Crown Micro-Tech MT-1000 Informations techniques télécharger pdf (Page 22)

Page 22

Micro-Tech 600/1200/2400 Power Amplifiers

5 Technical Information

5.1 Overview

Micro-Tech

amplifiers incorporate several technologi-

cal advancements including real-time computer simu-

lation of output transistor stress, low-stress output

stages and an advanced heat sink embodiment.

Custom circuitry is incorporated to limit temperature

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.

Micro-Tech

amplifiers are protected from all common

hazards that plague high-power amplifiers including

shorted, open or mismatched loads; overloaded power

supplies; excessive temperature, chain-destruction

phenomenon, input overload and high-frequency blow-

ups. The unit protects loudspeakers from input and

output DC, as well as turn-on and turn-off transients.

Real-time computer simulation is used to create an

analogue of the junction temperature of the output de-

vices (output transistors). Current is limited only when

the device temperature becomes excessive—and only

by the minimum amount required). This patented ap-

proach called Output Device Emulation Protection (or

ODEP

) maximizes the available output power and pro-

tects against overheating—the major cause of device

failure.

Crown also invented the four-quadrant topology used

in the output stages of each

Micro-Tech

amplifier (see

Figure 5.1). This special circuitry is called the

grounded

bridge

. It makes full use of the power supply by deliv-

ering peak-to-peak voltages to the load that are twice

the voltage seen by the output devices.

As its name suggests, the

grounded bridge

topology

is referenced to ground. Composite devices are con-

structed 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 delivered to the load by increasing

conductance simultaneously in the high-side NPN and

low-side PNP stage, while decreasing conductance of

the high-side PNP and low-side NPN.

The two channels may be used together to double the

voltage (Bridge-Mono) or current (Parallel-Mono) pre-

sented to the load. This feature gives you flexibility to

maximize 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 distortion values.

Aluminum extrusions have been widely used for heat

sinks in power amplifiers due to their low cost and rea-

sonable performance. But measured on a watts per

pound or watts per volume basis, the extrusion tech-

nology doesn’t perform nearly as well as the heat sink

technology developed for

Micro-Tech

amplifiers.

The heat sinks in a

Micro-Tech

amplifier are fabricated

from custom convoluted fin stock that provides an ex-

tremely high ratio of area to volume, or area to weight.

All power devices are mounted directly to massive heat

spreaders that are electrically at the Vcc potential.

Making the heat spreaders electrically alive improves

thermal performance by eliminating the insulating in-

terface underneath each power device. The chassis

itself is also used as part of the thermal circuit to maxi-

mize utilization of the available resources.

5.2 Circuit Theory

Each channel is powered by its own power transformer

T100 or T200. Both channels share a common low-

voltage supply. The secondary output of T100 is full-

wave rectified by D109 and is filtered by a large

computer grade capacitor. A thermal switch embed-

ded in the transformer protects it from overheating.

The low-voltage fanformer 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.

5.2.1 Stereo Operation

For simplicity, the discussion of Stereo operation will

refer to one channel only. Mono operation will be dis-

cussed later. For specific circuit references, see the

block diagram in Figure 5.1 and the schematics pro-

vided at the back of this manual.

The signal at the ¼-inch phone jack input passes di-

rectly to the balanced gain stage (U104-A and

U104-B). The balanced gain stage causes balanced

to single-ended conversion using a difference ampli-

fier. From there, gain can be controlled with a potenti-

ometer. The error amp (U104-C) amplifies the

difference between the output signal and the input sig-

nal from the gain pot, and drives the voltage translator

stage.

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 38 39

Commentaires sur ces manuels

Pas de commentaire

Crown Micro-Tech MT-1000 Informations techniques Page 22

Commentaires sur ces manuels

Produits connexes et manuels pour Amplificateurs audio Crown Micro-Tech MT-1000