ADDAC System 711 (2022–)

Two channels of clean, passive signal transformation that make your modular sound like it was recorded through a console from 1975.

Overview

The ADDAC System 711 Balanced Inputs doesn't add distortion, doesn't color the tone with harmonics, and doesn't boost or cut anything. It translates. It's a passive module, no power required, built around a pair of audio transformers that take unbalanced signals from your modular and convert them to fully balanced outputs via XLR. In that conversion the signal gains weight and presence, and a kind of acoustic realism that most Eurorack systems lack by default. It's not loud and not flashy, but once you've run your mix through it, going back feels like eating cardboard after real bread.

This isn't a "me too" utility module. The 711 was designed as a companion to the ADDAC712 Vintage Pre and other modules in the 700 series that draw on 1970s analog console circuitry. Those modules saturate and clip and warp. The 711 does the opposite and grounds the signal, like the straight man in a comedy duo. The transformer is a unity 1:1 type, so it doesn't amplify or attenuate voltage, and it works across the full 20 Hz to 20 kHz range without rolling off the extremes. That sounds boring on paper. In practice there's a slight magnetic cushioning effect: highs lose their digital edge, lows tighten up, and the midrange gets a gentle forwardness that mimics high-end studio patch bays.

There are no knobs, no switches and no CV inputs. Just two channels, each with a 3.5mm input and an XLR output. The left input is normalled to the right, so mono signals are easy, but stereo is where it works best. Plug in your mixer's main outs and send them balanced to an audio interface or PA. Because it's passive, it doesn't care if your system runs at ±12V or ±15V, or if you're using digital oscillators, analog filters, or granular clouds from a microcontroller. It just works.

Specifications

Manufacturer	ADDAC System
Production Years	2022–
Original Price	€100 (assembled), €80 (DIY kit)
Format	Eurorack
Width	6 HP
Depth	40 mm
Power Requirements	None (passive)
Inputs	2x 3.5mm (unbalanced, left normalled to right)
Outputs	2x XLR (balanced)
Transformer Type	Unity 1:1 audio transformer
Frequency Response	20 Hz – 20 kHz
Impedance Matching	Yes, balanced conversion
Signal Path	Passive, transformer-based
Build Option	Available as assembled module or DIY kit
Panel Color	Black anodized aluminum
Mounting	Standard Eurorack 3U
Country of Origin	Portugal
Series	ADDAC700 Series (Analog Heritage)

Key Features

Transformer-Balanced Conversion Without the Noise

Most Eurorack modules live in a low-impedance, unbalanced world. That works fine until you send the signal outside the case. Long cable runs pick up hum, ground loops flare up, and digital switching noise creeps in. The 711 solves this with audio transformers. These aren't the cheap kind that color your signal with hash or roll off the top end. They're designed for flat response across the audible spectrum. With the signal converted from unbalanced to balanced, you can run XLR cables over tens of meters without picking up interference. That's invaluable for live sets, studio patching, or feeding vintage outboard gear that expects professional-level input.

But the benefit isn’t just technical. Transformers interact with signals in a way that’s hard to quantify. They introduce a tiny amount of magnetic hysteresis, a soft limiting at extreme levels, and a slight phase coherence that makes transients feel more “planted.” It’s not distortion, not exactly—more like the difference between a pencil sketch and a charcoal drawing. The 711 doesn’t change the image, but it deepens the contrast.

Passive Simplicity That Lasts

Because the 711 requires no power, it draws zero current from your bus board. No +12V, no -12V, no worries about daisy-chain loading. That makes it one of the safest modules you can install, with no risk of frying your power supply or causing a brownout. It also leaves almost nothing to fail. No op-amps to drift, no capacitors to leak, no trimmers to misalign. The only potential failure point is the transformer itself, and those are typically rated for decades of continuous use. Owners report running these modules 24/7 in studio racks with no degradation.

Being passive, it also doesn't care about signal polarity or DC offset. If you're running experimental digital modules that output wonky voltages, the transformer isolates the downstream gear and protects your interface or mixer from unexpected bias. It's not a protection circuit per se, but it acts like one.

Designed for the Full Signal Chain

The 711 wasn't made to sit alone. ADDAC positioned it as the entry point for external signals coming into a modular system, or the final stage before leaving it. Pair it with the ADDAC712 Vintage Pre and you have a complete front-end: unbalanced line or instrument signals enter the 712, get gain-staged and harmonically enriched, then pass through the 711 for a clean, balanced output. You can also reverse the chain. Bring balanced outputs from a mixer into the 711 and convert them to unbalanced for processing inside the case.

The 6 HP width is deliberate. Next to 3 HP noise generators and 1 HP attenuators, 6 HP for two transformers might seem extravagant. But the transformers need physical space, and the layout avoids crosstalk or magnetic coupling between channels. The faceplate is thick, black anodized aluminum, with cleanly labeled jacks and no wasted real estate. It looks like a module that belongs in a professional rack, not a hobbyist's DIY case.

Historical Context

The 711 arrived in 2022 as part of ADDAC System's 700 series, a deliberate shift toward "analog heritage" in a format increasingly dominated by digital brains and complex algorithms. While other manufacturers chased generative sequencing, FM resynthesis, or touchscreen interfaces, ADDAC went back to the discrete circuitry, transformers, and op-amp designs of the 1970s. The 711 doesn't do anything new. It revives a solution that was standard in recording studios 50 years ago but had been all but forgotten in modular synthesis.

Back then, every high-end console had transformer-balanced I/O. Neve, API, Helios - they all used them because they worked. Transformers rejected noise, handled high signal levels, and gave the console its "sound." When Eurorack emerged, cost and size constraints pushed designers toward active, op-amp-based balancing circuits, which are cheaper and smaller but don't behave the same. The 711 is a functional fix for a real problem in modern modular setups.

And it arrived at a moment when modular was being used more seriously in professional environments. Artists weren’t just making weird noises anymore—they were recording albums, scoring films, playing festivals. Suddenly, clean, noise-free signal routing mattered. The 711 answered that need with a solution that was both retro and forward-thinking. It’s telling that ADDAC didn’t just slap a transformer into a module and call it a day—they designed the whole thing around it, making sure the mechanical layout, grounding, and jack placement supported the audio integrity.

Collectibility & Value

The 711 isn't a "grail" module. It's available, relatively affordable, and doesn't command scalper prices. As of 2026, assembled units sell for €100-€130 depending on region and availability, while DIY kits go for €80. Unlike rare digital modules or limited-run oscillators, there's no frenzy around it, just steady demand from people who need one.

Condition is straightforward. Since it's passive, there's little to degrade. The most common issue reported is bent jacks from over-tightening XLR cables, and even that is rare. The DIY kit comes with SMD components pre-soldered, so novice builders can assemble it without much risk of cold joints or miswiring. Exploding Shed, one of the main distributors, includes full build guides and support, so failures are usually user error, not design flaws.

Maintenance is nearly nonexistent. No recalibration, no cleaning of potentiometers, no firmware updates. If it doesn't work, it's likely a cold solder joint or a damaged cable, and both are easy fixes. Because it doesn't draw power, it won't contribute to a failing bus board or cause voltage drops elsewhere in the case.

For buyers, the real question is necessity. If you're recording directly from modular, using long cable runs, or integrating with pro audio gear, you need balanced outputs. If you're only patching within a case and using a standard audio interface, you might not miss it.