Re: Final final 1kHz oscillator

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:rdtqjj9cbj8od0a7p4e99jfa2nsgf663r0@4ax.com...

On Tue, 19 Nov 2024 20:59:04 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vhibce$1t7v2$1@dont-email.me...

On 18/11/2024 2:58 pm, Edward Rawde wrote:

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:n7iijjdeqecl0kmub0bq5in0dbm60m7qam@4ax.com...

On Thu, 14 Nov 2024 11:14:28 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:
>

"JM" <sunaecoNoChoppedPork@gmail.com> wrote in message news:t5fajjdteskfftvkf84iqsp2vc4b9ta5kj@4ax.com...

On Fri, 8 Nov 2024 15:43:41 -0500, "Edward Rawde"
<invalid@invalid.invalid> wrote:

>
I've taken John May seriously, and reworked my phase shift oscillator to use three op amps, all with their non-inverting inputs
tied to ground.
>
The results aren't all that impressive, the lower harmonics are about 65dB below the fundamental. Start-up is slow - it takes
about five seconds of simulation before the circuit settles down into steady state operation, and that after I dropped the
integrating capacitor from 6.8uF to 680nF. The nice thing about the circuit is that I can explain what each bit is doing. I can
see a few tweaks that might be worth trying.
>

>
The simulation died after 3 seconds, as if insufficient gain to sustain oscillation.
>
You seem to have a lot of components.
Are you sure you really need all those ferrites?
>
Here's my really definitely final final offering.
>
A comfortable 90dB down at 2kHz and > 100 dB elsewhere.
Also looks clean either side of 1kHz.
Whether or not this has anything to do with reality I do not know.
The diode stabilizer string will be temperature dependent,
requiring readjustment of R4 and a total of three adjustments are needed.
Only three op amps (two packages) are needed.
>

..

>
>
Thats a pretty unusual circuit.  Was the original intent to create a
balanced output?

Actually it was so that the diodes feeding the level control circuit made equal contribution.
Also I wanted to reduce component count if possible so I went looking for differential output op amps
and found the LT1994. I wasn't very happy with the +/- 6V rail limitation but decided I could live with it.

>
If you're trying to measure harmonics at a low level with ltspice you
need to set it up correctly.  You need to turn off the raw file
compression (plotwinsize=0 option) and make sure the data is not
stored as single precision (the default) by setting option numdgt > 6.
Your also need to set the maximum timestep to something in the region
of 1/1000 (or 1/2000) of the fundamental period.  If there's
convergence issues you might try setting vntol=1e-12 and reltol=1e-6,
and possibly setting itl2-4 to about 1000.

Thank you very much for this information. I learn something new about LTSpice every day.

>
I tried your circuit with the dc servo removed (it was just
complicating things) and changed the fet control a little.  The fet
your using isn't a great choice - look for something with a large
pinchoff voltage and a large idss, and jig things so that it operates
with vgs close to zero and with very little voltage swing across it.
As it was you were operating it pretty much at pinchoff.

I chose the J113 to be sure of sufficient gate control range since the output of the driving op amp isn't going to go below 6V in an
LT1994 circuit.

>
You dont need to run your sims for long as some others have said.  A
few cycles is all you need.

That makes sense. If it's a continuous repeating signal then why would you need more than a few cycles as long as you wait for the
circuit to settle?

 See if the attached runs for you.  When
doing the fft use a blackman-harris window, H2,H3 should be about
-120,-150dBc.

It runs fine and has the best performance I've seen so far in a simulation.

You should test the LT1944 in isolation as it may not
model distortion at all (most LT spice models are works of fiction).

This is certainly a big concern.
I likely won't get to build this circuit in reality but it wouldn't be a surprise to me if a real circuit has very different
behaviour, particularly from a distortion point of view.

>
There is an option in ltspice to stop it turning U's into mu.
>

Where is it?

Thank you very much for your contribution, it is much appreciated.

My goal was to find out whether a very low distortion sinewave oscillator could be made without using lamps, thermistors or opto
devices.

Based on the circuit you posted and in an attempt to get rid of the LT1994 I used the two op amp oscillator from one of your
previous posts and came up with the following circuit. It works but shows an issue at 2kHz not even 80dB down. What's causing that
harmonic?

You may want to shorten the simulation time and put initial conditions in.

Version 4
SHEET 1 2196 932
WIRE 352 -592 256 -592
WIRE 480 -592 416 -592
WIRE 784 -592 672 -592
WIRE 1072 -592 864 -592
WIRE 1072 -560 1072 -592
WIRE 256 -544 256 -592
WIRE 256 -496 256 -544
WIRE 352 -496 256 -496
WIRE 480 -496 480 -592
WIRE 480 -496 432 -496
WIRE 1072 -464 1072 -480
WIRE -192 -432 -192 -480
WIRE 384 -384 384 -400
WIRE 480 -368 480 -496
WIRE 480 -368 416 -368
WIRE 672 -368 672 -592
WIRE 672 -368 480 -368
WIRE 784 -368 672 -368
WIRE 944 -368 864 -368
WIRE 1168 -368 1008 -368
WIRE 256 -352 256 -496
WIRE 352 -352 256 -352
WIRE 480 -336 416 -336
WIRE 256 -304 256 -352
WIRE 384 -304 384 -320
WIRE 480 -304 480 -336
WIRE -192 -256 -192 -352
WIRE -192 -256 -272 -256
WIRE -272 -240 -272 -256
WIRE 448 -192 368 -192
WIRE 560 -192 512 -192
WIRE 960 -192 880 -192
WIRE 1072 -192 1024 -192
WIRE 256 -176 256 -224
WIRE 256 -176 160 -176
WIRE -192 -160 -192 -256
WIRE 160 -112 160 -176
WIRE 368 -96 368 -192
WIRE 432 -96 368 -96
WIRE 560 -96 560 -192
WIRE 560 -96 512 -96
WIRE 880 -96 880 -192
WIRE 944 -96 880 -96
WIRE 1072 -96 1072 -192
WIRE 1072 -96 1024 -96
WIRE 256 -32 256 -176
WIRE 448 0 448 -16
WIRE -192 16 -192 -80
WIRE 160 16 160 -32
WIRE 160 16 112 16
WIRE 192 16 160 16
WIRE 320 16 288 16
WIRE 368 16 368 -96
WIRE 368 16 320 16
WIRE 416 16 368 16
WIRE 960 16 960 0
WIRE 560 32 560 -96
WIRE 560 32 480 32
WIRE 624 32 560 32
WIRE 672 32 624 32
WIRE 752 32 736 32
WIRE 880 32 880 -96
WIRE 880 32 832 32
WIRE 928 32 880 32
WIRE 416 48 368 48
WIRE 1072 48 1072 -96
WIRE 1072 48 992 48
WIRE 1168 48 1168 -368
WIRE 1168 48 1072 48
WIRE 928 64 880 64
WIRE 448 80 448 64
WIRE 112 96 112 16
WIRE 192 96 112 96
WIRE 320 96 320 16
WIRE 320 96 272 96
WIRE 960 96 960 80
WIRE 368 112 368 48
WIRE 880 112 880 64
WIRE 112 192 112 96
WIRE 640 192 112 192
WIRE 1168 192 1168 48
WIRE 1168 192 720 192
FLAG -272 -240 0
FLAG -192 -480 V+
FLAG -192 16 V-
FLAG 384 -400 V+
FLAG 384 -304 V-
FLAG 480 -304 0
FLAG 1072 -464 0
FLAG 256 -544 vg
FLAG 880 112 0
FLAG 368 112 0
FLAG 624 32 vout2
FLAG 448 -16 V+
FLAG 448 80 V-
FLAG 960 0 V+
FLAG 960 96 V-
SYMBOL voltage -192 -448 R0
WINDOW 123 0 0 Left 0
WINDOW 39 10 135 Left 2
WINDOW 0 12 7 Left 2
WINDOW 3 15 104 Left 2
SYMATTR InstName V1
SYMATTR Value 6
SYMBOL njf 192 -32 M90
WINDOW 0 -37 23 VRight 2
WINDOW 3 -9 -3 VRight 2
SYMATTR InstName J1
SYMATTR Value J113
SYMBOL voltage -192 -176 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 6
SYMBOL schottky 1008 -384 R90
WINDOW 3 32 32 VTop 2
WINDOW 0 0 32 VBottom 2
SYMATTR Value BAS40HY
SYMATTR InstName D1
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 176 80 M90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 50
SYMBOL res 176 -128 M0
WINDOW 0 38 42 Left 2
WINDOW 3 36 66 Left 2
SYMATTR InstName R2
SYMATTR Value 1k
SYMBOL res 272 -208 R180
WINDOW 0 40 70 Left 2
WINDOW 3 45 42 Left 2
SYMATTR InstName R1
SYMATTR Value 1k
SYMBOL OpAmps\LT1678 384 -352 M0
WINDOW 0 -56 49 Left 2
WINDOW 3 -47 89 Left 2
SYMATTR InstName U2A
SYMBOL res 336 -480 R270
WINDOW 0 33 55 VTop 2
WINDOW 3 -3 55 VBottom 2
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL res 880 -384 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 10k
SYMBOL cap 416 -608 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 100�
SYMBOL res 880 -608 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 10K
SYMBOL voltage 1072 -576 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value -0.2
SYMBOL res 1040 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 16K
SYMBOL res 848 16 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 8K
SYMBOL cap 1024 -208 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 10n
SYMBOL cap 736 16 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 20n
SYMBOL res 528 -112 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 10.02K
SYMBOL cap 512 -208 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C5
SYMATTR Value 10p
SYMBOL res 736 176 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R14
SYMATTR Value 9870
SYMBOL OpAmps\LT1679 448 32 R0
SYMATTR InstName U1
SYMBOL OpAmps\LT1679 960 48 R0
SYMATTR InstName U4
TEXT -496 136 Left 2 !.tran 0 200 0 1u uic
TEXT -496 88 Left 2 !.options plotwinsize=0 numdgt=7 method=trap
TEXT -248 -584 Left 2 ;1kHz sinewave oscillator. 20 Nov 2024.