of frequencies. A pushbutton switch allows the
equalizer circuit to be switched from the listen program
line to the record program line.
The LF and HF Filters follow the equalizer amplifier.
These are active filters using operational amplifiers.
When switched in, the LF filter attenuates frequencies
below 50 Hz at a rate of 12 dB per octave. The HF
Filter attenuates frequencies above 7 kHz at a rate of 12
dB per octave.
The listen program signal then is fed to the main out-
put jacks. The OUTPUT 1 and OUTPUT 2 jacks receive
the same signal but can be turned on or off by the
Speaker/Output 1 and 2 pushbuttons.
RECORD PROGRAM LINE
The RECORD program signal from the RECORD input
switch goes first through a unity gain amplifier and then
to the COMPANDOR switching where the Compandor
can be inserted into the record program path. The
Compandor circuit is described later. The record pro-
gram then goes to the RECORD EXTERNAL PROCESSOR
jacks. These jacks, like the LISTEN EXTERNAL PRO-
CESSOR jacks, have switching contacts so that the signal
passes through when plugs are not inserted in the jacks.
When an external processor is used, the record pro-
gram leaves the C 34V through the EXTERNAL PRO-
CESSOR TO jack and returns via the FROM jack. When
a processor is not connected, the signal passes directly
through the jacks.
An equalizer amplifier with unity gain follows. A
pushbutton switch allows the 5 band equalizer controls
to be switched from the Listen program line to the
Record program line. This feature allows equalizing the
record signal before it is fed to a recorder.
The equalizer amplifier feeds to electronic interlock
switching and then finally to the record output jacks.
The switching is arranged so that if the Record input
selector is positioned to select the output of a recorder,
the Record program line will not feed the record output
jack connected to that recorder. This prevents recorder
feedback.
COMPANDOR
The Compandor will expand or compress the
dynamic range of the program material. The Compan-
dor can be switched to the Listen or Record program
lines or turned off. Program to the Compandor is ap-
plied to a voltage controlled amplifier (VCA) which
operates as a variable gain block. Control voltages for
this VCA are developed from a sample taken from the
left and right channel input signals to the VCA. The
electronic processing of this sample is detailed. It in-
cludes band shaping, logarithmic conversion, full wave
rectification, level setting, expansion or compression
ratio regulation, attack timing, and DC amplification.
The resulting processed voltage controls the gain of the
VCA to cause logarithmic gain expansion when expan-
ding the program, or the opposite, logarithmic gain
compression when compressing the program.
MONITOR AMPLIFIER
The monitor amplifier is a 20 watt per channel stereo
power amplifier. The monitor input selector switch
allows the amplifier to be driven from the LISTEN or
RECORD program lines or from an external input. It is a
push pull complementary class AB amplifier using a dif-
ferential input stage. The amplifier includes the Mcln-
tosh Power Guard* protection circuit. The Power Guard
circuit compares the amplifier output signal with its in-
put signal. If there is a difference between the
waveforms of these signals, Power Guard activates an
electronic attenuator at the input of the amplifier which
reduces the amplifier input level. This automatic control
system makes it impossible to drive the monitor
amplifier into clipping. Thus, clipping distortion and
loudspeaker damage due to clipping are eliminated.
AUTO TURN-ON
A turntable plugged into the green outlet at the rear
of the C 34V can control the on-off operation of the
C 34V. Current flow to the turntable is sensed and con-
trols a silicon control rectifier (SCR). When the SCR con-
ducts a relay closes. This relay turns on power to the
C 34V and to the black AC power outlets. Power is also
controlled by the C 34V Power On pushbutton.
•protected by US Patent #4048573)
TECHNICAL DESCRIPTION 19
To Next Page
Loading...
Need help?
General
