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Figure 95 - Top Inside View of the C1000P
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 C1000 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 C1000, as it does not match the
classic McIntosh Volume Control Audio Taper. The C1000
incorporates electronic circuitry together with sophisticated
firmware to produce electronically the classic McIntosh Vol-
ume Control Audio Taper, while maintaining the channel
balance and freedom from control noise.
The Volume Control on the Front Panel of the C1000 is
actually a special digital optical encoder. As the Volume
Control is rotated, a beam of Infra Red Light is picked up
Figure 96 - Top Inside View of the C1000T
by two internal sensors as a series of digital pulses. Refer to
figure 97. The number of and time between pulses are
counted by a Microprocessor which in turn controls the
McIntosh designed Precision Electronic Attenuator that pro-
vides 213 steps in 0.5dB increments and maintains the chan-
nel balance to within +
0.1dB.
With most Preampli-
fiers 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 free-
dom from input over-
load, but the back-
ground noise level is higher especially at lower settings of
the volume control. In example No. 2, by placing the Vol-
ume Control after the Amplifying Circuitry there is a reduc-
tion in dynamic range and input overload of the Preampli-
fier, but has the benefit of lower background noise levels.
The only correct 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 overload and a background noise level that actu-
Technical Description
Figure 97
47
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