and out of the unit. Additional LED status indicators are also provided, offering a clear view of the 2-wire DC power and auto null functions.
Pro Audio Quality
The Model 46’s audio circuitry was de- signed in the spirit of professional audio equipment, rather than that found in typical party-line intercom gear. High-performance components are used throughout, providing low-distortion, low-noise, and high head- room. Using passive and active filters, the frequency response is limited to approxi- mately 100 Hz to 8 kHz. This range was se- lected to provide excellent performance for human speech, while maximizing the ability of the hybrids to create substantial “nulls.” When the Model 46’s internal DC power sources are selected to provide 2-wire party-line intercom power, enhanced audio performance can also be expected. The quality of the DC supply circuits is excellent, with very little noise, hum, or “hiss” being added to the 2-wire connections. In addi- tion, the impedance characteristics of each interface’s DC powered (“wet”) channels was tailored to be essentially identical to that of the unpowered (“dry”) channel. This unique situation allows the automatic null- ing circuitry to provide excellent, consistent results for both the powered and unpow- ered channels.
Attention to detail is a hallmark of the Model 46’s design. For example, during the brief auto nulling process an interface channel’s 4-wire input and output signal is muted, preventing unwanted audio from reaching the connected equipment. Associated with the 2-wire interfaces is circuitry that, under software control, applies 200 ohm termi- nating impedances to the 2-wire party-line
circuits. This, along with other circuitry that monitors DC voltages present on the
2-wire circuits, ensures that audio instabil- ity associated with unterminated circuits will rarely occur. As previously mentioned the Model 46’s 2-wire DC power sources offer a unique level of performance. Their ability to deliver power while maintaining audio quality is simply unmatched.
Special Applications
While the Model 46 is designed to directly integrate into typical applications, it’s ready to support the “one-in-a-million” situations too. To accomplish this DIP switches, accessible on the back panel, allow some of the automatic features to be disabled. For example, one switch allows the auto-terminate feature to be disabled. While this feature can help maintain audio quality, advanced users might need to dis- able it. This would allow full control over the Model 46’s four hybrid circuits, en- abling them to be used completely inde- pendently. A second DIP switch changes the way in which the front-panel auto null push button switches operate. Normally pressing one of the buttons begins the process of auto nulling both channels associated with an interface. The alter- nate switch mode allows each auto null sequence to be activated independently. One tap of the auto null button will begin the auto null process for interface one. Two taps of the button will begin the auto null process for channel two. For installer- selected applications, three opto-coupled inputs allow selected Model 46 features to be remotely controlled. These features include remote auto nulling for each inter- face and remote “mic kill” activation.
