Lab.gruppen C Series Quick Start Manual Download Page 11

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C Series

Quick Start Guide

Constant voltage 70 V and 100 V systems setup
and operation

When using C Series amplifiers to drive constant voltage (high-impedance)
speaker systems at 70 Vrms or 100 V peak, you can in most cases simply connect
the speakers to the amplifier output terminals, select the correct VPL setting, and
place the amplifier in service.

Output Current Peak Limiter (CPL)

The Current Peak Limiter (CPL) ensures that the amplifier will not be damaged
by trying to deliver current to the outputs exceeding the physical limitations the
transistors. The CPL keeps the amplifier within the Safe Operating Area. The CPL
is non-adjustable and has different limit values depending on model type. The
maximum output current values for the four C…X models are:

• C 88:4, 35.5 Arms per channel

• C 68:4, 24.5 Arms per channel

• C 48:4, 17.5 Arms per channel

• C 28:4, 12 Arms per channel

• C 16:4, 8.5 Arms per channel

CPL activity is indicated by illumination of an orange LED for each channel on the
front-panel. Warnings also are shown in the DeviceControl software’s GUI.

A steadily illuminated orange CPL LED indicates a short circuit situation (or very
low impedance). The output will mute for 6 seconds before measuring the output
impedance again. This will continue until the short circuit is fixed, at which time
the output will automatically un-mute. An input signal must be present to allow
detection of short circuit or low impedance conditions.

TIP:

If the CPL LED is steadily illuminated orange while the output is muted and

the -4 dB signal LED is NOT on, then the amplifier output is detecting a short
circuit or low impedance condition. The problem can be solved by checking input
and output cables and examining the state of the loudspeaker load. If there is no
short circuit present, then the condition may be rectified by lowering the VPL or
input levels.

If the CPL indicator is lit continuously, then the amplifier is delivering excessive
current and is being forced into a current limiting state (output muted).

GPIO connection and operation

Introduction

The C Series amplifiers incorporate a sophisticated and comprehensive set of
protection features. Faults and warnings are indicated on the front-panel and
reported via the NomadLink network for indication on the DeviceControl GUI.

Safe Operating Area Detector (SOAD)

The Safe Operating Area Detector (SOAD) compares output voltage against
output current to ensure that the output transistors are working inside their safe
operating area.

The SOAD provides fault monitoring and input to the Current Peak Limiter
(CPL). The SOAD has no dedicated indicator, and its operation is revealed only in
conjunction with features such as the CPL.

Very High Frequency protection

All C Series amplifiers include protection circuits that detect continuous Very
High Frequency (VHF) content in the input signals. The detection begins at
approximately 10 kHz and moves upwards to include ultrasonic signals. If VHF
signals are detected, the output will mute for 6 seconds before re-measuring.
Once no continuing VHF signal is detected, the output un-mutes and returns to
normal operation.

This feature recognizes that continuous full-scale VHF signals do not appear in
“natural” sources such as music. Any such signals can therefore be considered as
a fault when present. VHF protection is essential for avoiding damage to high
frequency drivers.

The VHF protection operational area is dependent on output power level and
frequency. The illustration below shows a decreasing threshold on the output
power level, starting at approximately 10 kHz and rising with a -6 dB slope.
This defines the VHF protection area. When continuous output power above the
threshold line is detected the VHF protection becomes active.

20 Hz

10 kHz

20 kHz

30 kHz

20 Hz

10 kHz

20 kHz

30 kHz

-6 dB slope

VHF protection
operation area

Max. Peak
output power

Max. Continous
output power

Output

power

Attack time

VHF protection

Slow

Fast

The Attack time for the VHF protection is increasingly shorter at higher
frequencies. For example, an ultrasonic continuous signal will cause the outputs
to mute rapidly, where it will take several milliseconds for a 10 kHz continuous
signal to trigger the output mute. This is shown in the illustration above.

The VHF protection is NOT a limiter and does not alter the amplifier’s frequency
response. It is implemented solely to detect continuous VHF content.
The amplifier will always pass VHF peaks at full power, with no effect on
musical “transients”.

The VHF protection is indicated by a yellow LED on the amplifier front-panel,
with output muting for six seconds when in action. It is reported as a fault via the
NomadLink network on the DeviceControl GUI.

TIP:

If you bench test the amplifier using a continuous, full scale sine-wave input

above 10 kHz, the VHF protection will activate and prevent measurement of full
peak output power. (Output will be muted long before maximum output power
is attained.) To measure the true peak output power, use a burst signal.

DC protection

DC protection is implemented on each output to prevent damage to connected
loudspeakers. DC present at the output will trigger muting and illuminate
the fault LED indicator. Any DC present at the output indicates a hardware
malfunction that requires servicing of the amplifier.

High-impedance warning (open load)

A high-impedance (open load) condition is indicated when an input signal above
approximately -29 dB is detected and no functioning loudspeakers are connected
to the amplifier. The fault in indicated by a red Sig/Hi-imp LED. The indicator is
green when a valid load is present under the same input signal conditions.

NOTE:

Since the high-impedance detection initially triggers only when the input

signal rises above -29 dB, it might cause the indicator to first turn green, and then
red, even in situations where no speaker is connected.

Low-impedance protection (short circuit)

A low-impedance or short-circuit fault is detected when current draw is high
(Current Peak Limiter active) and when, simultaneously, output signal is low
(-4 dB LED does not illuminate). When this occurs, the amplifier protects the
output stage from damage by muting the output signal and bypassing the
circuits. Indication of this fault is a constant orange illumination of the Current
Peak Limiter (CPL) LED on the front-panel. The protection will sequence at six
second intervals to re-measure conditions. If the low-impedance fault is no
longer detected, the amplifier will un-mute.

NOTE:

If the CPL turns constant orange, the output is muted, and the -4 dB signal

LED is ON, then the amplifier has gone into maximum current protection. This
situation is caused by an excessive input signal and is not due to a short circuit.
Turn down the input signal to avoid or remedy this situation.

Temperature protection

Thermal measurement points are provided on each output channel as well as
on the power supply. If these sensors detect temperatures above the specified
maximums, a high temperature warning will be indicated by a flashing Temp LED
on the front panel. The warning also will be transmitted to the Device Control GUI
via the NomadLink network.

As the amplifier approaches a thermal protection threshold, the warning LED
sequence will start with short “on-time” bursts. If the amplifier continues to
overheat and approaches the temperature limit, the flashing sequence will
be defined by longer and longer on-time bursts until the protection mode
is activated.

If the temperature becomes too high to continue safe operation, the
overheated output channel(s) will be muted until the temperature returns to an
acceptable level.

Fully active temperature protection (with muting) is indicated by a constantly
illuminated Temp LED. It will also be indicated as a fault via the NomadLink
network on the DeviceControl GUI.

Temperature measurements will continue at six second intervals. The
output will un-mute when the channel or power supply returns to a safe
operating temperature.

Power Average Limiter (PAL)

The Power Average Limiter (PAL) controls the current-drawing relationship
between the power supply and the mains inlet. PAL limits the maximum average
power consumption according to the power supply capabilities, ensuring that the
PSU will not overload. In addition, in the larger models that potentially could pull
more current from the mains than the mains fuses are specified to handle (more
than 16 A), PAL limits the amplifier’s maximum current draw to prevent blowing
the mains fuse.

Soft-Start

High powered amplifiers with inadequate inrush limiting can pull considerable
current from the mains at turn-on. This can result in fast acting mains breakers
tripping. Such is not the case with C Series amplifiers in most circumstances.
The C Series amplifiers have very low inrush power as the capacitors are charged
slowly, and in a controlled manner, ensuring that breakers will not trip.

Several amplifiers will, under normal conditions, be able to be powered up
simultaneously. If you do experience problems powering up multiple amplifiers
simultaneously (normally experienced only in very large installations), use the
NomadLink network and the NLB60E to establish a power sequence with pre-set
delays before the start-up of each subsequent amplifier.

Front-panel monitoring

Level indicators

Four signal/level/clip LEDs per channel are contained on the C Series front panels

•

Orange

CPL (Current Peak Limiter) flashing indicates signal exceeds the limits

of the output devices and limiting is in effect.

•

Red

VPL/CLIP indicates that the signal has exceeded maximum output

voltage. (Maximum voltage is determined by rear-panel VPL settings.)

•

Green

- 4 dB indicates output signal has reached this level.

•

Green

- 10 dB indicates output signal has reached this level.

•

Signal / Hi-Imp

(Green/red) indicates an output signal above -44 dB. If it

turns RED, this indicates that a high-impedance (“open” connection) has been
detected at the output. This can be a fault such as a disconnected cable or
malfunctioning loudspeaker driver. However, it could indicate acceptable high
impedance, such as a sub-bass enclosure with high impedance at a certain
frequency. When the -10 dB signal LED is on AND the Hi-Imp LED turns red
then the amplifier has detected an open load (no speaker is connected).

For more detailed signal level indications use the DeviceControl
software application.

Level adjust

Level adjust potentiometers (one per channel) are located behind the removable
dust-filter cover on the amplifier’s front-panel. It is not possible to adjust the
level settings with the cover in place.

Step

Attenuation

Step

Attenuation

1 (Min)

-Inf. dB

-8.7 dB

-Inf. dB

-7.4 dB

-50 dB

-6.0 dB

-40 dB

-4.5 dB

-35 dB

-2.7 dB

-21.5 dB

-0.6 dB

-21.5 dB

-0.3 dB

-14.7 dB

-0.1 dB

-12.9 dB

0 dB

-11.4 dB

21 (Max)

0 dB

-10.0 dB

The potentiometer’s operational range is 0 dB to -infinity in 31 steps. Attenuation
is logarithmic, with 12 o’clock position being -10 dB. See table to the above
with increments.