McIntosh C 504, Руководство пользователя

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Technical Description
The C 504 is c o m p r i s e d of six basic sections. They
are: phono amplifier, high level amplifier, equalizer
amplifier, o u t p u t / h e a d p h o n e amplifier, input selector
s w i t c h i n g , and power supply. Their circuit descrip-
tions follow.
PHONO AMPLIFIER
The phono amplifier uses a high t e c h n o l o g y in-
tegrated circuit operational amplifier. Its differential
input stage has been optimized for low noise and low
distortion performance. Open loop gain of this in-
tegrated circuit is 100,000. W i t h high open loop gain a
large amount of negative feedback can be used
around the phono amplifier to further reduce noise
and d i s t o r t i o n . The feedback network also provides
precision RIAA frequency c o m p e n s a t i o n . The net-
work uses 1 % metal f i l m resistors and 5 % poly film
capacitors. To achieve low noise performance it is
essential that the feedback network have very low im-
pedance. As a c o n s e q u e n c e , 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 m i l l i w a t t s , a great
margin beyond that w h i c h is required.
Input sensitivity of the phono amplifier is 2.2
millivolts. The gain of the amplifier is 41.1 dB at 1000
Hz. The phono amplifier has a very wide d y n a m i c
range. At 1000 Hz the phono input circuit will accept
100 millivolts w i t h o u t overload, a voltage far greater
than the output of any current magnetic phono car-
tridge. Phono input overload therefore is virtually im-
possible. A signal level of 10 millivolts at the phono
input at 1000 Hz will produce 1.13 volts at the tape
output. The tape output has a source impedance of
200 o h m s and is designed to operate into a load im-
pedance of 5,000 o h m s or greater.
HIGH LEVEL AMPLIFIER
At the input to the high level or loudness amplifier
the signal passes through the MONO/stereo switch,
then through the volume control, and into the
amplifier. In the past, loudness controls have typical-
ly used simple passive circuits c o n n e c t e d to a tap on
the volume c o n t r o l . As a consequence, c o m p e n s a t i o n
accuracy was dependent on many variables such as
volume control position and differences in the input
level. The C 504 uses active circuitry. The same type
of integrated circuit operational amplifier that is used
in the phono amplifier is used here. It has two feed-
back loops. One feedback loop is flat. The other feed-
back loop c o n f o r m s to the Fletcher-Munson equal
loudness c o m p e n s a t i o n . A potentiometer is placed
between these t w o feedback loops making it possible
to select any c o m b i n a t i o n of the two from a flat
response to full loudness c o m p e n s a t i o n . The overall
gain of the stage is 20 dB at mid-frequencies and is
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