Design a class AB audio amplifier

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I am required to design a class AB audio amplifier to deliver 10W to an 8Ω speaker as shown, but I don’t know where to start. The bandwidth is to cover the range from 20Hz to 18kHz. Input voltage is 500mV rms.

Image source: Electronics Tutorials – Class AB Amplifier Driver Stage

This is what I have done so far

CALCULATIONS.

• R_L = 8 Ω

• P_AVG = 10W

• Bandwidth from 20 Hz to 18 kHz

• V_(0 peak) = √(2×10×8) = 12.65v

• V_CC = V_(0 peak)×2+2 = 27.3V ≅ 28V

• I_(0 peak) = V_(0 peak)/R_L = 12.65/8 = 1.58A

Each transistor current is given by:

• I_(0 peak)/2 = 1.58/2 = 0.79A

Assuming β = 113

• I_(B Q1) = I_(B Q2) = I_E/(β+1) = 0.79/114 = 6.93mA

Assuming I_D = 1A, then:

• I_bias = 1mA+1mA+6.93mA+6.93mA = 15.86mA

Setting V_C = 14V, then:

• R4 = (28V-14v-0.7v-0.7V)/15.86mA = 794.5Ω

Setting V_E = 1V

• R_3+R_3^II = 1V/15.86mA = 63.05Ω

Input current is assumed to be 500mA
Q_3 gain is given by:

• V_(O peak rms)/V_(in rms) = √(8×10)/500mA = 17.88Ω

Setting Q_3 gain to 20:

• R_3^II = ((28V-14V)/15.86mA)/20=44.14Ω
• R_3=63.05-44.14 = 18.92Ω
• I_B = I_C/β = 15.86mA/100 = 0.1586mA

Setting I_1 = 20 I_B:

• I_B = 20×0.1586mA = 3.172mA
• R_2 = 1.7V/3.172mA = 535Ω
• R_1 = (28V-1.7V)/3.172mA = 8291Ω

Designing for C_1 and C_3:

• r_e = 26mV/15.86mA = 1.64Ω
• R_1 ||R_2 = 502.57Ω
• R_3^II = 44.14Ω
• R_th = 41.96Ω
• C1 = C3= 1/(2×π×f_L×R_th) = 1/(2×π×20×44.14) = 189.65μF

Designing for C_2:

• R_th = 69.6759Ω
• C_2 = 10/(2×π×f_L×R_th) = 10/(2×π×20×69.6759) = 1142μF

When I simulate the circuit, the output voltage is quite small and the output power is much less than 10W.

What could be the issue?

The final circuit I came up with is shown.