Abstract: An optical high-impedance preamplifier for processing signals over a large dynamic and automatically operating control range. The automatic control is provided by a variable impedance which is arranged in series with the source circuit of a current-stabilized input MOSFET of the optical preamplifier. As a result thereof, no overloading or loss of sensitivity occurs at a high or low input level.

Abstract: An equalizing network for attenuation/frequency characteristic equalization. The equalizing network comprises a plurality of attenuation branches B.sub.1 to B.sub.8 which are operative in mutually different frequency sub-bands covering a wide frequency band. A negative feedback amplifier 10 has its negative feedback factor set for each frequency sub-band by means of a potentiometer P.sub.1 to P.sub.8 which is part of the relevant attenuation branch. Resistors 17, 18, 19 and 20 form the negative feedback circuit for the amplifier 10 and provide voltage-dividing, to alter the feedback factor and thus the gain of the amplifier 10, for the individual frequency sub-bands as determined by the potentiometer settings. Attenuation branches pertaining to non-adjacent frequency sub-bands are grouped together in two groups X and Y to obviate the need for separation amplifiers for each attenuation branch.