Dual VCA (2VCA)

LGE214 Dual Exponential Voltage Controlled Amplifier

Based around the original Serge 2VCA topology and updated with precision-matched SMD transistors, the LGE214 provides two clean, low-noise exponential VCAs designed for flexible signal control anywhere in a modular system. Rather than acting as final output mixers, these VCAs are ideal for patch-level dynamics, modulation shaping, and internal signal routing. Each channel features an exponential (audio-taper) response with approximately 12 dB per volt sensitivity across its operating range. At very low control voltages (below roughly 0.5 V), the gain rapidly falls to complete attenuation, producing extremely quiet operation with minimal bleed—perfect for envelope-controlled dynamics. High control-voltage rejection keeps CV artifacts out of the audio path, while the gain structure prevents overload, limiting maximum gain to approximately 2× for clean, stable performance.

The result is a compact, precise, and highly musical dual VCA suitable for both audio and control-voltage processing.

Panel Functions and Operation

The module contains two identical VCA channels, arranged vertically on the panel.

Channel Controls and Jacks

Each section includes:

IN
Signal input for audio or control voltages. The incoming signal is routed through the exponential VCA core.

CV
Control-voltage input that determines the gain of the VCA. Higher CV levels increase signal amplitude according to an exponential response. Typical uses include envelope generators, LFOs, sequencers, or other modulation sources.

GAIN
Manual gain (bias) control. Sets the base level of the VCA when no CV is present and determines the operating range of the incoming control voltage. Fully counter-clockwise yields near-complete attenuation; clockwise increases the open gain.

OUT
Processed output signal after voltage-controlled amplification.

Basic Operation

1. Patch a signal into IN.

2. Connect an envelope, LFO, or other modulation source to CV.

3. Adjust GAIN to set the desired base level or response depth.

4. Take the processed signal from OUT.

With no CV applied, the GAIN knob acts as a manual level control. With CV present, the knob sets the offset or sensitivity of the response.

Typical Uses

• Envelope-controlled audio dynamics

• CV-controlled modulation depth

• Internal signal routing and patch-level level control

• Dynamic modulation scaling

• Ring-mod style effects when driven by audio-rate CV signals

Circuit Overview

Internally, the module uses a CA3096-style matched transistor exponential converter driving a CA3280 OTA-based gain cell, followed by precision output buffers. This architecture produces the characteristic exponential response, low noise floor, and fast attenuation behavior associated with the classic Serge design while improving thermal matching and long-term stability through modern matched SMD devices


Build Notes / Calibration:
Coming soon
Jumper C12/C14 for DC Coupling

LGE214 Dual VCA (2VCA) DIY Build Documentation:

Main Board
LGE214 Main PCB Bill of Materials
LGE214 Main PCB Schematic
LGE214 Main PCB Layout w/ Designators

I/O Board
LGE214C I/O Board PCB Bill of Materials
LGE214C I/O Board PCB Schematic (wiring diagram)
LGE214C I/O Board PCB Layout w/ Designators
Mechanical Parts BOM generally required for building Low-Gain Electronics Modules

Serge Modular Ecosystem Compatibility
Modern Serge-style 4U systems use two primary mounting standards: Loudest Warning–style and Random*Source–style.
Low-gain Electronics modules follow the Loudest Warning–style mounting format (unless stated otherwise) and are electrically
compatible with all Serge-style systems, though mounting (panels) and power adapters may be required for some installations.
Please contact us if you have further questions about this.