Lab.gruppen C Series C 16 4 Operation Manual page 8

7 OPERATION AND PERFORMANCE
7.1 Introduction
The following sections provide comprehensive infor-
mation on amplifier connection, setup, operation, and
performance. The detailed information included here
is essential to realizing the full functionality of the C
Series amplifiers.
7.2 Operation precautions
• Make sure that the Power switch and the Remote
switch on the amplifier front-panel are set to
"off" before making any input, output or network
connections, and also before manipulating the
DIP-switches on the rear-panel.
• Make sure that the AC mains voltage is correct
and matches the voltage printed on the rear-panel
of the amplifier (115 V or 230 V).
• Make sure that no signal is present at the input
to the amplifier when powering up. This could
produce an unintentionally loud initial volume
from the speakers.
7.3 Signal flow and headroom
7.3.1 Signal flow blocks
All C Series amplifiers have the same signal flow
and feature set. The only difference is the amplifier's
maximum output current per channel.
The input stage of all C Series amplifiers has a high
sensitivity to provide ample system headroom. This
in effect means that the input stage is almost impos-
sible to clip.
14 C Series C 68:4, C 48:4, C 28:4 and C 16:4 Operation Manual
Overall amplifier input gain is adjusted using the
input stage DIP-switches. Please note that the gain
setting is global, affecting all four channels. Following
the input stage, the dedicated level control on each
channel allows signal attenuation from 0 dB to minus
infinity.
The CPL (Current Peak Limiter) section dynamically
limits the input signal based on three parameters:
sensed current level, feedback from the output stage,
and sensed voltage clip from the VPL (and output
amplifier voltage clip if "Soft Clip" activated). This
ensures that power output is maintained within the
design limits of the amplifier.
The adjustable VPL (Voltage Peak Limiter) sets the
maximum output voltage and therefore also the
maximum output power. Eight (8) different voltage
stages are available using the DIP-switches on the
rear-panel. See table in Appendix section with VPL
ratings at typical loads.
The sophisticated output section monitors faults
and generates appropriate warnings, which are
displayed on the amplifier front-panel and transmitted
through the NomadLink network. These alerts allow
the operator to adjust system settings and thereby
avoid problems. In the rare event that conditions are
extraordinarily severe, the amplifier will shut down
until the fault or problem setting has been rectified
or adjusted. These sensing circuits are also employed
to feed back voltage and current level information,
via a side chain, to the limiters. Sensing circuits
also transmit local amplifier module temperature
and power supply temperature to the appropriate
protection mechanisms. Read the Protection, Faults
and Warnings section for further details.
7.3.2 headroom, sensitivity and VPL / Gain
settings
The input amplifier and limiter system is designed to
accommodate extremes of performance. Typically,
exceeding maximum input by much as +10 dB will
only result in a 1% increase in distortion. The
following schematics illustrate how the adjusable
VPL and Gain circuitry affect input sensitivity and
output power:
The tables to the left of the drawing below show
input sensitivity for C 68:4 with an 8 ohm load and
141 V peak (max.) and 42 V peak (min.) respectively
for the eight different gain stages between +23 dB
and +44 dB. The resulting output power is displayed
in dBu, Vrms and Watts in the tables to the far right.
Complete input sensitivity tables for all VPL and
Gain settings for all C Series models, can be found
at www.labgruppen.com.
C 68:4 VPL and GAIN settings
C Series C 68:4, C 48:4, C 28:4 and C 16:4 Operation Manual 15
OPERATION AND PERFORMANCE 7
The headroom available through the input stage to
the clip limiter is shown by the dotted lines as +10
dB at 141 V peak and +20.4 dB at 42 V peak. These
lines illustrate the additional signal level that can be
accepted at the input before any significant distortion
will appear at the input stage.
If you use the level potentiometer in the
signal chain to reduce the level by an amount
greater than the headroom relative to input
sensitivity, AND you drive the amplifier to
clip level, you are in danger of clipping the input stage
before the current or voltage peak limiters are
activated.
When bridging two channels, you must add
+6 dB to the input sensitivity to achieve
maximum output voltage due to the
automatic -6 dB gain compensation
inserted by the amplifier.