USING THE C-20 CONTROL FUNCTIONS:
The C-20 controls are designed for utility and repeatability under varying conditions and make only subtle
impact on the basic character and accuracy of the speaker. We encourage you to experiment with fine tuning the
system to your particular requirements.
You’ll find two LED’s to the immediate left of the power switch on the C-20 Control Amplifier:.
The top (green) LED lights up indicating there is AC power to the amplifier and the POWER SWITCH is turned “On”.
The lower (red) LED indicates a clipping or overload condition. Occasional flashing of this indicator is a gentle
warning you are reaching the system’s limits. If the red LED glows continually, severe clipping is occurring and
the input signal or system gain should be reduced to avoid the risk of possible system damage.
Located in the center of the front panel, a unique system status display informs you of the operating state of your
system. Three small LED’s(green for average SPL, yellow for AC line voltage, and blue for heat sink
temperature)respond to your setting the square MODE switch to the right of the System Status Display to the
desired mode.
SPL: This is a reading of the long term average sound pressure level calibrated at 2 meters from the C-20 monitor, and
derived from the amplifier output voltage. Peak sound levels are ignored. The readout is designed to report overall
listening levels and to help realize consistent monitoring from hour to hour, session to session and room to room.
Levels under 68 dB are shown as “00”; levels over 120 dB are shown as “HI”. Since monitoring level has a
profound influence on the perception of sonics, periodically checking SPL helps to assure consistent results.
VAC: This is a reading of the AC power line voltage being supplied to the C-20. It is useful for assuring that power
conditions are correct and sufficient for all the equipment on the circuit. Sustained readings below 110 V may limit
your maximum output levels, and could indicate that the AC circuit is overloaded. Continuous readings above
125 V indicate an AC circuit problem, which could lead to amplifier failure.
TMP: This is a reading of the output heat sink temperature in Centigrade. Typically, you should expect this to
run between 50°C and 80°C, depending on listening and ambient conditions. If you find that your Control
Amplifier unit tends to run hotter than 80°C, it is recommended that you improve the ventilation around it. The C-
20 Control Amplifier contains a heat-prevention circuit that automatically shuts the amplifier down if heat sink
temperature reaches 100°C.
This function controls input sensitivity with settings at -10dB, -3dB, +4dB, +11dB and (M)ute to provide noise-
free, consistent gain matching with a wide variety of equipment. The proper setting is the lowest sensitivity
possible (highest dB number) which allows the speaker to reach the maximum desired output without source
clipping. Professional devices typically specify full output at +4dB, most consumer audio products reach full
output at -3dB; most computer sound cards at -10dB. Consult the owner’s manual for the source device your
connecting to the C-20 Control Amplifier for its output level specifications and set the SENSITIVITY control
accordingly.
POWER INDICATORS:
SYSTEM STATUS DISPLAY:
SENSITIVITY:
Fig. 5 C-20 Control Amplifier Front Panel
