Luxman m 2000 service manual

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SERVICE MANUAL

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MODEL: M -2000
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We are sure that you could understand an entire circuitry more precisely by use Of
the diagram of power amp section together with the whole block diagram. As for the signal paths,
both channels are identical with only the difference of the TR number. Therefore only the left

channel diagram is shewn , and explanation is made accordingly. Transistors are marked with Q.
l) 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, different from the ordinary one, composed by two transistors

Q101 and Q102. The former is for emitter follower of QlOl.

Signals are impedance-converted through this circuit, and therefore electrical
isolation is made between the output 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.

2) Pre-Driver Circuit

Signals converted into low impedance at emitter follower circuitIare 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 possible fluctuation of
mains voltage and temperature drift, and has been widely used as Operational Amplifier with 10' s
in computors or measurement instruments etc. The two PNP transistors Q201, Q202 for the 13:
stage differentail amplifier are arranged quite symmetrically, and the emiter of the bath
transistors are connected to (+) power supply through a common resistor. The base of 0201 accepts
the input signal, while that of Q202 accepts the feedback signal. Due to adoption of the two
transistors of the same standard, equivalent current is to the base of the both transistors.
As emitter current for two pieces will rise up accordingly, which corresponds to negative feedback.
0n the other hand, if subtle (+) potential may appear at the speaker terminals by the drift 05
transistors caused by other factors but signals, for instance, the raise up of temperature .
this (+) potential is led to the base of Q202 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 of 0201 varies to (+), which reduces the collector current to have (-) potential 8':
collector. The voltage is amplified by the 2nd differential amplifier by the 2nd differential
amplifier Q203, Q204, which makes the (+) potential stable at the speaker terminals, and makes
it possible to keep balanced 0 potential.

The 2nd differential amplifier operates same as the lst one, though not perfectll
symmetrical. The constant current drive by Q205 is applied, since this stage aims at voltage
amplification. The emitter follower circuit is arranged annexed to the differential amplififir
with a pair of (2206 and Q207. (Q206 is for the emitter follWEr and Q207 is for its constant
current driving.) Therefore, impedance flucuation caused by the speaker loads would not afftct

the pre-driver stage.

With this pre-driver circuit, stable driving with low distortion is feasible up to
high frequency range with smaller phase compensation comparing with conventional high power
enlplifiers. As for the power supply circuit 'for class "A" operation sections up to the
differential stage, a real automatic voltage regulator is adopted to avoid bad influence whit?!
may possibly be caused by the flucuation of AC mains voltage or the current flucuation in the

POWer amplifier section.