Shure A15BT - User Manual

Printed in U.S.A.
©2009 Shure Incorporated
27C1916 (Rev. 5)
The A15BT matches, bridges, or isolates balanced and unbalanced devices of different
impedances and levels.
Impedance: XLR socket (Female), 33,000Ω
XLR plug (Male), 7500Ω, easily converted to 600Ω.
Unbalancing: Either end can be unbalanced by connecting pins 1 and 3.
Voltage difference: From 33,000Ω to 7500Ω, 6.4 dB
From 33,000Ω to 600Ω, 17.4 dB.
MEDIUM-IMPEDANCE SELECTION
As supplied, the A15BT XLR plug is at 7500Ω. To convert to 600Ω, refer to Figure 1 and
proceed as follows:
Remove the three-pin plug element by turning the screw counterclock-wise and 1.
withdrawing the element from the case.
Remove the GREEN lead pin jack from pin 3, and insulate the jack and bare 2.
lead.
Remove the tape from the pin jack on the WHITE lead and push the jack rmly 3.
onto pin 3.
Replace the plug element in the housing and fasten the screw rmly in place 4.
(turn clockwise).
Model A15BT User Guide
BRIDGING TRANSFORMER

Summary

A15 BT Bridging Transformer Features and Configuration

Medium-Impedance Selection

Instructions for converting the A15BT XLR plug from 7500Ω to 600Ω.

Typical Applications of the A15 BT

Connecting 600Ω Output to High-Level Input

How to connect a 600Ω line output to the A15BT's 33,000Ω socket for bridging.

Matching High-Impedance Microphone to Recorder

Unbalancing both ends of A15BT for microphone to recorder connection.

Unbalanced Aux Input to Balanced Low-Impedance Output

Using A15BT to convert a balanced low-impedance device to an unbalanced Aux input.

Balanced 600Ω Line Output for Aux Input Units

Connecting A15BT to an Aux output unit for a balanced 600Ω line output.

A15 BT Specifications and Diagrams

Frequency Response

Details the frequency response of the A15BT from 20 Hz to 20,000 Hz.

Impedance, Voltage Ratio, and Driving Source Levels

Specifies XLR impedance, voltage ratios, and maximum driving source levels.

Case and Dimensions

Describes the physical characteristics including case material and product dimensions.

Connector Wiring Diagram

Illustrates the internal wiring and pin connections for the XLR connectors.

Limited Warranty Information

Overview

The Shure Model A15BT is a versatile bridging transformer designed to facilitate seamless audio connections between devices with varying impedances and levels. Its primary function is to match, bridge, or isolate balanced and unbalanced audio equipment, ensuring optimal signal transfer and compatibility.

The A15BT is engineered to address common audio interfacing challenges, such as connecting a high-impedance microphone to a medium-impedance recorder, or integrating a 600Ω line output with a high-impedance auxiliary input. Its design allows for flexible configuration, making it a valuable tool for audio professionals and enthusiasts alike.

A key feature of the A15BT is its impedance matching capability. The device includes an XLR socket (female) with a 33,000Ω impedance and an XLR plug (male) that can be configured for either 7500Ω or 600Ω. This flexibility allows users to adapt the transformer to a wide range of audio equipment, optimizing signal levels and minimizing potential signal loss or distortion. The ability to switch between 7500Ω and 600Ω on the XLR plug side is particularly useful for interfacing with different types of recording devices or mixers.

The A15BT also offers unbalancing functionality, allowing either end of the transformer to be unbalanced by simply connecting pins 1 and 3. This feature is crucial when connecting balanced outputs to unbalanced inputs, or vice versa, providing greater versatility in system integration.

In terms of voltage difference, the A15BT can accommodate significant variations. When bridging from 33,000Ω to 7500Ω, it provides a 6.4 dB voltage difference. For connections from 33,000Ω to 600Ω, the voltage difference increases to 17.4 dB. These capabilities ensure that signals are appropriately scaled between devices, preventing overloading or under-driving of inputs.

The device's typical applications highlight its utility. For instance, to connect a 600Ω line output from a preamplifier, mixer, or recorder to a high-level, high-impedance, unbalanced (Aux) input, the user would connect the 600Ω output to the 33,000Ω XLR socket of the A15BT. The XLR plug on the A15BT would then be unbalanced and converted to either 7500Ω or 600Ω, depending on the desired level and signal-to-noise ratio, before connecting to the Aux input. In this setup, the A15BT effectively "bridges" the 600Ω line output, ensuring proper signal transfer.

Another common use case involves matching a high-impedance microphone output to a medium-impedance input (approximately 10,000Ω) on a reel-to-reel or cassette recorder. Here, both ends of the A15BT would be unbalanced. The microphone output connects to the 33,000Ω XLR socket, and the 7,500Ω XLR plug connects to the recorder. This configuration ensures that the microphone's signal is appropriately matched to the recorder's input, preserving audio quality.

For scenarios where an unbalanced Aux input needs to accept a balanced low-impedance output, the A15BT again proves invaluable. The 33,000Ω XLR socket on the A15BT is unbalanced and connected to the Aux input. The XLR plug is then converted to 7500Ω or 600Ω and connected to the balanced low-impedance device. This setup allows for seamless integration of different types of audio signals.

Furthermore, when a balanced 600Ω line output is required from a unit with an Aux output, such as the Shure SCM268, the A15BT can be used. The 33,000Ω XLR socket is unbalanced and connected to the Aux output. The A15BT XLR plug then provides a balanced line output at either 600Ω (at approximately a –20 dBm level) or 7500Ω, offering flexibility for various professional audio setups.

Maintenance features for the A15BT are straightforward and user-friendly, particularly for adjusting the medium-impedance selection. As supplied, the A15BT XLR plug is set to 7500Ω. To convert it to 600Ω, users can follow a simple, step-by-step process. First, the three-pin plug element is removed by turning a screw counterclockwise and withdrawing it from the case. Next, the GREEN lead pin jack is removed from pin 3, and both the jack and the bare lead are insulated. Then, the tape is removed from the pin jack on the WHITE lead, and this jack is firmly pushed onto pin 3. Finally, the plug element is replaced in the housing, and the screw is fastened clockwise. This process allows users to easily reconfigure the transformer without requiring specialized tools or extensive technical knowledge, ensuring the device can be adapted to evolving system requirements.

The physical construction of the A15BT also contributes to its reliability and ease of use. It features a full magnetic shield and a steel case with a gray enamel finish, providing durability and protection against electromagnetic interference. Its compact dimensions make it easy to integrate into existing audio setups without occupying excessive space.

In summary, the Shure Model A15BT bridging transformer is a robust and adaptable device designed to simplify complex audio interconnections. Its ability to match impedances, unbalance signals, and handle varying voltage levels, combined with its user-friendly configuration options, makes it an essential component for achieving optimal audio performance across diverse professional and personal audio applications. The straightforward maintenance procedure for impedance selection further enhances its practical utility, allowing users to easily customize its functionality to meet specific needs.

Shure A15BT Specifications