Meters - Mackie M-2600 Owner's Manual

So what are the pros and cons of these two
approaches? The reason some amplifier
manufacturers use the constant gain approach
is because the noise specification looks better.
It's a fact of physics that as the gain of the
amplifier increases, the circuit noise is amplified
and increases too. By maintaining a constant
gain, the noise spec for an 800W amplifier can
look as good as the noise spec for a 100W am-
plifier. The downside to this is that you have
to crank up the mixer level feeding the input
of the amplifier, losing headroom and possibly
increasing the noise level from the mixer
(unless you have a Mackie mixer with low-
noise VLZ circuitry!).
Conversely, constant sensitivity demands
that as the power increases, so must the gain.
Yes, the output noise of the amplifier will
increase, but you maintain the critical head-
room available from your mixer. The noise is
generally not a problem in live sound reinforce-
ment situations. If it is, you can turn down the
GAIN control a few clicks to find a happy
compromise between noise floor and the
available headroom . As an added benefit, you
can drive multiple amplifiers with the same
signal and get the maximum power available
from all of them.
Mackie subscribes to the philosophy of
constant sensitivity. Our amplifiers can be
driven to full power with an input level of
+4 dBu (1.23V rms).
18
You may wonder why we
didn't use just one stereo
control to control both sides.
That's in case your applica-
tion requires a left/right
imbalance (due to an irregu-
larly shaped room) or if you're using the two
sides for completely different purposes (moni-
tor in channel 1 and side-fill in channel 2, for
instance). Besides, they look cool.

METERS

The M•2600's meters indicate the relative
output level of the amplifier referenced to full
power. The numbers next to the meter's LEDs
are in dB below full power.
Ideally, the M•2600's –20, –9, –6, and –3
LEDs will flicker at normal signal levels, while
the OL LED may flicker occasionally during
peak moments.
OL is short for overload. Overloading, or
clipping, occurs when the output voltage no
longer linearly follows the input voltage and
simply stops. This causes a sine wave to "square
off," or get "clipped off." Thus, the term clipping.
Fear not — this scenario is quite unlikely.
Even with the GAIN controls fully up, the
M•2600 amplifier easily accepts professional
"+4 dBu" operating levels.
If the OL (Overload) LED
is blinking frequently or
continuously, turn down
the source signal (i.e., the
mixer's master faders).