Lab.gruppen LAB 2002 - Manual (Page 10)

Design features
Cooling
The LAB.GRUPPEN amplifier runs very cool due
to a patented heat sink called Intercooler
TM . The
output devices (bi-polar) are mounted directly on a
copper heat sink thereby avoiding thermal losses
normally found when using mica washers (the heat
sink is mounted horizontally in front of a pressure
chamber) The air flow is constant along the whole
heat sink,
thanks to a horizontal pressure chamber in front of it,
(in a conventional tunnel design the end of the heat
sink opposite to the fan invariably gets hotter than
that directly in front of the fan). When cool air hits
the geometric fins of the Intercooler
TM , turbulence is
produced thereby enabling efficient cooling.
Light weight
The switch mode amplifiers has a very good power
to weight ratio, (280w/Kg) making it one of the most
powerful 2u amplifiers available.. The light weight is
achieved not only by the PSU, but the Intercooler
TM
and the 9 piece anodized alloy chassis contribute
greatly, rear rack supports are unnecessary in most
applications.
Switch mode power supply (SMPS)
Switch mode power supplies are the modern
solution to the problems of size and weight.
However, early examples of SMPS used in power
amplification were not ground breaking, and l
literally adopted the type of supply found in many
computers today. The LAB.GRUPPEN SMPS is
different in that it is regulated.
How is this achieved? In contrast to other designs,
that use push pull or series resonant converters we
have managed to produce a SMPS that has the
same characteristics as a conventional supply. We
have avoided the pitfalls of push-pull converters,
by eliminating the need for limiting on the
secondary side of the switch transformer. This is
achieved by using sense windings, injecting a
magnetic pulse from the AC- line during a pulse
time segment which is separated from the output
charge current pulse.
2
1
3
0
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25 30 35 40 45 50
Current [A]
V
o
ltage [V
]
Figure 14. Current-voltage characteristic of different power
supply topologies.
1) Conventional power supply show voltage drop due to
internal resistance
2) Regulated power supply used by LAB.
3) Unregulated switch mode power supply with current
limiting.
Whilst the SMPS may sound complex it is actually
very straight forward with high reliability. The net
result is good bass and fast response. Because the
supply is regulated, the power amplifier will
produce the same power output even if the AC line
falls by more than 20% !
Efficiency is also assured, and in the case of the
LAB 2002 this is especially apparent ; its power
supply draws only 4 kW and yet it produces 2 x
1400 W (in a conventional amplifier this would
yield only 2 x 650 W- nearly 3 kW are wasted as
heat.
Traditional PSU’s behave erratically at certain
frequencies, during low frequency cycles (bass),
particularly in clip conditions, their output
impedance's rise thereby producing uncontrollable
speaker cone movement. Under these conditions clip
states are more audible.
LAB.GRUPPEN SMPS produces its rated power
output at all frequencies regardless of speaker
demands and AC line conditions.
Minimum Load Switches (MLS
(TM) )
Thanks to the regulated SMPS, the maximum
power available for the output stages can be
adjusted without increased heat dissipation or
efficiency loss. This allows users to match the
output power with the loudspeaker impedance.
The LED bargraph is also adjusted to give a correct
reading. Because the amount of power delivered into
a load is dictated by its impedance (at 2 ohms you
use the least voltage but use the most current), you
can cheat with the MLS switches thereby enabling
powers in excess of the normal power rating to be
produced.
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