Lab.gruppen LAB 4000 - Manual (Page 11)

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Current [A
Voltage [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.
Traditional PSUs 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.
MLS™-switches
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.
Safety approvals
LAB.GRUPPEN amplifiers are designed to meet the
IEC65 (now called EN 60 065), a stringent electrical
safety approval from the International Electro-
technical Commission. The IEC65 is recognized
world-wide with most countries having an
equivalent.
EMC approvals
EMC stands for Electro Magnetic Compatibility.
This implies that the equipment should have low
emission of radio frequencies, directly as
electromagnetic fields in the air, and as conducted
from the cables from and to the unit. The unit should
also be able to handle electromagnetic fields, high
voltage flashes, and radio interference, coming into
the unit via the air or cables.
Emission
The regulation now cover the frequency range from
150 kHz to 300 MHz. The maximum level radiated
from a unit has to be below 100 µV, ( 0.0001 V ).
Immunity
The equipment should be able to handle three
different types of interference:
• Electrostatic discharges up to 8 kV, hitting the
chassis or cables.
• Transients and bursts up to 1 kV, conducted
through the cables to the unit.
• Electromagnetic fields up to 3 V/m, radiated on
the unit and the cables in the frequency range of
27 - 500 MHz.
We have extended the tests in two cases and chosen a
standard used for heavy industrial situations. First,
we have tested conducted disturbances in the
frequency range 150 kHz - 80 MHz, by injecting 3V
amplitude modulated (80%) signals into all the
cables ( inputs, outputs and mains ). This covers
noise from AM transmitters, which are still in use in
some areas. Secondly, we have extended the range for
electromagnetic fields to 26 - 1000 MHz, with a level
of 6 V/m and 80% AM modulated.
In the range 895 - 905 MHz, we test with a field
strength of 35 V/m and 100% pu lse modulation.
This emulate the signals from a mobile phone close
to the unit. In all cases the noise plus distortion is
below 1%, at normal operation level, ( normal
operation level is 1/8 of full power or -9 dB under
clip point according to IEC 65).
EMC-declaration
This audio power amplifier conforms with the
EMC-directive and relates to the following
standards:
EN 55 103-1, E3
EN 55 103-2, E3
EN 60 065, class I
Appendix A
Mains voltage selection