sealed with tiny leads protruding from either end. Refer to figure
10.These leads extend into the tube and overlap one another with a separation of a few thou- sandths of an inch. The leads are
made from a ferrous material that is influenced by a magnetic field.
They are first plated with gold as a base material, then with rhodium and finally ruthenium. Ruthenium is the best contact material known.
The glass assembly is then placed in the center of a multilayer coil of copper wire. The entire assembly is molded together in a tough shock absorbing material. The switch and coil connectors extend from the bottom in the form of printed circuit board terminals. When a DC volt- age is applied to the coil, current flows and creates a mag- netic field. The force of the field causes the leads to bend and contact one another inside the sealed glass tube. The inert gas eliminates corrosion of the contacts and insures a low resistance, distortion free switch.
All inputs, outputs, and data ports are controlled by logic circuits in the MA7000. The logic is changed by front panel
The equalizer section uses several high technology operational amplifiers. The amplifier stage has been op- timized for the best transient performance and minimum distortion. Five other operational amplifiers are arranged in a circuit configuration that is the equivalent of a series turned circuit. A control potentiometer inserts this series tuned circuit into either the feedback or input section of the equalizer amplifier. This provides a 12dB boost or cut at the frequency of the tuned circuit. Refer to figure 11. The overall gain of the stage is 0dB when the potentiometer is at its center detent position. In this position the tone control elements are completely removed from the signal path.
Power Amplifier Design Philosophy
The design philosophy incorporated in the MA7000 involved several different techniques, all based on sound scientific logic. Every stage of voltage or current ampli- fication must be as linear as possible prior to the use of negative feedback. McIntosh engineers know how to prop- erly design negative feedback circuits so they contribute to the extremely low distortion performance expected from a McIntosh Amplifier. The typical McIntosh owner would
Figure 11
never accept the approximately 100 times higher distortion of many
All transistors are selected to have nearly constant cur- rent gain over the entire current range they must cover. The 12 Power Transistors used in each channel of the MA7000 Power Output Circuitry, have matched uniform current gain, high current bandwidth product and a large active region safe operating area. These Power Transistors are the very latest in semiconductor technology and incorporate a new design known as Thermal-
Trak™. Refer to figure 12. This allows for the instantaneous and accurate monitoring of the Power Transistor Temperature. The MA7000 Power Output Circuitry has a specially de- signed bias circuit to take full advantage of the ThermalTrak™ Power Transistors and thus precisely controls the power amplifier opera- tion over a wide range of music conditions
with the benefits of lower distortion and cooler operation. Precision metal film resistors and low dielectric absorption film capacitors are used in all critical circuit locations.
The output signal of the circuit is coupled together in the unique McIntosh MA7000 Output Autoformer. It provides low distortion power transfer at frequencies from below 20Hz to well beyond 20,000Hz with optimum impedance points of two ohms, four ohms and eight ohms. The unequaled expertise of McIntosh in the design and manufacturing of autoformers is legendary in the high fidelity industry.
The high efficiency circuit design of the MA7000 con- tributes to low operating temperatures. More than 1,000 square inches of heat sink area keep the MA7000 operating safely with convection cooling. No fans are needed.
ThermalTrak™ - is a trademark of Semiconductor Components Industries,
LLC (SCILLC)
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