ADDITIONAL INFORMATION
LOUDSPEAKER LOAD IMPEDANCE CONSIDERATIONS
CHANGING LINE VOLTAGE RATING
ADJUSTlNG BIAS
The 9180/9270 Amplifier is suitable for use with a wide variety of loudspeaker types and load impedances. Though not rated for impedances below 4 ohms, the amplifier is capable of driving lower impedances. Operation at low impedances is limited by the thermal dissipation capacity of the heatsinks and the airflow around the unit. Operation at very high power levels into low impedances for extended periods may overheat the amplifier, but no damage will occur due to the Thermal Protection System.
In the Mono Mode, some additional consideration is required when driving low impedances. When a stereo amplifier is converted (bridged) into a single channel mono amplifier, each half of the bridged amplifier “sees” only half of the loudspeaker’s load impedance. For example, when driving an 8 ohm load in the Mono Mode, each channel is actually loaded to 4 ohms. Therefore, little advantage is gained when attempting to drive 4 ohm loads (2 ohms per channel) in the Mono Mode, because of the reduced power available at extremely low impedances. It is usually better to use a stereo amplifier of higher power rating (rather than two bridged amplifiers of lower power) when driving low impedances.
The 9180/9270 Amplifier is equipped with a simple means to adjust the AC line voltage rating for 100, 120, 220, or 240 volts AC, 50/60 Hz. The configuration is labelled above the power cord connector. If the amplifier will be used in a location that requires a different line voltage, use the following procedure to change the configuration. Review the modification instructions before attempting this procedure. If any doubts exist about one’s ability to change the line voltage, it is advisable that the procedure be conducted by a qualified technician.
WARNING! UNPLUG THE UNIT FROM AC POWER BEFORE ATTEMPTING THIS PROCE- DURE. FAILURE TO DO SO CAN RESULT IN SEVERE ELECTRICAL SHOCK.
1)Remove the top cover by removing the seven allen head screws (three on each side, one at rear center).
2)Using the diagram “Component Layout” as a guide, find the white Voltage Selector plug on the printed circuit board located behind the front panel Power Switch. Note that this plug has several alternate positions. Each position is labelled for where the end of the plug is to be aligned for each appropriate voltage. Move this plug to the new desired position, making sure that the plug is fully seated on the mating pins.
3)Depending upon which new voltage is chosen, it may be necessary to change the AC line fuse. Locate the
fuse with a new |
9180: 100 and 120 VAC: 7 amp 220 and 240 VAC: 4 amp
9270: 100 and 120 VAC: 10 amp 220 and 240 VAC: 5 amp
4)Replace the cover.
5)Obtain a new voltage configuration label from the factory, and affix over the original markings on the rear panel. Alternately, prepare a small
The 9180/9270 Amplifier employs a single control per channel to set the bias operating point of the output stage. This bias point is factory set, and normally should not require adjustment for the life of the product. However, should improper bias be suspected, or if repairs have been made that would require a readjustment of bias, the following procedure should be used. Review the instructions before attempting this procedure. If any doubts exist about one’s ability to set the bias, it is advisable that the procedure be conducted by a qualified technician.