Crown Com-Tech 1610, Руководство по обслуживанию

Страница: 25 / 459

Com-Tech 810 and 1610 Amplifier Service Manual
]
5-6
Rev. 0
5.6 Dual Operation
For simplicity, the discussion of Dual operation will refer
to one channel only. Mono operation will be discussed in
Sections 5.8 and 5.9 Please refer to the block diagram
in Figure 5.3.
The signal at the
P.I.P. barrier block passes directly into
the balanced input stage. The balanced input stage
causes balanced to single-ended conversion using a
difference amplifier. Next the variable gain stage ampli-
fies or attenuates the signal. The gain of this stage is set
by the position of the input sensitivity switch and the
back panel Input Attenuation control. The error amp
amplifies the difference between the output signal and
the input signal from the gain pot, and drives the voltage
translator stage.
From the error amp, the voltage translator stage chan-
nels the signal to the Last Voltage Amplifiers (LVAs),
depending on the signal polarity. The +LVA and the –
LVA, with their push-pull effect through the bias servo,
and drive the fully complementary output stage.
The bias servo is thermally coupled to the heat sink, and
sets the quiescent bias current in the output stage to
lower the distortion in the crossover region of the output
signal.
With the voltage swing provided by the LVAs, the signal
then gains current amplification through the Darlington
emitter-follower output stage.
The bridge-balanced circuit receives a signal from the
output of the amplifier and detects the difference be-
tween it and the signal at the Vcc supply. The bridge-
balanced circuit then develops a voltage to drive the
bridge-balanced output stage. This results in the Vcc
supply having exactly one half of the output voltage
added to the quiescent voltage.
The protection mechanisms that affect the signal path
are implemented to protect the amplifier under real-world
conditions. These conditions are high instantaneous cur-
rent, excessive temperature, and output device opera-
tion outside safe conditions.
Two transistors act as a conventional current limiter, sens-
ing current in the output stage. If current exceeds safe
levels, the limiters remove the drive from the LVAs, limit-
ing current in the output stage to a safe level.
To further protect the output stages, the patented ODEP
circuitry is used. It produces an analog output propor-
tional to the always changing
safe operating area of the
output transistor. This output controls the translator
stage previously mentioned, removing any further drive
that may exceed the
safe operating area of the output
stage.
A thermal sensor supplies the ODEP circuits with infor-
mation on the operating temperature of the heat sink on
which the output devices are mounted.
Should the amplifier fail in a way that would cause DC
across the output lead, the DC protection circuit senses
this on the negative feedback loop and shuts down the
output stages until the DC is removed.
5.7 Bridge-Mono Operation
By setting the dual/mono switch on the back panel to
Bridge-Mono, the user can convert the
Com-Tech
amplifier into a bridge-mono amplifier. With a signal
applied to the Channel 1 input jack, and the load
between the positive (+) output terminals on the back
panel, twice the voltage can be output.
The Channel 1 output feeds the Channel 2 error amp.
Because there is a net inversion, the Channel 2 output is
out of polarity with Channel 1. This produces twice as
much voltage across the load. Each of the channel’s pro-
tection mechanisms work independently if a fault oc-
curs.
5.8 Parallel-Mono Operation
With the dual/mono switch set to Parallel-Mono, the out-
put of Channel 2 is paralleled with the output of Chan-
nel 1. A suitable high current-handling jumper must be
connected across the positive (+) output terminals to
gain the benefits of this operating mode.
The signal path for Channel 1 is the same as previously
discussed, except that Channel 1 also drives the output
stage of Channel 2. The Channel 2 balanced input, error
amp, translators and LVAs are disconnected and no
longer control the Channel 2 output stage. The Channel 2
output stage and protection mechanisms are also
coupled through S1 and function as one.*
In Parallel-Mono mode, twice the current of a single chan-
nel is available. Because the Channel 2
ODEP circuit is
coupled to Channel 1, you have added protection if a
fault occurs in the Channel 2 output stage. The Channel
2
ODEP circuit limits the output of both output stages by
removing the drive from the Channel 1 translator stages.
_______________________
* Note: When the amplifier’s dual/mono switch is moved to the Parallel/
Mono position, the Channel 2 IOC indicator will illuminate. This is a
normal condition in this configuration.