and Perfect Circuit, typically priced around $284. Used units appear on Reverb and eBay, usually between $200 and $250 depending on condition. There's no collector's premium, since its value is purely functional. If you find one missing its included TRRS cable, deduct at least $30. Replacements are hard to source and often don't work correctly because of wiring inconsistencies in generic cables.
Reliability is high. With no digital components or firmware, there's little to go wrong. The most common issue reported is intermittent audio from the TRRS connection, usually from dirt or wear on the jack, and contact cleaner fixes it easily. The envelope followers are analog circuits with no user-serviceable parts, but failures are rare. Power draw is minimal, so it won't overload a bus board. For buyers, the main check is the included cable: verify it's the original ADDAC-branded one with proper shielding and correct pinout. Also test both envelope followers with a sine wave to make sure they track amplitude smoothly. No mods or upgrades exist.
If you're building a hybrid setup or want to try resampling, granular processing, or app-based effects in your modular chain, the 804 remains one of the most straightforward solutions. It won't add distortion, color, or effects. Newer modules offer USB-C or digital audio streaming, but they often give up the immediacy and reliability of the 804's analog path.
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