from 'The Gramophone' February 1966
The Armstrong 221 amplifier is essentially the
same as the Model 222 all-valve amplifier (reviewed in October 1964)
with the addition of transistor booster stages for a low sensitivity
magnetic pickup and a few other important refinements. Indeed a
common instruction booklet is supplied for the two amplifiers, the
222 continuing to be marketed for users of ceramic cartridges (pickup
input rating 80mV at 2 Megohms).
Both versions are available in chassis form or
in teak cases for freestanding on a shelf. The smart styling of
the current range of Armstrong units has won them a Design Centre
selection. The grey, silver ringed control knobs are each mounted
at the centre of a greenish grey square on the front panel. There
are five knobs to control input selection, volume, balance, treble
and bass. Three push buttons are provided on the Model 221. The
first introduces a 'loudness' contour—that is the extreme
bass and treble frequencies are raised in relative level to give
a more balanced sound spectrum at low listening levels: the second
is labelled "Monitor" and is intended for use with tape
recording equipment which provides a 'monitor' output from the tape.
There is an auxiliary tape monitor input for this purpose, and the
push-button permits instantaneous comparison (through the Model
221 and its loudspeakers) of the input signal and that recorded
on the tape. The third push- button introduces a treble filter giving
a 12dB per octave cut above 8 Kc/s.
The remainder of the controls are common to the
Models 221 and 222 and include a rumble filter slide switch (at
the rear of the chassis).
The extra stages of the Model 221 are mounted
on a single printed circuit board adjacent to the input selector
switch and comprise a pair of BC107 transistors in each channel.
A sensitivity of 3.5mV at 50 K is achieved, the boosted signal being
fed in parallel with the standard high impedance pickup inlet sockets.
The amplifier proper employs an ECC83 double triode and two ECL86
triode-pentodes in each channel and was fully described in the earlier
The amplifier was found simple to set up and use,
and listening tests with good quality loud-speakers and a variety
of inputs including magnetic and ceramic cartridges soon proved
it to be capable of very good reproduction. The bass and treble
controls gave reasonable, if not drastic, boost and cut: the HF
filter was adequate for noisy discs without being sharp enough to
act as an old-fashioned 'scratch filter': the LF filter was more
gradual than one would like, bearing in mind that the most important
use for such a filter is to reduce motor rumble on medium- or low-priced
gramophone turntables—and for this a sharp cut off below about
30 c/s is preferred.
Exhaustive measurements were made of all modes
of operation, the functions which are common to the Model 222 being
found to match those in the earlier review. As with the previous
unit, the treble control had to be advanced slightly from the mid-position;
this done the response was substantially flat, corresponding to
the claimed ±1dB from 30 to 20,000 c/s. Bass control range
was ± 11dB at 70 c/s; treble control was +14dB, -9dB at 10
Kc/s. The LF filter produced 6dB attenuation at 35 c/s as claimed,
but with a fairly gradual slope; the HF filter operated at the 8
Kc/s turnover frequency with a slope of about 12dB per octave.
The performances of the left and right channels
were within 1dB throughout, as was checked by plotting each response
separately and laying one graph over the other. Crosstalk and noise
were commendably low, being -50dB at 1 Kc/s and -54dB relative to
the rated output, respectively. On the magnetic pickup input, signal-to-noise
ratio was 43dB using a Decca ffss Mk. Ill pickup as load. This form
of loading was chosen to simulate working conditions, and a figure
several decibels better would be expected if spurious hum pickup,
etc., were allowed for. The total harmonic distortion was 0.2% at
5 Watts, 0.7% at 8 Watts, and 1.2% at 9 Watts.
The Armstrong Model 221 gave a good account of
itself during extended periods of listening to records and radio.
It is smart in appearance and with average or even low efficiency
loudspeakers will supply ample power for living room listening.
The extra price, compared with the Model 222, is fully justified
for anyone intending to use a low output magnetic pickup cartridge
either now or in the future.