Philips AH-572 stereo preamplifier (Equip. Report, Nov. 1977)

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A Distinctly Unconventional Preamp from Philips

The Equipment:

Philips AH-572, a stereo preamplifier in metal case.

Dimensions: 18 by 6 inches (front panel), 13 3/4 inches deep plus clearance for controls and connections.

Price: $599.95.

Warranty: "limited," two years parts and labor.

Manufacturer:

Philips High Fidelity Laboratories, P.O. Box 2208, Fort Wayne. Ind. 46801.

Comment: Philips, in the AH-572, has addressed itself to a question that is, we suppose, as old as high fidelity itself how is one to build a full-feature preamp (or any other unit of similar complexity) so that its workings can be under stood at a glance even by the uninitiated? The Philips answer is an illuminating front-panel block schematic whose various elements turn on and off along with the feature each represents. This is one of the innovations that claim the attention immediately: the other is the capacitance switching. Instead of pushbuttons or levers. Philips has elected to use ridged touch plates, with integral LEDs to show whether the switching action is on or off.

In combination these two elements-cosmetic though they admittedly are-set the AH-572 apart from the com petition. The luxury/convenience personality that they establish is a major factor in both the enjoyment and the utility inherent in the product. But they are not entirely successful in the utility department. In keeping the "schematic" simple, Philips has omitted some functions (the filters and tone defeat, for example) whose operation therefore can be checked only at the LEDs: the output se lectors (the user has the choice of two switchable outputs) conversely are indicated both on the schematic and on the LEDs. Also, we would suggest that the front panel should be placed so that it won't be touched accidentally: you can trigger the capacitance switching without being aware of it when your hands are busy in the immediate vicinity. In addition, the LOUDNESS stopped working on our samples-a problem Philips says it found and corrected in all but the earliest. Buyers whose loudness switching misbehaves can get the fix at a warranty station.

In spite of these cavils, the concept is attractive and, for the first time around at least, well executed. It is complemented by a couple of nice touches on the back panel.

There are two unswitched convenience outlets (rated at 200 watts apiece) and two that are switched (100 watts apiece)--a generous array. There is a master power switch.

(With it on and the front-panel power touch-plate off, there presumably is a slight drain to activate the touchplate; but the various operations triggered by the touch-plates, draw current only while the plates are being touched-meaning, for one thing, that when you kill the power by any of the available means, including pulling the plug, the switches will remain on or off as they were beforehand once the power is restored.) Finally, there are four screwdriver phono-sensitivity adjustments, one for each channel and for each of the phono inputs.

The as-delivered performance of these inputs is shown as measured by CBS in the "Additional Data" table; the sensitivity of each is exactly on Philips' specs and can be varied from 1.5 millivolts to 17 millivolts. The former extreme-sensitivity setting yields a signal-to-noise ratio of 67 dB (a little better than spec); at 17 millivolts the S/N ratio measures 82 dB--almost as good as the high-level inputs.

The settings at which you end up using these phono preamp sections will, of course, depend on the output of your cartridge(s) and its relationship to that of your tuner and other ancillary components.

The remainder of the unit's performance too is good (all distortion measurements are, for example, considerably better than spec), though at first glance the lab's square-wave-response photos may not suggest it. The ultrasonic ringing implied by the 10-kHz square wave actually appears to be the result of very sharp filtering just above 40 kHz, which is designed into some preamps to prevent the output from demanding greater slew rate than the associated power amp can deliver-therefore causing transient distortion. Though we obviously could hear no behavior that would have been less good had Philips not limited ultrasonic bandwidth, neither could we detect any ill attributable to the visually "poor" square-wave-response.

The switchable high filter, incidentally, strikes us as well calculated to suppress intrusive hiss: the low filter seems a little over-energetic in attacking rumble since it eliminates an appreciable portion of orchestral underpinning as well.

When the turntable is audibly rumble-free, as one would expect in any price class comparable to that of the 572 it self, something closer to a subsonic filter might be a preferable alternative.

Over-all, the internal design of the preamp strikes us as very good without being as innovative as the external de sign. And it is therefore the externals-the cosmetics, if you will-on which the product will stand or fall in the estimation of the user. This is an exceedingly personal matter, bound to trigger widely diverging reactions, and it there fore must be carefully assessed by each potential user for himself.

----------------- Philips Model AH-572 Preamp----Additional Data

Output at clipping (channels driven simultaneously)

L ch 16 volts R ch 16 volts

Frequency response + 0-1/2 dB. 13 Hz to 20 kHz RIAA equalization + 0,-1/2 dB, 20 Hz to 20 kHz Input characteristics (for 2 volts output) Sensitivity phono 1 2 mV' phono 2 10 m,1* tuner 190 mV aux 190 mV tape A, Et 190 mV Phono overload (clipping point at 1 kHz) phono 1 160 mV* phono 2 800 mV* High filter Low filter Muting S N ratio 68 dB 79 dB 88 dB 88 dB 88 dB

-3 dB at 5 kHz, 12 dB, oct.

-3 dB at 110 Hz, 12 dB /oct

- 20 dB IM distortion (at 2 volts) 0.0024% THD (2 volts output. 20 Hz to 20 kHz)

L ch: .0.0081%

R ch: 0.0086%

*User variable: see text

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