Motivation for the BC1 Amplifier 4 Unsophisticated amplifier

Motivation for the BC-1 Amplifier 4 Unsophisticated amplifier for the less experienced 4 Easily built 4 Illustrate basic design techniques 4 Demonstrate performance obtainable from a simple design 4 125 -watt BJT design with 2 output pairs Bob Cordell

Three-stage Power Amplifier Bob Cordell

Simple Power Amplifier Bob Cordell

Basic Thompson Topology 4 Three stages: - differential pair input stage (IPS) - voltage amplifier stage (VAS) - emitter follower output stage (OPS) 4 Input pair loaded with current mirror 4 Common emitter VAS loaded with current source 4 Darlington emitter follower output stage 4 Miller feedback compensation Bob Cordell

Thompson Topology Bob Cordell

BC-1 Featured Improvements 4 4 4 4 4 Current mirror load with “helper” transistor Clamping diodes on IPS output 2 -transistor (2 T) VAS Locanthi T-circuit 3 -EF output stage Fast output transistors High driver bias current Dual Vbe multiplier bias spreader “Natural” current limiting Comprehensive protection circuit Bob Cordell

Input Stage, VAS and Pre-driver Bob Cordell

Output Stage Bob Cordell

Protection 4 Natural current limiting 4 Speaker relay 4 Short-circuit 4 Over-temperature 4 DC offset 4 Power supply under-voltage 4 Rail failure/reversal 4 Turn-on, turn-off muting Bob Cordell

Short Circuit Detection Bob Cordell

Protection Control Circuit Bob Cordell

DC Offset and Power Good Detection Bob Cordell

Power Supply Bob Cordell

Power and Grounding Topology Bob Cordell

Performance 4 Wide frequency response: 1 Hz – 400 k. Hz 4 Clean 10 k. Hz square wave: 1. 2 µs, no ringing 4 High slew rate: 50 V/µs 4 THD-1 <0. 001% 1 W – 100 W, 8Ω or 4Ω load 4 THD-20 <0. 004% 1 W – 100 W, 8Ω (0. 008%, 4Ω) 4 S/N 100 d. B, A-weighted, 9 n. V/√Hz input-referred 4 Damping Factor > 200 to 2 k. Hz, 45 at 20 k. Hz 4 High output current: >400 W burst into 2Ω Bob Cordell

Frequency Response Bob Cordell

Square Wave Response Bob Cordell

Damping Factor vs. Frequency Bob Cordell

THD+N vs. Power Bob Cordell

THD+N vs. Frequency Bob Cordell

Output Stage THD vs. Power & Bias Bob Cordell

Complete Amplifier (less protection) Bob Cordell

BC-1 Printed Circuit Boards 4 Laid out and fabricated by Rich Savas 4 Will be made available 4 Initial prototype shown – design may change Bob Cordell