reception complementary rfi distortion signals are formed in the collectors of transistors 16 and 18 to produce out of phase signals at junction 30 resulting in a cancellation of the rfi signal and its induced distortion by virtue of this operation of transistors 16 and 18 normal audio signals are summed directly to produce twice the collector output while rfi induced distortion is substantially cancelled further coil 12 and capacitor 14 form an improved rfi filter with the capacitor being deployed across the base to the emitter junctions of transistors 16 and 18 in the normal frequency range capacitor 14 has no appreciable ac voltage across it capacitor 14 is designed to become operative only in the rf frequency range at which time it forms an rf signal shunt into equalization network 34 fig2 is illustrative of a detailed preamplifier circuit incorporating the above inventive aspects described with respect to the general circuit diagram of fig1 the circuit of this figure includes those components previously described for the circuit of fig1 which are numbered correspondingly the circuit for operational amplifier 32 is enclosed within the broken line box indicated by the reference numeral 32 the equalization network includes resistors 36 capacitors 38 and rheostat 40 which serves as a gain adjustment switch 42 which also forms a part of the equalization network serves to change the preamplifier frequency response and is of common usage in the art transistors 16 and 18 complement one another to cancel rfi induced distortion as previously explained for fig1 rfi filter components 12 and 14 operate functionally similar as in the previously described circuit of fig1.