Jbl 6233 service manual

Page 2

More Than Raw Power

Although high power amplifiers have been available for
some time. they generally have been bulky units designed
primarily for consumer use rather than for the more rigorous
requirements of studio. reinforcement or PA applications
For the most part. they perform adequately. but lack

reliability when used under road conditions. even with
additional cooling.

The primary design goal was to build a rugged. high power
amplifier of the highest quality, smallest size and lightest
weight possibleThis goal hasbeen achieved in the Model
6233. a reliable. two-channel amplifier that mounts in three
EIA standard rack spaces and weighs less than 16 kg [35 lb)
Intended for use in recording studios, wide-range sound
systems and similar applications, the 6233 delivers stable.
virtually distortion»free amplification for sustained time
periods at any power level. up to and including full output.
without requiring additional coolingThe 6233 is clean as well
as powerful: Each channel is capable of delivering 300 W
continuous sine wave into a 4 a load. or 200 W into an

8 0 load with total harmonic distortion of less than 0.05%,
20 Hz» 20 kHz. In addition. the two channels can be bridged
for single-channel operation, in which case the 6233 will
deliver 700 W continuous sine wave into 8 n (the minimum
recommended impedance in the bridged configuration) or
400 W into 16 o. 20 Hz»20 kHz at no more than 0.05% THD,

Input sensitivity of the 6233 is high: full rated output can be
achieved with an input of only 0.77 V. Rise time is 4 us into a
4 0 load or 3 HS into an 8 0 load. and the unit has a slew
rate greater than 20 V/HS. The result is accurate. well-defined
high frequency performance that is transparent and effortless,
and which does not become veiled. muddy or harsh at even
the highest power levels.

The 6233 is the first amplifier in its power class to use

an inverter power supply. This saves weight and space: the
6233 is approximately one-third the size and weight of a
comparable conventional amplifier, making it far more
convenient to pack and transport, The inverter also provides
transformer isolation from the power line. unlike other
lightweight power supplies.

The inverter power supply uses high-speed switching
.echnology. long proven in computers. to convert (or. more
correctly. invert) the 50/60 Hz power line frequency to

20 kHz. This allows use of a 0.9 kg (2 lb) transformer instead
of the 23 kg (50 lb) transformer normally required.The
transformer output is then rectified to the DC voltages
required by the amplifier modules. The inverter power supply
has an output capacity greater than 2 kW. more than enough
reserve to support both amplifier channels without strain
under any conditions.

Advanced Circuit Design

Full complementary symmetry in each channels outputstage
allows broad bandwidth without the imbalance inherent in

a quasi-complementary approach. it also helps improve
amplifier power response. reduce distortion and eliminate
turn»on transients. Fourteen 150 W output transistors per
channel greatly improve reliability. because each transistor
typically operates at only a fraction of its capacity. regardless
of amplifier power level.

The 6233 employs forced-air cooling: each transistor is
mounted on an individual heat sink and optimally positioned
in a cooling tunnel extending from the front to the rear of
the amplifier A two»speed fan forces air through the tunnel;
thermal sensors in each channel and in the power supply
increase fan speed as required. A thermal protection device
in each channel suspends operation of only that channel

it it overheats. and the device automatically resets when the
module cools to a safe operating temperature. The 6233
will operate in ambient temperatures as high as 50°C (122°F)
without degradation of performance.

Each channel of the 6233 operates independently and is fully
protected against short circuits. mismatched loads. excessive
temperatures and installation errors. Either channel can
enter the protect mode without affecting the other. The 6233
will remain stable under all conditions. including operation
into reactive loads presented by long cable lengths and
high-quality loudspeakers. Most importantly. the protective
circuitry cannot chatter when activated. (Chattering. a by~
product typical of the protective circuitry in large amplifiers.
occurs when the circuitry releases too soon. sending a large
burst of current that can destroy high frequency drivers.)

Versatility

Five sequential indicator lights for each channel allow the
operator to monitor visually the power reserve available.

A unique sensing circuit triggers the top. red light when the
output level is 2 dB below clipping; each successive light
indicates an output level of 6 dB (V. power) less than the light
above it. The lights are far more useful than VU meters.
because they are an accurate performance indicator even
when the power line voltage drops and can also be read
quickly and accurately from a distance.

Any source device capable of driving a load of 20 kn or

less can be used? The amplifier inputs are unbalanced. the
configuration typical of most applications. However. the high
input sensitivity of the 6233 allows it to achieve full output
when driven by almost any source. balanced or unbalanced.

To provide additional flexibility. at the expense of some loss
in bandwidth. each channel of the 6233 is provided with a

II the rated load impedance of the source Gel/ICE iS greater than 20 m. high
frequency response will be compromised In such cases. a line amplifier should
be used to lower impedance