Ayon Audio STEALTH DAC, Preamp, Fantastic tube DAC

Beautiful tube DAC in great working condition with new tubes.

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Details:

What’s
in a model name? Well, sometimes not much at all when it’s merely an
arbitrary numerical designation and a potential source of confusion for
my slightly dyslexic mind. On the other hand, Ayon’s choice of model
name strikes me as perfectly befitting a DAC, implying an unobtrusive
delivery of the musical message by a digital device. The Stealth does
just that by following a road less traveled. To be clear, the Stealth is
more than just a DAC. Think line-level preamp offering two line-level
inputs, an electronic volume control, as well as a world-class DAC.

Let’s
start by taking a peak at the analog side of this DAC/pre. The massive
aluminum chassis hides several vacuum tubes which are allowed to
“breath” through a number of small grilles in the top plate and sides.
Ayon is a firm believer in tube technology, and in particular triodes,
for reasons that have to do with inherent linearity under minimal-or
zero-feedback conditions, benign distortion and overload
characteristics, and capacity for simple circuitry. The analog output
stage is amplified in balanced fashion to allow for both RCA and XLR
analog outputs. Each signal leg consists of a Russian 6H30 dual triode,
connected in parallel, and operated as a pure, no-feedback, Class A
voltage amplifier. That’s as purist as it gets, and Ayon is proud of the
fact that there are only five components in each 6H30 signal path. This
is a great-sounding tube, but if and when it fails, replacement as I
discovered is a tedious task. Several weeks into the review process, one
of the left channel 6H30s went bad. To remove the top panel requires
loosening ten Allen-head screws through access holes in the bottom
panel. As compensation, you get to ogle the beautiful hand-assembled
internals.

All filament supplies are DC, and voltage levels are
regulated. There is also an automatic tube soft-start during each
turn-on cycle. Voltage gain can be toggled on the back panel between
low-gain (2.5V) and high-gain (5V) settings. The power supply features
two power transformers and a choke-coupled filter bank. I was surprised
to learn that the Stealth is tube rectified. A quartet of Chinese 6Z4
rectifier tubes is connected as a bridge rectifier. This is not the
cheapest scheme to implement, and the question that comes to mind is why
tube rectifiers in a digital device? The answer, according to Ayon, is
because this approach sounds more dynamic than any other means of
rectification. That alone should inform you about Ayon’s commitment to
the best technical solutions irrespective of cost.

A Cirrus Logic
CS8416 192kHz receiver chip decodes incoming PCM digital data from the
coaxial, BNC, TosLink, I2S, and AES/ EBU inputs. An XMOS asynchronous
USB input accommodates up to 24/192kHz PCM data. Indicators on the right
side of the display show the incoming PCM frequency rate: 44.1, 48,
88.2, 96, 176.4, or 192kHz. Incoming SPDIF data can be upsampled to
24/192kHz. This feature can be “switched” on and off on the remote
control. All sample-rate conversion is performed by a Burr-Brown SRC4193
asynchronous sample-rate converter timed by an external crystal clock
oscillator operating at 24.575MHz. DSD inputs include two BNC (DSD-L and
DSD-R) digital inputs and one BNC for word clock. In addition, the
Stealth is also outfitted with one optional I2S DSD-over-PCM (DoP)
digital input. I’m not that sophisticated a digital user. Hence, the
scope of the review was limited to PCM data inputs, either PCM digital
out from a Sony XA-5400ES SACD player or USB input from my MacBook Pro
computer running Amarra V2.6 software.

The DAC chipset is the
highly regarded ESS Sabre ES9018, a 32-bit audio DAC that features
ultra-low distortion levels, a time-domain jitter eliminator, and
integrated DSP functions. Customizable filter characteristics allow for
user-programmable filters with custom roll-off slopes. The Filter button
on the remote allows selection of either Filter 1 (slow roll-off) or
Filter 2 (fast roll-off). Filter 1 is said to sound a bit smoother than
Filter 2, which is characterized by Ayon as being a bit more analytical.
I suspect that your ultimate preference would be system-dependent;
however in the context of the ENIGMAcoustics Mythology M1 loudspeaker, I
had a clear preference for Filter 2. I found it to be simply more
resolving of microdynamic nuances and more incisive spatially. Filter 1
did sound smoother but at the cost of homogenizing spatial outlines and
dissipating some dynamic tension. I also had a clear preference for
upsampling 44.1kHz PCM data to 24/192kHz. Taken together, the resulting
presentation was not only more spacious and better focused, but also dug
a bit more deeply into the mix and retrieved more ambient information.
It’s easy enough to click these buttons on the remote and experiment in
real time to determine what sounds best in your system.

The
volume control is based on the Texas Instruments (Burr-Brown Division)
PGA2320 IC, a digitally controlled analog volume control designed
specifically for professional and high-end consumer-audio applications.
Internal operational amplifier stages are used to generate an
attenuation/gain range of -95.5dB to 31.5dB. According to Ayon, this
control is strictly used for analog signal attenuation with all of the
gain being developed in the tube linestage. Thus, the display volume
range is from 0 (max volume) to -60 (minimum volume) in 1dB steps. There
is also a built-in balance function accessible from the remote that
allows left-right channel attenuation in 1dB steps up to a total of 6dB.

I’ve
run the Stealth directly into a power amp and have found its volume
control to exhibit low coloration levels. I love its functionality;
nevertheless, the question of how the PGA2320 compares to a conventional
resistive potentiometer deserved an answer. It turns out that the
Stealth’s volume control can be bypassed by switching over to Fixed
Volume mode on the remote control, in which case the audio signal goes
directly to the analog output stage. I connected the Stealth to the
PrimaLuna DiaLogue Premium line preamplifier with its conventional Alps
Blue Velvet motorized conductive-plastic potentiometer. I was then able
to switch between Fixed and Variable volume modes on the Stealth and at
equal volume levels try to discern any sonic difference with the PGA2320
in and out of the signal path. Although not necessarily a definite
test, I did prefer listening with the Stealth in Fixed (2.5V) volume
mode. There were improvements in spatial presentation (depth perspective
and image outline separation). Additionally, the treble range was a bit
purer sounding. These results suggest that the Stealth’s volume control
does introduce a slight solid-state sonic signature.

It didn’t
take me long to realize that I was in the company of a superb DAC, one
that was free from annoying digital artifacts and that could flesh out
tone colors with startling realism. One of the hardest things for a DAC
to get right is violin overtones, especially on recordings that are less
than perfect. Many DACs don’t react well to recording hot spots adding
spurious grain, hash, and even sizzle to the reproduction. Not a
pleasant phenomenon and one that had soured me on digital sound for many
years. By contrast, the Stealth sailed right through recordings that
had given me trouble in the past. Solo violin’s upper range was
reproduced with proper levels of sheen and textural purity. The sound of
massed strings, and in particular that of violins, the most numerous
orchestral string instruments, represents another difficult challenge
for any digital device, and one in which most CD players have scored
poorly. The sound of massed violins should be layered and the spatial
impression ought to float like a feather within the confines of the
soundstage with plenty of tonal warmth and textural purity. And in these
respects, the Stealth was able to put a smile on my face. Its
performance at the frequency extremes bettered that of all previous DACs
I’ve lived with, including the EAR-Yoshino DACute I reviewed in Issue
238. Treble transients were exquisitely refined and bass lines left
nothing to be desired, being well defined and pitch-perfect.

The
Stealth wasn’t just about tonal color fidelity and textural refinement.
It lit a fire under the soundstage. Musical lines boogied with passion
and drama. The dynamic range from loud to very loud was reproduced
without hesitation or compression. A recording’s ambient information was
readily discernible, as was low-level detail often fuzzed over by
lesser DACs. I’m fussy about soprano voice and like to discern vibrato
to the point of being able to count the number of pitch modulations per
second. Not many divas out there can hit the ideal of seven cycles per
second. With the Stealth in your system you’ll be able to resolve this
sort of detail.

After auditioning numerous DACs over the years I
have come to realize that a large slice of the sonic difference between
individual units could be ascribed to the analog stage, and specifically
tube versus solid-state designs. A tubed output stage appeared to
present the soundstage more dimensionally. No matter how sophisticated
the digital circuitry was, when mated to an op-amp buffer or gain stage,
image outlines pancaked and depth perspective took a hit. And then
there was the matter of textural grain. That’s the stuff that my
auditory system generally finds to be indigestible. Some solid-state
buffers had achieved a respectable level of smoothness, but it usually
came at the cost of dynamic sterility. It seems to me that the best
approach to defanging a DAC is to introduce tubes into the mix as early
as possible. And that’s exactly what Ayon has done with the Stealth. It
is perhaps a tad richer harmonically than the real thing, but it is far
removed tonally from the sort of romantic, overly lush presentation that
has been dubbed “vintage tube sound.” The Stealth is about tonal
accuracy, but what you think of it will depend greatly on the associated
amplifier and speakers. Mate it with reference-caliber gear and it will
walk the line of neutrality.

In the pursuit of digital playback
perfection, the Stealth ranks in the DAC elite. It’s all about the music
and the Stealth delivers a superb musical experience. You could do a
lot worse at a higher price point, but I doubt that you would do any
better at its asking price. It’s a DAC that I could happily live with
for years to come.

Inputs: One each coax SPDIF, BNC SPDIF, AES /EBU, USB, I2S, TosLink; three BNC jacks for DSD
Outputs: Unbalanced on RCA jacks, balanced on XLR jacks
Output impedance: 300 ohms (balanced or unbalanced)
Total harmonic distortion: < 0.002% at 1kHz
Power consumption: 55W
Dimensions: 48 x 11 x 40cm
Weight: 16 kg
Price: $10,600