Marantz 3800 - Dolby Noise Reduction Circuit Functionality; Technical Specifications of the Model 3800

5.
DOLBY NOISE REDUCTION
CIRCUIT
A.BASIC DOLBY PROCESS
The Model 3800 full-process Dolby Noise
Reduction (NR) Circuit enables Dolby encoding
and decoding to be performed simultaneously.
An incoming flat signal can be Dolby encoded,
recorded onto tape, monitored from the tape,
and DOLBY decoded in one operation, allowing
the end result to be immediately compared to
the original source signal.
The Dolby circuit increases the amplitude of
low-level, mid- and high-frequency signals during
recording and reduces the amplitude of these
signals by an identical amount during playback.
As a result, the playback signal is identical to
the original source signal, but the level of back-
ground noise generated by a tape or record is
greatly reduced. A Dolby FM broadcast is
subjected to the first phase of the noise
reduction process before being transmitted.
When these signals pass through the Dolby
decoder circuit, the mid- and high-frequency
noise is greatly reduced.
Section 2 contains the maintenance procedures
for the Dolby (NR) circuit in the Model 3800.
TECHNICAL SPECIFICATIONS
B. USE OF THE DOLBY (NR) CIRCUIT ASA
DYNAMIC NOISE FILTER
As previously described in the Basic Dolby
Process, high-level, high-frequency signals pass
through unchanged in both phases of the Dolby
process (encode and decode). As the level
decreases, however, filtering increases (during
playback) until the signals are 35 dB or more
below the level determined by the PLAY CAL
Controls at which point the maximum filter-
ing effect takes place. The Dolby playback
(decode) circuitry is, in effect, a variable or
dynamic noise filter.
In this regard, the Dolby playback circuitry can
be used as a substitute for a high filter. But
unlike a regular high filter whose effect on
treble response is constant at all loudness levels,
the Dolby-derived filter activates itself only
when needed, that is, only during soft passages
where background noise becomes noticeable.
To use the Dolby playback circuit as a dynamic
noise filter, set the DOLBY switch to PLAY.
The amount of filtering action is determined
by the setting of the PLAY CAL Controls. For
normal programs, adjust the PLAY CAL Con-
trols on each channel so that the average
program level, as indicated on the Dolby Level
VU Meter, indicates approximately O VU.
Technical
specifications
highlighting
performance
features
are
listed
in
Table
1-1.
Note: DOLBY circuit OFF
RATED OUTPUT LEVEL
Preamp Output
Phono Amplifier at Scope Output
GAIN
*Phono/Mic to Preamp Output
*Phono/Mic to Recording Output
*High Level Input to Preamp Output
60dB +2dB
40dB + 1.25 dB
20dB +1.0dB
Table 1-1 Performance Specifications