Final final 1kHz oscillator

I found a simpler solution - copy the relevant arrangement in John May's circuit. It did work - after a fashion - but as I got closer to getting it to a state where it could do what I wanted, the circuit got less and less willing to simulate.

I suspect an accumulation of typo's in component values - I do try to go the through the schematic to find and purge them. But the last few passes haven't shown up anything. Frustrating. My father's advice in similar situautions was to "drop it in drawer for six months, then take another look". It has worked in the past.

"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vhp713$12bnt$ snipped-for-privacy@dont-email.me...

I also found a simpler solution. Taking on board advice from JM and others.

The circuit below does 0dB into 600 ohms and it only takes about 20 minutes to complete the simulation on my computer.

When it's done, select a sample of about 1 second near the end and FFT. Select Use current zoom extent and Blackman-Harris window.

It will say all harmonics are more than 120dB down.

I'm not saying this level of performance is achievable or measurable in reality so I don't see any point simulating further.

The actual distortion in reality will likely be that of the op amps so choose the lowest distortion op amp you can find.

Oh and if you need to know the exact function of any of the 21 components in this circuit just ask. I'd feel embarrassed to have produced a circuit using over 70 components which only claims 65dB down on harmonics.

Does anyone know how to change the default trace in LTSpice? When I click Run/pause it shows the wrong node so then I have to Delete This Trace and click output. How do I make it default to output?

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schottky 1056 -432 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 47 SYMBOL res 176 -144 M0 WINDOW 0 38 42 Left 2 WINDOW 3 36 66 Left 2 SYMATTR InstName R2 SYMATTR Value 100k SYMBOL res 272 -240 R180 WINDOW 0 40 70 Left 2 WINDOW 3 45 42 Left 2 SYMATTR InstName R1 SYMATTR Value 100k SYMBOL res 320 -528 R270 WINDOW 0 33 55 VTop 2 WINDOW 3 -3 55 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res 944 -432 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL cap 400 -656 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 100µ SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM31CR60G107ME39" type="X5R" SYMBOL res 656 -496 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL res 1008 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 16K SYMBOL res 816 16 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 8K SYMBOL cap 976 -208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 10n SYMBOL cap 704 16 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 20n SYMBOL res 576 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 10.02K SYMBOL cap 544 -208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL res 736 208 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 9985 SYMBOL OpAmps\\LT1679 496 32 R0 SYMATTR InstName U1 SYMBOL OpAmps\\LT1679 928 48 R0 SYMATTR InstName U2 SYMBOL OpAmps\\LT1679 384 -400 M0 SYMATTR InstName U3 SYMBOL OpAmps\\LT1679 800 -688 M0 SYMATTR InstName U4 SYMBOL res 896 -832 R0 SYMATTR InstName R17 SYMATTR Value 10k SYMBOL res 896 -640 R0 SYMATTR InstName R18 SYMATTR Value 12k SYMBOL res 1280 0 R90 WINDOW 0 -4 57 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 600 SYMBOL res 1440 176 R180 WINDOW 0 47 75 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R8 SYMATTR Value 600 TEXT -496 136 Left 2 !.tran 0 30 0 1u uic TEXT -496 88 Left 2 !.options plotwinsize=0 numdgt=7 method=trap TEXT -296 -648 Left 2 ;1kHz low distortion sinewave oscillator. TEXT -288 -616 Left 2 ;21 Nov 2024.

I found that adding a couple of 14nmH ferrite beads around the transistors and the FETs stopped the simulation dropping out after getting stuck on a too-short time step.

The current version isn't simulating all that fast - I let it run over-night and the amplitude control feed back loop turned out to have been underdamped to the point of instability - it kept on hitting the rails and overshooting back into them. The current version - with more damping - is now on it's second millisecond.

Of course you would. The point of producing the circuit is to find out what it can do, and change it to make it work better. That way you get to understand what the circuit is doing and why it is doing it, which isn't your strong point.

There isn't one in the version I downloaded. When I start a simulation I get offered a blank display, and have to select a trace to be displayed before I can see anything.

Beats me.

I found that adding a couple of 14uH ferrite beads around the transistors and the FET stopped the simulation dropping out after getting stuck on a too-short time step.

The current version isn't simulating all that fast - I let it run over-night and the amplitude control feed-back loop turned out to have been underdamped to the point of instability - it kept on hitting the rails, recovering and overshooting back into them. The current version - with more damping - is now on it's second millisecond.

Of course you would. The point of producing the circuit is to find out what it can do, and change it to make it work better. That way you get to understand what the circuit is doing and why it is doing it, which isn't your strong point.

There isn't one in the version I downloaded. When I start a simulation I get offered a blank display, and have to select a trace to be displayed before I can see anything.

Beats me.

Ok well when you've got a circuit which rivals the one I posted for harmonic distortion and component count let me know.

Silly me. I thought that's what I'd been doing all along.

Same here. Therefore it has to be storing alternative behaviour in one of that files it creates. I have since found that this is a plt file.

It turns out that the solution to this problem is to delete the plt file. However I don't know exactly what the circumstances are for this file to be created.

Aha I must have accidentally saved the plot settings somehow. Right click the plot and choose file. If you save plot settings it does just that.

Component count isn't all that important. If you can replace an expensive or hard to get component with a couple of cheap ones, that's a win.

Alternative ways of doing much the same job are also interesting - patent evasion used to be a popular sport. Once the patentable details are buried inside a programmable device it's less worthwhile.

Lawyers don't like going into technical detail - RCA won a colour TV patent case against EMI in a US Court because the judges couldn't be persuaded that quadrature modulation was exactly the same thing as sine/cosine modulation.

Perhaps.

I've worked in plenty of places where using four times as many components as you could have used (and hence four times the cost) would not be seen as a win.

Sure. There are plenty of examples of that, such as make it a beam tetrode instead of a pentode.

Sony didn't care about the PAL patents. They just put a hue control on their early sets.

Right. And sometimes saving space/weight trumps saving cost, so fewer components at increased $ expense is a win.

Ed

I'm working on it. Since we don't trust the spice models to get the distortion exactly right, it's not a particularly well-chosen target.

Additional components in the simulation that you could probably leave out of a real circuit. I've found another place to put a ferrite bead which speeds up the simulation ever more, but it is till not all that quick.

I'm not going to be constrained by that.

Four times the number of components isn't four times the cost, as I did point out. I got brownie points once for replacing a fifty pence 25-turn trimming potentiometer with a more settable trimmer with the same footprint at five times the cost.

What we lost on the cost of the part we more than won back in a half-hour drop in setting up time. The original designer should have put in coarse and fine pots, which would have been more parts, but still cheaper than my quick and dirty fix.

The EMI-RCA court battle preceded PAL versus NTSC. It was about how you added colour information on top of the original black and white brightness signal.

John May claims to have observed it in reality. I trust him on that.

But you haven't actually answered when I have.

...

Ok I'll settle for matching the harmonic distortion level, even if you need 1000 components.

We all know that Bill. In any case NTSC (which uses quadrature) and PAL (which also uses quadrature along with an additional trick or two) and probably also SECAM (which uses FM) are all history now unless you need to generate a signal locally for an existing set.

...

The current version has the second harmonic 103dB below the fundamental, the third harmonic 80dB down. I had to run it over-nigh to get a couple of seconds of operation - the second second looked good.

A couple of millivolts of second harmonic makes it through to the FET gate from the full-wave rectifier. If I can lag it by another 156usec it may reduce the harmonic content, rather than increasing it. So far the revised circuit has only clocked up 4msec of operation. Maybe I'll have more tomorrow.

I haven't bothered counting the components. Some of them could be ditched when the design gets closer to a definitive version. The three transistors get around a potential output swing limitation which probably won't be a problem.

The current version has been running overnight and has got to three seconds, and the DFT from 2.8 to three seconds shows third harmonic about 90db below the fundamental. The noise floor is about 100dB down and the other harmonics are barely visible above it.

Here's the .asc file. There are extra components put in to make it simulate faster - L1 and L14 are the obvious examples, but L10, L11 and L12 got put in for the same reason. I suspect that if I had put in equivalent series resistance and inductance for C22 as well as for C6 and C15 I might not have needed some of them.

There is some other tidying up I could do, and that should get get the simulation speed up. I got a new circuit from John May last night, and it not only spits out a very clean sine wave but also simulated very fast. I forgot to put it on solid state disk before I ran it, and it took as long to get one of the waveforms off the spinning hard disk as it had done to run the simulation.

Ny tidying up is going to wait until I've got ten seconds worth of simulation out of the current circuit, and can look at the details of what's going on deep in the circuit

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336 -2176 Vcc FLAG 416 -624 Vee FLAG -560 -1152 0 FLAG 16 -1520 Vout FLAG 1248 -960 0 FLAG -1488 -1520 Fet-gate FLAG 1104 -1456 Vcc FLAG -1040 -832 Vee FLAG -288 -1456 0 FLAG -1840 -1264 0 FLAG 336 -1888 0 FLAG 1200 -1616 0 SYMBOL Opamps\\LT1360 208 -1248 R0 SYMATTR InstName U1 SYMBOL res 48 -1344 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R1 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res -64 -1152 R0 WINDOW 3 41 74 Left 2 WINDOW 0 43 31 Left 2 SYMATTR Value 4k02 SYMATTR InstName R2 SYMATTR SpiceLine tol=1 SYMBOL cap -160 -1136 R0 SYMATTR InstName C1 SYMATTR Value 3.3n SYMBOL schottky 352 -1360 R0 WINDOW 3 -88 64 Left 2 WINDOW 0 -44 -8 Left 2 SYMATTR Value BAS70L SYMATTR InstName D1 SYMBOL schottky 352 -928 R0 WINDOW 3 -100 68 Left 2 WINDOW 0 -40 -2 Left 2 SYMATTR Value BAS70L SYMATTR InstName D2 SYMBOL res 352 -1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 208 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 20k SYMATTR SpiceLine tol=1 SYMBOL res 480 -1408 R0 WINDOW 0 41 41 Left 2 WINDOW 3 34 79 Left 2 SYMATTR InstName R2a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 560 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 720 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2c SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 704 -832 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 22n SYMBOL cap 192 -1056 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 3.3p SYMBOL res 48 -896 R0 WINDOW 0 39 33 Left 2 WINDOW 3 40 74 Left 2 SYMATTR InstName R1b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL OpAmps\\opamp2 -176 -1584 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U3 SYMATTR SpiceModel LME49710 SYMBOL voltage -1104 -1120 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -1104 -976 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL cap -480 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -448 -1520 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL cap -64 -1728 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL cap 1776 -1664 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C8 SYMATTR Value 680n SYMBOL res 1520 -1760 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 33k SYMBOL Opamps\\LT1056A 1664 -1456 R0 SYMATTR InstName U5 SYMBOL cap 1456 -1120 R0 SYMATTR InstName C10 SYMATTR Value 3.3µ SYMBOL cap 1584 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 3.3p SYMBOL res -1616 -1360 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 27 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL Opamps\\OP27 576 -1264 R0 SYMATTR InstName U2 SYMBOL FerriteBead -224 -1712 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L1 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 576 -672 R0 SYMATTR InstName L2 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 752 -1408 R0 SYMATTR InstName C15 SYMATTR Value 100n SYMBOL cap 752 -800 R0 SYMATTR InstName C16 SYMATTR Value 100n SYMBOL res 1392 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 51k SYMBOL FerriteBead -176 -928 R0 SYMATTR InstName L4 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -336 -2000 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C17 SYMATTR Value 100n SYMBOL cap -336 -1168 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C18 SYMATTR Value 100n SYMBOL res -1584 -1664 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R21 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 944 -1184 R0 SYMATTR InstName C21 SYMATTR Value 100n SYMBOL FerriteBead 960 -1408 R0 SYMATTR InstName L7 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -512 -1888 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R22 SYMATTR Value 2.49k SYMATTR SpiceLine tol=1 SYMBOL FerriteBead -320 -2112 R0 SYMATTR InstName L8 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -752 -1984 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C7 SYMATTR Value 100n SYMBOL FerriteBead -736 -2128 R0 SYMATTR InstName L3 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead -656 -896 R0 SYMATTR InstName L9 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -864 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C23 SYMATTR Value 100n SYMBOL npn -1632 -1152 R0 SYMATTR InstName Q1 SYMATTR Value BC547B SYMBOL npn -1696 -1152 M0 SYMATTR InstName Q2 SYMATTR Value BC547B SYMBOL res -1584 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R23 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -1776 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R24 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -1776 -1744 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R25 SYMATTR Value 6.8k SYMATTR SpiceLine tol=0.1 SYMBOL pnp -1824 -1440 M180 SYMATTR InstName Q3 SYMATTR Value BC557B SYMBOL res -1888 -1664 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R27 SYMATTR Value 18k SYMATTR SpiceLine tol=1 SYMBOL res -1888 -1024 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R28 SYMATTR Value 6.8k SYMATTR SpiceLine tol=1 SYMBOL cap -1856 -1456 R0 WINDOW 0 28 4 Left 2 WINDOW 3 21 62 Left 2 SYMATTR InstName C3 SYMATTR Value 100n SYMBOL OpAmps\\opamp2 -1408 -1792 M0 WINDOW 3 10 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U8 SYMATTR SpiceModel LME49710 SYMBOL res -160 -1600 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R26 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL res -768 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 4.87k SYMATTR SpiceLine tol=1 SYMBOL cap -784 -1584 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C19 SYMATTR Value 10p SYMBOL FerriteBead 208 -672 R0 SYMATTR InstName L5 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 208 -2128 R0 SYMATTR InstName L6 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 320 -1968 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C20 SYMATTR Value 100n SYMBOL cap -96 -816 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C22 SYMATTR Value 100n SYMBOL njf -1376 -1584 R0 SYMATTR InstName J1 SYMATTR Value MMBF4391 SYMBOL References\\LTC6655-1.25 1232 -1120 R0 SYMATTR InstName U4 SYMBOL OpAmps\\opamp2 -656 -1504 R0 WINDOW 3 13 108 Left 2 SYMATTR Value LME49710 SYMATTR InstName U9 SYMATTR SpiceModel LME49710 SYMBOL FerriteBead -1760 -880 R0 SYMATTR InstName L10 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL FerriteBead -1568 -880 R0 SYMATTR InstName L11 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL FerriteBead -1760 -1600 R0 SYMATTR InstName L12 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL res -1200 -1664 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R7 SYMATTR Value 390 SYMATTR SpiceLine tol=0.1 SYMBOL cap -64 -1824 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C9 SYMATTR Value 10p SYMBOL FerriteBead 576 -1936 R0 SYMATTR InstName L13 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -944 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 82 SYMATTR SpiceLine tol=1 SYMBOL res 1120 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 51k SYMBOL cap 1184 -1728 R0 SYMATTR InstName C12 SYMATTR Value 15n SYMBOL FerriteBead 496 -816 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L14 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 704 -1088 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C13 SYMATTR Value 10p TEXT -1424 -776 Left 2 !.MODEL BAS70L D \n+ IS = 3.22E-9 \n+ N = 1.018 \n+ BV = 77 \n+ IBV = 1.67E-7 \n+ RS = 20.89 \n+ CJO = 1.608E-12 \n+ VJ = 0.3891 \n+ M = 0.3683 \n+ FC = 0.5 \n+ EG = 0.69 \n+ XTI = 2 \n.ENDS TEXT -336 -528 Left 2 ;R2 a,b,c, Vishay Beschlag ACAS06S0830372P1AT precision 10k resistor array \n R1a, R1b Maxim MAX5492LB10000+T 10K resistive divider in a SOT-23-5 package TEXT -720 -464 Left 2 !.MODEL MMBF4391 NJF VTO=-4.6 BETA=0.02779 LAMBDA=0.00595 RD=1 RS=1 IS=1e-14 CGD=14p CGS=10.5p PB=1 B=1 KF=1e-18 AF=1 FC=0.5 mfg=Motorola TEXT -720 -408 Left 2 !.lib LME49710.lib TEXT -2000 -392 Left 2 !.tran 0 10s 0s startup

After running the simulation to 10 seconds I get 80dB down at 3kHz with an FFT on a sample of the last second and a Blackman-Harris window. Looks like the noise level either side of 1kHz may be higher than that.

When evaluating architecture there's little to be gained by using a complicated opamp model. Use a simple 1 or 2 pole model to begin with.

Try the attached file, I've used a simple model to speed up the simulation, and made a slight circuit change. This shows the harmonics due to the control loop to be sub 130dBc. Of course the amplifier harmonic distortion is not simulated, but neither was it in the simulation by Mr Rawde.

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FLAG 16 -1520 Vout FLAG 1248 -960 0 FLAG -1488 -1520 Fet-gate FLAG 1104 -1456 Vcc FLAG -1040 -832 Vee FLAG -288 -1456 0 FLAG -1840 -1264 0 FLAG 336 -1888 0 FLAG 1200 -1616 0 FLAG -1456 -1168 0 SYMBOL res 48 -1344 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R1 SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res -64 -1152 R0 WINDOW 3 41 74 Left 2 WINDOW 0 43 31 Left 2 SYMATTR Value 4k02 SYMATTR InstName R2 SYMATTR SpiceLine tol=1 SYMBOL cap -160 -1136 R0 SYMATTR InstName C1 SYMATTR Value 3.3n SYMBOL schottky 352 -1360 R0 WINDOW 3 -88 64 Left 2 WINDOW 0 -44 -8 Left 2 SYMATTR Value BAS70L SYMATTR InstName D1 SYMBOL schottky 352 -928 R0 WINDOW 3 -100 68 Left 2 WINDOW 0 -40 -2 Left 2 SYMATTR Value BAS70L SYMATTR InstName D2 SYMBOL res 352 -1472 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 208 -1536 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 20k SYMATTR SpiceLine tol=1 SYMBOL res 480 -1408 R0 WINDOW 0 41 41 Left 2 WINDOW 3 34 79 Left 2 SYMATTR InstName R2a SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 560 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL res 720 -928 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2c SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL cap 704 -832 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 22n SYMBOL cap 192 -1056 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 3.3p SYMBOL res 48 -896 R0 WINDOW 0 39 33 Left 2 WINDOW 3 40 74 Left 2 SYMATTR InstName R1b SYMATTR Value 10k SYMATTR SpiceLine tol=0.1 SYMBOL voltage -1104 -1120 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL voltage -1104 -976 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL cap -480 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL res -448 -1520 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R4 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL cap -64 -1728 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 15n SYMATTR SpiceLine V=63 Rser=0.04 Lser=12n SYMBOL cap 1776 -1664 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C8 SYMATTR Value 680n SYMBOL res 1520 -1760 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R10 SYMATTR Value 33k SYMBOL cap 1456 -1120 R0 SYMATTR InstName C10 SYMATTR Value 3.3u SYMBOL cap 1584 -1552 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C11 SYMATTR Value 3.3p SYMBOL FerriteBead -224 -1712 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L1 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 576 -672 R0 SYMATTR InstName L2 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 752 -1408 R0 SYMATTR InstName C15 SYMATTR Value 100n SYMBOL cap 752 -800 R0 SYMATTR InstName C16 SYMATTR Value 100n SYMBOL res 1392 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R20 SYMATTR Value 51k SYMBOL FerriteBead -176 -928 R0 SYMATTR InstName L4 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -336 -2000 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C17 SYMATTR Value 100n SYMBOL cap -336 -1168 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C18 SYMATTR Value 100n SYMBOL res -1584 -1664 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R21 SYMATTR Value 5K SYMATTR SpiceLine tol=0.1 SYMBOL cap 944 -1184 R0 SYMATTR InstName C21 SYMATTR Value 100n SYMBOL FerriteBead 960 -1408 R0 SYMATTR InstName L7 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -512 -1888 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R22 SYMATTR Value 2.49k SYMATTR SpiceLine tol=1 SYMBOL FerriteBead -320 -2112 R0 SYMATTR InstName L8 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -752 -1984 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C7 SYMATTR Value 100n SYMBOL FerriteBead -736 -2128 R0 SYMATTR InstName L3 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead -656 -896 R0 SYMATTR InstName L9 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap -864 -1152 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C23 SYMATTR Value 100n SYMBOL npn -1632 -1152 R0 SYMATTR InstName Q1 SYMATTR Value BC547B SYMBOL npn -1696 -1152 M0 SYMATTR InstName Q2 SYMATTR Value BC547B SYMBOL res -1584 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R23 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -1776 -1024 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R24 SYMATTR Value 1.2k SYMATTR SpiceLine tol=0.1 SYMBOL res -1776 -1744 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R25 SYMATTR Value 6.8k SYMATTR SpiceLine tol=0.1 SYMBOL pnp -1824 -1440 M180 SYMATTR InstName Q3 SYMATTR Value BC557B SYMBOL res -1888 -1664 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R27 SYMATTR Value 18k SYMATTR SpiceLine tol=1 SYMBOL res -1888 -1024 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R28 SYMATTR Value 6.8k SYMATTR SpiceLine tol=1 SYMBOL cap -1856 -1456 R0 WINDOW 0 28 4 Left 2 WINDOW 3 21 62 Left 2 SYMATTR InstName C3 SYMATTR Value 100n SYMBOL res -160 -1600 R270 WINDOW 0 27 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName R26 SYMATTR Value 10.7k SYMATTR SpiceLine tol=1 SYMBOL res -768 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 4.87k SYMATTR SpiceLine tol=1 SYMBOL cap -784 -1584 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C19 SYMATTR Value 10p SYMBOL FerriteBead 208 -672 R0 SYMATTR InstName L5 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL FerriteBead 208 -2128 R0 SYMATTR InstName L6 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL cap 320 -1968 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C20 SYMATTR Value 100n SYMBOL cap -96 -816 R0 WINDOW 0 -60 15 Left 2 WINDOW 3 -62 54 Left 2 SYMATTR InstName C22 SYMATTR Value 100n SYMBOL njf -1376 -1584 R0 SYMATTR InstName J1 SYMATTR Value MMBF4391 SYMBOL References\\LTC6655-1.25 1232 -1120 R0 SYMATTR InstName U4 SYMBOL FerriteBead -1760 -880 R0 SYMATTR InstName L10 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL FerriteBead -1568 -880 R0 SYMATTR InstName L11 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL FerriteBead -1760 -1600 R0 SYMATTR InstName L12 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f mfg="Würth Elektronik" pn="7427503 WE-UKW 40060" SYMBOL res -1200 -1664 R0 WINDOW 0 41 37 Left 2 WINDOW 3 36 71 Left 2 SYMATTR InstName R7 SYMATTR Value 390 SYMATTR SpiceLine tol=0.1 SYMBOL cap -64 -1824 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C9 SYMATTR Value 10p SYMBOL FerriteBead 576 -1936 R0 SYMATTR InstName L13 SYMATTR Value 1000n SYMATTR SpiceLine Ipk=0.2 Rser=0.562 Rpar=750 Cpar=350f mfg="Würth Elektronik" pn="782422601 WE-CBA 0402" SYMBOL res -944 -1728 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 82 SYMATTR SpiceLine tol=1 SYMBOL res 1120 -1792 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 51k SYMBOL cap 1184 -1728 R0 SYMATTR InstName C12 SYMATTR Value 15n SYMBOL cap 704 -1088 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C13 SYMATTR Value 10p SYMBOL OpAmps\\opamp -1408 -1792 M0 SYMATTR InstName U2 SYMBOL OpAmps\\opamp -656 -1504 R0 SYMATTR InstName U3 SYMBOL OpAmps\\opamp -176 -1584 R0 SYMATTR InstName U5 SYMBOL OpAmps\\opamp 208 -1248 R0 SYMATTR InstName U6 SYMBOL OpAmps\\opamp 576 -1264 R0 SYMATTR InstName U7 SYMBOL OpAmps\\opamp 1664 -1456 R0 SYMATTR InstName U8 SYMBOL res -1584 -1408 R0 WINDOW 0 43 37 Left 2 WINDOW 3 47 73 Left 2 SYMATTR InstName R9 SYMATTR Value 5K SYMATTR SpiceLine tol=0.1 SYMBOL cap -1472 -1232 R0 SYMATTR InstName C14 SYMATTR Value 1u TEXT -928 -568 Left 2 !.MODEL BAS70L D + IS = 3.22E-9 + N = 1.018 + BV = 77 + IBV = 1.67E-7 + RS = 20.89 + CJO = 1.608E-12 + VJ = 0.3891 + M = 0.3683 + FC = 0.5 + EG = 0.69 + XTI = 2 TEXT -336 -528 Left 2 ;R2 a,b,c, Vishay Beschlag ACAS06S0830372P1AT precision 10k resistor array R1a, R1b Maxim MAX5492LB10000+T 10K resistive divider in a SOT-23-5 package TEXT -720 -464 Left 2 !.MODEL MMBF4391 NJF VTO=-4.6 BETA=0.02779 LAMBDA=0.00595 RD=1 RS=1 IS=1e-14 CGD=14p CGS=10.5p PB=1 B=1 KF=1e-18 AF=1 FC=0.5 mfg=Motorola TEXT -720 -408 Left 2 !.lib LME49710.lib TEXT -1464 -576 Left 2 !.tran 0 1s 0s 1u uic TEXT -1464 -640 Left 2 !.lib opamp.sub TEXT -1464 -608 Left 2 !.ic v(vout)=5 TEXT -1464 -672 Left 2 !.options plotwinsize=0 numdgt=16

Thanks for that. I've got it into a form that my copy of LTSpice recognises as a .asc file, so I have looked at it.

I haven't run it yet because I'm running yet another variant of the circuit, which has got to 2.4 seconds, and I'll leave it running overnight.

I'm currently curious about the effect of the phase of the 2kHz component in the control signal (coming from my full-wave rectifier), and a fast simulating version of the circuit is just what I need to get that sorted out. I had thought that that it would be trivial to get the phase right, but my first attempt didn't get close.

I could go mad and put a version of the circuit into KiCad and create a printed circuit layout and get some Chinese firm to make and load the board.

It would be an extravagance, but nothing dramatic.

"Always invert" except when its better not to. For example, see Fig 6-7 of the OPA1656 data sheet. The distortion is around 6dB lower for the non-inverting configuration. This chip was designed to have very low variation in common-mode capacitance with voltage. John

...

I get 140dB down at 2kHz, 130dB down at 3kHz

I could too but I already know what 1kHz sounds like and I doubt that my ears can tell the difference between harmonics 120 and