Sinewave oscillator without gain control.

Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need an
oscillator which does better than that when it passes through the required output level.
The circuit below was simulated in LTSpice 24.1.0 with all updates.
There are reasons why I'm not sure I'd trust version 17.x of LTSpice to give the most accurate results but I haven't tested this
circuit in any other version.
After starting the simulation, wait until it has simulated about 7 seconds and then stop the simulation. Close the annoying log
window which 24.1.0 will produce.
You can now select a sample of about 100ms when it passes through 0dB (just under 2V) and run an FFT on it with Blackman-Harris
window.
This will show that this circuit is approaching 120dB down on harmonics.
So if you want to do better than that then you'll need an oscillator circuit which has better performance to begin with. You can
then add gain control for constant level.
I've not so far found an oscillator circuit in LTSpice with better harmonic distortion performance than this one.
You can, of course, try to use filtering to reduce the unwanted harmonics. Removing the first four harmonics produced by this
circuit will get it approaching 130dB but don't ask me how that would be measured in reality or what it would cost to do so even if
it can be measured.

Version 4.1
SHEET 1 2196 932
WIRE 0 -416 0 -448
WIRE 208 -288 48 -288
WIRE 944 -288 848 -288
WIRE 1136 -288 1008 -288
WIRE 112 -208 112 -240
WIRE 48 -192 48 -288
WIRE 80 -192 48 -192
WIRE 480 -192 416 -192
WIRE 608 -192 544 -192
WIRE 848 -192 848 -288
WIRE 944 -192 848 -192
WIRE 1136 -192 1136 -288
WIRE 1136 -192 1024 -192
WIRE 208 -176 208 -288
WIRE 208 -176 144 -176
WIRE 256 -176 208 -176
WIRE 288 -176 256 -176
WIRE 0 -160 0 -336
WIRE 80 -160 0 -160
WIRE -224 -144 -224 -240
WIRE 0 -112 0 -160
WIRE 0 -112 -64 -112
WIRE 112 -112 112 -144
WIRE 416 -96 416 -192
WIRE 480 -96 416 -96
WIRE 608 -96 608 -192
WIRE 608 -96 560 -96
WIRE 848 -96 848 -192
WIRE 896 -96 848 -96
WIRE 1008 -96 976 -96
WIRE 1136 -96 1136 -192
WIRE 1136 -96 1088 -96
WIRE 0 -80 0 -112
WIRE -64 -64 -64 -112
WIRE 496 0 496 -16
WIRE 416 16 416 -96
WIRE 416 16 352 16
WIRE 464 16 416 16
WIRE 928 16 928 0
WIRE 1136 16 1136 -96
WIRE 1168 16 1136 16
WIRE 1296 16 1248 16
WIRE 1456 16 1360 16
WIRE 1520 16 1456 16
WIRE -224 32 -224 -64
WIRE -64 32 -64 0
WIRE 0 32 0 0
WIRE 608 32 608 -96
WIRE 608 32 528 32
WIRE 640 32 608 32
WIRE 720 32 704 32
WIRE 848 32 848 -96
WIRE 848 32 800 32
WIRE 896 32 848 32
WIRE 432 48 416 48
WIRE 464 48 432 48
WIRE 1136 48 1136 16
WIRE 1136 48 960 48
WIRE 864 64 848 64
WIRE 896 64 864 64
WIRE 496 80 496 64
WIRE 1520 80 1520 16
WIRE 928 96 928 80
WIRE 1520 176 1520 160
WIRE 352 224 352 16
WIRE 480 224 352 224
WIRE 640 224 560 224
WIRE 1136 224 1136 48
WIRE 1136 224 720 224
FLAG 496 -16 V+
FLAG 928 0 V+
FLAG 1520 176 0
FLAG 1456 16 output
FLAG -224 32 0
FLAG 496 80 0
FLAG 928 96 0
FLAG -224 -240 V+
FLAG 432 48 half
FLAG 864 64 half
FLAG 112 -112 0
FLAG 112 -240 V+
FLAG 256 -176 half
FLAG 0 32 0
FLAG 0 -448 V+
FLAG -64 32 0
SYMBOL voltage -224 -160 R0
WINDOW 123 0 0 Left 0
WINDOW 39 10 135 Left 2
WINDOW 0 10 0 Left 2
WINDOW 3 15 104 Left 2
SYMATTR InstName V2
SYMATTR Value 32
SYMBOL res 1040 -208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 15k
SYMBOL res 816 16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 8.2K
SYMBOL cap 1008 -304 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10n
SYMATTR SpiceLine V=16 Irms=647m Rser=0.0322889 Lser=0 mfg="KEMET" pn="C0201C103K4PAC" type="X5R"
SYMBOL cap 704 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 22n
SYMATTR SpiceLine V=4 Irms=356m Rser=0.150334 Lser=0 mfg="KEMET" pn="C0402C223K7PAC" type="X5R"
SYMBOL res 576 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 10k
SYMBOL cap 544 -208 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 22p
SYMATTR SpiceLine V=16 Irms=0 Rser=0.3482 Lser=551p mfg="W�rth Elektronik" pn="885012006019 WCAP-CSGP 0603" type="NP0"
SYMBOL res 736 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 1388
SYMBOL res 1264 0 R90
WINDOW 0 -4 57 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R7
SYMATTR Value 600
SYMBOL res 1536 176 R180
WINDOW 0 47 75 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R8
SYMATTR Value 600
SYMBOL res -16 -320 M180
WINDOW 0 40 70 Left 2
WINDOW 3 37 41 Left 2
SYMATTR InstName R5
SYMATTR Value 100k
SYMBOL res -16 16 M180
WINDOW 0 40 70 Left 2
WINDOW 3 38 43 Left 2
SYMATTR InstName R10
SYMATTR Value 100k
SYMBOL cap -48 0 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C1
SYMATTR Value 10n
SYMATTR SpiceLine V=50 Irms=291m Rser=0.34258 Lser=0 mfg="KEMET" pn="C0805F103K5RAC" type="X7R"
SYMBOL cap 1360 0 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C6
SYMATTR Value 10000n
SYMATTR SpiceLine V=25 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM188R61E106MA73" type="X5R"
SYMBOL res 992 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 150k
SYMBOL res 576 208 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R15
SYMATTR Value 8.2k
SYMBOL res 1104 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R16
SYMATTR Value 47k
SYMBOL OpAmps\LT1058 112 -240 R0
SYMATTR InstName U5
SYMBOL OpAmps\LT1678 928 48 R0
SYMATTR InstName U3
SYMBOL OpAmps\LT1678 496 32 R0
SYMATTR InstName U4
TEXT -304 200 Left 2 !.tran 0 30 0 1u uic
TEXT -304 152 Left 2 !.options plotwinsize=0 numdgt=7 method=trap
TEXT -272 -568 Left 2 ;1kHz low distortion sinewave oscillator.
TEXT -272 -536 Left 2 ;23 Jan 2025.