NAD 2600 - POWER; INPUT LEVEL; SOFT CLIPPING INDICATOR; PROTECTION INDICATOR

thing which shares a common ground with the amplifier's inputs You can use the input-level controls to correct these fixed
(such as a switching comparator or a distortion analyzer).
(5) After the preceding conditions have been satisfied,
re-set the Bridging switch. It is held in place by a plastic
bracket fastened by two screws. Use a small screwdriver
to loosen the bracket screws, turning each about a half-
turn counterclockwise; then slide the switch to ON (MONO).
The bracket will move with the switch. Re-tighten the screws
to secure the switch in its new position. Finally, turn the
power on.
(6) To return the amplifier to normal stereo operation at a
later date, first turn off the power. Loosen the bracket screws,
re-set the Bridging switch to OFF (STEREO), and tighten the
bracket screws to prevent the switch from being moved acci-
dentally. Restore normal Left and Right input connections,
and re-connect loudspeaker wires to the speaker terminals
as described above under SPEAKERS.
FRONT PANEL CONTROLS
1. POWER
Press the Power button to turn on the amplifier. The
green LED glows when the power is on. Press the Power
button again to switch the amplifier off.
2. INPUT LEVEL
The amplifier is equipped with separate input level
controls for the two channels. Normally both controls should
be turned to maximum. But there are several circumstances
in which reduced settings may be useful:
(1) Level-Matching. !n a multi-amplifier system, use
these controls to match the output of this amplifier to others
in the system.
(2) Extended Volume-Control Range. Many stereo sys-
tems have so much voltage gain that the speakers (or your
ears) are over-driven at any preamplifier Volume-control
setting higher than 11 or 12 o’clock. As a result you are
confined to using only the lower half of the Volume control's
range, where adjustments are imprecise and where most
Volume controls produce channel-balance errors.
The solution is to turn the power amplifier’s input-level
controls down part-way (to about 1 o'clock, for example) in
each channel. Now you can turn up your preamplifier’s
Volume control further, making effective use of most of its
range. (Suggestion: adjust the power amplifier’s input level
controls so that your preferred maximum sound levels usu-
ally occur at about 2 or 3 o’clock on your Volume control.)
As an added benefit, this procedure suppresses any
noise produced by the preamp’s high-level circuitry (e.g. any
residual hum or hiss that does not go away when the Volume
is turned down).
(3) Balance Correction. Small errors in channel balance
can dramatically degrade the apparent “depth” and “air” of
the stereo image. Such balance errors may be due to normal
production-line differences in speaker sensitivity, differences
in the acoustic environment around the two speakers, and
slightly different distances from your chair to each speaker.
balance errors, freeing your preamplifier’s balance control to
correct balance errors in recordings.
Switch the preamp to mono and sit in your normal
listening location. Ideally the “phantom” central image
should seem to be floating in mid-air halfway between the
left and right speakers. If it is located off-center, closer to
one speaker, turn down the input-level control for that chan-
nel slightly in order to center the phantom mono image.
Then restore the preamp to normal stereo operation.
If you have turned the input-level controls down part-way
to adjust the overall volume level, do this balance correction
as the final step.
NOTE: In bridged mode, the volume is adjusted with the
Left input level contro! only.
3. SOFT CLIPPING INDICATOR
This amber LED glows when the Soft Clipping switch
(on the rear panel) is ON.
4. PROTECTION INDICATOR
The amplifier can safely and cleanly drive impedances
as low as 2 ohms with wide-range musical signals whose
peak level is 500 watts or more. But if called upon to de-
liver high power continuously into a low impedance, the
output transistors may overheat. In this case, protection
relays will automatically disconnect the speakers and the
PROTECTION light will illuminate.
If this occurs, switch off the Power. When the output
stage cools, the relays will automatically re-connect the
speakers, and normal operation can be resumed. In most
cases a very slight reduction in volume level will prevent
further interruptions in the sound.
If the protection relays interrupt the sound frequently,
several possible causes should be considered: a loose
strand of wire causing a partial short-circuit between speaker
terminals, or continuous high-power operation into a very low
impedance in the Bridged mode, or any obstruction of the
free flow of air needed to ventilate the amplifier and dissipate
its heat.
If the protection relay interrupts the sound even
when the amplifier is cool, return the amplifier to your NAD
dealer for service. The protection circuit may be responding
to protect the speakers from an internal fault, such as an
improper DC voltage at the speaker terminals.
5. OVERLOAD INDICATOR
This is an “audible clipping” indicator. It flashes on
when the amplifier is over-driven into audible distortion.
An input/output comparator continually compares the ampli-
fier’s output signal in each channel with the corresponding
input waveform; any difference that lasts long enough to
be audible (longer than a few thousandths of a second)
triggers the LED on. If this indicator illuminates frequently,
you should reduce your volume levels slightly (or purchase
a second Model 2600 and use both amplifiers in the bridged
mode for greater power).
NAD ELECTRONICS
BOSTON/LONDON
©1900 BY NAD 41 PRINTED ON JAPAN
OM-674A 8703