Phase Linear Dual 500 (1978)

Five hundred and five watts per channel, thirty-six output devices, and a rear heatsink the size of a small briefcase — Phase Linear's Series Two statement piece.

Overview

Phase Linear built the Dual 500 Series Two around a single, uncompromising number: 505 watts per channel into 8 ohms, measured from 20 Hz to 20 kHz with total harmonic distortion held to no more than 0.09 percent. That is the figure the company led with in its 1978 advertising, and it is the figure that defines the amplifier. The Dual 500 is not a subtle piece of equipment — it is a power amplifier engineered to deliver headroom that most loudspeakers of the era could only dream of demanding.

The design rationale, as Phase Linear's own advertising framed it, is worth understanding. The company argued that a loudspeaker reproducing a musical peak can require up to ten times the average power being delivered. If the amplifier lacks sufficient reserve, it clips, and clipping produces distortion that audibly degrades the sound. The Dual 500's answer to this is brute-force power reserve, delivered through an output stage whose power semiconductor complement the manufacturer rated at 8000 watts. Audio (June 1978, p.13) carried the company's claim that this represented the highest power-handling capability in the audio industry at the time.

The output stage itself is built around 36 output devices, mounted on a massive rear-mounted extruded aluminum heat sink assembly. That heat sink is not decorative. It includes a self-contained, thermally activated forced-air cooling system — in plain terms, a fan that kicks in when the amplifier gets hot.

The front panel carries an exclusive 32-segment LED display for instantaneous indication of output activity, paired with a special 4-segment clipping indicator that warns of hazardous overloads. For a certain kind of listener, that LED array is the whole point — watching the segments light up with the music's dynamic peaks turns the amplifier into a piece of visual equipment as much as an audio one. The clipping indicator is the more practical feature, giving an honest warning before the amplifier runs out of headroom.

One of the Dual 500's more interesting design choices is its high/low impedance operating modes, which can be activated either automatically or manually. The purpose is increased amplifier efficiency when driving low-impedance speakers. The manufacturer designed the amplifier to handle speaker impedances down to 2 ohms, which makes it adaptable to both demanding home applications and rugged professional use. Electronic energy limiters and independent fusing of the power supply are also part of the package, intended to prevent the possibility of damaging overloads — a meaningful inclusion given the amplifier's output potential.

The Dual 500's place in the Phase Linear story is worth noting. According to the company's own advertising, Phase Linear introduced what it called the first real high-power, high-fidelity amplifier in 1971, and the Series Two line — highlighted by the new Dual 500 — represented the next step in that lineage. A separate period report cited a slated price of $1,395.00, so buyers may encounter either figure depending on the source and the date.

What the Dual 500 represents, more than anything, is a particular philosophy of audio design: that power reserve is not a luxury but a requirement, and that the way to achieve it is through sheer output-device count and thermal engineering. Whether that philosophy appeals is a matter of taste. The amplifier does not flatter; it controls. For owners who prize grip and headroom over coloration, that is exactly the point.