Digitally Controlled 2 Channel Audio Attenuator

The RDL RU-VCA2A is a digitally controlled, two-channel audio attenuator designed for precise local or remote control of mono and stereo line-level signals. It provides a 96 dB attenuation range in accurate 0.5 dB steps, with noiseless zero-crossing adjustments and close level tracking between channels. Balanced or unbalanced inputs and outputs, several control methods, adjustable ramp rates, and MASTER/SLAVE expansion make it adaptable to a wide range of audio control systems.

Ideal Use Cases

The RU-VCA2A is suited to systems that require repeatable volume adjustment from the equipment location, a remote control point, or multiple remote locations. Its two channels can control a stereo source together or provide attenuation for mono applications. It is particularly useful when an installation calls for pushbutton operation, momentary control pulses from an external device or rotary encoder, or level control through a 0 to 10 Vdc signal or remote 10 kΩ linear-taper potentiometer.

Its data-bus and MASTER/SLAVE capabilities also make the module appropriate for installations where one controller must adjust multiple RU-VCA2A or RU-VCA6A modules. The dedicated EQ RAMP output supports integration with the RDL ST-LEQ1 Loudness Equalizer.

Why Choose This Model

The RU-VCA2A combines broad attenuation range with fine control resolution. Its 96 dB range is divided into 0.5 dB steps, allowing measured adjustments without coarse changes in level. Zero-crossing adjustment steps provide noiseless operation, while precise tracking keeps the two audio channels aligned during stereo attenuation.

Selectable power-up behavior can return the module to either a PRESET level or the LAST level used. This gives the installer control over how the audio system behaves after power is restored. A front-panel display uses eight LEDs to show relative audio level, with separate green MAX and red MIN indicators.

Installation and Integration

Two line-level inputs accept balanced bridging connections above 10 kΩ or unbalanced connections. The two 150 Ω balanced audio outputs may also be connected unbalanced. The module operates from 24 Vdc at 120 mA with a ground-referenced supply. Recommended power supplies are the PS-24AS for the USA and PS-24AX for international use; the power supply is not included.

Control can be configured for internal or external pushbuttons, external momentary pulses, a rotary encoder, 0 to 10 Vdc, or a 10 kΩ potentiometer. In momentary mode, holding an UP or DOWN control automatically ramps the level. A pulse shorter than 0.5 second changes the level by one step. Following a 0.5-second delay, the UP and DOWN ramp times can each be adjusted independently on the front panel from 3 to 10 seconds.

In 0 to 10 Vdc mode, the PRESET function is disabled. A single remote control location can be implemented with a 10 kΩ linear-taper potentiometer. The ground-referenced RAMP output can operate the level display on RDL remote controls, but it is not intended to drive additional VCA 0-to-10 V inputs. EXTERNAL CONTROL DATA jacks support MASTER/SLAVE expansion.

Performance Highlights

The audio path covers 10 Hz to 50 kHz within ±0.5 dB. THD+N is below 0.005% from 20 Hz to 20 kHz, while headroom exceeds 18 dB above +4 dBu. Residual noise is below -90 dB when referred to +4 dBu at unity gain. Common-mode rejection is greater than 65 dB from 50 to 150 Hz.

These specifications are paired with balanced or unbalanced signal compatibility, two independently tracked channels, fine digital steps, and selectable ramp behavior. The module is rated for operation in ambient temperatures from 0°C to 50°C.

What Makes It Different

The RU-VCA2A brings multiple control approaches into one compact module. It can respond to front-panel controls, remote pushbuttons, momentary control pulses, a rotary encoder, analog dc control, or a potentiometer. It can retain the last setting, return to a selected preset after power-up, or serve as the MASTER for additional compatible modules.

Separate RAMP and EQ RAMP outputs further distinguish its integration capabilities. The RAMP output supports remote level indication, while the EQ RAMP output has a dc taper intended specifically for the RDL ST-LEQ1. The enclosure measures 5.75 inches wide by 1.65 inches high by 3.54 inches deep, or 3.9 inches deep with connectors.

Final Assessment

The RDL RU-VCA2A is a focused solution for two-channel line-level attenuation where control precision, flexible remote operation, and system expansion are required. Its 96 dB range, 0.5 dB resolution, zero-crossing adjustment, adjustable UP and DOWN ramps, balanced or unbalanced connectivity, and selectable MASTER/SLAVE operation provide a versatile control platform without adding unsupported processing functions.