ADDAC System ADDAC711 ()

Two channels of transformer-isolated input for your modular. No hum, no buzz.

Overview

The ADDAC711 is a dual-channel isolated DI (direct input) box for Eurorack. It isn't a synth voice or a filter, and it doesn't make sound. It keeps noise out. It sits at the gateway of your system and blocks the electrical gremlins that turn clean signals into 60-cycle hum when you plug in a mixer, audio interface, or vintage outboard gear. It is built around a unity 1:1 audio transformer, which gives galvanic isolation. That means it breaks the direct electrical connection between your external gear and your modular, so ground loops and impedance mismatches never get started.

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

Manufacturer	ADDAC System
Dimensions	6 HP
Depth	40 mm
Current Draw	40 mA +12V, 40 mA -12V, 0 mA 5V
Frequency range	Operating in the 20 Hz to 20 KHz range
Outputs	Two fully balanced outputs (via XLR connectors)
Input connectors	Accepts XLR balanced, TS Mono jacks, and TRS balanced jacks
Switch functions	LIFT/FLOAT/GND 3-way switch
Number of channels	Two independent channels
Made in	Portugal

Key Features

Transformer-Based Isolation

The heart of the ADDAC711 is the unity 1:1 audio transformer. It isolates your external audio sources from your modular system and physically decouples the grounds, which stops ground loops. This is more than impedance buffering. The signal passes through unchanged in level (unity gain), and the module covers the full 20 Hz to 20 kHz range. It's a classic solution, built 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 GND mode, input and output grounds are tied together. That's fine when everything shares a common ground and behaves. In FLOAT mode, the grounds are completely separated, which can eliminate hum when you connect gear on different power circuits. LIFT mode is a compromise: the ground is connected through a 100R resistor and a 10nF capacitor, which blocks DC while letting RF noise dissipate. That reduces buzz without creating a full ground loop.

Dual Channels with Visual Feedback

Each of the two channels has its own front-panel gain control and a signal overload warning LED. The LED matters because overdriving the transformer can introduce subtle distortion. That might be wanted in some cases, but the 711 is built for transparency. The LED lets you back off the gain before clipping occurs. 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, for sending signals to mixers, interfaces, or outboard processors.

Build and Availability

The module comes either fully assembled or as a DIY kit. At 40 mm deep, it fits 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.

Historical Context

ADDAC System introduced the ADDAC711 Balanced Inputs alongside the ADDAC710 Balanced Outputs as part of the ADDAC700 series, a family of interface modules designed to protect the modular ecosystem from external noise. The 710 handles output isolation, shielding your external gear from the electrically noisy environment of a modular synth. The 711 does the reverse and shields the modular system from noise coming in. Together they form a bidirectional barrier against hum and interference. The 711 addresses a common pain point in hybrid setups, where integrating modular with traditional studio gear often leads to grounding conflicts.

Collectibility & Value

The ADDAC711 has held steady demand among modular users who regularly interface with external gear. Original pricing information is limited, but one source lists an original price of $489.00 AUD. Current market values are lower. Recent listings show new units 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. On eBay, a listing shows a current price of US $288.00, which points to active but not frenzied resale interest. There is no data on common failures or maintenance issues, and no reports of production years or discontinuation, which suggests it remains in circulation. The 711 is more of a utilitarian keeper than a speculative collectible.