Random thoughts on sinewave oscillators

This is a sort-of-Colpitts (not quite) oscillator that uses a BUF602 unity-gain buffer amp. Phase noise is pretty good.

Yes. The old Touch-Tone keypads had just such an oscillator, with voltage gain due to a multi-tapped coil in a ferrite pot core. The circuit and analysis was in an article published in the BSTJ.

Joe Gwinn

Somehow it was truncated?

This is what it was supposed to be:

If you move the ground to the emitter of Q3 and slide R8 through the power supply to the collector of Q3 you can see that it is a conventional phase shift oscillator with feedback through a three section RC network.

kw

That connects to the collector, as it is now and forms the first section of the RC network. (voltage sources are zero impedance from the point of view of AC). C4 is a coupling capacitor - its value and the high impedance of R4,R5 and Q1 mean it has little effect on the phase shift.

The revised .asc file is a bit of a mess. You've added R11 to get the output frequency close to 1KHz.

What you should have done is to have used 0.1% 10.5k resistors -it's an E96 value and you can buy them off the shelf - at R1 and R2.

That got me to 1.001kHz.

Since the capacitors at C1 and C2 can at best only be +/-1% tolerance parts - you can't buy anything better off the shelf - this is quite close enough.

You can use a trimming potentiometer to get closer to the target frequency, but that does have its downsides.

R4 certainly does make the circuit settle faster - how is a bit of a mystery - but you've created a total mess with R5,R7, R8, and R10. It's not clear what you were trying to do.

I found that I could get by without R4 provided that I stuck with sensible resistance values at R7 and R8 - R7 went up to 6.2k and I put

The cheapest plastic +/-1% film capacitors I could buy from Element-14 in Australia cost $A1.53 each so it isn't a particularly low cost circuit.

"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vf20si$96u8$ snipped-for-privacy@dont-email.me...

That would be fine in reality but so far this is only simulation.

So I'd leave it in.

R10 was experimental like R4 and has been removed.

If I wanted to build this for experimental purposes I'd have R4 150 ten turn and R5 100k ten turn. I'd also do it through hole.

If I were you I wouldn't get too excited over what, so far, is only a simulation. It could be bad for your blood pressure. I think reality would be a very different matter if the circuit were built for real but I don't have a suitable spectrum analyzer so there isn't much point doing that.

Is this better? I still can't do better than 40dB for unwanted harmonics no matter what I do. Except perhaps filter the output. Maybe a notch at 2KHz.

Version 4 SHEET 1 2196 916 WIRE -160 -304 -256 -304 WIRE -16 -304 -160 -304 WIRE 160 -304 -16 -304 WIRE 400 -304 224 -304 WIRE -160 -272 -160 -304 WIRE 400 -272 400 -304 WIRE -256 -256 -256 -304 WIRE -16 -208 -16 -304 WIRE -256 -160 -256 -192 WIRE -256 -160 -288 -160 WIRE -160 -160 -160 -192 WIRE -160 -160 -256 -160 WIRE -80 -160 -160 -160 WIRE -48 -160 -80 -160 WIRE 80 -160 48 -160 WIRE 112 -160 80 -160 WIRE 240 -160 192 -160 WIRE 272 -160 240 -160 WIRE 400 -160 400 -192 WIRE 400 -160 352 -160 WIRE -288 -112 -288 -160 WIRE -80 -96 -80 -160 WIRE -48 -96 -80 -96 WIRE 80 -96 80 -160 WIRE 80 -96 32 -96 WIRE 240 -48 240 -160 WIRE 240 -48 48 -48 WIRE 272 -48 240 -48 WIRE 400 -48 400 -160 WIRE 400 -48 352 -48 WIRE -384 32 -512 32 WIRE 128 32 -384 32 WIRE -512 80 -512 32 WIRE 128 96 128 32 WIRE -384 112 -384 32 WIRE 48 112 48 -48 WIRE 96 112 48 112 WIRE 384 128 160 128 WIRE 400 128 400 -48 WIRE 400 128 384 128 WIRE 528 128 400 128 WIRE 608 128 528 128 WIRE 96 144 -80 144 WIRE -80 224 -80 144 WIRE 16 224 -80 224 WIRE 176 224 16 224 WIRE 256 224 240 224 WIRE 384 224 384 128 WIRE 384 224 336 224 WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE -512 320 -512 160 WIRE -512 320 -592 320 WIRE -592 336 -592 320 WIRE -512 336 -512 320 WIRE -384 336 -384 176 WIRE -384 336 -512 336 WIRE -368 336 -384 336 WIRE -288 336 -288 -32 WIRE -288 336 -368 336 WIRE -80 336 -80 320 WIRE -80 336 -288 336 WIRE 16 336 16 304 WIRE 16 336 -80 336 WIRE -512 464 -512 336 WIRE -368 496 -368 336 WIRE -512 656 -512 544 WIRE -368 656 -368 560 WIRE -368 656 -512 656 WIRE 128 656 128 160 WIRE 128 656 -368 656 FLAG 528 128 output FLAG -592 336 0 DATAFLAG -464 32 "round(($)*100)/100" SYMBOL voltage -512 64 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 SpiceLine Rser=0.1 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 352 208 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL cap 240 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 15n SYMBOL cap 32 304 R180 WINDOW 0 -33 54 Left 2 WINDOW 3 -49 18 Left 2 SYMATTR InstName C2 SYMATTR Value 15n SYMBOL polcap -400 112 R0 SYMATTR InstName C4 SYMATTR Value 100µ SYMBOL OpAmps\\LT1057 128 64 R0 SYMATTR InstName U2 SYMBOL res -176 -288 R0 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL res 208 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.2k SYMBOL res 368 -176 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 15k SYMBOL diode 160 -288 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL res 384 -288 R0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL njf 48 -208 R90 WINDOW 0 -39 17 VRight 2 WINDOW 3 -10 -13 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -512 448 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 SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -384 496 R0 SYMATTR InstName C5 SYMATTR Value 100µ SYMBOL res -96 224 R0 SYMATTR InstName R2 SYMATTR Value 12k SYMBOL polcap -240 -192 R180 WINDOW 0 -35 53 Left 2 WINDOW 3 -47 17 Left 2 SYMATTR InstName C3 SYMATTR Value 10µ SYMBOL res 48 -112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL res -272 -16 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R4 SYMATTR Value 82 SYMBOL res 368 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 80k TEXT -496 352 Left 2 !.tran 0 2 1 startup TEXT -536 -392 Left 2 ;Edward Rawde's 1KHz sinewave oscillator. 20 Oct 2024.\nCan the sine purity be improved any further?

Actually, having just looked at the time domain waveform, I'd say that's no good at all.

Change R5 to 56k. Now that looks reasonable but only 35dB down at 2KHz. Maybe I'll notch that out.

It still works if I replace the transistors with an op amp non inverting follower - no inversion in sight. How would you re-describe that?

Exactly the same argument applies - any current coming out of the opamp must come from the power supplies and so goes through R8. The gain to the PS pin can be much more than unity.

Some circuit designs exploit this feature - I think I have seen John Larkin describing one. There are also designs in The Art of Electronics using it.

Bingo! Yes that’s it

This will probably mess up the thread structure, but here's another variation. It struck me that the current spike being pulled from the amp through D1 is probably messing up the op amp's output stage, so I decided to buffer the op amp output with a PNP to minimise this.

The 4th harmonic is now almost 50dB below the fundamental.

You could probably do even better with a more elaborate circuit that kept the output frequency away from the gate of the FET. My more ambitious simulation put in a precision rectifier to get a DC output that I could compare with a voltage reference with an integrator, whose output was low pass filtered before it went into the AD734 to adjust the gain.

A pure integrator would introduce too much phase shift to allow a stable control loop, so there was a resistor in series with the integrating capacitor to give you a sensible settling time for the loop.

That wasn't any kind of low cost approach.

Version 4 SHEET 1 2196 916 WIRE -352 -608 -480 -608 WIRE 128 -608 -352 -608 WIRE 464 -608 128 -608 WIRE 464 -576 464 -608 WIRE 464 -480 464 -496 WIRE 464 -480 320 -480 WIRE 320 -416 320 -480 WIRE -160 -256 -256 -256 WIRE -80 -256 -160 -256 WIRE -16 -256 -80 -256 WIRE 48 -256 -16 -256 WIRE 160 -256 112 -256 WIRE 240 -256 224 -256 WIRE 320 -256 320 -336 WIRE 320 -256 304 -256 WIRE -160 -240 -160 -256 WIRE -256 -224 -256 -256 WIRE -16 -176 -16 -256 WIRE -256 -128 -256 -160 WIRE -160 -128 -160 -160 WIRE -160 -128 -256 -128 WIRE -80 -128 -160 -128 WIRE -48 -128 -80 -128 WIRE 80 -128 48 -128 WIRE 160 -128 80 -128 WIRE 256 -128 240 -128 WIRE 320 -128 256 -128 WIRE 448 -128 400 -128 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 64 -64 48 -64 WIRE 80 -64 80 -128 WIRE 80 -64 64 -64 WIRE 256 64 256 -128 WIRE 256 64 48 64 WIRE -480 80 -480 -608 WIRE 128 96 128 -608 WIRE -352 112 -352 -608 WIRE 48 112 48 64 WIRE 96 112 48 112 WIRE 432 128 160 128 WIRE 448 128 448 -128 WIRE 448 128 432 128 WIRE 528 128 528 -432 WIRE 528 128 448 128 WIRE 608 128 528 128 WIRE 656 128 608 128 WIRE 96 144 -80 144 WIRE -80 224 -80 144 WIRE 16 224 -80 224 WIRE 224 224 16 224 WIRE 304 224 288 224 WIRE 432 224 432 128 WIRE 432 224 384 224 WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE -480 320 -480 160 WIRE -480 320 -560 320 WIRE -560 336 -560 320 WIRE -480 336 -480 320 WIRE -352 336 -352 176 WIRE -352 336 -480 336 WIRE -336 336 -352 336 WIRE -256 336 -256 -128 WIRE -256 336 -336 336 WIRE -80 336 -80 320 WIRE -80 336 -256 336 WIRE 16 336 16 304 WIRE 16 336 -80 336 WIRE -480 464 -480 336 WIRE -336 496 -336 336 WIRE -480 656 -480 544 WIRE -336 656 -336 560 WIRE -336 656 -480 656 WIRE 128 656 128 160 WIRE 128 656 -336 656 WIRE 464 656 464 -384 WIRE 464 656 128 656 FLAG -560 336 0 FLAG -80 -256 FET_gate FLAG 64 -64 TP FLAG 608 128 output SYMBOL voltage -480 64 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 SpiceLine Rser=0.1 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 352 224 R90 WINDOW 0 -20 5 VBottom 2 WINDOW 3 21 -5 VTop 2 SYMATTR InstName R1 SYMATTR Value 10.5k SYMBOL cap 288 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 15n SYMBOL cap 32 304 R180 WINDOW 0 -33 54 Left 2 WINDOW 3 -49 18 Left 2 SYMATTR InstName C2 SYMATTR Value 15n SYMBOL polcap -368 112 R0 SYMATTR InstName C4 SYMATTR Value 100l SYMBOL OpAmps\\LT1057 128 64 R0 SYMATTR InstName U2 SYMBOL res -160 -208 R0 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL res 208 -128 R90 WINDOW 0 -21 6 VBottom 2 WINDOW 3 18 3 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.34k SYMBOL res 368 -128 R90 WINDOW 0 -17 16 VBottom 2 WINDOW 3 15 7 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL diode 48 -240 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL res 320 -368 R180 WINDOW 0 15 28 Left 2 WINDOW 3 15 -8 Left 2 SYMATTR InstName R9 SYMATTR Value 4.7k SYMBOL njf 48 -176 R90 WINDOW 0 -38 17 VRight 2 WINDOW 3 -7 -47 VRight 2 SYMATTR InstName J1 SYMATTR Value 2N3819 SYMBOL voltage -480 448 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 383 -483 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -352 496 R0 SYMATTR InstName C5 SYMATTR Value 100l SYMBOL res -80 272 R0 SYMATTR InstName R2 SYMATTR Value 10.5k SYMBOL polcap -240 -160 R180 WINDOW 0 24 57 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C3 SYMATTR Value 10µ SYMBOL res 16 -64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL FerriteBead 192 -256 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L1 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL FerriteBead 272 -256 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L2 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL pnp 528 -384 R180 SYMATTR InstName Q1 SYMATTR Value 2N2907 SYMBOL res 464 -544 R0 SYMATTR InstName R4 SYMATTR Value 4.7k TEXT -184 472 Left 2 !.tran 0 20s 0s startup

"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vf5dkk$tubm$ snipped-for-privacy@dont-email.me...

Yes that works well, thanks for taking the time to produce it.

There were issues with resistors being out of position for unknown reasons but easy to correct.

My next question is why does this circuit, which is based on yours, show unwanted amplitude modulation at the top of the time domain trace but only to a very small extent underneath.

Changing the diode to a BAT54 improves it.

Version 4 SHEET 1 2196 916 WIRE -352 -608 -480 -608 WIRE 128 -608 -352 -608 WIRE 464 -608 128 -608 WIRE 464 -576 464 -608 WIRE 464 -480 464 -496 WIRE 464 -480 320 -480 WIRE 320 -416 320 -480 WIRE -160 -256 -256 -256 WIRE -80 -256 -160 -256 WIRE -16 -256 -80 -256 WIRE 48 -256 -16 -256 WIRE 160 -256 112 -256 WIRE 240 -256 224 -256 WIRE 320 -256 320 -336 WIRE 320 -256 304 -256 WIRE -160 -240 -160 -256 WIRE -256 -224 -256 -256 WIRE -16 -176 -16 -256 WIRE -256 -128 -256 -160 WIRE -160 -128 -160 -160 WIRE -160 -128 -256 -128 WIRE -80 -128 -160 -128 WIRE -48 -128 -80 -128 WIRE 80 -128 48 -128 WIRE 160 -128 80 -128 WIRE 256 -128 240 -128 WIRE 320 -128 256 -128 WIRE 448 -128 400 -128 WIRE -256 -64 -256 -128 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 64 -64 48 -64 WIRE 80 -64 80 -128 WIRE 80 -64 64 -64 WIRE 256 -16 256 -128 WIRE 304 -16 256 -16 WIRE 448 -16 448 -128 WIRE 448 -16 384 -16 WIRE 256 64 256 -16 WIRE 256 64 48 64 WIRE -480 80 -480 -608 WIRE 128 96 128 -608 WIRE -352 112 -352 -608 WIRE 48 112 48 64 WIRE 96 112 48 112 WIRE 432 128 160 128 WIRE 448 128 448 -16 WIRE 448 128 432 128 WIRE 528 128 528 -432 WIRE 528 128 448 128 WIRE 608 128 528 128 WIRE 656 128 608 128 WIRE 96 144 -80 144 WIRE -80 224 -80 144 WIRE 16 224 -80 224 WIRE 224 224 16 224 WIRE 304 224 288 224 WIRE 432 224 432 128 WIRE 432 224 384 224 WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE -480 320 -480 160 WIRE -480 320 -560 320 WIRE -560 336 -560 320 WIRE -480 336 -480 320 WIRE -352 336 -352 176 WIRE -352 336 -480 336 WIRE -336 336 -352 336 WIRE -256 336 -256 16 WIRE -256 336 -336 336 WIRE -80 336 -80 320 WIRE -80 336 -256 336 WIRE 16 336 16 304 WIRE 16 336 -80 336 WIRE -480 464 -480 336 WIRE -336 496 -336 336 WIRE -480 656 -480 544 WIRE -336 656 -336 560 WIRE -336 656 -480 656 WIRE 128 656 128 160 WIRE 128 656 -336 656 WIRE 464 656 464 -384 WIRE 464 656 128 656 FLAG -560 336 0 FLAG -80 -256 FET_gate FLAG 64 -64 TP FLAG 608 128 output SYMBOL voltage -480 64 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 SpiceLine Rser=0.1 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 400 208 R90 WINDOW 0 -20 5 VBottom 2 WINDOW 3 21 -5 VTop 2 SYMATTR InstName R1 SYMATTR Value 10.5k SYMBOL cap 288 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 15n SYMBOL cap 32 304 R180 WINDOW 0 -33 54 Left 2 WINDOW 3 -49 18 Left 2 SYMATTR InstName C2 SYMATTR Value 15n SYMBOL polcap -368 112 R0 SYMATTR InstName C4 SYMATTR Value 100l SYMBOL OpAmps\\LT1057 128 64 R0 SYMATTR InstName U2 SYMBOL res -176 -256 R0 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL res 256 -144 R90 WINDOW 0 -1 46 VBottom 2 WINDOW 3 35 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.34k SYMBOL res 416 -144 R90 WINDOW 0 -4 61 VBottom 2 WINDOW 3 39 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL diode 48 -240 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL res 336 -320 R180 WINDOW 0 15 28 Left 2 WINDOW 3 15 -8 Left 2 SYMATTR InstName R9 SYMATTR Value 4.7k SYMBOL njf 48 -176 R90 WINDOW 0 -38 17 VRight 2 WINDOW 3 -9 -11 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -480 448 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 383 -483 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -352 496 R0 SYMATTR InstName C5 SYMATTR Value 100l SYMBOL res -96 224 R0 SYMATTR InstName R2 SYMATTR Value 10.5k SYMBOL cap -240 -160 R180 WINDOW 0 24 57 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C3 SYMATTR Value 10µ SYMATTR Description Polarized Capacitor SYMATTR Type polcap SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60G106ME15" type="X5R" SYMBOL res 64 -80 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL FerriteBead 192 -256 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L1 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL FerriteBead 272 -256 R90 WINDOW 0 -16 0 VBottom 2 SYMATTR InstName L2 SYMATTR Value 14µ SYMATTR SpiceLine Ipk=3 Rser=0.0122 Rpar=870 Cpar=1000f SYMBOL pnp 528 -384 R180 SYMATTR InstName Q1 SYMATTR Value 2N2907 SYMBOL res 448 -592 R0 SYMATTR InstName R5 SYMATTR Value 4.7k SYMBOL res 400 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 820k SYMBOL res -272 -80 R0 SYMATTR InstName R4 SYMATTR Value 15 TEXT -184 472 Left 2 !.tran 0 20s 0s startup

"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vf5dkk$tubm$ snipped-for-privacy@dont-email.me...

If the problem is asymmetry in the drive from the amplifier then why not symmetricalize it like this.

An FFT from 6s to 20s shows reasonably clean performance at 1kHz and a simple filter should be able to get more than 50dB down at other harmonics.

R9 at 100 ohms is even better.

Manual adjustment of R5 will be needed in any real circuit.

I'd probably make R10 10 ohm variable, R9 1k variable and R5 100k variable and then use the extremely scientific process of adjusting all three for best performance.

I may not be able to reply further for a few days after today.

Version 4 SHEET 1 2196 916 WIRE -352 -608 -480 -608 WIRE 128 -608 -352 -608 WIRE -160 -496 -256 -496 WIRE 48 -496 -160 -496 WIRE 496 -496 112 -496 WIRE -160 -480 -160 -496 WIRE -256 -464 -256 -496 WIRE -256 -368 -256 -400 WIRE -160 -368 -160 -400 WIRE -160 -368 -256 -368 WIRE -256 -320 -256 -368 WIRE -256 -320 -304 -320 WIRE -160 -256 -256 -256 WIRE -16 -256 -160 -256 WIRE 48 -256 -16 -256 WIRE 496 -256 496 -496 WIRE 496 -256 112 -256 WIRE -160 -240 -160 -256 WIRE -256 -224 -256 -256 WIRE -16 -176 -16 -256 WIRE -304 -128 -304 -320 WIRE -256 -128 -256 -160 WIRE -256 -128 -304 -128 WIRE -160 -128 -160 -160 WIRE -160 -128 -256 -128 WIRE -80 -128 -160 -128 WIRE -48 -128 -80 -128 WIRE 80 -128 48 -128 WIRE 160 -128 80 -128 WIRE 256 -128 240 -128 WIRE 320 -128 256 -128 WIRE 448 -128 400 -128 WIRE -304 -80 -304 -128 WIRE 496 -80 496 -256 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 64 -64 48 -64 WIRE 80 -64 80 -128 WIRE 80 -64 64 -64 WIRE 256 -16 256 -128 WIRE 304 -16 256 -16 WIRE 448 -16 448 -128 WIRE 448 -16 384 -16 WIRE -304 32 -304 0 WIRE 256 64 256 -16 WIRE 256 64 48 64 WIRE -480 80 -480 -608 WIRE 128 96 128 -608 WIRE -352 112 -352 -608 WIRE 48 112 48 64 WIRE 96 112 48 112 WIRE 432 128 160 128 WIRE 448 128 448 -16 WIRE 448 128 432 128 WIRE 496 128 496 0 WIRE 496 128 448 128 WIRE 608 128 496 128 WIRE 656 128 608 128 WIRE 96 144 -80 144 WIRE -80 224 -80 144 WIRE 16 224 -80 224 WIRE 224 224 16 224 WIRE 304 224 288 224 WIRE 432 224 432 128 WIRE 432 224 384 224 WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE -480 320 -480 160 WIRE -480 320 -560 320 WIRE -560 336 -560 320 WIRE -480 336 -480 320 WIRE -352 336 -352 176 WIRE -352 336 -480 336 WIRE -336 336 -352 336 WIRE -80 336 -80 320 WIRE -80 336 -336 336 WIRE 16 336 16 304 WIRE 16 336 -80 336 WIRE -480 464 -480 336 WIRE -336 496 -336 336 WIRE -480 656 -480 544 WIRE -336 656 -336 560 WIRE -336 656 -480 656 WIRE 128 656 128 160 WIRE 128 656 -336 656 WIRE 464 656 128 656 FLAG -560 336 0 FLAG 64 -64 TP FLAG 608 128 output FLAG -304 32 0 SYMBOL voltage -480 64 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 SpiceLine Rser=0.1 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 400 208 R90 WINDOW 0 -20 5 VBottom 2 WINDOW 3 21 -5 VTop 2 SYMATTR InstName R1 SYMATTR Value 10.5k SYMBOL cap 288 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 15n SYMBOL cap 32 304 R180 WINDOW 0 -33 54 Left 2 WINDOW 3 -49 18 Left 2 SYMATTR InstName C2 SYMATTR Value 15n SYMBOL polcap -368 112 R0 SYMATTR InstName C4 SYMATTR Value 100l SYMBOL OpAmps\\LT1057 128 64 R0 SYMATTR InstName U2 SYMBOL res -176 -256 R0 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL res 256 -144 R90 WINDOW 0 -1 46 VBottom 2 WINDOW 3 35 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.34k SYMBOL res 416 -144 R90 WINDOW 0 -4 61 VBottom 2 WINDOW 3 39 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL schottky 48 -240 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL njf 48 -176 R90 WINDOW 0 -38 17 VRight 2 WINDOW 3 -9 -11 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -480 448 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 383 -483 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -352 496 R0 SYMATTR InstName C5 SYMATTR Value 100l SYMBOL res -96 224 R0 SYMATTR InstName R2 SYMATTR Value 10.5k SYMBOL cap -240 -160 R180 WINDOW 0 -27 59 Left 2 WINDOW 3 -33 2 Left 2 SYMATTR InstName C3 SYMATTR Value 10µ SYMATTR Description Polarized Capacitor SYMATTR Type polcap SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60G106ME15" type="X5R" SYMBOL res 64 -80 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL res 400 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 820k SYMBOL schottky 112 -512 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -176 -496 R0 SYMATTR InstName R4 SYMATTR Value 47k SYMBOL cap -240 -400 R180 WINDOW 0 -27 61 Left 2 WINDOW 3 -37 8 Left 2 SYMATTR InstName C6 SYMATTR Value 10µ SYMATTR Description Polarized Capacitor SYMATTR Type polcap SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60G106ME15" type="X5R" SYMBOL res 480 -96 R0 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL res -320 -96 R0 SYMATTR InstName R10 SYMATTR Value 2.2 TEXT -184 472 Left 2 !.tran 0 20s 0s startup

"Bill Sloman" snipped-for-privacy@ieee.org wrote in message news:vf5dkk$tubm$ snipped-for-privacy@dont-email.me...

I don't think the circuit below can be improved on in simulation and it's anybody's guess what reality would say.

Shouldn't be hard to get 60dB down with a suitable filter.

Version 4 SHEET 1 2196 916 WIRE -352 -608 -480 -608 WIRE 128 -608 -352 -608 WIRE -160 -496 -256 -496 WIRE 48 -496 -160 -496 WIRE 496 -496 112 -496 WIRE -160 -480 -160 -496 WIRE -256 -464 -256 -496 WIRE -256 -368 -256 -400 WIRE -160 -368 -160 -400 WIRE -160 -368 -256 -368 WIRE -256 -320 -256 -368 WIRE -256 -320 -304 -320 WIRE -160 -256 -256 -256 WIRE -16 -256 -160 -256 WIRE 48 -256 -16 -256 WIRE 496 -256 496 -496 WIRE 496 -256 112 -256 WIRE -160 -240 -160 -256 WIRE -256 -224 -256 -256 WIRE -16 -176 -16 -256 WIRE -304 -128 -304 -320 WIRE -256 -128 -256 -160 WIRE -256 -128 -304 -128 WIRE -160 -128 -160 -160 WIRE -160 -128 -256 -128 WIRE -80 -128 -160 -128 WIRE -48 -128 -80 -128 WIRE 80 -128 48 -128 WIRE 160 -128 80 -128 WIRE 256 -128 240 -128 WIRE 320 -128 256 -128 WIRE 448 -128 400 -128 WIRE -304 -80 -304 -128 WIRE 496 -80 496 -256 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 64 -64 48 -64 WIRE 80 -64 80 -128 WIRE 80 -64 64 -64 WIRE 256 -16 256 -128 WIRE 304 -16 256 -16 WIRE 448 -16 448 -128 WIRE 448 -16 384 -16 WIRE -304 32 -304 0 WIRE 256 64 256 -16 WIRE 256 64 48 64 WIRE -480 80 -480 -608 WIRE 128 96 128 -608 WIRE -352 112 -352 -608 WIRE 48 112 48 64 WIRE 96 112 48 112 WIRE 432 128 160 128 WIRE 448 128 448 -16 WIRE 448 128 432 128 WIRE 496 128 496 0 WIRE 496 128 448 128 WIRE 608 128 496 128 WIRE 656 128 608 128 WIRE 96 144 -80 144 WIRE -80 224 -80 144 WIRE 16 224 -80 224 WIRE 224 224 16 224 WIRE 304 224 288 224 WIRE 432 224 432 128 WIRE 432 224 384 224 WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE -480 320 -480 160 WIRE -480 320 -560 320 WIRE -560 336 -560 320 WIRE -480 336 -480 320 WIRE -352 336 -352 176 WIRE -352 336 -480 336 WIRE -336 336 -352 336 WIRE -80 336 -80 320 WIRE -80 336 -336 336 WIRE 16 336 16 304 WIRE 16 336 -80 336 WIRE -480 464 -480 336 WIRE -336 496 -336 336 WIRE -480 656 -480 544 WIRE -336 656 -336 560 WIRE -336 656 -480 656 WIRE 128 656 128 160 WIRE 128 656 -336 656 WIRE 464 656 128 656 FLAG -560 336 0 FLAG 64 -64 TP FLAG 608 128 output FLAG -304 32 0 SYMBOL voltage -480 64 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 SpiceLine Rser=0.1 SYMATTR InstName V1 SYMATTR Value 12 SYMBOL res 400 208 R90 WINDOW 0 -20 5 VBottom 2 WINDOW 3 21 -5 VTop 2 SYMATTR InstName R1 SYMATTR Value 10.5k SYMBOL cap 288 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 15n SYMBOL cap 32 304 R180 WINDOW 0 -33 54 Left 2 WINDOW 3 -49 18 Left 2 SYMATTR InstName C2 SYMATTR Value 15n SYMBOL polcap -368 112 R0 SYMATTR InstName C4 SYMATTR Value 100µ SYMBOL OpAmps\\LT1057 128 64 R0 SYMATTR InstName U2 SYMBOL res -176 -256 R0 SYMATTR InstName R6 SYMATTR Value 47k SYMBOL res 256 -144 R90 WINDOW 0 -1 46 VBottom 2 WINDOW 3 35 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 6.34k SYMBOL res 416 -144 R90 WINDOW 0 -4 61 VBottom 2 WINDOW 3 39 55 VTop 2 SYMATTR InstName R8 SYMATTR Value 13k SYMBOL schottky 48 -240 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL njf 48 -176 R90 WINDOW 0 -38 17 VRight 2 WINDOW 3 -9 -11 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -480 448 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 383 -483 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -352 496 R0 SYMATTR InstName C5 SYMATTR Value 100µ SYMBOL res -96 224 R0 SYMATTR InstName R2 SYMATTR Value 10.5k SYMBOL cap -240 -160 R180 WINDOW 0 -27 59 Left 2 WINDOW 3 -33 2 Left 2 SYMATTR InstName C3 SYMATTR Value 10µ SYMATTR Description Polarized Capacitor SYMATTR Type polcap SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60G106ME15" type="X5R" SYMBOL res 64 -80 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 SYMBOL res 400 -32 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 820k SYMBOL schottky 112 -512 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL res -176 -496 R0 SYMATTR InstName R4 SYMATTR Value 47k SYMBOL cap -240 -400 R180 WINDOW 0 -27 61 Left 2 WINDOW 3 -37 8 Left 2 SYMATTR InstName C6 SYMATTR Value 10µ SYMATTR Description Polarized Capacitor SYMATTR Type polcap SYMATTR SpiceLine V=4 Irms=0 Rser=0 Lser=0 mfg="Murata" pn="GRM155R60G106ME15" type="X5R" SYMBOL res 480 -96 R0 SYMATTR InstName R9 SYMATTR Value 100 SYMBOL res -320 -96 R0 SYMATTR InstName R10 SYMATTR Value 2.2 TEXT -184 472 Left 2 !.tran 0 20s 5s startup