Luxman m 6000 service manual

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h M6065

SERVICE MANUAL

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CIRCUIT DESCRIPTION

Emitter Follower Circuit

Output signals of a control amplifier etc. are led to the input terminals (MAIN IN) of
this power amp, and level-controlled at the input level control of a detent volume equivalent
to the high-grade attenuator with 22 contact-points of ldB decrement.

Then fed into the Emitter Follower circuit, which is, unlike the ordinary one,
composed by two transistors Q601 and Q602. The former is for emitter follower and the latter
is for the constant current drive of the emitter follower of Q601. Signals are impedance-
converted through this circuit, and therefore electrical isolation is made between the (WWW:
stage of a control amp and the pre-driver circuit of this amplifier to eliminate interference

between both circuits. Thus stable amplification with low distortion is attained.
Pre-Driver Circuit

Signals converted into low impedance at emitter follower circuit are then fed to the two-
stage differential amplifier, a kind of balanced DC amplifying circuit, to meet voltage
amplification. The differential amplifier is always stable against the fluctuation of mains
voltage and temperature drift, and has been adopted widely in computers or measurement instruments
etc. by means of ICs as Operational Amplifier.

The two transistors (2301, 0302 for the 1st stage differential amplifier are arranged quite
symmetrically, and the emitter of the both transistors are connected to (+) power supply through
a common resistor. The base of Q301 accepts the input signal, while that of Q302 accepts the
feed back signal. Due to adoption of two transistors of the same characteristic, equivalent
collector current and emitter current are available when the same signals are fed to the base of
the both transistors. As emitter current for two pieces of resistors will flow through the
emitter resistor, the emitter potential will rise up, which corresponds to the amount of negative
feedback. On the other hand, if subtle (+) potential may appear at the speaker terminal by the
drift of transistors caused by other factors but signals, e.g., the raise up of temperature,
this (+) potential is led to the base of Q302 via the feedback circuit, when (+) signal of the
same phase will appear at the emitter resistor. In this case, the potential at the emitter
resistor varies to (+), which reduces the collector current to have (-) potential at collector.
The voltage is amplified by the 2nd differential amplifier Q303, (2304, which makes the (+)
potential stable at the speaker terminals, and helps keep balanced 0 potential.

The 2nd differential amplifier operates same as the lst one, though not perfectly symmetrical-
The constant current driven by 0305 is applied, since this stage aims at voltage amplification. The
emitter follower circuit is arranged annexed to the differential amplifier with a pair of Q306
and 0307 which electrically isolates the "Class A" operation at the differential stage and the
"Class B" operation at the power amp stage. (Q306 is for the emitter follower and Q307 is for its
constant current driving.). Therefore, impedance fluctuation caused by the speaker loads would
not affect the pre-driver stage. With this pre-driver circuit, stable driving with low distortion
is feasible up to high frequency range with a slighter phase compensation comparing with
conventional high power amplifiers.

As for the power supply circuit for the "Class A" operation sections up to the differential
stage, a real automatic voltage regulator is adopted to avoid bad influence which may possibly be
Caused by the fluctuation of AC mains voltage or the current fluctuation in the power amplifier

section.

Power Output Circuit

Adopted is a pure complementary push-pull circuit composed by the power transistors of NPN
group and PNP group which are all specially developed for LUXMAN. In order to produce such a
high power of 300w/ch, two parallel triple push-pull stages utilizing 12 power transistors designed
for high power output are arranged at the final stage. And the parallel push-pull stage utilizing