Technology Brief Class TD, Regulated SMPS and Intercooler Explained

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The LAB GRUPPEN C Series sets a new benchmark for power
density in commercial audio ampliers. The agship C 68:4
produces up to 6800 W of total output (4 x 1700 W @ 4 ohms) in a
2U cabinet weighing about 12 kg (26.4 lbs). Despite the prodigious
power produced inside an astonishingly compact package, C Series
ampliers will not overheat under normal use conditions. By keeping
cool, they provide many years of reliable service – with state-of the-
art sonic performance – in all types of installed sound applications.
To achieve this extraordinary combination of power density,
performance and reliability, LAB GRUPPEN engineers applied the
world’s most advanced amplier technologies – many patented or
proprietary – in development of the C Series.
Class TD Design
Technology: For decades, the class AB output stage set the standard
for high audio quality in power amplication. Although Class AB
ampliers are known for excellent sound, they do not use power
efciently. A great deal of heat is dissipated by the output stages,
requiring large heat sinks and bulky fans to keep the output transistors
inside safe temperatures. Larger power supplies are needed to
produce power eventually dissipated as heat.
Two other familiar approaches to power amplication offer improved
efciency, though each comes with drawbacks. Class D switching
ampliers employ pulse width modulation (PWM) techniques to
achieve very high efciency, but most implementations of “pure”
class D involve compromises in sound quality. Class H designs boost
efciency by modulating the power supply voltage with the input
signal, “tracking” the input in order to provide the instantaneous
voltage needed for optimum operation of the output devices.
However, maximum efciency with class H is achieved only within a
relatively limited dynamic range.
The fundamental concepts behind both class D and class H ampliers
have been in the literature for decades, and are not covered by
patents. However, specic circuits implementing these concepts
can be patented, as is the case with LAB GRUPPEN’s breakthrough
Class TD amplier topology. The TD stands for “tracking class D,”
which means that the power supply tracks the audio signal at all
frequencies, supplying the required rail voltage while at the same
time reserving additional headroom. The high-speed switching
principles of class D are employed as well, though the nal output
stage remains a proven class AB component. The entire audio path
remains analog, with the signal never converted to digital pulses
and then ltered as in some class D designs. Very high efciency
is achieved without the ripple effect typical of a PWM output stage.
Benefits: LAB GRUPPEN’s Class TD works perfectly under all load
conditions. The output maintains its at frequency response even
into complex loads with nominal impedances as low as 2 ohms.
Outputs may be bridged, reliability is very high, and there is no
interference with nearby RF equipment. Superior efciency allows
greater power density while minimizing cooling requirements,
yet sound quality matches that of the best class AB design.
Regulated Switch Mode Power Supply(R.SMPS™)
Technology: The power supply unit (PSU) in each C Series
amplier is an advanced, regulated design that is remarkably
compact and exceptionally efcient. The transformer uses
an enhanced ferrite core to create magnetic eld capacity
equivalent to iron core transformers of far greater bulk. The
ingeniously simple layout is extremely efcient, generating less
heat and reducing overall amplier current draw from the mains.
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Mains Voltage [V]
Rail Voltage [V]
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Characteristics of different power supply designs:1) The Lab.gruppen
R.SMPStm used in the C Series provides stable voltage rails even when mains voltage
drops as low as 90V (@115V nom.) or 180V (@230V nom.).
2) The rail voltage of a conventional power supply (typically a toroidal
transformer) drops proportionally (or worse) with mains voltage sag.
3) The rail voltage of other typical unregulated SMPS designs drops severely
due to semiconductor losses. Current limiting or low-voltage conditions shut
down the supply instead of continuing to lower the rail.
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Technology Brief
Class TD, Regulated SMPS, and Intercooler®
C Series:
Installation-Dedicated Amplifiers
Both superb sound quality and high efficiency are made possible
thanks to Class TD technology