RDL STMDA3 Microphone Level Distribution Amplifier

Herman # RDLSTMDA3




The STM‑DA3 is designed for use in quality commercial sound, broadcast and recording applications. The 1.2 kΩ balanced input accepts a wide variety of microphone input levels without loading professional low impedance microphones. A multi‑turn trimmer is user adjustable for either gain or loss in order to match the facility standard microphone levels. Three balanced outputs provide nearly total isolation between the output lines. Unlike mic‑splitting transformer systems, the STM‑DA3 also provides audio isolation. In fact, the audio isolation is so good that a +4 dBu signal fed into one output is still below the noise floor on the adjacent output. Loading of one output including a direct short, has no effect on the other outputs.

The STM‑DA3 is built on the electrical architecture of RDL's low‑noise studio quality mic preamplifiers. Dynamic or condenser microphones may be used with the STM‑DA3. Standard 24 V phantom is supplied to the input when the supply voltage is connected to the PHM terminal. Optimum operating level is set using RDL's unique Dual‑LED VU meter, located adjacent to the terminal block. A green LED illuminates at 15 dB below optimum level. The intensity of the green LED progresses from minimum to full intensity over a 15 dB range. The adjacent red LED illuminates when the operating level exceeds the optimum level. This makes the STM‑DA3 easy to set up without any external test equipment, and operating levels may be monitored at the module

For Mic to Line level distribution, use the RDL STM‑LDA3.
  • Feed 1 Microphone to 3 Microphone Inputs
  • Electrical and Audio Isolation
  • Studio Quality Low‑Noise, Low‑Distortion Performance
  • Excellent Phase Response
  • Versatility of STICK‑ON® Compactness


1.2 kΩ balanced

Outputs (3):

‑45 dBu, 150 Ω balanced

Gain Range:

17 dB (Adjustable, 25‑turn trimmer)

Control Fully CCW:

Gain = ‑5 dB

Control Fully CW:

Gain = 12 dB

Frequency Response:

30 Hz to 20 kHz (+/‑ 0.2 dB)


< 0.1%


< 80 dB (below ‑50 dBu output, ‑50 dBu input)


> 20 dB (‑50 dBu output, ‑45 dBu input)


> 60 dB (100 Hz to 5 kHz)

Output Isolation:

> 135 dB (balanced audio)
> 150 dB (common mode)

Power Requirement:

GROUND‑REFERENCED, 24 to 33 Vdc @ 40 mA

Ambient Operating Environment:

0° C to 55° C

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