STARTING WITH THE A21
The A21 stereo amplifier is relatively simple to use and,
provided it is used within its limits, it requires no special
care in everyday operation.
It achieves claimed specifications right from the start,
even though it still needs 5-7 days of burning in to
perform its best in the subjective audio terms.
Afterward, it is generally enough to leave it powered
on for half an hour before the critical listening.
It is not harmful if A21 is left constantly powered up,
however a general recommendation to turn such
devices off whenever out of home applies regardless.
Also, it is important not to block the opening holes at
the bottom, back, and top plate, as they provide air
circulation into and from the unit interior, and thus
ensure proper cooling.
CONNECTIONS
The A21 mains connector is standard IEC C14 and is
located at the back panel. Every unit is produced to
match the mains voltage in the customer’s country.
The A21 is a balanced amplifier, however it sports both
unbalanced and balanced inputs. Thus, on its back
panel, there are three unbalanced RCA and two
"Combo" connectors. These Combo connectors can
accept both balanced (XLR or 6.3 mm "TRS" phone
jack) and unbalanced sources (6.3 mm "TS" phone
jack). The input impedance is 38 kOhm for unbalanced
inputs and from each balanced pole to the ground,
and 76 kOhm between the poles of the balanced
inputs, so the A21 is a friendly load for the majority of
sources.
The A21 employs also a buffered pre-out, which can be
useful for bi-amping, or to connect the active
subwoofer. This output is provided as an unbalanced
RCA connection only.
The output loudspeaker connectors are Audial made
pure copper binding posts, which accept the usual 6.3
mm spades or 4 mm banana plugs.
The A21 does not invert polarity (absolute phase).
Hence with the source which also does not invert
polarity, the speakers should be wired in phase.
The A21 also sports the ground connector. This ground
is the chassis ground and can be used for cable
shielding, or as a system earth connection. This
connection should not be used as an audio ground /
return path.
IMPORTANT: The A21 is a balanced amplifier, so both
the positive and negative loudspeakers output
connectors carry audio signals. Please, DO NOT
connect the negative output to the ground!
USING THE A21
Apart from the mains switch, the A21 has only one
control knob, which is both the volume and balance
control, and the input switch. The amplifier settings are
shown on the display.
Normally, the volume is set by rotating the knob. The
volume is set in 1 dB steps, and has the "mute", and 63
steps between the 0 dB and maximum position.
The inputs are selected by pressing the knob.
By long pressing the knob (for 2 seconds), the amplifier
enters the balance menu. The display, instead of the
volume position, in its second row then shows the
balance position. The balance can be set in 1 dB steps
(from "Center" to 31 dB left or right). By another long
pressing of the knob (again for 2 seconds), or by its
inactivity for 5 seconds, it will go back to the regular
volume control operation. If the balance is set out of
the center, the appropriate reminder will remain on the
right side of the upper row of the display.
The volume and balance positions and input selection
are non-volatile after the power off, that is, the same
setting will apply on the next power-up. This however
applies to the volume setting only if it was set for at
least 5 seconds before the power off, to the balance
setting only after exiting the balance menu, and to the
input setting it applies unconditionally.
5
Audial A21
