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Bowled over with the Mark & Daniel line, George sought a high-power class D amp line to complement these power-hungry speakers. So George and design consultants Mike Kerster (a major design force behind several Sonic Frontiers products) and Michael Thompson of Thompson By Design went to work on the AMP-D1 stereo amp (CDN$1,695), the AMP-D2 monoblocks (CDN$2,395/pr) and the PRE-A1 active linestage (CDN$1,595), all of which were sent along with the Aragorn system.

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 their comparator/modulator circuitry 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.

Audio Zone didn't just take the stock Hypex board and drop it into the amps. Always striving to maximize sound quality, George indicated that Michael Thompson was instrumental in tweaking the boards to optimize sound quality. I wasn't privy to the exact changes but you'll notice in the photos that the outer material of some caps had been removed. For some background on Class D amps see Wikipedia.

Unlike other class D amps, Audio Zone's models utilize traditional linear power supplies as opposed to switching power supplies for the simple fact that Audio Zone doesn't believe the latter sound as good. Not yet anyway. On the other hand, I know Bel Canto uses switching supplies and several of their amps have received glowing reviews right here at the moons.

The AMP-D2 delivers 200 watts into 8 ohms, 400 Watts into 4, with a peak power of 500 watts. The D1 delivers roughly half that. Both feature an aluminum case with machined anodized front plates. On the rear panel are the binding posts, power switch, IEC inlet and both RCA and balanced XLR inputs. A small red LED on the front panel indicates power status. Both D1 and D2 amps feature soft-start power up to prevent initial inrush current transients.

Looking under the hood, I was surprised by the small size of the Hypex module. Dominating the interior was the massive power supply. Along with the amps I received a prototype of Audio Zone's new active remote controlled PRE-A1. This design uses a low voltage, low current cascode circuit. The claimed advantages of the cascode circuit are high gain, greater bandwidth, high slew rate and better stability. On the rear panel are six pairs of RCA jacks for three sources, tape out, two pre outputs plus a pair of balanced XLR outputs. On the front panel are two rotary knobs for source selection and volume control plus a push button mute.

As with the amps, the interior looked solid and well built, with a big Plitron power toroid. The outer casing was aluminum with an anodized front plate. The included remote was a generic plastic jobbie that George tells me will be replaced by a more substantial remote in the future. At the time of this review, the PRE-A1 remained in development, with some voicing and minor tinkering still to take place. However, it was definitely from the squeaky clean, detail, transparent side of the sonic ledger. In fact I thought it was remarkably transparent whether paired with the AZ amps or my Manley Labs Mahis. It was also extremely quiet and operated flawlessly.

Build quality of the Audio Zone gear was excellent and I encountered no operational problems. All components remained cool to the touch no matter how high I cranked the volume. George also supplied a complete cable loom courtesy of Dynamic Designs' new Lotus series. I received enough cable to permit biamping with the D2 monos on the bass drivers while the D1 looked after the mid/treble drivers. George discovered these Dynamic Designs cables some time ago and found them an ideal affordable match with his amps and M&D speakers. I played around with the cables briefly and found them essentially noise free, open, dynamic, with a neutral tonal balance. The interconnects retail for US$400/1m/pr, the digital cable is US$350/1m and the speaker cables are US$750/8' pr.