ADDAC System ADDAC711 ()

Two channels of clean, transformer-isolated entry for your modular — no hum, no buzz, just signal.

Overview

If your modular rack ever crackles with ground loop hum the second you plug in a mixer, audio interface, or vintage outboard gear, the ADDAC711 isn’t flashy — but it might be the most peaceful module you’ll ever install. It’s not a synth voice, not a filter, not something that makes sound. Instead, it keeps noise out. Specifically, it’s a dual-channel isolated DI (direct input) box built for Eurorack, designed to sit at the gateway of your system and block the sneaky electrical gremlins that turn clean signals into 60-cycle nightmares. Built around a unity 1:1 audio transformer, the ADDAC711 provides galvanic isolation — meaning it breaks the direct electrical connection between your external gear and your modular — eliminating ground loops and impedance mismatches before they become problems.

Made in Portugal by ADDAC System, this 6 HP module handles two independent input channels, each with its own gain control, overload LED, and a clever LIFT/FLOAT/GND switch that gives you surgical control over grounding behavior. Whether you're feeding in a vintage drum machine, a live mic, or a guitar, the 711 ensures it arrives cleanly, without dragging in noise from other gear. It’s the kind of module you don’t appreciate until you’ve spent hours chasing hum, only to realize your audio interface and synth are fighting over ground. Then, one insertion later, silence — or at least, the right kind of silence.

Specifications

Key Features

Transformer-Based Isolation

At the heart of the ADDAC711 is a unity 1:1 audio transformer, which provides true galvanic isolation between your external audio sources and your modular system. This isn’t just impedance buffering — it physically decouples the grounds, stopping ground loops in their tracks. The transformer ensures the signal passes through unchanged in level (unity gain), preserving dynamics and frequency integrity across the full 20 Hz to 20 kHz range. It’s a classic solution, but one that’s been carefully implemented here with high-quality components to avoid the phase shifts or high-frequency roll-off that can plague cheaper isolation boxes.

Flexible Grounding Control

The LIFT/FLOAT/GND switch is where the 711 earns its keep in real-world setups. In GND mode, input and output grounds are tied together — fine when everything shares a common ground and behaves. In FLOAT mode, the grounds are completely separated, which can eliminate hum when connecting gear on different power circuits. LIFT mode is a smart compromise: the ground is connected through a 100R resistor and a 10nF capacitor, which blocks DC while allowing RF noise to dissipate, reducing buzz without creating a full ground loop. It’s a small detail, but one that reflects thoughtful engineering for live and studio troubleshooting.

Dual Channels with Visual Feedback

Each of the two channels has its own front-panel gain control and a signal overload warning LED. That LED is more useful than it sounds — overdriving the transformer can introduce subtle distortion, and while that might be desirable in some cases, the 711 is built for transparency. The LED lets you back off the gain before clipping occurs, ensuring clean signal transfer. The inputs use Neutrik combination XLR-1/4" jacks, so you can plug in mics, line-level gear, or instruments without adapters. Outputs are balanced XLR, making it easy to send clean, noise-resistant signals to mixers, interfaces, or outboard processors.

Build and Availability

The module is available both as a fully assembled unit and as a DIY kit, a nod to ADDAC System’s roots in the maker-friendly Eurorack scene. At 40 mm deep, it fits comfortably in most cases, though users with ultra-shallow racks should measure clearance. It draws 40 mA on both +12V and -12V rails, with no 5V draw — standard for passive-ish signal path modules with active LEDs and switching.

Historical Context

ADDAC System introduced the ADDAC711 Balanced Inputs alongside the ADDAC710 Balanced Outputs as part of their ADDAC700 series, a family of interface modules designed to protect the modular ecosystem from external noise. While the 710 handles output isolation — shielding your external gear from the electrically noisy environment of a modular synth — the 711 does the reverse: it shields the modular system from noise coming in. Together, they form a bidirectional barrier against hum and interference. The 711 specifically addresses a common pain point in hybrid setups, where integrating modular with traditional studio gear often leads to grounding conflicts. It’s not a sound-generating module, but in a world where clean signal flow is half the battle, it’s quietly essential.

Collectibility & Value

The ADDAC711 has maintained steady demand among modular users who regularly interface with external gear. While original pricing information is limited, one source lists an original price of $489.00 AUD, though current market values tell a different story. As of recent listings, new units appear for sale around $320.15 USD, while used prices vary widely — from $150 to €200 (approximately $215 USD as of 2025). One bundled listing offered the 711 and 710 together for $278.76, suggesting some buyers value them as a pair. On eBay, a listing shows a current price of US $288.00, indicating active but not frenzied resale interest. There is no data on common failures or maintenance issues, and no reports of production years or discontinuation, suggesting it remains in circulation. Given its niche but critical function, the 711 is more of a utilitarian keeper than a speculative collectible — people buy it because they need it, not because they expect it to appreciate.

eBay Listings

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