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Safety
6
Protection Features
CKi Series amplifiers incorporate several circuits to protect both themselves
and loudspeakers. Crest Audio has attempted to make the amplifiers as fool-
proof as possible by making them immune to short and open circuits,mis-
matched loads,DC voltage and overheating. If a channel goes into ACL gain
reduction mode,the speaker load will remain connected but clipping percent-
age or output power will be instantly reduced. When a problem occurs that
causes a channel to go into a protection mode,the Protect LED for that
channel will glow. DC voltage on the output,excessive subsonic frequencies
or thermal overload will cause the channel’s output relay to open,discon-
necting the speaker load until the condition is corrected.
Automatic Clip Limiting (ACL)
Any time a channel is driven into continuous clipping,the clip limiter
circuit will reduce the channel gain to a level just slightly into clipping,
which protects the speakers against the damaging,high power,contin-
uous square waves. Situations that may activate the clip limiter include
uncontrolled feedback, oscillations, and improper equipment setting
or a malfunction upstream from the amplifier. Normal program tran-
sients will not trigger the clip limiter; only steady, excessive clipping
will. The ACL LED will glow brightly and continuously when limiting
occurs.
IGM Impedance Sensing
CKi Series amplifiers feature innovative circuitry that allows safe oper-
ation into any load. When an amplifier sees a load that overstresses
the output stage, the Instantaneous Gain Modulation (IGM) circuit
adjusts the channel gain to a safe level. This method of output stage
protection is far superior to the conventional,brute force-type limit-
ing found on other amplifiers. The IGM circuit is sonically transparent
in normal use and unobtrusive when activated.
Thermal Protection
The internal fan will keep the amplifier operating well within its
intended temperature range under normal conditions. If a channel’s
heat sink temperature reaches 75°C (which may indicate an obstruct-
ed air supply),that channel will independently protect itself by discon-
necting its load and shutting down until it has cooled. During this
time,the Protect LED will light,the Active LED will extinguish and the
cooling fan will run at its highest speed.
Short Circuit
If an output is shorted,the IGM and thermal circuits will automatical-
ly protect the amplifier. The IGM circuit senses the short circuit as an
extremely stressful load condition and attenuates the signal,protect-
ing the channel’s output transistors from over-current stress. If the
short circuit remains, the channel will eventually thermally protect
itself by disconnecting the load.
DC Voltage Protection
If an amplifier channel detects DC voltage or subsonic frequencies at
a channel output,the respective output relay will immediately open to
prevent loudspeaker damage.The Protect DC LED will light.
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