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Product Review
 

Wytech Onyx Pure Class A Single-Ended Triode Monoblock Power Amplifiers

December, 2004

Jason Victor Serinus

 

Specifications:

 

● Power Output: 13 Watts RMS per Channel
● MFR: 9 Hz to 22 kKz +0/-1 dB
● Input Impedance: 60 kOhms
● Gain: 29 dB
● Dynamic Headroom: 2 dB [Music Peaks Up To
    40 watts]
● Power Supply Storage: 280 Joules
● Universal Voltage Select: 115/230 Volts 50/60
    Hz
● Power Consumption 125 Watts Each

● Dimensions: 8.5" H X 9.5" W x 16" d
● Weight" 31 Pounds/ea

● MSRP: $4,500/pair USA

Wyetech Labs

 

www.wyetechlabs.com

Introduction

When I first contacted Roger Hebert of Wyetech about reviewing his preamps (see reviews in our archives), he proposed that I also review his Onyx monoblock power amplifiers.

Several members of the audiophile industry whom I trust subsequently told me that the sound of Wyetech’s top-of-the-line Topaz amps is extraordinary. Whether they were referring to the Topaz 221A stereo ($9,000 for 18 watts RMS/channel), the 572B stereo ($9,250 for 23 watts RMS/channel), or the special order Topaz 572M monoblocks ($18,500 for 45 watts RMS/channel), I am not certain. All I know is that their praise whet my appetite for the time when I could put the 13W Onyx babies into action.

Reviewing the Onyx monoblocks constitutes my first opportunity to mate the Khorus Talon X Mk. II (efficiency between 90.5 dB and 91 dB) with low-powered single-ended triode amplification.

The Design

The following information is adapted from the Onyx Owner’s Manual.

Each Onyx monoblock uses a single Dual Triode 9-PIN base 5814A [JAN Military NOS] tube in the input/driver stage, and two Dual Triode OCTAL base 6080WC [JAN Military NOS] tubes in the output stage. 6AS7GAs can be used as a substitute. The tubes come carefully packed in separate cardboard boxes secured within the shipping boxes. Wyetech stocks a full supply of replacement tubes, with prices listed on its website.

All stages of the Onyx operate in pure Class "A1" single-ended and contain automatic self-biasing circuitry. The design employs large value Solen polypropylene coupling capacitors, plus a custom built HAMMOND output transformer for extended low frequency response.

 



Each of the output triodes is individually self-biased, with only the plates tied together in a quasi-parallel configuration. The 11 pound output transformer provides 13 watts RMS per monoblock with the claim of “absolute stability into all low impedance loads.” Output windings are toggled via two high current switches to allow selection of impedance for 2, 4, 8, or 12 Ohms. No feedback of any kind is employed in the design.

An internal toggle switch allows selection of toroidal power transformer voltage input for 115V/230V 50-60 Hz operation. Three output windings provide full-wave rectification using spike and noise suppression circuitry.

Separate DC power supplies are used to provide total isolation between the input and output stages. These consist of a triple pi filter for the 300 volt output rail and a double pi filter for the 450 volt input and driver rail. Rectified and filtered DC provides the power for the input tube filament of the 1st and 2nd stages. The other two output tube filaments are provided with AC connected in a balanced configuration to eliminate hum-induced distortions.

Components are mounted on a PCB, designed manually in house, which is made from FR4 glass epoxy with double sided copper traces and plated through holes. Both sides of the board have a protective green solder mask. A silkscreen is printed in white showing the component layout and parts value.

 

The board features enlarged power and signal line traces which are said to attain a level of analog integrity that automatic routing circuit programs cannot attain. Wiring to the PCB is attached via screw-down crimp terminals to allow for ease of repair should the need ever occur where the board would need to be removed.

The signal path length on the PCB board is reduced to less than 6". Final assembly of parts to the PCB is done by hand-soldering of all components, which is claimed to allow more solder on joints than automated flow-soldering techniques.

The Onyx features a time-delay power-on relay that provides extended tube life and proper power sequencing for stabilized circuitry. The filament voltage is turned on for 45 seconds before applying the DC voltage. A toggle switch enables power to the automatic sequencing circuit that delays operation until the green [ready] LED comes on after the initial 45-second delay. Because the design does not require warm-up, these amps are ready to go within a minute of turning them on.

Listening

I positioned the monoblocks on maple cutting boards, isolating them from vibration using Ganymede ball-bearing supports. All cable connections were treated with Caig Pro Gold.

It may sound like damning with faint praise – certainly not my intent – but I especially enjoyed the Onyx for background listening. While highs and bass were certainly present, and the monotone coloration I once suffered through while auditioning $18,000 Audio Note single-ended triodes was thankfully nowhere in evidence, on my speakers, the Onyx lacked both the treble brilliance and bass slam of more powerful amplification. In their place, however, I discovered a feathery grace of a lower midrange and a level of midrange fullness that, while impossible to confuse with a rich sound, was quite musically satisfying.

I never attempted to play music as full blooded as Rachmaninoff’s Symphonic Dances or the Berlioz Requiem. When I did try to listen to Terry Evans sing the blues, the tight slam of percussion was not to be heard. Even on the Chesky disc of Rosa Passos and Ron Carter, the bass, while assuredly present, lacked ultimate body. How much of what I missed was due to low wattage, and how much to the fact that I don’t have extraordinarily efficient speakers, I cannot say.

What I can say is that I very much enjoyed the warmth and heart of Passos’ sensual voice. Whether I was listening to string quartets or piano sonatas, there was a specialness to the midrange too rarely experienced from high-end amplifiers. I wouldn’t term the sound I heard “real,” but I very much enjoyed it. Auditioning a number of the holiday recordings reviewed this month was an especial treat.

Conclusions

Single-ended triodes have their own unique magic. With the Onyx, Roger Hebert has managed to circumvent some of the most common faults encountered in such amplification: truncation of highs and lows, with extremes replaced by a monochromatic midrange. There is an uncommon feathery delicacy to the Onyx’s midrange and upper bass that makes for a special listening experience. Mated with speakers of sufficient efficiency, the Onyx monoblocks are sure to win new converts to the world of single-ended triode amplification.

Editor's Note: For the Onyx, speakers with a sensitivity of 96 dB/w/m or higher are really necessary for optimum performance. When so properly mated, single-ended Class A triodes can produce a sound that is simply delightful, and like no other you might have ever heard.


- Jason Victor Serinus -

REFERENCE SYSTEM:


Digital Front End
Sony 707ES transport modified by Alexander Peychev of APL Hi-Fi
Theta Gen VIII DAC/Preamp
Theta Carmen II transport (on loan)

Amplification
Jadis Defy 7 Mk. II about to be upgraded to the current model

Loudspeakers
Talon Khorus X speakers MK. II (with latest modifications and Bybee filters on woofers and tweeters)

Cabling
Nordost Valhalla single-ended and balanced interconnects and balanced digital interconnects
Nordost Valhalla bi-wired speaker cable
Nordost Silver Shadow digital interconnect for DVD-V
Nordost Valhalla Power Cables

Also on hand and sometimes used:
Interconnects: WireWorld Gold Eclipse 5 and Gold Starlight 5 digital, Harmonic Tech Magic One, Acoustic Zen Silver Reference II balanced, and Nirvana BNC-terminated digital.
Power cables: Elrod EPS Signature 2 and 3 plus EPS 1, 2, and 3; WireWorld Silver Electra 5, PS Audio X-treme Statement, Harmonic Tech, and AudioPrism SuperNatural S2.

Accessories
PS Audio P600 Power Plant power synthesizer with MultiWave II
ExactPower EP15A
PS Audio Ultimate Outlet; PS Audio Power Ports
Michael Green Deluxe Ultrarack, Basic Racks and Corner Tunes
Ganymede supports in main digital chain and under speakers
Michael Green Audiopoints, and Black Diamond Racing Cones elsewhere
Shakti stones on amp, Theta, and transport
Stillpoints ERS EMI/RFI sheets on most components
Bedini Dual Beam Ultraclarifier
Audioprism CD Stoplight
Marigo Signature Mat for use atop CDs
Ayre demagnetizing CD and the original Sheffield/XLO demagnetizing and break-in CD.

 

 

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