Jensen AVS-1500 Stereo Receiver Review

The components of Jensen Sound Laboratories’ novel modular audio/video entertainment system have not only been carefully engineered for compatibility with each other, they have also been “human-engineered” for ease and convenience to the nontechnical consumer. At the heart of the system is the AVS-1500 receiver, combining a high-quality AM/FM-stereo tuner, an integrated amplifier rated to deliver 50 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.05 per cent total harmonic distortion, and a 133-channel TV tuner. All tuning functions use digital synthesis under microprocessor control, and all control settings are “memorized” so that they are restored when the receiver is next turned on.

The video display of the system is a high-definition monitor available in either 19- or 25-inch (diagonal) size. The audio outputs are delivered to compact columnar speakers that Jensen designed specifically for this application. They have a very low external magnetic field, permitting them to be placed directly against the video monitor (if that is desired) without distorting either the linearity or the color values of the picture. The speakers are available in two versions, essentially identical except for height, for use with the 25- or 19-inch monitor.

To complete the system, Jensen offers a deluxe VHS videocassette recorder (VCR) that complements the receiver in its flexibility and styling. Separate wireless (infrared) remote-control units are supplied for the receiver and the VCR, permitting their installation for maximum convenience without loss of operating flexibility.

We used the entire Jensen audio/video system in our subjective evaluation of the AVS-1500 receiver, although laboratory measurements were performed only on its AM, FM, amplifier, and TV-audio sections. The operating features of the complete audio/video system are so numerous that we do not have the space here to list most of them, much less comment on them in any detail (see box on page 32 for Jensen’s specs and ratings for the other components in the system). Our specific remarks about the video components or the related control facilities of the receiver will be limited to those features we used sufficiently to form opinions about.

The AVS-1500 receiver is 17 inches wide, 18 inches deep, and 4-5/8 inches high, and it weighs 27 pounds. Its entire exterior is finished in satin silver. The top and bottom edges of the front panel are rounded, and no knobs are visible in normal operation. All AM and FM tuning, TV-channel selection, input-source selection, and volume adjustment are accomplished by means of flush-mounted, flat strip switches that respond to light pressure.

The inputs include FM, am, tv, video 1 and video 2, tape, phono, and simul (for reception of FM/TV simulcasts). There are six radio-preset channels (P1, P2, etc.), each of which can be used for both an AM and an FM frequency. To the right of these on the front panel of the AVS-1500 are pressure strips for selecting TV channels (the channel number appears in a black window next to the selector), adjusting volume, and tuning (for AM and FM stations). The blackout window between the volume and tuning controls contains a digital display of FM and AM frequencies, LED readouts of signal strength and volume setting, and identification of the various special operating modes of the receiver.

At the left of the panel are the illuminated power button and a door button. Pressing the latter causes a hinged section of the panel to swing downward across its full width, revealing a number of less-often-used controls. These include the bass and treble tone controls and the balance control as well as pushbuttons for the acoustic enhance and synthetic stereo modes (these are used to enhance mono program sources and will be described later), loudness compensation, independent switching of two sets of speaker outputs, mono/stereo mode, memory set (for the station-preset controls), scan (for automatic tuning to the next receivable station), and CATV (for selecting cable-TV channels). There is also a decoder button for connecting a video game or CATV decoder to the system.

At the left of the concealed area are a headphone jack and a knob to select the program source for headphone listening, which is independent of the source being heard or watched through the regular receiver outputs. This knob can be used to select all the normal signal sources except video 2 (for a videodisc player) and AM. A small knob controls headphone volume, also independently of the regular volume control. The remaining knob control is for the DNR (dynamic-noise-reduction) circuit. Advancing it clockwise increases the effect of the DNR circuit, which rolls off the high-frequency response in a manner controlled by the signal level and its high-frequency content to reduce audible hiss without a subjective loss of highs.

A couple of operating features of the AVS-1500 are both unusual and functional.

First, the volume setting is indicated by a row of LED’s that looks like the system employed in some receivers using microprocessor-controlled digital volume adjustment. The resemblance is merely superficial, however, since the AVS-1500’s volume is controlled by a conventional potentiometer driven by a small motor, which provides a smooth volume change instead of the discrete steps of a digital system. Second, the lower control knobs are normally flush with their subpanel, which allows the door to close flush with the top front panel of the receiver. The knobs cannot be turned when the door hinges open, but pressing and releasing a knob causes it to emerge from the subpanel for easy operation.

On the rear apron of the Jensen AVS-1500, besides the expected input and output jacks for the stereo receiver functions, there are standard phono jacks for video 1, the video and audio inputs and outputs from a videocassette recorder (VCR), and for video 2, which is intended for use with a nonrecording accessory such as a videodisc player and therefore has only a video input jack. The receiver provides stereo audio outputs for tape recording the sound portion of a videodisc. Although standard phono plugs are used for the video connections, the video connecting cables are 75-ohm coaxial types.

Also on the rear apron is a phono-jack output for the video-monitor connection, as well as a coaxial jack for connecting the VCR r.f. output to the TV. A remote-control connector to the Jensen TV monitor switches its power from the power switch of the receiver (its picture-tube heater is always on so that the picture appears almost immediately). In addition to the binding-post AM and FM (300- and 75-ohm) antenna terminals and a pivoted AM ferrite-rod antenna, there are coaxial antenna jacks for the VHF TV antenna, the decoder input (which can also receive a home-computer signal), and an aux antenna input, as well as 300-ohm UHF TV antenna binding posts. There are two a.c. outlets, one of them unswitched (for the VCR, so that its clock and timer settings will be retained when the receiver is turned off).

The infrared wireless remote control is exceptionally compact (6-1/4 x 2-1/4 x 9/16 inches) and contains buttons for the six preset AM or FM channels, numerical input buttons for the TV channels (from 2 to 83, plus all currently used CATV channels), all input selections except for the VCR, an audio-mute switch, and a system power switch. In addition, the remote control has miniature duplicates of the channel-selection, volume, and tuning pressure controls.

The Jensen AVS-1500 audio/video receiver is supplied with the remote control, a full set of audio and video connecting cables, a 75- to 300-ohm antenna-matching transformer, and an FM dipole antenna. Price: $990.

Laboratory Measurements

Because of the large size and mass of the AVS-1500 (relative to its power rating), its top, over the heat sinks, became only moderately warm during its one-hour preconditioning and the high-power tests that followed. With both channels driving 8-ohm loads at 1,000 Hz, the output waveform clipped at 64 watts per channel, for a clipping-head-room rating of 1.1 dB. With 4-ohm loads, the clipping power was 85 watts per channel. The AVS-1500 is not rated for driving 2-ohm loads, and because of its rote as a center for a specific audio/video system, with specified (or at least recommended) peripherals, we would not expect it to be used with such a load. Nevertheless, it delivered about 20 watts per channel to 2 ohms, at which point the internal protective relay shut off its outputs. With the pulsed dynamic-headroom test signal, the maximum output was 80 watts into 8 ohms, for a dynamic-headroom rating of 2 dB, 92 watts into 4 ohms, and 130 watts into 2 ohms.

The 1,000-Hz distortion was about 0.002 to 0.006 per cent in the output range of 1 to 50 watts, reaching 0.01 per cent at just over 60 watts. With 4-ohm loads, the distortion was slightly higher, 0.006 to 0.007 per cent up to 30 watts and 0.015 per cent at 80 watts. At the rated 50-watt output into 8-ohm loads, the distortion was less than 0.01 per cent from 70 to 2,000 Hz, rising to about 0.02 per cent at 30 Hz and to just under 0.1 per cent at 20,000 Hz. At reduced output powers the distortion curve was very similar. The second-order intermodulation distortion, with input signals at 18 and 19 kHz, was —72 dB, and the third-order distortion was —79 dB, both referred to 50 watts. The amplifier slew factor exceeded our measurement limit of 25, and it was stable with reactive loads.

The tone-control response characteristics were conventional, although almost all the control action occurred in the last part of the knob rotation from its center setting. The loudness compensation boosted both low and high frequencies moderately. With loudness compensation on and at the maximum volume setting, the amplifier response rolled off slightly above 2,000 Hz, to — 5 dB at 20,000 Hz, but with loudness compensation off and the tone controls centered it was fiat. The RIAA phono response was within +1, — 0 dB from 20 to 20,000 Hz.

For a reference output of 1 watt, the amplifier required an input of 22 millivolts (mV) through a high-level (tape) input and 0.35 mV through the phono input. The respective A-weighted noise levels were —77 and —73.5 dB referred to 1 watt. Phono overload occurred at comfortably high levels of 160 to 175 mV, depending on frequency. The input impedance of the phono preamplifier was 47,000 ohms in parallel with 70 picofarads.

The noise reduction afforded by the DNR system was 10.5 dB (CCIR/ARM weighting) at its maximum setting. The effect of DNR on the static frequency response was very slight at intermediate settings, but at the full setting of the control the response rolled off at 6 dB per octave above a frequency that varied between 10.000 and 1.000 Hz for signal levels between 0 and — 30 dB (referred to 50 watts).

We made limited tests of the two signal-enhancing systems of the AVS-1500 in order to establish their operating principles. The acoustic enhance mode cross-couples the two channels with a phase shift between them that varies with frequency. Its principal audible effect was to roll off the highs and boost the bass, and it imparted an enhanced sense of lateral spread to the sound. The synthetic stereo—intended primarily as an enhancement of mono TV sound— introduces a slight time delay on the mono signal, affecting frequencies below 10,000 Hz, before adding that signal to the original on one channel and subtracting it from the other. The resulting frequency response exhibits a “comb” characteristic, with sharp output nulls occurring at intervals of 150 Hz. The audible effect of this was to “spread” the sound so that it was no longer likely to be mistaken for mono, imparting at times a feeling of listening to “out-of-phase” stereo sources. Neither of the two sound-enhancing systems would be of great value for normal stereo reproduction, but they might be useful with close speaker spacing (for example, if the speakers flanked the video monitor).

The FM tuner had a usable sensitivity of 12.8 dBf (2.4 microvolts, or μV), exactly as rated. The stereo sensitivity was established by the switching threshold of 19 dBf (5 μV). The respective mono and stereo 50-dB quieting sensitivities were 15 dBf (3 μV) and 36 dBf (35 μV). The ultimate signal-to-noise ratio (S/N) of the FM tuner was a good 77 dB in mono and 71 dB in stereo, and the respective distortion readings at a 65-dBf (1,000-μV) input were 0.065 and 0.22 per cent. The FM frequency response was +1.5, —1 dB from 30 to 15,000 Hz. The channel separation was better than 35 dB up to 6,500 Hz, with a maximum of about 55 dB at 1,000 Hz and a minimum of 30 dB at 15,000 Hz. The frequency response of the AM tuner section was ±1.5 dB from 35 to 1,750 Hz and down 6 dB at 3.000 Hz relative to the 1,000-Hz level.

The IHF IM distortion of the FM tuner was measured with test signals at 14 and 15 kHz. In mono, the second-order (1,000-Hz) distortion product was —77 dB, and the third-order products at 13 and 16 kHz were at —50 dB. In stereo the readings were not very different, —73 and —52 dB, respectively, besides the usual display of additional IM products arising from the FM demodulation process (at levels between —65 and -80 dB, and therefore not audible under normal program masking conditions).

We made two measurements of the TV tuner’s audio performance and obtained a frequency response of ±1.5 dB from 30 to 20,000 Hz. The audio signal-to-noise ratio of the television section was 49 dB (A-weighted). This may not seem like much compared with a typical FM-stereo tuner specification, but TV audio is broadcast with one-third as much carrier-frequency deviation as FM stereo, which automatically results in a worse theoretical S/N.

Comment

Judged as a conventional AM/FM stereo receiver, the Jensen AVS-1500 performed very satisfactorily, and it is uncommonly handsome. It does just about everything one expects of such a receiver, and it does it just about as well as any other we have used. The FM tuner disconcerted us briefly when we found that it has no interstation noise muting if one tunes “manually” (stepping the station frequency by pressing the tune controls). In the scan mode, however, the audio is muted as the tuner steps in the selected direction until it stops at a signal of suitable strength.

The remote control worked perfectly, and the motor-driven volume control was easy to master (it operates slowly and smoothly enough to prevent any excessive “overshoot”). The combination of the signal-enhancing and DNR circuits enabled us to hear almost any program, including TV sound, at its best. Yet it does not prevent a purist from listening to stereo as it was meant to be heard. Although we did not make any measurements on the AVS-5250 speakers, they sounded fine.

The ability to operate two sets of speakers from the receiver means that one can always enjoy a favorite pair of speakers for stereo listening while retaining the utility of the Jensen speakers for TV. (The external magnetic field of many speakers prevents their use in close proximity to a TV monitor, but we were unable to detect any external field from the Jensen AVS-5250 speakers even with a sensitive gaussmeter.)

As a TV receiver, the AVS-1500, used with the AVS-3250 25-inch monitor, was very impressive. One could hardly ask for better picture quality, and the accompaniment of equally good TV sound made the combination most attractive. The same reaction extended to the AVS-4400 VCR, a feature-laden supplement to the system.

Video is certainly here to stay as a key part of our home entertainment systems, and we must say that Jensen has done a superior job of integrating it with audio, retaining the best of both with no significant sacrifice or compromise of performance or flexibility in either one. In fact, we felt that the styling of the electronic components of the system was superior to most current stereo components, exhibiting a rare combination of good taste, good engineering, and functional design.

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