ADDAC System ADDAC701 (2010–2018, Rev2: 2020–)

A tiny analog VCO with a big voice, where waveform mixing and rock-solid tuning live in an 8 HP slot

Overview

Plug in the ADDAC701.REV2 for the first time and you’ll notice two things fast: how quiet it is when idle, and how rich the sine wave sounds—smooth, round, and free of the hash that plagues cheaper analog oscillators. This isn’t a digital approximation or a DSP trick; it’s a full analog core built around the CoolAudio version of the legendary CEM3340 chip, the same architecture that powered synths like the PPG Wave and the Prophet-5’s later revisions. But ADDAC didn’t just clone the past—they packed in modern refinements that make this one of the most stable, flexible compact VCOs in Eurorack. It tracks across seven octaves without breaking a sweat, handles both audio and sub-audio duties (from 0.01 Hz to 40 kHz), and gives you four simultaneous waveform outputs—sine, triangle, sawtooth, and rectangular—so you can route different waves to different destinations without stacking multiples.

What really sets the 701.REV2 apart is the onboard mix section. Three knobs—SIN/TRI, SAW/RECT, and a central MIX—let you blend any combination of waveforms into a single, morphing output. Turn the SIN/TRI knob and you’re not just fading between those two; you’re actually crossfading their harmonic content in real time, creating evolving timbres that feel organic, almost vocal at times. The MIX knob then balances that pair against the SAW/RECT pair, so you can go from a pure sine to a jagged, PWM-rich pulse wave with just two hands on the panel. It’s not CV-controllable, which some might see as a missed opportunity for automated waveshaping, but the hands-on blending is intuitive and immediate—perfect for live tweaking. And because the mix output is normalized, you’re not losing anything by using it; the individual waveforms still fire from their dedicated jacks.

Positioned in the ADDAC700 series as the foundational analog oscillator, the 701.REV2 sits below more experimental modules like the Stinggy Filter (705) or the Cracklebox (708), but it’s far from basic. It replaced the original ADDAC701, which had tuning instability and limited LFO functionality, and the REV2 fixed those with better temperature compensation and a redesigned circuit. Compared to competitors like the Doepfer A-110-1 or the Intellijel Dixie II+, the 701.REV2 trades some raw character for precision and density. It won’t scream like a Moog or snarl like a Serge, but it won’t drift out of tune during a 10-minute ambient patch either. It’s the synth equivalent of a Swiss watch—unflashy, reliable, and deeply competent.

Specifications

Key Features

Waveform Mixing That Feels Like Sculpting

Most compact VCOs make you choose one waveform or route multiples to blend externally. The ADDAC701.REV2 hands you a mixing console on the front panel. The three-knob system—SIN/TRI, SAW/RECT, and MIX—doesn’t just crossfade; it lets you shape the harmonic DNA of your sound in real time. Want a triangle wave that slowly warps into a sawtooth while a pulse wave sneaks in underneath? Twist two knobs and patch an LFO to the PWM CV. The result isn’t just modulation—it’s motion. And because all individual waveforms remain available at their own outputs, you can use the mix output as a primary voice while sending, say, the pure sine to a frequency shifter or the sawtooth to a filter for parallel processing. It’s a rare balance of integration and flexibility.

Stability Without Sacrificing Character

Analog oscillators have a reputation for drifting, especially in cheaper builds. The 701.REV2 combats this with internal temperature compensation and the modern CoolAudio CEM3340, which tracks more accurately than vintage silicon. Owners report it holds pitch across long sessions, even in un-air-conditioned studios. That doesn’t mean it’s sterile—there’s still warmth in the sine, bite in the saw, and a satisfying thickness to the pulse wave when modulated. It’s not trying to emulate a specific vintage synth, but it’s not clinical either. It splits the difference: warm enough for analog purists, stable enough for digital-minded composers.

Compact Power with Full Patch Access

At just 8 HP, the 701.REV2 packs in more than some 16 HP oscillators. You get linear FM with attenuator, two PWM CV inputs (mixable), hard/soft sync selection, octave switch, fine tune, and a dedicated LFO/VCO mode switch that changes the frequency scaling. The auxiliary output adds another layer of utility—patch it to output any selected waveform, normal or inverted, at variable level. This is especially useful for creating feedback loops or sending inverted waves to modulation destinations. The only real omission is through-zero FM, which you’ll find on modules like the Befaco Even VCO or Doepfer A-111-3, but for most users, the linear FM input covers the essential frequency modulation needs.

Historical Context

The ADDAC701 arrived during the mid-2010s Eurorack boom, when boutique builders were reimagining analog synthesis for a new generation. ADDAC System, based in Lisbon, had already carved a niche with hybrid digital-analog designs, but the 701 was a statement of analog credibility. The original version, released around 2010, used older CEM3340 chips and suffered from tuning inconsistencies, especially in LFO mode—so much so that some users reported retuning every few minutes. By 2020, ADDAC revisited the design with the REV2, leveraging modern components and user feedback to deliver a tighter, more reliable module. This wasn’t just a refresh; it was a course correction. At a time when many manufacturers were chasing digital complexity or esoteric interfaces, ADDAC doubled down on core analog functionality—tuning stability, waveform fidelity, and hands-on control—proving that simplicity, when well-executed, could still stand out. The 701.REV2 also arrived as Behringer flooded the market with ultra-cheap 3340-based oscillators, making ADDAC’s focus on build quality and thoughtful design even more relevant. It wasn’t the cheapest option, but it wasn’t trying to be—it was the oscillator you’d keep when you tired of retuning or debugging.

Collectibility & Value

The original ADDAC701 is effectively obsolete—rarely found, often unstable, and not recommended for purchase unless you’re prepared to recap and recalibrate it. The REV2, however, has become a quiet staple in modular racks worldwide. New units sell for around €158–$173, making it a budget-friendly high-end VCO. Used prices hover between $120–$150 depending on condition, with little premium for “mint” examples—this is a utilitarian module, not a collectible art piece. That said, its reliability and compact size make it a favorite among touring musicians and skiff builders, so functional units rarely stay on the market long.

Failures are uncommon but not unheard of. The most reported issue in early REV2 units was a capacitor flaw that affected LFO mode and octave switching, causing tuning jumps when patched to sequencers. ADDAC acknowledged this and issued a fix—replacing a single capacitor—which most technicians can perform in minutes. Later production runs include the corrected component, so buyers should look for units manufactured after mid-2020. Beyond that, the module is solid: no ribbon cables to snag, no delicate trim pots, and a robust aluminum faceplate. The only wear points are the potentiometers and jacks, but given the build quality, they’re likely to outlast most cases they’re installed in.

If you’re buying used, test for tuning stability over 10–15 minutes, check that the LFO/VCO switch functions correctly across all octaves, and verify that the mix section produces clean transitions without dropouts. Patch an LFO into the PWM input and listen for smooth, jitter-free modulation. Also confirm that the sync input responds to both hard and soft settings—some users report one mode failing due to a cold solder joint on the switch. Overall, the 701.REV2 is one of the lowest-risk analog VCOs on the used market, provided you avoid the earliest Rev2 batches.

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