Fully Balanced Circuitry

balance and freedom from control noise.

cuitry. This design topology allows for the virtual cancela-

The Volume Control

Optical Disc

tion of all forms of distortion, both audible and measurable,

on the Front Panel of

along with extremely low background noise levels.

Infrared LED

the C500 is actually a

In the typical Preamplifier, one set of circuits have to

special digital optical

amplify the positive and negative going parts of the audio

encoder. As the Volume

sound wave form. In the C500, the implementation of fully

Control is rotated, a

balanced circuitry has the positive going audio sound waves

beam of Infra Red Light

Sensors

amplified by one set of circuits. In a similar manner the

is picked up by two in-

negative going audio sound waves are amplified by another

ternal sensors as a series

set of circuits. Refer to figure 100. Audio signals connected

of digital pulses. Refer

Figure 97

to figure 97. The number of and time between

pulses are counted by a Microprocessor which

in turn controls the McIntosh designed Preci-

sion Electronic Attenuator that provides 213

steps in 0.5dB increments and maintains the

channel balance to within + 0.1dB.

With most Preamplifiers the Volume Con-

trol is placed ahead of the Amplifying Cir-

cuitry, refer to figure 98 on the next page, ex-

ample No.1. This design provides a great dy-

namic range and freedom from input overload,

but the background noise level is higher espe-

cially at lower settings of the volume control.

In example No. 2, by placing the Volume Con-

trol after the Amplifying Circuitry there is a

reduction in dynamic range and input overload

of the Preamplifier, but has the benefit of

lower background noise levels. The only cor-

rect way to design a high performance Pream-

plifier is with two volume controls, refer to

example No.3. This provides the benefits of

wide dynamic range, freedom from Input over-

load and a background noise level that actu-

ally goes down as the volume control setting is

Figure 98

reduced. The actual improvements in

this McIntosh design achieve a noise

Signal to Noise vs. Volume Level of the

floor of 118 dB, refer to figure 99.

C500 Preamplifier versus High Performance

The special controlling circuitry for

Mechanical and Electronic Volume Controls

-95

this dual volume control design is

(dB)

known as the McIntosh “Dynamic

-100

Mechanical

Control Multiplexer”.

Noise

-105

Electronic

-110

C500

Signal

To compliment the level of perfor-

-115

mance achieved in one of McIntosh’s

famous Power Amplifiers with Quad

-120

-95

-85

-75

-65

-55

-45

-35 -25 -15

-5

Balanced Circuitry, the C500 Pream-

Volume Level (dB)

plifier also utilizes fully balanced cir-

Figure 99