Abstract: A comparator circuit and voltage level detector comprising such comparator circuit including a first operational amplifier having a differential input, first and second voltage dividers being coupled to, respectively, a variable and a constant voltage source, outputs thereof being coupled to the differential input for supplying a differential input voltage thereto. The first operational amplifier having an output being coupled to its differential input and providing an output voltage stepwise varying between first and second voltage levels at an inversion of the differential input voltage. In order to lower power consumption and increase the accuracy of level detection, one of the first and second voltage dividers is being provided with a stepwise variable voltage dividing factor, which is controlled by the output voltage of the first operational amplifier to increase the magnitude of the differential input voltage by a step value upon such inversion of the differential input voltage.

Abstract: A car radio with an electronic anti-theft device, which device includes circuitry for electrically detecting the removal of the car radio from its build-in recess, and by which the function of the car radio is blocked as long as the anti-theft device is not deactivated after the removal. A simple arrangement with a highly reliable mode of operation is obtained in that the circuitry for electrically detecting the removal of the car radio includes a monitoring circuit, by which the presence of a connection from the car radio to at least one loudspeaker is monitored continuously, and by which the anti-theft device is activated immediately after the interruption of this connection.

Abstract: A circuit arrangement for transmitting audio signals includes a signal amplifier having four power amplifiers each with an input and an output, a first and a third one of the four power amplifiers are non-inverting for applied audio signals, and a second and a fourth one of the four power amplifiers are inverting, the inputs of the first and second power amplifiers receiving a first audio signal and the inputs of the third and fourth power amplifiers receiving a second audio signal. In a first configuration mode for audio signals of low amplitude, the first and fourth power amplifiers each form a single-ended amplifier and the outputs of the second and/or the third power amplifier carry a reference potential. In a second configuration mode for audio signals of higher amplitude, the first and second power amplifiers form a first bridge amplifier, and the third and fourth power amplifiers form a second bridge amplifier.

Abstract: A signal amplifier includes four amplifier stages which can be arranged in two different configuration modes, a first configuration mode in which a series arrangement of two loads is arranged between output terminals of a first and a third one of the amplifier stages, a reference potential being applied to a node between the loads, a first signal to be amplified being applied to an input of the first amplifier stage, and a second signal to be amplified being applied to an input of the third amplifier stage, and a second configuration mode in which a first one of the loads is arranged between the output terminal of the first amplifier stage and an output terminal of a second amplifier stage, and a second one of the loads is arranged between the output terminal of the third amplifier stage and an output terminal of a fourth amplifier stage, and the first signal to be amplified being applied to an input of the first amplifier stage and an input of the second amplifier stage and the second signal to be amplified

Abstract: An amplifier for sound signals is made up of an even number of power amplifiers each of which have each an output, wherein each amplifier output can be switched to a first terminal of an associated loudspeaker and in which the second terminals of the loudspeakers can be switched to an output of a buffer amplifier. In order to minimize power losses, the buffer amplifier supplies at its output a DC voltage which is about half the value of the supply voltage of the power amplifiers. In addition, half the power amplifiers supply an output signal that is inverted relative to their input signal.

Abstract: The invention relates to a fading arrangement in electrical reproduction apparatus, for fading the signals supplied to two reproduction units by a signal source, comprising a variable resistor whose resistance track co-operates with wiper means which, when moved along said track, connect a fading resistance which decreases from the maximum value to the minimum value in series with one reproduction unit and a fading resistance which increases from the minimum value to the maximum value in series with the other reproduction unit. Additional variable resistors (R.sub.Z) are arranged in parallel with the reproduction units (R.sub.L1, R.sub.i1 +R.sub.L1 ; R.sub.L2, R.sub.i2 +R.sub.L2). During the common movement of all the wiper means the additional wiper means vary the resistance values of the additional resistors (R.sub.2, 100 R.sub.2) oppositely, in such a way that the resistance value of the additional resistor (R.sub.