33
Technical Description
a substantial amount of time in pursuit of the “Perfect
Volume Control System”.
A conventional Mechanical Potentiometer for a
volume control
is totally unac-
ceptable for use
in the MA8000.
Mechanical
Controls have
poor track-
ing especially
when it comes
to maintaining
channel bal-
ance 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 control-
ling the volume can be designed to be free from noise
and maintain channel balance, however the audio ta-
per produced by the typical Electronical Volume Con-
trol Circuit is unacceptable for use in the MA8000, as
it does not match the classic McIntosh Volume Control
Audio Taper. The MA8000 incorporates electronic
circuitry together with sophisticated firmware to
produce electronically the classic McIntosh Volume
Control Audio Taper, while maintaining the channel
balance and freedom from control noise.
The Volume Control on the Front Panel of the
MA8000 produces a series of digital pulses. The num-
ber of these digital pulses are counted by a Micropro-
cessor which in turn controls a Precision Electronic
Attenuator. This provides a logarithmic change in
volume and maintains the channel balance throughout
the volume control range. The benefits of the digi-
tally controlled volume attenuator is wide dynamic
range, low distortion and low noise. Refer to figure 81
for the Block Diagram of the MA8000 Preamplifier
and Micro Controller.
Moving Coil Preamplifier
One of the popular types of Phono Cartridges for
Turntables used today are “Moving Coil”. Due to their
design, the Moving Coil Cartridge’s output voltage is
typically in the range of 300 to 500 microvolts (mil-
lionth of a volt) and thus requires additional amplifica-
tion in order to match the output voltage of a “Moving
Magnet/Induced Moving Magnet” cartridge type with
Figure 80
Figure 81
MA8000 Preamplier and Micro Controller Block Diagram
OUTPUT
MUTING
6
6
PHONO MC
PHONO MM
PHONO MC
PHONO MM
OUTPUT
2 BAL
UNBAL
TO
BAL
RS232
RIGHT
REC
OUTPUT
LEFT
REC
OUTPUT
AUX
AUX
TUN
TUN
BAL
TO
UNBAL
BAL
TO
UNBAL
BAL
TO
UNBAL
BAL
TO
UNBAL
BUFFER
BUFFER
8-BAND
EQUALIZER
EQUALIZER
BYPASS
SWITCH
EQUALIZER
BYPASS
SWITCH
8-BAND
EQUALIZER
OUTPUT
MUTING
OUTPUT
MUTING
OUTPUT
MUTING
OUTPUT
MUTING
OUTPUT
2 BAL
OUTPUT
MUTING
UNBAL
TO
BAL
OUTPUT
MUTING
OUTPUT
MUTING
BALANCED
32-Bit/192kHz
DAC
DIGITAL
INPUTS
SAMPLE
RATE
CONVERTER
USB
DECODER
S/PDIF
RECEIVER
DIG 1
DIG 2
DIG 3
DIG 4
USB-D/A
TO
POWER
AMPLIFIER
CONTROL
RIAA
AMP
RIAA
AMP
RIAA
AMP
RIAA
AMP
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