How to Operate the C500, con’t and Technical Description
Technical Description
McIntosh Laboratory, the company who introduced the world’s first amplifier that could be called “High Fidelity”, has done it again. The McIntosh Engineering Staff has cre- ated a Preamplifier without compromise, using the most ad- vanced McIntosh circuit design concepts.
The C500 is the third generation of a two chassis design with fully balanced circuitry that started with the introduc- tion of the C100 in 1997. In the two chassis design, the power supplies and digital control circuitry are contained in the Controller Chassis and the second chassis contains the Preamplifier Circuitry. This prevents the possible introduc- tion of hum and noise into the audio signal. In the C500, an additional refinement has been added to help assure total channel isolation, dual mono design. There are two indepen- dent power supplies, one for each channel, and the Pream- plifier also contains two totally independent preamplifier circuits.
Creating an Preamplifier with this level of performance did not come easily. Many months of design, testing and measuring were required. Extensive controlled listening tests, the ultimate form of measuring, were made before the final design was accepted.
Silent Audio Switching
All of the Audio Signal Switching in the C500 is performed by 50
Figure 92
from either end. These leads extend into the tube and over- lap one another with a separation of a few thousandths of an inch. The leads are
made from a fer- rous material that is influenced by a magnetic field.
They are first plated with gold as a base material, then with rhodium and finally ruthe- nium. Ruthenium is the best contact material known. Refer to figure 93.
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 voltage is applied to the coil, current flows and creates a magnetic 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.
Volume Adjustments
The most frequently operated control on a Preamplifier is the Volume Control. The desired volume level can vary by the type of music, size of our listening room and even the time of day with which we listen. So it is no surprise that McIntosh has devoted a substantial amount of time in pur- suit of the “Perfect Volume Control System”.
A conventional Mechanical Potentiometer for a volume control is totally unacceptable for use in the C500 Pream- plifier. Mechanical Controls have poor tracking especially when it comes to maintaining channel balance and after a period of time they tend to introduce noise into the audio signal, as they are rotated. The one desirable thing they have is the rate of change in volume for degrees of rotation, known as the audio taper. Using Electronic Circuitry for controlling the volume can be designed to be free from noise and maintain channel balance, however the audio taper pro- duced by the typical Electronical Volume Control Circuit is unacceptable for use in the C500, as it does not match the classic McIntosh Volume Control Audio Taper. The C500 incorporates electronic circuitry together with sophisticated firmware to produce electronically the classic McIntosh Vol- ume Control Audio Taper, while maintaining the channel
33
