550x • 17
The number one enemy of any power amp is heat. We have listed the minimum impedance of the 550x at 4 ohms so that the
extraordinary amount of power available in this two-rack-space configuration is not compromised by exposing the power amp
to the additional heat that operation at 2.6 ohms or 2 ohms would generate. (SWR recommends that, when rackmounting your
550x, leave at least one open rack space to allow for proper ventilation and cooling.) Consequently, damage to the power
amplifier section of the 550x may occur if speaker enclosures with total impedances less than the minimum loads listed
above are connected to the speaker output section. The owner's manual that came with your speaker cabinet should state its
total impedance. On SWR speaker enclosures, the total impedance is generally indicated on the speaker's input panel.
So how do you determine the total impedance of two cabinets hooked up to your 550x? Here's a quick key of the two most
common setups:
One 8 ohm enc one 8 ohm enclosure = 4 ohms total impedance (OK)
One 8 ohm enc one 4 ohm enclosure = 2.6 ohms total impedance (not OK)
Here's another formula: To figure out the total impedance of two or more cabinets of equal value hooked up in parallel, divide
the impedance of one cabinet by the number of cabinets:
Impedance of one cabinet / number of cabinets = total impedance
(For an even more in-depth discussion of impedance and power rating issues, go to the SWR website at www.swrsound.com,
click on "Products", then click on "Technical articles", then click on "Plug and Play - Setup Tips for Amps and Speakers"–an
article by SWR founder Steve Rabe that ran in the August '92 issue of Bass Player Magazine.)
550x POWER DELIVERY CAPABILITIES (POWER RATINGS)
After determining how the number of cabinets you wish to run affects the total operating impedance, you need to take into
account the power handling capabilities of your speaker cabinets as compared to what the 550x can deliver at that imped-
ance. Those ratings are as follows:
550 Watts @ 4 ohms
375 Watts @ 8 ohms
So if you have two 8 ohm speaker cabinets, they will each get up to 275 watts of power, and more during transient peaks. A
single 4 ohm cabinet will get 550 watts of power, and again, more during peaks. Make sure your speaker cabinet(s) can han-
dle the power.
Also be aware that when running the amp at 4 ohms with extreme settings on the Gain and Master controls and the Limiter cir-
cuit disengaged, you may hear audible clipping of the power amp. If so, you have exceeded the maximum capacity of the
power amp. POWER AMP CLIPPING CAN CAUSE DAMAGE BOTH TO ITSELF AND YOUR SPEAKER CABINETS. Either re-engage
the Limiter (by pushing in on the Effects Blend control) to help smooth out the peaks, or back off on the Gain and Master con-
trols.
Remember, it's always better to have a little too much power than just barely enough. If you find yourself constantly wanting
more power than the 550x provides, either:
a) tell your bandmates to turn down
b) tell the monitor engineer to turn you up
c) (best option) take the time to investigate getting an external power amp and/or additional speaker
cabinets to supplement your rig.
One last time: The best two-cabinet setup is to use two 8-ohm enclosures.
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