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BRIDGE MODE OPERATION
The following KXR amplifiers feature Bridge Mode Operation; KXR600, KXR1000, KXR1500 & KXR2000.
Bridge mode is a professional feature that is actually fairly complex.It is a means of devoting the entire
power of your amplifier to a single audio input. But you cannot simply connect a single speaker to one
channel output and use it... it requires a very unusual wiring configuration and very solid understanding of
speaker impedance and power handling. Unless you really know what you are doing with it, don't use it.
We'd better explain... in bite-sized pieces;
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Bridge mode devotes the entire power output capacity of the amp to the Channel A input.
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That may sound simple but the way in which the amplifier achieves this is not so simple.
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If you understand how a balanced audio connection works you'll know that it provides three
wires within an audio cable; one of them is simply an earth, the other two each carry half of the audio
signal – one carries the positive half of the signal and the other carries the negative half.
•
When you place an amplifier in bridge mode, it uses channel A to amplify the positive half
of the signal and uses channel B to amplify the negative half of the signal.
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So the first thing to understand about bridge mode is that you can't use it with an
Unbalanced audio input.
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This also has a dramatic effect on how you connect your speakers to the amplifier.
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With a pair of Balanced audio connections in normal operation, the two polarities of the
signal (within each individual Balanced connection) are amplified within each channel of the amp (with
the two channels of the amplifier operating in parallel)... so both channels of the amplifier
accommodate a connection each and are basically doing the same thing at the same time.
•
In bridge mode, because each side of the amplifier is now being fed by one input but
dealing with opposite polarities of the audio signal, they are no longer doing the same thing at the
same time... when channel A is 'sucking', channel B will be 'blowing'.
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This means that if you leave a pair of speakers connected in the normal manner, one
speaker will only be getting the positive half whilst the other speaker will only be getting the negative
half of the audio signal.
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What is worse is that the amplified signals are only delivered to just one (the positive)
terminal of each output channel of the amplifier (sorry we did say it wasn't simple).
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The amplifier will continue to attempt to drive the speakers just as hard but the entire
thing will be messed up and sound dreadful.
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The answer is to connect a single speaker across both channels of the amplifier.
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This means that with KXR amplifiers you cannot use the Speakon outputs in bridge mode.
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With KXR amplifiers you need to use the Binding Posts to connect a single speaker.
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Connect the positive wire of your speaker cable to the positive Binding Post of channel A.
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Connect the negative wire of your speaker cable to the positive Binding Post of channel B.
The problems don't end there either. You need to be aware that bridge mode potentially delivers
considerably more power to your speakers. In much the same way that attempting to use an over
powered amplifier to drive an under sized speaker is obviously a recipe for trouble... so is trying to use
bridge mode to coax more volume from low impedance speakers. Bridge mode can be useful for using an
amplifier to drive a speaker with a higher impedance than usual (perhaps driving a single 16 Ohm speaker
with an amplifier you might use to drive a pair of 8 Ohm speakers). But this has it's own problems
because a higher impedance speaker will actually demand more power from your amplifier (even at lower
volumes) than it is used to delivering to a lower impedance speaker... and that can over strain your
amplifier.
Bridge Mode is activated by pressing the recessed switch (you will need a small screwdriver or other
similar implement to reach it) marked 'Bridge' which is located near the volume controls on the front
panel. When activated the accompanying LED beside the switch will illuminate.
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