Yamaha P2075 Operating Manual page 4

BRIEF OPERATING INSTRUCTIONS
Front Panel
PROTECTION
| POWER AMPLIFIER P2075
© INPUT ATTENUATOR(S)
The P2075 has two log-linear input attenuators. Each control
is marked in 31 dB-calibrated steps, and detented for extra
accuracy. The attenuators provide a smooth, noise-free
transition from maximum level (zero attenuation) to silence
("infinite" attenuation). The attenuators are recessed (flush
with the front panel) to avoid damage or accidental setting
changes.
Calibrated input attenuators offer numerous advantages.
They allow predictable and repeatable setups in portable
sound systems, as well as in permanently installed systems
which are pre-checked in the shop and later installed at
another location. Whether the amplifiers are used on stage in
portable sound systems or installed in studios, factories,
meeting rooms, theatres, arenas or elsewhere, their calibrated
attenuators allow easy, accurate input sensitivity adjustments.
The calibrated attenuators permit operators to adjust the
level of two channels with precise tracking.
@ INPUT LEVEL INDICATORS (SIGNAL, CLIP)
A pair of LEDs above the input attenuator monitor the signal
level. The green "SIGNAL" LED turns on whenever the
signal present at the amplifier output is 2 volts RMS or
higher. Since this is equivalent to 1 watt into a 4-ohm load,
or 1/2 watt into an 8-ohm load, the SIGNAL LED basically
indicates that some program material is present. The red
"CLIP" LED turns on when the output stage is about to clip,
either from an overdriven input or an overloaded output.
This "flags" the operator, suggesting the attenuator be
turned down or the speaker load corrected to avoid distor-
tion.
Fig. 1
POWER SWITCH, POWER & PROTECTION INDI-
CATORS
An alternate-action switch turns the AC power on and off.
When the power is ON, a red LED immediately above the
switch is illuminated. Immediately after turning. power оп, a
second red LED above the PROTECTION label will also be
on, indicating the speaker output is disconnected from the
load by a protection relay. After a few seconds, the PRO-
TECTION LED should turn off, indicating that the outputs
is activated (the slight delay allows time for the internal
amplifier circuits to stabilize and thus avoid turn-on thump).
The PROTECTION LED blinks when the heat sink tempera-
ture exceeds 60°C. For General model, at a heat sink tem-
perature of 85° С the relay is turned off and output is cut.
HINT REGARDING TURN-ON OF THE
POWER AMPLIFIER
Unless you are turning on all the equipment in the sound
system simultaneously with a switched strip of power
outlets, be sure to turn on everything else before you
turn on the amplifier(s). By turning on the power
amplifier last, you can prevent turn-on "thumps"
generated by the console, graphic EQ, electronic cross-
over, or other accessory signal processors from possibly
damaging speakers. The opposite procedure should be
used to shut off the system: first turn off the ampli-
fiers, then the rest of the equipment.
This power amplifier has a relay which is timed to
turn on the speaker outputs after the amplifier's power
supply is fully charged up, thus preventing any turn-on
noise. Timing of the amplifier's turn-on circuit is usually
sufficient to accommodate all the turn-on anomalies
from other pieces of gear in a system, making it accept-
able to use a single switched power strip in a perma-
nently installed or "packaged" portable sound system.