Studio Technologies MODEL-41
Line Level Audio to IFB Circuit Interface


The Model 41 is designed to create broadcast-standard IFB circuits from line-level audio sources. The unit's primary application is to interface analog outputs associated with digital matrix intercom systems with broadcast IFB user devices. The Model 41 provides four independent IFB circuits. Each IFB circuit provides DC power and two analog audio signals to support the connected IFB user devices. The Model 41's audio quality is excellent; little hiss, hum, or other artifacts are present. To ensure optimal operation, the unit provides resources for visually and audibly monitoring the audio output signals. In addition, the DC output voltage is monitored for over-current and short circuit conditions.

Installation of the Model 41 is very simple. Audio input connections are made using a 25-pin D-subminiature connector. The IFB output circuits interface using standard 3-pin XLR-type connectors. The compact, one-rack-space package is constructed using heavy-gauge steel components. The unit's mains power input can range from 100 to 230 volts, 50/60 hertz. This "universal input" ensures correct operation virtually anywhere in the world.

To help confirm proper installation and ensure correct operation, the Model 41 includes a full-featured audio monitor section. Two 5-segment LED meters provide an indication of the audio levels as they appear directly on the IFB output connectors. This capability makes it simple to adjust and maintain correct audio levels so that optimal IFB performance can be maintained. A headphone output is also provided, allowing "real world" checking of IFB audio quality. In addition to being able to manually select the IFB circuit to be monitored by the meters and headphone output, an "auto scan" mode is also included. This allows each of the four IFB circuits to be monitored in a continuously repeating sequence.

The Model 41 is compatible with virtually every digital matrix intercom system, including those from Clear-Com®, Drake, Telex®/RTS®, and Riedel®. Interfacing requires only the connection of analog output ports from the intercom system to the Model 41's audio inputs. Optimal performance might be gained by configuring the nominal audio level of the intercom system's "virtual" IFB output ports to match the Model 41's +4 dBu input level. With the Model 41's excellent audio and power delivery performance it’s an ideal alternative to the interface devices offered by the intercom system vendors. Using the Model 41 the intercom system's audio quality can be maintained all the way to the IFB users.


  • Transformer-coupled inputs
  • Excellent audio quality
  • Superior power-feed performance
  • Four independent IFB circuits
  • Single rack-space mounting
  • Universal mains input powering


General Audio:
Frequency Response:
Pin 2 Outputs (DC with Channel 1 Audio): 20 Hz-20 kHz ±2.5 dB (80 Hz-20 kHz ±0.25 dB)
Pin 3 Outputs (Channel 2 Audio): 20 Hz-20 kHz ±0.25 dB
Distortion (THD+N): 0.01%, measured at 1 kHz, +4 dBu, pin 2 outputs (DC with channel 1 audio)
S/N Ratio: 80 dB, ref +4 dBu out, 20 Hz-20 kHz, pin 2 outputs (DC with channel 1 audio)
Crosstalk: 81 dB, typical, ref +4 dBu in, 20 Hz-20 kHz

Audio Inputs: 8, organized as four 2-channel inputs
Type: transformer balanced, capacitor coupled, compatible with balanced or unbalanced sources
Impedance: 10 k ohms, nominal
Nominal Level: +4 dBu

IFB Circuits: 4
Type: DC power with two channels of unbalanced audio
Connections: common on pin 1, DC (+30 V nominal) modulated with channel 1 audio (–10 dBu nominal) on pin 2, and channel 2 audio (–10 dBu nominal) on pin 3
Maximum Audio Output Level:
  Pin 2: +9 dBu with +23 dBu on audio input
  Pin 3: +14 dBu with +28 dBu on audio input
DC Current Output: 200 mA maximum

Monitor Section – Headphone Output:
Type: 2-channel (stereo), drives headphones by way of 100 ohm series resistors
Compatibility: intended for connection to headphones with impedance of 100 ohms or greater
Maximum Voltage: 8 Vpp, 100 ohm load

Monitor Section – Output Voltage Detection: measures DC voltage level directly on pin 2 of IFB circuit output connectors. Status LEDs flash when level is less than approximately 24 volts DC.

Audio Inputs: 25-pin D-subminiature female, 4-40 threads
IFB Outputs: 3-pin male XLR-type
Headphone Output: ¼-inch 3-conductor phone jack
AC Mains: 3-blade, IEC 320 C14-compatible (mates with IEC 320 C13)

AC Mains Requirement: 100-230 volts, 50/60 Hz, 0.7 A maximum @ 100 volts, 0.4 A maximum @ 230 volts

Dimensions (Overall):
19.00 inches wide (48.3 cm)
1.72 inches high (4.4 cm)
9.58 inches deep (24.3 cm)

Mounting: one space in a standard 19-inch rack

Weight: 6.6 pounds (3.0 kg)

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