ADDAC System ADDAC205 (2023)
A dual-channel oscilloscope and arbitrary waveform generator that fits in 10 HP.
Overview
Say you are deep in a patch, chasing a modulation that keeps slipping out of phase, and the rack has no built-in scope. That is where the ADDAC205 comes in. It is a real-time visualization tool with two high-contrast OLED screens, each acting as a full dual-channel oscilloscope. You can watch audio signals, debug CV glitches, or trace the rise and fall of an envelope. It does all this in a 10 HP slot, tucked between a filter and a VCA.
Each scope also works as an arbitrary waveform generator (AWG). It outputs sine, triangle, and sawtooth waves at 8-bit resolution and a 44.1 kHz sample rate. That is not audiophile-grade, but it is plenty for control signals, clock division, or crude audio generation in a pinch. So the module is part diagnostic instrument and part sound source. It is not flashy, but it gets indispensable once you try to do anything precise.
The ADDAC205 sits in the ADDAC200 series as an analog CV utility. It ranks just below the more esoteric test gear like the ADDAC200A current ammeter, and above basic signal conditioners like the CV inverter or amplifiers. It is not the first module you grab when building a synth voice. It is the one you wish you had installed when your LFO starts jittering or your sample-and-hold won't lock. Next to a bench oscilloscope it is limited: no bandwidth specs, no probe inputs, no AC coupling. For in-rack signal monitoring it works well. Unlike digital scope modules that rely on external software or complex firmware, it keeps things simple: four buttons, a menu-driven interface, and immediate feedback on screen. No drivers, no latency.
Specifications
| Manufacturer | ADDAC System |
| Production Years | 2023 |
| Original Price | €449 |
| Format | Eurorack |
| Width | 10 HP |
| Depth | 5 cm |
| Power Supply Compatibility | ±12V and ±15V |
| Max Current Draw | 150mA |
| Bus Board Connector | 8×2 IDC (Doepfer style) |
| CV Inputs | ±10V |
| CV Outputs | 0–5V |
| Screen Refresh Rate | 128Hz |
| Oscilloscope Channels | 2 per scope (4 total inputs) |
| Arbitrary Waveform Generator | Yes (Sine, Triangle, Sawtooth) |
| AWG Resolution | 8-bit |
| AWG Sample Rate | 44.1 kHz |
| Trigger Input | 1 per oscilloscope |
| Control Interface | 4-button menu navigation |
Key Features
Two Full Oscilloscopes in 10 HP
Two independent dual-channel oscilloscopes, each with its own OLED display, are packed into a module barely wider than a standard attenuator. The screens are monochrome and high-contrast, and they refresh at 128Hz. That is fast enough to catch transient spikes and slow enough to avoid flicker. Each scope handles two input channels, switchable via front-panel toggles, so you can compare waveforms side by side or stack them for phase analysis. There is no zoom or timebase control beyond the basic menu settings. That is still enough for checking signal integrity, verifying modulation depth, or syncing clocks. The module can trigger externally, so you can lock the display to a gate or clock pulse. That makes it more useful than a passive voltage monitor. It is designed for Eurorack levels, so you don't need attenuators or probes. Just patch and observe.
Arbitrary Waveform Generation with Real Utility
The AWG function is a fully functional signal source in each scope section. It generates sine, triangle, or sawtooth waves at 8-bit resolution. That sounds crude on paper, but it is clean enough for control voltages and surprisingly musical when used for audio. The 44.1 kHz sample rate avoids aliasing in the audible band, and the 0-5V output range fits modular expectations. You won't use it as your main oscillator, but as a secondary LFO, a reset source, or a backup envelope shaper it is useful. There is no frequency modulation or waveform morphing. It is a utility, not a sound generator. It does its job reliably, and without stealing CPU cycles from a digital brain.
Menu-Driven Simplicity Without Bloat
No touchscreens, no firmware updates, no hidden modes requiring three-button combos. The ADDAC205 uses four physical buttons to navigate a straightforward menu system: select channel, adjust scale, set trigger, or switch to AWG mode. You don't need to memorize shortcuts or dig through submenus to get a waveform on screen. The interface assumes you are using it while patching, not programming it like a computer. The build is just as plain. There are no SD card slots, no USB ports, and no bidirectional communication. It is a self-contained tool, which means fewer points of failure and no dependency on external software.
Historical Context
The ADDAC205 arrived in 2023. By then Eurorack had long since moved beyond pure analog synthesis into hybrid territory, where digital signal processing and embedded microcontrollers were as common as VCOs and filters. Still, there was a gap in real-time diagnostics. You could use a DAW to monitor signals via audio interface, or rely on LED meters that gave only a rough idea of level, but nothing let you see a waveform inside the rack. A few manufacturers had experimented with scope modules, but most were either too deep, too narrow in function, or too reliant on firmware to be practical. ADDAC System, known for modules like the ADDAC111 .WAV player and ADDAC506 stochastic generator, saw the niche and filled it.
The ADDAC205 wasn't the first oscilloscope in Eurorack, but it was the first to balance utility, size, and reliability well enough to be a credible tool rather than a novelty. It followed test equipment modules from brands like Intellijel (with their Metropolis scope function) and Expert Sleepers (with their precision measurement tools). It stood apart by offering dual independent displays and integrated signal generation. It also reflected a broader trend: patches were growing more complex, and debugging tools were needed. As musicians began chaining together digital sequencers, clock dividers, and FM algorithms, visualizing timing and voltage became more of a necessity than a luxury. The ADDAC205 didn't try to replace a bench scope. It brought the most useful features into the rack, where they could be used in real time.
Collectibility & Value
As of 2026, the ADDAC205 remains in production and available from authorized dealers, with a secondary market that is stable but not speculative. New units sell for around €449, while used examples in good condition typically go for €350 - €400. There is no collector premium yet, and given its utilitarian nature, it is unlikely to become a "grail" module. The market is fair, and you are not paying vintage tax for something designed to be used. Its value lies in function, not rarity, so condition matters. The OLED screens are the main concern. They are rated for long life, but prolonged static displays, like a constant DC voltage trace, can lead to image retention or burn-in over time. Buyers should power on the unit and cycle through waveforms to check for ghosting or dead pixels.
Other failure points are minimal. The 8×2 IDC power connector is standard, and the internal circuitry is well laid out with no known weak components. The AWG section uses onboard memory for waveform storage, and there are no reports of corruption or failure in the field. Because it is a digital-analog hybrid, it is less prone to drift than pure analog modules. Firmware updates are delivered via ADDAC's website and require a manual flash, which owners should verify before purchase. The ADDAC205 is worth the investment if you are doing complex sequencing, modular recording, or live performance where signal integrity is critical. It is not a "fun" module, but it can save you hours of troubleshooting. If you are on a budget, it is easy to skip.
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