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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quality brand, originally made in the USA, will be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.
~
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DECEMBER1988
21
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