Overview - Orban 8100A/XT2 Operating Manual

Technical Information
6-3
2. CIRCUIT DESCRIPTI N
On the following pages, a detailed description of each circuit ' s function is accompanied by a
component-by-component description of that circuit. Keywords are highlighted throughout
the circuit descriptions to help you quickly locate the information you need.
See the 8100A/1 Operating Manual for detailed information about 8100A/1 circuitry. The
relationship between 8100A/1 and XT2 circuitry is discussed here.
Whenever circuitry is duplicated for the left and right channels, only the left channel will be
described.
1) OVERVIEW
The BLOCK DIAGRAM in Section 6.4 illustrates the following overview of XT2 functions.
Together, the XT2 and 8100A/I form an integrated audio processing system. The XT2 adds
bass equalization, six-band limiting, and multiband distortion-cancelling clipping between the
8100A/l ' s high-frequency limiter and its distortion-cancelling 15kHz low-pass filter.
The 8100A/1 automatically senses when the XT2 is plugged into Accessory Port #2 and puts
the high-frequency limiter and main clipper in PROOF mode, since these functions are now
performed by the XT2. The 8100A/l ' s dual-band compressor, distortion-cancelling 15kHz
low-pass filter, and
c mpress r
and LIMITER control lines operate differently when the XT2
is in use, as described below. Virtually all other 8100A/1 circuitry remains active and retains
its normal function.
To prevent the 8100A/l ' s dual-band compressor from " fighting " the XT2 ' s six-band limiter
due to time-constant incompatibilities, the time-constants of the dual-band compressor are
altered. The 8100A/l ' s RELEASE TIME control adjusts the speed of compressor response.
Settings toward SLOW retain transient definition and permit the compressor to function as a
slow " hand on the pot " , riding gain without affecting short-term density or texture. Settings
toward FAST result in increased density. The MASTER G/R meters on the 8100A/1 will exhibit
less gain reduction and will move more slowly in the 8100A/1 + XT2 System than they
would in an 8100A/1 without the XT2.
The input signal (already pre-emphasized by the 8100A/1) is applied to a bass equalizer,
which can provide 0-1 OdB of peaking boost with a center frequency of 65Hz and a " Q " of
1.4 (approximately 1 octave). Because the XT2 often increases the brightness of program
material, some bass boost is usually desirable to keep the sound spectrally well-balanced.
The boost frequency has been chosen to create very " punchy " bass, particularly on speakers
with reasonably extended bass response.
The six-band limiter follows the bass equalizer. A set of six parallel filters divides the signal
into frequency bands. The highest and lowest bands arc low-pass and high-pass respectively;
the other bands are band-pass.