Soundcraftsmen PCR800 Power Amplifier Review
Designing an amplifier that is relatively compact, lightweight, and inexpensive but can deliver large amounts of "clean" power is an engineering problem that calls for innovative solutions. One answer comes from Soundcraftsmen in the form of a power amplifier that uses a technique called phase-control regulation in its power supply.
The technique is an efficient and space-saving means of controlling the average power supplied to the output stages of an amplifier without compromising the performance of those stages. The result, Soundcraftsmen's PCR800, can deliver 205 watts per channel, yet it weighs less than 21 pounds and measures only 8-1/2 x 12 x 4-7/8 inches.
Also contributing to the amplifier's impressive overall performance is the use of power MOSFET's (metal-oxide semiconductor field-effect transistors) in the output stages. These transistors are inherently free from "thermal runaway" effects, which can easily destroy a typical bipolar-transistor output stage unless it is protected against excessive output current.
The PCR800 has no conventional current-limiting protection circuitry, but it is able to drive low load impedances (even a short circuit) indefinitely without damage or even a temporary interruption of service. Low-impedance power ratings are 300 watts per channel into 4 ohms and 275 watts into 2 ohms. Bridged operation turns the PCR800 into a 600-watt mono amp.
Since the MOSFET's will get hot under extreme high-signal conditions, the amplifier is fan-cooled. Air enters in the rear and exhausts through slots in the front panel. Normally the fan runs very quietly at a low speed. Thermal sensors on critical parts of the amplifier will increase the fan speed with rising temperature, however.
In normal service, the PCR power supply delivers just enough current to the amplifier to meet the output-signal requirements, thus minimizing the generation of unnecessary heat in the unit. Continued high-level operation causes the supply gradually to reduce the voltage to the output stages, thereby limiting the maximum deliverable power and the corresponding heat generated to safe values without shutting the amplifier down. Price: $449.
When we drove the PCR800 at one-third rated power for the standard FTC preconditioning process, its fan switched to high speed within a minute or two. Before the required hour had passed, the PCR circuits had reduced the amp's supply voltage sufficiently to limit the output to perhaps 30 or 40 watts (which is still adequate for most home listening needs). The amplifier's exterior remained cool except at the air-exhaust slots. Within a couple of minutes after we reduced the drive level, it returned to normal operation and the fan speed was lowered. During our measurements of distortion and clipping power, the fan frequently speeded up (this has no effect on the operation of the amplifier), but it usually slowed down again within moments after we reduced the input signal. The red TRUCLIP LED indicators glowed when either channel's output was clipped even slightly. There were no unwelcome surprises during our tests, and the amplifier appeared to live up to the "bulletproof" status that is implied by the manufacturer's literature.
The clipping headroom of this amplifier was somewhat less than we have been measuring in recent times. Since it generally met or surpassed its performance specifications, this merely suggests to us that the published specifications of the amplifier are closer to its actual performance than those of some other amplifiers. It was also interesting to find that the dynamic headroom was less than we have measured on many other amplifiers. This is probably due to the tight regulation provided by the PCR power supply, in contrast to the essentially unregulated supplies of many other amplifiers. In fact, when driving 4- and 8-ohm loads, the dynamic output was actually less than the steady-state clipping output.
The distortion of the PCR800 was not only very low, but always decreased with decreased power output (many amplifiers have more distortion at lower power levels than at rated power). Across the full audio range, the distortion never exceeded 0.035 per cent at any power up to rated output, and even driving 2-ohm loads did not result in unduly high distortion. The amplifier was completely stable driving complex simulated speaker loads.
Our only reservation about the PCR800 concerns its fan cooling system. A cooling fan must not be audible in normal amplifier use, or the amp's designer's best efforts in reducing noise and distortion come to naught. This is especially important for digital program sources, with their dead-silent backgrounds. While the fan of the PCR800 is one of the quietest we have used, it can be heard in a very quiet room. In its high-speed mode, the only word describing the fan is loud, but fortunately this is unlikely to happen in a home system unless you are playing rock music at a fairly high "live" level-and then even the fan noise will be masked by the music! Of course, in many installations it may be possible to enclose or shield the amplifier or to locate it where its fan cannot be heard. We urge you to audition not only the amplifier but also its fan.
The fan, however, is part of the PCR800's design that contributes to the impressive ruggedness of the amplifier as well as its excellent electrical characteristics. Its designers aimed to make it withstand almost any of the common amplifier abuses and no doubt a few of the less common ones! We should say that they hit their target squarely. This is a lot of amplifier for the money, totally functional in its design, both electrical and physical. For example, we found the two clipping indicator lights more informative and useful than a front panel full of LED's or meters.
Two of these amplifiers operated in the bridged mode would make an impressive and extremely powerful pair. Soundcrafitsmen sells a Combi-Dapter ($49) that will hold two PCR800's in a single chassis that is the same width as a normal hi-fi component.
On the whole, the Soundcraftsmen PCR800 is a fine amplifier - powerful, rugged, reliable, compact, and lightweight-and it is very reasonably priced as well. One could hardly ask for more.