Low distortion sinewave oscillator without big capacitor.

Well, Win Hill always said it was more of an art than a science.

I've got my name three patents, so I'm demonstrably capable of having ideas. I am hostile to people who tout bad ideas.

That's what brainstorming is about, but some ideas are hopelessly goofy.

Practical ideas. Ideally practicable ideas.

He's scarcely the first to have that insight. Alan Dower Blumlein expressed much the same opinion, and he died before I was born.

There are lots of ways of making a circuit that can work, and it's nice when you can get one that's not only effective, but also comprehensible.

Don't you think it would be better to just explain why you think an idea is bad Bill? And also, if necessary, to just explain how and why you think it should be done. Being hostile doesn't make you look good and it does the opposite of persuading others that their ideas are bad. So why be hostile at all?

"JM" snipped-for-privacy@gmail.com wrote in message news: snipped-for-privacy@4ax.com...

I'm not sure I understand how the multiplier could be implemented with just a long tailed pair.

The derived circuit below doesn't seem to have any discernible distortion at all as far as I can tell in an LTSpice FFT. Not until you get above about 100KHz where it's 160dB down.

Version 4.1 SHEET 1 3020 2548 WIRE -1936 -288 -1936 -336 WIRE -240 -224 -608 -224 WIRE 480 -224 -160 -224 WIRE -1936 -160 -1936 -208 WIRE -1840 -160 -1936 -160 WIRE -1648 -160 -1760 -160 WIRE 80 -160 -1584 -160 WIRE -608 -96 -608 -224 WIRE -240 -96 -608 -96 WIRE 80 -96 80 -160 WIRE 80 -96 -160 -96 WIRE -1936 -64 -1936 -160 WIRE -1936 -64 -2272 -64 WIRE -2400 -32 -2400 -288 WIRE -2272 0 -2272 -64 WIRE -2208 0 -2272 0 WIRE -2112 0 -2144 0 WIRE -608 32 -608 -96 WIRE -496 32 -608 32 WIRE -352 32 -416 32 WIRE -272 32 -352 32 WIRE -112 32 -192 32 WIRE -64 32 -112 32 WIRE 80 32 80 -96 WIRE 80 32 0 32 WIRE 144 32 80 32 WIRE 288 32 224 32 WIRE 336 32 288 32 WIRE 480 32 480 -224 WIRE 480 32 400 32 WIRE -1328 48 -1328 0 WIRE -1008 48 -1072 48 WIRE -880 48 -944 48 WIRE -1936 64 -1936 -64 WIRE -2272 96 -2272 0 WIRE -2224 96 -2272 96 WIRE -2112 112 -2112 0 WIRE -2112 112 -2160 112 WIRE -2000 112 -2112 112 WIRE -2400 128 -2400 48 WIRE -2224 128 -2400 128 WIRE -608 144 -608 32 WIRE -496 144 -608 144 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224 R0 SYMATTR InstName Q1A SYMATTR Value BCM847BS SYMBOL npn -1872 304 M0 SYMATTR InstName Q1B SYMATTR Value BCM847BS SYMBOL zener -1296 1088 R270 WINDOW 0 36 32 VTop 2 WINDOW 3 -4 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value BZX84B9V1LY SYMBOL res -1696 1088 R0 SYMATTR InstName R20 SYMATTR Value 2k SYMBOL cap -480 944 R0 SYMATTR InstName C10 SYMATTR Value 1000n SYMBOL res -800 1136 R0 SYMATTR InstName R21 SYMATTR Value 1.5k SYMBOL res -800 1280 R0 SYMATTR InstName R22 SYMATTR Value 10k SYMBOL cap -704 1312 R0 SYMATTR InstName C11 SYMATTR Value 10n TEXT -2576 632 Left 2 !.tran 0 10 0 1u startup TEXT -2576 576 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -2688 1104 Left 2 !.MODEL BCM847BS NPN IS = 1.822E-14 NF = 0.9932 ISE= 2.894E-16 NE = 1.4 \n+ BF = 324.4 IKF = 0.109 VAF = 82 NR = 0.9931 ISC = 9.982E-12 NC = 1.763 \n+ BR = 8.29 IKR = 0.09 VAR = 17.9 RB = 10 IRB = 5E-06 RBM = 5 RE = 0.649 \n+ RC = 0.7014 CJE = 1.244E-11 VJE = 0.7579 MJE = 0.3656 TF = 4.908E-10 \n+ XTF = 9.51 VTF = 2.927 ITF = 0.3131 PTF = 0 CJC = 3.347E-12 VJC =

I usually do.

I have been known to do that. You should know - I've done it to you, here, and I'm about to do it to John May whom I really like and approve of.

Few people can ever be persuaded that their ideas are bad. John Larkin definitely isn't one of them.

The same mechanism that persuades people that their bad ideas aren't too bad allows them to gloss over any criticism that isn't thoroughly explicit.

On 5/04/2025 10:12 am, JM wrote:

I've reworked my version of the circuit to incorporate most of John May's changes. I really dislike the Zener diode at D3 and have solved that particular problem in a different way. My updated version has a

I'm inclined to agree with the proposition that two dual transistors is an over-kill, but my attempts at getting a long-tailed pair solution to work didn't get anywhere. I need to rip up a few more ill-founded schemes.

Version 4 SHEET 1 3020 2548 WIRE 80 -208 -288 -208 WIRE 800 -208 160 -208 WIRE -288 -96 -288 -208 WIRE 80 -96 -288 -96 WIRE 400 -96 160 -96 WIRE -288 32 -288 -96 WIRE -176 32 -288 32 WIRE -32 32 -96 32 WIRE 48 32 -32 32 WIRE 208 32 128 32 WIRE 256 32 208 32 WIRE 400 32 400 -96 WIRE 400 32 320 32 WIRE 464 32 400 32 WIRE 608 32 544 32 WIRE 656 32 608 32 WIRE 800 32 800 -208 WIRE 800 32 720 32 WIRE -752 48 -816 48 WIRE -624 48 -688 48 WIRE -288 144 -288 32 WIRE -176 144 -288 144 WIRE 208 144 208 32 WIRE 256 144 208 144 WIRE 608 144 608 32 WIRE 656 144 608 144 WIRE -816 160 -816 48 WIRE -752 160 -816 160 WIRE -624 160 -624 48 WIRE -624 160 -672 160 WIRE -32 160 -32 32 WIRE -32 160 -112 160 WIRE 400 160 400 32 WIRE 400 160 320 160 WIRE 800 160 800 32 WIRE 800 160 720 160 WIRE 832 160 800 160 WIRE -176 176 -288 176 WIRE 256 176 224 176 WIRE 656 176 624 176 WIRE 224 208 224 176 WIRE 624 208 624 176 WIRE -1968 224 -1968 144 WIRE -1008 272 -1104 272 WIRE -816 272 -816 160 WIRE -816 272 -944 272 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WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 10000n SYMBOL OpAmps\\LT1679 384 528 R90 WINDOW 3 37 22 VRight 2 SYMATTR InstName U1 SYMBOL pnp -2032 736 M180 WINDOW 3 84 0 Left 2 SYMATTR Value 2N3906 SYMATTR InstName Q5 SYMBOL res -1984 208 R0 SYMATTR InstName R12 SYMATTR Value 56k SYMBOL res -1760 384 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R25 SYMATTR Value 2.7Meg SYMBOL cap -2176 544 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 10p SYMBOL res -1984 784 R0 SYMATTR InstName R27 SYMATTR Value 1 SYMBOL npn -2096 1152 M0 SYMATTR InstName Q6 SYMATTR Value 2N3904 SYMBOL npn -1728 1152 R0 SYMATTR InstName Q1B SYMATTR Value BCM61B SYMBOL npn -1424 1232 R0 SYMATTR InstName Q8 SYMATTR Value 2N3904 SYMBOL npn -1968 1712 R0 SYMATTR InstName Q1A SYMATTR Value BCM61B SYMBOL res -1552 1632 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R28 SYMATTR Value 15k SYMBOL res -1376 784 R0 SYMATTR InstName R29 SYMATTR Value 100k SYMBOL res -2448 528 R0 SYMATTR InstName R32 SYMATTR Value 10k SYMBOL res -2448 752 R0 SYMATTR InstName R33 SYMATTR Value 15k SYMBOL cap -944 256 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C12 SYMATTR Value 1000n SYMBOL res -656 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 14k SYMBOL cap -688 32 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL cap -1600 384 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 100n SYMBOL res -1648 1456 R180 WINDOW 0 31 76 Left 2 WINDOW 3 31 40 Left 2 SYMATTR InstName R17 SYMATTR Value 120k SYMBOL OpAmps\\LT1679 -704 288 R0 SYMATTR InstName U2 SYMBOL OpAmps\\LT1679 -272 1200 M0 SYMATTR InstName U3 SYMBOL OpAmps\\LT1679 -2224 688 R0 SYMATTR InstName U4 SYMBOL cap -2560 768 R0 SYMATTR InstName C9 SYMATTR Value 10n TEXT -2792 1560 Left 2 !.tran 0 10 0 1u startup TEXT -2792 1504 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -2248 -112 Left 2 ;Low distortion 1KHz oscillator. Edward Rawde 30 March 2025.\nBased on designs by JM and BS. TEXT -2848 128 Left 2 !.MODEL BCM61B NPN\n+ IS = 1.822E-14\n+ NF =

You can be critical without being hostile.

Are you sure that's the correct circuit? It looks very similar to a circuit you posted yesterday and LTSpice 24.1.5 says 125dB down at 4 KHz.

Just modulate the tail current and select how much to steer to the output by directly driving the bases rather than indirectly as in your circuit. The following link shows one example topology, and a four quadrant differential I/O version. Compare the linearity of each of them.

Best to use the Hanning windows at these levels if you're not already doing so.

Very interesting. Thank you.

Yes that stabilizes, but only 70dB down.

Adjust the maximum timestep.

"JM" snipped-for-privacy@gmail.com wrote in message news: snipped-for-privacy@4ax.com...

The 4qm circuit is clearly superior. Here's my attempt at using it so far. No doubt this can be improved. What's the best way to implement E1 in practice?

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Oops. Sorry. It looks as if I closed LTSpice without saving the circuit, so what I posted was the file I'd started from, rather than the one I had been running.

I don't think that I will bother reconstructing it. Overnight I got to thinking about doing roughly what John May proposed this morning and I'll see how my version comes out.

But, as I said, making it critical enough so that people realise that they have been criticised, rather than settling for basking in the attention, does come across as hostile, particularly to people who are seeking flattery, rather than critical comment.--Bill Sloman, Sydney

Rats. After I went to bed last night I came up with pretty much exactly that circuit - I even worried about having to move Vtap.

Needless to say, I like it.

Barry Gilbert is the father of the Gilbert multiplier circuit. I'm fairly sure he had patents on most of the interesting aspects - presumably now expired. I met him once - Analog Devices took him around a bunch of their UK customers, including Cambridge Instruments when I was working there. He was looking for customers for his RF chips, which were amazing, but of no interest to us.

I find the Blackman-Harris option works pretty well. I don't think that LTSpice uses long enough words to avoid rounding error problems at the

-160dB level.

I used a similar sort of numerical integration routine in my Ph.D. work in chemical kinetics in the late 1960's, and had to resort to double and triple precision arithmetic to avoid rounding error problems. The IBM

As I've already said, I like it. I've played with it a bit.

The ON-Semiconductor NSS40301MDR2G NPN dual comes with a 2mV guaranteed maximum difference in base-emitter voltages (at the same emitter current). Edward Rawde's Nexperia BCM61B dual part has matched current gain, but no guarantee on the Vbe. The Nexperia BCM847BS does offer 2mV base-emitter matching, and would presumably work just as well.

Putting in the ON-Semiconductor dual means that your gain control circuit doesn't have to waste output swing coping with part-to-part variation.

I've added a cascode transistor (Q1, it should be Q4) to minimise any Early effect distortion.

I've snipped out the op amp driving the base of Q3. Once you'd gone AC-coupled, it wasn't doing anything useful.

And I've put a string of eight diodes in series with R10. They nominally compensate for the temperature dependence introduced by the four rectifier diodes D2, D12, D13 and D14. In this version of the circuit the rectifiers knock about 0.6 volts off a sine wave that peaks at 3.8V, about a quarter of the 15V rail. I haven't run the numbers to fix the best number of diodes, but something between six and eight looks okay.

The harmonics aren't great - most of them are about 90dB below the fundamental, but the seventh is only 85dB down.

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32 VTop 2 SYMATTR InstName C2 SYMATTR Value 10n SYMBOL res -144 -272 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10K SYMBOL res -144 -128 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R5 SYMATTR Value 82k SYMBOL res 80 1120 R90 WINDOW 0 5 56 VBottom 2 WINDOW 3 27 56 VTop 2 SYMATTR InstName R10 SYMATTR Value 390k SYMBOL diode -288 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMATTR Value 1N914 SYMBOL res -368 912 R0 SYMATTR InstName R11 SYMATTR Value 40.2K SYMBOL res 240 592 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R18 SYMATTR Value 10K SYMBOL res 96 432 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R19 SYMATTR Value 10k SYMBOL diode -336 656 M0 SYMATTR InstName D2 SYMATTR Value 1N914 SYMBOL diode -96 656 M0 SYMATTR InstName D12 SYMATTR Value 1N914 SYMBOL diode 48 656 R0 SYMATTR InstName D13 SYMATTR Value 1N914 SYMBOL diode 496 656 M0 SYMATTR InstName D14 SYMATTR Value 1N914 SYMBOL res -368 736 R0 SYMATTR InstName R13 SYMATTR Value 68k SYMBOL res -128 736 R0 SYMATTR InstName R14 SYMATTR Value 68k SYMBOL res 80 736 M0 SYMATTR InstName R15 SYMATTR Value 68k SYMBOL res 464 736 R0 SYMATTR InstName R16 SYMATTR Value 68k SYMBOL voltage -1776 128 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 15 SYMBOL voltage -1776 272 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V4 SYMATTR Value 15 SYMBOL OpAmps\\LT1679 -464 112 R0 SYMATTR InstName U5 SYMBOL OpAmps\\LT1679 -32 112 R0 SYMATTR InstName U6 SYMBOL OpAmps\\LT1679 368 112 R0 SYMATTR InstName U8 SYMBOL res -432 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL res -640 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 560 SYMBOL cap -752 224 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C8 SYMATTR Value 1000n SYMBOL res -928 960 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R6 SYMATTR Value 75k SYMBOL cap -944 928 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C4 SYMATTR Value 10000n SYMBOL OpAmps\\LT1679 64 528 R90 WINDOW 3 37 22 VRight 2 SYMATTR InstName U1 SYMBOL res -1792 944 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R32 SYMATTR Value 12k SYMBOL res -1792 720 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R33 SYMATTR Value 3k3 SYMBOL cap -1104 208 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C12 SYMATTR Value 1000n SYMBOL res -880 96 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 20K SYMBOL cap -912 -16 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 10p SYMBOL OpAmps\\LT1679 -928 240 R0 SYMATTR InstName U2 SYMBOL OpAmps\\LT1679 -880 1072 M0 SYMATTR InstName U3 SYMBOL cap -1872 768 M0 SYMATTR InstName C9 SYMATTR Value 100n SYMBOL cap 128 928 R0 SYMATTR InstName C10 SYMATTR Value 100n SYMBOL npn -1232 464 M0 WINDOW 3 -176 -16 Left 2 SYMATTR InstName Q1B SYMATTR Value NSS40301MDR2G SYMBOL npn -1520 464 R0 WINDOW 3 -78 157 Left 2 SYMATTR InstName Q1A SYMATTR Value NSS40301MDR2G SYMBOL res -816 576 M0 SYMATTR InstName R21 SYMATTR Value 100 SYMBOL res -1152 688 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R22 SYMATTR Value 100K SYMBOL res -1392 1104 R0 SYMATTR InstName R23 SYMATTR Value 120K SYMBOL res -1280 1136 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R24 SYMATTR Value 2.7Meg SYMBOL cap -1280 1216 M180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C11 SYMATTR Value 100n SYMBOL res -1472 80 R0 SYMATTR InstName R26 SYMATTR Value 100k SYMBOL npn -1440 736 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL cap -1040 592 R0 SYMATTR InstName C6 SYMATTR Value 10n SYMBOL res -752 576 R0 SYMATTR InstName R12 SYMATTR Value 75k SYMBOL diode -1568 432 M0 SYMATTR InstName D3 SYMATTR Value 1N914 SYMBOL diode -1568 336 M0 SYMATTR InstName D4 SYMATTR Value 1N914 SYMBOL npn -1520 256 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res -1600 80 R0 SYMATTR InstName R17 SYMATTR Value 100k SYMBOL cap -864 816 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1000n SYMBOL diode -192 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D5 SYMATTR Value 1N914 SYMBOL diode -96 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D6 SYMATTR Value 1N914 SYMBOL diode 0 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D7 SYMATTR Value 1N914 SYMBOL diode 128 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D9 SYMATTR Value 1N914 SYMBOL diode 224 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D10 SYMATTR Value 1N914 SYMBOL diode 320 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D11 SYMATTR Value 1N914 SYMBOL diode 416 1248 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D15 SYMATTR Value 1N914 TEXT -1512 -152 Left 2 !.tran 0 20 0 startup TEXT -1512 -208 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -2208 1096 Left 2 !.MODEL NSS40301MDR2G NPN\n+is=6.87023e-12 bf=445.496 nf=1.08926 vaf=60.529\n+ikf=7.23313 ise=2.38192e-09 ne=4 br=23.6872\n+nr=1.10701 var=8.89608 ikr=1.25064 isc=1e-16 \n+nc=1.13174 rb=905.334,irb=2.30349e-07 rbm=1e-10\n+re=0.00600548 rc=0.0300274 xtb=1.2219 xti=4,\n+eg=1.05 cje=3.80477e-10 vje=0.912237 mje=0.397194,\n+tf=5.90916e-10,xtf=0.0998483,vtf=7.09172,itf=0.010481,\n+cjc=8.35472e-11 vjc=0.702862 mjc=0.43477 xcjc=0.899998,\n+fc=0.414631 cjs=0 vjs=0.75 mjs=0.5 \n+tr=5.64658e-08 ptf=0,kf=0 af=1

Not sure I see the point if it's only 80dB down Bill. @ 7Khz in LTSPice 24.1.5

I can almost get that from a simple phase shift oscillator and a 1KHz tuned circuit.

The last time I included a diode string like that in one of my circuits (which I seem to recall had better than 80dB performance) you told me it was nuts.

LTSpice isn't all that reliable as predictor of low level distortion. Having an armoury of different circuits to try when you finally get around to building and testing something real may be useful.

I'm sure that you think so. John Larkin thought that a bang-bang amplitude control was worth suggesting...

It probably was. In this case there are better ways of getting a rectified output than a simple series diode - I've posted circuits which incorporate precision rectifiers which get rid of the forward drop through the diode, and I've built circuits that used synchronous rectifiers built around transmission gates where the output isn't shifted by a temperature dependent diode drop. It went into a GaAs single crystal puller as a retrofit.

The main point of the diode string was as a satirical comment on that aspect of the design you posted, which probably counts as being hostile, but I am hostile to ill-thought out designs, hard though it is to get the design time to sort them out. I've got stuck with sorting out other peoples half-baked designs often enough, but only after my bosses had had their noses rubbed in the unfortunate consequences.