3
1. Car Power Amplifier
ON/OFF
REM
L
R
AUDIO PROCESS
Q901-
903
POWER
ON
IC901
DC-DC
CONV.
8
8
1
9
4
16 3
10
THERMISTORS
PROTECT
LATCH 1, 2
T901
Q904-
907
REGULATION
Q912
L
R
Q910,
Q911 REG.
BATT.
+12V
TO
SPEAKERS
+
-
50V
+
-
14.2V
0.6V
LATCH
0V
0.2V
POWER
LED
MUTE
SW
+12V
OSC.
OUT
+20V
THERMO
LED
LEDS:
OFFSET
SPEAKER
CURRENT
-20V
OSC.STOP
0V
36.4kHz 10Vp-p
FIGURE 1-2 - POWER AMP. BLOCK (XM1502/2150)
14A125 1490 11/14/02
Center - If both left and right inputs were used with a single speaker output, the sounds common to both channels
are doubled to the speaker, making this configuration useful as a center channel. Center channel operation is
possible because of two signal inversions. The inverted right channel is applied to the bottom end of the speaker.
The combined effect is two audio inversions or reinforcement of signal common to both channels.
Ground Connections – Audio, Power and Case
Refer to Figure 1-1. The audio and power grounds are kept separate in this unit (R811 = 2.2k ohms) to prevent
alternator and power noise from getting into the audio. For repair purposes, the two grounds (audio and power)
can be connected together for testing, but the connection must be made when there is no audio output to
prevent a sudden surge path.
The amplifier’s case is connected to the power ground via a 30-ohm lamp. The lamp’s low DC resistance places
the metal case at ground potential yet prevents a voltage applied to the mounted case from blowing the fuse and
disabling the amplifier. An inadvertently applied voltage at the case would just light the lamp.
Power Output – Stereo vs. Mono
The RMS power output is 150 watts at 0.04% THD / per channel (stereo). In monaural where both channels are
applied to a single speaker (bridged), the power is doubled to 300 watts. If a bit more distortion is accepted, the
same output can be rated at 380 watts at 0.1 THD.
Circuit Block Concept / Overview
Refer to Figure 1-2. Modern high power car power amplifiers contain:
• Pulse power supply to deliver ground isolated multiple operating voltages.
• Audio processing stage for the left and right channel amplification.
• Protection (latch) circuitry. The protection circuit will shut off the pulse power supply and hold it off if:
1. The amplifier gets too hot (thermistors);
2. If the speakers draw too much current (latch 1); or
3. The signal is unsymmetrical (latch 2).
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