from High Fidelity Magazine, September 1962
AT A GLANCE: The new EICO ST-84
is an attractive, versatile, easy-to-use dual-channel preamplifier
and audio control unit that can be mated with any basic amplifier
and can accept all standard program sources. It is available factory-built
at $89.95, or in kit form for $59.95. Performance of the kit-built
version, assembled and tested at United States Testing Company,
Inc., was found to be generally excellent with effectively no distortion,
though some discrepancies were measured in the unit's tape head
equalization characteristic. Manufacturer: Electronic Instrument
Co., Inc. (EICO), 33-00 Northern Blvd., Long Island City 1, N.Y.
DETAIL: The appearance of the ST-84 is characteristic of
the "new look" that has been designed for EICO components,
being at once handsome and functional, with the front panel controls
arranged for maximum convenience. At the extreme left is a 7-position
input selector with positions for three pairs of high-level inputs
and four pairs of low-level inputs (tape head, two magnetic phono
cartridges, and microphone). To the right of this control is a 7-position
mode selector providing the usual variety of monophonic and stereo
operating conditions. Then come the balance and volume controls,
with concentric bass and concentric treble controls at the right
end of the panel. Above these control knobs are slide switches for
tape head equalization (positions are provided for both the 3¾
ips and 7½ ips tape speeds), a tape monitor function, loudness
contour, rumble filter, and scratch filter. On the rear of the preamplifier
there are seven pairs of input jacks and two pairs of output jacks
(to amplifier and tape recorder), as well as one switched and one
unswitched AC convenience outlet.
USTC found the performance of the ST-84 to be
excellent in several respects. Its frequency response is flat within
plus or minus 0.5 dB from 20 cps to 20 kc. It rolls off to minus
3 dB at 44 kc on the high end and extends to below 5 cps on the
low end. The preamplifier introduces no measurable harmonic distortion
with signals of up to 3 volts output. IM distortion, at 1-volt output,
also was nonmeasurable. In fact, the only distortion measured at
all was a negligible 0.1% IM at 3 volts output.
The preamplifier's sensitivity for 1-volt output
is 0.168 volts on auxiliary, 1.57 mV on phono, 2.58 mV on microphone,
and 0.84 mV on tape head. The signal-to-noise ratio of the preamplifier
is 74 dB in the auxiliary position, 53 dB in the phono position,
57 dB in the microphone position, and 47 dB in the tape head position.
The "noise" that remained was predominantly hum, but the
signal-to-noise ratio is good enough so that the hum would be inaudible
at normal listening levels.
The phono equalization characteristic (RIAA) was
excellent above 100 cps and remained good down to 30 cps where the
error was only 2 dB. Tape equalization (for signals direct from
a tape head—that is to say, a tape playback deck that lacked
its own preamplifier) was not as good, although the equalization
for the 7½ ips tape speed was generally excellent above 400
cps. At 100 cps, the equalization had a 4.5-dB drop, and at 40 cps
the error increased to 8 dB in comparison to the NAB standard. The
equalization for the 334-ips tape speed remained fairly close to
the EIA standard for this speed above 400 cps, but fell off below
this frequency to minus 9 dB at 40 cps.
tone controls provided 11 dB of bass boost and cut at 100 cps and
approximately 16 dB of treble boost and cut at 10 kc. The rumble
filter characteristic was considered relatively poor, in that it
attenuated a large portion of the bass response in the musical program.
With the rumble filter on, the 100-cps response is cut 5 dB, the
50-cps response is cut 8.5 dB, and the 30-cps response is cut 11.8
dB. The scratch filter also might have a more desirable shape; it
attenuates signals at the approximate rate of 5 dB per octave above
3 kc. Thus, while these filters will remove noise in program material,
they also may attenuate a fair amount of the program itself. In
any case, noise filters—even on costlier units— rarely
are completely satisfactory and with good program material really
should be left off.
The loudness contour in the ST-84 is effective,
but operates in a somewhat unusual way. Instead of providing a boost
to the low frequencies, as is generally done, it attenuates the
mid- and high-frequencies (about 20 dB at 1 kc). Thus, to obtain
the desired end result of using a loudness contour (reasonably full
response at low listening levels), the level control should be readjusted
by the listener.
Aside from the unit's questionable tape equalization
characteristic (which, of course, would be of concern only to those
who would use it with a preamplifier-less tape deck), the EICO ST-84
is a generally first-rate control unit going at a relatively low
How it went together
Construction of the ST-84 was somewhat impeded
by the change in position of certain components shown in one drawing
from their orientation in a previous drawing. This orientation meant
that the leads cut in previous steps now were too short and required
extension: where instruction indicated a lead length that turned
out to be excessively long, the leads had to be stripped and tinned
a second time after the first cutting to size. Too, the multi-operation
steps called for at one point caused some small amount of confusion
after getting into the swing of single-operation steps; this was
solved by checking-off each operation within the steps. In addition,
the colour-code indicated for a given resistance value erred, requiring
cross-check with the circuit diagram.
Three missing components—a phono jack
insulator and two resistors—were quickly obtained from the
manufacturer upon request. Two other parts-a 0.025-µfd disc capacitor,
and 12AX7 tube—showed up as faulty after the kit had been
built and put into operation. These were replaced and the unit performed
correctly. But USTC feels that these problems, while they could
be solved by an experienced kit builder or technician, could cause
consternation and delay to the beginner.
This unit was well packaged for shipping purposes.
Individual components were grouped in cartons or envelopes. Assembly
time was about twenty-eight hours.