Wersi CD 600, Инструкция по сборке

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AM 320-01-808
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6. DH 11 (Digital Reverb Unit, 12 Bit)
The input signal (plug 1, pin 5) is applied to the input of IC
14 (NE 571), pin 6) via C 31.
C 31 serves for high-frequency emphasis.
With IC 14a and IC 16 a (TL 084) dynamics are com-
pressed and levels are limited to maximum 5 Vss (D 7, D
8). The Iowpass filter following (IC 16b, c, d) serves as
band limiter (4 kHz: approximate -60 dB).
Now that frequency response and dynamics are adjusted to
the digitalization process, the signal is kept on a constant
amplitude value by IC 13 (LF 398, Sample & Hold) during
the necessary conversion time required by the analog-
digital-converter.
IC 11 translates the analog signal into a 12-bit code.
This code is split up into 2 bytes that are fed through to
the CPU (IC 1, 68B09) one after the other by IC 5 and
IC 6 (74 LS 244).
The CPU is controlled by the program (short and long
reverb, fast and slow echo) stored in IC 2 (2k EPROM).
From the CPU, the digital information (data) is placed into
memory (IC 7, 8k RAM), read out with time delay, added
to other data, saved again, etc.
The frequency of this process caused by the 12-bit code of
the ADC results in reverb times of up to 4 seconds; CPU
and RAM have a bandwidth of 16-bit.
The complete signal (12-bit again) is again split up into
2 bytes and routed to the digital-analog-converter
(DAC 1230, IC 12). This converter produces an output
current, which represents the digital value.
This current is converted into a voltage potential by IC lSc
(TL 084), which still has amplitude jumps and unwanted
frequency portions, due to the previous digitalization
process.
The following low-pass filter (IC 1Sa, b, d) smoothes the
signal, i.e., filters out the disturbing portions. C 40 and IC
14b reverse the high-frequency emphasis and the dynamics
limiting process described in the beginning.
The reverberated and delayed output signal is applied either
to pin 6 (single-channel operation) via JU 1 or is doubled
by IC 17 (TDA381O) so that a second "stereo" channel is
produced. By means of exactly determined phase rotations
in certain areas of the frequency range, this IC generates a
second output channel (pin 9). Further stereo processing of
the two channels produces proper stereo imaging.
Switching over between the various operation modes (short
and long reverb, fast and slow delay) is done by the NM of
the CPU by sending pulses to pin 12.
Reset activates the program sequence.