Page 1
(9
(2
5107
0201 0202 Q203 0204
110
010
Attenuafor
(l - (-
Differential -
(3
,
Amp
08102
Bias
(4)
Constant Current Circuit
Input Jack
0
Short Circuit
P t
t
Overheat Protector
DC Pr rector
(8)
NFB Circuit
Output Tarminal
0205 0206 0207 0208
0109
PNP Darlington Power Amp
SUMMARY OF CIRCUITRY
The input is fed, via an attenuator, to
the gate of the first stage dual FET
differential amplifier (3). The diode
connected between the two gates is the
protective circuit for input overloads
(1).
The NFB signal (8) is applied to the
gate shown. The dual FET differential
amplifier functions under ideal condi-
tions due to the connection of the
constant current supply (4) to the
common source.
The current is reversed in the current
mirror circuit (2), driving Q110 in the
cascade amplifier (5) and 0108, which
DA-80
form the push-pull configuration, at
constant current. A pair of transistors
with common bases and symmetrical
emitters are enclosed to the same can
in the current mirror circuit. This en-
sures that the current flowing in each
transistor is the same, independent of
the ambient temperature. Q110 and
Q108 are cascade connected, consisting
of transistors with extremely good high
frequency characteristics and equiva-
lent characteristics.
The bias circuit (6) gives the optimum
bias as set by VR102, passes through
the short-circuit protector (7), then
through Q107, 0109, the drive-stage
transistors for the Darlington power
amplifier (9) (10), then to the power
transistors Q201
-
Q204, and Q205
0208, of the Darlington-connected
power output stage. The configuration
adopted for the Darlington power am-
plifier has NPN (9) and PNP (10) tran-
sistors in a fully complementary single-
ended push-pull class A output stage.
The circuitry has ample stability for
class A DC amplifier operation, with
all possible circuit elements that could
cause degradation of sound quality
eliminated.
AID
Current Mirror
(2)
Attenuator
Overload Protector
Input Jack
-
Differential
Amp
0
NPN Darlington Power Amp
(51
(9
0107
0110
0201
0202
.0
fibs
V
0108
Short Circuit
Ef
Protector
Output Tarminal
(7)
0
VRI02
0)
Bias
0203
0209
Cir
0109
0 0
PNP
Darlington Pow r Amp
v-ž_
Constant Current Circuit
(8I
Overheatt Protector
Transformer
DC Protector
,--0
0-
G
DC Power Supply
+V
n
,308)
Vcf1(
30V)
DC Power Supply
C
+V
"
+40V)
(
Vr
(
40V)
-L/R INDEPENDENT
POWER SUPPLY
INDICATION
-SIGNAL CIRCUIT
SINGLE CHANNEL
DC Power Supply
DC Power Supple
+Vcc1(+30V)
-..-
n
(
30V)
4V,,f(*4001
V ( 40V)
DA-80M
Current Mirro
Cascade Amp
NPN Darlington Power
Power Amp
Voltage Selector
Po
e
r
Transfor me
o-
C
-–º
+V (+37V)
VI,
37V)
+VGAL-37V)
V«f( 37V)
DC Power Supply
--..
0-ec
DC Power Supply
2
Page 2
240Vr-
r
117V
IDLING INSTRUCTION
(1)
Location in use
This amplifier features class-A opera-
tion, and special care should be taken
with respect to heat radiation. Avoid
locations exposed to direct sunlight,
and place the unit, as far as possible,
where there is a good circulation of air.
Leave a clearance of at least 5 cm (2")
above the amplifier. Also you should
avoid places where dust is liable to be
attracted.
(2)
Protective circuits
Four different kinds of protective cir-
cuit are used to protect either the am-
plifier or the speakers from damage or
loss.
1.
Overload (input) protection: The
input needed for maximum output
is 0.89 V. Should this reach 50 V,
a 'clip' circuit operates to prevent
the amp. from being driven to full
output.
2.
PC limiter: This circuit limits the
current which flows through the
output transistors to prevent them
from being destroyed by the ex-
tremely large current which would
otherwise flow if the speaker
terminals were short-circuited.
3.
Temperature protection: This cir-
cult was designed to cut off the
electrical power supply to the
amplifier as soon as exceptionally
high temperatures are reached. It
prevents the amp. from being
damaged by rises in the ambient
temperature.
4.
Speaker protection: The speakers
will be protected from direct
current signals greater than ±5 V
appearing at the amplifier output
terminals in the face of direct
current signals from the pream-
plifier or from switching tran-
sient noise. Protection is by cutting
off the amp. electrical power sup-
ply, and is effective even if the
amp. itself is damaged.
The above protective circuits built
into the amplifier provide protec-
tion against the most unlikely
eventualities, but you should take
care to use the amp. so that the
protective circuits are not caused
to operate.
If, for the causes detailed in 3 and
4, the protective circuits cut off
the electrical power supply, switch
the amplifier off, determine the
cause, and remove it before switch-
ing the electrical power on again.
If the protective circuit functions
in the same way again, cutting
off the power a second time, please
read the TROUBLESHOOTING
GUIDE on the 7 page.
(3)
When using condenser-type speak-
ers
Since condenser-type (or electrostatic)
speakers only have a DC impedance of
the order of one ohm, near-DC signals
arising from eccentric or warped re-
cords, or from external vibration, will
cause the short-circuit protection to
operate, which will be heard as a 'click-
ing' or 'popping' noise. If this situation
should arise, you should insert a one
or two-ohm resistor (rated 30 Watts)
between the speaker and the amplifier
output terminal as shown, and set the
AC/DC switch to AC.
(4)
When using the DA-80/80M as the
mid- or high-frequency amplifier in
a
multi-amplifier configuration
When the DA-80/80M is used for the
mid/high frequency amplifier, the
channel divider cuts out the low fre-
quency component of the signal, so
that there is no possibility of DC or
other very low frequency signal of very
high amplitude being applied to the
speakers. The possibility does remain,
however, of the speakers being dam-
aged by the switching noise from the
channel divider or by mistakenly pull-
ing out an input jack plug. The AC/DC
switch should therefore be set to AC,
and a non-polar capacitor of 10µF in-
serted in the case of driving a tweeter,
and of 100 tF for a squawker.
(5)
Measurements
This amplifier boasts extremely high
quality circuitry, and if meaningful
measurements are to be taken of its
exceptionally good performance, only
correspondingly high quality measur-
ing instruments and sophisticated
measuring techniques should be used.
(6)
Others
DA-80
*
The AC Outlets are not linked to the
amplifier power switch.
*
There are two models of the DA-80,
one intended for 100~117V operation
and the other for 200~230 V opera-
tion. In both models the switch for
selection of the actual operating volt-
age to be used is to be found on the
underside of the amplifier.
100V-108V aria
109V-117V aria
To comply with the voltage where
this equipment is used, this plate
has to be removed and re-set after
switched to the required voltage.
>
A
2 i oV -2 0 V aria
DA-80M
A choice of mains supply voltages for
the DA-80M is given by the voltage
selector under the chassis. This offers
a choice of 100V, 117V, 220V, and
240V. If you need to change the oper-
ating voltage, first remove the protec-
tive metal device, and then set the
arrow so that it points to the voltage
closest to that which you will use.
O
200V-2 I uV aria
3
