SWR Sound 2X10C - Manual (Page 11)

WORKINGMAN’S 2X10C • 11
NOTE: Inserting a plug into the Effects Receive jack activates the Effects Blend control. The control receives this command
through the ground created by the phone plug making contact with the jack. The plug must be a mono plug (tip and ground). If you
have a stereo plug only, it will be necessary to tie the ring and the ground together.
COMBO CABINET JACK/PLUG ASSEMBLY
The black cable/plug assembly that comes out of the cabinet and is connected to the rear panel (near the text marked "Combo
Cabinet") is the means by which the power amp in your Workingman's 2x10C sends its signal to the speaker complement. Both the
plug and the jack it connects to are a special size, slightly less than the typical 1/4" found on instrument and speaker cables alike.
SWR strongly recommends that you not disconnect this cable, as it is not meant to be (nor can it be) used as either an extension
speaker output or a speaker cabinet input. For proper connection of an extension speaker to your Workingman's 2x10C, please read
below.
EXTENSION SPEAKER OUTPUT SECTION
This section of the manual will deal with the proper connection of extension speaker cabinets to the power amplifier in the
Workingman's 2x10C. We recommend that you read this section carefully, as power amplifiers, impedance and speaker cabinets are
all crucial in determining how best to operate your new Workingman's 2x10C with an extension speaker cabinet.
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.
Solid-state 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 resistance 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 overheat, short out and fail com-
pletely. In other words, THE LOWER THE OPERATING IMPEDANCE OF THE AMPLIFIER, THE HOTTER IT WILL GET.
WORKINGMAN'S 2X10C POWER AMPLIFIER MINIMUM IMPEDANCE RATINGS
Here's what this means to the power amp in the Workingman's 2x10C. Like most combos, the Workingman's 2x10C contains a mono
power amp, which makes things fairly simple. The operating impedance of the internal speaker system in your
Workingman's 2x10C is 8 ohms, so that's your starting point. When you add an extension cabinet to the Workingman's 2x10C,
invariably the total operating impedance of the amplifier will get lower. The Minimum Impedance Rating of the Workingman's
2x10C is 4 ohms. This means that you can safely connect to the extension speaker jack:
- One 8 ohm speaker enclosure (4 ohms total impedance)
- Two 16 ohm speaker enclosures (4 ohms total impedance)
Operation at 4 ohms will provide 400 watts, a nice increase over the 260 watts available when used in a stand-alone configuration.
But as previously mentioned, the lower the operating impedance, the hotter the amplifier will run. An amp that runs at or near its mini-
mum impedance all the time may wear the life of its components faster than normal. Furthermore, damage to the power amplifier