biquad alo 3

Biquad Alo 3 Passive Analog Telephone Interface, 3 Lines

The Biquad ALO-3 is a 3-line hybrid telephone interface, rack standard, to be used in radio and TV studios. Has an identical circuit to all the other ALO models and does not require the use of a power supply making it easy to use. Allows the connection up to three listeners simultaneously.

On the telephone line input and also on the audio inputs and outputs has RFI filters avoiding electromagnetic interference. It also has protection against electric discharges from the telephone line that protects the equipment. Can work on conventional telephone lines or PBX extensions with variations between 20 and 50V with a minimum current of 20mA.

Balanced audio inputs and outputs with XLR connectors, isolated by transformers that guarantee high quality and immunity to noises, providing a clear and clean sound. Has audio control gain on the back panel and completely independent hybrid circuits for each listener allowing conference between them through the mix-minus on the audio console.

​The hybrid circuit (transformation from 2 to 4 wires) is totally electronic and active and has an adjustment for echo cancellation that provides isolation around 50dB @ 1KHz.

On the front panel, the equipment has an ON/OFF key that attends the telephone call, a call indicator led that is on while the equipment is functioning, a return volume control to the listener and also an audio output volume control to the mixing console.

Very versatile, ALO 3 is the ideal equipment to be used in transmission and recording studios in order to extract or insert quality audio on the conventional telephone line POTS.

Its case has a high standard finishing with a brushed stainless steel panel.

  • Type: Standard telephone line input;
  • Connector: RJ-11 (6p4) female;
  • Characteristic impedance: 600Ω;
  • It works with voltages between 20 and 50 V of the central power supply (PABX accepted).
  • For the perfect functioning of the equipment, it is desirable that the central supply 50mA of current.
  • ** The minimum working current is 20mA.
  • Type: Telephone line output to connect a conventional telephone device;
  • Connector: RJ-11 (6p4) female;
  • Characteristic impedance: 600 Ω;
  • Mechanically switched output, when the equipment is inoperative the telephone output is an extension of the input. When the equipment starts operating, this output is deactivated.
Audio Input (Return to Listener)
  • Balanced mono type, magnetically isolated by high-quality transformer;
  • Impedance:> 10 kΩ;
  • Connector: XLR Female;
  • Gain Control: the gain adjustment on the rear panel allows input signals from -10 to + 4dBu.
  •  In addition to adjusting the work gain, the equipment provides the front panel with volume adjustment for the listener, which can be adjusted from -∞ to 0dB in relation to the audio input level.
Audio Output
  • Balanced mono type, magnetically isolated by high-quality transformer;
  • Impedance: <150Ω;
  • Connector: XLR Male;
  • Gain Control: -∞ to 0dB. The nominal output level is 0dBu, but it depends on the quality of the telephone connection.
Hybrid Circuit
  • Type: Totally electronic without the use of transformers. The transformation from 2 to 4 wires is done by a specific integrated circuit for this purpose;
  • Echo cancellation: adjustable on the rear panel depends on the electrical characteristics of the telephone line.
  • Protection against lightning strikes that prevents the equipment from burning.
* In the laboratory, the cancellation reached was 56 dB @ 1kHz; ** Good protection of the product is essential for the protection to work properly. Dimensions
  • Padrão rack (L x A x P): 482,0 mm x 44,5 mm x 120 mm;
  • 19” x 1,75” x 4,7” pol.;
  • Weight: 1.4 Kg without packaging;
  • 2.4 Kg with packaging.
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Biquad ALO-3


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2-Year Warranty


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