Marantz 250 - Rectifier-Relay Board Functionality

CHANNEL A
AUOIO IN
CHANNEL O
AUDIO IN
ËCH
= TOPOWER
CIRCUIT AMPLIFIER
GROUND.
Bevoe
TO POWER
AMPLIFIER
GROUND
Figure 2, Rectifier/Relay Board Simplified Schematic
RECTIFIER-RELAY BOARD
The output of the power amplifier is applied to the
wipers of relay K301 on the rectifier relay board,
Figure 2. Relay K301 energizes after a minimum
delay of two seconds after turn on. The length of
the delay is a factor of the time constant of R306,
R309, and C302. This delay at turn-on is to pre-
vent any transient surges from reaching the output
terminals. Additionally, resistors R302 and R305
sample the audio output signals. Should a constant
DC level over *4.5 volts, or a high amplitude signal
below 10 Hz be present, Q301 will turn on, short-
ing the base of Q303 to ground. C302 begins to dis-
charge and K301 de-energizes. If a constant DC
level over -4.5 volts is present, the voltage drop
across R304 bucks the voltage present at the base of
Q303 and K301 de-energizes. The output from
K301 is applied to the SPEAKER TERMINALS.
Eighty six volts AC is applied to CR301 through
CR304 which develop the +58 and -58 volts for
the power amplifier board. CR305 and CR306
* develop the positive voltage to energize K301.
Enom aum een
CHa d GUTPUT TERMINAL Deh
EC SR
Figure 3. 250 Metering Circuit Simplified Diagram