Nakamichi CA-5A II Preamplifier Review

The Nakamichi CA-5A II is an improved version of the earlier CA-5 Control Amplifier (preamplifier). The changes include both additional control features and circuit modifications. The Series II circuit design closely resembles that of Nakamichi’s top Control Amplifier, the CA-7A. The principal changes from the “minimalist” control design of the CA-5 are the addition of defeatable tone controls, two-way tape-dubbing facilities, and three selectable gain settings for the moving-coil (mc) phono input.

Despite its external simplicity, the CA-5A II is a highly flexible preamplifier. It has five high-level inputs, and the single phono input is switchable between mc and mm modes by a small toggle on the rear apron. Another toggle switch selects capacitances of 100, 200, or 300 picofarads (in parallel with a nominal 50,000-ohm resistance) as an input termination for mm cartridges or gains of 24, 30, or 36 dB for mc cartridges. The MC-cartridge termination, normally 100 ohms, can be changed to another value (from 3 to 50 ohms) by dealer installation of additional resistors supplied with the preamplifier.

The high-level inputs are tuner, CD player, auxiliary, and two tape decks. A single knob selects one of the high-level inputs or the phono input. A separate tape-monitor knob (set to source when a tape input is not used) has positions for playback from either tape deck and for copying a tape from either machine to the other.

The other front-panel controls are entirely conventional. Normally, the tone controls are completely removed from the signal path; a separate button activates them.

Like the CA-7A, the CA-5A II uses a multi-regulated, isolated-ground power supply for maximum isolation of all circuits. Following its master regulator, the power supply has separate regulators for the left and right channels of the MC phono preamplifier, the mm phono preamplifier, the RIAA phono equalizer, the line-level amplifiers, and the tone-control amplifiers. Still another regulator powers the relays used for signal switching. According to Nakamichi, this isolated-ground system provides the same performance that would result from entirely separate power supplies for each stage.

Since the amplifying circuits of the CA-5A II were designed for negligible distortion without overall feedback, only a moderate amount of feedback is required to meet its exceptional performance specifications. Unlike most preamplifiers, in which input-signal selection is done by semiconductor switches or conventional rotary switches, the inputs and tape-monitoring connections of the CA-5A II are selected by hermetically sealed relays, which are located on the circuit board to minimize path length and noise pickup. The relay contacts are gold-plated silver-palladium alloy, and not only are the coils energized by their own regulated power source, but to prevent possible noise or interference from common ground paths, neither side of the power supply is grounded. A low-leakage toroidal power transformer is used to prevent induced hum from an external field.

The Nakamichi CA-5A II, which is finished in black, measures 17-1/8 inches wide, 11-5/16 inches deep, and 2-1/2 inches high. It weighs 11-1/4 pounds. Price: $995.

Lab Tests

Driving an EIA standard load of 10,000 ohms in parallel with a 1.000-picofarad (pF) capacitor, the 1.000-Hz output of the Nakamichi CA-5A II clipped at 7 volts. Because the overload was slightly asymmetrical and gradual, a 2-percent distortion level did not occur until the preamplifier’s output reached 8 volts.

At maximum gain, a 0.5-volt reference output required a signal of 41 millivolts (mV) through the high-level inputs, 2.2 mV through the mm phono input, and 0.107 mV through the MC phono input (using its 24-dB gain setting). The A-weighted noise levels for these inputs, referred to a 0.5-volt level, were respectively -84.6, -76.5, and -77.5 dB. The crosstalk between high-level inputs was — 73 dB at 1,000 Hz, but from a high-level input to mm phono it was unmeasurable (below —90 dB).

The 1,000-hz harmonic distortion was less than 0.003 percent at output levels from 0.1 to 3 volts, reaching 0.0045 percent at 7 volts. The mm phono-input termination was 40,000 ohms in parallel with capacitances of 115, 200, or 270 pF, depending on the setting of the switch in the rear of the unit. The phono preamplifiers overloaded at inputs between 268 and 278 mV (mm) and between 16.5 to 17.3 mV (mc) over the audio range from 20 to 20,000 Hz.

The tone-control characteristics were excellent, with less than a 1 -dB effect on the midrange level between 400 and 3,000 Hz. The treble curves were hinged at about 7,000 Hz, and the turnover frequency of the bass curves shifted between 100 and 170 Hz as the control was varied. With the controls in their center positions (or bypassed), the frequency response varied less than 0.1 dB overall from 20 to 20,000 Hz. The RIAA phono equalization was so accurate that we had to use the most expanded scale on our response plotter to measure it; the total variation was about 0.05 dB from 20 to 20,000 Hz.

Comments

The extensive use of precision components (typically with tolerances of 1 percent or better) in the CA-5A II was clearly responsible for its extraordinary response flatness and equalization accuracy. The design simplicity that has long been a hallmark of Nakamichi electronic products is again exemplified by this fine preamplifier. If you don’t want to risk the (debatable) degrading effects of tone-control circuits on the sound, or even the slightest change in response flatness, you need only touch a button to remove them from the signal path. In fact, merely placing the tone controls in their detented positions (though they are still in the circuit) will provide a frequency response flatter than that of almost any CD player. And, if you do want to use tone controls, those on the CA-5A II are among the best of their kind.

Within the limits of our measurements, the CA-5A II met or surpassed its ratings. Realistically, ultra-low distortion readings or superflat frequency response have no necessary correlation with sound quality, although they certainly do no harm! More important, we think, are the operational qualities of the product—how effectively it performs its assigned task and whether there are any undesired side effects. In these respects, no one could fault the CA-5AII. We can no more comment on its “sound” than we can on that of signal cables. As far as we are concerned, it has no sound of its own at all but is a virtually perfect system control amplifier. That is what the Nakamichi engineers intended it to be, and they have succeeded admirably.

The Nakamichi CA-5A II is fairly costly, but there are many higher-priced preamplifiers on the market (and, of course, plenty of less expensive ones). The choice is the buyer’s, but our experience leaves us with no doubt that this preamplifier does all that is claimed for it, and then some. Who could ask for more?

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