Shure A15BT Bridging Transformer Matches Balanced and Unbalanced Levels and Impedences


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Dale #:SHUR-A15BT

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  • The Shure A15BT balanced transformer matches, bridges, or isolates balanced and unbalanced devices of different impedances and levels.

    The A15BT has a 33,000 ohm primary (three-socket) end and either a 7500 ohm or 600 ohm secondary (three-pin) end. Either end can be unbalanced by connecting pins 1 and 3. The A15BT solves problems of matching, bridging, or isolating balanced or unbalanced devices of different impedances and levels. Voltage loss from the 33,000 ohm primary to the 7500 ohm secondary is 6.4 decibels; to the 600 ohm secondary, it is 17.4 decibels.

     To couple a preamplifier, mixer, or recorder with a 600 ohm line output to a device with a high-level, high impedance, unbalanced (Aux) input, connect the 600 ohm output to the 33,000 ohm balanced-line side of the A15BT. Unbalance the A15BT secondary and connect it to the Aux input. Choose either the 7500 ohm or 600 ohm winding, depending on which provides the proper level and best signal-to-noise ratio. In this configuration, the A15BT "bridges" the 600 ohm line output.

  • ImpedanceXLR Pin Connector (M): 7500 ohms or 600 ohms
    XLR Socket Connector (F): 33,000 ohms
    Voltage Ratio7500 ohms600 ohms
    Medium-impedance to
    +6.4 dB+17.4 dB
    High-impedance to
    -6.4 dB-17.4 dB
    Maximum Recommended Input Levels
    Driving Source
    Impedance (ohms)
    Winding Being
    Driven (ohms)
    Level (Volts)
    CaseFull magnetic shield, steel with gray enamel finish
    Dimensions19 mm (3/4 in.) diameter; 89 mm (3 1/2 in.) long
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