Crown Power Line Three Power Amplifier Review

The Crown Power Line 3 basic power amplifier is rated to deliver 90 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.05 per cent distortion, or 140 watts into 4-ohm loads with no more than 0.1 per cent distortion. Like the other Power Line amplifiers, it features Crown’s proprietary Multi-Mode circuit, which continuously varies the operating mode of the amplifier between class A and class B according to the instantaneous signal output it is called upon to deliver. The purpose of the Multi-Mode system is to provide the lowest possible distortion at all signal levels together with maximum overall circuit efficiency.

Unlike the variable-mode (or variable-class) circuits used in some other amplifiers, which affect only the output stage, the Multi-Mode circuits control the operating conditions of the three highest-level amplification stages (pre-driver, driver, and output). At low output-power levels (up to 20 milliwatts) all three stages operate in class-A mode, which is inherently completely free of crossover distortion as well as being the most nearly linear amplification mode. Crown points out that with ordinary music program material the amplifier actually operates in this mode most of the time. As the instantaneous power of the signal waveform rises above 20 milliwatts, the output transistors change to class-B operation, the highest-efficiency mode of a linear audio amplifier. Since the drivers and pre-drivers continue to operate in class A, Crown calls this the “Class A plus B” mode.

Finally, at the highest power levels, the driver and pre-driver stages change to class-AB operation so that they can drive the output transistors (operating in class B) to their full power output (a class-B amplifier requires actual driving power, instead of only a voltage or current input, in order to develop its full output). Crown refers to this as the “Class AB plus B” mode. These three basic operating conditions of the Multi-Mode circuit vary more or less continuously throughout the signal waveform and are separately determined for the positive and negative portions of the waveform cycle.

The Power Line 3 is protected against overdrive or improper load conditions by several internal systems. A fast-acting limiter instantaneously holds the output power to a maximum safe value in the event of an output short or undesirably low load impedance. According to Crown, this circuit produces a muffled snapping sound when it operates, but it will not be activated if the load impedance is 4 ohms or higher. Since the Power Line 3 is completely direct-coupled from its input jacks to the speaker outputs, the speakers are protected with a low-frequency interrupt circuit that places the amplifier in a stand-by mode if it senses more than 10 millivolts of direct current at the output. Each channel has its own thermal protection system, which also places the amplifier in stand-by mode until it has cooled to a safe temperature. Finally, an a.c.-line fuse protects the entire amplifier against a catastrophic internal failure. The very comprehensive manual for the Power Line 3 provides recommendations for fusing the speaker lines externally.

The Crown Power Line 3’s front panel has a silver-colored satin finish with matching handles and knobs. The chassis and large heat-sink fins that extend to the rear are finished in fiat black. The front panel contains a pushbutton power switch, two in-put-level knobs with thirty detented settings, and a headphone jack. Two groups of colored LED’s between the knobs, designated a “Frequency Analyzing Display,” show the approximate frequency content of the program (for each channel, yellow, green, and red lights, respectively, come on for low-, medium-, and high-frequency signals). Above the display are two red lights marked IOC (input/output comparator). The Power Line 3 has circuits that constantly compare the input and output waveforms, and any difference between them causes the corresponding channel's IOC light to flash. This is a very sensitive type of clipping indicator whose warning signal precedes any audible distortion.

On the rear of the Crown Power Line 3 are two pairs of five-way binding posts for the speaker outputs and a slide switch that connects the amplifier for bridged mono operation. In the mono mode, the power ratings and recommended load impedances are doubled (to 180 and 280 watts and 16 and 8 ohms), the signal is connected to the left input, and the speaker is connected to the two “hot” output terminals. The two phono-input jacks and the line fuse complete the rear-apron features.

The Crown Power Line 3 is 19 inches wide, 10-l/8 inches deep, and 5-1/4 inches high (the handles extend 2-3/8 inches in front of the panel). It weighs about 25 pounds. Price: $949.

Laboratory Measurements

Following its preconditioning period, the exterior of the Crown Power Line 3’s chassis (and especially its heat-sink fins) was very hot to the touch, although no part of it became more than faintly warm to the touch after hours of normal listening operation. The 1,000-Hz output clipped at 104 watts per channel into 8 ohms, 169 watts into 4 ohms, and 53 watts into 2 ohms. The clipping headroom was approximately 0.63 dB for 8 ohms and 0.82 dB for 4 ohms. With the 20-millisecond burst signals of the dynamic-power test, the maximum output was 124, 191, and 51.2 watts, respectively, for loads of 8, 4, and 2 ohms. The dynamic headroom was 1.4 dB for 8 ohms and 1.35 dB for 4 ohms.

With both channels driving 8-ohm loads at 1,000 Hz, the harmonic distortion was less than 0.002 per cent from below 1 watt to beyond the 90-watt rated output of the amplifier. With 4-ohm loads it was typically about 0.002 per cent up to 100 watts, rising to 0.0035 per cent at 150 watts and 0.0047 per cent at 160 watts. Distortion measurements could not be made over the full range of power outputs with 2-ohm loads because of the operation of the protective system at higher power levels, but the distortion was in the range of 0.003 to 0.005 per cent up to at least 10 watts output.

At the rated 90-watt output into 8-ohm loads, the distortion was about 0.002 to 0.003 per cent in the midrange, rising below 100 Hz and above 4,000 Hz to maximum readings of 0.09 percent at 20 Hz and 0.02 per cent at 20,000 Hz. At half-power and one-tenth power the distortion was very nearly the same as at full power. The IHF intermodulation (IM) distortion was measured with 18- and 19-kHz input signals at a peak output equal to that of a 90-watt sine-wave signal. The second-order distortion at 1,000 Hz was not detectable (it was less than —96 dB), and the third-order component at 17 kHz was —92 dB relative to 90 watts. The amplifier’s slew factor was 3.2, with the full-power waveform changing from sinusoidal to triangular at about 65 kHz. The Power Line 3 was stable with reactive simulated speaker loads and with a standard IHF reactive load.

The amplifier’s sensitivity for a 1-watt reference output was 0.135 volts, and the A-weighted noise level was below our measurement limit of —90 dB referred to 1 watt. The frequency response was flat down to 5 Hz (our lower measurement limit) and down by 0.1 dB at 20,000 Hz and 3 dB at 160 kHz. The Frequency Analyzing Display operated with an output as small as 1.5 milliwatts, making it visible under all normal listening conditions. The low light was on for frequencies between 5 and 180 Hz, the med light was on from 180 to 2,500 Hz, and the high light was on for frequencies higher than 1,700 Hz.

Comment

Obviously Crown’s engineers have devoted considerable effort and ingenuity to their Multi-Mode circuit design, and we do not doubt that it works as described. In our listening tests, repeated A/B comparisons between the Power Line 3 and two other, more powerful amplifiers failed to reveal any audible differences, which did not surprise us in view of the three units’ almost identical measured performance (except for output power).

The Power Line 3 is an absolutely first-rate product, solidly built and attractively styled. From its nominal 90-watt rating it might seem to be a relative lightweight (middleweight?) in terms of output power, but it is well equipped to hold its own against almost any amplifier on the market. And with the many speakers whose actual impedance falls to 4 or 5 ohms at some frequencies, the Power Line 3 begins to show some of its true mettle. Touching the exposed metal surface of the amplifier during and after an extended period of operation gives convincing evidence of its high effective operating efficiency; very few components we have tested—let alone high-powered amplifiers—run as cool as this one.

The IOC indicators are a truly useful feature since they give an extremely accurate indication of the onset of clipping. If they are not lit, the amplifier is not distorting, period. This is in sharp contrast to the “power” displays featured on many receivers and other amplifiers, whose true function seems to be merely cosmetic. On the other hand, we were unable to figure out any really useful purpose for the Frequency Analyzing Display other than to provide a mild form of visual entertainment.

The Crown Power Line 3 is a rather expensive amplifier, and buyers of products in its price range are usually looking for special qualities beyond mere low-distortion amplification. Crown’s products in general stand apart from the mass of consumer audio components by virtue of their design features, ruggedness, and distinctive appearance. The Power Line 3 obviously belongs in the Crown family. Its design, function, and performance all reflect the company’s long tradition.

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