STEREO POWER MC24O AMPLIFIER
CONTENTS
GENERAL DESCRIPTION |
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TECHNICAL DESCRIPTION |
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PANEL FACILITIES |
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INSTALLATION |
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CONNECTIONS |
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Input—Stereo |
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Input—Twin Amp |
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Input—Mono |
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Output—Stereo or Twin Amp |
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Output—Mono |
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Line Output—Stereo or Twin Amp |
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Line Output—Mono |
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AC Power |
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OPERATION |
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ADJUSTMENTS |
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GUARANTEE |
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OWNER'S MANUAL
O
MC24
MC240 STEREO POWER AMPLIFIER
GENERAL DESCRIPTION
Over one million watts of amplifier output power capacity have been manufactured by Mclntosh since 1947. In this 1,000,000watts 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. Mclntosh Laboratory is the only manufacturer in the entire industry to guarantee the lowest distortion at all audio frequencies, at full power. The U.S. Patent Office has recognized the advanced technology of the Mclntosh circuit by granting 6 patents.1
Long life, flexibility, highest quality construction are characteristic designs in every Mclntosh instrument. Wide electrical and thermal margins of safety for all components and tubes, advanced engineering, and cool operating design add to the long life built into every Mclntosh product. Reliability prolongs your investment without expensive maintenance costs.
The MC240 has on one chassis two 40 watt power amplifiers. In addition to use as a stereo amplifier, the flexibility of the MC240 permits it to be used as a monophonic amplifier that delivers 80 watts, or as two separate 40 watt amplifiers with each channel amplifying completely separate programs, or as two amplifiers for use with an electronic crossover network. Such flexibility permits maximum use for greatest return from your investment.
TECHNICAL DESCRIPTION
The patented Mclntosh Unity Coupled circuit and output transformer have established Mclntosh amplifiers as the unchallenged leaders in the audio field.
Before 1947, low distortion at high power and high efficiency was impossible. A completely new engineering approach resulted in an amplifier that for the first time permitted high power with distortion below 1%. That new engineering produced the Mclntosh Unity coupled circuit and the Mclntosh bifilar wound output transformer. With the introduction of the Mclntosh amplifier new standards for distortion-free performance were established.
turn of primary number one is next to the same turn of primary number two. There is almost complete magnetic coupling between the two wires. The magnetic coupling is reinforced by the capacitance between the two wires.
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OUTPUT |
Fig. 1 —Representation of bifilar winding.
The Mclntosh output transformer is unique. It has two primary windings which are wound bifilarly. In the bifilar technique both
primary wires are wound side by side. Each Fig. 2 —Representation of Mclntosh output circuit.
1U.S. Patent No's: 2,477,074; 2,545,788; 2,646,467; 2,654,058; 2,860,192; 2,929,028.
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In the Mclntosh Unity Coupled circuit one of the bifilar primary windings is connected through the power supply to the plate and cathode of one of the output tubes. The other bifilar primary winding is similarly connected to the other tube.
All low distortion high power amplifiers use push-pull output circuits known as Class AB1, AB2 or B. Two tubes are arranged in a balanced circuit. This permits each tube to operate alternately somewhat over half the time. Compared to full time operation of the tubes, the push-pull method reduces heating and permits more power from a given type of tube. Despite this advantage of the conventional push-pull circuit one problem in particular remained to be solved. When current in each tube is cut off to begin the idle period distortion is produced at the instant of cut off and again at the instant when current flows. This form of distortion is known as Notch Distortion and was well illustrated by Mr. Pen Tung Sah in the "Proceedings of the I.R.E." Volume 24, pp 1522-1541 in 1936.
Imperfect coupling between the primary windings found in all conventional output transformers produces the condition which permits notch distortion. Trying to improve coupling in a conventional transformer decreases the power response at both low and high frequencies, heating the output tubes and lowering the available power output.
The Mclntosh Unity Coupled output circuit and bifilar transformer is the first commercial breakthrough that eliminates notch distortion by coupling both output tubes almost to perfection. In the Mclntosh transformer the extremely close coupling of the bifilar windings removes the condition which permits notch distortion. Furthermore the the two output tubes are arranged as partial cathode followers. Half of the output circuit is in the cathode and half in the plate of each tube. The output tubes now are operating in a local feedback loop which, reduces their
distortion, reduces their internal generator resistance, and reduces their balance requirements. The Mclntosh circuit in reality perfects push-pull high efficiency output circuits.
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 groups of primary layers, then secondary layers alternately until the total transformer is wound. Interleaving helps to extend the Mclntosh power band width to over 100,000 cycles. Since 1947 this new technology has been built into every Mclntosh 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 MC240. 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 a thermistor in the MC240 limits 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 79 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 .1 ohms). Current is thus limited when the MC240 is first turned on but is not limited as the unit warms.
ELECTRICAL SPECIFICATIONS
Power Output:
Stereo or twin amplifier—40 watts continuous per channel
Monopnonic—80 watts continuous
Harmonic Distortion:
Less than 0.5% at rated output or less,
20 cycles through 20,000 cycles. Typical performance is 0.3% or less at 20 cycles and 20,000 cycles at full power. Typical performance in the mid frequencies is 0.1% or less at full power.
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