AMPLIFIER |
MC275 |
STEREO POWER |
|
5
MC27
MC275 STEREO POWER AMPLIFIER
INTRODUCTION
The MC275 Commemorative issue amplifier and owner's manual are faithful reproductions of the originals, produced from May, 1961 through July, 1973. A few changes were made to the original amplifier design to reflect technology advances and contemporary system requirements.
Gold plated Balanced Audio Input connectors are added to take advantage of the greater noise reduction capabilities of Balanced Cables. High current capacity Gold Plated Output terminals are also in-
cluded. Close tolerance film resistors, polypropelene capacitors and fiberglass printed circuit boards are used.
This amplifier is dedicated in remembrance of the late Gordon J. Gow, coinventor of the original Mclntosh Unity Coupled circuit. Mr. Gow was Vice President of Mclntosh Laboratory Inc. from its inception in 1949 until 1977 when he was elected President. He held the position of President until 1989.
GENERAL DESCRIPTION
Over one million watts of amplifier output power capacity have been manufactured by Mclntosh since 1949. 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. 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.
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 MC275 has on one chassis two 75 watt power amplifiers. In addition to its use as a stereo amplifier, the flexibility of the MC275 permits it to be used as a monophonic amplifier that delivers 150 watts, or as two separate 75 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.
*1,000,000 Watts was the total power output produced in 12 years from 1949 through 1961. In 1992 alone, Mclntosh will produce amplifiers with a total power output of more than 5,000,000 watts with less than 1/100 watt of distortion capacity.
1U.S. Patent Nos.: 2,477,074; 2.545,788; 2,646,467; 2,654.058; 2,860,192; 2.929,028. |
1 |
TECHNICAL DESCRIPTION
The patented Mclntosh Unity Coupled circuit and output transformer have established Mclntosh amplifiers as the unchallenged leaders in the audio field.
Before 1949, 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.
PRIMARY NO. 1 |
PRIMARY NO. 2 |
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 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.
INPUT |
OUTPUT |
Fig. 2—Representation of Mclntosh output circuit.
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 AB1AB2 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 when current flows. This form of distortion is known as Notch Distortion as 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 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.
The MC275 uses an advanced design of the Mclntosh output transformer. The new
2
Loading...