Current voltage characteristic of different power sup-
ply topologies.
1) Conventional power supply show voltage
drop due to internal resistance
2) Regulated power supply used by Lab.gruppen
3) Unregulated switch mode power supply with
current limiting.
the same characteristics
as a conventional sup-
ply. We have avoided
the pitfalls of push-pull
converters, by elimina-
ting the need for limi-
ting on the secondary
side of the switch trans-
former. 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.
Protection circuits
Lab.Guppen power amp-
lifiers have many advanced
protection features that
will protect both power
amplifier and speakers
connected to it, should
a fault condition arise.
Under normal
use these
features are
inaudible and
all protection
circuits are
independent.
◆
DC protection
There are two types of DC protection;
Fuses on the supply branches of each
channel (this is an IEC 65 requirement),
and a Crowbar protection that shorts
the output.
◆
Thermal protection
Protects the amplifier from over-
heating and causing damage to the
output stages. Indicators come on
before the signal is muted.
◆
Short circuit protection
Protects the amplifier by limiting the
power being driven into the short circuit.
Some amplifiers are equipped with
Lab.Gruppen’s Adaptive Limiting system
(ALS™), which holds the output devices
in their safe operating areas yet permits
high peak currents.
◆
Clip limit protection
All amplifiers are equipped with clip
limiters, which can be enabled via the
amplifiers’ rear panels. They are not
simple DC detectors, but actually main-
tain a maximum distortion of 1%
reaching the loudspeakers. As a by-pro-
duct, when the amplifier comes out of a
protect condition, the output level has a
slow rise time. The effect is like turning
the gain up slowly.
◆
VHF protection
Protects the loudspeaker against non-
musical signals, outside the audible area.
This protection is not a simple R.F. filter,
as found in other designs.
LAB.GRUPPEN POWER AMPLIFIERS
Lab.Gruppen was founded in 1979, and have since then been
designing and manufacturing power amplifiers and active cross-
overs/ speaker processors, utilizing ground breaking technologies.
Apart from high reliability and excellent sound quality, the power
amplifiers are characterized by good power to weight ratio and
size. The crossovers and speaker processors are noted for good
value for money as well as total flexibility.
It is however, the switch mode power amplifiers that have made
Lab.Gruppen world leaders in this field since 1987.
Lab.Gruppen products are currently exported to more than
twenty countries including the Americas, Africa and Asia.
Transformer core made of ferrite, used in the
Lab.gruppen switch mode amplifiers, compared with
conventional transformer made with iron core.
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 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 converters, we have
managed to produce a SMPS that has
Upper curve shows the LAB 2002 power bandwidth in
4 ohms. US made conventional unit below.
Switch mode amplifiers
Apart from exellent sound quality, the
switch mode amplifiers possess high
power to weight ratio (480 W/kg in the
case of the LAB 4000 – the best in any
class), and a regulated power supply.
This product line consists of the
LAB 4000, LAB 2002, LAB 1600, LAB
1300C and the LAB 1200C.
The LAB 1200C is a four channel ampli-
fier, which can be configured in a variety
of ways, anything from 4
2
350 W to
2
2
600 W, at eight ohms!
The LAB 2002 and the LAB 4000
utilizes a switch mode output stage, which
makes it three times more efficient than
a conventional class AB amplifier.
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% !