The Power Output Amplifier - TANDBERG 12 Service Manual

5.1.7 The power output amplifier
T h e p o w e r o u t p u t a m p l i f i e r i s s h o w n i n f i g . 4 7 . T h e
o u t p u t s t a g e i s a s i n g l e e n d e d p u s h - p u l l a m p l i f i e r
c l a s s B . Q 3 0 l a n d Q 3 0 2 a r e c o n n e c t e d i n c o m m o n
e m i t t e r c o n n e c t i o n a n d d r i v e s t h e i n v e r t e r s t a g e .
The phase inverler stage consists of the .o-[l.m"n-
t a r y t r a n s i s t o r s Q 3 O 3 a n d Q 3 0 4 . T h e q u i e s c e n t c u r _
r e n t o f Q 3 0 5 a n d Q 3 0 6 i s a d i u s r e d b y m e a n s o f R 3 . l 0 .
The center voltage of the iransistors e305 and e306
is adiusted by R305.
T h e t r e b l e a n d b a s s c o n l r o l s a r e o b t a i n e d b v t h e
frequency dependent negative feedback circuit from
t h e o u t p u t o f t h e a m p l i f i e r t o t h e e m i t t e r o f e 3 0 1 .
The poientiometer R4 together with C3O2 forms the
treble control while the potentiometer R5 together
w i t h C 3 0 3 f o r m s t h e b a s s c o n t r o l .
The temperature stabiiizing of the phase inverter
s t a g e Q 3 O 3 a n d Q 3 0 4 a n d t h e o u r p u t s t a g e e 3 0 5
and Q306 is obtained by the NTC resistor (negative
t e m p e r a t u r e c o e f f i c i e n t r e s i s t o r ) R 3 l l . T h e o u t p u t s i g _
nal is fed to the speaker (left channel) via C3Og.
I
I
q
c 3 0 5 *
l 0 0 u R 3 0 8
3 5 V
1 K
R 3 0 t
t 0 K
c 3 0 1
2,5 p
F R O M
V O T U M E
C O N T R O L
3 1 4
200
I
I
R 3 1 7
8 2
+ 2 7 U
C E N T E R C H A N N E T
3p
5W
R 316
(
A A S S
T R E E L E
{
n
I
o 3 0 4
A C 1 2 8
\ N J I U
Q 305
A 0 1 5 0
1 4 v
ffi
) til
o 3 0 6
AD I5O
R 3 1 0 R 3 t 3
28
Fig. 47. The power outpui cmplif ier, schemolic.