Lab.gruppen LAB 4000 User Manual

USER MANUAL HEADLINES

Unpacking 2

Warnings 2

User responsibility 2

1. Speaker damage

2. Speaker output hazard.

3. Radio interference.

Introduction 3

1. Front panel

2. Rear panel

Installation 4

1. Mounting

2. Cooling

3. Operating voltage

4. Grounding

5. Power consumption

6. Denmark: National deviation

7. Switzerland: National deviation

8. Input connections

9. Connecting speakers

10. Impedance matching (MLS-switches)

Operation modes 8

1. Stereo

2. Tandem mono

3. Bridged mono

4. Stereo reverse

Operation 8

1. Operation precautions

2. Powering up -Soft start

3. Input attenuators

4. Gain switch

5. Indicators

LAB 4000

USER MANUAL

Rev. 3

Design features 10

• Cooling

• Light weight

• Regulated power supply

• Safety approvals

• EMC approvals

Specifications

11

•

EMC-declaration

Appendix A 12

•

Mains voltage selection

Maintenance 12

Troubleshooting 12

Warranty and disclaimers 13

• General

• International

Technical assistance and services 13

• International

• Factory services

Protections 9

1. Clip-limiter

2. Thermal protection

3. VHF protection

4. Short circuit protection

5. Adaptive Fuse Saver (AFS)

6. AC mains voltage protection

7. D.C. protection

1

Unpacking

Carefully open the shipping carton and check for
any noticeable damage. Every LAB.GRUPPEN
amplifier is tested and inspected before leaving the
factory and should arrive in perfect condition. If
found to be damaged, notify the shipping company
immediately. Only the consignee may institute a
claim with the carrier, for damage incurred during
shipping. Be sure to save the carton and packing
materials for the carrier's inspection.
It is also advisable, to save the carton and packing
material, even if the amplifier is undamaged.
Should you ever need to ship the amplifier, use the
original packing.

Warnings

Read this before you are operating your amplifier:

• Do not use this amplifier if the power cord is

broken or frayed.

• Always operate the unit with the chassis

ground wire connected to the electrical safety
earth.

• Do not parallel or series connect an amplifier

output, with any other amplifier output. Do
not connect the amplifier output to any other
voltage source, such as battery, mains source,
or power supply, regardless of whether the
amplifier is turned on or off.

• Do not run the output of any amplifier back

into another channel's input.

• Do not block the air intake or exhaust ports.

Do not operate the amplifier near heat
producing devices such as radiators, stoves etc.

• Do not spill water or other liquids into or on

the unit. Do not operate the amplifier if
suspected or standing in liquid.

• Do not remove top or bottom covers. Removal

of the cover will expose hazardous voltages.
There is no serviceable parts inside and
removal may void warranty.

• Keep this manual for future reference.

User responsibility

1. Speaker damage
Your amplifier is very powerful and can be

potentially dangerous to both loudspeakers and
humans alike. Many loudspeakers can be easily
damaged or destroyed by overpowering, especially
with the high power available from a bridged
amplifier. Always check the speakers continuous
and peak power capabilities.
Even if the gain is reduced by using the amplifier's
front panel attenuator, it is still possible to reach
full output power, if the input signal level is high
enough.

2. Speaker output hazard
Power amplifiers are capable of producing
hazardous output voltages. To avoid electrical
shock, do not touch any exposed speaker wiring,
while the amplifier is operating. See page 6 about
outputs for proper connection of speakers.

3. Radio interference

This product has been tested, and complies with the
limits for the European Electro Magnetic
Compatibility (EMC) directive. These limits are
designed to provide reasonable protection against
harmful interference between electrical equipment.
This product uses radio frequency energy, and if not
used or installed in accordance with the operating
instructions, it may cause interference to other
equipment, such as radio receivers. However, there
is no guarantee for no interference even if the
amplifier is EMC approved.
If the amplifier cause interference, which can be
easily determined by turning the amplifier on and
off, the user can correct the interference by one or
more of the following steps:

1. Increase the proximity between the equipment.

2. Connect the AC cord to an outlet on a different

circuit from that to which the affected unit is
connected.

3. If a radio receiver is interfered (normally

amplitude modulation); reorient the antenna.

4. Check if the affected unit complies with the

EMC limits for immunity, (CE-labelled).

If not, address the problem with the manufacturer
or supplier. All electrical products sold in the EC
must be approved for immunity against
electromagnetic fields, high voltage flashes, and
radio interference.

2

Introduction

Thank you for purchasing a LAB.GRUPPEN power amplifier. The amplifier you have chosen is the culmination
of many years of Research and Development. This amplifier makes amplification more controllable instead of
the traditional "Boring black box" you have become accustomed to.
Please take some time and read this manual to familiarize yourself with the advanced features of this amplifier.

The front panel

634 56 8 9

CH. A

-10

-12

-16

-20

-40

-80
dB

1

Figure 1. Front panel

1. Carry/protection han dle
Both handles can be used to carry the amplifier, they

als o act as protect ion for the front panel. If so desired
they can be remove d (by removing the screws behind
the front panel) for fixed installations, or racks where
the front covers are to shal low.

2. Input level attenuators
These controls are used to alter the signal level

entering the amplifier. They are calibrated in dB to
help set up active loudspeaker systems or cut down
unwanted noise from the input signal.
(See page 9).

3. Over temp erature protect indicator
This indicator is lit if the amplifier tries to operate

above its maximum operating temperature(90oC).
The indicator first comes on as a warning to either
turn down the input level or check the cooling
arrangements after which point the amplifier will
mute the input signal. When the cooling fans have
returned the output heat sinks to the normal
operating temperature the input signal is unmuted.

4. VHF protect indicator

This indicator lights when constant signals, above
12 kHz at full power, are present at t he output
terminal s. When this happens the input signal is
muted and the process cycles until the VHF signal is
no longer present. (See page 9).

VHF

TEMP

CLIP

-5

-10

-15

-20

CH. B

-25

-10

ON

-7

-5

-3

-1

0

-12

-7

-16

-5

-20

-3

-40

-1

-80

0

dB

4000 CONVERTIBLE POWER AMPLIFIER

5. Clip/limit indicator

This indicator tells when the amplifier output is
clipping or limiting. The two different states can be
told apart:

• When the clip limiter is engaged it flickers

briefly. (See page 10).

• When the clip limiter is not engaged it lights for

a longer period.

6. Fan grill filter.
A foam filter is located behind the front panel to

prevent dust entering the amplifier.

7. Power actuator

This is used to start th e amplifier.
(See page 5 and 8)

8. AC ind icator

Indicate if AC voltage is present .

9. AFS indicator

Indicate if the adaptive fuse saver is activated.

AFS

AC

722

3

The rear panel

1

OUTPUT CH.B

MLS

Switch

dB

0

-2

1+ CH.B+

1- CH.B-

-4

-5

On

Clip LimiterClip Limiter

Off

Made in Sweden

4 5 6 8 5

CH. B

XLR

1/4“

Pin 1 Gnd Sleeve
2 Pos Tip

3 Neg Ring

INPUT

Rever se Pol. B

Norm al Pol. B

Mono Bridge

230V AC 40-440Hz

Power consumption: 2300 wattsMust be grounded

7

Link A+B

Gain 29 dB

Gain 41 dB

Stereo

4 1

CH. A

On Off

Clip Limiter

4000

Patent pend

Clip Limiter

Ser. N:o Removed!

OUTPUT CH.A

MLS

Switch

dB

0

-2

-4

1+ CH.A+

-5

1- CH.A-

2

3 9 3 2

Figure 2. Rear panel

1. Speaker connector
This type of speaker connector may be unfamiliar to

some users. A full description is found in the
operation section. (See page 7).

2. MLS™ switches
These switches are used to select the maximum

output power . (See page 7).

3. Clip limiter switch.
Turns the clip limiter on and off. (See page 9).

4. Input jack
Altern a tive to using input XLR or for linking inputs

with other amplifiers. (See page 6).

Installation

1. Mounting

The amplifier is two rack units high (2U) and will
mount in a standard EIA 19 inch rack. Amplifiers
may be stacked directly on top of each other. There
is no need for spacing between units. If it is the
intention to fill a rack with amplifiers, we
recommend racking is started from the bottom of
the rack. It is also recommended that rear supports
are used for amplifiers mounted in the middle of
the rack, especially if used as part of a portable
system.

2. Cooling

Your amplifier uses forced air cooling system to
maintain a low and even operating temperature. All
LAB.GRUPPEN amplifier, which are fan
ventilated, have front to rear cooling. There are
several reasons for this, one is that there's usually
cooler air outside the rack than inside and therefore
the amplifiers can run at higher continuos power
levels without thermal problems. Never try to
reverse the air flow, as the Intercooler® need a

pressure chamber between the fans and heat sink,
and this only works in one direction of the air flow
(see Design features on page 8).

5. Input signal XLR (See page 6).

6. Phase reverse swi tch for chan nel B

For reversing the input signal phase of channel B to

allow bridged operation. (See page 8).

7. Link switch

Allows a single input to drive both channels

simultaneously. (See page 8).

8. Gain select switch

Allows amplifier gain to be switched between 29dB

and its normal gain at 0.775mV input sensitivity.
(See page 9).

9. AC line cord (See page 5)

Should a heat sink get too hot, its sensing circuit
will mute the hot channel. If the power supply
overheats, another sensing circuit will mute all
output channels, until it cools down to a safe
operating temperature.
Make sure that there is an adequate air supply in
front of the amplifier and that the rear of the
amplifier has sufficient space to allows the exhaust
to escape. If the amplifier is rack mounted, do not
use covers or doors on the front or rear of the rack.
For fixed installations with a central cooling
system, usually found in fixed installations with a
dedicated rack room, it may be necessary to
calculate the maximum heat emission. Refer to
Power consumption on page 5.

3. Operating voltage

A label just below the mains cable on the rear of
the amplifier indicates the AC mains voltage, for
which the amplifier is wired. Connect the power
cable only to the AC source referred to on the label.
The warranty will not cover damage caused by
connecting to the wrong type of AC mains.
For converting a 230 volt amplifier to 115 volt or
vice-versa, see Appendix A.

4

LAB.GRUPPEN switch mode amplifier use

y

ge p

a

primary switching, i.e. the mains is rectified
directly before the transformer, which means that
the power supply is insensitive to the mains
frequency and will operate from DC to 400 Hz.
The amplifier is supplied with an approved European
AC line connector. If this connector is not
appropriate for your country, it can be cut off and
wired to a suitable connector in the following way :

BROWN LIVE

BLUE NEUTRAL

is faulty, its mains fuse will blow, due to this
automatic ground system.
If however you wish to tie the signal ground to
chassis,
connect the XLR-connector’s shell lug to pin 1. In
the interest of safety never d i s c onnect the earth pin
on the AC cord.
For all units that are EMC approved (radio
interference), there is an AC mains filter. This filter
needs the chas sis ground for reference, ot herwise a
current loop is formed via the signal ground.
Use the balanced input to avoid hum and
interference.

GREEN/YELLOW EARTH

7. Power consumption

There are three ways to determine the power/current
Once the AC connector is connected to a suitable AC
supply, the amplifier can be started with the AC
actuator. When you power up the amplifier it takes a
couple of seconds to check its circuits (this is known
as the "soft start" or "slow start" sequence), the fans
then blow at high speed before going onto "idle" and
the 2 bottom green LED’s come on to show the
output ci rcuit s are receiving the correct rai l voltage.

consumption of the amplifier:

First, the peak current draw at full output
power. Under this condition the power will trip the
wall breaker within 30 second and the amplifier
will operate for less than 2 minutes before
thermally limiting. During this time, the
temperature of the power supply will be stabilised
at a temperature that will have no effect on the
insulation rating of the AC line cord.

4. Denmark: National deviation
concerning installation of the LAB 4000:

Danish safety regulation only permits 8A main
fuse. As the LAB 4000 use an internal primary
mains fuse of 15A, the LAB 4000 must be
equipped with an industrial mains connector rated
for 16A, or as an alternative be fixed installed to a
16A circuit.

Secondly, the maximum expected average
current under worst case program material which is
1/3 of full power according to the FTC-standard. At
this level the music will be in the state of constant
clip and is therefore the highest power level one can
obtain without completely obliterating the program.

At last, the "normal operating power", as
measured according to the safety standard IEC 65
and used by a majority of safety agencies. The

5. Switzerland: National deviation
concerning installation of the LAB 4000:

Swiss safety regulation stipulates that mains
connector of the type 23 must be used.

normal operating power is measured using pink
noise, with an average output power equal to 1/8 of
full power. The one eighth of the total power is as
loud as you can play music while making some
attempt to avoid obvious clipping. It also

6. Grounding

There is no ground lift switch or terminal on this
amplifier. The signal ground is always floating via a
resistor to chassis and the grounding system is
automatic. If a potential above 0.6V presents itself
between signal ground and chassis ground, a short

corresponds to a headroom of 9dB, which is very
low for an audio program.
In 2 ohms operation, the AFS-protection of the
amplifier circuit will not permit long term current
draw and the component temperature rise will
stabilises well below the rating.

circuit is introduced between the two, thereby
enabling electrical protection. If a unit in t he syst em

MAX OUTPUT POWER MAINS INPUT POWER

Power Full Power 1/3 Power 1/8 Power Idle

sine wave note 1 note 2

LAB 4000 8 ohms 2X 1300 3500 1400 800 130

4 ohms 2X 2100 6000 2300 1300 130
2 ohms 2X 2400 6900* 2900 1500 130

note 1 Avera

The amplifier driven to clip levelnote 2 IEC standard power rating.

Table 1.

* Will be reduced b

ower with music as program sourceNormal" music power with 9dB he

AFS protection

The current draw can be calculated by dividing the mains input power by the mains voltage.
We recommend you to design the power distribution for at least the current at 1/8 power and 1/3 power for
heavy duty demands like discos etc.
The heat power can be calculated as the following example:
We consider a headroom of at least 9dB and a 4 ohms load on an amplifier producing 2100 watts per channel.
The 1/8 power per channel is then; 2100 / 8 = 263 watts, total output; 2 x 263 = 525 watts.

5

The power consumption according to the chart above is then 1300 watts.

The heat power produced is the difference between the power consumption and output power;
1300 - 525 = 775 watts per amplifier.

8. Input connections

XLR Input connectors are balanced and wired
according t o the IEC 268, that is pin 2 hot, and
wired in the following way:

PIN 1 GROUND/SHIELD
PIN 2 HOT
PIN 3 COLD

Figure 3. XLR input connector pinout

There are also TR S jacks for l inking et c. They are
wired as follows:

TIP HOT
RING COLD
SLEEVE SHIELD/GROUND

Figure 4. TRS phone plug

The input impedance is high enough (20 kohms
balanced) to allow ”daisy-chaining”, or multiple
parallel input connections. To daisy chain, use the
TRS jacks provided on each channel. The i nput
circuits also have a high enough headroom , to accept
the maximum output level from virtually any low
level signal source.

Figure 5. Rear panel connectors

Figure 6. Balance d line

To connect an unbalanced source, tie pin 3 (ring on
TRS jack) down to the shield of the connector. If
you leave one pin disconnected, you will lose 6 dB

in gain.

Figure 7. Unbalanced line connection

A more optimal method for handling unbalanced
source s is shown in Figure 8.This is similar to the
connection for balanced lines, but pin 3 is tied down
to shield, at the source side instead. The hum and
noise rejection for the cable i s equivalent to that for a
balanced l ine. To minimize hum in the audio, use
balanced inputs whenever possible.

Figure 8. Balanced line with unbalanced equipment

CH. B CH. A

XLR
Pin 1 Gnd Sleeve
2 Pos Tip
3 Neg Ring

Must be grounded

1/4“

INPUT

Revers e Pol. B

Lin k A + B

Ster eo

Normal Pol. B

Mono Bridge

230V AC 40-440Hz

Power consumption: 2300 watts

Ga in 29 dB

Ga in 41 dB

4000

Do not use XLR and TRS jacks on the same
chann el si multaneously for mixing or other
purposes.

6

9. Connecting speakers

Channel Impedance MLS Power Comments

8

820

B8-2dB 820W reduction

A40dB 2100W High

k

B40dB 2100W power

A80dB 1300W Power

B2-5dB 1660W

A8-2dB 820W Power

B40dB 2100W

Speaker connections are made via the two Neutrik
NL4FC Speakon connectors (1).
They are the only connectors currently available to
meet the EC safety requirements. They are wired in
the following manner:

Pin -1 Speaker ground.

Pin +1 Speaker positive.

Pin -2 No connection.

Pin +2 No con n ection.

Figure 9. Speakon connector

Please note that this i s the standard wi ri ng
convention for Speakon connectors adopted world­wide.

Never connect either output terminal to ground
or to some other output or input terminal (see
warning on page 2).

For normal two-channel operation, connect each
speaker load across the outputs positive and ground
terminals. Pay attention to speaker polarity;

loudspeakers connected out of polarity degrade
sound quality and may be damaged as a
consequence.

Keep the speaker cable wires as short as possible,
and use a good quality stranded speaker cable. Do
not use shielded wire, such as microphone or guitar
cable. Remember that the speaker cable robs the
power of the amplifiers in two ways:
Increases the load impedance and introduces
resistive power losses, so called I2R losses.

10. Load matching (MLS-switches)

The MLS switches is located on the rear panel. The
MLS switches offer a impedance matching, so you
can drive the LAB 4000 in 2 ohms without
increased heat losses.
As stated earl ier the LAB 4000 can produce 2100
watts into both 4 and 8 ohms. This is done with the

The fixed positions shown in Table 2. guarantee
2100 watts but higher powers can be achieved
utilising higher MLSTM positions when connected
to lower impedance's s ee Table 2.
As you can see from Table 2 the LAB 4000 can
produce in excess of 2100 watts

aid of the MLSTM switches( 2 ).

LAB 4000

LOAD CONFIGURATION -5 dB -4 dB -2 dB 0 dB

16 ohms Stereo (2 channel) 220 w 260 W 410 W 650 W

8 ohms Stereo (2 channel) 430 W 520 W 820 W 1300 W

4 ohms Stereo (2 channel) 830 W 1000 W 1600 W 2100 W

2 ohms Stereo (2 channel) 1660 W 2000 W 2200 W 2400 W [1]

16 ohms Bridged mono 860 W 1040 W 1640 W 2600 W

8 ohms Bridged mono 1660 W 2000 W 3200 W 4200 W

4 ohms Bridged mono 3320 W 4000 W 4400 W 4800 W [1]

[1] Component tolerance dependent
[2] Continuous power, one channel driven or peak power both channels driven.

(Thermal protection may occur at high continuous power).
Power in watts (EIA 1 kHz, 1% THD)

Table 2.

MLS SWITCH SETTING

3050 W [2] 3200 W [2]

OUTPUT CH.B

Switch

MLS

dB

0

-2

1+ CH.B+

1- CH.B-

Figure 10. MLS switches on rear panel

-4

-5

MLSTM positions can be di fferent for each channel

and a variety of combinations can be achieved see
Table 3 .

A

-2dB

W Power

pea

matching

sharing

The way to find the best MLSTM position for your
application is by experimentation, the amplifier is
very well protected (even down to 0.3 ohms), but
where speed is of essence stick to the fixed
positions.
The thing to remember with the LAB 4000 that it is
a power converter and when you select ML S

TM

positions you are allocating a portion of power from
5000 watts.

7

Operation modes

1. Stereo operation

For stereo (dual channel ) operation, leave the Link
and Phase reverse switches in the undepressed
position. In this mode, both channels operate
independently of each other, with their level
attenuators controlling their respective levels.

Never connect either output terminal to ground
or in parallel. The recommended minimum

nominal impedance, for stereo or tandem operation,
is 2 ohms per channel.

2. Tandem mono

For tandem ( dual channel-single input) operation ,
depress the Link switch. Both channels can now be
driven by a signal, at either input connector. The
output connection is the same as in stereo mode.
You can use either TRS connectors for linking out
etc. Do not use the remaining XLR and TRS
connectors for mixing or other purposes. Both
level attenuators are active, allowing you to set
different levels for each channel.

Never connect either output terminal to ground
or in parallel.

3. Bridged mono

To bridge the amplifier, depress the Link switch (7)
and Phase revers e switch (6). Both channels are then
driven by a single signal at either input. You can
use any remaining input connectors for linking etc.
Do not use the remaining XLR and TRS as input
jacks simultaneously for mixing or other purposes.

Figure 11. Bridge mono connection

Both level attenuators must be at the same
position. We recommend you to put them in the 0
dB (full) position.

4. Stereo reverse

This mode is similar to the Tandem mono mode.
Apart from depressing the Link switch , you also
depress the Phase reverse switch, like in the Bridge
mono. Channel B is now phase reversed. To
compensate for that, connect pin +1 on chan nel B

Speakon to speaker negative terminal and pin -1
on channel B to speaker positive terminal.

To obtain an output, connect the speaker leads to

pin +1 on channel A Speakon to speaker
positive terminal and pin +1 on channel B
Speakon to speaker n egative terminal . Do not

con n ect eith er of the -1 (n egative) pin s of the
Speakons. Do not connect speakers to ch annel
A or B in the normal manner in bridge mode, as

this can cau se serious d amage.

The recommended minimum nominal impedance
for bridged mono is 4 ohms (equivalent to driving
both channels at 2 ohms).
Driving bridged loads of less than 4 ohms may cause
a thermal overload.

Operation

1. Operation precautions

• Make sure that the power switch is off before

making any input or output connections or
operating the switches on rear panel. See pages
4-7 about installation.

• Make sure that the AC mains is correct and the

same as that is printed on the rear panel of the
amplifier. See pages 5-6 , about operating
voltage and power consumption.

Figure 12. Stereo reverse mode

Channel A output is connected as in the normal
stereo mode. By having channel A and B operating
in opposite polarity, the energy storage in the
power supply is more efficient. This means that the
amplifier can deliver up to 10% more power than in
tandem mono mode. This is significant for signals
below 100 Hz (sub bass etc.).

• Make sure that the switches on the rear panel

for operation modes ,clip limiters, and the
MLS™ switches are in the correct position.
See this page, about operation modes, page 9
about clip limiters and page 7 for the MLS
switches.

• It is always a good idea to turn down the gain

controls during power up, to prevent speaker
damage, if there is a high signal level at the
input.

8

2. Powering up -Soft start

When you power up the amplifier it takes a couple of
second s to check its circuits (this is known as the
"soft start" or " s l ow st art" s equence), the fans then
blow at high speed before going onto "idle" and the
two bottom green LED’s come on to show the
output ci rcuit s are receiving the correct rai l voltage.

3. Input attenuators

The two input level attenuators on the front panel,
alter the signal level for their respective amplifier
channel in all modes. They are calibrated in dB to
help setting up active loudspeaker systems or cutting
down unwanted noise from the input signal.
In bri dged mode, both controls must be in the same
position, so that the speaker load will be shared
equally between the channels.

4. Gain switch

The gain switch located on rear panel is for changing
the i nput sensitivity of the amplifier. This can be
handy when using low or high nominal input signals
e.g. m ost professional mixing consoles operate at a
nominal level of +4dBu therefore use the 29dB
position (depressed switch), to give you plenty of
fader movement. On the other hand, for a disco
mixer that operates at a nominal level of 0dBu, use
the upper position setting, which has a sensitivity of
0 dB for full power in 4 ohms.

VHF

TEMP

CLIP

-5

-10

-15

CH. A

-10

-12

-16

-20

-40

-80

-20

-25

ON

-7

-5

-3

-1

0dB

4000

CH. B

-10

-7

-12

-16

-20

-40

-5

-3

-1

-80

0dB

5. Indicators

The two bottom green ”ON” LEDs indicate that the
output circuits are receiving the correct rail voltage.
The ”-25 dB” LEDs glow when the output signal
is greater than -25dB, 0dB is referenced to full
output power. These LEDs also act as signal
present indicators.
The rest of the green LEDs forms a bar for output
levels from -20dB to -5dB.
The Clip/limit indicator tells when the amplifier
output is clipping or limiting. The two different
states can be told apart:

• When the clip limiter is engaged it flickers

briefly.

• When the clip limiter is not engaged it lights for

a longer period.
The remaining yellow LEDs indicate if any
protection circuits are acti vated. These are described
below.

Figure 13. Front indicators

Protection features

Each LAB.GRUPPEN amplifier has many advanced
protec tion features, that will protect both the
amplifier and the speakers connected to it, should a
fault condition arise. Under normal use these features
are inaudibl e. Al l protect ion circuits are independent.

Clip limiter

The clip limiter is included to prevent dangerous clip
signals reaching the speaker and damaging it. It
works by monitoring the output and comparing the
distortion produced between the input and output of
the amplifier. If the distort i on exceeds 1%THD for
any reason ( voltage or current clipping), the limiter
reduces the input signal proportionally. Note that, if
the signal is distorted or cli pped before it reaches
the amplifier, the clip limiter will not be activated.
Under normal operation the clip limiting is
inaudible. The limiter can be turned On or Off by
depressing the relevant clip limit switch (2).

Some manufacturers of Loudspeaker processors do
not recommend the use of clip limiters in amplifiers,
as t hey tend to upset the tracking of the processor’s
limiters.
Apart from this one exception, LAB.GRUPPEN
recomm end leaving the clip limiters switched "on"
(button depressed).

As a by-product, when the amplifier comes out of a
protect condition, the output level has a s low rise
time -the effect is like turning the gain up slowly.

Thermal protecti on

When the amplifier is driven very hard i nt o low
impedance, t he cool ing fans go into high speed. If
the conditions that cause this continue, the
temperature indicator(s) will light as an indication
that the amplifier will soon thermal out.
After five seconds the amplifier will go into thermal
protect, by muting the input signal. After 15-20
second s the amplifier will cool down the

Intercooler®and the cycle will begin again.

Thermal protection starts when the Intercooler
reaches a tem perat ure above 900 C

VHF p rotection

When a signal of more than 12kHz, at full output
power, is present at the output connectors for more
than five seconds, the VHF protection mutes the
input signal (this is indicated on the front panel (4)
labeled VHF ). After five second s t h e cycl e starts
again.

®

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This is a useful feature as there are currentl y no
commercially available compression drivers that can
take 500 watts of power at 10 kHz!! this circuit is
inaudi ble under normal use, however it can be turned
off.

If the VHF protection is required to be turned off
i.e. for studio monitors, please consult your
supplier, as this is a non-user adjustment.

Short circuit protection

All LAB.GRUPPEN amplifiers are completely
short circuit protected. The protection circuit
permits very high peak currents, but still holds the
output devices within the safe operation area. If a
short circuit is maintained, the channel affected will
eventually go into thermal protection and the cycle
will start again.

will not be activated during normal use, even if the
music will be in the state of constant clip.

AC mains voltage protection

If the AC mains voltage is outside the allowed
operation voltage ( over or under voltage) , the
power supply will shut down itself. When the
mains voltage is above the minimum start voltage
and below its maximum operating voltage the
amplifier will restart again.
It takes a couple of seconds to check its circuits (this
is known as the "soft start" or "slow start" sequence),
the gain will slowly and gradually raised back to
normal, and the fans then blow at high speed before
going onto "idle". The two green ”ON” LED’s
indicate when then power supply is operating
properly.

Adaptive Fuse Saver, AFStm-limiter;

The AFSTM ci rcuit continuously monitors the mains
current. If the average mains current is too high for a
16 ampere slow blow fuse, as it can be during so
called bench tests, the AFS™-limiter will limit the
mains current to a safe level. If the

AFS-limiter is activated this will be indicated by
the AFS-LED on the front panel. The AFS limiter

Design features

Cooling

The LAB.GRUPPEN amplifier runs very cool due
to a patented heat sink called IntercoolerTM . 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 ai r fl ow 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 IntercoolerTM, turbulence i s
produced thereby enabling efficient cooling.

Light weight

The switch mode amplifiers has a very good power
to weight ratio, (480w/Kg) making it one of the
most powerful 2u amplifiers available.. The light
weight is achieved not only by the PSU, but the

IntercoolerTM and the 9 piece anodized alloy chassis

contribute greatly, rear rack supports are unnecessary
in most applications.

D.C. protection

There are two types of DC protection:
Fuses on the supply branches of each channel (this is
an IEC 65 requirement).
A Crowbar bar protection that shorts the output.
Both these circuits come into effect o n ce a DC level
of 10 volts or more is detected on either channel.

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 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.
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 4000 this is especially apparent ; its power
supply draws only 6 kW and yet it produces 2 x
2100 W.

10

90

A

80

70

60

50

40

Voltage [V]

30

20

10

0

051015 20 25 30 35 40 45 50

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.

Current [

Traditional PSUs behave erratically at certain
frequencies, during low frequency cycles (bas s),
particularly in clip conditions, their output
impedance' s ris e 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 regardl ess 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 gi ve a correct
reading. Because the amount of power delivered into
a load is dictat ed by it s im pedance (at 2 ohms you
use the least voltage but use the most current), you
can cheat with the MLS s witches thereby enabling
powers in excess of the normal power rating to be
produced.

Safety approvals

LAB.GRUPPEN amplifiers are designed to m eet the
IEC65 (now called EN 60 065), a stringent electrical
safety approval from the International Electro-
technical Commission . The IEC65 is recognized

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1

3

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
als o be abl e 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 ).

Immuni ty

The equipment should be able to handle three
different types of interference:

• Electrostatic discharges up to 8 kV, hitting the

chassi s or cables.

• Transients and bursts up to 1 kV, conducted

through the cables to the unit.

• Electromagneti c fields up to 3 V/m, radiated on

the unit and the cables in the frequency range of
27 - 500 MHz.
We have ext ended the tests in two cases and chosen a
standard used for heavy industrial situations. First,
we have tested conducted disturbances in the
frequ ency range 150 kHz - 80 MHz, by injecting 3V
amplit ude 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 t o 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
cli p point accordi ng 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

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LAB 4000 is normally shipped for 230 volt AC
operation only. For export there is a 115/230 volt
AC option available. To check if the amplifier is
equipped with this option, please follow these
steps:

1. Make sure that the LAB 4000C is unplugged

from the mains voltage.

2. Remove the top and bottom cover.

3. If the four electrolytic capacitors close to the

front are rated 1500uF 200VDC, the amplifier
is for 230 volt operation only

4. If the four electrolytic capacitors close to the

front are rated 2200uF 200VDC, the amplifier
has the 115/230 volt option.

5. Locate the jumper(s) on the solder side of the

circuit board close to the mains switch.

6. To select the desired mains voltage, install the

jumpers as shown in Figure 15.

7. For 230 volt operation; use a T 15A fuse (slow

blow), for 115 volt change to a T 30 A fuse
(slow blow).

8. Replace the amplifier top and bottom cover.

9. For 115 volt operation; stick a ”115 VAC”

label on top of the 230 VAC label on rear
panel.

115V

230V

115V

Figure 15. 230 VAC or 115 VAC selection

Warning: This modification should only
be made of an experienced service
technician.

Maintenance

Under normal use the amplifier should give years of
trouble free service. The only user maintenance
required from the user is to vacuum the front grill
periodically.
In some extreme cases it may be necessary for your
supplier to clean the inside of the amplifier. These
conditions usually occur after prolonged use in
environments using "cracked- oil" smoke machines.
If you are using your amplifier for heavy duty use
i.e. concert touring or industrial music it is
recommended that you have your amplifier serviced
every 3 years, purely as a preventative measure

Troubleshooting

These are typical things to check if you think your
amplifier is faulty:

Fault: No output.
If the output bargraph is functioning there is
nothing wrong with the amplifier, and the likely
cause is an unsecured Speakon.
Check that the VHF protection is not activated. If
it is, remove possible high frequency oscillations
from the relevant input.

Fault: The amplifier goes into thermal protection
when driven at low level.
Check that your loudspeaker has not got a short
circuit in its windings, (this can occur when the
speaker coil gets warm).

Fault: The amplifier goes into protect with power
indicators off.
Check that the AC line voltage is not outside the
amplifier’s operating range (130-260 volts).
Over/under-voltage protection may have occurred.
If the amplifier is connected by mistake to a 3
phase supply (415v), an internal non-resetable fuse
or resistor may have blown. Then return the
amplifier to your supplier.

Fault: The amplifier does not respond even after
checking above items.
In the unlikely event, that there is a non-user
rectifiable fault, return the amplifier to your
supplier or an approved service centre.

Lab Gruppen cannot be held responsible for
damage or injury, as a result of the top cover
being removed.

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Warranty and disclaimers

• General

This product is manufactured by LAB.GRUPPEN
and is warranted to be free from defects in
components and factory workmanship under normal
use and service, for a period of one year from the
date of original purchase.
During the warranty period, LAB.GRUPPEN or its
nominated agents, will undertake to repair, or at its
option, replace this product at no charge to its
owner, when failing to perform as specified,
provided the unit is returned undamaged and
shipping pre-paid, to factory or authorised service
facility.
No other warranty is expressed or implied.
This warranty shall be null and void, if the product
is subjected to:

1) Repair work or alteration by person other than
those authorised by LAB.GRUPPEN or its agents.

2) Shipping accidents, war, civil insurrection,
misuse, abuse, operation with incorrect AC voltage,
operation with faulty associated equipment and
normal wear and tear. Units, on which the serial
number has been removed or defaced, will not be
eligible for warranty service.

3) LAB.GRUPPEN shall not be responsible for
any incidental or consequential damages, with
respect to the products warranted.

LAB.GRUPPEN reserve the right to make changes
or improvements in design or manufacturing,
without assuming any obligation to change or
improve products previously manufactured.

• International

Please contact your supplier for this information, as
rights and disclaimers may vary from country to
country.

Technical assistance and services

• International

If your LAB.GRUPPEN product needs repair,
contact your LAB.GRUPPEN dealer or distributor,
or contact LAB.GRUPPEN by fax, to obtain the
location of the nearest authorised service centre.

• Factory services

In the event that your LAB.GRUPPEN product
needs factory service, you shall contact
LAB.GRUPPEN service department for return
instructions and a Return Authorisation number.

Please note on product return:

1. Use the original packing

2. Include a copy of the sales receipt, your name,

return address, phone number, fax number and

defect description.

3. Mark the Return Authorisation number on the

outside of the packing.

4. Ship the product prepaid to:

LAB.GRUPPEN
Gullregnsvägen 16
434 44 Kungsbacka
SWEDEN

Telephone: [phone]
Fax [phone]
e-mail [e-mail]

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