LATEST ADDITIONS

About three weeks ago, while perusing the gear in a local audio retail establishment, I overheard a salesman, who could well have been selling used cars, giving a classic spiel to an obviously confused customer. "You see, sir, all preamplifiers basically sound alike, especially with line-level inputs. The only differences are in the number of features." He went on to tell his prey that spending big bucks for high-end products such as Krell or Mark Levinson (neither of which he sold) would be a big mistake. I choked back my automatic response of a certain bovine term, but thought it better to continue my fly-on-the-wall masquerade.

As mentioned by two readers in this month's "Letters," amplifiers are used to drive loudspeakers but are almost exclusively measured into resistive loads. The reasons for this are twofold: 1) real loudspeakers both produce neighbor-annoying sound levels and tend to break when driven with typical amplifier test signals; and 2) the question as to which "standard" loudspeaker should be used is impossible to answer---at least the conventional resistive loads are consistent and repeatable.

The D-250 is the flagship of Audio Research's power amplifier range and, at 250 watts per channel, is the most powerful all-tube stereo amplifier currently available in the US. Under the circumstances, then, it is not surprising that it should also be one of the heaviest and largest.

The $395 NAIT, rated at 20Wpc, is a good-sounding little amp. It's very open and spacious-sounding, but, like the $250 Rotel RA-820BX, sometimes sounds a little hard in the upper registers.

I remember having a conversation with an audiophile some time ago about the thorny subject of choosing an amplifier. He was convinced, on the basis of an article he had read in <I>Stereo Review</I>, that all amplifiers of a given power rating sound pretty much the same. Although he was sufficiently well off to buy just about anything on the market, he didn't want to waste his money. He chose the amplifier for his system by going through the <I>Audio</I> Annual Directory Issue, calculating the price:watt ratio for each amplifier that was listed, and then bought the amplifier with the lowest price/watt figure that had enough power to drive his speakers. He didn't do any comparative listening and didn't consider buying anything that cost more for the same power, because he knew already that it wouldn't sound any different.

This is something we don't see too often: an entirely new approach to power amplifier design. As Quad points out in its literature for the 405, class-A operation of transistors provides the lowest distortion, but drastically limits the amount of power an output transistor can deliver without overheating. (Most transistor amps use class-AB output operation, in which each of a pair of power transistors handles part of each signal cycle and shuts down during the other part. Imperfect synchronism between the two halves causes the familiar "crossover distortion," which accounts for most solid-state sound. In class-A operation, each output transistor draws current though the entirety of each signal cycle, eliminating the crossover transition but doubling the amount of time current is drawn, and thus tending to cause the transistor to heat up more.)

<I>A truly great preamplifier lets everything through, both music and distortion, but with such generosity that neither...is cramped and narrow.</I>&mdash;<B>Larry Archibald</B> (footnote 1)