Onkyo A-8190 Amplifier
Onkyo's A-8190 integrated amp combines technical finesse-the sort that has been confined to audio-only gear in most past models-with video-source switching that usually appears either in receivers of less impressive audio pedigree or in add-on control boxes of no pedigree whatsoever. At the same time, its front panel is significantly simpler and more straightforward than those of most audio-video designs we've tested, partly because the A-8190, unlike a receiver, sidesteps the complications imposed by a tuner section.
The A-8190 has audio input connections for phono (switched at the front panel for fixed- or moving-coil cartridges) and two high-level (aux) sources, labeled for tuner and CD player. There are input and output connections for two audio tape decks as well as preamp output jacks to feed signals to an external amp. The video connections include video and stereo-audio inputs for a videodisc player, inputs and outputs for a VCR, and a video-only output to feed a monitor or TV receiver. All connectors are pin jacks. The only other back-panel features are the AC convenience outlets and the heavy-duty binding posts that accept bared wires to feed two pairs of loudspeakers. The amplifier is rated at 100 watts (20 dBW) per channel into 8 ohms.
The front panel has input-selector buttons corresponding to each of the back-panel inputs plus a second (direct) CD selector that bypasses the tone, balance, mode, and muting controls for the purest possible signal. Below these selectors are two rotary recording-source selectors, one for each audio deck. In addition to the standard audio-input positions, each selector has positions for off (to disconnect its recording outputs when they're not needed, so that attached equipment won't load the main signal feed), for dubbing from the other audio recorder, and for dubbing the audio from a video source chosen by the nearby video selector.
The latter control, which also has an off position, connects the VCR or videodisc audio to the audio recorders, the videodisc audio and video to the VCR, the sound selected at the Tape 2 selector to the VCR audio input, or the video from disc or VCR to the monitor as visual background to whatever audio source is selected at the main pushbuttons. At least, that's the way Onkyo's manual describes this last mode. We prefer to think of it as the setting for receiving TV/FM stereo simulcasts.
Beneath the large volume knob are buttons to choose mode (mono/stereo) and phono input sensitivity (MM/MC). Next come the balance and tone controls, which include the usual detented treble and bass knobs plus one marked contrabass. The last-calibrated from "defeat" at minimum rotation through "20" at maximum-acts as a unique loudness control of sorts, as we'll explain shortly. Its action is altered as well by the setting of two buttons immediately above it, which switch between full level and "muting" (attenuation); all three tone controls can also be defeated altogether by another button nearby. The remaining front-panel controls are the speaker selector (A, A+B, B, off), which is just beyond the headphone jack, and the main power switch.
Diversified Science Laboratories found that with the contrabass control defeated, the so-called muting switch drops the overall level by 15.1 dB instead of the usual 20 dB. If the contrabass control is rotated to the right, attenuation in the deep bass is reduced (depending on the setting), leading to a rising bass response. With full unmuted level, extreme rotation of the control boosts bass below 100 Hz by a maximum of 10 dB, shelving below about 50 Hz. With the lower, muted output, response at the maximum contrabass setting rises at roughly 5 dB per octave throughout the bass, delivering some 20 dB of boost at 20 Hz relative to the 1-kHz output.
Though Onkyo doesn't expand on it in the manual, the basic intent seems clear. The contrabass control can be used as a woofer-extender at full level, gently boosting the range in which typical speakers roll off. When you want to reduce level, use of mute (a name that's even more inappropriate than usual here) automatically adds a degree of loudness compensation. If you prefer, you can use either or both options just for loudness compensation, further honing it to your taste with the bass control.
The bass control itself also shelves- near +10 dB at the extreme settings and reaching to around 100 Hz before tapering off to the reference level a little above 1 kHz. The treble control overlaps these curves only slightly and reaches about + 8, - 11 dB at 20 kHz, evidently shelving at higher frequencies. The curves are more symmetrical than often is the case, and the effect of the controls is consequently quite predictable and free of quirks.
Phono response at the fixed-coil (MM) setting is extremely flat. Its very gradual rise toward the extreme top and slighter prominence in the deep bass are too small to be of any consequence. With the moving-coil setting, response is, if anything, even flatter above 100 Hz. In the deep bass, it begins to roll off; by 5 Hz, in the heart of the warp region, it is down by more than 10 dB, which may be welcome in some systems. There is no infrasonic filter as such, and fixed-coil response rolls off by only 3/4 dB at 5 Hz.
Onkyo has taken extra pains to prevent potential signal contamination, however slight it may be. Such design goals as keeping signal paths as direct as possible-not only for the "CD direct" option, but in all preamp functions-are almost taken for granted in top models. Unique in our experience, however, is Onkyo's Real Phase power-supply design, which is intended to prevent phase modulation of the signal in response to the reactive load components that are inevitable with real loudspeakers (as opposed to test resistors). Toward this end, Onkyo has inserted a second transformer between the power transformer and the rectifiers in order to supply mutual inductance between the positive and negative sides of the main transformer's secondary, preventing independent surges in each.
The amplifier section has dynamic ratings down to 2 ohms, though Onkyo doesn't recommend using exceptionally low impedances with the A-8190. Instead, the instructions follow the usual pattern: 4 ohms per speaker if one pair is used, 8 ohms apiece for two pairs. The lab did substantially confirm the specs, with progressively greater power output for each reduction in load impedance (and, therefore, no evidence of current limiting) until the 2-ohm dynamic test, where the protective circuitry tripped before useful measurements could be made. With the loads Onkyo recommends, however, unfettered power is manifestly available.
Moreover, we were impressed by what we heard in playing our most demanding CDs through the A-8190. To some extent, our positive reaction was no doubt occasioned not only by the extra care Onkyo has taken in its circuitry, but also by the exceptional clarity of the control layout, given the complexities of audio-video switching. As the heart of an up-to-the-minute, high-performance audio-video system, it would be hard to find a more satisfying design than that of the A-8190.
