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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: Final final 1kHz oscillator
Date: Sun, 10 Nov 2024 17:21:26 -0500
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"Cursitor Doom" <cd@notformail.com> wrote in message news:ee92jjllg5kudr83e8bvvbsjba754aecjs@4ax.com...
> On Sun, 10 Nov 2024 18:00:01 +0000, Cursitor Doom <cd@notformail.com>
> wrote:
>
>>On Sun, 10 Nov 2024 17:45:00 +0000, Cursitor Doom <cd@notformail.com>
>>wrote:
>>
>>>On Sun, 10 Nov 2024 12:12:34 -0500, "Edward Rawde"
>>><invalid@invalid.invalid> wrote:
>>>
>>>>"Cursitor Doom" <cd@notformail.com> wrote in message news:bs81jjt7d064jc1ktmvihgn30qkhf67taj@4ax.com...
>>>>> On Sun, 10 Nov 2024 00:49:36 -0500, "Edward Rawde"
>>>>> <invalid@invalid.invalid> wrote:
>>>>>
>>>>>>"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vgnkgg$3p31a$1@dont-email.me...
>>>>>>> On 9/11/2024 7:39 pm, Edward Rawde wrote:
>>>>>>>> "Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vgn4gm$3lcor$1@dont-email.me...
>>>>>>>>> On 9/11/2024 7:43 am, Edward Rawde wrote:
>>>>>>>>>> This is the simplest circuit I can come up with.
>>>>>>>>>> Harmonics are more than 80dB down in simulation.
>>>>>>>>>> FFT the last 30 seconds.
>>>>>>>>>> There is only one harmonic stopping me claiming 90dB but the exact FFT result can depend
>>>>>>>>>> on exactly how much output is selected for the FFT. You may see different results.
>>>>>>>>>>
>>>>>>
>>>>>>I have fixed my circuit but it raises more questions than it answers.
>>>>>>This circuit deliberately has no text and no u symbols so should be ready to simulate.
>>>>>>If you let it complete (about 20 minutes on a fast PC) the FFT should show at least 80dB purity and there aren't many 
>>>>>>harmonics
>>>>>>standing in the way of 90dB.
>>>>>>Startup isn't fast and it takes at least 20 seconds of simulation to fully settle.
>>>>>
>>>>> Spectral purity might be fine for all I can tell but the output
>>>>> amplitude is all over the place,
>>>>
>>>>Change R9 to 1.07Meg does it amplitude stabilize now?
>>>>Adjustment will be needed in any real circuit.
>>>
>>>Indeed, but for a simulation we should be seeing identical results!
>>>I've made the change as you suggested and it's increased the sim time
>>>considerably. I'll post again when it's completed.
>>
>>Update: looking *much* better at 25% done. Settled after 7.5s. I will
>>let it run its course anyway and post again at the end with the final
>>outcome.
>
> Looks really stable now; 4.5V peak to peak and none of the
> fluctuations of the earlier simulations. Weird how it took *so* much
> longer to complete this time,  though.

An FFT on the last 10 seconds should show peformance approaching 90dB down.

I likely won't be working on this any further unless anyone else wants further discussion.

The goal was to get the purest possible sine wave at the lowest cost and in simulation I don't think I can improve on this circuit.
I'm not able to build this circuit and even if I did I don't have equipment capable of measuring distortion 90dB down.

I'd still like to know why LT1057 doesn't work in position U2. It's not like rail to rail is needed.
LT1678 works exactly as expected. LT1057 probably would in reality but not sure I'd risk it.

I'd also like to know exactly how and why U3 stabilizes U1 and the operation of D1 and D2.
Would this work the same in reality?

The diode clamp should probably be made from a single diode and another op amp with two resistors to allow the clamp level to be 
easily adjusted.

If it's ever buil for real I'd make R1, R2, R7, R8 easily changeable.
I'd also make R3 220 ohm ten turn and R9 1Meg 10 turn in series with 470k.

The definitely final circuit is included below.
This has no text or titles or dates so add that yourself if you wish.

Version 4
SHEET 1 2196 932
WIRE -64 -576 -96 -576
WIRE 48 -576 16 -576
WIRE 128 -528 112 -528
WIRE 208 -528 192 -528
WIRE 288 -528 272 -528
WIRE 368 -528 352 -528
WIRE 448 -528 432 -528
WIRE 528 -528 512 -528
WIRE 640 -528 592 -528
WIRE 640 -512 640 -528
WIRE -32 -464 -32 -480
WIRE 48 -448 48 -576
WIRE 48 -448 0 -448
WIRE -96 -432 -96 -576
WIRE -64 -432 -96 -432
WIRE 112 -416 112 -528
WIRE 112 -416 0 -416
WIRE 160 -416 112 -416
WIRE 208 -416 160 -416
WIRE 336 -416 288 -416
WIRE 400 -416 336 -416
WIRE 512 -416 400 -416
WIRE 624 -416 512 -416
WIRE -96 -384 -96 -432
WIRE -32 -384 -32 -400
WIRE 48 -368 48 -448
WIRE 336 -368 336 -416
WIRE 160 -352 160 -416
WIRE 400 -352 400 -416
WIRE 512 -288 512 -416
WIRE 624 -288 624 -416
WIRE -96 -272 -96 -304
WIRE -96 -272 -192 -272
WIRE -96 -240 -96 -272
WIRE 48 -240 48 -288
WIRE 160 -240 160 -288
WIRE 336 -240 336 -288
WIRE 400 -240 400 -288
WIRE -192 -176 -192 -272
WIRE -224 -128 -256 -128
WIRE -96 -128 -96 -160
WIRE -96 -128 -128 -128
WIRE -80 -128 -96 -128
WIRE 144 -128 -80 -128
WIRE 288 -128 224 -128
WIRE 352 -128 288 -128
WIRE 512 -128 512 -224
WIRE 512 -128 432 -128
WIRE -256 -48 -256 -128
WIRE -208 -48 -256 -48
WIRE -80 -48 -80 -128
WIRE -80 -48 -128 -48
WIRE 288 -16 288 -128
WIRE 288 -16 64 -16
WIRE 352 -16 288 -16
WIRE 512 -16 512 -128
WIRE 512 -16 432 -16
WIRE -256 0 -256 -48
WIRE 144 48 144 32
WIRE -272 96 -352 96
WIRE -208 96 -272 96
WIRE 64 96 64 -16
WIRE 112 96 64 96
WIRE 512 96 512 -16
WIRE 512 96 272 96
WIRE -32 128 -96 128
WIRE 112 128 -32 128
WIRE -352 144 -352 96
WIRE 624 144 624 -224
WIRE 656 144 624 144
WIRE 752 144 720 144
WIRE -208 160 -208 96
WIRE -32 160 -32 128
WIRE 112 160 64 160
WIRE 624 160 624 144
WIRE 624 160 272 160
WIRE 752 176 752 144
WIRE 144 224 144 208
WIRE -32 256 -32 224
WIRE 64 272 64 160
WIRE 160 272 64 272
WIRE 288 272 160 272
WIRE 400 272 352 272
WIRE 512 272 512 96
WIRE 512 272 480 272
WIRE 64 288 64 272
WIRE 160 288 160 272
WIRE 752 288 752 256
WIRE 880 288 752 288
WIRE 928 288 880 288
WIRE -352 320 -352 224
WIRE -352 320 -432 320
WIRE 928 320 928 288
WIRE -432 336 -432 320
WIRE -352 336 -352 320
WIRE -208 336 -208 224
WIRE -208 336 -352 336
WIRE -96 336 -96 128
WIRE 64 384 64 368
WIRE 160 384 160 352
WIRE 160 384 64 384
WIRE -352 416 -352 336
WIRE 64 416 64 384
WIRE -208 432 -208 336
WIRE 192 432 144 432
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