High Gain Mic Preamp-35 to 75 dB Gain

Ideal Use Cases

The RDL STM-3 is designed for applications that require a low-noise microphone signal to be raised to line level. Its input accommodates either a 500 Ω balanced microphone connection or a 5 kΩ unbalanced connection, while its two outputs support +4 dBu balanced and -10 dBV unbalanced equipment. This combination makes the preamp suitable for integrating microphones with different input and output formats. Filtered 24 Vdc phantom capability supports microphones that require phantom power, and RF-filtered inputs help limit radio-frequency interference at the input stage. Adjustable gain provides the flexibility needed for microphone sources requiring substantial amplification.

Why Choose This Model

The STM-3 combines adjustable 45 to 75 dB gain with two balanced or unbalanced outputs in a compact module. It is particularly useful when one microphone input must feed two line-level outputs or when balanced and unbalanced equipment must be accommodated within the same signal path. Output formats include +4 dBu at 150 Ω for balanced connections and -10 dBV for unbalanced connections. The published performance includes a 50 Hz to 30 kHz frequency response, low residual noise, and less than 0.05% THD+N at 50 dB gain. These specifications provide concrete guidance for matching the module to a system’s signal-level and performance requirements.

Installation and Integration

The module measures 0.7 inches high, 3 inches wide, and 1.6 inches deep, allowing it to fit where installation space is limited. Its power requirement is ground-referenced 24 Vdc at 25 mA. Recommended power supplies, which are not included, are the PS-24AS for the USA and PS-24AX for international use. The phantom power input is rated at 24 Vdc and 10 mA maximum. Before integration, confirm the required input format, output level, impedance, and power arrangement. The STM-3 supports both balanced and unbalanced signal paths, but each connection should be matched to the associated microphone and line-level equipment. Its specified ambient operating range is 0° C to 55° C.

Performance Highlights

Gain is adjustable from 45 to 75 dB, giving the STM-3 substantial amplification capability for microphone-level sources. Frequency response extends from 50 Hz to 30 kHz within ±1.5 dB. At 50 dB gain, total harmonic distortion plus noise is specified at less than 0.05%. Common-mode rejection ratio is greater than 50 dB from 50 Hz to 20 kHz. Residual noise is specified below -70 dB relative to +4 dBu when measured with a 150 Ω source. Headroom is greater than 20 dB with a 24 Vdc supply; the published specification also lists 14 dB with a 12 Vdc supply. Together, these figures define the module’s gain range, bandwidth, noise, rejection, distortion, and level-handling performance.

What Makes It Different

The STM-3 brings several signal-interface functions together in one compact preamp. It accepts high- or low-impedance microphone inputs, converts microphone input to line-level output, and provides two output connections that can be used in balanced or unbalanced systems. Its phantom capability is filtered and specified at 24 Vdc in accordance with IEC 61938:2013. RF-filtered inputs add another defined layer of input filtering. Rather than limiting integration to one nominal connection standard, the module supports a 500 Ω balanced input, a 5 kΩ unbalanced input, +4 dBu balanced outputs, and -10 dBV unbalanced outputs. Adjustable output levels further support system matching.

Final Assessment

The RDL STM-3 is a focused microphone-to-line preamp for systems requiring high gain, multiple output formats, phantom capability, and compact dimensions. Its adjustable 45 to 75 dB gain range is supported by detailed specifications for frequency response, THD+N, CMRR, residual noise, and headroom. Two balanced or unbalanced outputs expand connection options, while the balanced and unbalanced input choices accommodate different microphone interfaces. The unit ships in a cardboard box measuring 2 by 2 by 4 inches, with a listed shipping weight of 0.195 pounds. For installations that match its 24 Vdc power requirement and specified signal formats, the STM-3 provides a clearly documented set of microphone preamplification and signal-conversion capabilities.