Yamaha AVC-50 Audio/Video Amplifier Review

The Yamaha AVC-50 combines a highly flexible audio/video control center with a “universal” remote control that also works with other Yamaha components. It is comparable in size and shape to a typical medium-power integrated audio amplifier, but it provides switching and signal-processing functions for several video sources in addition to the usual audio inputs. Its power section is rated to deliver 45 watts per channel continuous output into 8-ohm loads (50 watts into 6 ohms) from 20 to 20,000 Hz with no more than 0.05 percent total harmonic distortion. The capabilities of the AVC-50, however, extend well beyond mere amplification and program selection.

The AVC-50 can be used several ways in an audio/video entertainment system. The recommended mode is as a preamplifier for the entire system, with its internal power amplifiers driving a pair of rear speakers and with a separate stereo power amplifier driving the front speakers. Alternatively, the AVC-50 could drive the front speakers and use an external amplifier for the rear pair. Another operating mode might be as a conventional integrated amplifier for a stereo sound system, including switching control of several video sources, but its unique sound-processing modes are not usable in such a configuration. Finally, the AVC-50 can be used solely as a preamplifier for a four-speaker system, with external power amplifiers for both the front and rear channels. This arrangement might be necessary if speakers having unusually low sensitivity are used in a large room, which would require more amplifier power than the AVC-50 can provide.

A row of eleven small pushbuttons select the program source supplied to the tape-recorder outputs.

The outputs are separate for audio and video sources, permitting a video program to be recorded or dubbed with a different audio track from its original one. The audiorecording options include phono, CD, tuner, auxiliary, two audio tape decks, and the sound portions of programs from a TV set, a videodisc player (VDP), and two VCR’s. A separate group of video-recording buttons selects the output from a TV, a VDP, or one VCR. The audio amplifier inputs include all of these sources, which are selected by pressing one end or the other of a rocker switch. Small lights on the front panel indicate the selected source. A similar control selects the picture source for viewing on a monitor.

The Yamaha AVC-50 does not have audio tone controls; the only concessions to frequency-response adjustment are buttons to select the BASS EXTENSION Or HIGH FILTER features. The large volume knob is the only regular operating control. The AVC-50 does, however, provide audio processing facilities not ordinarily found in integrated amplifiers. A small PROCESSING MODE switch on the front panel has three positions for enhancing stereo sources in a four-speaker system: NATURAL SURROUND, HALL SURROUND, and DOLBY SURROUND. The last is the well-known matrix-decoding system (with time delay) used for reproducing the soundtracks of movies and video recordings made with the Dolby Surround process.

Yamaha’s own natural surround system, based on comb filters, can be used to add a sense of space (particularly depth) to most stereo programs. The hall surround effect is similar, but the addition of an adjustable analog time-delay circuit before the comb filters makes the sound more suggestive of a large music hall. A knob next to the processor switch continuously varies the delay from 10 to 30 milliseconds. It is detented at the 20-millisecond setting, which is suggested for general use.

The stereo surround modes do not function with mono programs, so Yamaha has provided two simulation modes for mono programs, also selectable with the processing switch. The SIMULATED STEREO circuit performs the comb-filtering operation on the mono signal, sending one “channel” to the front and rear speakers on the left side and the other channel to the right side. The SIMULATED SURROUND circuit is similar, but it adds the adjustable time delay to the mono signal before it is filtered and divided.

The processing mode switch has a defeat setting that passes the unaltered input signal(s) to the front and rear speakers. An input balance knob on the front panel is used principally to balance the channel levels before they are processed by any of the surround modes, and conventional left-right signal balancing is done with a small screwdriver adjustment on the rear apron of the amplifier.

The remaining front-panel controls are for the video-enhancement functions of the AVC-50. An on/off button activates these circuits, and another button selects either the incoming (playback) or the outgoing (recording) signal for enhancement. A small detail knob compensates for the loss of detail when recording a video program. It can be used to exaggerate the detail of a signal before it is recorded and again, if desired, to enhance the detail of the playback program. A sharpness control applies a similar correction to the edge outlines in the picture, while the video level control merely adjusts the overall video signal level for suitable brightness. In all cases, it is suggested that the on/off button be used to compare the appearance of the original program with that of the enhanced program during the adjustment process.

In addition to controlling the AVC-50’s key front-panel features (volume, video and audio input selection, front and rear levels, audio muting, and power switching), the remote control performs comparable functions for other Yamaha components (identified by an RS logo) that can be connected to the amplifier, including tape decks, CD players, and record players. The rear apron of the AVC-50 is much like that of other integrated amplifiers, with input and output jacks for video and audio sources, insulated clips for connections to front and rear speakers, and five AC outlets, three of them switched. The VCR 2 inputs are duplicated on the front panel, a convenience for temporary use of a VCR that is not part of the regular system. The Yamaha AVC-50, finished in black, measures 17-1/8 inches wide, 12 inches deep, and 4-3/8 inches high, and it weighs 14 pounds. Price: $449.

Lab Tests

During the 1-hour preconditioning period at one-third rated power, the top of the AVC-50 became quite hot directly over the internal heat sinks, but over most of its surface the temperature was moderate. Its outputs clipped at 60.5 watts per channel when driving 8-ohm loads at 1,000 Hz. Into 4 ohms, the amplifier clipped at 68 watts, and into 2 ohms at 60.5 watts.

The dynamic power output with the standard 20-millisecond burst was 95 watts into 8 ohms, 128 watts into 4 ohms, and 105 watts into 2 ohms. We also extended the pulse times to determine the amplifier’s “power envelope.” Although the available power dropped steeply between 20 and 50 milliseconds, it effectively leveled off from 75 to 300 milliseconds, remaining at 65 to 70 watts with bursts in that range. The slew factor was 8 (the output waveform at rated power became triangular at about 200,000 Hz).

The amplifier’s stability when driving a complex reactive simulated speaker load was somewhat marginal, with extended ringing at 50.000 Hz on a square-wave signal, but the amplifier did not oscillate under any conditions we could apply. The reactive load factor was 0.96 dB at 63 Hz. Its 1,000-Hz harmonic distortion was about 0.005 percent over much of the power range up to the 8-ohm clipping point. The distortion was only slightly higher, about 0.007 percent, into 4 ohms, and into 2 ohms it averaged less than 0.05 percent. It reached its maximum of 0.03 to 0.05 percent at 20 Hz and above 10.000 Hz with the rated 45 watts into 8 ohms and at half-power, but it was under 0.01 percent over most of the amplifier’s usable power range. At one-tenth rated power the distortion measurements had slightly higher minimum readings.

The amplifier’s frequency response was flat within about ±0.2 dB from 30 to 20,000 Hz and was down 1.5 dB at 20 Hz. The high filter began to roll off the response above 5,000 Hz, with its — 3-dB point at 8,500 Hz. The bass extension terminology seemed to be something of a misnomer, since this circuit rolled off the response at about 16 dB per octave below 50 Hz! There was, however, a gentle rise in output below 200 Hz, to a peak of about 2.5 dB at 70 Hz, which may be what Yamaha considers to be a bass extension. The RIAA phono equalization was impressively accurate, varying ±0.1 dB from 25 to 12,000 Hz, and down only 0.3 dB at 20,000 Hz.

We also measured the responses of the comb filters used for the audio enhancement processing and the characteristics of the time-delay circuit. In the simulated stereo mode (for mono signals), the right-channel response was broadly maximized in the 100- to 300-Hz range and around 5,000 Hz, with nulls at 20, 1,000, and 17,000 Hz. The left-channel signal was at its maximum at 20 to 30 Hz, 1,000 Hz, and 20,000 Hz, roughly complementing the other channel, and it had deep nulls at 150 and 4,500 Hz. The time-delay circuit provided only a single delay, adjustable from 8 to 30 milliseconds, with its detented center setting providing a delay of 19 milliseconds.

Comments

There is a growing number of audio/video integrated amplifiers, receivers, and signal processors on the market. Most of the amplifiers and receivers are conventional audio products combined with a video switching capability. Yamaha has taken an additional step with the AVC-50. While it is still basically an audio amplifier—and a good one, as our tests show—the usual tone controls have been replaced by circuits especially designed to improve the sound of video-related programs.

There is nothing intrinsically novel or unusual about using comb filters or time delays to enhance the ambience of reproduced sound. Some of these circuits have been much more sophisticated than those in the AVC-50, using more elaborate comb filters or multiple time delays to impart a more “natural” quality to the sound. None of these systems will work miracles, however, and people who have used them, even after an initial positive reaction to the processed sound, have often eventually become disillusioned.

Listening to the Yamaha AVC-50, we found its special effects always pleasing, definitely enhancing the listening experience. It is our impression that Yamaha intended the AVC-50 to produce just that effect, with no pretensions of taking you from your listening room into a concert hall. Even this kind of enhancement probably will not appeal to purists or most “high-end” audiophiles, but the AVC-50 is not aimed at them.

We found the AVC-50’s processing features at least as beneficial for mono programs as for stereo. We used it to drive the rear speakers in a four-speaker installation, and we liked what we heard. The remote control of volume and program switching was very convenient, and Yamaha’s use of a motor-driven potentiometer instead of electronic control circuits continues to impress us as the best way to handle that task. Overall, the Yamaha AVC-50 is a versatile, effective audio/video control amplifier that is well worth considering if you have a multitude of program sources in your entertainment system or if you are thinking of adding surround-sound capability.

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