Highly stable constant-voltage power source device

An audio device including:

• at least one active circuit to be driven at a constant voltage and provided with a signal path for passing an audio signal whose highest frequency is higher than the maximum audible frequency, the current necessary for driving the active circuit being dependent on the level of the audio signal;
• a first constant voltage power source device for said active circuit having a low impedance characteristic and a high noise elimination ratio for a wide frequency range, said constant voltage power source device further comprising:
• a pair of input terminals supplied with an unregulated D.C. input voltage derived from an A.C. power source;
• a pair of output terminals connected to the active circuit;
• a power supply line for connecting one of the input terminals to one of the output terminals;
• a ground line for connecting the other of the input terminals to the other of the output terminals;
• a constant-current circuit provided in the power supply line for providing a constant output current;
• and
• a constant voltage circuit connected between the power supply line and the ground line in parallel with the active circuit and having the single input terminal coupled to the power supply line;
• the constant output current of the constant-current circuit being greater than the maximum current necessary for driving the active circuit;
• the constant-voltage circuit (i) increasing the current flowing therethrough as the current necessary for driving the active circuit decreases, and (ii) decreasing the current flowing therethrough as the current necessary for driving the active circuit increases, whereby a highly stable output voltage is applied to the active circuit.