There is certainly no need for a linear audio amplifier any more.
This is -70dB at 3kHz and -80 dB at 2kHz
Switching frequency is between about 400 and 550kHz.
Simulation isn't fast. If you want to try it then after fixing much line wrappage you will need the files from here in the same folder.
BF721 seems to be obsolete. Any suggestions for an alternative?
Version 4.1 SHEET 1 5624 2596 WIRE -96 -16 -192 -16 WIRE 48 -16 -96 -16 WIRE 160 -16 48 -16 WIRE 448 -16 160 -16 WIRE 576 -16 528 -16 WIRE 1264 -16 576 -16 WIRE 1904 -16 1264 -16 WIRE 2016 -16 1904 -16 WIRE 2384 -16 2016 -16 WIRE 1264 0 1264 -16 WIRE 2384 0 2384 -16 WIRE -96 16 -96 -16 WIRE 160 16 160 -16 WIRE -192 32 -192 -16 WIRE 48 64 48 -16 WIRE 1008 96 928 96 WIRE 1104 96 1008 96 WIRE 1264 96 1264 80 WIRE 1360 96 1264 96 WIRE 1488 96 1360 96 WIRE 1632 96 1488 96 WIRE 1760 96 1632 96 WIRE 160 112 160 96 WIRE 160 112 112 112 WIRE 1632 112 1632 96 WIRE 2384 112 2384 80 WIRE 928 128 928 96 WIRE -192 144 -192 96 WIRE 1008 144 1008 96 WIRE 160 160 160 112 WIRE 1760 160 1760 96 WIRE -96 208 -96 96 WIRE 48 208 48 160 WIRE 48 208 -96 208 WIRE 96 208 48 208 WIRE 1632 208 1632 192 WIRE 1696 208 1632 208 WIRE 1104 224 1104 96 WIRE -96 256 -96 208 WIRE 576 256 576 -16 WIRE 1008 272 1008 224 WIRE 1040 272 1008 272 WIRE 1632 336 1632 208 WIRE 1664 336 1632 336 WIRE 1760 336 1760 256 WIRE 1760 336 1728 336 WIRE 2016 336 2016 -16 WIRE 1008 352 1008 272 WIRE 1104 368 1104 320 WIRE 1152 368 1104 368 WIRE 1264 368 1264 96 WIRE 1264 368 1216 368 WIRE 1760 368 1760 336 WIRE 1792 368 1760 368 WIRE 1872 368 1856 368 WIRE -96 384 -96 336 WIRE 1264 400 1264 368 WIRE 1360 400 1360 96 WIRE 1488 400 1488 96 WIRE 1872 416 1872 368 WIRE 1904 416 1872 416 WIRE 1920 416 1904 416 WIRE 16 432 -80 432 WIRE 160 432 160 256 WIRE 160 432 96 432 WIRE 224 432 160 432 WIRE 400 432 304 432 WIRE 1872 464 1872 416 WIRE 1872 464 1856 464 WIRE -400 480 -432 480 WIRE -368 480 -400 480 WIRE -224 480 -288 480 WIRE -144 480 -224 480 WIRE 576 480 576 336 WIRE 576 480 464 480 WIRE 1760 512 1760 368 WIRE 1792 512 1760 512 WIRE 1760 528 1760 512 WIRE -432 544 -432 480 WIRE -224 560 -224 480 WIRE 1632 560 1632 336 WIRE 1632 560 944 560 WIRE -80 576 -80 528 WIRE 144 576 -80 576 WIRE 400 576 400 528 WIRE 400 576 208 576 WIRE 1264 624 1264 464 WIRE 1360 624 1360 464 WIRE 1360 624 1264 624 WIRE 1488 624 1488 464 WIRE 1488 624 1360 624 WIRE 1760 624 1760 608 WIRE 1760 624 1488 624 WIRE 1856 624 1856 560 WIRE 1856 624 1760 624 WIRE 1920 624 1856 624 WIRE 2016 624 2016 496 WIRE 2016 624 1920 624 WIRE 2032 624 2016 624 WIRE 2080 624 2032 624 WIRE 2224 624 2160 624 WIRE 2288 624 2224 624 WIRE 2336 624 2288 624 WIRE 2384 624 2336 624 WIRE -80 640 -80 576 WIRE 144 640 -80 640 WIRE 400 640 400 576 WIRE 400 640 208 640 WIRE 2384 656 2384 624 WIRE 1104 672 1104 368 WIRE 1152 672 1104 672 WIRE 1360 672 1216 672 WIRE 1488 672 1360 672 WIRE 1632 672 1488 672 WIRE 1760 672 1632 672 WIRE 2288 672 2288 624 WIRE -432 688 -432 624 WIRE -224 688 -224 640 WIRE 1632 688 1632 672 WIRE 944 704 944 560 WIRE 944 704 272 704 WIRE 1760 736 1760 672 WIRE 944 768 48 768 WIRE 1632 784 1632 768 WIRE 1696 784 1632 784 WIRE 2288 784 2288 736 WIRE 2384 784 2384 736 WIRE 48 800 48 768 WIRE 272 800 272 704 WIRE 576 832 576 480 WIRE 656 832 576 832 WIRE 752 832 656 832 WIRE 848 832 752 832 WIRE -80 848 -80 640 WIRE -16 848 -80 848 WIRE 400 848 400 640 WIRE 400 848 336 848 WIRE 848 848 848 832 WIRE -80 912 -80 848 WIRE 400 912 400 848 WIRE 1632 912 1632 784 WIRE 1664 912 1632 912 WIRE 1760 912 1760 832 WIRE 1760 912 1728 912 WIRE 2032 912 2032 624 WIRE 576 944 576 832 WIRE 656 944 656 832 WIRE 752 944 752 832 WIRE 848 944 848 912 WIRE 1760 944 1760 912 WIRE 1792 944 1760 944 WIRE 1872 944 1856 944 WIRE 48 960 48 896 WIRE 48 960 -16 960 WIRE 160 960 48 960 WIRE 272 960 272 896 WIRE 272 960 160 960 WIRE 336 960 272 960 WIRE 1360 976 1360 672 WIRE 1488 976 1488 672 WIRE 1872 992 1872 944 WIRE 1904 992 1872 992 WIRE 1936 992 1904 992 WIRE -160 1040 -240 1040 WIRE 1872 1040 1872 992 WIRE 1872 1040 1856 1040 WIRE 2384 1040 2304 1040 WIRE -80 1056 -80 1008 WIRE 160 1056 160 960 WIRE 400 1056 400 1008 WIRE 656 1056 656 1024 WIRE -240 1072 -240 1040 WIRE 752 1072 752 1024 WIRE 848 1072 848 1024 WIRE 848 1072 752 1072 WIRE 2304 1072 2304 1040 WIRE -160 1088 -160 1040 WIRE 1760 1088 1760 944 WIRE 1792 1088 1760 1088 WIRE 2384 1088 2384 1040 WIRE 1760 1104 1760 1088 WIRE 944 1136 944 768 WIRE 1632 1136 1632 912 WIRE 1632 1136 944 1136 WIRE -160 1200 -160 1152 WIRE -80 1200 -80 1136 WIRE -80 1200 -160 1200 WIRE 160 1200 160 1136 WIRE 160 1200 -80 1200 WIRE 400 1200 400 1136 WIRE 400 1200 160 1200 WIRE 448 1200 400 1200 WIRE 576 1200 576 1024 WIRE 576 1200 528 1200 WIRE 1008 1200 1008 416 WIRE 1008 1200 576 1200 WIRE 1360 1200 1360 1040 WIRE 1360 1200 1008 1200 WIRE 1488 1200 1488 1040 WIRE 1488 1200 1360 1200 WIRE 1760 1200 1760 1184 WIRE 1760 1200 1488 1200 WIRE 1856 1200 1856 1136 WIRE 1856 1200 1760 1200 WIRE 1904 1200 1856 1200 WIRE 2032 1200 2032 1072 WIRE 2032 1200 1904 1200 WIRE 2384 1200 2384 1168 WIRE 2384 1200 2032 1200 WIRE 848 1264 848 1072 WIRE 2224 1264 2224 624 WIRE 2224 1264 848 1264 FLAG -192 144 0 FLAG -96 384 0 FLAG -224 688 0 FLAG -432 688 0 FLAG -240 1072 0 FLAG 656 1056 0 FLAG 928 128 0 FLAG 2288 784 0 FLAG 2384 784 0 FLAG 2384 112 0 FLAG 2304 1072 0 FLAG -400 480 in FLAG 2336 624 out FLAG 1904 416 gu1 FLAG 1904 992 gu2 FLAG 1904 -16 v+ FLAG 1920 624 vout FLAG 1904 1200 v- SYMBOL pnp 96 256 M180 WINDOW 0 55 63 Left 2 WINDOW 3 52 32 Left 2 SYMATTR InstName Q4 SYMATTR Value BF721 SYMBOL res -80 240 M0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL polcap -176 32 M0 SYMATTR InstName C2 SYMATTR Value 10000n SYMBOL res 144 0 R0 SYMATTR InstName R7 SYMATTR Value 220 SYMBOL res 544 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R29 SYMATTR Value 10 SYMBOL pnp -144 528 M180 WINDOW 0 47 60 Left 2 WINDOW 3 48 34 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N5401 SYMBOL pnp 464 528 R180 WINDOW 0 56 67 Left 2 WINDOW 3 53 39 Left 2 SYMATTR InstName Q2 SYMATTR Value 2N5401 SYMBOL res 112 416 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 47 SYMBOL res 320 416 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 47 SYMBOL npn 336 912 R0 WINDOW 0 -32 27 Left 2 WINDOW 3 -87 73 Left 2 SYMATTR InstName Q6 SYMATTR Value BC847B SYMBOL npn -16 912 M0 WINDOW 0 -25 28 Left 2 WINDOW 3 -82 73 Left 2 SYMATTR InstName Q5 SYMATTR Value BC847B SYMBOL res -96 1040 R0 SYMATTR InstName R8 SYMATTR Value 220 SYMBOL res 384 1040 R0 SYMATTR InstName R10 SYMATTR Value 220 SYMBOL res -240 544 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL res -272 464 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 100 SYMBOL voltage -432 528 M0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value SINE(0 1 1000) SYMBOL res 544 1184 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R28 SYMATTR Value 10 SYMBOL polcap -144 1088 M0 SYMATTR InstName C3 SYMATTR Value 10000n SYMBOL npn -16 800 R0 SYMATTR InstName Q7 SYMATTR Value BF820 SYMBOL npn 336 800 M0 SYMATTR InstName Q8 SYMATTR Value BF820 SYMBOL res 144 1040 R0 SYMATTR InstName R9 SYMATTR Value 330 SYMBOL res 592 240 M0 SYMATTR InstName R14 SYMATTR Value 5.6Meg SYMBOL res 592 928 M0 SYMATTR InstName R15 SYMATTR Value 3.9Meg SYMBOL res 1248 -16 R0 SYMATTR InstName R16 SYMATTR Value 3.3k SYMBOL zener 1280 464 R180 WINDOW 0 43 31 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D8 SYMATTR Value STZ5_6N SYMBOL pnp 1696 256 M180 WINDOW 0 65 65 Left 2 WINDOW 3 66 30 Left 2 SYMATTR InstName Q10 SYMATTR Value PBSS5140T SYMBOL res 1648 96 M0 SYMATTR InstName R18 SYMATTR Value 330 SYMBOL diode 1728 320 R90 WINDOW 0 64 33 VBottom 2 WINDOW 3 -30 32 VTop 2 SYMATTR InstName D9 SYMATTR Value BAT54HY SYMBOL ind 2064 640 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 28µ SYMATTR SpiceLine Rser=1m SYMBOL pnp 1792 560 M180 WINDOW 0 65 65 Left 2 WINDOW 3 66 30 Left 2 SYMATTR InstName Q12 SYMATTR Value PBSS5140T SYMBOL diode 1792 352 M90 WINDOW 0 62 35 VBottom 2 WINDOW 3 -31 57 VTop 2 SYMATTR InstName D3 SYMATTR Value BAS16HY SYMBOL res 1776 512 M0 SYMATTR InstName R20 SYMATTR Value 750 SYMBOL pnp 1696 832 M180 WINDOW 0 65 65 Left 2 WINDOW 3 66 30 Left 2 SYMATTR InstName Q9 SYMATTR Value PBSS5140T SYMBOL res 1648 672 M0 SYMATTR InstName R17 SYMATTR Value 330 SYMBOL diode 1728 896 R90 WINDOW 0 62 33 VBottom 2 WINDOW 3 -33 32 VTop 2 SYMATTR InstName D10 SYMATTR Value BAT54HY SYMBOL pnp 1792 1136 M180 WINDOW 0 65 65 Left 2 WINDOW 3 66 30 Left 2 SYMATTR InstName Q11 SYMATTR Value PBSS5140T SYMBOL diode 1792 928 M90 WINDOW 0 62 41 VBottom 2 WINDOW 3 -35 57 VTop 2 SYMATTR InstName D12 SYMATTR Value BAS16HY SYMBOL res 1776 1088 M0 SYMATTR InstName R21 SYMATTR Value 750 SYMBOL npn 1040 224 R0 SYMATTR InstName Q15 SYMATTR Value BC847B SYMBOL res 992 128 R0 SYMATTR InstName R27 SYMATTR Value 4.7k SYMBOL zener 1024 416 R180 WINDOW 0 43 31 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D5 SYMATTR Value STZ5_6N SYMBOL pnp 112 160 R180 WINDOW 0 70 63 Left 2 WINDOW 3 64 29 Left 2 SYMATTR InstName Q3 SYMATTR Value BC857B SYMBOL res -80 0 M0 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL res 640 928 R0 SYMATTR InstName R22 SYMATTR Value 1k SYMBOL res 736 928 R0 SYMATTR InstName R12 SYMATTR Value 22k SYMBOL res 832 928 R0 SYMATTR InstName R13 SYMATTR Value 220 SYMBOL cap 832 848 R0 SYMATTR InstName C4 SYMATTR Value 100p SYMBOL diode 208 560 R90 WINDOW 0 4 80 VBottom 2 WINDOW 3 -22 -49 VTop 2 SYMATTR InstName D1 SYMATTR Value BAT54HY SYMBOL diode 144 624 M90 WINDOW 0 4 -17 VBottom 2 WINDOW 3 -28 115 VTop 2 SYMATTR InstName D2 SYMATTR Value BAT54HY SYMBOL polcap 1344 400 R0 WINDOW 0 39 32 Left 2 WINDOW 3 27 63 Left 2 SYMATTR InstName C5 SYMATTR Value 100000n SYMBOL polcap 1344 976 R0 WINDOW 0 39 32 Left 2 WINDOW 3 27 63 Left 2 SYMATTR InstName C7 SYMATTR Value 100000n SYMBOL diode 1152 352 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D6 SYMATTR Value BAS21HY SYMBOL diode 1152 656 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D7 SYMATTR Value BAS21HY SYMBOL cap 1472 400 R0 WINDOW 0 42 32 Left 2 WINDOW 3 26 61 Left 2 SYMATTR InstName C6 SYMATTR Value 100n SYMBOL cap 1472 976 R0 WINDOW 0 42 32 Left 2 WINDOW 3 26 61 Left 2 SYMATTR InstName C8 SYMATTR Value 100n SYMBOL cap 2272 672 R0 SYMATTR InstName C1 SYMATTR Value 680n SYMBOL res 2368 640 R0 SYMATTR InstName RLoad SYMATTR Value 8 SYMBOL voltage 2384 -16 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 35 SYMBOL voltage 2384 1072 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 35 SYMBOL GANE2R7-100CBA 2000 416 R0 SYMATTR InstName U1 SYMBOL GANE2R7-100CBA 2016 992 R0 SYMATTR InstName U2 TEXT -224 1304 Left 2 !.tran 0 100m 0 1u startup TEXT -232 1400 Left 2 !.MODEL PBSS5140T PNP IS = 2.642E-13 NF = 0.9198 ISE = 1.298E-14 NE = 1.169 BF = 475 IKF = 0.5722\n+ VAF =
28.49 NR = 0.92 ISC = 3.89E-15 NC = 1.161 BR = 36.73 IKR = 0.2593 VAR = 15.08 RB = 25\n+ IRB = 0.0007 RBM = 0.3 RE = 0.1863 RC =
0.09505 XTB = 2.265 EG = 1.11 XTI = 5.73 CJE = 8.437E-11\n+ VJE = 0.6511 MJE = 0.3358 TF = 8.5E-10 XTF = 3.565 VTF = 2 ITF = 0.8 PTF = 0 CJC = 3.165E-11\n+ VJC = 0.5326 MJC = 0.4006 XCJC = 1 TR = 1.6E-09 CJS = 0 VJS = 0.75 MJS = 0.333 FC = 0.9597 TEXT -232 1584 Left 2 !.MODEL BF721 PNP(IS=5.35E-16 ISE=9.81E-17 ISC=1.00E-13 XTI=3.00 BF=1.40E2 BR=1.00E-2 IKF=2.41E-2\n+ IKR=1.00 XTB=1.5 VAF=1.49E2 VAR=9.18E1 VJE=3.00E-1 VJC=3.00E-1 RE=1.85E-2 RC=2.22 RB=1.99E1\n+ RBM=2.41E-2 IRB=1.10E-2 CJE=4.20E-11 CJC=1.65E-11 FC=5.00E-1 NF=8.73E-1 NR=9.84E-1 NE=1.03\n+ NC=2.00 MJE=4.13E-1 MJC=7.00E-1 TF=1.11n TR=0 ITF=3.00 VTF=9.99E5 XTF=5.76E2 EG=1.11\n+ VCEO=300 ICRATING=50m MFG=SIEMENS) TEXT -240 1768 Left 2 !.MODEL BF820 NPN IS=9.109E-15 NF=0.9949 ISE=5.02E-24 NE=2.5 BF=141.1 IKF=0.009124 VAF=22.16 NR=0.9917\n+ ISC=6.582E-12 NC=1.397 BR=11.42 IKR=0.02146 VAR=93 RB=1 IRB=1E-06 RBM=0.5 RE=0.3288 RC=0.5195 XTB=0\n+ EG=1.11 XTI=3 CJE=1.504E-11 VJE=0.7202 MJE=0.3499 TF=1.26E-09 XTF=298.9 VTF=2.447 ITF=0.1815 PTF=0\n+ CJC=3.751E-12 VJC=0.158 MJC=0.2757 XCJC=0.1041 TR=1E-08 CJS=0 VJS=0.75 MJS=0.333 FC=0.895 TEXT -224 1344 Left 2 !.options plotwinsize=0 TEXT -176 -160 Left 2 ;Based on