3. ADVANTAGE AND OPERATION OF
POWER AMPLIFIER CIRCUITRY SECTION
\,
3-1. Advantage
vQThere is neccessity not to decrease the phase response tillcurrent on each stage to increase the through-rate, the
DC range in order to increase the music signal response ofperformance on high frequency range is conspicuously
extremely low frequency range. Therefore, this amplifier isimproved.
employing no capacitors except ones for phase compensa-OTo avoid the voltage deviation, regulated power supply
tion, and has an almost perfect transient characteristics.circuit composed of ZD0'1, ZD02 is employed.
OThe first stage FET(2SK97) is a dual FET of even characteris-
tics and has a large Cm and no-leakage current at normal3-2. Operation
temparature.The use of differential amplification at first stage dual FET,
To avoid the influence by temperature drift, such as center(FET01, FET02) and connection of the FET to the differential
voltage (0V) deviation, this FET is used as differential am-amplif ier composed of TR01, TR02, make possible to obtain
plifier and operates at cross point which is the optimumenough gain and remarkable low distortion.
point of drain current (at about 3mA) against the tempera-The output signals of TR0'1 and TR02 are untiphase.
ture drift.The output signal of TR02 adds to TR05, on the other hand,
QTransistors, TR05 and TR07, the push-pull pre-driver stagethe output phase of TRO1 is inverted byTR03,then, it becomes
functions as current differential amplifier that the stabilizedinput signal of TR04 and TROZwhich are cascoded connection.
operation can be obtained. In addition, the collector cur-The output signals at TR05 and TR07 are inphase that the op-
rent of these transistors is enough high to make linearity
eration of this stage is push-pull drive and current differential
excel lent.amplification. The power amplifier of the f inal stage is
com-
OSince this Amplif ier employs phase advancer circuits [C06,posed of SEPP (Single Ended push-pull) symmetry comple
C08, C15, R29, C16 and R30J, which have not been fre-mentary
\zin 3-stage darlington connection type.
quently used, to compensate the phase characteristics onTR@ and TR10 are composing current limiter circuit
to protect
vhigh frequency range and is also made to have enoughpower transistor from break-down by overload.
4. ADJUSTMENTS
4-1. Driver Circuit Board Adjnstments(See the picture of top view on page 3.)
Note: 1. Master Volume...... ......Minimum3. For adjustment, run the unit for more than 3 minutes after
1. Room Temperature.the power is switched on.
suBfEcr ,or,r"r*,MEASURE OUTPUTADfusr I oolrrr ro*CONDITION
|
DC Volt Meter Speaker TerminalF-2721DC 0V+5mV" Set VR01 and VR02 to center
vR01, vR02oosition.
o Then, for the purpose of pro-
Same as above Same as aboveceeding the accurate adjust-0V+5mVF-2722DC
ment, set the voltaee to 0 volt
VRO1, VRO2
by VR01 first and V-RO2 next.
Same as aboveTP Terminal (+) (-) F-2721DC 20mV+1mVo By turning VR03 counterclock-
ot F-2721VRO3wise, the- bias current is de-
creased gradually.
Same as aboveTP Terminal (+) (-)F-2722DC 20mV+1mV
of F-2723VRO3 |
ACEC
