Amp Mode; Clip Limit; Subsonic Filter - Mackie FRS Manual

10. AMP MODE

This switch determines the input signal routing
within the amplifier. For most applications, you will use
the stereo setting. However, some applications might
be better suited for using either the mono or the bridge
setting.
Stereo: This is the normal position used when ampli-
fying stereo signals. This mode accepts separate left and
right inputs (1 and 2), and routes them to the channel
1 and channel 2 outputs. Each channel's level control
adjusts the gain for its own channel, and each channel
is independent.
Mono: This mode (also known as dual-mono) is used
when you want to send a mono signal to both outputs.
It accepts a single input (input 1), and routes it to both
the channel 1 and channel 2 amplifiers. Each channel's
level control adjusts the gain for its own channel.
Bridge: This mode (also known as bridged-mono)
accepts a single input (input 1), and uses both ampli-
fier outputs to power one speaker. Use the channel 1
level control to adjust the gain (turn the channel 2 level
control all the way down). The hookup diagram at the
bottom of page 6 shows how to connect a speaker in
bridged mono.
WARNING: In bridged mode, both connec-
tions to your speaker are live; that is, neither
is grounded through the chassis (because the
black binding posts are not used).

11. CLIP LIMIT

When engaged, this switch protects your loudspeakers
from the effects of clipping. It is designed to be virtually
transparent, meaning you probably won't even notice
any audible difference when the switch is turned on.
We recommend that you leave this switch on at all
times. However, if you are working at quiet levels, or you
have already placed a compressor/limiter in the signal
path, you can leave this switch off.
The limiter senses when the amplifier is about to be
overdriven and attenuates the overall level just enough
to keep the signal from clipping. Clipping occurs when
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DESIGNED BY MACKOIDS IN WOODINVILLE, WA, USA • MANUFACTURED IN CHINA FABRIQUE EN CHINE • COPYRIGHT ©2008
"MACKIE", AND THE RUNNING MAN FIGURE ARE TRADEMARKS OF LOUD TECHNOLOGIES, INC.
10
FRS SERIES AMPLIFIERS
FAST RECOVERY
POWER AMPLIFIER
CHANNEL 2
the output voltage no longer linearly follows the input
voltage. As the amplifier output voltage increases, it will
eventually run into the internal DC power supplies and
start to flatten out. The flat tops represent a DC voltage
reaching your speakers, which interrupts the natural
movement of the speaker's voice coil. High frequency
harmonics are also produced which can play havoc with
your tweeters. Square waves sound awful, and could
possibly damage your speakers and/or your reputation.
Speakers are designed to handle good clean
continuous signals, but give them a clipped
signal and even high-power speakers can be
damaged. For example, a 100 watt amplifier
that is clipping, can damage speakers that are rated at
400 watts.
The limiter is especially handy when you're working
with loud output levels. Having the signal spikes (kick
drum, for instance) attenuated a bit can actually in-
crease the apparent loudness of the overall mix without
diminishing the "power" behind the spikes. It is also a
useful protection device for those unexpected moments,
such as the lead singer actually hitting the right note,
a mike stand or the drummer falling over, dropping the
tone arm, or an attack of killer feedback.
With the limiter engaged, you can still over-
drive the amplifier into clipping and cause
distortion. It just takes a stronger signal to
do it. So even with the limiter turned on, you must pay
attention to the OL LEDs.

1. SUBSONIC FILTER

Turn this switch on to engage a low-frequency cutoff
(high-pass) filter at 30 Hz. The frequency range below
30 Hz is attenuated.
The amplifiers can amplify signals below 20 Hz, but
most speakers can't reproduce frequencies that low.
By engaging the subsonic filter, you allow the amplifier
to power only the frequencies you can hear. In addi-
tion, this filter can reduce low-frequency stage noise
(footsteps) and accidental microphone pops that could
damage a loudspeaker.
Leave this off if your amplifier is powering a subwoof-
er, or if your speakers can reproduce low frequencies
such as the kick drum range.
BRIDGED CHANNEL 1
SPEAKER OUTPUTS
Use only class 3 wiring
PIN PIN PIN
1+ BRIDGED 1+ 1+
1 2+ 1
PIN
CH 2 2+ 1+ CH 1
2 1
FILTER
SUBSONIC @ 30Hz
CLIP LIMIT
AMP MODE
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