MAS Charisma Preamplifier (Jan. 1994)

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Though new to this country, MAS (Metaxas Audio Systems), of Melbourne, Australia, has earned a solid reputation among Europe an enthusiasts for its audio components, which are unique in many of their design features and em body the personal philosophy of their designer, Kostas Metaxas.

MAS products are characterized by uncompromising circuit design and physical construction, Metaxas says, the primary goal being to provide the most nearly ideal performance possible, especially with regard to sound quality. Aesthetic considerations have not been neglected, however. All of the components’ controls have a silky-smooth, positive feel, and the knobs are machined from solid aluminum bar stock before being polished to a smooth satin finish.

The MAS line includes preamplifiers, power amplifiers, integrated amplifiers, a CD player, and loudspeakers, all carrying such unusual and distinctive names as Marquis, Iraklis, Solitaire, and Opulence. We tested the Charisma preamplifier, the company’s least expensive component.

The MAS Charisma is a basic pre amplifier, almost minimalist in some respects. Like MAS’s other electronic components, it has a separate power supply, with a toroidal transformer and two-stage filtering to minimize power-line hum, that is joined to its chassis by a detachable cable approximately 3 feet long.

The Charisma is designed to be powered continuously, and neither the power supply nor the preamplifier it self has a power switch. In fact, Metaxas suggests that the Charisma be powered for at least 24 hours before any critical listening. Since the preamplifier becomes quite warm, it requires adequate ventilation.

A bare-bones control center, the Charisma provides no tone controls or filters. Its three high-level inputs, marked tuner, compact disc, and video, are selected by a knob. A small toggle switch selects the phono input, and another controls the tape recording and monitoring functions. Since the Charisma cannot be turned off in the usual sense, it has a third toggle switch, marked muting, that silences the preamplifier by the simple expedient of disconnecting its outputs and shorting them to ground. A red LED on the panel, marked AC, glows when the preamplifier is powered. Another LED, marked DC, glows only when there is a DC component in the output signal, a sign that there is a problem (the Charisma circuit is direct-coupled from input to output). Should such a problem occur, a relay grounds the outputs to protect the power amplifier and speakers.

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POWER SUFPLY: 4"x2"x9.5”



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Output at clipping 11.5 volts

Sensitivity (for a 0.5-volt output)

CD 33mV

phono 0.13mv

Noise: (A-weighted, referred to a 0.5-volt output)

CD -93db

phono -68.5dB

Phone-input overload (1-kHz equivalent levels)

20Hz: 37mV

1 and 20 kHz: 35mV

R1AA phono-equalization error

20 Hz to 20 kHz +0.2. -1.4dB

Frequency response

CD: 20 Hz to20 kHz +0.02. -0.01 dB

Distortion (THD + N at I kHz)

2 volts output: 0.0022%

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The volume-control knob, at the right end of the panel, has forty lightly detented settings, with ten index markings on the panel. The adjacent balance control, which also has ten panel markings, has a smooth, continuous rotation. It is unlike any other balance control we have used. Instead of differentially varying the gains of the two channels, it merely lowers the level in one channel at a time, depending on which way it is turned from the center position, leaving the other fixed. It has a limited adjustment range of 4 dB in either direction.

The Charisma’s back panel is well populated with phono-type connectors for the signal inputs and outputs, plus a binding post for grounding a turntable or another component to the preamplifier for hum reduction. Consistent with the elegance and superb construction evident throughout this component, the signal connectors are machined from brass and gold-plated.

MAS says the Charisma’s preamp and power-supply chassis are both made of nonmagnetic material. To the eye, it appears chrome-plated, its mirror-like surface presenting an attractive contrast to the preamp’s black panel and polished aluminum knobs.

The Charisma’s phono stage has DIP (dual in-line package) switches on its circuit board that enable the cartridge terminating resistance to be adjusted between 60 and 47,000 ohms. Except for several common settings, this can involve a certain amount of calculation to determine the overall value of as many as eight resistances in parallel. Similar internal switches can be used to set the phono-preamplifier gain to suit a wide range of cartridge output levels. All our measurements were made using the factory-set phono values.

The MAS Charisma met or surpassed its specifications in practically every test we performed. Although we did not use it with a turntable, its RIAA equalization was very accurate (with a reasonable rolloff below 20 Hz). As received, the preamp was set up for a moving-coil cartridge and had a terminating resistance of about 2,600 ohms. Its noise level through a high- level input was very low (about the same as that of a CD player), and though the noise was considerably higher through the phono input, it still met the manufacturer’s rating.

The Charisma can deliver a rather high output voltage before clipping. The phono-preamplifier overload level was satisfactory for moving-coil cartridges, but its gain would have to be reset with the internal switches for most moving-magnet cartridges.

Although Metaxas says that the Charisma’s metalwork is nonmagnetic, we found that magnets clung to it about as strongly as they did to a steel plate. But since there are no high current AC components present in the preamplifier itself, there would seem to be no reason for any concern about induced hum.

An unexpected discovery was the low input resistance of the high-level inputs (tuner, CD, video), which measured only 8,900 ohms. That will not cause any problems with most signal sources, but some might suffer a loss of deep-bass response when driving such a low load resistance.

The Charisma does indeed get hot, justifying the manufacturer’s admonition to avoid obstructing its ventilation slots or placing it on top of a hot component such as a receiver or amplifier. Most large receivers and amplifiers we have tested (up to power ratings of 200 watts or so) do not get as hot in normal operation as this com pact preamplifier does.

As for the Charisma’s sound—if you are one of those who finds significant sonic differences between preamplifiers, you should listen for yourself. This one was as flat-sounding and noise-free as any you will find, and I heard nothing that could be said to originate in it. It is a very smooth- handling unit, as quiet and precise as they come, easy to use, and significantly more compact than any I have seen in some time. I would have no hesitation in recommending it to any one willing to spend $1,850 for a basic preamplifier—especially anyone who uses a moving-coil phono cartridge, for which the Charisma would seem to be ideal.

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