McIntosh C500C Owner's Manual download pdf (Page 33)

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 Electro-Magnetic devices. This includes the selection

of the desired Audio Input Source for Listening, for Record-

ing Outputs, External Signal Processing Loop, Final Audio

Output Selection and the Audio Muting Function. These

Electro-Magnetic devices switch silently, without adding

noise to the Audio Signal for the lifetime of the C500

Preamplifier. The Balanced Input Switching Printed Circuit

Boards for one channel of the C500 are shown in figure 92.

Electro-Magnetic Switching is a proven technology that

uses the latest in materials and manufacturing methods.

Each switch consists of a glass tube filled with an inert oxy-

gen-free atmosphere and sealed with tiny leads protruding

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

Figure 93

How to Operate the C500, con’t and Technical Description

Figure 92

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McIntosh C500C Owner's Manual Page 33

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