Benchmark Audio DAC3 DX and AHB2 amplifiers Review

The ROON Headroom trick

Before I discuss the combinations of components used in this review and the outcome, I would like to introduce a feature of the Roon media playback software. The Headroom adjustment in Roon’s digital interface software is really not a trick, but a setting and proper use of it is a nifty trick to vastly influence a system.

The feature is accessed by touching the small, colored dot to the right of the metadata shown during playback, i.e. Title of song and artist. A tiny window will open and you should choose the option “Digital Engine”. Once opened, that window will yield more options. Open the “Headroom Adjustment” option. Once inside you will see an option for turning on the Headroom adjustment and another to automatically apply changed settings. Select both of them. Then note the small field in which you can alter the Headroom adjustment itself. The default setting of the Headroom adjustment is -3 dB. As I worked with the setting, moving it from the -3dB level upwards toward a positive 3dB I heard sweeping changes to the sound of the system. I realized I had stumbled onto a very important setting.

Indeed, John Siau, Benchmark’s VP and Director of Engineering, has this to say about the Roon “Headroom” setting:

“It is a gain reduction function that reduces the signal level before any DSP operations occur. This also reduces the signal level going to the DAC. This reduction provides enough headroom to prevent DSP overloads. Most importantly, it prevents the gross DSP overloads that can occur when an upsampling function reconstructs the audio waveform between samples. All sigma-delta D/A converters use oversampling or upsampling. The headroom function prevents the digital clipping of intersample overs (signal peaks that exceed 0 dBFS). Benchmark converters have an extra 3.01 dB of headroom in the entire digital path and the Roon headroom function should be turned off (or be set to o dB). Virtually all other D/A converters will benefit from this function. In my opinion, this should never be set less than about 1.5 dB and it should be set at the full 3 dB if MP3 files will be played. I have written six papers on the topic of intersample overs. The people at Roon and JRiver are aware of the intersample over problem, but sadly, most converter manufacturers have ignored this issue. Intersample overloads generate false high frequency percussion sounds. This defect is entirely preventable using the headroom function or a DAC with built-in headroom.”

I experimented with the Headroom setting and as I increased upward the setting from the default -3dB, the performance improved markedly. As I raised the value of the setting the system seemed to be freed from constraints. Holistically, the equipment seemed to wake up and the sound was more engaging due to dynamic and definition improvements.

The difference was so dramatic that I resolved not to use the -3dB setting. As I pushed it past the “0” setting and into positive territory, the result was obvious distortion. The Headroom adjustment is a seriously potent control! Set it too low and the system seems constrained performance-wise, but set it too high and the system veers off into distortion, a symptom of the saturation of the digital signal and a result of the digital clipping of intersample overs that John discussed. If the setting was too high, the result was a demonstration of the important point John made in regard to the Benchmark DAC 3 DX having an extra 3.01 dB of headroom in the signal path. That extra headroom did not work well with the increased setting of the Roon’s Headroom; it was too much. John suggests a setting of less than 1.5, which I concur; the distortion started going away under a setting of 2. However, care should be taken to find one’s optimum setting, and it will reside between -3 dB on the low side and 2 dB on the high side.

Do not be overly aggressive in adjusting the Roon Headroom setting! Even movements of .1 dB or -.1 dB are significant and audible while listening. A change of a .5 dB increment is huge and will skew the system’s performance. I have never adjusted a system more than a range of 2.5 dB variance up or down. Usually, optimal performance resides in a range of less than 1dB, i.e. from -.5dB to .5dB. This is not to be taken as a universal range for all speakers and systems. I suggest beginning with the default setting (-3dB) and moving it no more than .5 dB at a time. You will hear the level, macrodynamics, definition, and even tonality change dramatically as you adjust the Headroom setting. Typically, better performance can be found in a range between -1dB and 1dB. If you take .1dB steps in that range you have twenty settings in which to discover that the overall character of the music will be more robust, sharper in delineation, tonally richer, and dynamically more contrasted. In my experience, when the setting went past the 0.0-point into positive integers, it seemed the signal would saturate quickly and distortion would set in. But, see discussion below regarding the Benchmark DAC3 DX headroom. If the setting was lowered much past -2 dB, cramping of dynamics came into play.

How does this relate to the Benchmark monoblocks? The AHB2 amp already has a GAIN adjustment on the back of the amp. With ROON’s headroom setting, it is as though the system gained another gain control, not just over the amp, but the entire rig. It is like a pair of binoculars that allow for one eyepiece to be adjusted, then the glasses. It is a sensationally powerful contouring agent to pull far more refinement, power and richness from the AHB2. Do not be lulled into thinking that since Benchmark has seemingly covered all the bases in regards to features, that the AHB2 cannot be improved. It can, and dramatically, with the Headroom adjustment.

Now, after giving all that guidance about the Headroom adjustment in use with multiple DACs, not only the DAC3 DX, to my ear the best setting is normally at “0”, or no Headroom adjustment at all! In the systems I built, the Headroom adjustment caused an audible decrease in the definition and fullness of the music. I found that when using the Benchmark DAC3 DX, if I set the Headroom adjustment to “0,” the circuitry for the feature was bypassed entirely. The signal path indicator provided by Roon detailing the steps involved in upconversion of the signal showed removal of the Headroom adjustment. However, I could not remove the Headroom circuitry when using the Exogal Comet; even when set to “0” it remained in use. I simply turned the Headroom function off at that point. The only thing to watch when reducing or eliminating the Headroom circuitry is that you do not overdrive the speaker as there will be no limiting influence to ameliorate the higher level of some recorded music. You do not want to push the Roon Headroom setting high, then blare your music; it will be distorted and potentially cause harm to speakers at higher listening levels. As often the case, you work with such settings at your own risk.

My final assessment regarding the use of the Roon Headroom setting may not perfectly parallel the technical advice given by John, however it does associate at several points. The key is to realize whether your DAC has a headroom adjustment and use the Roon Headroom feature accordingly. It is a splendid additional tool to adjust a system to yield your favored performance.

3 speaker systems, three successes

I would like to thank Benchmark Audio for not imposing a time limit on this review. More than once when approaching a review of a product I have been urged by a manufacturer to get a review done in four to six weeks. I typically, politely decline, as anyone can conduct a sloppy, quick review. As I was given a longer time frame for this review I was able to work with several combinations of gear and three speaker systems.

Delightful would be a succinct summary of the emotional and intellectual experience of hearing the Vapor Audio Joule White, Kingsound King III and PureAudioProject Trio15 PAP Horn1 speakers with the Benchmark components. All of these are incisive speakers that reveal iffy solid-state products. Weaknesses are readily exposed. Even though the King III was more challenging for the Benchmark components in terms of driving the speakers to high levels, the sound quality attained was the best to date for that speaker system. The Vapor Joule White and PureAudioProject Trio15 PAP Horn 1 were very easy to drive and were highly complementary with the Benchmark pairing.

However, as I said at the onset of the article, what of the question in regard to features? Was the feature-saturated Benchmark combo hindered in any way compared to a simpler combination of gear? Again, the four components in question were the DAC3 DX, AHB2 Amplifier (2), Exogal Comet, and the Belles ARIA Monoblocks, and I tried them in all their permutations. I tend to go through rounds of component matching and system building when conducting reviews, as more experiences yield more insight into the nature of the components. I do not sit around waiting for something amazing to happen simply by playing a component (read “Burn In”), I am building systems, making wonderful things happen. While someone else may be waiting for a change, I have heard ten changes. I built more systems than what is shown here, but these are discussed for illustrative purposes.

Exogal Comet + Belles Aria monoblock amplifiers

The speaker system used for the iterations of components discussed below was the Vapor Audio Joule White, and the source for the comparisons was the Salk Audio StreamPlayer III. In terms of the components to be rotated, I began with the most feature-poor setup and progressed toward the most feature-rich setup. The Comet converts all incoming digital signals, including DSD, to one created by its own algorithm. The Belles Aria monoblock amplifiers have no adjustments. This truly is a “one trick pony” setup.

This rig was commendable in providing a clear, tonally rich, very warm sound. As a “take what you get” result it fared well, and emphasized midrange bloom versus emphasis on top and bottom frequencies. It reminded me of the polite Pathos Classic One MkIII integrated amps that could hardly be made to sound harsh.

This system was short on power to drive the less efficient Kingsound King III electrostatic speakers. However, it was polite with the sometimes fiercely precise, ceramic Accuton midrange of the Vapor Audio Joule White. It landed smartly in the easygoing sound with easy setup category. The major disadvantage was that contouring the sound was limited to cabling only. Any aspect of sound quality I might consider deficient or overemphasized could be brought to heel only so far.

This is where ROON’s Headroom adjustment was immensely helpful. It allowed me to play with the relative strength of the treble and bass especially. However, this advantage is only in ROON, so I cannot make too much of it, and there is a degree of lost definition in utilizing the Headroom setting. The Benchmark components also had this feature available to use, and they reacted with as much vigor as the Comet and ARIA amps.

Exogal Comet + Benchmark AHB2 amplifiers

The next setup was not as I had anticipated. I had already run the Benchmark combo through their paces in order to get a feel for their operation together. However, to assess what each component contributed, rather than go with the Benchmark products together I separated them to first isolate the amp’s performance. I wanted to see if moving incrementally from a mixed brand setup to the all Benchmark setup would result in a clearly noticeable improvement. So, I began with the StreamPlayer III, Exogal Comet DAC with Plus Power Supply, AHB2 Amps in Mono mode (480wpc into 6 Ohm), and the Kingsound King III electrostatic speakers. The cabling was all Clarity Cable, including the Supernatural USB and Supernatural Speaker Cable, with one addition. I added a pair of Silnote Audio Anniversary Speaker Cables feeding the Legacy Audio XTREME XD Subwoofers in order that the system would have LF presence beyond the 28Hz the speakers produced.

This was the most challenging system I could throw at the AHB2 amps, as the output of the Comet was relatively low. When paired with the AHB2 amps they struggled to drive the King III to unrestricted listening levels. This was not entirely unexpected, as I had previously paired the Red Dragon S500 class D amplifiers in mono, which output 500wpc, with the Exogal Comet and the King III. That pairing also was taxed to the limit. In both cases the Comet, while sonically beautiful, was not an ideal match with the AHB2 due to its lower output.

Nevertheless, this setup revealed some important information about the AHB2.

The Benchmark responded readily to the influence of the Headroom adjustment. I toyed with several settings, narrowing down the range until the adjustment was fixed at -.8 dB, which allowed the AHB2 to take on a character of an even more powerful amplifier, and yet retain its low noise level.

The openness and information retrieval of the system was superb. Pieces of music that I play for discovery of a rig’s capacity to dig out detail impressed me deeply. Some of these pieces are Paul McCartney and the Wings’ “Live and Let Die”, Yello’s “Tiger Dust”, or more recently Jake Shimabukuro’s “Low Rider”; each one the King III brought forth better than I had experienced in the past, even though I have used some big name, much more expensive amps. It is an amazing thing to hear electrostatic speakers having layers of previously undetected sonic smudging wiped away as progressively better amps are used. All this was discovered even though the synergy between the Comet and AHB2 was not maximized. This tells me that the innate quality of the AHB2 is at a level that even if used in a rig that is not fully optimized it stands a good chance of still being perceived as exceptional.

Things were about to get better. When I swapped out the Comet for the AHB2’s sibling, the DAC3 DX, the picture changed. Now the amps had enough power and dynamic impact, though not overwhelmingly so. The King III could be driven more forcefully, and only in the instance of two very low-level recordings did I feel the amps failed to drive the speakers effortlessly to the 90dB range. Remember, I do not seek to push systems to “live” levels for many reasons, including distortion levels, potential hearing damage long term, etc.

Even in Monoblock mode, the AHB2 and DAC3 DX did not seem capable of level-unlimited playback with these less efficient speakers regardless of program material. That is so even though the Gain setting on the back of the AHB2 and the internal XLR output pads were at their highest output. I hasten to point out that level-unlimited playback is notoriously difficult for most amps driving electrostatic speakers. Typically, high current solid-state designs made expressly for lower impedance speakers are sought because of the demand as impedance drops in the upper frequencies. Listeners of very quiet performances recorded at lower levels should pause before pursuing this combination of gear with difficult to drive speakers. Again, this is not a deficiency in design, but is true of many well-designed amplifiers.

Now, having said that, the AHB2 isn’t even rated for 2-Ohm speaker operation. It is said to be stable into demanding loads, and it was. I pushed the amps to full output for short periods of time and they were unflinching. There was no detectable deterioration of sound quality; the claim that the amps do not distort is true in my experience. Even at the highest gain setting, the AHB2 is very, very quiet. I can have the level jacked up and the music queued to play, and there is no giveaway that the amps are on, much less music primed to launch. One of the thrills I received repeatedly from the AHB2 was of a powerful performance exploding onto my senses from a black hole-like background.

To highlight how vast the differences that exist between speakers are in terms of efficiency and what is needed to drive them, I had an utterly different experience when driving the Vapor Audio Joule White. This speaker is 4 Ohm, 90 dB sensitive, and is far easier to drive by even lower powered amps. The AHB2 was loafing while powering the Joule White. The range of operation of the volume control could only comfortably be raised to about the 10 O’clock position, right at the point where I was tempted to open up the DAC3 DX and adjust the XLR output pads. But, there was just enough range to accommodate all my preferences in listening levels. If I had adjusted the pads, then whenever I wished to run the King III electrostatic speaker I might need to revert the settings. I decided to leave the DAC3 DX well enough alone. However, if I were not switching speakers I would have adjusted its output pads to gain a wider range of volume control.

Benchmark DAC3 DX + AHB2 together

Synergy is a nebulous concept when it comes to audio systems. Once a component leaves the production floor, is procured and utilized with other products, the objective character of synergy that was designed into it as it was intended to be used with sibling components all but disappears. If the collection of equipment is pleasing to the particular ear it is said to have a high degree of synergy, and if it isn’t, not much is said of synergy. Synergy is not as nebulous when one can actually hear its effect in a comparison between components in a short period of time. As I worked through the permutations of gear when I arrived at the Benchmark DAC and amps, the potential advantage in them being feature-rich was clear.

The technologies and features of the DAC3 DX and AHB2 dovetailed, resulting in plenteous richness as well as precision. The chief distinction between the Comet/ARIA combo and the Benchmark combo was a more even treatment of the frequency spectrum, a removal of the warm emphasis of the first pairing. Earlier on, at the assessmentof the AHB2 with the Exogal Comet, the AHB2 was deemed the “weak link”. But now, with its sibling component, it was transformed. About two months prior to the arrival of the AHB2 amps I enjoyed the AVM Ovation SA 6.2 monoblock amplifiers with the same Joule White speakers. In combination with other equipment, the Ovation amps were under no great competition. However, with the DAC3 DX, I could envision exchanging the Ovation amps for the AHB2 without suffering great loss of quality.

Another surprise was that with all the adjustments offered between the DAC and amp, I could move the tonal palate of the Benchmark components toward that of the Exogal and Belles pairing, not exactly but significantly. The Benchmark set was tidier and leaner, but not in a distracting or dissatisfying manner. It may sound cliché, but the Benchmark components had a more studio sound to them, tight, lean and clear. The low-end was weaker and less full than that produced by the Exogal and ARIA, but perceptually tighter. The most striking similarity was in terms of timbre. By using the Digital Engine feature of ROON, and the Headroom adjustment I was able to cool off or warm up the system to bring it closer to the performance of the Comet/ARIA pairing.

I need to state the conclusion of these comparisons carefully.

I did not find the DAC3 DX and AHB2 to dominate the Exogal Comet and Belles ARIA monoblock amps; both setups were engaging and had their strengths. The outcome of this particular comparison between “feature-poor” and “feature-rich” products was a tie. That may come as a shock to some who fall to one side or the other on these brands. Neither the purportedly superior simple signal path of the feature-poor components, nor the many sonic options of the feature-rich components stole the show. I have been reinforcing the point that the saving grace of the Benchmark combination is flexibility. With another set of cables, another source, another speaker would the Comet and ARIA amps fare as well? The odds are that as the systems varied, the flexibility of the DAC3 DX and AHB2 would come to the fore.

An exceptional showing

The most memorable experience I had with the AHB2 and DAC3 DX was with a relative newcomer in speakers, PureAudioProject, a company straddling the worlds of the DIY enthusiast and the domestic audiophile consumer. PureAudioProject (hereafter PAP) makes high quality “kit” speakers that ship in flat pack boxes, built to high tolerances and featuring respected parts such as Mundorf crossovers of Germany. These owner-assembled speakers are eminently capable performers. The PAP Horn1 variant which I just reviewed is to my ears the finest of the series to date. A field coil version of the Trio15 has just been developed, and it may be one of the few types of drivers able to give the Horn1 a run for the money. I will let you know, as I am scheduled to review it.

Perhaps it was an affair with a new technology that thrilled me; after all, this was the first hybrid horn speaker I had reviewed. That may have been part of it, but certainly not all of the cause for my enthusiasm for the combination of the Benchmark electronics and PAP speakers. What accounted for the excitement was the cascade of variables, features allowing for tuning of not just DAC/preamp to Amp, as seen above, but also the speaker! Yes, the PAP Horn1 is itself adjustable, too! It offers the capability to exchange resistors and capacitors on the crossover board – made easy by the use of screw down terminals for the leads of these parts – as well as jumpers to allow a more streamlined or complex signal path, thus varying the sound of the speaker innately. There are not too many things more exciting to a System Builder than adding another set of variables to fine tune a system!

When all of this is coordinated, the system becomes a rich playground of sound. Nearly any aspect of performance preference can be satisfied. I was able to induce bass laden bottom-end, or conversely a relatively lighter bass weighting that was overshadowed by the midrange and treble. Or, I might choose to reverse those qualities, or pull them into a balance across the frequency spectrum.

The most glorious aspect of this system was the sense that the sound “went on for miles”, as though the farthest extent of the soundstage faded in the distance somewhere beyond perception. The system also was exemplary in showcasing the effect of “layered” sound, the ability to render highly complex music with overlaid effects or instruments with such subtly that the ear could flit between each element and readily lock onto it in order to enjoy it’s nuances. It is not difficult for the eyes to appreciate a 4K TV picture experience; the extreme resolution makes appreciation nearly autonomous. Similarly, the extreme resolution of the Benchmark/PAP combo made appreciation of detail reflexive.

I stumbled upon harpist Monica Ramos as I plowed through the detritus filled new music at Tidal, a rare jewel among a ton of compost-worthy media. Her light touch on the instrument was evident and the expansion of the harp strings’ reverberation in the recording space was rendered beautifully by the Horn1 and Benchmark components. This is a paltry MP3 file from Tidal, however by the time it had been processed by the DAC3 DX and Digital Engine of the ROON processor, incorporating the Headroom trick, it was redeemed as a worthy piece of music to catalogue.

Every so often I surprise the members of my local listening group with something unexpected, just to make sure the goal is to have fun. One of the more memorable surprises was playing Disco music to a multi-colored USB mini disco light. Do you want to see a grown audiophile break down in laughter? Tell him to close his eyes – mandatory for a big reveal – and upon opening them experience“Saturday Night Fever”, complete with multi-colored light show! There’s nothing quite like a psychedelic rendition of the Bee Gee’s “Staying Alive” or “Calypso Breakdown” by Ralph MacDonald done up huge with the four 15” Neo woofers and immediacy of the horn driver to tickle the emotions. The music? Admittedly tacky! The performance? Surprisingly good, given the limited quality of the recordings! When my guests stopped laughing and started listening, they admit it sounded good.

Something more sublime is found in Gregory Porter’s “Real Good Hands”, where as a suitor Porter begs his future father-in-law to judge him fairly as he asks for his daughter’s hand in marriage. The refinement of the Benchmark/PAP pairing is such that the intended earnestness in Gregory’s voice is evident. The piece is excellent for assessing performance of the lower-end of the frequency spectrum of a system as he not only sings, but also speaks as he embarks on the song. If you become familiar with this one piece of music, dialing in Porter’s spoken voice, you can grasp the anticipated outcome of the bass performance of the system holistically.

Precision is king in Benchmark pro-oriented products

In this age of ultra-refinement in the production and playback of music, Benchmark Media shows that it is to be recognized as a paragon of musical integrity at an affordable price point. Wishful thinking toward very high quality by budget-constrained audiophiles has been answered by Benchmark. A high veracity result can be obtained with different genres of speaker systems reliant upon the DAC3 DX and AHB2. The DAC3 DX and AHB2 are ferociously competitive performing units that when optimized leave what could be considered a marginal gap between them and statement products.

There are many variables in systems that can diminish performance, and the DAC3 DX and AHB2 address several important ones, namely, the quality of the preamp function, the precision of the DAC, the adjustability of the preamplifier’s output, and the ability to adjust the gain of the amp. The audiophile does not need to guess at matching gear when Benchmark offers real world solutions to mismatches. For this reason, and for commendable sonic performance with a variety of speakers, the DAC3 DX and AHB2 are recommended as high value, high performance choices which should be suitable to be match with other brands. However, they shine brightest when used together, all but assuring a very high quality (read “high synergy”) result with a focus on the definition and dynamic range of playback.

I suspect that especially younger ears, and the ears of those who spend much time with headphones, will appreciate the Benchmark sound. I appreciate them as I have experienced many less accurate systems, and I revel in high purity playback. The only listener who will need to consider carefully prior to commitment to Benchmark is the lover of warm, perceptually “softer” or “laid back” sound, who pays much more attention to tonality than detail. Those who are seeking a highly revealing sound, perhaps considered “honest” or “truthful”, and invigorating, would find great satisfaction with these components. I will close with a scintillating thought pertaining to my impression of the AAA amplifier technology in comparison to other Class D amps I have used. You may find this brief treatment of the comparison unsatisfying, however, I only have so much time to allot to any given review. My finding? The AHB2 is an almost assured upgrade from class D amps, but together with the DAC3 DX forms the core of a quite respectable high performance audio system.

Associated Components:
Source: Salk Audio StreamPlayer Generation III with ROON interface
Streaming Music Service: Tidal
DAC:  Eastern Electric Minimax DSD DAC Supreme with Burson, DexaNewClassD and Sparkos Labs Discrete Opamp Upgrade; Exogal Comet DAC and upgrade power supply, LampizatOr Big 7
Preamp: TEO Audio Liquid Preamplifier; VAC Renaissance Signature Preamplifier MkII;  Cambridge Audio 840E
Amps: Red Dragon S500; First Watt J2 (two); Exogal Ion (PowerDAC); AVM Ovation SA 6.2 Stereo Amplifier
Integrated:
Speakers:  Legacy Audio V Speaker System; Kings Audio Kingsound King III; Legacy Audio DSW Clarity Edition; Kings Audio King Tower omnidirectional; Vapor Audio Joule White 3; PureAudioProject Trio15 (Voxativ and Horn versions)
Subwoofers: Legacy Audio XTREME HD (2)
IC’s: TEO Liquid Splash-Rs and Splash-Rc; TEO Liquid Standard MkII; Clarity Cable Organic RCA/XLR; Snake River Audio Signature Series Interconnects; Silent Source “The Music Reference”
Speaker Cables: TEO  Cable Standard Speaker; Clarity Cable Organic Speaker; Snake River Audio Signature Series Speaker Cables; Silent Source “The Music Reference”
Digital Cables: Clarity Cable Organic Digital; Snake River Audio Boomslang; Silent Source “The Music Reference”
USB: Verastarr Nemesis; Clarity Organic
Power Cables: Verastarr Grand Illusion; Clarity Cable Vortex; MIT Oracle ZIII; Xindak PF-Gold; Snake River Audio Signature Series; Silent Source “The Music Reference”
Power Conditioning: Wireworld Matrix Power Cord Extender; Tice Audio Solo