Voltage amplifying stages (first stage and predrive stage) are all connected to the cascade for obtaining wide band, and Pc is distributed for improving reality.
NFB is applied at the final stage of voltage amplifying to enable low distortion and high stability at a relatively low level of 40dB.
The input level control employs the metal-grazed volume having attenuation characteristics according to PC-50C of the BTS Code. The input impedance is designed in such a manner as to obtain 25K Ohms at its maximum value, and the required attenuation characteristics and impedance characteristics at a ATT load resistance of 100K Ohms.
Values of Capacitors
Values of Capacitors C101(A) and C201(B) located at the inlet of the driver circuit board are determined with ultra-bass range and shock noise protection in mind when the power switch is on. When the values are small, the peak occurs at low frequency, while when the values are relatively large, rise of TR101 is delayed due to a charging time constant when the power switch is turned on.
The Predrive Stage consists of transistors TR108, TR109(A), TR208, and TR209(B), being cascade connected. Fuse resistance is utilized for emitter resistance when determining gain and input impedance, thereby improving the safety factor of the Predrive Stage.
The Output Stage, which is darlington-connected to the driver, is a triple push-pull complementary OCL system, using the high power transistor of Vceo=200V and Pc Max=150W. The output signal picked up at midpoint between the plus and minus terminals is delivered to the speakers through L101(A) and L201(B).
Power Supply Circuit
The Power Supply transformer uses a toroidal iron core which is half the size and weight of the El type core with the same capacity, thus significantly reducing the size and weight.
Peak Meter Circuit
The use of high brid IC incorporating logarithmic compression, full-wave rectifying and peak detecting functions offers high stability and reliability for the peak meter. The response characteristics conform to DIN Standard; rise by the sue of the meter is -0.5dB at 1kHz for 10msec, and -1dB for 5msec.