1kHz sinewave -153 dB

In case anyone is interested (and I know most people aren't but at least it's on topic) this circuit has the following features.

1. Almost constant output level from startup. It does take time to fully stabilize (about 40 seconds) but during that time the peak output level only changes by 60mV.

1. An FFT on the last 6 seconds with Blackman-Harris window shows 2kHz at -153 dB

Performance can probably be improved further with fine adjustment of some component values. Any suggestions for further improvement (whether for lower cost or better performance) are welcome.

JM mentioned some time ago that adding buffers for the rectifier phases would improve performance. He wasn't wrong but the ones used here may be overkill. If you know of a cheaper buffer which will do the same job please let me know.

It won't be cheap to build, if it's ever built. I'd expect test equipment to cost a lot more, assuming equipment exists which can measure at 153 dB down.

LTSpice 24.1.8 with all component updates (9th May 2025) was used for this simulation.

This circuit only exists in an LTSpice simulation. Reality may be different.

If you want to simulate the full 60 seconds then you probably want to run it overnight.

My next move will be to move this circuit to QSpice. I'll have to use generic op amps but it will be interesting to get familiar with QSpice. Does anyone know of any suitable op amp and/or buffer models I can import into QSpice?

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OpAmps\\LT1679 160 160 R0 SYMATTR InstName U8 SYMBOL res -608 272 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL res -944 272 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 560 SYMBOL cap -1072 272 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C8 SYMATTR Value 1000n SYMBOL cap -1072 1344 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 10000n SYMBOL pnp -1440 720 R180 WINDOW 3 84 0 Left 2 SYMATTR Value 2N3906 SYMATTR InstName Q4 SYMBOL res -1520 400 R0 SYMATTR InstName R12 SYMATTR Value 82k SYMBOL res -864 400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R25 SYMATTR Value 2.7Meg SYMBOL cap -1328 560 M0 SYMATTR InstName C7 SYMATTR Value 10p SYMBOL npn -1440 1104 R0 WINDOW 0 -6 -6 Left 2 WINDOW 3 104 -101 VRight 2 SYMATTR InstName Q1A SYMATTR Value NSS40301MDR2G SYMBOL npn -1584 1104 M0 WINDOW 0 -15 -5 Left 2 WINDOW 3 97 -72 VRight 2 SYMATTR InstName Q1B SYMATTR Value NSS40301MDR2G SYMBOL npn -1728 1216 M0 WINDOW 0 -5 -19 Left 2 WINDOW 3 106 -40 VRight 2 SYMATTR InstName Q2B SYMATTR Value NSS40301MDR2G SYMBOL npn -1456 1216 M0 WINDOW 0 -6 -7 Left 2 WINDOW 3 99 -31 VRight 2 SYMATTR InstName Q2A SYMATTR Value NSS40301MDR2G SYMBOL res -1184 1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R28 SYMATTR Value 68k SYMBOL res -1808 112 R0 SYMATTR InstName R29 SYMATTR Value 100k SYMBOL res -1040 544 M0 WINDOW 0 42 42 Left 2 WINDOW 3 40 72 Left 2 SYMATTR InstName R32 SYMATTR Value 10k SYMBOL res -1040 704 M0 WINDOW 0 45 37 Left 2 WINDOW 3 43 69 Left 2 SYMATTR InstName R33 SYMATTR Value 15k SYMBOL cap -1296 -48 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL cap -736 400 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 100n SYMBOL res -1664 1632 M180 WINDOW 0 31 76 Left 2 WINDOW 3 36 43 Left 2 SYMATTR InstName R17 SYMATTR Value 22k SYMBOL OpAmps\\LT1679 -1248 672 M0 SYMATTR InstName U3 SYMBOL cap -976 720 M0 WINDOW 0 -35 12 Left 2 WINDOW 3 -48 47 Left 2 SYMATTR InstName C9 SYMATTR Value 10n SYMBOL res -1392 1632 M180 WINDOW 0 41 79 Left 2 WINDOW 3 39 45 Left 2 SYMATTR InstName R20 SYMATTR Value 27k SYMBOL npn -1728 752 M0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL cap -672 0 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C13 SYMATTR Value 10p SYMBOL cap 112 544 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C14 SYMATTR Value 10p SYMBOL diode -336 688 M0 WINDOW 3 40 37 Left 2 SYMATTR Value BAT54HY SYMATTR InstName D8 SYMBOL diode -128 688 M0 WINDOW 0 -43 36 Left 2 WINDOW 3 43 34 Left 2 SYMATTR InstName D9 SYMATTR Value BAT54HY SYMBOL diode 288 688 M0 WINDOW 3 44 35 Left 2 SYMATTR Value BAT54HY SYMATTR InstName D10 SYMBOL OpAmps\\LT1010 384 -32 R0 SYMATTR InstName U7 SYMBOL res 544 64 R0 SYMATTR InstName R26 SYMATTR Value 600 SYMBOL res 704 224 R0 SYMATTR InstName R27 SYMATTR Value 600 SYMBOL cap 544 16 R90 WINDOW 0 61 18 VBottom 2 WINDOW 3 -33 1 VTop 2 SYMATTR InstName C11 SYMATTR Value 10000n SYMBOL cap -1664 256 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C12 SYMATTR Value 100n SYMBOL OpAmps\\LT1057 -1024 1424 M0 SYMATTR InstName U9 SYMBOL OpAmps\\LT1057 -80 512 R90 WINDOW 0 41 16 VRight 2 WINDOW 3 42 77 VRight 2 SYMATTR InstName U4 SYMBOL OpAmps\\LT1057 -1312 224 R0 SYMATTR InstName U1 SYMBOL res -816 272 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R31 SYMATTR Value 8.9 SYMBOL OpAmps\\LT1010 -496 528 R90 WINDOW 0 40 7 VRight 2 WINDOW 3 41 83 VRight 2 SYMATTR InstName U2 SYMBOL OpAmps\\LT1010 -288 528 R90 WINDOW 0 42 -1 VRight 2 WINDOW 3 42 86 VRight 2 SYMATTR InstName U10 SYMBOL OpAmps\\LT1010 336 528 R90 WINDOW 0 46 -1 VRight 2 WINDOW 3 44 81 VRight 2 SYMATTR InstName U11 SYMBOL res -688 1456 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 220k SYMBOL res 256 1392 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R10 SYMATTR Value 68k SYMBOL res 256 1600 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R13 SYMATTR Value 68k SYMBOL npn 48 1216 R0 WINDOW 0 -6 -6 Left 2 WINDOW 3 96 183 VLeft 2 SYMATTR InstName Q5A SYMATTR Value NSS40301MDR2G SYMBOL res 128 1600 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R15 SYMATTR Value 18k SYMBOL res 128 1088 M0 SYMATTR InstName R16 SYMATTR Value 220 SYMBOL npn -144 1392 M0 WINDOW 0 -6 -6 Left 2 WINDOW 3 49 49 Left 2 SYMATTR InstName Q5B SYMATTR Value NSS40301MDR2G SYMBOL res -192 1088 M0 SYMATTR InstName R21 SYMATTR Value 220 SYMBOL res -384 1536 R0 SYMATTR InstName R22 SYMATTR Value 10Meg SYMBOL cap -272 1552 R0 SYMATTR InstName C10 SYMATTR Value 100n SYMBOL res -464 1648 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R23 SYMATTR Value 10k SYMBOL res -608 1328 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R24 SYMATTR Value 10k SYMBOL res -576 736 R0 SYMATTR InstName R30 SYMATTR Value 56k SYMBOL res -368 736 R0 SYMATTR InstName R34 SYMATTR Value 56k SYMBOL res -160 736 R0 SYMATTR InstName R35 SYMATTR Value 56k SYMBOL res 256 736 R0 SYMATTR InstName R36 SYMATTR Value 56k SYMBOL res -240 1072 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R37 SYMATTR Value 220 SYMBOL cap -160 1104 R0 SYMATTR InstName C15 SYMATTR Value 1000n SYMBOL OpAmps\\LT1057 -544 1408 M0 SYMATTR InstName U12 SYMBOL OpAmps\\LT1057 32 1376 M0 SYMATTR InstName U13 SYMBOL res -864 1312 R0 SYMATTR InstName R14 SYMATTR Value 82k SYMBOL res -864 1536 R0 SYMATTR InstName R38 SYMATTR Value 15k SYMBOL cap -928 1552 R0 WINDOW 0 -35 12 Left 2 WINDOW 3 -48 47 Left 2 SYMATTR InstName C16 SYMATTR Value 10n SYMBOL cap -528 1232 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C17 SYMATTR Value 10p SYMBOL cap 0 1328 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C18 SYMATTR Value 10p SYMBOL OpAmps\\LT1010 -80 640 R90 WINDOW 0 39 -7 VRight 2 WINDOW 3 37 92 VRight 2 SYMATTR InstName U14 SYMBOL res -576 832 R0 SYMATTR InstName R39 SYMATTR Value 12k SYMBOL res -368 832 R0 SYMATTR InstName R40 SYMATTR Value 10k SYMBOL res -160 832 R0 SYMATTR InstName R41 SYMATTR Value 10k SYMBOL res 256 832 R0 SYMATTR InstName R42 SYMATTR Value 8k SYMBOL res -1536 256 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R43 SYMATTR Value 2.7k SYMBOL res -944 1344 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL cap -1024 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1000n SYMBOL cap -1312 48 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C19 SYMATTR Value 220n SYMBOL res -1200 48 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R44 SYMATTR Value 15k SYMBOL res -1264 176 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R7 SYMATTR Value 820k TEXT -1976 -112 Left 2 !.tran 0 60 0 1u startup TEXT -1976 -168 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -1480 -176 Left 2 ;Low distortion 1KHz oscillator. 9th May 2025.\nBased on designs and ideas by JM, BS, ER.\n153 dB down at

2kHz in LTSpice 24.1.8 simulation. TEXT -1280 888 Left 2 !.MODEL NSS40301MDR2G NPN\n+is=6.87023e-12 bf=445.496 nf=1.08926 vaf=60.529\n+ikf=7.23313 ise=2.38192e-09 ne=4 br=23.6872\n+nr=1.10701 var=8.89608 ikr=1.25064 isc=1e-16 \n+nc=1.13174 rb=905.334,irb=2.30349e-07 rbm=1e-10\n+re=0.00600548 rc=0.0300274 xtb=1.2219 xti=4,\n+eg=1.05 cje=3.80477e-10 vje=0.912237 mje=0.397194,\n+tf=5.90916e-10,xtf=0.0998483,vtf=7.09172,itf=0.010481,\n+cjc=8.35472e-11 vjc=0.702862 mjc=0.43477 xcjc=0.899998\n+fc=0.414631 cjs=0 vjs=0.75 mjs=0.5 \n+tr=5.64658e-08 ptf=0,kf=0 af=1