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The principle of the amplifier Audison LR604XR

2015-01-06 20:17  
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 This article describes an amplifier Audison LR604XR principle. The principle is simple there, we recommend that combine text carefully read the complete schematic. To better grasp this principle, it is recommended to read several times on this principle.

1. Layout 

   DCDC converter and analog parts are separated with a wall of filter caps (on internal power rails). Parts are quite densely packed; rectifier diodes are mounted on flat individual heatsinks above the PWM controller ICs (I understand the designer: there is no space left on the upper contact strip, and placing diodes on the lower one will need long, noisy and lossy power traces). This, as well as mica grease transistor pads, will add difficulties to repair man, actually I replaced mica with long silicon strips.

2. Too many blocks…

Input REMOTE line switches on a low-drop input switch, that powers a low-current internal 12V rail. This switch goes on at 8V with 1V hysteresis, powering low-power PWM controller IC pin (it has two Vdd pins, low and high current), protection switches and multiplexer, and a switch controlling regulators in the power amp section. High-current PWM controller pin (gate drivers Vdd) is powered from main 12V input via a series resistor.PWM controller is based on a derelict  SG3525A , in voltage feedback mode. A traditional push-pull DCDC converter has three features to note. One is an RC ground current breaker, isolating power ground from analog ground, this is not uncommon. Another is a smart heat-sensitive duty cycle limiter. And a third is an oddest gate drive network (see below).Protection is built along three lines: (a) Overheat shutdown (b) Instant output current in each channel (c) DC at amplifier outputs. Protection output has two alert modes: (a) Shutdown – highest all-out priority, kills DCDC power (b) Output Disable – disconnects analog switches, keeping DCDC unit running.The only ICs are: PWM controller and opamps in the crossovers section. All protection circuitry is discrete, actually taking less space than alternative designs on LM339 and CMOS logic. Despite component density, PCB traces are quite thick, with decent spaces, and a surprisingly low via count.

3. Power Supply

 

Inside Story: Audison LR604XR amplifier

 

 

Inside Story: Audison LR604XR amplifier

Inside Story: Audison LR604XR amplifier

4. Power Amps

Inside Story: Audison LR604XR amplifier

Inside Story: Audison LR604XR amplifier

Each power amp takes 6 cm of heat sink’s contact strip. Bias transistor and pre-output transistors (TO-92 cases) are also clamped to the heatsink with a special wave-shaped clip, so that three devices take as much space as one TO220 device.

Note that all four output channels are services by one regulator control switch and two regulator sets.

5. Protection circuits

Inside Story: Audison LR604XR amplifier

Inside Story: Audison LR604XR amplifier

Protection circuit is distributed all over the board – current sensors are placed by the power amps, two DC sensors – separately in the analog part of the board, protection triggers – close to the PWM controller. 4 current and 2 DC sense lines are joined in open-collector AND logic; low state in each line opens Q93 (normally closed) and, thru a Q65-Q63 switch, sends high Shutdown signal to PWM controller. Trigger latches up in Shutdown mode unless REMOTE signal is switched on and off again. Note the smart timing filters in Q65 base chain.Shutdown also controls Q91-Q64 switch that turns muting circuits to open (high level) and close (low level). R65-C55-R64-D66 enable delayed turn-on and quick turn-off in normal operation.

VN:F [1.6.9_936]

 


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