Northern Airborne Technology 247 - Manual (Page 4)

Model 247 Audio Mixing Amplifier
SM247 Installation and Operation Manual
Section 1 Rev: 1.00 Issue 2 Page 1-1
ENG-FORM: 800-0115.DOT
CONFIDENTIAL AND PROPRIETARY TO NORTHERN AIRBORNE TECHNOLOGY LTD.
Section 1 Description
1.1 Introduction
Information in this section consists of product description, design features and specifications for the
Model 247 Audio Mixing Amplifier. The Model 247-001 is also included in this manual – any other
derivative product information shall be contained in the applicable manual supplement, which may be
obtained from Northern Airborne Technology Ltd. as required.
Review all notes, warnings and cautions.
1.2 Product Description
The Model 247 Audio Mixing Amplifier contains three electrically independent audio mixing circuits with
four input channels and one output channel each.
The Model 247 is designed for use as a multipurpose mixing amplifier for mixing Aural Warning, Cockpit
Voice Recorder or virtually any aircraft audio signals. Each input is adjustable to accept 0.25 Vrms
microphone input signals, headphone audio signals from a standard aircraft audio system, or receiver
input signals up to 50 mW. Mic bias for each input channel is user selectable. Access for gain
adjustment and mic bias selection is made by cover removal.
Outputs from the Model 247 are designed to drive any impedance from 8 ohms up to 10K ohms. Output
power is limited by 100 ohm resistors on each output. If additional inputs are needed beyond the four
inputs provided for each mixing circuit, an output from one mixer circuit can be fed to the input of another
mixer thereby increasing the size of the mixer. The Model 247 can also drive headsets for headset
amplifier applications.
The Model 247 gain is established at a maximum of 12 dB with the bias/ground jumpers installed.
However, for input signals which do not require DC BIAS or a 600 ohm input impedance, the bias/ ground
jumper for a given input can be removed which will result in an additional 6 dB gain increase (doubling of
the gain).
1.3 Design Features
The Model 247 standard configuration is designed for driving non-DC biased (ground referenced) loads.
The Model 247-001 includes bi-polar output capacitors for compatibility with DC biased loads such as DC
biased microphone inputs to other equipment.
1.4 Specifications
1.4.1 Electrical Specifications
Power Supply: 28 VDC at 150 mA maximum (each circuit).
Maximum current (3 mixer circuits combined) = 450 mA
Input impedance: 600
Ω (15KΩ with gnd/bias jumper removed)