Microphone Preamplifier-50 dB Gain

The RDL STM-1 is a compact, high-quality microphone preamplifier designed for commercial sound and broadcast applications. It provides 50 dB nominal gain, filtered 24 Vdc phantom power, and two output formats for connection to balanced professional equipment or unbalanced audio devices. Its specified 50 Hz to 30 kHz frequency response, low distortion, and compact format make it a focused solution for integrating a microphone into a fixed audio system.

Ideal Use Cases

The STM-1 is suited to commercial sound systems and broadcast installations that require microphone-level signals to be raised to standard output levels. Its 500 Ω balanced and 5 kΩ unbalanced input specifications support balanced or unbalanced microphone connections. The two outputs provide a +4 dBu, 150 Ω balanced signal and a -10 dBv unbalanced signal, accommodating professional balanced equipment as well as devices using an unbalanced input level.

Filtered 24 Vdc phantom power also makes the preamplifier appropriate for microphone installations that require phantom power. The published phantom specification references IEC 61938:2013.

Why Choose This Model

The STM-1 concentrates its functionality on a clearly defined task: providing 50 dB nominal microphone gain with balanced and unbalanced connection options. This makes it useful when an installation calls for a compact preamplifier without additional processing features. The two output formats allow the model to serve systems operating at either +4 dBu balanced or -10 dBv unbalanced levels.

Its electrical performance is documented with a THD+N specification below 0.05%, common-mode rejection greater than 50 dB from 50 Hz to 20 kHz, and residual noise below -70 dB relative to +4 dBu with a 150 Ω source at 50 dB gain. These stated values give system designers concrete criteria for evaluating the preamplifier within a signal chain.

Installation and Integration

The STM-1 requires a ground-referenced 24 Vdc power source rated at 25 mA. The recommended power supplies are the PS-24AS for the USA and PS-24AX for international use; the power supply is not included. Its phantom power input specification is 24 Vdc at 10 mA maximum.

For signal integration, installers can use the 500 Ω balanced or 5 kΩ unbalanced input configuration and route the preamplified signal through either of the two specified outputs. The ambient operating range is 0°C to 55°C. Engineering resources listed for the product include an engineering functional block CAD file and front and end panel diagrams in American DXF format. A PDF specification sheet and high-resolution TIF images are also identified in the source data.

Performance Highlights

The nominal gain is 50 dB, while the frequency response extends from 50 Hz to 30 kHz within ±1.5 dB. THD+N is specified at less than 0.05%, and CMRR is greater than 50 dB across 50 Hz to 20 kHz. Residual noise is rated below -70 dB relative to +4 dBu when measured with a 150 Ω source at 50 dB gain.

Headroom is specified at greater than 20 dB with a 24 Vdc supply. A separate published figure states greater than 14 dB with a 12 Vdc supply, although the listed power requirement for the STM-1 is ground-referenced 24 Vdc at 25 mA. Together, these specifications define the model’s gain, bandwidth, noise, rejection, distortion, and signal-level capabilities without relying on unspecified performance claims.

What Makes It Different

The STM-1 combines microphone amplification, filtered 24 Vdc phantom power, and both professional balanced and unbalanced output levels in a compact unit. Instead of limiting integration to one output standard, it provides +4 dBu balanced and -10 dBv unbalanced connections. Its input specifications likewise cover balanced and unbalanced arrangements.

The product data also includes practical logistics information: a cardboard box package measuring 2 x 2 x 4 inches, a WEEE weight of 0.145 pounds, and a shipping weight of 0.195 pounds. These are packaging and shipping specifications rather than chassis dimensions.

Final Assessment

The RDL STM-1 is a purpose-built choice for commercial sound or broadcast systems requiring a compact microphone preamplifier with 50 dB nominal gain. Its balanced and unbalanced input support, dual output formats, filtered 24 Vdc phantom power, and published performance measurements make its role in an installed signal chain straightforward to evaluate. Buyers should plan for a separate compatible 24 Vdc power supply, using the recommended regional model where appropriate.