QSC PLD Series User guide

PLD Series Power Amplifier
Application Guide
for Portable PA
www.qsc.com

2 QSC Audio Products LLC
Application Engineering Team
Address
QSC Audio Products., LLC.
1675 MacArthur Boulevard
Costa Mesa, CA 92626-1468
USA
Main Switchboard
Tel: [phone] (US and Canada)
Tel: [phone]
Fax: [phone]
E-Mail: [email protected]
Application Engineering
E-Mail: [email protected]

PLD Series Amplifiers 3
Application Guide—Portable PA Rev. E, Apr. 2015
Table of Contents
1. Introduction...................................................................................................................................................................................................... 5
Why PLD?...................................................................................................................................................................................................................................................5
PLD: A new paradigm..............................................................................................................................................................................................................................6
Electrical power.......................................................................................................................................................................................................................................9
FAST (Flexible Amplifier Summing Technology™)..........................................................................................................................................................................12
Amplifier Navigator™............................................................................................................................................................................................................................15
Presets .....................................................................................................................................................................................................................................................16
2. Real-World Applications with PLD................................................................................................................................................................ 20
Loudspeaker power capacities...........................................................................................................................................................................................................20
Application: Stereo passive tops and subs.......................................................................................................................................................................................21
Application: Stereo passive mains with two monitor mixes.........................................................................................................................................................22
Application: Stereo passive tops and subs with two monitor mixes...........................................................................................................................................23
Application: Mono passive tops and subs with two monitors on one mix.................................................................................................................................24
Application: Stereo full-range mains with four monitor mixes ....................................................................................................................................................25
Application: Stereo passive tops and subs with two monitor mixes...........................................................................................................................................26
Application: Stereo passive tops and mono sub..............................................................................................................................................................................27
Application: Stereo passive tops and two mono subs....................................................................................................................................................................28
Application: Stereo bi-amp mains ......................................................................................................................................................................................................29
Application: Stereo bi-amp mains with two monitor mixes..........................................................................................................................................................30
Application: Mono bi-amp tops and sub............................................................................................................................................................................................31
Application: Stereo full-range mains.................................................................................................................................................................................................32
Application: Stereo passive tops and subs.......................................................................................................................................................................................33
Application: Stereo passive tops and subs.......................................................................................................................................................................................34
Application: Stereo bi-amp mains ......................................................................................................................................................................................................35
Application: Stereo bi-amp mains ......................................................................................................................................................................................................36
Application: Stereo bi-amp tops and mono subs, with two monitors on one mix.....................................................................................................................37
Application: Stereo bi-amp tops and subs ........................................................................................................................................................................................38
3. PLD Series Specifications ............................................................................................................................................................................... 39

4 QSC Audio Products LLC
Application Engineering Team
Copyright © 2015 by QSC Audio Products, LLC. Allrights reserved.
QSC is a trademark of QSC Audio Products, LLC, registered in the U.S. and other countries.
Felxible Amplifier Summing Technology, Intrinsic Correction, and Amplifier Navigator are trademarks of QSC Audio Prod-
ucts, LLC.
Windows® is a registered trademark of the Microsoft group of companies.
Mac is a trademark of Apple, Inc., registered in the U.S. and other countries
Speakon is a trademark of Neutrik.
All other marks are property of their respective owners.

PLD Series Amplifiers 5
Application Guide—Portable PA Rev. E, Apr. 2015
1. Introduction
Why PLD?
The role of a power amp is simple: the proverbial function is a virtual straight wire with gain. Take the input signal and
make it bigger to push a loudspeaker. Given this, you certainly might be forgiven for thinking that big amplifier innovation
ended some years ago. And to be honest, power amps in recent years have increasingly met levels of performance and
reliability that were impossible some 20 or 30 years ago.
The PLD Series amplifiers from QSC take it all a few steps further while adding such versatile features as digital signal pro-
cessing, Flexible Amplifier Summing Technology™ (FAST), and particularly high power and channel density.
The three models in the PLD range are the PLD4.2, the PLD4.3, and the PLD4.5. All are four-channel amplifiers, though
those four channels can be configured and combined in different ways to make one, two, three, or four channels, all in a
two-rack-space package.

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Application Engineering Team
PLD: A new paradigm
The innovative technology built into the PLD amplifiers represents a very new paradigm of audio amplification, one with-
out many of the restrictions and burdens that we’ve had to bear in the past.
Channel density, power density
Among professional power amps, the most common size is 2RU, and the vast majority also have two audio channels. That
means that if you happen to need, say, eight channels of amplification, you’ll need at least 8 rack spaces in your equip-
ment racks—maybe even more, if they are very high-power 3 RU or 4 RU models.
But imagine, with PLD you could now have those same eight channels of ampli-
fication—with up to 2000 watts each—in only four rack spaces, with a total weight
of only 44 pounds.

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User interface
The front panel of a PLD amp features a 400 × 240 pixel color screen that, along with the master control knob and both
mute and select buttons for each channel, serves as the user interface (UI).
The UI handles all amplifier configuration and is completely menu driven. Unlike past QSC amplifier models, there are no
configuration switches on the rear panel.
Built-in processing
An ample amount of digital signal processing (DSP) is built into the PLD Series amplifiers. The DSP serves a dual purpose:
first is to manage the operation of the amp—by controlling the functions of the power supply, the protection systems, the
fan speed, signal routing and mixing—and the second is to execute the necessary loudspeaker and system processing that
used to require one or more external devices.
The processing functions available include:
• Five bands of parametric EQ per channel.
• High- and/or low-pass filtering, with choice of frequency, slope, and filter type. High and low shelving are also avail-
able.
• Limiting, with selectable threshold and ratio, as well as selectable power limiting.
• Delay, up to 75 ms on each channel
Weight savings
Some of us remember when even a 1,000-watt amp wasn’t something you could just grab and lift with one arm.
Now, thanks to advanced switch-mode power supplies, which operate at high frequencies and therefore can convert thou-
sands of watts in small, lightweight power transformers, and highly-efficient class D amplification technology, which can
turn those thousands of watts into audio power with a minimal number of semiconductor devices and relatively small heat
sinks, we can have four-channel amplifiers rated at 2,000 watts per channel that weigh only 22 pounds.
The potential savings in labor, freight, and wear and tear are enormous, especially for weekend warriors and regular gig-
ging.

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Application Engineering Team
Physical layout
The PLD Series feature a neat, organized layout of the rear panel connectors and master power switch. The four XLR
inputs feature male loop-through connectors to allow easy daisy-chaining of input signals. There are six NL4 Speakon con-
nectors, including two that are exclusively used for bridged mono operation, that offer connections for all possible individu-
al, parallel, or bridged arrangements of amp channels.
For diagnostic, configuration, management, and other functionality, a USB Type B connector provides access to the amplifi-
er’s DSP through the free downloadable Amplifier Navigator application (available on the QSC web site).
For a roadworthy and secure power connection, a locking (when used with a corresponding power cable) IEC connector
helps make sure the system turns on every time you flip the switch.
The fan draws cooling air from the back of the amplifier chassis and pushes it through the internal heat sinks, to be ex-
hausted out the front panel perforations. Directing the air flow in this manner helps prevent a buildup of heated air within
the equipment rack.
The rack ears at the rear corners provide support in racks equipped with rear rails. To avoid stress and damage to the chas-
sis, we recommend attaching the rear rack ears to the equipment rack, especially in portable and mobile applications.
Block diagram
From input to output, the PLD Series power amps are unique. The electronically balanced inputs feed an analog input cir-
cuit with selectable sensitivity (at maximum gain)—either +4 dBu (1.23 V) or +14 dBu (3.88 V)—or selectable maximum
voltage gain: 26 dB (20×), 29 dB (28×), 32 dB (40×), or 35 dB (56×). These settings also help scale the input signal
more optimally to the analog-to-digital converter (ADC). The +4 dBu setting is more suitable for levels from consumer or
semi-pro audio equipment, and the +14 dBu is more suitable for professional-level signals. The gain settings, on the other
hand, are well suited for making design calculations in multi-amp systems.
An interesting aspect of a PLD Series power amp is the versatile configurability between its inputs and its output power
sections. Although the amp has four inputs and four outputs, they do not necessarily correspond one-to-one (although
they can be configured that way). Instead, a 4×4 matrix router (“Source Select” in the block diagram following this section)
allows the user to assign one or more inputs to the various output power sections. This is all done in the digital domain, in
the amp’s DSP circuitry.
From there, each output channel has a full assortment of processing features available for EQ, filtering (including cross-
over), dynamics (RMS and peak limiting), polarity, and delay (up to 50 ms on each channel).
Selectable via the menu are Intrinsic Correction™ processing profiles for select QSC loudspeaker systems, which allow
optimized voicing. Profiles for a number of other popular loudspeaker models are also selectable.

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Electrical power
Electrical power has always been a potential constraint on portable production audio systems, whether they’re run from a
building’s AC mains or from portable power—i.e., a generator. Power amplifiers are by far the biggest consumers of electri-
cal power in an audio system, and through the PLD Series’s significant advances in power factor, efficiency, and universal
voltage capability, the constraints presented by available power just aren’t as limiting any more. With PLD, your system
can produce more audio power for a given amount of available AC, in more places and in more applications, than before
possible.
Power factor
Electrical usage has become a growing concern in recent years. AC-powered devices have a characteristic called power
factor that describes the relationship of the current waveform to the voltage waveform. If the current waveform through
a device coincides exactly and proportionally with the voltage waveform applied across it, its power factor is 1. Examples
of devices with perfect power factor are space heaters and incandescent light bulbs (without dimmers), which present a
purely resistive load to the AC mains. The total power used and/or dissipated by an AC device, in watts, is equal to rms
voltage times rms current times power factor. Therefore, power factor tells us how much of the current provided by the
mains actually gets used as power (this includes wasted power due to inefficiencies in the device).
In devices where the current waveform is still sinusoidal but shifted out of phase with the voltage, as often happens with
AC motors under various load conditions, or is not sinusoidal, as with most electronic power supplies, the power factor
is somewhat less than 1. That means the AC mains actually have to deliver more current than what actually gets used as
power. This may require building substantial excess current capacity into an AC system with no real return on that invest-
ment.
Unfortunately, electronic power supplies—even the heavy line-frequency (non switch-mode) ones that are colloquially
called “linear”—are actually highly nonlinear. As the use of electronic devices increases and resistive appliances such as
incandescent lighting decreases, this nonlinearity presents a growing challenge to the AC mains power generation and
distribution systems and may even require them to be oversized. This is because of “peak rectification,” where the alter-
nating current (AC) is converted into direct current (DC) and fed into reservoir capacitors to smooth out the voltage. The
diodes—semiconductor “check valves” that allow current to flow in one direction but not the other—that do the rectifying
do not actually conduct current until the instantaneous voltage of the AC is slightly higher than the DC voltage stored in the
capacitor.
The result is that the current flows only at the peaks of the AC voltage waveform, leading to a current waveform that isn’t a
sine wave like the voltage; instead it comprises sharp spikes alternating positive and negative every half cycle. Needless to
say, the power factor can be a figure much less than 1 (typically around 0.65).

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Application Engineering Team
Because the current needs of the device are compressed into a very narrow conduction angle, the peak values of the
current can be excessively high. High current peaks cause two types of problem in the AC system itself: power loss (I2
× R) in the wiring, which becomes heat in the wires, outlets, etc.; and distortion because of nonlinear voltage drop (I ×
R), which squashes the tips of the voltage waveform. The high harmonic content of the current peaks sometimes causes
noise radiation issues.
Concern about the pervasive effects of nonlinear power supplies has even led governmental and international agencies to
establish limits and standards on power factor in electronic products, especially those that draw large amounts of current.
The narrow conduction
time in the rectifiers
of a non-PFC power
supply, above, results
in sharp current peaks,
below.
Power factor correction
An advantage of switch-mode power supply technology used in the PLD4.3 and PLD4.5 amplifiers is that we design
power factor correction into them; the current flows throughout the whole voltage waveform and not only at the peaks.
Conventional, non-switch-mode power supplies cannot do this in a practical way.
Power factor correction, as employed in the power supply of these two models, makes the current waveform more nearly
sinusoidal to closely match the AC voltage and achieve power factor figures of at least 0.9 (and even upwards of 0.95 un-
der heavy duty). This practically eliminates any significant harmonic currents and voltage waveform distortion, and reduces
current peaks as well.
In its class of professional power amplifiers, only the PLD Series from QSC offers power factor correction in any models.