Gain Controls
The
CR5’s
gain controls are located on the back of the amplifier. This prevents tampering with the gain controls
when the amplifier is rack mounted. The gain controls are calibrated in dB (decibels), corresponding to the audio
voltage present at the speaker output jacks. Where many amplifiers are used in an installation, the gain controls
scaled in dB allow the user to precisely set the audio output level of one
CR5
amplifier channel relative to the other
CR5
amplifier channels. This only works if the amplifiers are receiving the same amplitude of input audio signal. The
0db or “full” position of the gain control refers to 31.6 volts RMS (which equals 250 watts into 4 ohms) on the output
of the amplifier when a 1.4 volt RMS voltage is present at the input jacks. Placing the gain control in the –3dB posi-
tion with 1.4 volt RMS voltage present at the input jacks will result in a 22.3 volt signal (which equals 125 watts into
4 ohms) at the speaker output.
Limiter
The limiter switch located on the back panel of the amplifier changes the mode of the limiter. When the limiter
switch is in the “peak” position, the limiter acts as a peak limiter with a short decay time. This allows the bass
thumps in music to drive the output of the amplifier into clipping for the duration of the thump, but will not
heavily clip a continuous signal like someone screaming into a microphone. When the limiter switch is in the
“average” position the release time of the limiter is extended and the limiter acts more like a leveler. This mode
is useful for public address applications where the full headroom of the amplifier is utilized and the quality of the
voice is maintained by using the soft clipping feature of the limiter.
Short Circuit Protection
The
CR5
is fully protected against all possible passive loudspeaker load conditions. It can operate with a “dead”
short continuously without damage (however, we don’t recommend that you short your
CR5
“just for fun”).
Shorts create a lot of stress on the output devices. If a short is present on the output of the amplifier with a signal
passing through the amplifier then the protect LED will illuminate and the amplifier will go into “sleep mode”
turning off the audio signal passing through the amplifier. After 8 seconds, the amplifier will allow the signal to
pass through the amplifier and check to see if the short has been removed. If the short is still present the amplifier
will go through the sleep mode cycle again. If the short has been removed, the amplifier will continue to drive
the speaker. The output protection will allow the output of the amplifier to drive up to 35 degrees of phase shift
at 4 ohms or a load impedance of 3 ohms with no phase shift.
Cooling & Thermal Protection
Passive cooling (this means that there isn’t any fan in the amplifier) was chosen for this design to provide years
of mantainence free operation. In dusty locations dirt may settle on the heatsinks. If the amplifier is permantly
installed in a location the heatsinks must be cleaned regularly.
When operating the
CR5
care should be taken to allow adequate cooling around the heatsink fins along the
sides of the chassis and not to block the ventilation holes in the top and bottom covers of the chassis. The
CR5
was designed to run cool under normal operating conditions, but restricting the airflow around or through the
amplifier could cause the amplifier to thermally shutdown.
If the temperature on the heatsinks of the
CR5
exceeds the safe operation temperature, then the amplifier will
shutdown illuminating both protection LED’s and turn off the audio signal to the speaker output jacks until the
heatsink temperature drops to a safe level.
Rack Mounting
The
CR5
was designed to mount into a standard 19” rack. Care must be taken to provide adequate ventlation around
the amplifier. Here are some tips to ensure that the
CR5
will have adequate cooling when mounted into a rack:
• Leave a blank rackspace above and below the amplifier when stacking equipment into the rack.
• If several
CR5
s are stacked in a rack, in addition to the tip above, provide fan forced cooling from the bot-
tom of the rack up through the amplifier stack.
The rack itself should have adequate ventilation to the outside air. Leave the front and back of the rack as
open as possible. If fans are used, draw the air in through the bottom front of the rack, drive the air up through
the amplifiers, allowing the air to vent out through the top back section of the rack.
Clip / Protection LED’s
The clip/protection LEDs on the front panel will blink to visibly indicate any signal excursion beyond the dynam-
ic headroom of the amplifier. The clip/protection LEDs will remain on when the amplifier goes into its protection
mode. The
CR5
will go into protection for one of three reasons:
• The power switch of the amplifier has just been turned on or off.
• The amplifier has a shorted speaker load on the output of the amplifier.
• The temperature on the heatsinks of the
CR5
exceeds the safe operation temperature.
