Features; Power Amp; Integrated Controller Circuitry - HK Audio XBA 18 Manuel

2 Features

2.1 Digital or Analog Signal Sources
You can operate the XBA 18 in two ways. The analog
preamp features a variable cutoff frequency, making
it easy to connect and adapt the enclosure to any
given audio system. Once you active the crossover
by setting the Crossover switch to On, you can ad-
just the cutoff frequency within a range of 60 to
100 Hz. The Gain knob is always active; it adjusts
the XBA 18's input sensitivity to match it your
system's signal level.
• Max. input sensitivity (with the Gain knob set to
the far right) is 0 dB.
• When feeding the DDO-controlled signal from
L.U.C.A.S ALPHA to the XBA 18, be sure to set the
Gain knob on the XBA 18's connector panel to the
L.U.C.A.S ALPHA symbol (see the diagram). Also
ensure you disable the crossover by setting the
Crossover switch to Off.
2.2 Digital Amping – Enhanced Efficiency and
Dynamics
With an efficiency rating topping the 90% mark,
Class-D digital power amps are far smaller, lighter,
and more compact than conventional amps. The
reduced thermal load on components clearly
increases reliability. The slew rate is much faster and
the attenuation factor much higher, resulting in
markedly more responsive and accurate
performance.

2.3 Power Amp

The single-channel PWM power amp is housed in a
separate chamber within the XBA 18. It comprises
limiter and protection circuits as well as a mains
power unit.
Integrated Protection Circuits
The XBA 18's power amp is equipped with circuits
protecting it against overcurrent at the speaker out-
put, as well as against overheating. The Protect LED
on the rear panel lights up when a protective circuit
activates.
2.4 Fan
Continuously running fans serve to cool the XBA 18.
They draw fresh air from the left vent and expel the
warm air through the right vent (as viewed from
back of the XBA 18). Located behind the vents are
5 mm foam rubber dust filters.
Important note!
Remove the metal panel to check the dust filters
regularly. Clean or replace clogged filters to ensure
ventilation is sufficient to cool the amp. Ensure the
vents at the back of the XBA 18 remain uncovered
and unobstructed.

2.5 Integrated Controller Circuitry

The XBA 18 is equipped with an active controller
providing crossover and limiter functions.
Input Circuit
The XBA 18's audio input is electronically balanced.
Input impedance is >47 k-ohms. The maximum
input level is 22 dBu. The audio input is furnished
with a high-frequency filter that prevents it from
picking up stray high-frequency noise.
Filter Functions
The integrated crossover function comprises a low-
pass filter with a 12 dB / octave slope and a variable
upper frequency limit that is adjustable within the
range of 60 to 100 Hz. The audio signal's polarity
can be inverted 180 degrees to match the polarity of
the PA requiring sub-bass reinforcement.
The XBA 18's integrated crossover function is
not required when an external active controller
(for example, the DDO or DFC) is used to drive
the XBA 18. In this case, you can circumvent the
XBA 18's crossover by flipping the Bypass switch.
A 20-Hz electronic high-pass called the Subsonic
Filter cuts extremely low frequencies from the audio
signal path. Although hardly audible, these ultra
low frequencies could push the 18" woofer too
hard, causing the membrane to travel too far and
destroying the speaker.
Note:
The Subsonic Filter and the XBA 18's Polarity switch
remain in the signal path when the crossover is
bypassed.
2.6 Limiter
The XBA 18's integrated controller circuitry is
equipped with a peak limiter that protects the
power amp and connected speakers against
excessively high signal levels.
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