100 Watt Bridge Amplifier Module Circuit

CASSETTE DECK

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#1
Schematic:

DSC00066.jpg

This is a bridge amplifier circuit that I designed and built a long time ago to deliver 100 watts into a low ohm load, less than 1 ohm, several pairs of 4 or 2 ohm speakers in parallel. I originally designed it to run off a 13.8 volt power supply (10 - 15 volts) and up to 40 volts with modifications. I designed it for automotive and home use, but later I built several amplifier modules for use in a physics laboratory for a variety of experiments including infrasonic.
It has a frequency range of 0 Hz (DC) to well above 20kHz.
This circuit works very well although several design improvements are needed to improve DC stability,
keep quiescent output voltage at exactly 50% of power supply voltage, additional temperature compensation and protection against thermal runaway, overload, short circuit protection and thermal shutdown.
The protection circuit and thermal switch shown in the schematic is a proposed modification and not actually in use.
There is a diode in reverse bias across each of the four MJ802 / MJ4502 output transistors not shown in the schematic.
I originally used 2N3055, MJ2955 complimentary transistors in the output stage but later on purchased 30 amp MJ802, MJ4502 transistors on special.
An unusual phase splitting method is used in the driver stage.
Complimentary drivers 2N6387, 2N6667 are darlington transistors.
Voltage gain is adjusted by changing the value of the 75 ohm resistors in the output voltage divider networks connected to the negative feedback loops.
 
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gadget73

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#2
never could get my head around solid state amplifiers. Far too many parts to follow a signal path through without making my head spin.
 

rtp_burnsville

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#3
Are the transistors in your amplifier design still available? Everytime I mess with a transistor amp some of the transistors are no longer available. What is even more frustrating are the numbers which you can't find data on to cross to something else. Motorola was really good at creating 'special' part numbers for a variety of manufactures.

Robert
 

CASSETTE DECK

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#4
Far too many parts to follow a signal path through
I've found that the best way to understand complex amplifier circuits is to identify each stage of the circuit and try to understand it's function. It is sometimes helpful to re-draw the schematic and highlight parts of the circuit for clarity.

Are the transistors in your amplifier design still available?
The transistors are still available but harder to find. Equivalents and many other transistors work well with this circuit. MJ15003 / MJ15004 20 amp transistors are fine for the output stage and still readily available. BD649 / BD650 8 amp darlington transistors are acceptable for the high current driver / phase splitter stage.
 
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