Luxman l 31 service manual

Page 1

SOLID STATE INTEGRATED AMPLIFIER

M31 +

SERVICE MANUAL

Page 2

TAPE NICK

[Power Supply]

Power supply to main amp: The power supply consists of two parts designed for supply of
power to the main amplifier and the pre-amplifier respectively. For the main amplifier driven
by a high current load, silicon diode D205 - D208 (Hi-Pi special) are used, and supply voltage

values are +35V and -35V.

Power supply to other than main amp: Power sources other than for the main amplifier are
obtainable by D203 (lNHOOS) with the half wave rectification circuit and ripple filter. Supply
voltage values at each section are; equalizer stage -37V, tone control stages -27V and inter-

mediate stages -24.5V.

[Pre Amplifier]

The pre-amplifier consists of an equalizer, an intermediate amplifier, and a tone control.
The equalizer adopts the Negative Feedback circuit using tow silicon transistors, 28A836 (QlOl),
QSClSHS (0102) per channel and is designed to provide proper equalization to the input signals.
Input signals given through the AUX-l, -2, and TUNER terminals bypass the equalizer and are fed
directly to the later stages of this amplifier.

Controls arranged after the equalizer stage are: REC. OUT CONNECTOR, TAPE-MONITOR SWITCH,
LOW-CUT FILTER, HIGH-CUT FILTER, MODE SELECTOR, VOLUME CONTROL, and LOUDNESS SWITCH. The
intermediate amplifier consisting of 0103 QlOu is a flat amplifier adopting 2-stage Negative
Feedback circuit which is designed to boost the equalizer, tuner or AUX. This covers sufficiently
the insertion loss by the tone control in the next stage and leads low impedance output to the
tone control for its smooth function. The tone control adopts the CB-NF-circuit of QlOS. Any
desired frequency response can be adjusted by the following controls: Variable resistor VRlOl
(BASS), and variable resistor VRlO2 (TREBLE). Major components of the pre-amplifier are arrang-
ed on the printed circuit board PBlOOB.

[Main Amplifier]

The main amplifier is of full stage direct coupling, one stage differential amplification,
predriving and fully complementary circuits. The power transistors 0207 28D37l(NPN) and Q309
28B531

All circuit components are assembled to the printed circuit board P131009. The differential
amplifier is consisted of 0201 and Q202, the pre-driving stage of 0203, and the driver transis-
tors, Q205 and (2206. Besides the above transistors, capacitors, resistors, and semi-fixed volume

controls are integrated in the circuit.

PHUND RIM AMP

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