JBL P-1000 Manual

erald Stanley has been with
Crown for nearly 40 years.
He started his career in
electronics by listening to short
wave broadcasts on old radios
that he repaired by scaveng-
ing parts from other old
radios. Working on RF (radio
frequency), IF (intermediate fre-
quency), and AF (audio frequency)
stages, Stanley’s youthful hobby led to a
long-standing interest in engineering
design. When he reached high school,
Stanley started working on vacuum tube
power amplifiers with high-feedback circuitry for
the home audio systems of friends and family.
Back in 1964, while a student at Michigan State, Stanley began
working for Crown in the tape recorder sector. (This was Crown’s main
business back then.) Designs of the mid-1960s incorporated transistors
rather than vacuum tubes and Stanley worked as a draftsman and power
amp designer on Crown’s first transistor components — including power
David Navone talks tech with Crown’s crown prince of power,
GERALD STANLEY, the man behind JBL’s massive GTI series amplifiers.
G
Reprinted from the September 2003 issue of
AutoMediaAutoMedia

amps for the tape recorders. In 1966,
the University of Michigan presented
Stanley with a graduate degree and
he began full time work designing
power amps and tape recorders for
Crown.
Since that time, Stanley has
designed tape recorders, signal
processors, audio amps, magnetic
resonance gradient amp, and semi-
conductor and audio test equipment
— including the Crown TEF. (We use
the TEF for acoustic measurements in
our Autosound 2000 Test Lab.) One
rather unusual project of Stanley’s
was the design of a speech rate trans-
lator that was used by the courts to
review hours of the Nixon tapes at
higher than normal speeds.
AUTOMEDIA recently had the
opportunity to sit and talk shop with
Gerald Stanley.
With Harman International’s acqui-
sition of Crown in 2000, it certainly
didn’t take long for the introduction
of the JBL A6000GTI 6000-Watt
power amplifier. Why was this
$6000 amplifier the first Crown
designed entry into the mobile
audio market?
The 6000 is a statement piece that’s
intended to not only set performance
records, but to make it obvious to all
that JBL is not just another auto amp
maker using the same tired old amp
technologies that have been in play
for decades. The 6000 uses a new
robust switch-mode technology that
allows higher voltage than has ever
been seen in the auto. The technolo-
gy, BCA, is short for balanced current
amplifier. There are simple explana-
tions of this class-I technology on the
Crown Web site www.crownaudio.com
. A more detailed description can be
found in US patent 5,657,219 and an
IEEE Transactions on Power
Electronics article Vol. 14, no. 2,
March 1999 pg. 372-380, titled
“Precision DC-to-AC Power
Conversion by Optimization of the
Output Current Waveform - The Half
Bridge Revisited”.
What’s unique about the operating
parameters about this amplifier?
The amplifier (monaural) has +/-165 -
Volt DC rails that power two 3 KW
BCA half-bridges. This allows three
modes of operation:
1. Two high-voltage amps each
driving 2-4 ohms with 160V+ peaks.
2. A single bridged output driving 2-
4 ohms with 320V+ peaks.
3. A single paralleled output driving
1-2 Ohms with 160V+ peaks.
The latter mode is proprietary as
ultra-low output impedance amplifiers
are paralleled without requiring ballast
or producing high circulating currents.
The output impedance is not impaired
to attain this mode of operation. (See
U.S. patent 6,297,975.)
Does the JBL A6000GTI amplifier
use Crown’s Grounded Bridge
Output Topology? If yes, please
elaborate. If not, why not?
Grounded bridge technology is not
required when you’re able to produce
high-voltage stages directly from half-
bridge topologies. Common class-D
designs cannot reliably attain high
voltages with usable fidelity due to
failure modes found in all high-voltage
MOSFETs. The BCA design prevents
current flow in the body diodes of it’s
MOSFET switches and thereby avoids
the failure mode entirely. Dissipative
amplifier designs suffer from thermally
driven failures such as secondary
breakdown and overt overheating.
In industrial settings it’s common to
place full-bridge switch-mode ampli-
fiers in series for increased voltage.
Grounded bridge operation is a mem-
ber of this class of operation. The tar-
get peak output voltages may be in
the thousands of volts in these set-
tings.
What are the power requirements
for this huge amplifier and how can
they be met by in a car audio instal-
lation?
The power requirements will require
the addition of a 600-Amp (cold crank-
ing) battery at a minimum. The longer
the desired run-time at high power,
the more batteries that will be
required. If power draw is to be sus-
tained at high levels, then the alterna-
tor must be augmented as well. While
the overall amplifier and its power
supply will produce a very high 75
percent operating efficiency at high
power, that’s still a significant potential
power draw.
Approximately how much long term
average power will the JBL
A6000GTI power amplifier draw
when it’s producing music at full
power with a duty cycle of typical
music?
The best rule of thumb is the 75 per-
cent efficiency rule. Many ask amplifi-
er efficiency questions based on “typi-
cal” music operation, but what is “typi-
cal” music for one user isn’t even
music to another.
How do you rate amplifier efficien-
cy in your list of important design
considerations?
The larger the amplifier and the more
limited the supply of power, the more
important the efficiency issue
becomes. For a 6 KWatt amplifier ,it’s
very important on both counts.
Can you explain the benefits of
Crown’s Dynamic Bass
Optimization when compared to
typical Bass Boost circuitry? Is the
DBO circuitry used in car audio
power amplifiers designed by
Crown?
The DBO has it’s origins with JBL, not
Crown. Experience has shown that

equalization is typically needed to
optimize the in-vehicle response of
high BL product drivers in an often
resonant environment. In the final
result, it’s always the listener that’s
the judge of what is best and that can
only be attained by giving flexibility.
Back in the late 1980’s, Richard
Clark used a pair of Crown car
audio power amplifiers in his
IASCA-dominating Cadillac. What
can you tell us about the design of
this early Crown amplifier and,
also, what happened to the distribu-
tion?
Crown can be rightfully accused of not
having taken the car audio market
seriously. For a brief period of time,
Crown sold a product wherein we’d
contracted the design and had it made
in Taiwan. It was a conventional class-
AB design with a switch-mode power
supply. Not having been willing to
develop the market, we simply pur-
sued more profitable things, such as
making gradient amplifiers for MRI.
At Autosound 2000, we have a six
amp set of your 10,000-Watt Crown
- Techron power amps in our test
lab. We configure them in series
and parallel for various tests and
they’re incredible. Did you have
anything to do with the design of
those monster amps?
Yes, I was the main designer of these
amplifiers that owe their heritage to an
industrial line of amplifiers made for
medical imaging in MRI machines.
Very large high-performance ampli-
fiers are used to drive the whole-body
gradient coils of such machines. The
BCA technology was also created to
first make gradient amplifiers.
Will Crown-designed car audio
amplifiers use ODEP (Output
Device Emulation Protection) cir-
cuitry? Is so, what will this do for
performance? If not, why not?
Junction temperature simulation or
ODEP can be applied to switch-mode
amplifiers but is of less importance
compared to its value in dissipative
amplifier designs. It’s better to make
less heat than to optimize and protect
dissipative processes.
When will installer-programmed
adaptive signal processing be
included in the design of power
amplifiers? The idea here is that
various speaker parameters could
be programmed into the amp’s
processor so that we could get 100
percent speaker performance —
with no danger of destroyed speak-
ers. Any thoughts here?
As to when, I cannot say. But, it is
true that more can be done with digital
signal processing to protect and
dynamically equalize loudspeakers
than is being done today.
How did you get involved in design-
ing audio components? Can you
tell us some of the highlights of
your career?
If you jump on Google
(www.google.com) and search on my
name you’ll find a couple of interviews
that have been done that give some of
my ancient history. I started in the
vacuum tube era, and moved on to
the dissipative solid-state designs and
am now in the third major generation
of audio power — the switch-mode
era. It’s been fun.
How large do you think car audio
amps will end up in the next 10
years? What are the practical lim-
its?
The adoption of 42-Volt DC electric
systems will be helpful to making larg-
er amps as the 6000 presently uses a
0-gauge power feed. Just as higher
voltage audio output makes the distri-
bution of low-loss audio more practi-
cal, so will higher voltage input power.
Do you think we’ll ever see the day
when the loudspeaker will be in a
“closed loop” with the power ampli-
fier as opposed to running them
“open loop” as we do today?
Yes, there will be some closed loop
systems, but note that they’ll encour-
age “canned” solutions which will
reduce the configuration options that
the customer will have. As an interest-
ing historical note, see U.S. patent
1,822,758. In 1929, after Harold Black
first invents negative feedback, the
patent office issued this patent to
Pierre Toulon wherein is shown the
first use of closed-loop on a loud-
speaker. Toulon’s patent on negative
feedback was actually issued before
Black’s but he did not file first.
Since you started designing high
powered amplifiers, what amplifier
components have experienced the
greatest advances?
The active elements have undergone
the most advancement. All power
designs are limited by the perform-
ance limits of the tubes, bipolar tran-
sistors, MOSFETs, etc.
Many car audiophiles feel that sub-
jective testing of amplifiers shows
that size is the most important fac-
tor in sound quality. Do you agree
or disagree?
Size is a vital part of the system, but
brute size alone is not sufficient.
Fidelity is always required. Switch-
mode amplifiers are very old — the
first instance can be traced to
Burnice Bedford in 1930, U.S. Patent
1,874,159. Not until recent years has
their fidelity been adequate to be
used in high-performance audio. To
that end, the BCA design leads the
charge.
Our thanks go to Gerald Stanley for
taking the time for this interview.
We’re looking forward with great inter-
est to Crown car audio components
and Gerald Stanley designs.

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