XTD-33 I
NSTRUCTION
M
ANUAL
U
LTRA
★
S
TEREO
L
ABS
, I
NC
.
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Theory of operation
Normal operation
Under normal operation, the input signal is conditioned and converted from
an analog waveform to digital information at a sample rate of 96 kHz (twice
that of a normal music CD). The digital data is then processed in a single chip
Digital Signal Processor (DSP) which analyzes the waveform, breaks the
signal into the appropriate audio bands and impresses the desired acoustic
curve onto the information. These acoustic curves are shaped to match a
manufacturer’s specific speaker response selected by the switches on the
XTD front panel. The data is then converted back to analog waveforms and
passed through individual volume controls to the output Transformer Simu-
lators. The Simulators provide a balanced line output which may also be used
in an unbalanced configuration by shorting the unused output to ground
Speaker Protection (Anti-Thump)
To minimize damage to the speakers, an anti-thump system shorts the
balanced line outputs together during power on or off. However, to assure the
best protection, it is recommended that the power amplifiers always be the
last to be turned on and the first to be turned off.
Backup System
It is USL’s policy to try to provide a “safety net” when possible. The backup
system here allows the XTD to continue to operate if the primary XTD power
supply fails or there is a malfunction in the Digital Signal Processing part of
the unit. The Backup Power Transformer constantly feeds into the analog
portion of the circuitry, should the primary supply fail, the backup will take
its place and the Power Supply LED will change from green to red. The Input
signals will be rerouted around the digital portion of the circuitry and into a
conventional analog crossover. This crossover can be configured as either a
two-or-three-band type by means of front panel switches. The signals are then
directed to the volume controls as noted in the Normal Operation above.
These crossovers are of a generic 12dB per octave type but would not be
optimized for all models of speakers. The crossover points are located at
approximately 500 Hz and 1800 Hz in the three-band mode and 500 Hz in
the two-band mode. Should the digital processing malfunction for some
unforeseen reason, turning the power switch off will activate the bypass
system. Obviously, the Backup System is intended for temporary use until the
unit can be restored to proper operation.
