Shure A15BT Bridging Transformer

Medium-Impedance Selection

As supplied, the A15BT XLR plug is at 7500 Ω. To convert to 600 Ω, refer to Figure 1 and proceed as follows:

1. Remove the three-pin plug element by turning the screw counterclockwise and withdrawing the element from the case.
2. Remove the GREEN lead pin jack from pin 3, and insulate the jack and bare lead.
3. Remove the tape from the pin jack on the WHITE lead and push the jack firmly onto pin 3.
4. Replace the plug element in the housing and fasten the screw firmly in place (turn clockwise).

Shure A15BT Bridging Transformer Typical Applications

To connect the 600 line output of a preamplifier, mixer, or recorder to a high-level, high-impedance, unbalanced (Aux) input:

Connect the 600Ω output to the 33,000Ω XLR socket of the A15BT. Unbalance the XLR plug on the Shure A15BT Bridging Transformer and convert it to 7500Ω or 600Ω to provide the proper level and best signal-to-noise ratio. Connect the A15BT to the Aux input. In this configuration, the A15BT “bridges” the 600Ω line output. Refer to the table on the back page for the maximum input level to the A15BT.

To match a high-impedance microphone output to a medium-impedance (approximately 10,000 Ω) input on a reel-to-reel or cassette recorder:

Unbalance both ends of the A15BT. Connect the microphone output to the 33,000 Ω XLR socket. Connect the 7,500 Ω XLR plug to the recorder.

For an unbalanced Aux input to accept a balanced low-impedance output: Unbalance the 33,000 Ω XLR socket on the A15BT and connect it to the Aux input. Convert the XLR plug to 7500 Ω or 600 Ω and connect it to the balanced low-impedance device.

When a balanced 600 line output is needed on a unit with an Aux output (such as the Shure SCM268):

Unbalance the Shure A15BT Bridging Transformer 33,000 Ω XLR socket and connect it to the Aux output. The A15BT XLR plug offers a balanced line output at both 600 Ω (at about a –20 dBm level) and 7500 Ω.