next up previous
Next: 4 Product Specification Up: Audio Power Amplifier Project Previous: 2 Areas of Research

3 Initial Design Decisions

3.1 Amplifier Class

The amplifier will operate in class A.

This was admittedly the toughest design decision to make. The following points were all in class A's favor:

  1. I intend to drive sensitive speakers with acoustic music, allowing the amplifier to be very low powered.
  2. A class A design cannot suffer from crossover distortion.
  3. A class A design is simpler than any class AB design, so there will be less to go wrong in the end.

The negative points that will need to be addressed in the design:

  1. 20% efficiency!
  2. High quiescent power dissipation, resulting in lots of heat.

Output Devices

The amplifier will use power MOSFET's as the output devices.

This was the natural choice for a class A design. Due to the negative temperature coefficient, a power MOSFET that is biased for a high quiescent drain current will be less likely to submit to thermal runaway than one that operates at low levels! Additionally, class A biasing will place the transistor right in the middle of its linear region.

Power Supply

The amplifier will use a power toroid, large bypass capacitors, a star grounding technique and have a safety grounded metal chassis. No power supply regulation will be done.

In addition, the amplifier will be constructed as a dual-mono topology, requiring a separate power supply for each channel of amplification.


next up previous
Next: 4 Product Specification Up: Audio Power Amplifier Project Previous: 2 Areas of Research

Mike Andrews
Tue Mar 25 01:37:10 EST 1997