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U S E R M A N U A L
Q - P O W E R 14
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P O W E R A M P L I F I E R
7
P R O T E C T I O N S
7. Protections
7.1 Power Amp Protection Systems
7.1.1 Clip Limiter
If the maximum output level is higher than the amplifier can deliver, the Clip Lim-
iter (if active) will reduce the output signal in order to limit distortion.
The Clip Limiter works on each channel independently, but can only be activated
for the channel pairs A/B or C/D respectively.
The Clip LED sensitivity on the display is designed to be very responsive and
accurate. This means that you will still see the Clip LEDs light up, even if the
clip limiter is working correctly. This allowes the user still to assess if there is real
clip, even if the clip limiter does prohibit audible distortion. The remaining (and
indicated) clip is then very small and usually low enough to be audibly perceive
as “clean” or undistorted signal, compared to a disabled clip limiter.
7.1.2 SOA Protection
Whenever the power transistors leave their Safe Operation Area (SOA), the
SOA-protection will limit the maximum output current in an extremely fast way,
to effectively protect the semiconductors from any damage. This protection will
usually only take place at loudspeaker impedances equal or lower 2 Ω. Audio
quality might be deteriorated when this limiter takes action.
7.1.3 DC Protection
Each output of the power amp is constantly monitored for persistent DC voltage
levels. If the approx. 5 V thresholds are exceeded at any of the outputs, the cor-
responding channel will be muted. If DC was only detected for a short moment,
the amplifier will release mute and resume operation. If DC is detected for longer
periods or repeatedly, the amplifier will switch to standby mode and disable the
main power supply.
7.1.4 DC Servo
To prevent DC offset at the speaker output the
Q-POWER 14
amplifier is fitted
with a DC Servo (hence there are no capacitors in the signal path!).
7.1.5 Output Current Limiter
The output current to the loudspeakers is permanently controlled in the output
stage. In case of exessive loading the maximum output current of the amplifiers
is automatically limited. This improves reliability without degrading sound quality
when driving complex loads.
7.1.6 Underimpedance Limiter
In case the SOA protection is triggered repeatedly, each amplifier module will
clip it’s maximum output level until SOA protection is not reached anymore. This
usually only takes place at loudspeaker impedances equal or lower approx. 2 Ω.
This limitation is done through pure clipping of the output voltage, so it will result
in audible distortion in case the Clip Limiter is not activated.
7.1.7 Output Short Circuit Protection
In case the attached loudspeaker impedance gets lower than approx. 0,6 Ω
(e.g. in case of any short-circuit inside the loudspeaker or the cabling) each
amplifier module will switch off completely for 3 seconds to protect internal elec-
tronics.
After 3 seconds, the module will try to resume operation (... and possibly again
trigger the circuit protection in case the short circuit is still present).
l
Note
This protection only works for mid to high output levels. Low output levels
will not be enough to trigger the short circuit protection, even if the short
is well below 0,6 Ω. At low output levels, the amplifier will only carry out
SOA, output current, underimpedance and possibly thermal limitation but
will continue to deliver music.
7.1.8 Thermal Limitation and Protection
There are sensors in each amplifier heatsink in order to ascertain it’s tempera-
ture. If a temperature of more than 85 °C is detected at the heatsinks, the input
signal on that channel is reduced proportionally to prevent further heating of the
amplifier. If the temperature exceeds approximately 95 °C, the corresponding
channel is muted completely.
