from High Fidelity Magazine, March 1963
AT A GLANCE: The Citation
A by Harman-Kardon is a twin-channel preamplifier and control centre,
to the best of our knowledge the first professional-calibre preamp
to employ "solid-state" (transistors and other semiconductors)
circuitry. As is characteristic of the Citation line, the A boasts
some unusual features and is designed according to wide-band response
philosophy. Measurements made at United States Testing Company,
Inc., indicate that the Citation A literally has flat response to
beyond one million cycles and distortion that is nonmeasurable by
the usual methods. Its listening quality is superb. The Citation
A thus is not only an unsurpassed audio component; it also marks
a major break-through in the application of semiconductors to high
fidelity sound. The model tested was factory-wired and is priced
at $350. The kit version is priced at $250. Dimensions are 14 7/8
inches wide, 5 5/8 inches high, 7 inches deep. Manufacturer: Harman-Kardon,
Inc., 55 Ames Ct., Plainview, L.I., N.Y.
IN DETAIL: The Citation A dramatically demonstrates
that transistors not only can do as well as tubes, but when correctly
applied and used - can do better.
To begin with, the unit has been beautifully styled
and crafted, inside and outside. The front panel contains twenty-one
controls and a stereo headphone jack, yet it does not look cluttered;
and everything is logically placed and neatly arranged. Many of
these controls are familiar, but some are in the professional class,
and not usually found on home audio equipment. Across the top of
the panel are separate bass and treble tone controls for each channel.
These are step-type controls that provide fixed amounts of cut or
boost. When in the "flat" position, they are electrically
out of the circuit and the signal bypasses the associated networks
with the resultant benefit: less distortion. To the right of the
tone controls are: a gain (volume) control that controls both channels
at once; a five-position mode selector (stereo, blend, A+B, monophonic
A, monophonic B); and a six-position signal selector (auxiliary,
tape amplifier, tuner, phono 1, phono 2, tape head). Below the tone
controls are two power switches: one turns on the entire sound system;
the other permits turning off the power amplifier only when listening
with headphones. The headphone jack is located at the lower left
of the panel. To its right is a row of four push-button switches
for channel reverse, rumble filter, loudness control, and tape monitor.
Next are: a blend control that doubles as a volume control for a
derived centre channel; a channel balance control; and a complete
set of tape and disc equalization controls. Disc equalization is
handled by separate turnover and roll-off controls. The tape adjustments
are most unusual in that they provide, separately for each channel,
a means of matching the preamplifier's circuit to the input signals
from an external tape deck by compensating for tape head characteristics
as well as for the capacitance of the connecting cables. They may
be used for tape speeds of 15, 7½ and 3¾ ips.
The rear of the Citation A contains input jacks
for all program sources, as well as two power amplifier output jacks
per channel, a derived centre-channel output jack, and tape recorder
feed jacks. Also, there are three switched AC and one unswitched
AC convenience outlets.
The unit contains a total of thirty-three transistors,
plus four zener diodes and four silicon rectifiers. Its main circuits
are contained in eleven printed circuit modules, each mounted on
its own glass-epoxy board. The boards are fitted into a slotted
rack along the rear of the chassis. Any module can be removed readily
for testing or servicing, as shown in the photograph. Should the
need arise; an entire module can be obtained as a replacement for
any defective stage at nominal cost.
The unit's power supply is rather unusual in design,
and is located at the rear of the chassis to the left. The supply
contains two full-wave rectifier systems, one to obtain the positive
voltages and the other to obtain the negative voltages required
by the preamplifier. The output of each rectifier is fed into a
transistor voltage regulator circuit for constant-value supply voltages
regardless of supply voltage or load current. The zener diodes are
used for added regulation and as voltage references.
preamplifier contains seven individual amplifier modules, each having
three transistors, and each acting as a stage of flat audio gain
and as isolation for the various functional stages such as the equalization
networks, tone controls, etc. Each amplification module, initially
designed to provide 67dB of gain, utilizes 34dB of feedback for
low distortion, and thus has a net, undistorted gain of 33dB. Two
of these modules are used in each channel as low level preamplification
stages with passive equalization networks between the modules. One
module is used as a voltage amplifier in each channel. The seventh
amplifier module is used as the output stage for the derived or
A+B centre channel.
There are also two emitter-follower modules each
containing two emitter-follower circuits. The emitter-follower circuit
is used as a unity-gain impedance-matching device. One emitter-follower
is located at the high level inputs to the preamplifier (just after
the volume control) and a second emitter-follower is found at the
end of the circuit where it feeds the amplifier and headphone output
The preamplifier also contains a two-transistor
time-delay module, which provides a 20-second warm-up period during
which time the preamplifier output jacks are shorted to ground.
The warm-up assures that the preamplifier is disconnected from the
basic or power amplifier until all the energy-storing devices (capacitors)
in the circuit have reached a steady-state condition. This prevents
overloading the power amplifier and driving the speakers too hard
during the warm-up period.
The output impedance of the Citation A is very
low, being on the order of 50 ohms. This value negates any frequency-limiting
effects of cable capacitance to a power amplifier and also is suited
for driving high quality headphones. Citation recommends using 400-ohm
impedance headphones for an optimum match to this output. Lower
impedance headphones may also be used but with a slight increase
in distortion. We listened over a pair of 8-ohm headphones and detected
no distortion. The A's input impedance at its high level inputs
is also rather low, being on the order of 27K ohms. This value helps
maintain the preamp's high-frequency bandwidth and is a suitable
match for most high quality program sources such as FM tuners and
tape deck preamplifiers which themselves have a low output source
impedance, such as a cathode follower. A few high fidelity components
may have high impedance outputs; such units can be used with the
A but with a possible loss of bass response.
Run at full gain, the Citation A provided a maximum
output signal level of 5.8 volts rms per channel. At this level,
frequency response from 20 cps to 20 kc was perfectly flat, within
±0.1dB. USTC then checked its response well below and above
the normally accepted 20-cps to 20-kc audio range. The results were
amazingly good: there was a 1.7dB peak at 1 megacycle, and response
continued beyond this point to 1.5 mc (1,500,000 cps) where it was
down only 3dB. At the low end, response was maintained perfectly
flat to below 5 cps (this frequency is the lowest at which USTC
can make measurements using sine waves). At full gain, then, the
over-all response of the Citation A was found to be +1.7, -3dB from
below 5 cps to 1.5 mc.
Since a preamplifier, however, is seldom, if ever,
operated at full gain, USTC repeated the measurements in the more
rigorous mode of "unity gain" in which the signal leaving
the preamplifier is the same voltage level as that entering it.
Under these conditions, frequency response from below 5 cps was
flat within +0, -1dB to 400 kc, rolling off to -3dB at 620 kc, and
to -7.5dB at 1 mc. This superb response characteristic is not matched
by any other known preamplifier.
The A's square-wave response was equally outstanding,
indicating excellent transient characteristics and virtually no
phase shift throughout its extremely wide range. At the usual test
frequencies of 50 cps and 10 kc, the A reproduced almost perfect
square waves that were hard to distinguish from the input test signals.
Because they were so excellent, USTC went to lower and higher test
frequencies to see just what the limits of this preamplifier were.
At 5 cps, the square-wave response was still nearly perfect, showing
no more than a 5% tilt in the flat portion of the waveform. Going
up in frequency USTC found that a 200-kc square wave—an unusually
high and demanding test signal—still had a very recognizable
and relatively undistorted square-wave shape, with a remarkable
rise-time of only 0.6 microseconds. These measurements were made
at unity gain.
The response of the Citation A through its magnetic
phono input was outstanding over the range from 20 cps to 20 kc,
showing no more than a negligible 0.5dB error at any frequency when
compared to the standard RIAA equalization curve. The NAB tape head
playback characteristic was excellent, being flat within +0, -2dB
from 20 cps to 20 kc.
Harmonic distortion in the Citation A was actually
less than the residual distortion of the measuring equipment and
thus could not be measured directly. However, using the more complicated
technique of direct harmonic analysis, USTC calculated the THD of
the Citation to be 0.026% at 1 kc and 2 volts output; and 0.065%
at 1 kc and 5.8 volts output on the left channel. The right channel
had even lower distortion. IM distortion was measurable, but was
very low in value, being 0.36% at 5.8 volts, and 0.08% at 2 volts
output on the left channel; and 0.26% at 5.8 volts, and 0.05% at
2 volts on the right channel.
The sensitivity of the Citation A was 270 millivolts
on the high-level inputs, 69 mV on the crystal phono input, 2.2
mV on the magnetic phono input, and 2.4 mV on the tape head input.
The signal-to-noise ratio was 77dB on the high-level inputs; 58dB
on the magnetic phono inputs; and 55dB on the tape head inputs.
The low-level input figures are obviously fine. The high-level measurement
is "unweighted"—that is, it includes a signal component
that actually is in the supersonic region due to the unit's extremely
wide response, and thus is inaudible. If the high-level signal-to-noise
figure were weighted, or made comparable to what would be derived
from an amplifier whose response rolled off in the 50 kc to 100
kc region instead of in the megacycle region, the figure would be
even more impressive, about 85dB. The Citation A thus is a truly
Because the Citation A has step-type, rather than
continuously variable, tone controls, USTC measured the response
of each step in each control separately and then plotted the results
as the curves shown here. As can be seen, these controls can provide
ample amounts of low or high frequency tone cut, but relatively
small amounts of bass or treble boost. This design is deliberate;
Citation "thinking" holds that the wide-band response—so
flat and undistorted—obviates the need for, or even the desirability
of, introducing excessive tone boost. Such boost can overload power
amplifiers and damage a speaker; what's more, it is felt that the
quality of the speakers logically used in a system that also included
the Citation A would require a minimum tinkering with tone controls.
Similar thinking with regard to the choice of a turntable in such
a system is seen in the design of the A's rumble filter which attenuates
relatively little of the very low frequencies - 4.3dB at 30 cps.
The loudness contour introduces no treble boost, but does supply
an ample amount of bass boost at low listening levels.
The relative absence of extreme variations
in the tone control action was found, in listening and use tests,
to be a completely correct and valid design approach. The extremely
wide response of the A, combined with its virtual lack of any form
of distortion, actually improved the sound of familiar program sources
and loudspeaker systems. When substituted in a system that had been
using a Citation I preamp, the most obvious improvement (over what
already had been considered to be an excellent-sounding response)
was in the transient, characteristics of music. Percussion instruments,
for instance, were lent a more live and realistic quality, with
excellent, sharp attack. The sound in general took on a more "opened
up" and lifelike quality. This enhanced clarity and transparency
was bestowed on discs, tapes, and broadcasts. The over-all effect
of using the A is, simply, more music and less listening fatigue.
The A was no less impressive driving high quality headphones. It
is, in sum, a unit that should meet the demands of the most critical
listener and audio perfectionist. It suggests that, by combining
this unit with a transistor basic amplifier of comparable quality,
a sound path could be set up that approaches the classic goal of
amplifier design—that is, a "straight wire with gain."