Befaco Even VCO

At 8 HP, it slips into tight Eurorack systems like a secret handshake—compact, confident, and built for precision.

Overview

The Befaco Even VCO is a voltage-controlled oscillator module designed for Eurorack synthesizers, built with an emphasis on stability and tracking accuracy. Owners report it delivers a classic analog oscillator experience, with clean tunability across a wide range—up to 10 octaves—making it suitable for everything from sub-bass fundamentals to ultrasonic textures. It's not flashy, but it’s serious engineering: designed for ultra-precise tracking, even under fluctuating power conditions, which matters in modular setups where voltage rails aren't always perfectly regulated. The module features a 10-position rotary octave selector, giving players immediate, tactile control over pitch range without hunting through fine-tune knobs.

While the core waveform outputs aren’t fully documented across all sources, one output—labeled “even”—is confirmed to deliver a sine wave at the fundamental frequency, suggesting a focus on harmonic purity. Additional modulation capabilities include linear FM, hard sync, and PWM, placing it firmly in the company of versatile, performance-ready oscillators. Some users have studied its source code to implement DPW (discrete time piecewise) alias suppression techniques in other designs, indicating a level of technical transparency and design integrity that appeals to DIY-minded synth enthusiasts.

Despite its strengths, the Even VCO has a reputation among builders and technicians for being finicky to calibrate. Multiple forum reports cite “impossible calibration” scenarios, with one user noting their unit was out of calibration upon arrival. Discussions on Sequencer.de suggest potential issues with voltage control accuracy due to incorrect resistor values, specifically pointing to the need for a 100 Ohm 3300ppm 0805 SMD tempco resistor in non-calibratable units. These are not widespread failure reports, but they do form a consistent thread: this is a module that demands care in build and setup.

Specifications

Manufacturer	Befaco
Model	Even VCO
Type	Eurorack Oscillator Module
Width	8 HP
Depth	22mm (28mm for DIY version including power connector) (Juno) / 47mm (Perfect Circuit)
Current Draw	36mA @ +12V, 26mA @ -12V
Frequency Range	Cleanly tuneable over 10 octaves
Tracking Accuracy	Up to 1 Cent per octave
Features	Linear FM, Hard Sync, PWM, 10-position octave selector
Outputs	Sine wave at fundamental frequency (“even” output)

Key Features

10-Octave Tunable Range with Rotary Octave Selector

Tuning across 10 octaves is no small feat in analog VCO design, and the Even VCO manages it with a dedicated 10-position rotary switch. This isn’t just about range—it’s about usability. Players can jump octaves instantly, which is invaluable during live performance or sound design sessions where timbral shifts need to be immediate. The switch provides mechanical feedback and eliminates the guesswork of dialing in octaves via a continuous knob, reducing drift and tuning errors.

Ultra-Precise Tracking Under Voltage Fluctuations

One of the Even VCO’s standout design goals is stability. It’s explicitly designed to maintain accurate pitch even when power supply voltages fluctuate—a common issue in densely packed Eurorack cases. According to available documentation, it achieves tracking accuracy within 1 cent per octave, which is exceptional for a discrete analog oscillator. This level of precision makes it viable for polyphonic patches or stacked oscillators where even slight detuning becomes audible.

Linear FM, Hard Sync, and PWM Modulation

Modulation flexibility is baked into the Even VCO’s architecture. Linear FM allows for dynamic pitch sweeps and metallic timbres when driven by envelopes or LFOs. Hard sync opens the door to aggressive, harmonically rich leads and digital-sounding sweeps. PWM (pulse width modulation) adds movement to square waves, enabling classic analog textures from hollow phasing to thick chorusing. These are standard features in high-end VCOs, but their inclusion here—paired with the module’s tracking stability—makes it a compelling voice for complex synthesis.

Even Output as Fundamental Sine Wave

Collectibility & Value

The Befaco Even VCO has appeared on the used market in working condition, tested and sold with a ribbon power cable, though described as showing signs of use. A new unit was listed at C$430.49, while a full DIY kit was priced at £98.00 (excl. VAT) from Thonk, and a ready-built version at 198 € from Thomann.de. These prices reflect its niche status—higher than entry-level DIY kits but below boutique hand-built modules. Calibration difficulties reported by users may affect long-term reliability and resale appeal, particularly for non-technical buyers. As a result, units that are properly calibrated and tested hold more value, and DIY builders should expect to invest time in setup.