time an impedance z 2 of the power supply becomes equ3 now assuming that c 1 c 3 c 5 the capacitances are the same we will have equ4 namely this circuit is equivalent to the circuit in which the capacitor c 11 already described in fig1 was increased by 1 5 times due to this the impedance of the power supply from the side of the amplifier a becomes 2 3 thereby enabling the impedance to be likewise reduced by 33 therefore the ac variation component of the collector voltage of the transistor q 1 decreases and the sound quality can be improved in this way the case of the amplification of the half cycle on the positive side has been described above further the half cycle amplification on the negative side will be similarly considered therefore the negative side half cycle amplification is omitted here fig7 shows an example of the applied form of the invention whereby the power supply voltage can be changed over among the n stages in this application a smoothing capacitor c n is connected between an n th order tap t n and an n 1 th order tap t n 1 and in the similar manner as above a capacitor c n 1 is connected between a tap t n 1 and a tap t n 2.