Instruction Manual for LA4 with 1.0.X Firmware ā REV A Page 23
LA4 System Overview
The Ultimate Line Amplifier
The LA4 delivers audio fidelity, speed and
accuracy over an utterly silent background.
Input selection, input MUTE and output
volume are 100% relay controlled. Gold-
contact relays provide a clean and
transparent path through the entire LA4. It is
designed to deliver the lowest possible
distortion and noise over a wide range of
volume settings. We believe that the LA4 line
amplifier is the finest line available at any
price.
Relay-Controlled Gain Stage
The relay-controlled gain stage provides 256
volume steps in precise 0.5 dB increments.
This gain stage features the finest gold-
contact relays available.
Relay closures are precisely timed to deliver
silky-smooth volume changes. No other relay-
controlled gain stage offers this level of
precision or performance.
The LA4 includes 2 independent fully-
balanced 256-step volume controls: one for
the left output, and one for the right output.
To make this all happen, the LA4 includes a
total of 40 precision relays.
Balance Controls
The line outputs feature balance controls that
are adjustable over a +/- 12 dB range.
100% Analog Signal Path
The LA4 is 100% analog. It is designed to be
driven from external D/A converters and
external analog sources. The LA4 is designed
to provide the ultimate analog signal path
between inputs and outputs. The LA4 eclipses
the performance of typical high-end
preamplifiers by achieving much lower noise
and distortion.
Fully-Balanced Signal Paths
The internal signal paths are fully balanced.
The inputs are routed to a balanced pair of
precision differential amplifiers. These drive
two sets of fully-balanced 256-step volume
controls. These balanced outputs from the
volume controls drive the line output drivers.
Each output connector has dedicated buffers.
Differential Amplifiers
The LA4 features precision differential
amplifiers on all inputs. These reject
common-mode noise, common-mode
distortion and common-mode interference.
This feature is especially important when
using D/A converters that lack their own
differential amplifiers.
Benchmark D/A converters include differential
amplifiers, but many competing converters
lack these stages which remove the common-
mode distortion produced by D/A chips.
Ultra-Wide Bandwidth
The frequency response of the LA4 extends
from 0.1 Hz to 500 kHz. This extended range
keeps the phase response extremely accurate
over the entire audio band. The entire audio
spectrum is delivered with the proper timing.
Bass is delivered with the correct timing
relative to other frequencies. Most audio
products deliver the bass slightly late. Bass
that arrives late tends to mask high-
frequency details. In contrast, bass that
arrives with the correct timing will sound
deep, full and well damped. For this reason,
all Benchmark products feature low-frequency
extension to 0.1 Hz.
The extreme 500 kHz high-frequency
extension delivered virtually perfect timing at
the high end of the audio spectrum. High
frequencies are delivered with precise timing
relative to low and mid frequencies. In
addition, the left-right differential phase is
virtually perfect at 20 kHz. These timing
characteristics preserve the precise placement
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