Crown ma-1202 Manual De Usuario

The bridge-balanced circuit (U104-B) receives a 
signal from the output of the amplifier, and differ-
ences it with 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 out-
put voltage added to their quiescent voltage. D309, 
D310, D311 and a trimmer resistor set the quiescent 
current point for the bridge-balanced output stage.

The protection mechanisms that affect the signal 
path are implemented to protect the amplifier under 
real-world conditions. These conditions are high 
instantaneous current, excessive temperature, and 
output device operation outside safe conditions. 

Q107 and Q108 sense current in the output stage 
and act as a conventional current limiter. When cur-
rent at any one instant exceeds the design criteria, 
the limiters remove the drive from the LVAs, thus 
limiting 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 out-
put proportional to the always-changing safe oper-
ating 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.

Thermal sensor S100 gives the ODEP circuits vital 
information on the operating temperature of the heat 
sink on which the output devices are mounted.

Should the amplifier fail in such a way that would 
cause DC across the output leads, the DC protection 
circuit senses this on the negative feedback loop 
and shuts down the power supply until the DC is 
removed.

By setting the back panel stereo/mono switch to 
Bridge-Mono, the user can convert the Macro-Tech 
into a bridged, single-channel amplifier. With a sig-

nal applied to the Channel 1 input jack and the load 
connected across the red (+) back panel 5-way 
binding posts, twice the voltage can be output.

The Channel 1 output feeds the Channel 2 error 
amp U204-A. 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 protection mechanisms 
work independently if a fault occurs.

With the stereo/mono switch set to Parallel-Mono, 
the output of Channel 2 is paralleled with the output 
of Channel 1. A suitable jumper capable of handling 
high current levels must be connected across the 
red (+) 5-way binding posts to gain the benefits of 
this mode of operation.

The signal path for Channel 1 is the same as previ-
ously discussed, except Channel 1 also drives the 

output stage of Channel 2. The Channel 2 balanced 
input, error amp, translators and LVAs are discon-
nected and no longer control the Channel 2 output 
stage. Disconnecting the front-end stages from the 
Channel 2 output causes the Channel 2 IOC circuit 
to note that the input waveform (which is not 
present) does not match the output waveform 
(which is driven by the Channel 1 input signal). 
This activates the Channel 2 IOC indicator any time 
the amplifier is switched to Parallel-Mono. 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 one 
channel alone can be obtained. Because the Chan-
nel 2 ODEP circuit is coupled through S1, this gives 
added protection if a fault occurs in the Channel 2 
output stage. The ODEP circuit of Channel 2 will 
limit the output of both output stages by removing 
the drive from the Channel 1 translator stages.