Crown ma-1202 Manual De Usuario

Your Macro-Tech amplifier incorporates several 
advanced technological features including real-
time computer simulation of output transistor 
stress, low-stress output stages, an advanced 
heat sink embodiment and the PIP2 (Program-
mable Input Processor) expansion system.

Custom circuitry is incorporated to limit tem-
perature and current to safe levels, making it 
highly reliable and tolerant of faults. Unlike 
many lesser amplifiers, it can operate at its 
voltage and current limits without self-
destructing.

Real-time computer simulation is used to cre-
ate an analogue of the junction temperature of 
the output transistors (hereafter referred to as 
"output devices"). Current is limited only when 
the device temperature becomes excessive (and 
by the minimum amount required). This pat-
ented approach is called Output Device Emula-
tion Protection (or ODEP). It maximizes the 
available output power and protects against 
overheating-the major cause of device failure.

The amplifier is protected from all common 
hazards that plague high-power amplifiers 
including shorted, open or mismatched loads; 
overloaded power supplies, excessive tempera-
ture, chain-destruction phenomena, input over-
load and high-frequency blowups. The unit 
protects loudspeakers from input and output 
DC, as well as turn-on and turn-off transients.

The four-quadrant topology used in a Macro-
Tech's grounded output stages is called the 
Grounded Bridge. This patented topology 
makes full use of the power supplies providing 
peak-to-peak voltages to the load that are twice 
the voltage seen by the output devices (see Fig-
ure 7.1).

As its name suggests, the Grounded Bridge 
topology is referenced to ground. Composite 
devices are constructed to function as gigantic 
NPN and PNP devices to handle currents which 
exceed the limits of available devices. Each 
output stage has two composite NPN devices 
and two composite PNP devices. 

The devices connected to the load are referred 
to as "high-side NPN and PNP" and the devices 
connected to ground are referred to as "low-
side NPN and PNP." Positive current is deliv-
ered to the load by increasing conductance 
simultaneously in the high-side NPN and low-
side PNP stage, while synchronously decreas-
ing conductance of the high-side PNP and low-
side NPN.

The two channels may be used together to dou-
ble the voltage (Bridge-Mono) or the current 
(Parallel-Mono) presented to the load. This fea-
ture gives you flexibility to maximize the power 
available to the load.

A wide bandwidth, multiloop design is used for 
state-of-the-art compensation. This produces 
ideal behavior and results in ultra-low distor-
tion values.

Aluminum extrusions have been widely used 
for heat sinks in power amplifiers due to their 
low cost and reasonable performance. However, 
measured on a watts- per-pound or watts-per-
volume basis, the extrusion technology doesn't 
perform nearly as well as the heat sink technol-
ogy developed for Macro-Tech amplifiers.

Our heat sinks are fabricated from custom con-
voluted fin stock that provides an extremely 
high ratio of area to volume, or area to weight. 
All power devices are mounted directly to mas-
sive heat spreaders that are electrically at the 
Vcc potential. Electrifying the heat spreaders 
improves thermal performance by eliminating 
the insulating interface underneath the power 
devices. The chassis itself is even used as part 
of the thermal circuit to maximize utilization of 
the available cooling resources.

Each channel is powered by its own power 
transformer T100 or T200. Both channels share 
a common low-voltage transformer TF-1. The 
secondary output of T100 is full-wave rectified 
by D109 and is filtered by a large computer-
grade capacitor. D104 through D107 provide 
boosted voltage to power LVAs and predrivers. 

A thermal switch embedded in each transformer 
protects it from overheating.

The low-voltage transformer output is rectified 
by diodes D1, D2, D3 and D4 to generate an 
unregulated 24 volts. Monolithic regulators U1 
and U2 provide a regulated ±15 volts.

For simplicity, the discussion of Stereo opera-
tion will refer to one channel only. Mono opera-
tion will be discussed later.

Please refer to the block diagram in Figure 7.1.

The input signal at the phone jack passes 
directly into the balanced gain stage (U104-C 
and U104-D). When the PIP module is used, 
the input signal first passes through the PIP's 
circuitry and then to the balanced gain stage. 

The balanced gain stage (U104-C and U104-D) 
causes balanced to single-ended conversion 
using a difference amplifier. From there, gain 
can be controlled with a potentiometer. The 
error amp (U104-A) amplifies the difference 
between the output signal and the input signal 
from the gain pot, and drives the voltage trans-
lator stage.

From the error amp U104-A, the voltage trans-
lator stage channels the signal to the Last Volt-
age Amplifiers (LVAs) depending on the signal 
polarity. The +LVA (Q104 and Q105) and the -
LVA (Q110 and Q111), with their push-pull 
effect through the bias servo Q318, drive the 
fully complementary output stage.

The bias servo Q318 is thermally coupled to 
the heat sink, and sets the quiescent bias cur-
rent in the output stage to lower the distortion 
in the crossover region of the output signal. 
Depending on the polarity of the output signal, 
D301, D302, D303 and D304 are used to 
remove the charge on the unused portion of the 
output stage.

With the voltage swing provided by the LVAs, 
the signal then gains current amplification 
through the Darlington emitter-follower output 
stage.