Self-Powered Concert Series
Service Manual
MP-2/4 Amplifier
Doc #: 05.033.040.01
Rev.: A
Date: 08/31/98
Page: 11 of 26
© 1998 Meyer Sound Laboratories, Inc. All rights reserved.
5) Power Supply Module:
The power supply provides the Amplifier/Heatsink module with ± 120 V DC and ± 45 V
DC, which is used for the Power MOSFET rails. This module also supplies ± 15 V DC to the
Amplifier/Heatsink module and the TPL Control Board for powering op-amps. Voltage is also
sent to the Communication Board via the Communication Board Power Cable although no
connection is shown in the diagrams.
This Module contains the circuitry for controlling the primary and secondary fans. Signals
from the temperature sensor (located on the heatsink) are fed into the fan control circuits. The
same signal is also sent to an over-temperature comparator. Output from the comparator is
joined with the fault signal line from the Amplifier/Heatsink module. The fault line is then
sent to the AC Mains "Fault Shut-Down Latch" via the sense cable.
The "un-mute" control for the amplifier is located on this board as well. A few seconds after
power-up, the "Turn-on Delay to Unmute" circuit sends a signal to the AC Mains module via
the sense cable. This signal closes Relay 1 on the AC Mains module, shunting the thermistor
out of the circuit. In addition, this same signal is looped back to the Power Supply board on the
sense cable. The return signal is then sent to the TPL Control Board via the 14-pin power cable
and the 15-pin header on the Amplifier/Heatsink module. This signal triggers the "un-mute"
relays on the TPL Control Board.
Note: If the sense cable is not connected properly, the amplifier will not unmute. This assures that the
thermistor is shunted before the audio signal is allowed to pass and the amplifier is allowed to draw high
current.
There is also a fan current sense circuit for each of the fans located on this board. Information
from the fan current sense circuit is sent to the Communication module via the Communication
Board Power Cable.
6) Amplifier/Heatsink Module:
Audio signal input from the TPL Control Board is first sent thru an Ultrasonic DIM filter to
remove unwanted high frequencies and harmonics. From there, the signal is sent to a summing
circuit, which introduces negative feedback and DC offset correction from the output. After the
signal has been corrected, it is input to the power MOSFET output stage via a pre-driver. The
multiple output transistors and supply voltages (typically known as Class H) provide high
power efficiency which allows the transistors to operate with low heat dissipation.
The output stage of the amplifier is connected to the drivers. In addition, feedback lines,
such as the DC Offset Corrector and Negative Feedback, monitor this output line. A DC Latch-
up Detector also monitors this output line. If this detector senses an offset of ±10 VDC for
greater than about 1 second, it sends a fault signal to the AC Mains "Fault Shut-Down Latch".
There is an output current sense circuit located on this board as well. It feeds off of the return
leg of the driver and sends the output current waveform to the TPL Detector circuit on the TPL
Control Board
SYSTEM BLOCK NOTE: Connector pin-outs may not match the illustration.
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