Muting Monitor Amplifier-2 Watt

Ideal Use Cases

The RDL ST-MA2 is a single-speaker monitor amplifier intended for conferencing and monitoring applications that require local amplification with external level control. It is suited to systems that need adjustable gain, fast muting, or remotely actuated attenuation without changing the primary audio source. Its balanced or unbalanced bridging input provides a 20 kΩ input impedance, while the amplifier output is designed for an 8 Ω speaker and can also drive 4 Ω loads.

Multiple control inputs support applications in which external equipment must mute the monitor or reduce its level by a defined amount. Two independent attenuation inputs provide individually selectable 3 dB and 6 dB steps, making the ST-MA2 useful when a monitoring level must respond to separate control conditions.

Why Choose This Model

The ST-MA2 combines a compact single-speaker amplifier with muting, stepped attenuation, and adjustable gain. It delivers 1.75 watts RMS continuously and up to 2 watts RMS maximum. This output is paired with switching specified at less than 50 microseconds, supporting fast audio transitions without the delay associated with slower control methods.

Muted attenuation exceeds 90 dB at 1 kHz, 85 dB from 300 Hz to 3 kHz, and 75 dB across the 20 Hz to 20 kHz range. These published attenuation levels provide concrete guidance for applications where the monitor signal must be substantially reduced. The two selectable attenuation settings also provide repeatable level changes rather than relying solely on manual gain adjustment.

Installation and Integration

The amplifier accepts a balanced or unbalanced bridging input with a 20 kΩ impedance. Its input level is specified as 10 dBV minimum for 2 watts RMS output. The output impedance is 8 Ω, with support for driving 4 Ω loads, allowing integration with a compatible single-speaker monitoring system.

The 3 dB and 6 dB attenuation settings are controlled through two independent inputs. Each control is activated by connecting it to ground and draws 0.3 mA. This arrangement permits external equipment to actuate either attenuation step as required. The amplifier requires ground-referenced 24 Vdc power at 200 mA for rated output or 220 mA at 2 watts RMS.

The recommended power supplies are the PS-24AS for USA use and the PS-24AX for international use. A power supply is not included. The specified ambient operating range is 0°C to 40°C.

Performance Highlights

The ST-MA2 covers a 45 Hz to 14 kHz bandwidth and has total harmonic distortion plus noise below 0.5%. Common-mode rejection is greater than 60 dB from 50 Hz to 120 Hz, while residual noise is specified below -80 dB relative to 2 watts RMS. Together, these specifications define the amplifier’s operating performance for speech, conferencing, and single-speaker monitoring.

Fast, silent audio switching is a central feature of the design. With a switching time below 50 microseconds, the amplifier can respond rapidly to external control commands. Adjustable gain provides an additional means of matching the monitor output to the connected system, while the fixed attenuation steps provide predictable temporary level reductions.

What Makes It Different

Unlike a basic low-power monitor amplifier, the ST-MA2 integrates multiple control functions into the amplification path. It provides full muting as well as two externally actuated attenuation levels. Because the 3 dB and 6 dB settings use independent inputs, they can be selected separately according to the required control arrangement.

The combination of balanced or unbalanced input compatibility, support for 8 Ω and 4 Ω speaker loads, adjustable gain, and defined attenuation performance gives system designers several integration options. Published CAD files, front and end panel diagrams, a functional block drawing, and a PDF specification sheet are also identified in the source data.

Final Assessment

The RDL ST-MA2 is a focused solution for single-speaker monitoring that requires more control than straightforward amplification. Its 2-watt maximum output, rapid silent switching, strong muted attenuation, adjustable gain, and independently activated 3 dB and 6 dB steps address conferencing and controlled-monitor applications. For systems operating from ground-referenced 24 Vdc power, it provides clearly specified audio, control, and load characteristics in a dedicated monitor-amplifier design.