Feed-Forward Error Correction

Feed-Forward Error Correction

by John Siau October 11, 2018

The Benchmark AHB2 power amplifier and HPA4 headphone amplifier both feature feed-forward error correction. This correction system is an important subset of the patented THX-AAA™ (Achromatic Audio Amplifier) technology. It is one of the systems that keeps these Benchmark amplifiers virtually distortion free when driving heavy loads. It is also the reason that these amplifiers can support 500 kHz bandwidths without risk of instability when driving reactive loads.

This paper explains the differences between feedback and feed-forward systems. As you read this paper, you will discover that you already understand the benefits of feed-forward correction because you use it instinctively to improve a feedback system commonly found in your automobile. If feed-forward correction can improve your driving experience, it may also improve your listening experience!

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Balanced vs. Unbalanced Analog Interfaces

Balanced vs. Unbalanced Analog Interfaces

by John Siau April 23, 2018

If you look at the back of any Benchmark product, you will find balanced XLR analog-audio connectors. As a convenience, we also provide unbalanced RCA connectors on many of our products. In all cases, the balanced interfaces will provide better performance.

We build our unbalanced interfaces to the same high standards as our balanced interfaces, but the laws of physics dictate that the balanced interfaces will provide better noise performance.

This application note explains the advantages of balanced interfaces.

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Relay-Controlled Volume - The Ultimate Solution for Analog Audio

Relay-Controlled Volume - The Ultimate Solution for Analog Audio

by John Siau April 11, 2018

Benchmark has introduced a new analog-to-analog volume control circuit that features a 256-step relay-controlled attenuator and a 16-step relay-controlled boost amplifier. The volume control has a +15 dB to -122 dB range in 0.5 dB steps and is a key component in the HPA4 Headphone / Line Amplifier.

Our goal was to produce an analog-to-analog volume control with the highest achievable transparency. We wanted to be able to place this volume control in front of our AHB2 power amplifier or in front of our THX-888 headphone amplifier board without diminishing the performance of either device. Our volume control would need to have lower distortion and lower noise than either of these amplifiers. Given the extraordinary performance of these THX-AAA amplifiers, this would not be an easy task!

This application note discusses the engineering decisions that went into the development of this new analog volume control circuit. The end result is a fully buffered volume control with a signal-to-noise ratio that exceeds 135 dB. THD measures better than the -125 dB (0.00006%) limits of our test equipment.

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Laboratory Use of the Benchmark AHB2 Power Amplifier

Laboratory Use of the Benchmark AHB2 Power Amplifier

by John Siau January 26, 2018

SEAS, a well-known manufacturer of high-quality loudspeakers, selected the Benchmark AHB2 as a key component for use in testing loudspeakers. They created an innovative test system that measures loudspeaker motor strength and moving mass with higher accuracy than previous methods. This new measurement system was documented in the December 2017 Journal of the Audio Engineering Society.

According to the AES paper, the SEAS team selected the Benchmark AHB2 for the following reasons:

"A Benchmark AHB2 amplifier is used, which has excellent signal-to-noise ratio and bandwidth, low output impedance, and is suitable for laboratory use (with advanced overload protection)."

The AHB2 was designed to outperform all competing power amplifiers in terms of noise and distortion. The result is an amplifier with unrivaled transparency.

Our goal was to create the ultimate amplifier for the enjoyment of music. It is nice to know that the AHB2 is also being used to test new and improved loudspeakers!

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Interpreting THD Measurements - Think dB not Percent!

Interpreting THD Measurements - Think dB not Percent!

by John Siau November 15, 2017

Distortion measurements (THD, THD+N and IMD) are traditionally expressed in terms of percent. But what do 1%, 0.1%, 0.01% or 0.001% mean in terms of loudness or audibility?

If you are like most people you just know that 0.001% is the best of the three numbers listed above. If you are a well-trained geek you will recognize that each added leading zero represents a 20 dB improvement. 0.01% is 20 dB lower than 0.1% and 40 dB lower than 1%. The well-trained geek will convert % to dB in order to give meaning to these numbers.

When THD is expressed in terms of dB, we can easily determine how loud the distortion will be in our playback system.

Will my audio electronics produce audible distortion?

Will the distortion produced by my audio electronics be inaudible?

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Inside the DAC2 - Part 3 - Power Supplies

Inside the DAC2 - Part 3 - Power Supplies

by John Siau July 13, 2016

The Benchmark DAC2 is an audio digital-to-analog converter. This application note explains the power supply configuration inside Benchmark'sDAC2 D/A converter. Inpart 1 of this series we discussed the importance of the analog section of an audio converter. In part 2 we discussed the unique high-headroom digital processing chain inside the DAC2. The analog and digital systems each contribute toward Benchmark's overall goal of transparent musical reproduction, but this goal can only be reached when these systems are supported by a well-designed power supply system. In many cases, classic solutions (linear power supplies, line-frequency transformers, and large banks of capacitors) fail to deliver adequate performance. The DAC2 takes a radically different approach.

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Inside the DAC2 - Part 1 - Analog Processing

Inside the DAC2 - Part 1 - Analog Processing

by John Siau June 04, 2016

The DAC2 is an audio digital-to-analog converter. Most people focus on the word "digital" and assume that all of the "magic" happens in the digital processing, but nothing could be further from the truth! A look inside most audio converters would show that about 90% of the components are analog!

This application note takes a look at the analog processing in Benchmark's DAC2 D/A converter.

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Grounding XLR Connectors - Neutrik USA

Grounding XLR Connectors - Neutrik USA

by Benchmark Media Systems June 01, 2016

"Neutrik is often asked whether the shiny silver tab (pictured below) on typical XLR cable connectors (Neutrik XX series, RX series, X series, etc.) should be connected to anything."

"In the course of the evolution of the AV industry, it has come to be that this tab is practically never terminated. This means, in turn, that the shell is not grounded. When in doubt, simply leave this tab unterminated."

"Whether or not they are internally wired to the shield signal, XLR cable connector shells always make an electrical connection to chassis connector shells once the two are mated."

"Typically, chassis connectors need to be grounded. The industry best practice is generally to tie all of the chassis connector shell, pin 1, and the enclosure shield to a common ground."

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Crossover Distortion - Video Clip

Crossover Distortion - Video Clip

by Benchmark Media Systems March 14, 2016

The AHB2 - A new and radically different audio power amplifier! Dick Olsher once said that "the first Watt is the most important Watt"

This short 8-second video clip demonstrates some of the differences.

 

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AHB2 Crossover Distortion Measurements

AHB2 Crossover Distortion Measurements

by John Siau March 10, 2016

Crossover Distortion - Measurements

The following measurements and scope photos demonstrate the effectiveness of the feedforward system in the AHB2.

From the first Watt to the last Watt, the AHB2 shows no evidence of crossover distortion. In contrast, all conventional class-AB amplifiers have crossover-distortion artifacts.

Dick Olsher once said that "the first Watt is the most important Watt". We agree!

 

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Amplifier Crossover Distortion

Amplifier Crossover Distortion

by John Siau March 10, 2016

Crossover Distortion - Introduction 

Most audio power amplifiers suffer from a defect known as "crossover distortion". This distortion is particularly troublesome at low output levels. At low power levels, the crossover distortion can rise to a high percentage of the output level and become the dominant source of distortion.

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How Should I Buy an Audio System?

How Should I Buy an Audio System?

by John Siau February 26, 2016

Two Distinct Types of Audio Products - Understand the Difference Before You Buy!

2013 Porsche 911 Carrera 4S (991) (9626546987)

Make your own choice!

"Buying an audio product is much like buying a car"

There are two distinct types of audio products. Some audio products are designed to be transparent while others are designed to provide a euphonic experience. These types are as different as a Porsche and a Cadillac.

There is not a right and wrong type of car. Likewise there is not a right and wrong type of audio product. The choice belongs to the user, but the user must be fully aware of the differences before they buy.

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Star Quad Cable Demonstration - Video

Star Quad Cable Demonstration - Video

by John Siau February 12, 2016

Benchmark has recorded a lab demonstration that shows what happens when a standard two-wire cable is exposed to common sources of magnetic interference.

You will be able to hear the interference, see it on an oscilloscope, and view its spectrum on an FFT. A star-quad cable is exposed to the same sources of magnetic interference and the results are compared. This demonstration shows the dramatic difference between the two cables. The star-quad cable provided a 20 to 50 dB reduction in magnetic interference, keeping the interference below audible levels.

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The Importance of Star-Quad Microphone Cable

The Importance of Star-Quad Microphone Cable

by John Siau February 12, 2016

Eliminate Magnetic Interference with Star-QuadCable

Studios, live sound venues and homes all have magnetic fields that can cause interference. Magnetic fields are produced whenever current flows through a wire. AC power cables, transformers, power supplies, computers, portable chargers, motors and light dimmers are among the devices that can emit strong magnetic fields. A microphone cable can pick up magnetic interference if it happens to pass near one of these devices. Cables can also pick up magnetic fields when they run adjacent to AC power. Star-quad cables typically reduce this magnetic interference by at least 20 to 30 dB. This is almost always enough to reduce the interference to inaudible levels.

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Will the HPA2 Drive My Headphones?

Will the HPA2 Drive My Headphones?

by John Siau February 04, 2016

Benchmark DAC1 and DAC2 converters are equipped with Benchmark’s HPA2™ headphone power amplifier. This is a high-current design with very low output impedance (less than 0.1 Ohms). It is capable of driving a wide variety of headphones while achieving extraordinarily low distortion. The full rated performance of the DAC is achieved at the headphone jack while driving two sets of headphones. THD+N is less than 0.0003% under full load. The HPA2™ may be the quietest and cleanest headphone amplifier available.

The HPA2™ has jumpers that allow it to be matched to the sensitivity of your headphones. These jumpers can be used to optimize the system performance.

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The HPA2™ Headphone Power Amplifier

The HPA2™ Headphone Power Amplifier

by John Siau July 22, 2015

Why do I need a Power Amplifier to Drive My Headphones?

Many Benchmark products include our HPA2™ headphone power amplifier. Unlike most headphone amplifiers, the HPA2™ is designed to behave like a small but very clean power amplifier. What makes the HPA2™ different, and what do we mean when we say that the HPA2™ is a "power amplifier"?

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Marantz AV8801

The Audio Path in Consumer-Grade Audio Products

by Benchmark Media Systems May 12, 2015

Explore the Differences Between Consumer and Professional Audio Products

Consumer products are usually packed with features but they often fall short when it comes to audio quality. These products deliver a level of performance that is acceptable to most consumers, and they do so at very affordable prices. Nevertheless there is often a large performance difference between consumer and professional audio products.

One of our customers, Jeff Switzer, owns a Marantz AV8801 pre-pro and he took a look inside to see how it was built. His detailed analysis shows how consumer product cost constraints limit audio performance.

Jeff's teardown analysis is a bit technical, but I know that some of our readers will appreciate the detail. For the rest of our readers, let me summarize by saying that there are real differences between consumer products and high-end professional audio products.

- John Siau, Benchmark Media Systems, Inc.

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The AHB2 - A Radical Approach to Audio Power Amplification

The AHB2 - A Radical Approach to Audio Power Amplification

by John Siau July 30, 2014

Radical!

The performance of the AHB2 would not have been achievable without taking a radical approach to power amplification. In many ways, the AHB2 is a complete 180 degree departure from traditional high-end amplifier designs. There is nothing ordinary about the Benchmark AHB2!

Take a look inside this unique audio power amplifier! 

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Don't Blame the Headphones!

Don't Blame the Headphones!

by John Siau July 25, 2014

Headphones Sounding Bad? It Could be Your Headphone Amplifier!

It is easy to build a headphone amplifier that produces sound.  It is an entirely different matter to produce an amplifier that is clear, clean, and enjoyable.  

Headphone amplifiers need to provide enough voltage and current to achieve a suitable listening level. They must also be able to cleanly deliver the required output. Furthermore, they need to be able to control the transducers.

If these goals are not achieved, a good set of headphones can sound bad.

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The CE Mark - A Photo-Tour of Immunity Testing

The CE Mark - A Photo-Tour of Immunity Testing

by John Siau June 25, 2014

Testing for Immunity to Interference

Most people have seen the CE mark on electronic equipment, but few have had the opportunity to witness the tests that are required to conform to the CE specifications. This post takes the reader on a behind-the-scenes photo-tour of the CE tests of Benchmark's new AHB2 power amplifier.

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