Kenwood L 07 M Service Manual

Page 2

CONTENTS

_,. 91-?-

EXTERNAL VIEW ................................ 3
INTERNAL VIEW ................................ 4
DISASSEMBLY FOR REPAIR ........................ 5
CIRCUIT DESCRIPTION ........................... 8
TROUBLE SHOOTING ............................ 15
DESTINATIONS' PARTS LIST ....................... 16
PARTS LIST .................................... 17
ADJUSTMENT ................................... 19
PC BOARD/SCHEMATIC

PROTECTION MOO-189040) .................... 20

POWER SUPPLY (X00-1900-10) ................... 21 '

POWE R~ AMP (X07-1520-10) ..................... 22

POWER CONNECTION (X07r1530-10) .............. 24
REVISED CIRCUIT ............................... 26
SEMICONDUCTOR SUBSTITUTIONS .................. 26
SCHEMATIC DIAGRAM ............................ 27
SPECIFICATIONS ................................ 28
Nate:

Product for Europe (L and T type)
has a middle case on the heat sink,

,
"$3

Page 9

I ;( )7M

CIRCUIT DESCRIPTION

If 01 and 02 are completely identical with each other,
the output being proportional to difference of input level
is generated at the output terminal as described previously.
When the same potential in the inaphase is applied to input
1 and input 2 respectively, no output is generated between
output 1 and output 2. This is because the emitter resistor
Re acts as a large negative feedback for both transistors.
In other words, the output does not come out since both
inputs mutually function to cancel the collector currents.

When the inputs are mutually in the anti-phase, the
signal component does not flow through the emitter resist-
ance and the negative feedback disappears. Thus the emit-
ter resistance does not permit the flow of AC component.
Since there is no feedback, the gain is increased by the
amount of feedback reduction. In this manner, when Fie
increases, its self-bias characteristic is emphasized and the
negative feedback is increased. This state is equivalent to
the fact that the emitter resistance Re is zero in terms of
AC component. If this resistance is increased, the common-
mode component can be distinguished from the differential-
mode component more effectively, thus obtaining a large
CMRFl value.

The value CMFtR (Common Mode Rejection Ratio) is an index
which indicates the quality of differential amplifier. The differential
amplifier provides a so-called differential-mode gain and a common-
mode gain.

The former is the result of amplified differential component
between input signals, while the latter is that of suppression of the
common-mode input signal. If the ratio of the former value to the
latter one is defined, it can be used as an index for expressing the
quality of differential amplifier since it inevitably indicates the rate
of the differential-mode signal that can be taken out without influ-

enced by the common-mode signal.
The CMRR is defined as follows:

Differential-mode gain (DMG) = (M
VIn1 -VIn2 Vin1=Vin2

_ Vout1 + Vout2
Common-mode gain (CMG) a (-Vin1 + Vin2 )Vin1 = Vin2

DMG

CMFF =W

The larger this value is, the more the differential signal
only can be amplified, It is already described that the
CMRR value is improved by the negative feedback effect of
the emitter resistance. In the field of audio equipment
design, the above differential amplifier is not used imme
diately, but a semi-differential circuit is adopted.

< Balanced > OUtPlfl Source Type Output

ICL DIFFERENTIAL AMPLIFIER

When a bipolar transistor is used in the input stage of
the differential amplifier, bias current must be fed to the
input circuit since the transistor is a current amplifying
element. Therefore a coupling capacitor must be installed.
However, in the case of FET, it is an element of voltage-
current amplification type. if a bias voltage is determined
carefully, the input coupling capacitor can be eliminated
by reducing the gate potential in bias circuit to zero. When
the input coupling capacitor can be eliminated, the phase,
distortion and transient characteristics are extensively im-
proved.

< ICL Differential >

pPA 63H

The parameters such as ID and VGS are subjected to
change with temperature, if these parameters used in the
differential amplifier do not have thermally unified charac-
teristics, the characteristic difference is directly amplified
in the form of output difference. The newly developed
pPAGSH is a dual FET molded into a single chip. It is
excellent in terms of characteristic dispersion.

< Fig. 5 MPA-63H Interior >

Page 11

CIRCUIT DESCRIPTION

The VCE-IC characteristics are based on the parameter
IB. When IB is constant, the VCE-IC characteristics are
expressed by a single curve. In a region where the VCE- lC
charactersitics are saturated, IC is almost constant regardless
of variations in VCE. Namely the circuit assumes the
constantecurrent characteristics. When a constant-current
circuit is used on the emitter side (source side) of the dif-
ferential amplifier, the CMRR value will be improved. If it
is used as an amplifier load, then it functions as a light load
and the Current can be always constant and sufficient.
With these advantages, it can be regarded as a high-imped-
ance circuit in terms of AC.

3-STAGE DARLINGTON CIRCUIT

The input impedance for a standard Zestage Darlington
connection is expressed as follows:
Rinihfel the2x FlL
However, since the load is a constantecurrent circuit in
the final differential stage, the output impedance becomes
high as described in the section of the constnat-current
circuit. Therefore, an overload occurs and distortion in,
creases if the input impedance on the Darlington side is
too low. Thus the circuit is provided with-three stages to
obtain a large hfe and the input impedance is increased to
reduce the load of the former stage.

Iot:lcl +loZ+|c3
Iol=|b|> I02=lb2> |c3:|b3> |b2=lbl +lcl
lb3=|b2+loZ=|b|+lcl +|oZ
=Ibl +|bl XIIIQI +(Ibl +|bl X
htel) hieZ
Ne =lct/lbl
=(mal +I)(h.92+I)(m,3+ l)7l
hia+l'=-hre
hfo=hIeI Xhl22Xh793

< hfe in 3-Stage Darlington Circuit >

OVERDRIVE LIMITER_.- Lit!-

For the output stage, the clipping point at time of
excessive input is determined by the source voltage, How-
ever, in the power amplifier like L-07M, the final stage is
arranged in parallel connection and trouble may occur if
clipping takes place in the final stage due to characteristic
dispersion in final transistors. The overdrive limiter circuit
is used to cause clipping before the final stage. The limiter
functions with the input of the initial driver stage. For
example, if the base potential of (leg is extremely raised
by the input signal, and when it is increased by the amount
of the on-level of De15 and 16 (1.2V) which is higher than
the level preset by D97, 11, and 12, then De15 and 16 are
turned on and the input signal level does not increase more
The same thing can be said for the opposite potential except
for the fact that the polarity is reversed. Reverse voltage
of DelE, 16 is 70 volts per diode. Since voltage almost
identical with the source voltage is applied to the opposite
diode at the clipping level, two diodes are used to obtain
allowance against overvoltages.

Signal component
over the preset level

< Overdrive Limiter Function >

ASU DETECTOR CIRCUIT

As shown in the diagram, the operational region of
the transistor is limited by VCE, IC, and PC with the maxi-
mum ratings. The electrolytic capacitor Ce7 is generally
charged by the positive components of the AC voltage
(signal) at the output terminal through R224 and Deg.
Thus the base potential of Oe15 is lowered and the detect-
ing sensitivity is reduced. With negative components, on
the other hand, Ce8 is charged through Re25 and D910
and the base potential of 0e16 is raised. Also in this case
the detecting sensitivity is reduced at a large signal. In case
the output terminal is short-circuited for a certain reason,
Ce7 and C68 are discharged and the collector current of
the power transistors is detected by the emitter resistor.
The resultant voltage drop is devided and applied to the
bases of Gel?) and 0e16. This is the function of the A80
circuit.

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