Nexo NUAR - Manual (Page 41)

BLOCK DIAGRAM DESCRIPTION
The so-called Physiologic Dynamic Control (see block diagram) is intended to avoid
unwanted effects as a result of a too long attack time constant. By anticipating the
operation of the temperature limiter, it prevents a high level Audio signal appearing
suddenly then being kept up for a period, which is long enough to trigger the temperature
limiter. Without this, a rough and delayed gain variation would result which would be quite
noticeable and unnatural.
The Physio control voltage acts independently on the VCA with its operation threshold
slightly lower (3 dB) that of the temperature limiter and a low compression ratio; its
optimised attack time constant allows it to start operating without any subjectively
unpleasant transient effects.
Interchannel regulation (19)
As described before, each transducer is individually servo-controlled for temperature. This
means in practice that, in case of a potential risk detected, protective operation would only
affect the concerned driver. Your driver will be protected but the overall system tonal
balance could be altered if the different channels are not heating at the same time. In
addition, triggering a temperature protection means that the loudspeaker has already lost
some efficiency (power compression up to 3dB in extreme cases)
The purpose of interchannel regulation is to cancel that effect by linking VCAs together.
When the protection is activated on one channel and reaches a predetermined threshold,
the regulation section begins to correct the balance between the different channels (HF,
MF, and LF) by acting on the concerned VCA.
Amplifier peak current limiter (20)
To prevent over-current on the output of the amplifier, this peak current limiter is
implemented, leading to a separate VCA (block (30)) from the one being used for
loudspeaker protection (block (26)). This protection is implemented here mostly in case of
default of the power supply, and will barely be triggered during normal use, because it is
set up at the limit of what can deliver the power supply of the amplifier.
Amplifier integrate current limiter (21)
This protection which is also triggering a VCA will compute the integration of the current
over time to check that the current drawn by the amplifier will not go above what is
acceptable for the mains. With musical signal should never trigger this protection, mainly
implemented for protection against continuous signal like sine wave and so on.
Amplifier peak voltage limiter (22)
This is a “soft clip” limiter that will reduce the output level though a VCA process to limit
the clipping of the amplifier.
Amplifier short circuit detector (24)
If a short circuit is detected on the output, the amplifier will mute itself, and will release the
mute a few second after automatically. This is shown on the front panel by a blinking of the
peak LED of the concerned channel, together with the “Amp protect” LED.
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