AV Receiver Reviews

All measurements were taken on the left channel, with the impedance switch set to 8ohms, except as noted.

The STR-DA9000ES's 2-channel analog frequency response, in Direct mode, from CD input to speaker output, measured –1.28dB at 10Hz, –0.35B at 20Hz, +0.37dB at 20kHz, and –25dB at 50kHz. The response from the multichannel input to the speaker output was –0.59dB at 10Hz, –0.16dB at 20Hz, +0.00dB at 20kHz, and –24.7dB at 50kHz.

The Dolby Digital response (optical input to speaker output) measured –0.16dB at 20Hz and +0.45dB at 20kHz in the left and center channels. With the surround left channel set to Small and the crossover frequency set to 80Hz, the response in that channel was –6dB at 47Hz at the bottom end (a slower rolloff than you'd expect from an 80Hz crossover setting) and +0.48dB at 20kHz at the top. The line output from the LFE channel, normalized to the response at 40Hz, was –1.05dB at 20Hz and –6dB at 113Hz.

The signal/noise ratio (A-weighted, 2.83V @ 8ohms) was –81.77dB. The gain measured 29.09dB, CD in to speaker out, with the level control set to +4.

The THD+noise in 2-channel operation at 2.83V into 8ohms measured 0.096% at 20Hz, 0.089% at 1kHz, and 0.073% at 20kHz. At 2.83V into 4ohms (impedance switch in the 4ohms position), the THD+N measured 0.216% at 20Hz, 0.242% at 1kHz, and 0.076% at 20kHz.

Into 8ohms loads (impedance switch set to 8ohms): With all seven channels operating, the Sony delivered 113Wpc at 20Hz and 167Wpc at 1kHz before clipping (1% THD+noise). With only two channels operating, at 1kHz, it clipped at 204Wpc (all figures to the nearest watt).

Into 4ohms loads (impedance switch set to 4ohms): With all seven channels operating, the STR-DA9000ES put out 105Wpc at 20Hz and 155Wpc at 1kHz before clipping (1% THD+noise). With only two channels operating, at 1kHz, it clipped at 227Wpc.

Into 4ohms loads (impedance switch set to 8ohms): With all seven channels operating, the Sony put out 97Wpc at 20Hz and 191Wpc at 1kHz before clipping (1% THD+noise). With only two channels operating, at 1kHz, it clipped at 337Wpc.

Comment: The Sony STR-DA9000ES turned in a few unusual measurements likely due to characteristics of its digital amplifier. The signal/noise ratio measured higher than we usually see—probably residual high-frequency noise from the ultrasonic lowpass filter required for the digital amplifier's operation. The power output met specification for 2-channel operation, but fell noticeably short of that output with all seven amps operating (Sony does not specifically state an output rating with more than two channels operating). This is common in receivers.

What is unusual is the reduction in power output at 20Hz (compared to the output at 1kHz) with all seven channels operating. At around 100Wpc at 20Hz, however, depending on the load, there will still be enough juice for almost all systems, particularly if you're using a separately powered subwoofer for the bass. Only if you run very large, power-hungry speakers full-range in all seven channels might you want to carefully check to make sure that the STR-DA9000ES will meet your needs. In my system, with or without a subwoofer, I never felt the need for more power and never heard any noise.—TJN

Sony Does Digital Amps

Fig.1: The output transistors function as an electronic on/off switch for the power supply voltage. While the amplifiers in the STR-DA9000ES are digital, its power supply is a conventional analog design built around a massive toroidal power transformer.

Properly executed, digital amplifiers offer a number of advantages, including high efficiency (less heat generated). Sony argues that their digital amplifiers, dubbed S-Master Pro, offer other benefits over analog designs. (S-Master is now in its third generation of Sony receivers, including the STR-DA9000ES.) These include simpler circuitry and the reduction of several types of distortion.

Fig.2: The output lowpass filter separates the audio signal from the high frequency noise in the output power pulse.

S-Master Pro uses the Direct Stream Digital (DSD) technology, which Sony developed for SACD. All inputs to the STR-DA9000ES are ultimately converted to DSD. The 1-bit DSD stream switches a pair of power-output FETs on and off (Fig.1). The output then consists of two components: one representing the original audio signal and the other encompassing ultra-high-frequency noise. The original waveform is recovered by passing this output signal through a lowpass filter (Fig.2).—TJN