Low distortion sinewave oscillator without big capacitor.

What he should have said was the you were messing up the ground returns by hooking up the +15V output of the second 7815 to the 0V rail.

He was avoiding spending a long time talking about grounding and shielding, which is a rather specialised subject.

In this particular thread your eight transistor is bonkers, but it works - not that I can see how. John May could see how it worked, and how it could be simplified to four transistors - and eventually down to two matched pairs. He doesn't like it, and prefers the single long-tailed pair approach, despite the fact that LTSpice says it offers poorer performance.

I like the long-tailed pair approach myself - I can see exactly how it works - but it's probably worth my time to work out exactly how the four transistor circuit actually works, and why it seems to offer lower distortion in LTSpice simulations. It's not the kind of project that anybody would fund, and the chance that I'd learn anything interesting is remote, but I'm not swamped with work at the moment.

I see. Thank you for letting me know what he was thinking Bill. Do you have some kind of time machine that you travel around in so you can have a better knowledge of what happened in a past situation when compared with someone who was actually there at the time?

Seems pretty obvious to me how it works Bill. If I didn't know how it was intended to work then it almost certainly would not work. I'm surprised that you can't see how it works.

You seem to be very good at knowing what other people can/could see Bill.

He provided three examples. All of which obviously work. The best one from my point of view is the one with lowest distortion. After all the goal, when I started looking into sinewave oscillators, was to see whether it's really necessary to use thermistors, lamps, opto devices or FETs.

Ah well I'm sorry if you aren't likely to learn anything interesting Bill.

I've learned a lot and will continue to do so.

There are other things I should be doing but analogue circuit design has a certain attraction, particularly when assisted by someone as capable as JM.

"Edward Rawde" snipped-for-privacy@invalid.invalid wrote in message news:vsso97$1imi$ snipped-for-privacy@nnrp.usenet.blueworldhosting.com...

Here's an almost fully practical circuit except for the current sources and sinks.

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2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C5 SYMATTR Value 1000n TEXT -3288 368 Left 2 !.tran 0 10 0 1u startup TEXT -3288 312 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -552 1176 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 =

On Mon, 7 Apr 2025 22:46:13 -0400, "Edward Rawde" snipped-for-privacy@invalid.invalid wrote:

I reversed the polarity of the control feedback and applied it to the inverting input of the first oscilllator stage, removed some redundant capacitors, and added some filtering to the gain control signal. Also altered some gain values to improve the dynamics (but that still has to be addressed).

Most real world designs would use a sample and hold circuit to sample the output at it's maximum point and use that to control the feedback, similar to the topology I think I posted a while ago. It might be worthwhile looking at that.

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ISE= 2.894E-16 NE = 1.4 \n+ BF = 324.4 IKF = 0.109 VAF = 82 NR =

But John May could take out half the transistors and produce a circuit that still worked. And you haven't made any attempt to explain how it does work.

And suspect that that there were a lot of variations that didn't work

I've got a rough idea, but not good enough to let me do anything interesting, or to write any kind of useful explanation of what is going on. Writing that kind of explanation is usually a necessary part of getting a circuit into production. Management needs it before they will spend the extra money on document the design for production, and the final test technicians and service engineers need it make sure that the circuit works and to be able to fix it when it doesn't.

It's a necessary engineering skill. See above.

Which you haven't measured on a real circuit yet. Since you don't seem to be all that sensitive to the risks from power supply feedthrough, doing that might be painfully educational

Have you come to a conclusion yet? As I seem to have mentioned before, it strikes me that the answer is that it's obvious necessary.

That's text-chopping.

We can hope.

I doubt if thinks that he is assisting you. Correcting is probably closer to the mark.

One reason for that is that a current source/sink can be approximated by a high value resistor so instead of using a current mirror a single resistor is likely to work fine. You might need to reverse the polarity of the voltage drive but there are many ways to do that in this circuit.

As I pointed out some time ago, you never explain how your circuits work Bill. It's like you just expect others to accept that you have superior knowledge. If you really could see what other people think then I think you might be surprised at the amount of laughter going on.

You can suspect what you like but that's just another example of you twisting the world into something you would like it to be.

Anyone with any understanding of this circuit at all knows that a very basic explanation of how it works is that you need to multiply the gain control level by a sample of the oscillator signal and feed the result back into the oscillator.

So if your signals are in the form of two currents which never change polarity then a one quadrant current multiplier should work fine.

You might then do some research to see if you can find any examples of circuits which meet that requirement.

I've yet to see you write an explanation of how a circuit works Bill. Instead I've only seen circuits using three or four times as many components as the last one JM posted in this thread and never any better than 70dB. Then you get upset when the rest of the world tries to tell you that although your circuit may have a few good ideas in it, it's worthless from a meeting the requirements point of view.

I prefer not to make any assumptions about what other people can or can't see. Particularly when I know nothing at all about them other than what has been posted here.

Of course Bill. I have absolutely no doubt that you would take great delight in my pain. And I have no doubt that you would not offer any meaningful assistance with the power supply design because you would rather watch me suffer. Offering assistance could reduce my suffering which wouldn't do at all.

I'd probably use 6V batteries arranged for +/- 18V for a first test of a circuit like this. With some series components for filtering and to stay below LT1679 36V max.

What's obviously necessary Bill? The last circuit JM posted has no measurable distortion worth mentioning that I can see.

I'd translate that into "I hope you never learn anything so I can continue to tell you how stupid you are".

Of course Bill.

He can't. He lives to be nasty.

The super low distortion oscillator thing is just another venue to call people stupid. It's a Spice-as-game thing, totally unrealistic in real life.

Thanks. That has the lowest distortion I've seen in a simulation so far.

I can't find the sample/hold circuit you mentioned, would you mind reposting it?

Thank you for your help with this. It is much appreciated.

On Tue, 8 Apr 2025 14:41:44 -0400, "Edward Rawde" snipped-for-privacy@invalid.invalid wrote:

I wouldn't have kept a copy. It would probably be overkill anyway, for a fixed frequency, and if the dynamics are not an issue, what you already have is more than adequate for any audio use case I can think of. You'd probably be better off writing decent spice models for the opamp parts you would actually use, and optimizing signal levels in the cct as is. Buffering the rectifier parts improve things somewhat.

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2 SYMATTR InstName U7 SYMBOL schottky -1424 848 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL diode -944 1184 R0 SYMATTR InstName D3 SYMATTR Value 1N914 SYMBOL res -1728 432 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R7 SYMATTR Value 15K SYMBOL cap -1936 432 R0 SYMATTR InstName C5 SYMATTR Value 100n SYMBOL UniversalOpAmp3 -928 240 R90 WINDOW 0 -69 -59 Left 2 SYMATTR InstName U12 SYMATTR Value2 Avol=5Meg GBW=90Meg Slew=20Meg SYMATTR SpiceLine Ilimit=25m Rail=0 Vos=0 Phimargin=40 SYMBOL UniversalOpAmp3 -128 224 R90 WINDOW 0 -71 -66 Left 2 SYMATTR InstName U13 SYMATTR Value2 Avol=5Meg GBW=90Meg Slew=20Meg SYMATTR SpiceLine Ilimit=25m Rail=0 Vos=0 Phimargin=40 SYMBOL UniversalOpAmp3 -496 208 R90 WINDOW 0 -58 -62 Left 2 SYMATTR InstName U14 SYMATTR Value2 Avol=5Meg GBW=90Meg Slew=20Meg SYMATTR SpiceLine Ilimit=25m Rail=0 Vos=0 Phimargin=40 TEXT -2080 -600 Left 2 !.tran 0 5 0 1u uic TEXT -2080 -632 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -3208 -592 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 =

Ok thanks for that.

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

Is the sample/hold circuit the one below?

After much digging I found it in a very interesting thread started by Bill Sloman on 5th February 2025 "The low distortion oscillator problem".

I can't get it to simulate in 24.1.5 something to do with unknown parameter in table{-2m,0,2m,1}

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That is a remarkably hostile reaction. Most engineers can eventually learn stuff, but some are slower at it than others. Encouraging the slower ones takes quite a lot of effort because you have to go into quite a lot of detail before you can get the message across, and it can get tedious, and isn't all that rewarding. I'd love to be able to congratulate you for your insights, but they've been a bit thin on the ground.

You must be joking. I've had some very clever colleagues who could do it fast. There's at least one case where I didn't spot my error until years later - the original solution worked fine but I eventually realised that there was a simpler way of getting there.

It's not a matter of seeing how it works, so much as finding the right point of view on the way it works.

I could put together transformers that worked for a long time before I got to grips with the transformer equation, which gave me a clearer insight into what was going on.

I've never seen you explain in any level of detail how your own circuits work Bill.

All explanations are designed to work for the audience they are aimed at. You don't insult the intelligence of people like Phil Hobbs by going into unnecessary detail. Lesser mortals may well feel short-changed.

Sloman A.W., Buggs P., Molloy J., and Stewart D. “A microcontroller-based driver to stabilise the temperature of an optical stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996) contains quite a lot of explanation, but I took care not to patronise the prospective audience by telling them more than I needed to.

I don't speak for Phil Hobbs or anyone else but I think Phil would be impressed with a well thought out highly detailed explanation of how a circuit works. He would not be at all insulted no matter what the level of detail was.

On Tue, 8 Apr 2025 21:04:25 -0400, "Edward Rawde" snipped-for-privacy@invalid.invalid wrote:

Yes. Change the braces to brackets. Example use shown below. H2,3 should be circa -170(ish)dBc. Note that I have switched most op amps outwith the control loop to simple models so that you can investigate the control loop in isolation (it's fairly easy to implement the sampling in hardware and it will be close to this in performance). Compare the circuit below with one with the original polyphase sampling (leave in the simple models) to determine any benefit. You are already beyond the point where real opamps will limit the performance - in this particular oscillator design.

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-2624 -256 M0 SYMATTR InstName I4 SYMATTR Value 650u SYMBOL res -1776 240 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R31 SYMATTR Value 1k SYMBOL res -1776 -240 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R34 SYMATTR Value 1k SYMBOL cap -1792 304 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C13 SYMATTR Value 33p SYMBOL npn -2080 224 M0 SYMATTR InstName Q2B SYMATTR Value {BN} SYMBOL npn -2432 224 M0 SYMATTR InstName Q2A SYMATTR Value {BN} SYMBOL npn -2336 224 R0 WINDOW 3 55 69 Left 2 SYMATTR Value {BN} SYMATTR InstName Q1B SYMBOL npn -2688 224 R0 WINDOW 3 53 71 Left 2 SYMATTR Value {BN} SYMATTR InstName Q1A SYMBOL res -2624 848 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R35 SYMATTR Value 1k SYMBOL npn -2624 640 R0 SYMATTR InstName Q3 SYMATTR Value 2N3904 SYMBOL cap -1792 -352 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C14 SYMATTR Value 33p SYMBOL voltage -1504 -608 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V3 SYMATTR Value 15 SYMBOL voltage -1504 -464 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V4 SYMATTR Value 15 SYMBOL res -1904 704 R0 SYMATTR InstName R17 SYMATTR Value 10k SYMBOL res -1904 560 R0 SYMATTR InstName R20 SYMATTR Value 5k SYMBOL cap -1792 720 R0 SYMATTR InstName C10 SYMATTR Value 10n SYMBOL res -1360 -80 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R21 SYMATTR Value 4K7 SYMBOL res -1568 -80 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R22 SYMATTR Value 1k SYMBOL res -1568 112 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R25 SYMATTR Value 1k SYMBOL res -1504 112 M0 SYMATTR InstName R28 SYMATTR Value 4k7 SYMBOL OpAmps\\LT1679 -2704 688 M180 WINDOW 3 18 51 Left 2 SYMATTR InstName U10 SYMBOL OpAmps\\LT1679 -2064 688 R180 WINDOW 3 16 46 Left 2 SYMATTR InstName U7 SYMBOL schottky -1456 400 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL diode -1232 736 R0 SYMATTR InstName D3 SYMATTR Value 1N914 SYMBOL res -1728 432 M270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R7 SYMATTR Value 15K SYMBOL res -1040 560 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R12 SYMATTR Value 110k SYMBOL g -592 624 M0 WINDOW 3 -255 133 Left 2 SYMATTR Value table(-2m,0,2m,1) SYMATTR InstName G1 SYMBOL cap -672 656 M0 SYMATTR InstName C6 SYMATTR Value 2p SYMBOL res -752 624 M0 SYMATTR InstName R13 SYMATTR Value 1 SYMBOL SpecialFunctions\\sample -928 560 M0 SYMATTR InstName A1 SYMBOL e -912 288 M0 SYMATTR InstName E1 SYMATTR Value -1 SYMBOL cap -1936 432 R0 SYMATTR InstName C5 SYMATTR Value 1u5 SYMBOL OpAmps\\opamp -1056 -32 R0 SYMATTR InstName U5 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg SYMBOL OpAmps\\opamp -624 -32 R0 SYMATTR InstName U6 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg SYMBOL OpAmps\\opamp -256 -32 R0 SYMATTR InstName U8 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg SYMBOL OpAmps\\opamp -1424 -32 R0 SYMATTR InstName U2 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg SYMBOL OpAmps\\opamp -1824 -160 R0 SYMATTR InstName U4 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg SYMBOL OpAmps\\opamp -1824 160 M180 SYMATTR InstName U9 SYMATTR SpiceLine Aol=5Meg SYMATTR SpiceLine2 GBW=60Meg TEXT -2080 -600 Left 2 !.tran 0 5 0 1u uic TEXT -2080 -632 Left 2 !.options plotwinsize=0 numdgt=15 TEXT -3208 -592 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 =

In the appropriate context. Sci.electronics.design has tended to brevity over the twenty-odd years I've been posting here and following the posts.

The phrase "insult the intelligence" doesn't refer to be people feeling insulted - rather to them being bored by unnecessary detail. He probably wouldn't feel insulted but he'd probably skip most of the detail.

The reference to explanations in different contexts doesn't seem to have registered with you.

LOL. You can't skip detail which isn't there.

You can certainly tailor your approach to the individual you're dealing with Bill. But it looks to me that you would rather tailor your approach in such a way as to make the other person appear as much of a "Lesser mortal" (your words) as possible.

Have you looked at JM's latest post (2:06 PM on the 9th) which demonstrates the sample & hold method? Do you still think it's "Very funny" (Your words in your own thread on 6th February).

What are you doing up at 5 AM anyway?

Very interesting. Thank you.