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
