Radio Design Labs STM-1 Stick-On Microphone Preamplifier

The Radio Design Labs STM-1 Stick-On Microphone Preamplifier is a compact professional audio preamplifier designed to convert microphone-level signals to standard line-level signals in commercial sound, broadcast, recording, intercom, and installed AV systems. Its fixed 50 dB gain provides consistent amplification without requiring front-panel adjustment, making it particularly suitable for applications where predictable signal levels and straightforward installation are important. The compact STICK-ON format allows the unit to be mounted directly to equipment or surfaces using the supplied adhesive system, while optional mounting accessories provide additional installation flexibility.

The STM-1 accommodates both balanced and unbalanced microphone sources, with a 500 Ω balanced input and 5 kΩ unbalanced input. It provides two output paths, including a +4 dBu nominal 150 Ω balanced output and a -10 dBV nominal unbalanced output, allowing the preamplifier to interface with a wide range of professional and consumer-level line inputs. The circuit incorporates RF filtering on the inputs and outputs, while its low distortion and low residual-noise characteristics support clean signal transmission in demanding audio environments.

The STM-1 also provides phantom-power capability for compatible condenser microphones. Phantom voltage is specified at 24 V DC and is internally filtered, while the unit can operate from a 24 V DC supply and can tolerate lower supply voltages with reduced headroom and phantom voltage. At a nominal 24 V DC supply, the preamplifier provides more than 20 dB of headroom, while operation from 12 V DC provides more than 14 dB of headroom. This flexible power arrangement makes the unit suitable for integration into distributed audio systems and other installations where available DC power may vary.

Designed for continuous-duty professional AV operation, the STM-1 combines a small physical footprint with performance characteristics suitable for permanent installations and specialized signal-conditioning applications. Its fixed-gain architecture, dual output capability, phantom-power support, and compact mounting format make it useful for microphone feeds, paging systems, broadcast facilities, recording installations, intercom systems, and other applications where a microphone signal must be reliably elevated to line level without occupying conventional rack space.