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QSC Audio Products, LLC
4.3 KSub
The KSub is a dual-12” bandpass design, constructed of premium birch. The wood
enclosure is texture painted with a water-based acrylic paint color RAL 9011. A single
large port sits behind the front panel. The two transducers are mounted vertically on
a piece a wood panel that is in the center of the enclosure. The two channel class
D amplifier module is similar in size, weight, and design compared with the top-box
models. Each amplifier channel is dedicated to powering, in phase with each other, a
single 12” transducer.
The KSub includes four low-noise casters. The subwoofer features a threaded pole
receptacle for a positive, wobble free connection to a threaded speaker pole (in-
cluded in box). There are two handles on the subwoofer enclosure - one on the top
panel and another on the bottom. Four round rubber feet are also on the bottom for
support.
4.4 Bucket of power (BOP) amplifier module
Startup sequence
When mains voltage is applied, the IC charges up its large supply capacitor via trickle-start circuitry inside the power supply
controller IC. Once a preset voltage threshold is reached on the cap, the IC shuts off the trickle start and begins switching
the power supply FETs. Once the supply is running, an auxiliary winding on the transformer powers the controller IC. Thus,
an auxiliary supply is not needed for BOP because the main supply is able to start itself. While the DSP is booting, audio is
muted since the DSP is not passing any signal. After booting, the DSP has an additional 4.5 second delay before the amplifi-
er comes out of muting, to allow all internal voltages to fully settle.
Power supply
The BOP’s switch mode power supply is a regulated, fixed frequency, active-clamped flyback. It is similar to a typical flyback
converter except that when the main switch is off another switch turns on and recovers the transformer energy into a res-
onant tank. A typical flyback power supply has good cross-regulation and can operate over a wide input voltage range, but
the power dissipation of a passive clamp limits the power level a flyback can
reasonably output; adding the active clamp allows a flyback converter to scale
to much higher power levels. Because the power supply accepts universal AC
voltages, the incoming mains voltage is bridge rectified to DC and stored in
a bank of 2 primary capacitors in parallel. This rectified voltage varies directly
with mains voltage. The main and clamp FETs, operating at 200kHz, couple
energy to the secondary diodes through the transformer. The regulated ±85V
secondary voltage is stored in a pair of secondary capacitors, one per rail. Reg-
ulation is taken across the 170V secondary voltage, relying on proper
circuit operation to keep the rails balanced. Adjusting the duty cycle of the
PWM signal driving the power supply FETs keeps the power supply’s output
voltage constant regardless of changes to input voltage or load.
Housekeeping voltages of ±15V and +7V nominal are created with separate
transformer windings from the main secondary rails, but all windings are tied
together at ground. Under load, the amplifiers will pull energy from the main
rails and the power supply will increase the duty cycle to compensate and
keep the main rails at ±85V; this means the housekeeping voltages increase
under load.
Summary of Contents for K8
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