Switched Mic Preamp-35 to 65 dB Gain

The RDL STM-2X is a compact switched microphone preamplifier designed for quiet remote control of a condenser microphone signal. Connecting the switch-control input to ground activates the signal, supporting either a remote toggle switch or a push-to-talk button. Its soft-switching transition takes less than 5 ms when switching on or off. The module accepts a 500 Ω balanced or 5 kΩ unbalanced input, supplies filtered 24 Vdc phantom power, and provides balanced mic-level and line-level outputs.

Ideal Use Cases

The STM-2X is suited to applications requiring remote activation of a condenser microphone without abrupt signal switching. It can be controlled from a toggle switch for maintained operation or a push-to-talk button for momentary activation. The two output formats accommodate equipment requiring either a standard +4 dBu line-level signal or a -45 dBu microphone-level signal. This flexibility makes the module appropriate when a single mic-level source must be switched and amplified for different downstream input requirements.

Why Choose This Model

This model combines remote microphone switching, phantom power, adjustable gain, and two balanced output levels in a compact enclosure. Line-output gain is adjustable from 35 to 65 dB, providing a broad range for bringing a microphone source to the specified +4 dBu line level. The microphone-level output offers an adjustable range from -15 to 15 dB and a specified output level of -45 dBu. Filtered 24 Vdc phantom power is specified according to IEC 61938:2013, allowing the module to support compatible condenser microphones without a separate external phantom-power unit.

Installation and Integration

The STM-2X measures 0.7 inches high, 3 inches wide, and 1.6 inches deep, or 1.7 by 7.6 by 3.9 centimeters. Its input supports either a 500 Ω balanced connection or a 5 kΩ unbalanced connection. Both the mic-level and line-level outputs are balanced and have a specified 150 Ω output impedance. Remote control is implemented by connecting the switch-control input to ground, with a maximum required current of 0.5 mA. The overall power requirement is ground-referenced 24 Vdc at 25 mA, while the phantom-power input is rated at 24 Vdc and 10 mA maximum. Recommended power supplies, which are not included, are the PS-24AS for the USA and PS-24AX for international use. The specified operating environment is 0°C to 55°C.

Performance Highlights

The published frequency response extends from 50 Hz to 30 kHz within ±1.5 dB. At 50 dB gain, THD+N is specified below 0.05%. Residual noise in the on state is below -70 dB relative to +4 dBu when measured with a 150 Ω source at 50 dB gain. The module provides more than 20 dB of headroom and common-mode rejection greater than 50 dB from 50 Hz to 20 kHz. When the signal is switched off, attenuation exceeds 100 dB at 1 kHz and exceeds 80 dB across 50 Hz to 20 kHz. Together with the under-5 ms soft-switching transition, these figures define the module’s behavior in both active and muted states.

What Makes It Different

The defining feature of the STM-2X is its integration of microphone amplification with remotely controlled soft switching. The control interface uses a direct connection to ground rather than requiring a separate command format. A condenser microphone can receive filtered 24 Vdc phantom power while its audio is controlled remotely, and the source can be delivered at either mic or line level. Adjustable gain for both specified output applications provides configuration flexibility without changing the connected source.

Final Assessment

The RDL STM-2X provides a focused solution for remotely switching and amplifying a condenser microphone. Its 35 to 65 dB adjustable line gain, balanced mic and line outputs, filtered phantom power, strong off attenuation, and compact dimensions are all clearly specified. For integration, confirm the required output level, gain setting, control-switch behavior, and appropriate 24 Vdc power supply before installation.