Pioneer GM-4200 Manual de serviço - Página 15

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7. CIRCUIT DESCRIPTION

• Isolator circuit

The differential amplification circuit, which is usually

combined with the operational amplifier and the resist¬

ance network, is arranged to the dedicated 1C.

The ripple removal ratio is further improved than the

conventional differentia! amplification circuit.

• Non-switching circuit type ID

By adding Q429 to Q432, distortion removal capacity is

improved.

• PWM POWER SUPPLY {Voltage detection circuit for

both positive and negative voltage.)

The PWM power supply is a circuit that maintains stable

secondary voltage in a DC-DC converter, regardless of the

voltage fluctuation and load fluctuation of the primary

voltage.

Former PWM power supply detected and controlled only

positive voltage of DC-DC converter. New PWM power

supply increases output in the lower range through detect¬

ing and controlling both positive and nagative voltages

and it creates a higher fidelity sound.

{Manufacture the current mirror using Q114andQ115, and

input —VH into the pin 16 of IC101 through Q116. 4-VH is

input through Q117. R131 toR134are the voltage dividers.)

• Troidal transformer and others

To improve efficiency and to delete the leakage flux, the.

"doughnut" type transformar is adopted. And corre¬

sponding to current increment, two fuse, choke coil paral¬

lel combinations. (L101, L102)

• DC servo

To reduce the DC component appeared in the output, DC is

fed back by means of IC201 and IC202. This circuit

performs the low-pass feed back of less than 200Hz simul¬

taneously.

• In this unit, the mode selecting circuit was simplified in the following manners.

phase

as (-).(For the speakers,left

and right channels are of the

same phase.)

Fig. 4

Figure shows the case of UC, EW carries out ® and (D on the

right channel.

For the above two reasons, a signal selector switch was

eliminated.

When you make a test, take care not to short-circuit

(OUTPUT) and (GND). Especially when you measure two

channels at the same time, a great care must be taken

because short-circuit is susceptible to take place at the

measuring instrument.