Yamaha RX-950 AV-receiver

In creating Yamaha's flagship stereo receiver, the RX-950, the engineers' goal was to provide performance equivalent to that of high-quality separate components. To this end, they employed Yamaha's patented Hyperbolic Conversion Amplification (HCA) circuit, which is claimed to provide true Class A amplification over a wider range of output power than conventional designs. The internal physical layout and electrical design of the amplifier, from input to output, are as direct and symmetrical as possible. Speaker outputs are switched by relays close to the speaker terminals, and both the input-selector switch and volume control are driven by small motors when the remote control is used. This feature eliminates the use of electronic signal switching, which can cause distortion.

Other construction features of the RX-950 reflect the same purist design philosophy. The wiring and component parts are of the highest quality, and to minimize the effects of vibration and mechanical resonance, the entire unit is mounted on a molded base, which is supported in turn by a heavy chassis plate and vibration-damping feet.

The RX-950 is also unusual among receivers in having an amplifier section designed to drive low-impedance loads. It is rated to deliver 120 watts per channel into 8 ohms from 20 to 20,000 Hz with no more than 0.015 percent total harmonic distortion (THD). Into 4 ohms, the rating is increased to 180 watts with 0.03 percent THD. It also carries EIA dynamic power ratings of 160, 210, and 340 watts into loads of 8, 4, and 2 ohms, respectively.

The preamplifier section has inputs for audio from a videodisc player or TV set, two tape decks (identified as VCR/Tape 2 and Tape 1/DAT), the tuner section, a CD player, and a phono cartridge. A pure direct button on the panel bypasses all signal circuitry except the volume control and connects the CD inputs directly to the power amplifiers. Other audio controls are behind a hinged door across the bottom of the panel. They include individual speaker selectors for two pairs of amplifier outputs, bass and treble tone controls (each with two selectable turnover frequencies), channel-balance and loudness-compensation knobs, and a REC-OUT selector that connects any input source to the recording outputs independently of the setting of the front-panel input selector. The loudness compensation, unlike most such circuits, is not linked to the volume-control setting but functions independently over a 40-dB range. A headphone jack is also located behind the hinged panel.

Except for the volume and input knobs and the pure direct and power buttons, the visible portion of the front panel is devoted to the receiver's tuner functions. The display window shows the tuned frequency, tuning mode, preset memory channel, and relative signal strength. The display is not affected by the selection of a different program source.

The main tuner controls are a group of buttons to the right of the window. They select AM or FM and automatic or manual tuning. Automatic tuning scans up or down the band until a station receivable in stereo is found. Manual tuning in FM switches the RX-950 to mono mode to improve reception of weak signals. Each of the eight preset station-selector buttons below the window can be assigned to any of five lettered banks by another button, providing a total of forty possible presets.

On the rear apron, the preamplifier outputs and main amplifier inputs are brought out separately and joined by removable links. This simplifies connecting signal-processing accessories without sacrificing the use of the tape-recording loop. There are also two additional sets of preamplifier outputs for driving power amplifiers and speakers in other rooms.

Each of the possible audio inputs from a video source has an associated video input jack, which is connected to the monitor OUT jack when that source is selected. The two sets of speaker outputs are heavy-duty insulated binding posts that accept either stripped wire ends or banana plugs. The tuner's inputs are spring clips for 75- or 300-ohm FM antennas and the supplied wire-loop AM antenna.

The wireless remote control that comes with the RX-950 is actually a system control for compatible Yamaha components (identified, like the RX-950, by "RS" following their basic model numbers). It operates the receiver's source-selection, muting, volume, and power-switching functions. Other buttons are dedicated to the basic operating functions of other components.

The RX-950, finished in black, measures 17-1/8 inches wide, 17-5/8 inches deep, and inches high. It weighs 33-1/4 pounds. Price: $899.

Lab Tests

Although the RX-950's speaker connectors are compatible with single banana plugs, they are inexplicably spaced slightly too far apart for dual banana connectors. We were able to insert them with a slight visible bending of the posts, but this is probably inadvisable as a regular practice.

The amplifiers in the RX-950 proved their conservative ratings by delivering 158 watts into 8 ohms at 1,000 Hz at the clipping point, equivalent to 1 percent THD plus noise (THD + N). With 4-ohm loads, the clipping power level was 245 watts. Relative to the rated output, the respective clipping-headroom figures were 1.2 and 1.3 dB. It is worth noting that this power capability was maintained over the full audio range: From 20 to 20,000 Hz the 8-ohm power exceeded 153 watts, and into 4 ohms it exceeded 235 watts.

Dynamic power measurements were equally impressive. Into respective loads of 8, 4, and 2 ohms, the 20-millisecond burst output was 195, 338, and 575 watts. The dynamic headroom into 8 and 4 ohms was 2.1 and 2.7 dB, respectively.

The amplifiers' THD + N when they were driving 8 ohms was 0.01 percent at 20 to 25 watts output, reaching about 0.015 percent at the rated 120 watts output. Into 4 ohms, the distortion was 0.02 percent between 10 and 20 watts and 0.032 percent at the rated 180 watts. The receiver's protection circuit shut it down when we attempted to drive it into clipping with 2-ohm loads, but by driving only one channel we measured its distortion as 0.02 percent from 20 to 60 watts and 0.03 percent at the clipping point of 300 watts.

The frequency response through the CD inputs was extremely flat, varying only ±0.02 dB from 20 to 20,000 Hz. There was no measurable difference between the normal and Pure Direct modes. The tone controls had a maximum range of about ±10 dB at the frequency extremes. Their turnover frequencies were as marked, 200 or 400 Hz for the bass, 2,500 or 5,000 Hz for the treble. The response in the vicinity of 1,000 Hz was essentially unaffected by the tone controls with the 200/5,000-Hz combination; the midrange variation was somewhat greater with the other turnover frequencies.

The loudness contours varied from a modest boost of 3 or 4 dB at the extremes of the audio range (at a -10-dB setting) to a large, 25-dB boost at 20 Hz and a 7-dB boost at 20,000 Hz (at the lower limit setting of -40 dB). Since the loudness compensation can be set by ear, independently of the main volume setting, it should be possible to obtain almost any desired degree of compensation at any listening level.

The RIAA phono-equalization response varied only ± 0.1 dB from 60 to 20.000 Hz and was down 0.6 dB at 20 Hz. The phono preamplifier overloaded at 1,000-Hz equivalent inputs between 115 and 130 millivolts (mV) at frequencies between 20 and 20,000 Hz. The phono-input termination was 44.000 ohms in parallel with a 110-picofarad (pF) capacitance.

Sensitivity, for a 1-watt reference output, was 13 mV at the CD inputs and 0.22 mV at the phono input. The A-weighted signal-to-noise ratio (or S/N), referred to 1 watt, was 81 dB for phono and 87 dB for the CD input. A spectrum analysis of the noise showed exceptionally low power-line hum levels: - 95 dB at 180 Hz and-97.5 dB at 60 Hz, relative to a 1-watt output.

The FM tuner frequency response was flat within ±0.2 dB from 50 to 11,000 Hz, falling to -1 dB at 20 Hz and - 3 dB at 15,000 Hz. Stereo channel separation was 50 to 54 dB in the 1.000- to 3,000-Hz range, falling to 25 dB at 20 Hz and 40 to 45 dB in the 13.000- to 15,000-Hz range. The AM tuner frequency response was +1.6, - 6 dB from 35 to 2,500 Hz, relative to the 1,000-Hz output.

FM usable sensitivity was a very good 6 dBf (1.1 μV). The 50-dB quieting sensitivity was 9.5 dBf (1.6 μV) in mono and 30 dBf (17.4 μV) in stereo.

At 65 dBf, the FM distortion (THD + N) was 0.09 percent in mono and 0.4 percent in stereo. The respective S/N measurements were 79 and 74.5 dB.

Other FM measurements included a 2.5-dB capture ratio (fair), 74 dB AM rejection (good), adjacent-channel selectivity of 13 dB and alternate-channel selectivity of 85 dB (both excellent), and image rejection of 39 dB (not very good, but not particularly unusual these days, either).

Comments

The Yamaha RX-950 proved to be one of the most robust high-performance receivers we have tested. Its amplifiers are both powerful and rugged, with an effective over-current protection system that shut down the receiver with a relay when it was driving 2-ohm loads at continuous high power levels. Dynamic power capability was equally impressive.

The FM tuner section was mostly excellent, with very high sensitivity and an exceptional 85-dB alternate-channel selectivity (as rated). The image-rejection ratio of 39 dB (slightly below Yamaha's specified 45 dB) was lower than we would expect of a top home receiver, although it should not cause any problems unless you live close to a major airport (we heard no image interference in our tests).

The RX-950 performed superbly in our listening tests, receiving some fifty clear FM signals with the supplied dipole wire antenna tacked to the wall. The stereo muting threshold of 24 dBf reduced the number of receivable stereo signals to thirty-nine, still very creditable performance. It should be noted that the distortion plus noise at low signal levels largely consisted of random noise; weak signals could be heard without audible distortion and, in fact, with little noise.

The RX-950 was very simple to operate, in contrast to many contemporary receivers whose panels are studded with pushbuttons. It is an impressive component, with enormous power capabilities, the ability to drive almost any speaker made today, and a very sensitive, selective FM tuner section. Assuming that its input-switching capabilities meet your needs, you could hardly ask for a finer stereo tuner/amplifier than this one. At its price, it is an excellent value as well as a first-rate receiver.