User manual MCINTOSH MC275CE

[. . . ] In this 1, 000, 000* watts of audio power there are less than 10 watts of distortion capacity and less than 1/100 watt of noise capacity!The dramatic difference in the quality of music reproduction when you listen through Mclntosh instruments is directly due to low distortion performance. Careful, devoted research is a way of life at Mclntosh. The world's finest amplifier is the creation of persevering, resourceful Mclntosh engineers. [. . . ] The MC275 uses an advanced design of the Mclntosh output transformer. The new 2 transformer design incorporates all of the benefits of the original Mclntosh design and even further improves the power band width. Leakage inductance (lack of coupling) between the primary and secondary windings of the output transformer limits the high frequency response of an amplifier. The primary and secondary windings of the Mclntosh output transformer are interleaved five times to improve coupling. The interleaving is accomplished by winding 5 groups of secondary windings spread uniformly with the primary windings and parallel connecting the secondary windings. Interleaving helps to extend the Mclntosh power band width to over 100, 000 cycles. Since 1949, this new technology has been built into every Mclntosh vacuum tube power amplifier. Good voltage regulation in the power supply permits overloads without overshoot or blocking, good transient response, and complete stability. To improve regulation a silicon rectifier power supply is used in the MC275. In addition to better voltage regulation, the silicon rectifier allows even higher operating efficiency, cooler operation, and longer amplifier life. To greatly extend tube and component life, 2 thermistors in the MC275 limit current surges produced when the equipment is turned on. The thermistor is a special type of resistor. Its resistance depends on its temperature. When the amplifier is off, the thermistor has a high resistance value (about 25 ohms). Just after the amplifier is turned on, the current which flows through the thermistor heats it and causes its resistance to decrease to a low value (less than 0. 5 ohms). Current is thus limited when the MC275 is first turned on but is not limited as the unit warms. 3 MC275 Tube Power Amplifier SPECIFICATIONS Performance Limits POWER OUTPUT, STEREO 75 watts into 16, 8 or 4 ohm loads is the minimum sine wave continuous average power output per channel from 20Hz to 20, 000Hz. The output RMS voltage is: 34. 6 volts across 16 ohms 24. 5 volts across 8 ohms 17. 3 volts across 4 ohms POWER OUTPUT, MONO PARALLEL 150 watts into 8, 4 or 2 ohm loads is the minimum sine wave continuous average power output from 20Hz to 20, 000Hz. The output RMS voltage is: 34. 6 volts across 8 ohms 24. 5 volts across 4 ohms 17. 3 volts across 2 ohms OUTPUT LOAD IMPEDANCE 16, 8 or 4 ohms stereo 8, 4 or 2 ohms mono parallel RATED POWER BAND 20Hz to 20, 000Hz TOTAL HARMONIC DISTORTION . 5% maximum harmonic distortion at any power level from 250 milliwatts to rated power from 20Hz to 20, 000Hz. INTERMODULATION DISTORTION . 5% maximum if instantaneous peak power output does not exceed twice the output rating for any combination of frequencies from 20Hz to 20, 000Hz. FREQUENCY RESPONSE (at 1 watt output) 20Hz to 20, 000Hz +0 -0. 2dB 10Hz to 100, 000Hz +0 -3dB NOISE AND HUM (A-Weighted) 100dB below rated output 4 Ratings IHF DYNAMIC HEADROOM 1. 1dB DAMPING FACTOR Greater than 10 INPUT IMPEDANCE 100, 000 ohms unbalanced 180, 000 ohms balanced INPUT SENSITIVITY Unbalanced, 1. 0 volt to 30 volts through gain control Balanced, 2. 0 volts fixed General Information POWER REQUIREMENTS 120 volts, 50/60Hz 240 watts at zero signal output 400 watts at rated output The amplifier may be connected for 100, 120, 220 or 240 volt 50/60Hz operation. Mechanical Information SIZE 16" wide (40. 6cm) by 7-1/2" high (19. 0cm) by 12" deep (30. 5cm) WEIGHT 67 pounds (30. 5kg) net, 75 pounds (34. 1kg) in shipping carton PANEL FACILITIES Fig. 3--The end panel of the MC275 showing all input and output facilities. INPUT The MC275 has a two-position MODE Slide switch to permit the amplifier to be used as a 75 watt per channel stereo amplifier or a 150 watt mono amplifier. [. . . ] UNBALANCED GAIN For stereo operation, position the L and R gain controls for decired sensitivity. When using Mclntosh preamplifiers, we suggest setting the gain controls to the 2. 5V position. For mono operation, use the R MONO control. IMPORTANT The excellent performance that is inherent in all Mclntosh amplifiers does not depend on the critical adjustment of bias or balance controls in the output circuit. [. . . ]