text: the modulating signals k 1 and k 2 , demodulated by a regenerated carrier , are applied to the inputs of two variable - gain amplifiers 3 and 4 via input terminals 1 and 2 . the output 5 of the amplifier 3 is connected via a first deemphasis circuit 6 to the input of an impedance transformer 7 , the output of which is connected to a first input terminal 8 of a modulating signal selection switch 10 . an output 9 of the amplifier 4 is connected via a second deemphasis circuit 11 to the input of a second impedance transformer 12 , the output of which is connected to a second input terminal 13 of the modulating signal selection switch 10 . the two deemphasis circuits 6 and 11 are connected to ground . the loudspeakers 19 and 20 , respectively , are connected to output terminals 15 and 16 of the modulating signal selection switch 10 via further signal processing circuits , for example amplifiers 17 and 18 , respectively . the switch 10 is a four - position change - over switch , the master contacts of which are mechanically coupled in known manner so that , considered from top to bottom in fig1 in the first position the signals on the input terminals 8 and 13 flow , separate from each other , to the loudspeakers 19 and 20 , respectively . in the second position they are mutually supplied from the terminal 8 for the monaural reproduction of a stereophonic signal . in the third position the same connection is provided in order to make the information signal k 1 which , for example , corresponds to the original sound of a film , audible via the two loudspeakers 19 and 20 . in the fourth position the signal k 2 is applied from the terminal 13 to the two loudspeakers , for example for reproduction in a different language . the switch 10 , the master contacts of which are connected to the output terminals 15 and 16 , respectively , is operated by means of an control circuit 21 , which can be adjusted to one of the four positions by means of a rotary knob 22 . the operation of this circuit 21 is shown by the interrupted line 23 to the master contacts of the switch 10 . the control circuit 21 may alternatively be in the form of an electronic drive . for stereo reception , a signal is so applied from the output 24 of the amplifier 4 to the input of the impedance - transformer 7 via a change - over switch 25 that at the point a , the difference between the signals from the output 5 of the amplifier 3 and the signal from the output 24 of the amplifier 4 is formed . simultaneously , the gain must , however , be adjusted . to this end , a connection is made between outputs 27 and 28 of the amplifier 3 by means of a change - over switch 29 in such a way that the gain of amplifier 3 is increased by a factor of 2 . it would of course alternatively be possible to reduce the gain of the amplifier 4 to 0 . 5 in a corresponding manner by means of a change - over switch . the change - over switches 25 and 29 are also adjusted to the required position by the control circuit 21 shown by an interrupted line 30 . obviously , these switches are closed only in the event of stereo reception ; in all the other receiving modes the gain of amplifiers 3 and 4 is not altered and the signals are not dematrixed . the amplifiers 3 and 4 , being cross - wise coupled differential amplifiers , are of such a construction that it is possible to change the gains thereof by applying direct current voltages , respectively , to the control inputs 31 and 32 , respectively . these direct current voltages are supplied by the outputs 33 and 34 of a differential amplifier 36 , the input signal of which is taken from the tap of a potentiometer 37 , which is arranged between the supply source + u and ground . when the position of this tap is changed , the output values of the differential amplifier 36 change in the opposite direction and consequently the gains of the amplifiers 3 and 4 are changed in the opposite sense . by moving the tap on the potentiometer 37 , a mutual match of the amplitudes of the modulating signals k 1 and k 2 applied to the impedance - transformer 7 in the event of stereo reception is possible for a minimum degrese of crosstalk . the amplifiers 3 and 4 have further inputs 37 and 38 , which are interconnected and connected to the output of a direct current amplifier 39 . the input of the amplifier 39 is connected to the tap of a potentiometer 40 , which is arranged between ground and + u . by adjusting the position of this tap , the gain of the amplifiers 3 and 4 can be changed in the equal sense . this enables a setting of the level for the two transmission channels . optionally , adjusting the position of the tap of the potentiometer 40 may alternatively be used for adjusting the volume . fig2 shows another embodiment of the block circuit diagram of fig1 corresponding components having been given the same reference numerals . the change - over switch 10 and the connections to the loudspeakers have been omitted . the output 5 of the amplifier 3 controls a current mirror circuit 41 and the output 9 of the amplifier 4 controls a current mirror circuit 42 . the output of the current mirror circuit 41 is connected to a current node b , which is connected to the input of the impedance transformer 7 . a first output 45 of the current mirror circuit 42 is connected to the input of the impedance transformer 12 . a second output 46 of the current mirror circuit 42 is connected via a switch 43 to the input of a third current mirror circuit 44 , whose output is also connected to the node b and , consequently , to the input of the impedance transformer 7 , a signal corresponding to the difference between the stereo signals 2 ( l + r ) and 2r , i . e . 2l , being then applied to the impedance transformer 7 to which the deemphasis element 6 is connected . the amplifiers 3 and 4 have equal gains , disregarding any small differences which were not fully compensated for by the matching operation ; likewise , the input current - to - output current ratios of the current mirrors 41 , 42 and 44 are usually the same . if , however , stereo sound is received and dematrixing must be effected , the transfer ratio in the current mirror circuit 41 becomes twice as high and the switch 43 is closed , after setting of the control circuit 21 by means of the rotary knob 22 . then the signal k 2 is also transferred to the node b from the output terminal 9 via the current mirror circuits 42 and 44 , the desired dematrixing then taking place . so , in the circuit shown in fig2 the amplifiers 3 and 4 are not changed - over by the said factor of 2 , but the relevant match is effected in the current mirror circuit 41 , which is also used for decoupling the output . furthermore , in the open condition , the switch 43 is not connected to the circuit of the signal k 1 but is only connected between the two current mirror circuits 42 and 44 . this switch may then be included in one of the current mirror circuits , in which a transistor which transfers the signal k 2 is made non - conductive by means of a direct current switching quantity .