SWR 550x Owner's Manual page 16

1. Use the Balanced (XLR) Output without using the internal speakers. This is especially useful in
recording when you are "miking" the speakers and only a direct signal is required for the moment.
2. Tune up without making sound onstage (and interfering with other band members) while using the
Tuner Out feature.
3. Defeat the "pop" you sometimes get when changing and/or unplugging instruments from the unit
(especially if you sometimes forget to disconnect your instrument cable from the amplifier before
disconnecting it from your bass, something that's always a good idea).
4. Defeat the "pop" present upon powering up the unit (though it causes no harm to the unit and/or
your speakers).
550x - SPEAKER OUTPUT SECTION
This section of the manual will deal with the proper connection of speaker cabinets to the power amplifier in the 550x. Some
of this ground has already been covered in the Getting Started–Connecting Your Speaker Cabinets section in the begin-
ning of the manual. This is meant to supplement that section and provide information in greater detail, as power amplifiers,
impedance and speaker cabinets are all crucial in determining how best to operate your new 550x.
HOW IMPEDANCE AFFECTS POWER RATINGS
People often have questions about impedance. What is it? The root of the word "impedance" is the verb "impede," which
means to block or resist. That's what impedance is–resistance to power.
Power amps do not have a pre-determined impedance. They deliver power at whatever impedance the speaker cabinet tells it
to. That's why you hear the term "slave amp"–amplifiers only do what they're told. So if someone tells you that they have a "4
ohm power amp," their terminology and understanding of the concept is way off the mark.
Unlike power amps, every speaker cabinet has a pre-determined impedance rating measured in "ohms." In most cases this
rating is either 4 or 8 ohms (though there may still be some old 2 ohm creakers out there). The higher the impedance of the
speaker cabinet, the more resistance to power it will offer. The lower the resistance of the speaker cabinet, the less resis-
tance to power it will offer. In other words, HIGHER IMPEDANCE MEANS LESS POWER CAN ENTER THE SPEAKER CABINET.
LOWER IMPEDANCE MEANS MORE POWER CAN ENTER THE SPEAKER CABINET.
You may be thinking that you've found the solution to the universe–just use speaker cabinets with really low impedances and
you can get skull-crushing power out of your amplifier, right? Wrong. There's a catch. Power amps have limits as to how low an
impedance they can drive safely. This is what's known as an amplifier's "Minimum Impedance Rating." If you try and operate a
power amp below its minimum impedance rating, it will give you lots and lots of power for about five minutes...and then over-
heat, short out and fail completely. In other words, THE LOWER THE OPERATING IMPEDANCE OF THE AMPLIFIER, THE HOTTER
IT WILL GET.
550x POWER AMPLIFIER MINIMUM IMPEDANCE RATINGS
Here's what this means to the power amp in the 550x. As mentioned previously, the 550x contains a mono power amp, which
makes things fairly simple. The Minimum Impedance Rating of the 550x is 4 ohms. This means that you can safely con-
nect:
- One 8 ohm speaker enclosure
- Two 8 ohm speaker enclosures
- Two 16 ohm speaker enclosures
- One 4 ohm speaker enclosure
16 • 550x