ADDAC 701 VCO (2019–)

A compact analog VCO that does a lot for its size. It is stable and loaded with features, but its tuning drifts a bit over long sessions.

Overview

The ADDAC 701 VCO Rev 2 is only 8 HP wide, but it is packed with features. It is not a minimalist oscillator that gives you one clean tone. It is a full analog voice generator with routing, mixing and modulation options. The frequency knob covers six octaves, and an octave switch doubles the range. It tracks cleanly thanks to the modern CoolAudio version of the CEM3340 chip. The manual fine-tune knob gives a full 12 semitones of adjustment, which is plenty for microtonal tweaks or for detuning a second oscillator.

The 701 is also flexible. It can switch into LFO mode, which moves it from tone generation into modulation. That switch does more than limit the frequency. It reconfigures the core behavior, so the same module handles slow sweeps or fast audio-rate FM without a separate low-frequency source. Linear FM has a dedicated attenuator, so you can dial in metallic bell tones or subtle harmonic movement without overdriving the input. The soft/hard sync switch sets how aggressively the waveform resets. Pulse width modulation has both manual control and CV input with attenuation, so you can go from a narrow click to a fat square wave and modulate it in real time.

It is not a perfect oscillator. Owners report that pitch stability is vastly improved over the original 701, but it still shows thermal drift, especially during the first 15 minutes of operation. Some units wander more than others. The module calibrates well out of the box, but long sets or temperature shifts in the studio can nudge it slightly off. The sawtooth and pulse are full-bodied and thick. The sine wave is clean, but it isn't quite surgical enough to serve as a pristine FM carrier in every application. For West Coast-style timbral exploration or East Coast-style leads, it works fine.

Specifications

Manufacturer	ADDAC System
Production Years	2019–
Original Price	€170 / $189
Module Type	Analog VCO / LFO
Form Factor	Eurorack
HP Size	8 HP
Depth	35 mm (3.5 cm)
Current Draw	60 mA +12V, 60 mA -12V
IC Core	CoolAudio V3203 (modern CEM3340 variant)
Frequency Control	Knob (6 octave range), Octave Switch (6 positions)
Fine Tune Range	±12 semitones
1V/Octave CV Input	Yes, tracks accurately over 7 octaves
FM Input	Linear FM with attenuator
Sync Input	Switchable: Soft, Off, Hard
Pulse Width Control	Manual knob + CV input with attenuator
Waveform Outputs	Sine, Triangle, Sawtooth, Pulse
Mix Output	Yes, via 3-knob mixer (SIN/TRI, MIX, SAW/RECT)
Mode Switch	LFO / VCO
Available As	Assembled module, DIY kit (€121)

Key Features

The Onboard Waveform Mixer: More Than a Convenience

Most oscillators make you choose a waveform or patch multiple outputs into a separate mixer. The ADDAC 701 has a dedicated three-knob mixing section. It blends sine/triangle, blends saw/pulse, and then crossfades between those two pairs. It is not CV-controllable, and owners note this as a missed opportunity for dynamic waveshaping. As a manual sculpting tool it is very useful. You can make a triangle-saw morph for a plucky lead, or blend sine and pulse to thicken a sub oscillator tone. The mix output is not just a sum. It is a new composite waveform that responds differently to filtering and modulation. This kind of integration in an 8 HP module was rare when the 701 Rev 2 launched, and it still feels generous.

CEM3340 DNA with a Modern Twist

The core of the 701 is the CoolAudio V3203, a modern reissue of the CEM3340. That is the same chip that powered the Prophet-5, the Oberheim OB series, and countless other classics. ADDAC also optimized the surrounding circuitry for better temperature compensation and tracking. The oscillator behaves predictably across voltages and holds pitch more reliably than many boutique 3340 implementations. It doesn't hit the "digital stability" some claim, but it is consistent for an analog core, especially over the advertised seven octaves. The triangle-to-sine converter is borrowed from the original 701 design. It remains one of the smoother analog conversions in the Eurorack world and avoids the stepped or buzzy artifacts some sine shapers produce.

LFO Mode: A Legitimate Dual-Personality Module

LFO mode does more than slow the oscillator down. It reconfigures the range and response for modulation duties. It is a fully functional LFO with the same waveform outputs and CV control options. You can use it to modulate filter cutoff, amplitude, or another oscillator's pitch in the same module footprint. The octave switch stays active for fine control over modulation speed. Because it is based on a real analog core, the LFO has subtle imperfections that can add life to a sequence. Some users initially reported tuning discrepancies when switching back to VCO mode after extended LFO use. ADDAC addressed this in later production runs by changing a capacitor value, so newer units shouldn't have the issue.

Historical Context

The ADDAC 701 VCO Rev 2 arrived in 2019, when Eurorack was crowded with feature-heavy, expensive oscillators. These were modules that cost $300+ and offered wavetables, digital synthesis, or complex modulation engines. The 701 went the other way and refined the analog fundamentals. It was a direct response to the discontinuation of the original ADDAC 701, which had developed a cult following but suffered from tuning instability and higher pricing. Behringer was flooding the market with ultra-cheap 3340 clones at the time. ADDAC positioned the 701 Rev 2 as a premium-but-accessible alternative that was better built, more stable, and had extras like the waveform mixer. It competed with respected analog modules like the Intellijel Dixie II+ and the Doepfer A-110-1, offering similar performance at a lower price and in less space.

The CEM3340 resurgence was also in full swing. After decades of scarcity, CoolAudio's reissue of the chip let smaller builders get that classic sound without relying on NOS parts. ADDAC combined the renewed availability with its own design approach: clean layouts, user-focused features, and European build quality. The 701 Rev 2 didn't try to reinvent the oscillator. It tried to perfect a proven formula.

Collectibility & Value

The ADDAC 701 VCO Rev 2 isn't a vintage item in the traditional sense. Production began in 2019 and continues today. On the used market, prices hover between €140 and €180 depending on condition and region, and the DIY kit fetches around €100-120. That is a modest depreciation from the original €170 price, which suggests strong owner retention and demand. Units sold as "new old stock" or with custom front panels (available in colors like bronze, red, or silver gray) can command small premiums, especially in Europe where ADDAC has a strong following.

Common issues are few. Early production units, particularly those made before mid-2020, may show the LFO/VCO tuning discrepancy mentioned in user forums. ADDAC issued a fix involving a capacitor swap, and service technicians observe that most newer modules ship with the correction already in place. Thermal drift is the most frequently cited flaw. The oscillator can go slightly sharp during warm-up and need a brief retune. This is typical for analog VCOs, but the 701 is more sensitive than some competitors. Regular recalibration using ADDAC's published procedure helps, but it is not a "set and forget" module.

When buying used, check that the waveform outputs are clean and free of crosstalk. Verify that the mix section behaves as expected, with no crackling or channel imbalance. The knobs are sturdy, but the PCB layout is dense, so inspect for signs of botched repairs or overheated components on a DIY-assembled unit. Failure rates are low, and the module has no known catastrophic weaknesses - no failing ICs, no flaky jacks. ADDAC still sells replacement panels and full DIY kits, which suggests long-term support.