HiFlight
Headphoneus Supremus
Below is my review of the Virtue Audio Sensation M451 as a possible amplification source for difficult-to-drive BALANCED headphones. This review is only the headphone part of a comprehensive 2-part review that is scheduled for later publication. The speaker portion of the review was done by another individual, as I have only used the amplifier with headphones.
Ron
Virtue Audio Sensation M451 Review
(Virtue for Headphones)
While I have owned or do currently own a Virtue One Classic, Virtue 2.2, Virtue Piano CDP and currently have on loan a Virtue Audio Sensation M451 with tube buffer, I am likely to be the only Virtue owner who has never heard a Virtue amplifier used with a loudspeaker of any kind! I have only used them with headphones!
How can that be? None of the Virtue amplifiers are equipped with headphone jacks and it’s well known that using conventional headphones with any Tripath-based amplifier is a sure-fire way, to well, smoke it. To answer this seemingly contradictory question, a bit of background information is needed...
You may know that I’m a headphone enthusiast. As a commercial pilot I spent countless hours passing time in hotel rooms; headphones have been my musical drug of choice for many decades now. I currently own a set of the highly-regarded but very difficult to drive AKG K1000's and K340's. These phones have efficiencies that are more similar to that of loudspeakers, rather than typical headphones.
Recently, several companies have introduced a new generation of planar headphones which have sensitivities as low as 83 dB/mW. Typical headphone amplifiers deliver just a few watts, barely enough to make such phones listenable, much less to achieve their potential.
Through experimentation I found driving these phones directly from the speaker terminals of traditional speaker amplifiers worked much better than using headphone amps, and for a lot less money.
However, there are important caveats, especially when using Tripath-based amplificers (aka “T-Amps”). For instance, it is necessary to balance the headphones, which simply means supplying each ear-cup with its own discrete + and – leads as if they were speakers. Shorting the leads is easy to do with certain wiring harnesses so it’s vital to replace the 3-connector TRS stereo plugs that often come with these headphones with a 4-pin pin or dual 3-pin XLR connectors. A simple matching pigtail then permits a direct connection to the amplifier speaker terminals.
As I have developed a fondness for Virtue amps, I accepted Virtue owner Seth Krinsky’s request to give the flag-ship, Sensation M451 a spin. He sent it with the Dodd tube buffer option, bypassed Sonicap input capacitors and 3 power supplies to compare.
The supplies included the 30v 130 watt SMPS AC adapter, a JT 30v 10 amp AC power supply (built by “cable guy” Jason Terpstra), and a Gary Dodd 24v dual battery power supply with charger. The standard, 24v 65 watt SMPS supply is just fine, but on a $1,000 amp, skimping on the PSU makes no sense.
As headphone aficionados know, phones present a much higher impedance profile than the nominal 4-8 ohms that most speaker amplifiers expect. Sensation is tuned for 6 ohms, yet nothing sounded odd at all with my higher impedance headphones. Regardless, I’m a tinkerer and figured out that if I bridged the + and – speaker terminals with high-quality Riedon non-inductive 8 ohm 12 watt resistors, the amplifier would “see” 4-8 ohms, regardless of which headphones I was driving. Seth told me that I might hear sibilance in speakers presenting loads above 20 ohms, but I did not with phones, perhaps because of the lower current draw when compared to loudspeakers.
For all listening tests, the following equipment was used:
Sources:
Virtue Piano M1 CD player via analog output
Logitech Squeezebox streaming music via optical output to my magiDAC.
iRiver H120 DAP line output. Music files were high-bitrate MP3 and Flac.
Headphones:
AKG K1000 120 Ohms, Sensitivity 74dB/mW
AKG K340 400 Ohms, Sensitivity 94dB/mW
HiFiMAN HE-6 50 Ohms, Sensitivity 83.5 dB/mW
Sony MDR-CD180 24 Ohms, Sensitivity 98 dB/mW (very efficient)
Tubes used in buffer: Amperex Bugle Boy 12AU7, GE 5-Star 5814A, GE 12AU7WA (CV4003), Baldwin long-plate 12AX7.
In order to check for noise from the power supplies, from the amplifier only, and from the amplifier with the tube buffer, I fired up the Sony phones first with the source muted.
The Sony phones are extremely efficient and are very revealing of low-level hum and hiss. They were not used to evaluate the music quality of the Sensation as they lack other sonic merit. I did not use any of my test equipment for noise measurements; headphones were used exclusively for all testing.
To start, I compared all three power supplies. I heard no hum or hiss from the battery supply and 130 watt SMPS except for a faint, 120hz hum when the amp was cranked wide open. The hum was only audible from inputs that had equipment connecting cables, so perhaps the hum was introduced externally.
The JT power supply, however, had very noticeable 120 hz hum at even minimum settings which increased at higher volume settings. I found the hum intolerable and did not use this supply for any of the music evaluations. Perhaps more inefficient phones would mask the hum but in my retirement, sonic compromise is not a virtue.
With the tube buffer switched into the circuit and still using the Sony, I could hear a slight 120 hz hum beginning at about half volume and reaching a moderate level at full volume. Some tubes exhibited somewhat more hum than others. The quietest was the Bugle Boy, vintage 1950! It was this tube that sounded best with all of the phones with any type of music so it remained as my default tube for the remainder of testing.
For my music comparisons, I used both CD recordings and high-bitrate MP3 rips from recordings made by a friend who I have heard live on many occasions, both inside rather intimate settings as well as outside live. These recordings are male vocals with mostly acoustical accompaniments. As I am very familiar with the sound of his live performances, it makes it quite easy to make audible comparisons between the live performances and the sound as delivered from my Sensation evaluation system.
I also used several CDs that were binaurally recorded using a dummy head. These recordings were 24 bit with a sample rate of 96 Khz. As is the case with all binaural recordings, headphones must be used to recreate the holographic imaging that is the hallmark of binaural recording.
I connected my equipment so as to provide the same signal input to both the Sensation and my Virtue TWO.2 which has served as my “go-to” amplifier for more than a year. This setup allowed me to quickly switch from one amplifier to the other for A:B comparisons.
My HE-6 planar headphones are probably the most accurate of the trio so I was anxious to test them first. They are also the most inefficient at 83.5 dB/mW and require an amplifier of considerable output current in order to reach their potential. Power supply was the 130 watt SMPS and to start, I turned OFF the tube buffer using the toggle switch inside, above the volume POT.
The resulting sound was very detailed and tended toward the analytical. Transients were fast and bass was very tight, easily reaching the lower limits of the recorded mix. Although quite detailed, highs were not abrasive or strident.
While very accurate, the music sounded like a good studio recording. It was lively but not live; revealing but not something I would listen to all day long.
I then auditioned my AKG K1000 phones with the same recordings and same power supply. Imaging and soundstage were significantly improved as, for all practical purposes, these phones can be considered similar to near-field speakers. As such, they provide a very natural speaker-like soundstage from nearly all input sources.
The K1000 headphones are often said to favor the higher frequencies while lows drop off quite rapidly below about 50 Hz. As such, a considerable amount of synergy is required between these phones and their amplifier in order to provide a SQ that does justice to this unique headphone design. Fortunately, the Sensation provides the necessary current and transient response to make the K1K's perform in an almost eerily realistic manner. I did, however, continue to feel that the soundstage was studio-like; a bit cramped and just too perfect.
When I switched to the battery power supply the background grew deeper and space expanded. The imaging was improving and I started to feel the music sounded more authentic, more “real.”
When I compared the sound of the Sensation to that of my TWO.2, using the same phones and same recordings, I noticed that the 2.2 had a slightly warmer and smoother presentation, albeit with somewhat less depth of soundstage. It is my feeling that this was due to the difference in input caps. The Sensation ships with the more detailed Sonicaps while the TWO.2 had warmer, more tube-like Auricaps.
So that’s when I switched on the tube buffer (turn off the unit before you do it!). Wow! Immediately, I was rewarded with the most lifelike and dimensional sound that I have ever heard from my evaluation phones! Tonally, there was little, if any difference, as the instrumental timbre and harmonics remained extremely accurate but the feeling of impact, weight and sense of space grew dramatically!
After listening to many of my evaluation tracks from both the Piano CDP as well music from my Squeezebox streaming music player, I determined that the tube buffer in combination with the battery power supply simply provided a greater sense of space, as if I was now listening in a hall rather than a room.
Decay of tones seemed be lengthened and the virtually unlimited amount of current available from the battery supply made low-frequency transients so realistic I could feel the visceral impact; whether real or imagined, this is what is often missing in amplifiers lacking in power supply current. It is also an area where T-amps tend to excel, especially those which are able to utilize high-capacity batteries as their source of power.
This particular listening combination was my favorite regardless of which of my phones I was using with the Sensation. The K1000 was especially synergistic with this combination of tube buffer and battery power supply. The lower octaves of the music had such a solid foundation and impact that the low-frequency roll-off one typically hears with these phones was not noticeable.
The HE-6 also delivered a soundstage that was convincingly lifelike. Bass often reached a depth that was felt more than heard. Highs were never sibilant and were always delivered with an almost unbelievable level of “sweetness”.
After many hours of listening, changing configurations, rolling tubes and swapping headphones, I am convinced that the Virtue Audio Sensation M451 is more than capable of driving any low-efficiency balanced headphone to any conceivable volume level while providing a sense of realism that I have never before experienced in any of my previous headphone amplifiers, whether tube or solid-state, regardless of price.
While I am in no way affiliated with Virtue Audio, I very much appreciate the willingness of the company to provide me the opportunity to evaluate their Sensation M451 amplifier as means of driving this new breed of planar headphones as well as the hard-to-drive AKG K1000 and K340.
For further information, please visit: www.virtueaudio.com and
http://www.audiocircle.com/index.php?board=152
As the saying goes: Try it, you'll like it!
Ron Kerlin
