User manual HAFLER SERIES 9270

[. . . ] Series 9180/ 9270 Power Amplifier NOTICE - IMPORTANT SAFETY INFORMATION The lightning flash with arrowhead symbol within an equilateral triangle is intended to alert the user to the presence of uninsulated "dangerous voltage" within the products enclosure, that may be of sufficient magnitude to constitute a risk of electric shock to persons. WARNING: TO PREVENT FIRE OR SHOCK HAZARD, DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE. The exclamation point within an equilateral triangle is intended to alert the user of the presence of important operating and maintenance (servicing) instructions in the literature accompanying the appliance. 1. READ INSTRUCTIONS All the safety and operating instructions of your Hafler equipment should be read before power is applied to the equipment. RETAIN OWNERS MANUAL These safety and operating instructions should be retained for future reference. HEED WARNINGS All warnings on the equipment and in the operating instructions are important and should be followed. FOLLOW INSTRUCTIONS All operating and use instructions are important and should be followed. [. . . ] Set the Stereo/ Mono Switch in the OUT position for Stereo Mode, or in the IN position for Mono Mode. Mono Mode operation requires different input and output connections: consult the sections of the manual titled "Inputs" and "Outputs". SOFT TURNON/OFF SYSTEM The 9180/9270 Amplifier is equipped with a Soft Turn-On/Off System that gradually activates the amplifier's circuitry to avoid spurious noises as the power supply stabilizes. At turn-off, this same system rapidly deactivates the amplifier's circuitry before the power supply begins to collapse, again eliminating any spurious noises. THERMAL PROTECTION SYSTEM The 9180/9270 Amplifier is equipped with a Thermal Protection System that constantly monitors the temperature of the heatsinks. When the heatsink temperature reaches a pre-determined level, the amplifier's circuitry is electronically shut down through the same system that provides the Soft Turn-On function. When the heatsinks cool to a safe operating temperature, normal operation of the amplifier resumes. -8- CIRCUIT HIGHLIGHTS The input stage of the 9180/9270 Amplifier utilizes four low-noise, High-g, JFET's (high transconductance junction field-effect transistors), in a fully complimentary, symmetric configuration. This circuit configuration results in excellent front-end headroom and a simple, straightforward connection to the remainder of the circuitry. The ultra low noise characteristics of the JFET's virtually eliminates noise "mixing" (intermodulation) with the music signal, reducing discordant product frequencies known as "noise grain", or "noise fuzz". The input stage is cascode connected to convert the low voltage input system to the high voltage output system, and "speeds up" the front end for superior bandwidth. The cascode stage is connected to an emitter-follower and current mirror configuration that amplifies the current level about ten times, necessary to drive the biasing string and final output stage driver emitter followers. The final output stage uses multiple lateral MOSFET's (Metal Oxide Semiconductor Field Effect Transistors): four devices per channel in the 9180, and six per channel in the 9270. These devices, unlike conventional bipolar transistors, have a negativetemperature coefficient, which means that they do not exhibit "thermal runaway". Thermal runaway is a phenomenon whereby a transistor heats up as it conducts more current, which causes it to get hotter, and conduct more current, and so on, until the device self destructs. Since MOSFET's are inherently self-protecting, no sonically degrading, complex circuitry is required to monitor and protect the output devices. Furthermore, these lateral MOSFET's exhibit a very linear input to output transfer function. Their connection in circuits and operating characteristics are very similar to vacuum tubes, which is perhaps responsible for their widely recognized sonic trait of being very "musical" and non-fatiguing. Conversion to Mono Mode is accomplished by driving the negative input (feedback point) of the right channel with the output of the left channel. This causes the right channel to mirror exactly the output of the left channel, but 180 degrees out of phase. This creates twice the voltage swing to be available across the two red output binding posts. This simple method of bridging the amplifier (involving only one resistor) eliminates the costly and sonically degrading invertor circuitry used in other amplifiers. The Thermal Protection System consists of thermistors (temperature sensitive resistors) mounted to the heatsinks, connected to a comparator system that activates when the heatsinks reach an unsafe operating temperature. The output of the comparator system is connected to a small MOSFET switch that turns off the input stage of the amplifier, which effectively shuts down the entire amplifier. When the heatsinks cool to a safe temperature, the amplifier is turned on again. [. . . ] SPECIAL NOTE ON VIDEO CABLE "GROUNDS": As mentioned above, the ground conductor of cable service and antenna feeds should be connected to earth ground. Often, however, due to long feed lengths, especially in apartment distribution systems, this ground will be of poor quality and could be a source of noise. This interference is usually characterized by a high frequency noise, rather than a hum or a buzz. If such interference is experienced, a separate earth ground connection should be made from the cable outlet nearest the audio/video equipment to a known good earth ground. If ground loops exist due to potential differences in the interconnects in rack mounted systems, then it is advisable to isolate the preamplifier chassis from the rack rails. [. . . ]