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HIFIREVIEW Harman Kardon PM665Vxi 150 watt stereo amplifier Harman Kardon is back. Those who remember this quality brand, originally made in the USA, will be delighted to learn that Harman Kardon products are as good as ever and again available in Australia. To set the ball rolling we review their top of the line integr·ated amplifier, the PM665Vxi. By LEO SIMPSON Harman Kardon refer to their PM665Vxi amplifier as a high voltage/ high current design. Arguably, it is a high current amplifier, as it is rated to deliver peak currents to the loudspeakers of up to ± 80 amps. This enormous current capability is provided so that the amplifier can cope with speakers which have very low impedances when fed with dynamic signals (ie, music instead of steadystate sinewave signals). It is also a relatively high power amplifier, rated to deliver 150 18 SILICON CHIP watts per channel into 80 or 40 loads. That equal power rating into 80 or 40 loads is interesting because most amplifiers deliver quite a lot more power into 40 loads. This is a natural consequence of the fact that a power amplifier is a close approximation to a voltage source (ie, it has a very low output impedance) and therefore delivers more power into lower impedances. On the PM665Vxi, Harman Kardon have turned that convention around by providing two switches on the back panel, to select the load impedance, 40 or 80. We did not have a circuit of the unit at the time of writing but we deduce that the switches change the supply voltage to the output stage: high for 80, lower for 40. The reason for doing so becomes clear after the amplifier has been running for half an hour or so; it gets quite hot. Evidently it operates with a high quiescent current (ie, the current when no signal is present) as part of the Harman Kardon philosophy of designing their amplifiers with a minimum of negative feedback. By operating with a high quiescent current the amplifier will effectively be in class-A mode for most of the time and so will be inherently more linear: hence less need for negative feedback. However, because of the relatively high quiescent current the designers have then sought to an apparent difference to the amount of boost and cut available. In the hands of a knowledgeable user variable turnovers can be worthwhile but with average listeners they could be a source of confusion. For the latter people we'd suggest they select 200Hz and 2kHz and leave it at that. The purists are catered for too, of course, and the tone controls can be switched right out of circuit with the Tone Defeat switch. Capacitance trimming The interior of the PM665Vxi is dominated by two large finned heatsinks and by two large power transformers on the lefthand side. Both the cover and bottom panels are entirely covered with ventilation slots to dissipate the heat from the heatsinks. minimise the increase in power dissipation caused when the amplifier is actually driving the load. To do this, the supply voltage is reduced when 40 loads are to be driven. This also gives a margin of safety for the output transistors, especially when they are called upon to deliver the very high currents they are rated for. The PM665Vxi is a big beast. It measures 443mm wide, 134mm high and 398mm deep, including knobs, rubber feet and rear projections. It is heavy too, weighing in at 14.2kg. Harman Kardon styling is strictly conventional; finished in black, with fine gold lettering. Along the lower half of the front panel is a row of rotary controls while along the top is a row of tiny pushbuttons to engage various functions. All the usual functions are there plus a lot of others. In fact, it is probably one of the most feature-laden integrated amplifiers presently available. For example, the tape monitor switch doubles as a VCR selector so it switches video signals as well as the stereo audio signals from hifi or stereo VCRs. Dubbing between two VCRs or two tape decks is provided by the Record Out switch, which is right next to the Tape Monitor switch. Turnover switches A comparatively rare feature on integrated amplifiers these days is the provision of variable turnover on the bass and treble controls. "Turnover" refers to the 3dB (ie, half power) boost or cut frequency obtained when the tone controls are set to their maximum or minimum settings. On most stereo amplifiers the bass turnover frequency would be around 300Hz while the treble turnover would be around 2kHz. The PM665Vxi has pushbutton selectable turnovers at 200Hz and 400Hz for the Bass control and 2kHz and 6kHz for the Treble. Usually, changing the turnover frequency will not markedly affect the maximum amount of boost and cut at the upper and lower audible frequencies but it will make quite An even rarer feature on amplifiers is the provision of capacitance trimming for the moving magnet cartridge inputs. This is very worthwhile since the flatness of frequency response obtainable from magnetic cartridges can vary quite markedly, depending on the load capacitance. To give optimum flatness in the high frequency response some cartridges require 200pF of capacitance or less while others require up to 500pF or more. Typically, the leads from the turntable to the amplifier will provide about 100-150pF of capacitance in each channel while the preamplifier inputs will typically add another lO0pF or so. By contrast, the "Cap Trim" switch on the PM665Vxi gives input capacitance loadings of normal (125pF), + l00pF, + 200pF and + 300pF. This gives a minimum capacitance of 125pF and a maximum of 425pF, so if you know the capacitance recommended by the manufacturers of the cartridge, you can pick the closest setting. The Harman Kardon also has a pair of phono inputs to cater for moving coil cartridges, as selected by a small button to the right of the Volume control. Some larger integrated amplifiers can be split into separate preamplifier and power amplifier stages by pulling out ·a couple of · bridging links between two pairs of RCA sockets on the rear panel. On the PM665Vxi, the four sockets are there (labelled Pre-out and Main-in) but instead of the bridging links there is a switch on the front panel. Other small pushbuttons are provided for Loudness, Subsonic and High Cut filters, Mode (mono or DECEMBER1988 19 The PM665Vxi has comprehensive facilities and includes a number of RCA sockets with yellow centres to distinguish them as video inputs and outputs. Two slider switches (top right) are used to select the load impedance (either 40 or 80). stereo) and Mute. We should note, at this point, that it is hard to tell the settings of these buttons at a glance, especially if the lighting is dim, which is normally the case in typical living rooms. This is not helped by the very small printing for -the labelling on the front panel. We believe this is too small for most people to read easily. On the rear panel, there is the usual array of RCA sockets for input and output signals and there are a number of RCA sockets with yellow centres to distinguish them as video inputs and outputs. The speaker terminals are good, being those shrouded binding posts which will take heavy wires. These are better than the spring-loaded terminals found on many stereo amplifiers. Ventilation This amplifier is one that should not be stacked with other equipment because it needs plenty of ventilation. Both its cover and bottom panels are entirely covered with ventilation slots to dissipate the heat from the large internal heatsinks. Removing the top cover reveals more details of the interior which is dominated by the two large power transformers on the lefthand side of the chassis. These make the unit much heavier on the left and somewhat difficult to lift, for that reason. 20 SILICON CHIP Specifications Continuous power output Rated harmonic distortion Power bandwidth Output current capability Frequency response Signal-to-noise ratio (with respect to rated power, A-weighted) Phono overload (at 1 kHz) Filters Dimensions Weight Both transformers are wellshielded to cut down on hum leakage. They are fitted with copper straps and metal sheathing over the laminations. This is particularly important in an amplifier which has to handle video signals as well as low level audio signals. As far as we can tell without access to a circuit, the power supply appears to be quite conventional, employing 16,400µF of capacitance for both the positive and negative supply rails. Gleaning information about the power amplifiers is more difficult but the output stages appear to use high power Darlington 1 50W into 40 or 80 (both channels driven) 0 .08% into 80; 0 .1 % into 40 1 OHz to 1 OOkHz ± 80 amps peak 0.2Hz to 150kHz, -3dB 80dB phono {moving magnet) 76dB phono {moving coil) 98dB video/CD 11 OdB main in {power amp only} 220mV RMS {moving magnet); 12mV RMS (moving coil) 6kHz, 6d8/octave {high cut); 15Hz, 6d8/octave (subsonic) 443 x 134 x 398mm 14.2kg (ie, bipolar not Mosfet) transistors which have large plastic encapsulations. There are four such transistors in each channel. Wide bandwidth Harman Kardon have a policy of using discrete components throughout their circuits. This is necessary, apart from anything else, because this company is noted for designing its amplifiers with very wide bandwidth. This amplifier certainly follows that philosophy. The frequency response from the high level inputs is quoted as 0.2Hz to 150kHz, at - 3dB points, at a power level of 1 watt. Similarly, the half-power bandwidth is quoted at lOHz to lOOkHz. These figures are quite exceptional. We had no trouble in confirming them. SPECTACULAR ELEASE vHa Performance Rated power output from the PM665Vxi is quoted at 150 watts per channel into 80 or 40, with both channels driven. Rated harmonic distortion is less than .08 % for 80 loads and less than 0.1 % for 40 loads. Our tests easily confirmed the power output although the typical distortion figures were somewhat better than those claimed. We measured around .02% across the board. Actually, a harmonic distortion figure of .02 % is not particularly low these days and competitive amplifiers would measure considerably better. However, Harman Kardon's figure is to be expected, as a result of designing the amplifier with a mm1mum of negative feedback. Even so, a figure of .02% is still very respectable. Rather than go through each performance parameter we can report that we were able to confirm all the other specifications listed in the separate panel. The telling is much quicker than the doing, of course, as it takes almost a whole day to confirm all the specs in a comprehensive integrated amplifier such as this. Sound quality And what about sound quality? It's every bit as good as you'd expect a top quality amplifier to be. With its comprehensive control facilities, bags of power, solid construction and conservative design, it is sure to give many years of musical satisfaction. If you're in the market for a new stereo amplifier, you should give the Harman Kardon range a careful audition. Recommended retail price for the Harman Kardon PM665Vxi is $1995. For further information, contact the Australian distributors Convoy International Pty Ltd, 400 Botany Road, Alexandria NSW 2015. Phone (02) 698 7300. ~ NEWSA-100 SPEAKER KIT Since the introduction of VIFA speaker kits in Australia in 1985, thousands of speakers have been built with superb results. VIFA is now proud to release four new speaker kits ranging from a mere $399 to $1199 per pair including cabinets. Never before have speaker kits been so popular in Australia than after the heavy devaluation of the dollar. Similar fully imported quality loudspeakers are today typically 2-2½ times more expensive. And these speakers may very well be using Danish VIFA drivers anyway, as VIFA supply more than 50 of the world's most respected loudspeaker manufacturers with drivers. But why the big savings? Because fully imported speakers suffer from 25% import duty, 20-30% freight, 30% sales tax and 28% handling charges (typically). So if you would rather put your money into better quality than in other people's pockets, VIFA speaker kits are the only way to go. Are they difficult to build? No, the kits are supplied with all parts needed including fully built crossovers and pre-cut flatpack cabinets ready to assemble. No soldering or carpentry skills are needed, just a Phillips head screwdriver, some simple hand tools and a few hours of your leisure time. Are they as good as people say? Read the reviews, listen and compare with any other speakers twice the price or more. Need we say anymore? VIFA for the quality conscious audiophile. For full details please contact Sole Australian Distributor: SCAN AUDIO Pty. Ltd. P.O. Box 242, Hawthorn 3122. Fax (03)4299309 Phone: 4292199 (Melbourne) (02 5225697 (Sydney) (0 3577433 (Brisbane) (09 3224409 (Perth) Stocked by leading stores throughout Australia (O! Polystyrene capacitors YES Made here in Australia? YES Made Special to Type? YES Where From? Allied Capacitors Australia Allied Capacitors Australia specialises in custom made good quality, high stability polystyrene capacitors . Why design circuitry which requires additional components to achieve a specific capacitance ; we can wind exactly the capacitance you need to match your design criteria within the ranges of 1OpF to 1 µF and up to 10,000VDC. Capacitors are manufactured to 0 .25%, 0.5%, 1.0%, 2.0% , 2.5% , 5%, 10% and 20% and are priced according to tolerance. All capacitors are tested to 2.5 times the rated voltage. ~--wwwwwwwwww · Interested? Call us now on: (02) 938 4690 OR Cut out and post this coupon to Post Office Box 7 40 Brookvale, N.S. W. 2100 I Yes, I am interested in your capacitors. I Please post me details of the following values: . .. I . .. VDC ... I . . . VDC ... I . .. VDC . .. I . . . VDC . Name (Please print) Address ~-------------~-~~~~~~~~~~~J DECEMBER1988 21