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.)

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.)

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.)

The cab's outside, the plane leaves in 50 minutes. Let's see...<A HREF="http://www.stereophile.com//amplificationreviews/530/">HeadRoom Supreme</A>, <A HREF="http://www.stereophile.com//accessoryreviews/531/">HeadRoom Bag</A>, portable CD player, CDs, Etymotic ER-4S Canal Phones....Oh, yeah&mdash;mustn't forget luggage or plane tickets. Guess I'm set to go.</I>

The cab's outside, the plane leaves in 50 minutes. Let's see...<A HREF="http://www.stereophile.com//amplificationreviews/530/">HeadRoom Supreme</A>, <A HREF="http://www.stereophile.com//accessoryreviews/531/">HeadRoom Bag</A>, portable CD player, CDs, Etymotic ER-4S Canal Phones....Oh, yeah&mdash;mustn't forget luggage or plane tickets. Guess I'm set to go.</I>

The cab's outside, the plane leaves in 50 minutes. Let's see...<A HREF="http://www.stereophile.com//amplificationreviews/530/">HeadRoom Supreme</A>, <A HREF="http://www.stereophile.com//accessoryreviews/531/">HeadRoom Bag</A>, portable CD player, CDs, Etymotic ER-4S Canal Phones....Oh, yeah&mdash;mustn't forget luggage or plane tickets. Guess I'm set to go.</I>

The cab's outside, the plane leaves in 50 minutes. Let's see...<A HREF="http://www.stereophile.com//amplificationreviews/530/">HeadRoom Supreme</A>, <A HREF="http://www.stereophile.com//accessoryreviews/531/">HeadRoom Bag</A>, portable CD player, CDs, Etymotic ER-4S Canal Phones....Oh, yeah&mdash;mustn't forget luggage or plane tickets. Guess I'm set to go.</I>

<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)

<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)

<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)