Digital Integrated Amplifier (1987-89)
Power output: 150 watts per channel into 8Ω (stereo) !!!
Frequency response: 5Hz to 50kHz
Total harmonic distortion: 0.004%
Damping factor: 1000
Input sensitivity: 0.1mV (MC), 2.5mV (MM), 150mV (line)
Signal to noise ratio: 76dB (MC), 87dB (MM), 110dB (line)
Channel separation: 67dB (MM), 58dB (line)
Output: 150mV (line), 2V (Pre out)
Digital inputs: 1 x optical, 2 x coaxial
Dimensions: 440 x 170 x 420mm
The KA-3300D is a showpiece of the Kenwood line-or, more specifically, of the company's Digital Series Audio Components. It's also the first component we've tested that boasts a built-in digital-to-analog (D/A) converter that accepts and decodes the direct-digital bit-stream output from components such as Compact Disc players and digital audio tape (DAT) decks with appropriate outputs. With this integrated amp, therefore, we take one more step toward an all-digital future.
There are actually three digital inputs and one digital output, all on the back panel. The first input is a fiber-optic coupler that mates via an optical cable with the digital-output jack on the Kenwood DP-3300D CD player. The second input is a standard gold-plated pin jack, as are the direct-digital recording and playback connections for a DAT deck. Since there is still no standard for audio-sys-tem fiber-optic connectors, Kenwood sensibly uses the optical link for hooking up its own CD player. Presumably, the standard pin jacks are employed for other digital connections so that you can mix brands. The D/A section automatically adopts the sampling frequency of the data stream (32, 44.1, or 48 kHz, depending on the source).
To choose a direct-digital input, you first push digital direct, located next to the volume knob. This overrides not only the analog input selectors, but also the balance, mode (stereo/mono), and infrasonic-filter controls. The volume control continues to function, however, as do the loudness, muting (which attenuates output by almost the full 30 dB specified by Kenwood), and tone controls-rather a lot of processing for a "direct" feed, it seems.
Final selection of the digital source is handled by three small buttons at the bottom right of the front panel. The first chooses between the digital and analog modes; the second switches between the two non-DAT inputs; and the third chooses the DAT input. Each has a pilot light-a welcome feature, since Kenwood is inconsistent about what the switch positions represent, and the wording of the manual (not one of Kenwood's best efforts, though we've certainly seen much worse) on this matter isn't as clear as it could be. The manual also leaves us unconvinced of the utility of the back-panel D/A direct-out connections. They are provided so that the KA-3300D "can be used as [a] standalone D/A converter unit by connecting the line-input jacks of another amplifier to [the D/A direct-out jacks]." Therefore, the digital controls and routing could be improved. This will probably occur in future products once analog/ digital cohabitation becomes the norm.
The analog input selectors occupy most of the narrow band between the upper panel and the bottom rank of controls. The main selectors are for phono, CD, tuner, aux, and monitor. Under the large volume knob is a button to select MC (moving-coil) or MM (fixed-coil) phono options. To the left of the monitor button are three smaller ones to select Tape 1, 2, or 3 as the monitored deck. A button that chooses between Aux 1 and 2 is located above the front-panel Aux 2 input jacks, which are nestled in the base. The Aux 1 inputs are on the back panel, as are all the remaining inputs.
Tucked under the left end is the headphone jack, which aesthetically balances the Aux 2 inputs. Above the jack and along the bottom rank of the front panel proper are the power switch, the mode switch, the bass and treble controls (each with a turnover-frequency switch), the infrasonic filter, and the loudness controls (a combination of an on/off switch and a level knob that sets the degree of compensation).
At the upper left are rotary controls for the speakers (the A pair, the B pair, both, or neither) and the tape outputs, the switching for the latter being unusually complex. The off position interrupts all feeds to the tape decks, preventing unnecessary loading of the signal fed to the power amp. There are also two dubbing positions: Tape 1 feeding 2 and 3, and Tape 2 feeding 1 and 3. The remaining three knob positions determine which signal-from the digital input, the CD analog input, or the tuner input-will feed to Tape 2 and 3. Tape 1 receives whatever signal is chosen with the main input selectors.
You can thus record digital signals from any of the three digital inputs, the analog CD signal, or the tuner to any of the decks. But only Tape 1 can be used for phono and aux signals. At first, this struck us as a mite odd, but it works well enough in practice. The switching evidently doesn't affect the digital feed to the DAT, which presumably also receives whatever is chosen at the main selectors. We could find no elucidation in the manual, and without a DAT deck on hand, we were unable to check.
The D/A subsystem itself incorporates a four-times oversampling digital filter and a seven-pole Butterworth analog filter. Separate converters are provided for the two channels. Further contributing to purity of output is the independent construction and shielding of the amplifier's three sections (digital, analog, and output) and the proprietary Sigma Drive that seeks to siphon off to ground any digital noise picked up within the analog and output sections.
Two other special Kenwood circuits are built into the power amp. DLD (Dynamic Linear Drive) acts as a buffer between the power-supply and amplifier sections to prevent line-voltage fluctuations from affecting performance. VIG (Voltage Interface Gate) similarly acts to prevent the extra current drawn to reproduce musical peaks from influencing the power supply voltage. As in some other premium amps, Kenwood uses separate circuitry to handle high and low levels.
As you can see from the lab data, the amplifier delivers comfortable but not extreme headroom and handles low-impedance loads with equanimity. Going from 4 ohms to 2 delivers less extra power than switching from 8 ohms to 4 (just over 1 dB, as opposed to almost 2). But there's also no evidence that the amplifier is running out of the considerable head of steam it has developed at that point-the equivalent of over 400 watts per channel on a dynamic basis into 2 ohms.
The availability of so much peak power makes it obligatory that the loudness compensation be adjustable so that it won't boom when the amplifier is driven way below full capability-as it must be most of the time in typical home environments. The 3300's loudness control is exceptionally well behaved; it supplies reasonably consistent increments of bass boost as the knob is rotated and shelves predictably below a turnover frequency that depends on the degree of boost.
In a sense, however, this precision is redundant: The dual-turnover bass control doesn't shelve (and hence doesn't boost infrasonics as much) and can be switched to put its maximum boost near either 25 or 50 Hz for the 200- and 400-Hz turnover options, respectively. This will deliver subjectively more pleasing loudness compensation for some listeners than the loudness control itself. Maximum bass boost or cut runs a hair over 10 dB at either setting, and the increments are even more regularly spaced than are those of the loudness control. Treble adjustment is comparable, with the 3- and 6-kHz turnover frequencies yielding response maxima near 20 kHz and in the ultrasonic range, respectively.
The infrasonic filter is quite gentle- a little too gentle, though, if you haven't taken sufficient care with your choice of tonearm and pickup and hence have warp-output problems. There is almost no infrasonic rolloff built into the phono-input section. Though there are no separate inputs, Kenwood gives you separate phono circuitry for MM and MC cartridges, rather than just an extra gain stage to boost an MC signal. The intent is to match the load requirements of each cartridge type more precisely than permitted by the usual shortcuts. Frequency response is very smooth in both sections, with a slight rolloff at the extreme top and a minute rise in the midbass. In the deep bass, MM response continues to rise (though still not to a significant degree), while the MC curve tails back to the 1-kHz reference level.
All of this is very impressive. Were it not for the digital connections, switching, and decoding, we'd view the KA-3300D simply as a superior integrated amplifier. But the real story lies in the way Kenwood has addressed the first stages (technical and conceptual) of the coming digital takeover. The internal D/A conversion and the use of optical coupling are just two results of this. Although we hope for simpler, more straightforward-if you will, more traditional-control schemes in future analog-digital hybrids, we're satisfied that Kenwood has succeeded electrically- and optically-with its first effort in a brand-new field.
DELIVERED WITH A FULL YEAR WARRANTY