12 QSC Audio Products LLC
Application Engineering Team
FAST (Flexible Amplifier Summing Technology™)
Four, three, two, or one channel
The four channels of a PLD amp can be run separately, but they also can be combined in novel ways.
You’re probably familiar with bridging, which couples two amp channels in series to produce up to double the output volt-
age of a single channel. PLD amp channels can be bridged, but unlike nearly every power amp on the market, they can
also be connected in parallel to beef up the output current capacity. This is most useful for loudspeaker systems with low
impedances, such as two or even one ohm. Thus, a PLD amp can be tailored in many different ways to suit the particular
needs of driving a wide range of loudspeakers.
You just can’t do this with any other amp. You can’t do this without QSC’s FAST, which keeps paralleled amp channels
matched and synchronized precisely so they do not blow each other up when they’re connected together.
A power amp is a voltage source, as is a battery. The difference is that while the battery puts out a constant DC voltage,
the power amp puts out a varying voltage in the form of an audio signal. But FAST allows you to use techniques that you
might be familiar with in using batteries to multiply the versatility of the amplifier.
Single
For example, a battery has a given output voltage and a certain capacity to deliver current into a load. Similarly, an amplifier
channel has a given output voltage capacity (the actual voltage varies with the signal) and current capacity.
A voltage source, whether it’s
a battery or an amplifier, has
certain voltage and current
capabilities.
Having two identical voltage sources in series
provides double the voltage capability but does
not increase current.
In PLD amplifiers, bridged mono is suitable for
higher load impedances—that is, 6Ω or higher.
Series (bridged mono)
To get twice as much voltage, add an identical second battery or amp channel. The current capacity remains the same,
however, so this is useful for higher-power loads that have a relatively high resistance or impedance.
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