Sony STR-DA7100ES AV Receiver
By Lawrence E. Ullman   •   October, 2005 Sony's new, $2000 STR-DA7100ES AV receiver carries forward the shiny silver hewn-from-solid-block look of previous ES-series receivers, such as the STR-DA9000ES ($4500) recently reviewed by TJN. Although the front panel looks like solid aluminum, it is actually a 2mm-thick formed sheet. Most of the controls are hidden behind a drop-down panel, leaving a clean front panel with just volume and input-selector knobs, half a dozen little buttons, and the display. The various knobs and controls have great tactile appeal, operating with a solid, positive feel and silky smooth action.

Internally, the chassis has a conventional layout, with individual, interconnected circuit boards rather than a computer-style motherboard and expansion-card architecture such as that found on the Sherwood Newcastle R-965 ($1999.95). The chassis is very crowded, with as many as four circuit boards forming a tightly stacked horizontal sandwich at the rear panel.

Digital Amplification
The STR-DA7100ES stars Sony's S-Master Pro digital amplifiers, which are spec'd at 170Wpc into 4 or 8Ω, 20 Hz–20 kHz @ 0.15% THD, two channels driven. An identical multichannel spec is given in the manual, but there is no mention of how many channels are being driven, so caveat emptor.

Unlike most digital amps, which use switching power supplies, the Sony's seven amp channels draw on a conventional power supply backed by a large transformer. In order to drive the S-Master Pro amps, all input signals (analog or digital) must ultimately be converted into Direct Stream Digital (DSD), a 1-bit format that Sony developed for SACD.

Digital amplifiers are known for their efficiency (high output power in a small cabinet with less heat), and indeed the Sony's power transformer and heat sinks are smaller than you'd expect for a 170W x 7-channel amplifier. A single fan is provided for cooling, and it is quiet enough to pass unnoticed. Even the Sony's relatively thin 18 AWG detachable power cord seems to reflect the efficiency of its digital amps. (By comparison, the last receiver I reviewed, the Arcam AVR250 ($1599), has a power cord with heavier, 14 AWG wires, even though it outputs less than half the Sony's rated power.)

In the past, digital amplifiers have mostly found favor in large PA installations and the like, where their efficiency and cool operating temperatures are highly valued. But the few early digital amplifier designs that made it into the home market did not find favor with audiophiles. I am sure that the state of the art has progressed over the years, but apart from subwoofer applications, digital designs have, up to now, rarely been used in full range amplifiers with audiophile aspirations. (With new designs from Bel Canto, Rotel, Sharp, Sony, Samsung, and others, however, that may be changing.—TJN)

The Old Switcheroo
Although it receives second billing below the S-Master Pro amps, HDMI video switching is the real star of the STR-DA7100ES's show, as it is the primary feature that differentiates this model from its predecessors. (HDMI is a digital interface that conveys both audio and video data over a single cable.) There are two HDMI inputs and a single output. The inputs can be selected from a dedicated front-panel button or from the remote. You can also assign an HDMI input to any of the regular AV inputs, which is useful if you want to "separate" an HDMI-equipped source's output, routing its video signal to the monitor via HDMI and its audio signal (analog or digital) into one of the Sony's regular AV inputs. Just to clarify, the HDMI inputs are merely switched, not processed in any way; whatever comes in, goes out again.

Like just about every recent high-end AV receiver, the Sony features video-format conversion, but with an HDMI twist. Incoming analog 480i video signals in composite, S-video, or component-video form can be digitized, upconverted to 480p, and output via HDMI. (Audio signals are not converted and must be dealt with separately.) Adjustments are provided for brightness, color, and tint, and all of these functions are programmable per input. In addition, the Sony's two assignable component-video inputs provide the same video conversion and processing functionality with composite and S-video sources, though the signal in that case is of course output to the display in analog component-video format. (HDMI signals cannot be "downconverted" to component video.)

But there's a fly in the HDMI upconversion ointment: component-video signals must be in 480i format in order to be processed and output via HDMI. All other component formats (480p, 720p, 1080i) must be routed through the Sony's component-video switcher. This significantly reduces the usefulness of the Sony's HDMI conversion functionality if—like me—you own one of the many HDTV set-top boxes that have only a component-video output. I ended up running the 720p component-video output of my Moxi HD DVR through the Sony's component-video switcher, and simply connected my V, Inc. Bravo D1 DVD player to the monitor's HDMI input. This negated, for my system, the "one-cable, one-input" convenience of video upconversion.