Benchmark Media High Resolution Amp


bob_reynolds
Bob, I'm also very interested. It suppose to somehow sum two amplifier's outputs making it linear without use of deep feedback. According to Benchmark's description when one output stage enters non-linear zone the other is already linear. This scheme combines efficiency of class AB with performance of class A.

Negative feedback, in class AB amplifiers has not only to linearize output transistors but also to compensate for sudden gain changes caused by "gm doubling" - basically a different gain when one (outside of bias) vs two (in bias window) transistors are working.
Kijanki, I only read the highlights on their web site. They mentioned using THX patents in their amp. Did you see any specific reference to patent numbers?

I had read an interview with their chief engineer last year and he mentioned that many amps on the market today cannot handle a high-res music signal. I recall that JA has also noted similar concerns in some of his amplifier reviews.

I didn't see any pricing info yet, did you?
No, I did not see any price info or patent reference. I will browse internet for any info.
What are those funny looking connectors on the back panel?
Thanks for the questions and comments about our new AHB2 power amplifier that incorporates two new technologies patented by THX.

THX Patent numbers are:
8004355
8421531

The amplifier is a joint development of Benchmark Media Systems, and THX.

I will be at the AES 2013 show in NYC and would be happy to discuss the new technologies incorporated into this new amplifier. For those of you who will not be attending the AES show, I will attempt to outline the engineering decisions that went into the AHB2.

It was my goal to create a power amplifier that matched the performance of the DAC2 D/A converter. After all, the performance of the D/A converter is only useful if it can be delivered by the downstream power amplifier.

In many ways, the AHB2 is a radical departure from conventional class AB amplifier design:

1) Low gain (9 dB) - allows +22 dBu input at amplifier clip - essential for low noise
2) Patented feed-forward error correction - virtually eliminates crossover distortion
3) Feed-forward design makes bias currents unnecessary, and non-critical - class B operation is possible with very low distortion
4) Multiple output stages run in parallel to eliminate crossover distortion - one output stage is active while another is in the crossover region
5) Class AB output stage uses very low bias current
6) Due to low bias currents, idle power consumption is only 20 W
7) Feed-forward design makes class H or G operation possible - no rise in distortion at class H or G switch point
8) Class H (or G) rail switching at a 1/3 power threshold
9) Tightly regulated power supply
10) High-bandwidth control loop on switch-mode power supply responds to amplifier loading over the entire audio band, and at ultrasonic frequencies
11) Amplifier does not rely on capacitive energy storage
12) Switch-mode power supply eliminates AC line magnetic interference to levels that are not possible with a linear power supply
13) >200 kHz bandwidth to achieve excellent inter-channel phase at 20 kHz.
14) < 0.1 Hz low frequency cutoff to minimize low-frequency phase shift
15) Feed-forward design improves damping factor

The AHB2 design was optimized for low distortion and low noise. It was not optimized for the highest possible efficiency that can be achieved with this new topology. Nevertheless the AHB2 is much more efficient than a conventional class AB design. Peak power does not vary with AC line voltage (due to regulated supply). Power drawn on one channel does not influence the power available from the other channel.

The AHB2 is a linear amplifier, it is not a switcher. For this reason, it produces very little out-of-band noise. A-weighted noise is only 2 dB less than noise measured over an 80 kHz bandwidth. This was an important design goal because ultrasonic noise can be folded into the audio band by non-linearities in speaker transducers.

If you have more questions, talk to me at AES, or post questions here.
__________________
John Siau
Gear Builder

VP Engineering

Benchmark Media Systems, Inc.
www.benchmarkmedia.com
Thanks for the questions and comments about our new AHB2 power amplifier that incorporates two new technologies patented by THX.

THX Patent numbers are:
8004355
8421531

The amplifier is a joint development of Benchmark Media Systems, and THX.

I will be at the AES 2013 show in NYC and would be happy to discuss the new technologies incorporated into this new amplifier. For those of you who will not be attending the AES show, I will attempt to outline the engineering decisions that went into the AHB2.

It was my goal to create a power amplifier that matched the performance of the DAC2 D/A converter. After all, the performance of the D/A converter is only useful if it can be delivered by the downstream power amplifier.

In many ways, the AHB2 is a radical departure from conventional class AB amplifier design:

1) Low gain (9 dB) - allows +22 dBu input at amplifier clip - essential for low noise
2) Patented feed-forward error correction - virtually eliminates crossover distortion
3) Feed-forward design makes bias currents unnecessary, and non-critical - class B operation is possible with very low distortion
4) Multiple output stages run in parallel to eliminate crossover distortion - one output stage is active while another is in the crossover region
5) Class AB output stage uses very low bias current
6) Due to low bias currents, idle power consumption is only 20 W
7) Feed-forward design makes class H or G operation possible - no rise in distortion at class H or G switch point
8) Class H (or G) rail switching at a 1/3 power threshold
9) Tightly regulated power supply
10) High-bandwidth control loop on switch-mode power supply responds to amplifier loading over the entire audio band, and at ultrasonic frequencies
11) Amplifier does not rely on capacitive energy storage
12) Switch-mode power supply eliminates AC line magnetic interference to levels that are not possible with a linear power supply
13) >200 kHz bandwidth to achieve excellent inter-channel phase at 20 kHz.
14) < 0.1 Hz low frequency cutoff to minimize low-frequency phase shift
15) Feed-forward design improves damping factor

The AHB2 design was optimized for low distortion and low noise. It was not optimized for the highest possible efficiency that can be achieved with this new topology. Nevertheless the AHB2 is much more efficient than a conventional class AB design. Peak power does not vary with AC line voltage (due to regulated supply). Power drawn on one channel does not influence the power available from the other channel.

The AHB2 is a linear amplifier, it is not a switcher. For this reason, it produces very little out-of-band noise. A-weighted noise is only 2 dB less than noise measured over an 80 kHz bandwidth. This was an important design goal because ultrasonic noise can be folded into the audio band by non-linearities in speaker transducers.

If you have more questions, talk to me at AES, or post questions here.
__________________
John Siau
Gear Builder

VP Engineering

Benchmark Media Systems, Inc.
www.benchmarkmedia.com
John,

Thanks for the information. I admit to not having the technical background to fully appreciate many of your points, but I do understand some of them.

Has pricing been decided?

Also, I wanted to say I very much enjoyed reading on your web site about the historical genesis of the amp and Benchmark in general.

Thanks again.
As far as pricing, I have read that it is not yet finalized but they are trying to keep it as low as possible and it will be under $3,000.
I had no idea how small the amp is...

http://www.stereophile.com/content/benchmark-debuts-high-dynamic-range-amplifier

Almost makes me consider passive speakers again.
The article says pricing is expected to be $2500. At 2500 I would bite.
"...It is now possible to produce and distribute recordings that have dynamic ranges that exceed 120 to 125 dB. However, it is hard to find a power amplifier that can deliver more than 100 to 105 dB of dynamic range."

Well, as soon as someone can provide me with a commercial recording that has more than 50 db dynamic range I would be interested in auditioning this amp. Until then, this seems to be a solution that addresses a non-problem...

-RW-
Re "it is now possible to produce and distribute recordings that have dynamic ranges that exceed 120 to 125 dB":

1)The dynamic range of a piece of music (as opposed to the dynamic range of the medium) refers to the difference in volume between the loudest notes and the softest notes. It is true that nearly all recordings have a musical dynamic range of less than 50 db, and in most cases far less.

One of the widest dynamic range recordings I know of is the Sheffield Labs recording of Prokofiev's "Romeo and Juliet." I have had occasion to examine its waveforms using a good audio editing program (Sony Sound Forge), and I found that the difference in volume between the loudest and softest notes is about 55 db, which is remarkable.

2)The dynamic range of the MEDIUM (and the equipment used to reproduce the recording) needs to be MUCH greater than the dynamic range of the music, in order to capture and provide the harmonic and other detail that is contained in the softest (and other) notes.

Apparently the quoted statement is using the term "dynamic range" to refer to the difference between the peak amplitude of the loudest possible note, and the smallest capturable harmonic or other detail that may be a constituent of any possible note.

Regards,
-- Al
Re "One of the widest dynamic range recordings I know of is the Sheffield Labs recording of Prokofiev's "Romeo and Juliet." I have had occasion to examine its waveforms using a good audio editing program (Sony Sound Forge), and I found that the difference in volume between the loudest and softest notes is about 55 db, which is remarkable."

Yes, but dynamic range is the difference between the loudest note and noise.

The difference between the loudest note and the noise floor of the recording can be very high. The noise floor of the recording can be dominated by room noise or electronic noise from the recording chain. With high-quality recording equipment, the room noise often becomes the limiting factor. A microphone in close proximity to a loud instrument in a quiet room can reach very high signal to noise ratios.
Actually Signal to Noise ratio SNR is the ratio of the loudest signal level to the noise. The Dynamic Range is the ratio in dB of the highest signal level to the lowest signal level. Curiously LPs, which have relatively lower Dynamic Ranges can often sound much more dynamic than CDs, which supposedly can have Dynamic Ranges around 90 dB or more.
So did anyone hear it?
John/Gearbuilder, my post that you quoted from was prompted by the post by Rlwainwright, which if taken at face value would seem to cast doubt on the value of the very wide dynamic range of your new product, that is cited at the link the OP provided.

My point was that the claims in your paper and the point he was making are not necessarily irreconcilable, because it seemed clear to me that the two of you are basing your respective statements on different definitions of "dynamic range."

I certainly agree with the last paragraph of your post just above. However, regarding:
Yes, but dynamic range is the difference between the loudest note and noise.
If you are asserting that this is or should be the exclusive definition of "dynamic range," I would respectfully submit that widespread usage of that term in various contexts suggests otherwise.

As I indicated in my previous post, a distinction should be drawn between the dynamic range of the music, and the dynamic range of the medium and/or equipment (and as I indicated in my previous post, the latter needs to be far greater than the former). It is extremely common for "dynamic range" in a musical context to be used to refer to the volume difference between the loudest and softest notes. Your definition is also arguably reasonable. A third possible definition would be the difference between the maximum possible volume ("full scale" in digital terms) and the noise floor. A fourth possible definition would be the difference between maximum possible volume and the minimum signal level that is discernable BELOW the noise floor.

All of these definitions are reasonable, IMO, and my perception has been that all of them are in common usage. Statements that don't make clear how the term is being used, or that are based on the assumption that there is only one acceptable definition, will be conducive to unnecessary misinterpretation and disagreement, as illustrated (I believe) by Rlw's response to your paper.

Regards,
-- Al
I think a lot of SS amps over the years have not handled all aspects of even CD redbook dynamics including transients particularly well. Newer, higher efficiency class D amps I have heard seem more up to the task in general.

Tube amps provide an alternative with different tradeoffs.

A different kind of amp designed to tackle things better sounds appealing. I owned a 70's vintage Class G receiver for many years. It had its appeals, mainly smaller size, even back then, and plenty of rough edges. I'm sure it wasn't even close to the best possible.

I guess I was under the impression that newer CLass D switching technologies would put older more ergonomic switching based designs that never seemed to catch on to rest for good, but maybe not.

So who heard the thing at RMAF and what did you think? Everything I have read to date indicates promise, if not a new revolution. Of course, BEnchmark's DACs are the product that seems to continuously help raise the bar. WHy not an amp to go with it?
Re "One of the widest dynamic range recordings I know of is the Sheffield Labs recording of Prokofiev's "Romeo and Juliet." I have had occasion to examine its waveforms using a good audio editing program (Sony Sound Forge), and I found that the difference in volume between the loudest and softest notes is about 55 db, which is remarkable."

Yes, but dynamic range is the difference between the loudest note and noise.

The difference between the loudest note and the noise floor of the recording can be very high. The noise floor of the recording can be dominated by room noise or electronic noise from the recording chain. With high-quality recording equipment, the room noise often becomes the limiting factor. A microphone in close proximity to a loud instrument in a quiet room can reach very high signal to noise ratios.
Anybody with any experience with this amp?

If I sell my Bryston PP300 (4B-SST) I want to try my Benchmark DAC2 connected directly to the ABH2 driving my KEF LS50's. Any opinions on my switch of amps?
The AHB2 is a linear amplifier, it is not a switcher. For this reason, it produces very little out-of-band noise. A-weighted noise is only 2 dB less than noise measured over an 80 kHz bandwidth. This was an important design goal because ultrasonic noise can be folded into the audio band by non-linearities in speaker transducers.

True, but only if tweeter's membrane can move at the switching frequency (such as mentioned 80kHz).