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AUDIO BOARD

AUDIO BOARD CIRCUIT

DESCRIPTION

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The audio board receives signals from the receive board, the headset microphone, intercom input and ,auxiliary input, and outputs to the transmit board, the headset earpiece, an external speaker, intercom out and auxiliary out (see block diagram).

Receive Expanders

Audio from the receive board is routed through Jl08, Jl09, JllO and Jlll to U1l2 and U1l3. The gain ofthese devices is controlled by the audio level at the rectifier pins .(4 and' 16). As the level in- creases, so does the gain, and this results in a 2: 1 linear expander characteristic. This complements the processing done in the transmitter. The audio is then buffered and delivered to the remote select switches.

Microphone Amplifier

From the headset connector the microphone signal is amplified by U103. Depending upon which type of microphone is used, S102 is set by the user to dynamic or electret. The electret position provides an 11 dB drop in gain to compensate for the extra output. The amplifier is peak limiting, and responds to either positive or negative peaks ex- ceeding about 1.1 volts in amplitude. Peak detec- tors Q106 and Q107 charge C120 and C121, driving QI05 toward pinchoff. This reduces the gain momentarily until the input signal is reduced. Visual indication of peak limiting is provided by D608 which is driven by U105 when the voltage at pin 6 exceeds half a volt. D 111 (version 3 and later) /isolates the time constant of the amplifier from'that of the LED driver. The latter is much shorter than the former, and causes the LED to extinguish im- mediately upon removing the input signal. On versions 1 and 2 the LED will remain lit for several seconds. VR604 is adjusted by the user for maxi- mum input with minimal limiting. QI04 is used to tum the microphone on and off and is driven by the push-to-talk latch circuit. When SIlO is pressed in and held, the state of Ul16B follows the switch and tums on Q110 and Q111 via D110. This lights D609 and gates on the microphone audio. Releas- ing S110 tums off the microphone.

3-27

U116A does not change state under these condi- tions because C~82 is discharged when the clock is pulsed. If, however, S110 is depressed twice in quick succession, C 182 will be charged for the second clock pulse and this will set U116A. Now the microphone is latched on via D109 and will remain on until S110 is depressed once again, resetting U 116A.

Auxiliary Input Amplifier

Audio from JlOl is attenuated and converted from balanced to single-ended by U101A. U101B, UI02A, Q101, QI02 and QI03 form a peak limit- ing amplifier identical to that described for the microphone above. S 101 not only enables the audio path for the auxiliary input but also lights D607 to half-brilliance to indicate active auxiliary. When peak limiting occurs U 105A shorts out R 120 and D607 is brought to full brilliance.

Intercom Driver

UI07A is configured as an AC current source whose output CUlTent equals the input voltage at C125 divided by the value of R158. Thus the voltage gain is dependent on the value of the load. In this way many such intercom stations can be connected in parallel without each successive sta- tion loading the line. A single load resistor is usually located in the power supply for the wired intercom. On versions 3 and later, U I07B is used to drive the lower end ofTIOl. This section is not a current source and was added to provide more headroom. To this end, U107 is operated from the higher voltage ahead of the regulator. S 104 is a 9 section DIP switch which is used to configure the base for compatability with a specific wired inter- com. S103 functions as either an intercom onloff switch.(Telex, Clearcom standard) or as a channel AlB switch (RTS, Clem'com TW). In the case where the intercom interface is disconnected by S 103, R 186 functions as the load resistor. The full secondary ofTlOl is used for 300 ohm intercoms; the tap is used for 200 ohm systems. On version 2 and later, S 112 allows selection of either low output (100 mY) or high output (800 mY).

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Telex BTR-200 Series manual Receive Expanders, Microphone Amplifier, Auxiliary Input Amplifier, Intercom Driver
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BTR-200 Series specifications

The Telex BTR-200 Series is a well-regarded solution in the realm of wireless intercom systems, widely utilized in broadcast, film, and live event production settings. Renowned for its reliability, user-friendly interface, and robust performance, the BTR-200 Series has become a staple for professionals seeking efficient communication solutions.

One of the standout features of the BTR-200 Series is its frequency agility. The system operates in the UHF band, allowing users to switch frequencies to avoid interference from other wireless devices. This adaptability is crucial in environments where multiple wireless systems operate simultaneously. Users can easily reprogram frequencies to ensure clear and uninterrupted communication among team members.

Another key characteristic of the BTR-200 Series is its impressive range. The systems can provide coverage up to 1,000 feet in line-of-sight applications, making it suitable for large venues. This extensive range ensures that communication remains intact even in expansive settings, such as concert halls or outdoor arenas. Additionally, the enhanced RF performance ensures minimal dropouts, contributing to seamless communication.

The BTR-200 Series also distinguishes itself with its digital circuitry, which enhances audio clarity and reduces noise. This reliance on advanced technology results in crisp communication that is essential for coordinating complex productions. The system also features a low-latency design, which is particularly valuable in live performance settings where timing is crucial.

In terms of user interface, the BTR-200 Series is engineered with simplicity in mind. The beltpack units and base station feature intuitive controls that enable quick adjustments, making them easy to operate even under the pressures of a production environment. Each beltpack supports individual volume control, allowing users to customize their audio experience according to their preference.

Moreover, the BTR-200 Series is built for durability and long-lasting operation. The robust construction of its components ensures reliability, even in challenging environments. Rechargeable batteries offer extended operating time while reducing the need for constant replacements.

In summary, the Telex BTR-200 Series stands out for its frequency agility, extensive range, digital audio clarity, user-friendly interface, and durable build quality. These features combined make it an ideal choice for professionals in the broadcasting and live event production industries, promoting seamless and efficient communication essential for successful operations. The BTR-200 Series remains a trusted solution, proving its worth time and again in various high-pressure scenarios.
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