Abstract: A transimpedance amplifier (18) receives an audio signal from a power audio amplifier (14) and provides a variable power level to a loudspeaker (16). A first variable gain amplifier (28) receives the audio signal and provides a variable gain to a power amplifier (40). The output signal of the power amplifier drives the loudspeaker. A sense amplifier (52) subtracts a voltage representative of current flowing through the loudspeaker from a voltage applied to the loudspeaker and provides a difference signal. A second variable gain amplifier (70) receives the difference signal and provides a variable gain to a load amplifier (80). The gains of the first and second variable gain amplifiers are inversely proportional. A resistive element (84) having a real impedance is coupled between an output of the load amplifier and the input of the transimpedance amplifier to maintain the complex impedance of the loudspeaker at the output of the power audio amplifier.

Abstract: A transimpedance amplifier (18) receives an audio signal from a power audio amplifier (14) and provides a variable power level to a loudspeaker (16). A first variable gain amplifier (28) receives the audio signal and provides a variable gain to a power amplifier (40). The output signal of the power amplifier drives the loudspeaker. A sense amplifier (52) subtracts a voltage representative of current flowing through the loudspeaker from a voltage applied to the loudspeaker and provides a difference signal. A second variable gain amplifier (70) receives the difference signal and provides a variable gain to a load amplifier (80). The gains of the first and second variable gain amplifiers are inversely proportional. A resistive element (84) having a real impedance is coupled between an output of the load amplifier and the input of the transimpedance amplifier to maintain the complex impedance of the loudspeaker at the output of the power audio amplifier.

Abstract: A system for activating a load such as an exhaust fan within an enclosed area concurrently with the activation of a lamp switch and for continuing the operation of the load for a predetermined period of time after the deactivation of the lamp switch. A monitor detects when the lamp switch is activated and provides an output signal representative thereof. A timer is provided which is deactivated when the monitor output signal is present but functions when the lamp switch is deactivated and after a preset but variable time provides a signal for deactivating the load. The timer includes a pulse generator and a counter which receives the output of the pulse generator and counts pulses when the lamp switch is deactivated and provides the deactivation signal for the load when it reaches a predetermined count.

Abstract: The present invention phase coherent crossover incorporates a method and apparatus for providing phase coherent crossover (PCC) signals. The PCC method and apparatus involve the utilizing of an all-pass filter for receiving an input signal and producing an all-pass signal, and a partial-pass filter also receiving the input signal and producing a partial-pass signal at a partial-pass output. The PCC method and apparatus further involve the combining of the partial-pass signal produced by the partial-pass filter with the all-pass signal produced by the all-pass filter to produce an opposite partial-pass signal at an opposite partial-pass output.

Abstract: The functionality of the keypad of a telephone test set is augmented by an interface circuit arrangement which enables keys of the keypad to be used to control both dialing signal generation and prescribed test functions, while effectively preventing interference between the operation of a dialing signal generator, to which the keypad is coupled during a first mode of operation, and that of test function signal generator circuitry, provided exclusive of the dialing signal generator, during a second mode of operation. Additionally, the test set includes a ringing signal coupling circuit for enabling the test set microphone, through which a telephone craftsperson voices audio speech signals to a speech signal processing circuit, to be used to audiblize the ringing signal, without impacting the normal voice input functionality of the microphone and associated speech signal processor.

Abstract: A telephone line test and display circuit for enabling a craftsperson to automatically monitor a plurality of communication aspects of a telephone line without impacting any communications that may be taking place over the telephone line being monitored includes a communication capability detection and indicator unit through which the craftsperson may observe the DC operational state (busy/idle, battery polarity, talk battery present) condition of the line by observing a pair of light emitting diodes. The light emitting diodes are color-coded in accordance with operational status conditions being monitored and are illuminated in either a steady state or flashing condition, depending upon the DC state of the line. Also contained with the test and display circuit is a frequency discriminator/display unit, having a set of light emitting diodes separate from those employed for monitoring the DC operational status of the telephone line.

Abstract: A telephone ringback apparatus includes a microprocessor-controlled communications device which is connectable with telephone equipment contained in a central office, such as a toll trunk facility, having the capability of identifying the number of a calling party. In response to the telephone user dialing a prescribed ringback access code, the apparatus signals the toll trunk facility causing it to transmit a message representative of the number of the telephone from which the user is calling. Upon receipt of this message the telephone number of the calling party is stored. A synthesized voice message is transmitted to the user instructing the user to hang-up. When the apparatus detects that the phone has been placed back on-hook, it proceeds to transmit dialing signals containing the previously stored number of the telephone, causing the calling party's telephone to ring.

Abstract: A telephone light adapter comprised of an electronic control box connected to a standard telephone and light fixture, the adapter energizing the light fixture when the control box is in an automatic mode for announcing an incoming telephone call, the light fixture remaining energized for a specified period of time after the termination of the call. The control box also energizes the light fixture when the telephone receiver is moved from the cradle position for dialing or when an extension telephone is in use. A three-position switch located on the control box permits the selection of mode of operation while a user switch permits manual operation.

Abstract: An improved telephone test set is disclosed which may be operated with low voltage line conditions. Transmitting and receiving voice communication circuits are connected in parallel with leads which are adapted to be connected to the tip and ring lines of a subscriber's telephone line to isolate the voice transmitting and receiving circuits from the voltage drop of a polarity guarding bridge which is connected to the signalling circuits of the telephone test set. A polarity indicating circuit to indicate the direction of current flow between the tip and ring lines of a subscriber's telephone line is connected in series with the voice transmitting and receiving circuits.

Abstract: A three-stage amplifier circuit specially configured to provide a high input impedance. An initial emitter follower transistor stage amplifies the current level of an ac input signal to produce a first intermediate signal, a common-base transistor stage amplifies the voltage level of the first intermediate signal to produce a second intermediate signal, and a final emitter-follower transistor stage amplifies the current level of the second intermediate signal to produce an output signal in phase with the input signal. A feedback circuit feeds back the output signal to the input of the common-base transistor stage, to supplement the first intermediate signal input. This effectively increases the input impedance of the common-base transistor stage and, likewise, the initial emitter follower transistor stage, whereby the amplifier circuit can be used to amplify signals produced by high impedance sources.