Amplifier And Load Protection Systems - Lab.gruppen PLM series Operation Manual

Operation and Performance
In reality, when some channels are delivering less than maximum rated power, energy reserves in the PSU
are available to permit other channels to deliver more power. The graph shows the peak output voltage over
time for a continuous sine wave is applied.
If all four channels are driven with the same signal into the same impedance (solid red line), then the rail
voltage (dotted red line) will drop faster than when two channels are delivering maximum power (solid blue
line) and two channels are delivering half-power (solid orange line). This is termed asymmetric loading; the
rail voltage for this is indicated by the dotted blue line.
It can be seen that higher power output is available for 25 ms bursts with asymmetric loading.
5.3

Amplifier and Load Protection Systems

The PLM is equipped with a comprehensive set of protection circuits. If operating conditions become suf-
ficiently extreme that any of these circuits become active, indication is provided by LEDs in one or more soft
function buttons 5-8, together with adjacent warning text. In addition to this, notification is also presented
within the Lake Controller software and within system log files.
5.3.1 Inter-Sample Voltage Peak Limiter (ISVPL)
The ISVPL is a high quality voltage limiter that can deliver seamless limitation to any desired level. Its
ensures that the voltage at the output terminals never exceeds the defined threshold.
It operates on these principles:
▸ The signal is delayed slightly to allow the ISVPL to look-ahead and reduce the gain before voltage in
excess of the threshold can appear at the output. This results in zero voltage overshoot at the output
with a rounded limitation up to the threshold.
▸ The amplitude of the output signal between digital samples is predicted which permits the ISVPL to
respond to analog peaks that may occur at the digital to analog converter.
▸ The release time of gain reduction is adaptive depending on the dynamics of the signal.
It is possible to select different ISVPL profiles for limiting optimization for a specific frequency band and
personal preference. The profiles are divided into two categories, with one category optimized for low
distortion and the other focusing on producing high sound pressure level (SPL). Within each category there
are profiles optimized for the different frequency bands.
5.3.1.1 Low Distortion Profiles
▸ Universal – The universal profile is a soft limiter that can be used for all frequencies and is conservative
in its action upon VCL and CPL.
▸ Sub/LF – The Sub/LF profile is tuned for frequency bands below 600Hz. It has longer attack and release
times and is less conservative when it comes to acting upon VCL and CPL.
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PLM Series Operation Manual rev 1.1.9