McIntosh C35 - SERVICE, Руководство пользователя

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FULL ELECTRONIC SWITCHING
All signal switching including input tape, tape-to-
tape, and mono is done elctronically using J-FET field
effect analog switches. All the front panel switches
control small amounts of DC voltage which turn the
FET analog switches on and off. The critical audio
signals are switched silently with instantaneous
muting between switch positions. No transient
switching noises or pops are present with this
superior design.
PHONO AMPLIFIER
The phono amplifier uses a high technology
integrated circuit operational amplifier. Its differential
input stage has been optimized for low noise and
low distortion performance. Open loop gain of this
integrated circuit is 100,000. With high open loop
gain, a large amount of negative feedback can be
used around the phono amplifier to further reduce
noise and distortion. The feedback network also
provides precision RIAA frequency compensation.
The network uses 1% metal film resistors and 5%
polypropylene film capacitors. To achieve low-noise
performance it is essential that the feedback network
have very low impedance. As a consequence, the
preamplifier must be capable of operating as a
power amplifier to drive this impedance. The actual
power output capability of this preamplifier stage is
more than 100 milliwatts, a great margin beyond that
which is required.
Input sensitivity of the phono amplifier is 2.5
millivolts. The gain of the amplifier is 40dB at
1000Hz. The phono amplifier has a very wide
dynamic range. At 1000Hz, the phono input circuit
will accept 90 millivolts without overload, a voltage
far greater than the output of any current magnetic
phono cartridge. Phono input overload, therefore, is
virtually impossible. A signal level of 10 millivolts at
the phono input at 1000Hz will produce 1 volt at the
tape output. The tape output has a source
impedance of 200 ohms, designed to operate into a
load impedance of 10,000 ohms or greater.
LOUDNESS AMPLIFIER
At the input to the high level or loudness
amplifier, the signal passes through the electronic
mono switch, then through the volume control, and
into the loudness amplifier. In the past, loudness
controls have typically used simple passive circuits
connected to a tap on the volume control. As a con-
sequence, compensation accuracy was dependent on
many variables such as volume control position and
differences in input level. The C 35 uses active
loudness control circuitry. The same type of in-
tegrated circuit operational amplifier that is used in
the phono amplifier is used here. It has two feed-
back loops. One feedback loop has flat response.
The other feedback loop conforms to the Fletcher-
Munson equal loudness compensation. A poten-
tiometer is placed between these two feedback loops
making it possible to select any combination of the
two from a flat response to full loudness compensa-
tion. The overall gain of the loudness stages is 20dB
and is not affected at mid frequencies by the posi-
tion of the loudness control.
EQUALIZER AMPLIFIER
The equalizer amplifier uses high technology
integrated circuit operational amplifiers. Its output
stage has been optimized for the best transient
performance and minimum distortion. Four other
operational amplifiers are each arranged in a circuit
configuration that is the equivalent of series tuned
circuits, one at each of the five center frequencies.
Each series tuned circuit is inserted via a control
potentiometer into either the input circuit or feed-
back circuit of the operational amplifier, thereby,
providing a boost and cut capability of 12dB for each
band of frequencies. The overall gain of the stage is
0dB.
CONTROL LOGIC
All inputs, outputs, CD, Tuner, SCR, and Video
Selector lines are controlled by logic circuits in the
C 35. The logic can be changed by front panel
switches or by the infrared remote control system
receiver in the C 35. The infrared receiver's informa-
tion comes from the remote transmitter HR 35. Input
selection, volume level, speaker selection, power
on/off can be made at the C 35 front panel.
Mclntosh tuners and CDs are controlled from the
remote transmitter. A back-up power supply keeps
all selections memorized when the C 35 power
switch is turned off as long as 120 volts AC power to
the C 35 is not interrupted.
TECHNICAL DESCRIPTION 15