Ortofon PPA600 Power Amplifier Review

The Ortofon PPA600 professional power amplifier is a rugged, powerful unit capable of delivering high-power outputs to low-impedance loads for extended periods without overheating or damage. Although it is relatively compact, the amplifier’s weight of almost 50 pounds reflects its solid construction.

The PPA600 is built on a steel chassis and has a steel cover plate, retained by eighteen screws, that all by itself is as heavy as some full-size CD players. Handles about 3/4 inch in diameter are mounted on both the front panel and the rear apron, where their 2-inch depth allows the amplifier to stand upright without damage to its output connectors. The front panel, slotted for rack mounting, measures 19 inches wide, 5-1/4 inches high, and 3/8 inch thick (thinning to 3/16 inch at the outer edges). The amplifier extends 13-3/4 inches behind the panel, and its rear apron contains two pairs of heavy-duty binding-post speaker outputs and line-level inputs through standard 1/4-inch pnone jacks. Two paralleled jacks are supplied for each channel to simplify paralleling the inputs of a number of amplifiers. The PPA600 has separate grounding terminals for the amplifier circuit and the metal chassis; these are normally joined by a wire link, but they can be separated for multiamplifier installations that require isolated grounds.

A good fraction of the amplifier’s internal volume is occupied by a huge toroidal power transformer. The manual indicates that the two channels operate as independent mono amplifiers, and from our examination of the interior it looked as if the power transformer has two windings connected to separate rectifiers and filter capacitors that supply the two channels.

Although the front panel is deeply grooved to resemble a heat sink, this is largely a matter of appearance. The power-output stages are assembled as a unit with a square cross section to form a horizontal chimney, one end of which is open to a 4-inch hole at the left side of the panel. Behind the rear opening of the chimney is the exhaust fan on the rear apron, which draws outside air through the chimney to cool the output transistors. The top cover is also screwed to the chimney to help conduct heat away from the amplifier circuits.

The thermostatically controlled fan does not begin operating until the heat-sink temperature rearhes 35°C (95°F). Its speed increases with temperature, and in the event that the internal temperature reaches 70°C (148°F) the affected channel shuts down, resuming operation when the temperature drops to 60°C (140°F).

The front panel has separate LED status lights for each channel. The green power lights come on when the amplifier is turned on. When a signal is applied, the green SIGNAL lights glow, and if the amplifier is driven into clipping, red OVERLOAD lights flash. They may remain on for a few seconds if the amplifier’s current limits are exceeded and also remain on if a constant (DC) voltage appears at the output terminals. A pair of green bridge lights show that the amplifier has been set to its BRIDGED mono mode by a switch on the rear apron.

The front panel also has separate level controls for the two channels. They are detented, operating in 1-dB steps near their maximum settings, 2-dB steps over much of their range, and 5-, 10-, and 20-dB steps at their minimum settings.

The Ortofon PPA600 is rated at 225 watts per channel with both channels driven into 8 ohms from 20 to 20,000 Hz with no more than 0.1 percent total harmonic distortion. The 4-ohm rated power is 350 watts per channel, and the 2-ohm output (with one channel driven) is rated at 600 watts. In the mono bridged mode, the rated 8-ohm output is 650 watts, increasing to 950 watts into 4 ohms. Other ratings include a 20,000-ohm input impedance, a frequency response of 10 to 60,000 Hz +0, —3 dB, and a damping factor of greater than 250. Price: $2,000

Comments

Our tests of the Ortofon PPA600 showed that it has the muscle and ruggedness to serve even in demanding professional applications. Not only did it withstand accidental output short-circuits with no ill effects, but it ran cooler (even during the grueling preconditioning period) than almost any tuner, CD player, or other component that we have tested. It is hard to imagine how it could become overheated under any operating conditions short of a lack of air for cooling (the installation instructions caution against impeding its fan drive air flow).

Unlike some high-power audiophile amplifiers, the PPA600 can be lifted by one man without risk although it does feel heavier than it is, possibly because of its compact dimensions. It is electrically stable and is one of the very few fan-equipped amplifiers we have used that is quiet enough to install in a music room.

Our examination of the amplifier’s interior revealed that the input-level controls, which feel like step switches with rather light and vague detents, are actually continuously variable potentiometers (miniature volume controls). The detent is external to the control, and, in fact, the level can be set to values between the detent steps, although this requires some care. Under the circumstances, it would seem that the detents could have been omitted entirely without impairing the usefulness of the amplifier. We also noted that the heavy binding-post speaker connectors on our sample were spaced almost 3/4 inches apart, but not exactly, so it was not possible to insert dual banana plugs. As the discrepancy was only about 1/32 of an inch, we assume that this was a sample defect.

Although professional audio equipment is usually not particularly suited to home use, even without considering its high price, the Ortofon PPA600 appears to be an exception to that rule. It gives every appearance of being an indestructible battleship of an amp tier that manages to do everything expected of a fine home amplifier. In fact, it had no operating or listening vices that we could discover. And although it is capable of operating safely in closed spaces, it looks good enough to be placed in full view.

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