Technics SU-V90D Integrated Amplifier Review

Technics calls the SU-V90D a “digital” integrated amplifier because a portion of its circuitry can transform the digital output of a CD player or DAT deck to analog stereo form. These circuits include an 18-bit, quadruple-oversampling digital filter followed by four 16-bit digital-to-analog (d/a) converters that provide the equivalent of 18-bit conversion for all signal levels below —12 dB. Unlike other “floating-bit” conversion systems, the Technics system uses two converters for each channel; they operate separately on the positive and negative portions of the signal waveform.

The quasi-18-bit conversion system used in the SU-V90D shifts the digital signal entering the d/a converters up or down by 2 bits as required to fit the signal into a 16-bit operating range. For high signal levels (between 0 and —12 dB), the converter operates as a conventional 16-bit device. When the signal drops below —12 dB, the converter’s range is shifted downward by 2 bits, extending its operation to the 16 bits of data from Bit 3 through Bit 18. Although the signal recorded on a compact disc has only 16 bits of information, the 18-bit digital filter of the SU-V90D creates the additional 2 bits. Whenever the converter range is shifted, a 6-dB attenuator is switched in or out of the analog signal path to compensate for the level shift that would otherwise occur.

The principal advantage claimed for this mode of operation is an improvement in 16-bit conversion accuracy. Low-level signals are “rounded off” in the output of a digital filter, resulting in a slight error (nonlinearity) in the signal supplied to the d/a converters. The addition of 2 more bits of effective resolution improves the low-level linearity of the system, since the effect of the rounding off is reduced by a factor of 16.

Digital features aside, the Technics SU-V90D is a high-quality amplifier rated to deliver 100 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.003 percent total harmonic distortion (THD). Into 4 ohms, the rating is 125 watts with 0.007 percent distortion.

The input source is selected by a group of flat, short-travel pushbuttons. The analog inputs include phono, CD, tuner, auxiliary, tape l, and TAPE 2/dat. The phono input is switchable for a moving-magnet (mm) or moving-coil (mc) cartridge via a front-panel button. The coaxial and optical digital input jacks on the rear apron of the amplifier are also selected by front-panel buttons.

A REC(ord) MODE button, used with the regular input selectors, permits any source to be selected for recording independently of the one being heard. An amber led above each input selector indicates the current choice, and a separate red light shows which source is being recorded.

The SU-V90D also has a Power Amp Direct operating mode that uses separate input jacks on the rear apron. When this mode is selected, the signal passes directly from the input jacks through a buffer amplifier to the power-amplifier input, bypassing most of the preamplifier circuitry and controls. A separate, low-noise volume control used in this mode is driven from the same shaft and knob as the regular volume control but has separate scale calibrations. The buffer amplifier, like the power amplifier itself, uses Technics’s Class AA circuit, a combination of voltage and current amplifiers said to provide exceptional input/output isolation and low distortion.

After conversion to analog form, digital input signals follow a path identical to that in the Power Amp Direct mode. Front-panel indicators show the sampling rate of the source (32, 44.1, or 48 kHz). Three small center-detented knobs operate the bass and treble tone controls (which have a bypass button) and the balance control. Other buttons control the loudness compensation, the 20-dB audio mute, and independent switching for two pairs of speaker outputs.

According to the manufacturer, the sound quality of the SU-V90D is enhanced by its use of “exotic” materials and components, including a new type of electrolytic capacitor, said to result in lower distortion in its Class AA stages, and oxygen-free copper (OFC) in its internal wiring and the windings of the power transformer. The input and output jacks are gold-plated. Three AC convenience outlets are provided, one of them switched. The speaker outputs are heavy-duty, insulated binding posts that accept only the stripped ends of the speaker wires (cables fitted with lugs or banana plugs cannot be used). The SU-V90D is a rather large amplifier, measuring 17 inches wide, 15-5/8 inches deep, and 6-1/4 inches high, and it weighs 29 pounds. It is finished in metallic gray with clear gold markings. Price: $1,100.

Lab Tests

The top of the SU-V90D became very hot during its 1-hour preconditioning period, but it ran quite cool during normal operation. Except as noted, all measurements were made in its analog mode. With both channels driven at 1,000 Hz into 8-ohm loads, the output clipped at 128 watts; into 4 ohms, the output at clipping was 175 watts. Although the amplifier is not rated to drive 2-ohm loads, with only one channel driven into 2 ohms the output clipped at 180 watts. In dynamic power measurements, the maximum output was 150 watts into 8 ohms, 242 watts into 4 ohms, and 180 watts into 2 ohms.

Driving 8-ohm loads at 1,000 Hz, the amplifier’s distortion (THD + noise) was between 0.0034 and 0.01 percent for outputs from 1 to 50 watts, reaching a maximum of 0.0185 percent at 100 watts. With 4-ohm loads, the distortion at outputs up to 40 watts was about the same, reaching 0.02 percent at 100 watts. The 2-ohm distortion readings were much the same, although they reached a peak of 0.02 percent at 170 watts, just before clipping occurred. The amplifier’s slew factor exceeded 25, and it was stable with reactive simulated speaker loads.

The frequency response, which was down 0.1 dB at 20 Hz and 0.5 dB at 20,000 Hz, was identical through both the Power Amp Direct and the normal inputs. The bass tone control had a sliding turnover frequency from 500 Hz to below 100 Hz, and the treble curves were hinged at 3,000 Hz. The maximum control range was approximately ±10 dB.

The loudness-compensation circuit boosted only the low frequencies, with a + 3-dB point at about 300 Hz. RIAA phono equalization was accurate within 0.25 dB overall from 20 to 20,000 Hz.

To check the performance of the SU-V90D’s internal digital circuitry, we used a Denon DCD-1500 II CD player and the CBS CD-1 test disc. First, we measured the frequency response of the CD player through its own d/a converters and filters; it was flat within +0.15, —0.09 dB from 20 to 20,000 Hz. We then connected the coaxial digital output of the DCD-1500 II to the input of the SU-V90D and repeated the measurement at the amplifier’s tape-recording outputs. A minute change in the shape of the curve at high frequencies was the only detectable difference; the overall variation was +0.09, —0.2 dB from 20 to 20,000 Hz. As far as frequency response is concerned, the Technics and Denon digital circuits were essentially equivalent.

A more distinct difference was detectable in low-level linearity measurements, however. Down to -70 dB, the Denon player and Technics amp had identical, and essentially perfectly linear, responses. In the left channel, they remained identical all the way down to the -90-dB limit of the measurement. In the right channel, however, the output from the Denon was about 2 dB high at -80 dB and 5 dB high at -90 dB. Through the Technics circuits, a 1-dB error was barely visible at -90 dB.

Comments

The Technics SU-V90D is an absolutely first-rate amplifier. Its control flexibility is superb, although some of its switching procedures are rather unconventional. Careful study of the complete, well-written manual should clear up any questions, however. The mechanical and electrical smoothness of the pushbuttons and volume control was outstanding. No electrical transients or other unwelcome effects were in evidence at any time during our use of the amplifier, and its listening quality was on a par with its measured performance.

We found no differences—either measurable or audible—between normal and Power Amp Direct operation. Although this was the first amplifier with built-in D/A converters we have used whose digital circuits measured as well as (or even slightly better than) those of a good CD player, extensive A/B playback comparisons using the analog and digital output from several CD players failed to show the slightest audible difference between them.

Our comparisons were somewhat complicated by the fact that the playback level shifted slightly (a small fraction of a decibel) when we switched between the amplifier’s analog and digital modes, but we are confident that any changes that might have been detected were truly insignificant.

Despite the claims often made for the supposed audible benefits of exotic materials such as oxygen-free copper wiring, we have never substantiated them. Likewise, the audibility with musical program material of the extension of d/a resolution from 16 bits to 18 bits (or more) has not been demonstrated. These design features do not appear to reduce the player’s performance in the least, however, and when they are used in an already high-quality product such as the Technics SU-V90D they probably have little effect on its price.

Our impression of the Technics SU-V90D is emphatically positive. It is one of the most solidly constructed and smoothest-handling components we have used—the volume control’s action was almost sensual—and it sounded every bit as good as it looked and felt.

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