LA4 Line Amplifier

The Ultimate Line Amplifier

 The LA4 is identical to the HPA4 except that it eliminates the headphone outputs. The LA4 is well-suited to customers who do not need the headphone amplifier.

The LA4 is a line-level preamplifier that is designed to sit between a reference-quality D/A converter and a reference-quality power amplifier. This is not an easy task. Most hi-fi preamplifiers introduce significant noise and distortion due to the necessity to provide volume control and input switching. To solve this problem, the LA4 is completely relay controlled and features analog amplifiers with vanishingly low distortion. It features relay gain control, relay input selection, and relay muting. The entire system incorporates the finest gold-contact relays available. The gain control has 256 steps in 0.5 dB increments. It also features a relay-controlled balance adjustment. Relay closures are precisely timed to deliver silky-smooth volume changes. No other relay gain control offers this level of precision or performance. The LA4 includes 2 independent 256-step attenuators: one for the left channel and one for the right channel. To make this all happen, the LA4 includes a total of 40 precision relays that switch high-precision metal-film resistors.

100% Analog Signal Path

The LA4 is 100% analog. It is designed to be driven from external D/A converters and external line-level analog sources. The LA4 is designed to drive any professional or hi-fi power amplifier. The LA4 provides the ultimate analog signal path between inputs and outputs. The LA4 eclipses the performance of typical high-end hi-fi preamplifiers by achieving much lower noise and distortion.

System Optimization

At any volume setting, the relay-controlled gain stage provides an optimized attenuator to match the upstream analog source to the downstream power amplifier. This optimization of the gain staging delivers the best possible system SNR for each volume setting. The LA4 will match high-output D/A converters to low-input power amplifiers and vice-versa. It will also provide an optimized interface to and from balanced and unbalanced devices. In addition, it will match high-level professional balanced interfaces to low-level hi-fi balanced interfaces (in either direction).

Speed and Precision

The bandwidth of the LA4 extends from 0.01 Hz to over 500 kHz. This means that the LA4 delivers very precise amplitude and phase accuracy over the entire audio bandwidth. Wave shapes are accurately reproduced, and the entire spectrum is delivered with precise timing. The LA4 will deliver musical overtones with life-like accuracy. This means that musical instruments are rendered without changing their sonic character.

Balanced and Unbalanced I/O

The LA4 features two balanced stereo inputs and two unbalanced stereo inputs. The line amplifier provides one balanced stereo output, one balanced mono sum, and one unbalanced stereo output.

System Integration

The LA4 includes IR remote control and can be operated using the optional Benchmark remote. The LA4 is designed to work with the Benchmark DAC2 and DAC3 converters but may be driven from any high-end D/A converter. When paired with a Benchmark DAC, a single remote control will operate both units.

The LA4 (line amplifier) or HPA4 (line amplifier + headphone amplifier) are the perfect complement to the Benchmark AHB2. These may be the only preamplifiers or line amplifiers that exceeds the signal to noise ratio of the ultra-quiet AHB2. This means that the LA4 will extract the full performance of the AHB2. In contrast, other preamplifiers limit the system noise performance because they cannot match the SNR performance of the AHB2. The LA4 and HPA4 are the only line amplifier/preamplifiers that we recommend inserting between a DAC and the AHB2. The LA4 or HPA4 can be inserted between a Benchmark DAC3 and AHB2 without degrading the system noise performance. With the LA4 or HPA4 inserted, the DAC3's 32-bit digital gain control is replaced by a more-resolving fully-analog relay gain control.

Two bidirectional 12V trigger ports can be used to link the LA4 with external D/A converters and power amplifiers. The trigger signal controls the power-up and power-down sequencing of the entire audio system. The trigger ports are compatible with most industry-standard trigger input or output ports, but can communicate bidirectionally with other Benchmark products.

Touch Screen

The touch screen provides easy access to advanced features such as balance control, input level offsets, input names, screen dimming, remote control, and function locking. Help screens explain the special functions.

Rotary Encoder

The volume control knob features a high-quality optical encoder that is rated for heavy use. An acceleration feature makes it easy to move through the 256 volume steps while maintaining 0.5 dB/step resolution. A press of the control knob will wake turn on or brighten the screen if you are using the screen sleep or auto-dim functions.

Convenience Features

The LA4 includes an on-screen mute button for the line outputs. Outputs can also be muted with the volume knob or with the optional remote control.

The LA4 includes an on-screen -20 dB "audio dim" button that instantly reduces the level by 20 dB. This function provides a temporary volume reduction and makes it easy return to the previous listening level. This control makes it easy to transition between a normal listening level and a background level. The -20 dB "dim" function is also accessible from the optional remote control.

Inputs may be renamed and unused inputs may be disabled. Input levels can be trimmed to provide input-to-input level matching.

Screen brightness is adjustable and timers can be set to dim or shut off the display. The screen can be locked to prevent access to advanced features.

Casework

The LA4 is available with a black or silver faceplate and is designed to match the Benchmark AHB2 power amplifier. It occupies the same footprint as the Benchmark DAC1, DAC2 and DAC3 converters. The case features a milled faceplate and milled sides. Top, bottom, and rear panels are made from thick aluminum and feature a brushed texture. The LA4 is built to last and will be a fine addition to your listening space.

DESIGNED, ASSEMBLED, AND TESTED IN THE USA

This Benchmark product was designed, assembled, and tested in the USA using USA and imported components. Most major components are made in USA.

Features

• Benchmark Low-Noise Line Amplifier

• 256-Step Fully-Balanced Relay Gain Control, 0.5 dB Steps

• Precision Timed Relay Closures

• Precision Metal Film Resistors

• Gold-Contact Relays

• Balanced and Unbalanced I/O

• 0.01 Hz to 500 kHz

• SNR > 135 dB

• THD < 125 dB (0.00006%)

• Touch Screen Control

• IR Remote Control (optional)

• 2 Balanced Stereo Line Inputs

• 2 Unbalanced Stereo Line Inputs

• 1 Balanced Stereo Line Output

• 1 Unbalanced Stereo Line Output

• 1 Balanced Mono Sum Output

• 2 Bidirectional 12V Trigger Ports

Balanced Line Outputs:

THD < -125 dB (0.00006%)

SNR > 135 dB, unweighted, 20-20 kHz

SNR > 137 dB, A-weighted

Frequency Response - 0.003 dB at 10 Hz, -0.001 dB at 20 kHz

- 3 dB Bandwidth exceeds 0.1 Hz to 500 kHz

Output Impedance 60 Ohms

Output Noise < 1.9 uV at Unity Gain, 20-20 kHz

Maximum Input and Output Voltage, 20 Vrms (+28 dBu)

Crosstalk < -133 dB @ 1 kHz, -116 dB @ 10 kHz

Dimensions:

219mm W x 98.55mm H x 211.58mm D - Including Feet

219.71mm W x 88.13mm H x 211.58 D - Excluding Feet

Weight:

1.6kg., 2.48kg. shipping

Power:

12W Typical Input Power

17W Maximum Input power

0.33 W Standby Power (when off)

Internal Universal Power Supply

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