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

A tiny analog VCO in an 8 HP slot, with waveform mixing and steady tuning

Overview

Plug in the ADDAC701.REV2 and two things stand out fast. It's quiet when idle, and the sine wave is 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 CEM3340 chip, the same architecture that powered synths like the PPG Wave and the Prophet-5's later revisions. ADDAC added modern refinements on top of it. The module tracks across seven octaves, covers 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.

The onboard mix section is what sets the 701.REV2 apart. Three knobs - SIN/TRI, SAW/RECT, and a central MIX - blend any combination of waveforms into a single output. Turn the SIN/TRI knob and you crossfade the harmonic content of those two waves in real time. 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 two hands on the panel. It's not CV-controllable, which some might see as a missed chance for automated waveshaping. The individual waveforms still come out of their dedicated jacks, so using the mix output costs you nothing.

The 701.REV2 is the foundational analog oscillator in the ADDAC700 series. It 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+, it 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.

Specifications

Manufacturer	ADDAC System
Production Years	2010–2018 (original), 2020–present (Rev2)
Original Price	$599 (original), €158 / $173 (Rev2)
Format	Eurorack
Width	8 HP
Depth	35 mm
Current Draw +12V	60 mA
Current Draw -12V	60 mA
Bus Board Connector	8×2 IDC (Doepfer style)
Oscillator Type	Analog Voltage Controlled Oscillator (VCO)
Core Chip	CEM3340 (CoolAudio)
Frequency Range	0.01 Hz – 40,000 Hz
Audio Range	1 Hz – 40,000 Hz
LFO Range	0.01 Hz – 400 Hz
Octave Range	6 octaves (via switch)
Fine Tune Range	±12 semitones
Waveform Outputs	Sine, Triangle, Sawtooth, Rectangular (Pulse)
Mix Output	Yes, via SIN/TRI, SAW/RECT, and MIX knobs
Pulse Width Modulation	Yes, with CV input and attenuator
Linear FM Input	Yes, with attenuator
Sync Input	Yes, switchable between Hard and Soft Sync
1V/Oct CV Input	Yes
Microtuning CV Input	Yes
LFO/VCO Mode Switch	Yes
Auxiliary Output	Yes, with waveform selection and invert option

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 puts a small mixer on the front panel. The three-knob system - SIN/TRI, SAW/RECT, and MIX - lets you shape the harmonic content of your sound in real time. Want a triangle wave that slowly warps into a sawtooth while a pulse wave comes in underneath? Twist two knobs and patch an LFO to the PWM CV. All the individual waveforms stay available at their own outputs, so 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.

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. It isn't sterile, though. There's still warmth in the sine, bite in the saw, and a thickness to the pulse wave when modulated. It doesn't try to emulate a specific vintage synth, and it isn't clinical either.

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 patches to any selected waveform, normal or inverted, at variable level. That's useful for feedback loops or for 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. 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. 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. Some users reported retuning every few minutes. By 2020, ADDAC revisited the design with the REV2, using modern components and user feedback to make a tighter, more reliable module. Many manufacturers were chasing digital complexity or esoteric interfaces at the time. ADDAC stuck with core analog functionality: tuning stability, waveform fidelity, and hands-on control. The 701.REV2 also arrived as Behringer flooded the market with ultra-cheap 3340-based oscillators. It wasn't the cheapest option, and wasn't trying to be.

Collectibility & Value

The original ADDAC701 is effectively obsolete. It's rarely found, often unstable, and not recommended for purchase unless you're prepared to recap and recalibrate it. The REV2 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. 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 sturdy aluminum faceplate. The only wear points are the potentiometers and jacks, and 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. The 701.REV2 is one of the lowest-risk analog VCOs on the used market, provided you avoid the earliest Rev2 batches.