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Reviewer: Paul Candy
Financial Interests: Click here
 Digital Source: CEC TL51X transport, PS Audio DL III DAC w/ Cullen Circuits Stage Three Mod
Analog Source: Pro-Ject RPM 5 turntable, Pro-Ject Speed Box, Pro-Ject Tube Box phono stage, Ortofon Rondo Blue cartridge
Integrated and power amps: Audiomat Opéra Référence integrated, Wyred4Sound SX-1000 monos
Loudspeakers: Green Mountain Audio Callisto on sand-filled Skylan stands, 2 x  REL Q108 Mk II subwoofers, AV123 Strata Mini, Hyperion HPS-738
Cables: Acoustic Zen, Audience, Auditorium 23, DH Labs, SilverFi, Wireworld Equinox 6, Silver Eclipse 6, Gold Starlight 6 & Starlight 6 [in for review]
Power cords: Audience, Gutwire, Harmonic Technology, Wireworld Aurora 5² & Silver Electra 5² [in for review]
Stands: Grand Prix Audio Monaco four-tier rack.
Powerline conditioning: Audience aR1p, BPT Pure Power Center with Wattgate, Bybee Quantum Purifier and ERS cloth options, GutWire MaxCon
Sundry accessories: Acoustic Revive RR-77, Auric Illuminator, Audio Magic/Quantum Physics Noise Disruptors, Caig Pro Gold, Echo Busters acoustic room treatments, Grand Prix Audio APEX footers with silicon nitride bearings, Isoclean fuses, dedicated AC line with Wattgate 381 outlet.
Room size: 11’ x 18’ x 8’, long wall setup, suspended hardwood floors with large area rug, walls are standard drywall over Fiberglas insulation.
Review Component Retail: $1,695 for PRE-A1, $2,895/pr for AMP-D2SE monos

Back in May of 2008, I reviewed the Mark & Daniel Aragorn loudspeakers along with Audio Zone’s new class D monoblocks and a prototype of their active PRE-A1 preamp. While the Aragorns did not float my boat, the Audio Zone gear did. They recently issued a special edition version of the monoblocks and the preamp finalized formal production.


The AMP-D2SE monos utilize the same Hypex class D module as the standard AMP-D2 but add a few  tweaks for improved sonics. According to Audio Zone’s George Tordai, those enhancements are:
  • National Semiconductor's new super op amp replaces traditional choice
  • All electrolytic capacitors on the main amp board are replaced by selected types manufactured by BHC in England 
  • Output filter capacitor is replaced by a premium polypropylene film & foil type 
  • Internal wiring is triple Cardas 19.5 Teflon litz speaker wire 
  • Premium selected power supply electrolytic caps 
  • Optional remote turn on circuit included.
  • Unique electric blue power indicator LED
  • Visible amp status indicator LED visible from bottom chassis ports.

Specifications remain the same. The amps output 200 watts  into an 8Ω load with up to 500-watt peaks with a frequency response of 10Hz to 50kHz +0/-3dB. Input impedance is 100kOhm. Output impedance is 20mOhm at 1kHz. Gain is 26dB. Unlike most class D amps, the D2SE uses a traditional analogue power supply with a bulky toroidal transformer rather than the more common switch-mode variety. On the rear panel, there is a pair of gold plated 5-way binding posts, a pair of 8mm sockets to allow preamp-controlled power on/off in multichannel applications, an IEC inlet and gold-plated RCA and XLR inputs. A small toggle switches between XLR or RCA input while an additional toggle allows two-channel users to bypass the additional circuitry of the multichannel control feature. A small blue LED on the front panel indicates power status. Also included is a soft-start circuit to prevent initial in-rush current transients.

Regarding the Hypex modules, I wrote the following in my review of the standard AMP-D2 monos: “For the amps, the Audio Zone design team sampled all the available class D boards and found Bruno Putzeys' Hypex modules best. They differ from many other firms' modules primarily in where the comparator modulator circuit resides. Most class D designs place theirs before an inductive-capacitive low-pass output filter (which is necessary in class D designs to remove unwanted high frequency switching noise) but since speakers are not purely resistive and present a variable load, the amp's frequency response will be altered by this scheme. This might explain the wildly differing opinions on the sonic characteristics of many class D amps. Hypex amps are spared this problem as the comparator/modulator sensing is implemented right at the speaker outputs. In this configuration the amp's frequency response should be flat as a pancake regardless of the load presented by the speakers”.

The PRE-A1 uses a low voltage, low current cascade circuit. The claimed advantages of a cascade circuit are high gain, greater bandwidth, high slew rate and better stability. The rear panel has six pairs of RCA jacks for three sources, tape out, two pre-outs plus a pair of XLR outputs. Two rotary knobs for source selection and volume control plus a push button mute adorn the front panel. The remote is a generic plastic jobbie that controls volume and mute only.


I had no issues with build quality or understated cosmetics but expect that most prospective owners would not mind paying a bit more for a matching metal wand. The AZ combo remained cool to the touch regardless of how long or hard I ran it. Initially I noted a fair degree of low-level buzz during quiet passages and between tracks.

After a bit of experimenting I determined that the preamp was the culprit as the amps were dead silent on their own or via the onboard volume control of my Shanling PCD3000A CD player. I then played around with various cables and component positioning.


I was able to banish the buzz by keeping the preamp away from other components and by using shielded cables. As soon as I swapped in unshielded cables such as the DH Labs Revelation interconnect or Audience’s powerChord ‘e’, the buzz returned. Unfortunately late in the review the left channel on the preamp quit. According to George, one of the Solen output caps came loose perhaps during transit or sometime during the review process and eventually failed completely. George further mentioned that the caps in my review loaner were not secured to the board but that all subsequent units now have the caps fastened and glued to the circuit board. Apart from those two gremlins, I enjoyed my time with this pre/power combo and it matched well with the various sources and speakers I had on hand.

 
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