Denon AVC-500 A/V Control Center Review

DENON’S AVC-500 A/V control center provides a number of control functions analogous to those found in stereo integrated amplifiers. It has input/output connections and switching, dubbing, and signal-processing facilities for up to three VCR’s, or two VCR’s and a video-disc player, as well as one high-level mono or stereo audio-only source such as a cassette deck or a CD player. It can deliver the selected video program to an external monitor and line-level audio signals to external amplifiers or powered speakers. The AVC-500 also includes a built-in power amplifier rated to deliver 25 watts per channel into 6-ohm loads from 20 to 20,000 Hz with no more than 1 percent total harmonic distortion. The amplifier can be used to power either normal (front) stereo speakers or rear-channel ambience speakers.

Signal-processing capabilities include a video enhancer to sharpen picture details, a dynamic-range expander, stereo-simulation circuitry for use with mono programs, and a surround-sound feature for adding ambience to stereo programs. In addition, the AVC-500 has a five-band graphic equalizer to vary the audio frequency response as desired. The nominal center frequencies are 63, 250, 1,000, 4,000, and 16,000 Hz, with control ranges of ± 10 dB. The AVC-500 makes it convenient to replace the audio portion of a video program while dubbing it, substituting the audio input from the tape/CD jacks. And its sound-processing features can be used to modify either the original audio program, or its replacement, while listening to or copying a tape.

The Denon AVC-500 is finished in black and resembles a typical integrated stereo amplifier, with pushbutton input selectors, knobs for volume and most other adjustments, and vertical sliders for the graphic equalizer. The front-panel headphone jack is connected to a circuit that automatically silences the speaker outputs when phones are plugged in. The control center measures about 17-1/8 inches wide, 11 inches deep, and 3-3/4 inches high. It weighs 12 pounds, 6 ounces. Price: $375.

Lab Tests

Although the Denon AVC-500 is rated only for driving 6-ohm loads, we also used our standard 8- and 4-ohm load resistors for testing its power-amplifier section. After preconditioning, the amplifiers clipped at 26 watts per channel at 1,000 Hz into 8 ohms, 29.5 watts into 6 ohms, and 27.6 watts into 4 ohms.

Under the same test conditions, the distortion measured less than 0.15 percent up to the clipping point and was almost completely independent of frequency. At the rated 25 watts into 6 ohms, it was typically 0.06 percent from 50 to 8,000 Hz, rising only to about 0.15 percent at 20 and 20,000 Hz. At half power the distortion was about half as much, and at one-tenth rated power it was roughly the same as at full power (a small crossover notch caused the relative percentage of distortion to increase as the power decreased). The 8-ohm performance was quite similar, with slightly higher distortion readings, and the power amplifiers did quite well with the 20-millisecond tone bursts of the dynamic power test.

The graphic equalizer matched its ratings exactly in respect to center frequencies and maximum control range. The dynamic-range expander’s properties were not as clearly defined in the ratings, and in any case its effect was slight, principally an overall level increase of about 2 dB when it was switched in and an expansion of about 2.5 dB over a 30-dB range of input levels.

We examined the effects of the surround mode by driving one channel with a single cycle of 1,000 Hz, followed by a long “off” period, and displaying the outputs of both channels on an oscilloscope. In the surround mode, the result was two equal and identical outputs, except that one was 180 degrees out of phase with the other. According to Denon, the surround-sound circuit consists of an L — R matrix, with variable mixing of the original left and right front-channel signals into their respective rear channels and also a 30-millisecond time delay. Turning the wide knob clockwise decreases the amount of front-channel signals mixed into the rear-channel output. The surround-sound effect was most noticeable at the maximum setting. The surround-processed output can be fed either to an external rear-channel amplifier or to the AVC-500’s own amplifier section with an external amplifier for the front speakers.

The operation of the simulated-stereo feature was quite different. To test it we drove both channels with the single 1,000-Hz pulse. The output from each channel was the amplified pulse, followed after a short interval by another of the same shape. In this case the wide control varied the level of the delayed signal, relative to the original one, in a range from —22.5 to + 11 dB. However, in the left channel the delayed signal was in phase with the main signal, while in the right channel its polarity was reversed. The delay was from 1.3 to 1.4 milliseconds. The processing is intended to enhance mono signals heard from the regular front speakers.

The AVC-500’s audio sensitivity, measured through the TAPE/CD input, was 92 millivolts for a reference output of 1 watt into 8 ohms, and the A-weighted noise level relative to that output was —81 dB. With the INPUT LEVEL knob at its normal maximum setting, the internal circuits overloaded at 1.6 volts, as indicated by the flashing LED next to the knob. If overload occurs, turning down the control will enable the unit to withstand input signals of any level.

Comments

In general, the Denon AVC-500 met or surpassed its performance specifications. The performance of a product like this is best judged subjectively, however. Therefore, we connected it between a VCR and a monitor, with a pair of 8-ohm bookshelf speakers driven by its amplifiers.

The video enhancer control did improve the apparent crispness of the picture, and without the unnaturally high contrast that sometimes accompanies this process. The audio expander produced a considerable volume increase, subjectively much greater than the couple of decibels we measured, but it did not seem to affect the dynamics to any significant degree. The simulated-stereo effect was like most phase-shifting systems we have heard; it can make a mono signal more interesting to listen to, but it is not likely to be mistaken for stereo by anyone who has heard the real thing.

The surround-sound feature was more satisfactory, especially with surround-sound-encoded programs. Used in moderation, it lent a sense of ambience to the sound, with enough “liveness” to distinguish the result from the simulated stereo sound and even from the unmodified stereo program. The graphic equalizer seemed to be as effective as any five-band equalizer can be and probably more so than a two- or three-range tone-control system.

The Denon AVC-500 can make things easier for the audio/video enthusiast who does a significant amount of video-tape copying, if only by eliminating the tedious changing of cable connections involved in using two or three VCR’s. And if you do audio dubbing on your video tapes, this unit can also simplify your task. It is a versatile component whose ultimate utility is likely to be determined largely by the ingenuity and particular needs of the user.

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