22
Headphone Amplifiers
The amplifiers, U1000, are configured to provide 2.3 dB non-inverting voltage gain in order to drive the head-
phones. The headphone amplifiers are not capable of being muted. The control
module must provide a mute
signal any time the headphones are plugged in. This causes the system to mute the speakers and ramp in the
headphone (flat) EQ required. The outputs of the amplifiers are biased to 3.25 volts due to the 2.3dB gain and
the 2.5 volt bias of the CODEC outputs. The worst case output voltage swing from the codec is 1.6 volts. Thus
with the gain of the amplifier circuit will cause the worst case output voltage from the headphone amplifiers to
from 1.15 to 5.35 volts, or 4.2 volts peak-to-peak.
The bias potential present at the output of the headphone amplifiers is removed from the headphone signals by
C1008 and C1008. The signals at the cathodes of these capacitors will be balanced around the GND reference.
The signal RMTRET present at both the AUX input components and the headphone amplifier circuits is a
dedicated ground trace to the remote control module that is terminated to GND near the codec. This prevents
noise due to power supply currents circulating in GND from coupling to either the AUX inputs or the headphone
Headphone Amplifiers
Left and Right
Audio from
CODEC
Out to I/O Board
and Headphone
Jack
