A4-1B Opto Valve Compressor

Captures the classic Scandinavian compression tone with a fully analog circuit.

Premium tubes and custom transformers deliver high-fidelity, rich, and warm audio.

Combines analog design with digital precision for seamless performance.

Digital controls enable faster adjustments and ensure reliable, noise-free operation.

Variable attack and release times for tailored compression.

Sidechain filtering includes low-pass, high-pass, and band-pass options.

De-esser mode ensures clean and precise vocal and instrument handling.

DAW integration allows remote control, automation, and preset recall.

Motorized knobs apply settings instantly to hardware.

Includes a VU-meter for monitoring input, output, and compression levels.

Automated calibration ensures consistent performance over time.

Remote operation through plugins or a standalone app.

Includes a free one-year membership with access to additional plugins and updates.

General Specifications

100% analog audio circuit

Custom-designed UK transformers

High-quality tubes for sonic performance

Pre-sorted opto-cell for compression precision

All tube-based push-pull amplifier

Continuously variable attack and release times

Audio Features

Ratio: 2:1 to 10:1

Threshold: off to -40 dBu

Attack: 0.5 ms to 300 ms

Release: 50 ms to 10 s

Gain: off to +30 dB

Maximum output level: +24 dBu

Maximum input level: +24 dBu

Noise level: < -80 dBu

Input impedance: 10 kOhms differential

Output impedance: <60 Ohm

Frequency response: 20 Hz to 20 kHz ±1 dB

Automation and Digital Features

Remote control via VST3, AAX, AU plugin, or standalone app

Proprietary motorized knobs for instant hardware settings

Automation for attack, release, gain, threshold, and ratio via DAW plugin

Comprehensive preset system for session recall and A/B testing

Extended sidechain filtering: low pass, high pass, band pass filters

De-esser mode with narrow band pass filter

Power and Design

Modern power supply with automatic voltage adaptation (95 V-245 V, 50-60 Hz)

DC heating for tubes to reduce noise and enhance warmth

Consistent stereo-link performance via calibration system

Operating temperature: 0-50C (32-122F)

Metering and Calibration

VU meter for input, compression, and output monitoring

Multiple reference levels for precise metering

Physical Dimensions and Weight

Device dimensions: 88 mm (H) x 483 mm (W) x 252 mm (D) / 3.47 in (H) x 18.98 in (W) x 9.92 in (D)

Device weight: 4.4 kg (9.70 lbs)

Box dimensions: 140 mm (H) x 640 mm (W) x 350 mm (D) / 5.51 in (H) x 25.20 in (W) x 13.78 in (D)

Box weight: 6.5 kg (14.33 lbs)

In-the-Box Contents

A4-1B analog compressor

Power cable

USB-C to USB-C cable

Get Started leaflet

Additional Features

Includes one year of Antelope Membership with Synergy Core Native plugins and updates

Optional A4 software suite available via membership plan