Luxman pd 272 service manual

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SERVICE L
MANUAL

DIRECT-DRIVE TURNTABLE
(WITHOUT CARTRIDGE) PD'272

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Control Circuit Operation

This control circuit works as a speed detector and is a F.G.

(Frequency Generator) servo circuit which detcts as a frequency the output

of the generator rotating on the same shaft as the motor. Below we will

explain the operation of each circuit part.

1)

2)

3)

4)

5)

F.G. (Frequency Generator)

It is a winding and a multi-gap head with a 72 pole magnet and 36 pairs
of teeth and generates a sine wave of 20Hz for 33-1/3 rpm and of 27Hz
for 45 rpm.

Amplifier Circuit (1)
It amplifies the F.G. output and is constructed of a 2 stage differential

amplifier circuit to obtain a dual cycle 50% square wave.

In order to double the frequency by the output of this circuit, adjust
the semi-fixed resistor VRl so the dual cycle of the square wave is 50%.

Frequency Step-up Circuit
Differentiate the inverted output and non-inverted output (along with
the square wave) of the above mentioned amplifier circuit and obtain a

fast rising and narrow differential pulse.
It adds each pulse to the switching transistors to get a saw tooth wave.

Each transistor turns ON the plus side by the pulse side by the pulse
and step-up (2x) of the frequency is possible.

Saw Tooth Wave Generating Circuit

It consists of a charging circuit by CR and switching transistor which
discharges in a short time the voltage charged in the condenser and
produces a saw tooth wave having a wave heighth that is almost inversely

proportional to the frequency.

Referenced Voltage Circuit
This is a circuit for obtaining the voltage to determine the speed of the
motor. The resistance potential makes the source voltage which is the

basic voltage.

In addition, in order to change the number of revolutions (rpm), it is
constructed so the set voltage is varied continuously by/changing the

potential ratio with a variable resistor.