High purity 1kHz oscillator

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Edward Rawde 1 year ago

But I suspect that component tolerances and mismatched FETs will ruin it.

Otherwise it should be easy to get 60dB down on unwanted harmonics with a better filter.

FWIW I likely won't be here for the next week.

Version 4 SHEET 1 2196 916 WIRE -160 -496 -256 -496 WIRE -16 -496 -160 -496 WIRE 48 -496 -16 -496 WIRE 512 -496 112 -496 WIRE -160 -480 -160 -496 WIRE -256 -464 -256 -496 WIRE -16 -416 -16 -496 WIRE -256 -368 -256 -400 WIRE -160 -368 -160 -400 WIRE -160 -368 -256 -368 WIRE -48 -368 -160 -368 WIRE 144 -368 48 -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 512 -256 512 -496 WIRE 512 -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 144 -128 144 -368 WIRE 144 -128 80 -128 WIRE 160 -128 144 -128 WIRE 272 -128 240 -128 WIRE 320 -128 272 -128 WIRE 448 -128 400 -128 WIRE -304 -80 -304 -128 WIRE 512 -80 512 -256 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 80 -64 80 -128 WIRE 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WIRE -80 240 -80 224 WIRE 16 240 16 224 WIRE 848 256 848 160 WIRE -352 336 -352 240 WIRE -352 336 -432 336 WIRE -80 336 -80 320 WIRE -32 336 -80 336 WIRE 16 336 16 304 WIRE 16 336 -32 336 WIRE -432 352 -432 336 WIRE -352 352 -352 336 WIRE -208 352 -208 240 WIRE -208 352 -352 352 WIRE 704 352 704 288 WIRE -32 368 -32 336 WIRE -352 432 -352 352 WIRE -208 448 -208 352 WIRE -352 608 -352 512 WIRE -272 608 -352 608 WIRE -208 608 -208 512 WIRE -208 608 -272 608 FLAG -432 352 0 FLAG 1168 144 output FLAG -304 32 0 FLAG 848 256 0 FLAG 704 352 0 FLAG 912 96 V+ FLAG 912 192 V- FLAG 128 80 V+ FLAG 128 176 V- FLAG -272 112 V+ FLAG -272 608 V- FLAG -32 368 0 SYMBOL voltage -352 144 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 -7 54 VBottom 2 WINDOW 3 37 50 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 -224 176 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 -37 23 VRight 2 WINDOW 3 -9 -3 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -352 416 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 10 0 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -224 448 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 416 -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 496 -96 R0 SYMATTR InstName R9 SYMATTR Value 100 SYMBOL res -320 -96 R0 SYMATTR InstName R10 SYMATTR Value 1.5 SYMBOL pjf 48 -416 R90 WINDOW 0 -34 29 VRight 2 WINDOW 3 -9 -1 VRight 2 SYMATTR InstName J2 SYMATTR Value J175 SYMBOL OpAmps\\LT1057 912 80 R0 SYMATTR InstName U1 SYMBOL res 672 112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 5.1k SYMBOL cap 752 112 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 68n SYMBOL res 688 192 R0 SYMATTR InstName R12 SYMATTR Value 13k SYMBOL res 816 -32 R0 SYMATTR InstName R13 SYMATTR Value 6.2k SYMBOL cap 704 16 R0 SYMATTR InstName C8 SYMATTR Value 15n TEXT -80 472 Left 2 !.tran 0 10s 2s startup TEXT -264 -616 Left 2 ;Edward Rawde's high purity sinewave oscillator. 22 Oct 2024

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Bill Sloman 1 year ago

<snip>

My message was that the current sucked out of U2 through D1 and D2 was a narrow spike, peaking at 0.3mA and repeating at 1kHz, which distorted the voltage at the output of U2.

Your revised circuit persists with this mistake, and the filter you've added around U1 doesn't do enough to compensate.

Using two FETs as your adjustable resistance does seem to get rid of the even-order harmonics, but it doesn't make enough difference to be worth the effort.

I do worry about component tolerances, and they won't make much difference to the circuit. Neither will mismatched FETs. The capacitative feedthough via the gate into the FET conduction channels is probably more of a worry, and that's built into the LTSpice FET model.

Bad layout can wreck pretty much any well-designed circuit, let alone badly designed ones. My professional career included a bit of cleaning up such layouts.

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Edward Rawde 1 year ago

That's what I thought you'd say, because there are now two spikes, but it does seem to reduce distortion. So I'd leave it in any experimental prototype and take the decision to remove it if real testing shows it's not sufficiently beneficial. The filter can be redesigned when a real circuit is tested. I didn't have time to do a more elaborate active filter.

I've had management think that a "proper" layout will turn a badly designed prototype circuit into something which does not need to be redesigned.

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Edward Rawde 1 year ago

"Edward Rawde" snipped-for-privacy@invalid.invalid wrote in message news:vf7c4h$1m5m$ snipped-for-privacy@nnrp.usenet.blueworldhosting.com...

Can anyone tell me what causes the following feature of the circuit below? This circuit is not exactly the same as the previous one but all versions seem to have this behaviour.

Run a simulation and view the output.

You can see that there's distortion until about 1.8 seconds when it disappears. View J1 or J2 gate voltage. You can see that the crud suddenly reduces at 1.8 seconds. What's causing that and is there a way to make the circuit always run in reduced crud mode?

I'll be back in about a week to thank whoever can explain this.

Version 4 SHEET 1 2196 916 WIRE 48 -576 16 -576 WIRE 544 -576 112 -576 WIRE 736 -512 688 -512 WIRE 864 -512 816 -512 WIRE -160 -496 -256 -496 WIRE -16 -496 -160 -496 WIRE 16 -496 16 -576 WIRE 16 -496 -16 -496 WIRE 48 -496 16 -496 WIRE 512 -496 112 -496 WIRE -160 -480 -160 -496 WIRE -256 -464 -256 -496 WIRE -16 -416 -16 -496 WIRE 800 -400 800 -416 WIRE 864 -384 864 -512 WIRE 864 -384 832 -384 WIRE 896 -384 864 -384 WIRE 1008 -384 976 -384 WIRE -256 -368 -256 -400 WIRE -160 -368 -160 -400 WIRE -160 -368 -256 -368 WIRE -48 -368 -160 -368 WIRE 144 -368 48 -368 WIRE 544 -368 544 -576 WIRE 560 -368 544 -368 WIRE 688 -368 688 -512 WIRE 688 -368 640 -368 WIRE 768 -368 688 -368 WIRE 864 -352 832 -352 WIRE 48 -336 16 -336 WIRE 544 -336 544 -368 WIRE 544 -336 112 -336 WIRE -256 -320 -256 -368 WIRE -256 -320 -304 -320 WIRE 800 -320 800 -336 WIRE -160 -256 -256 -256 WIRE -16 -256 -160 -256 WIRE 16 -256 16 -336 WIRE 16 -256 -16 -256 WIRE 48 -256 16 -256 WIRE 512 -256 512 -496 WIRE 512 -256 112 -256 WIRE 864 -256 864 -352 WIRE -160 -240 -160 -256 WIRE -256 -224 -256 -256 WIRE 512 -224 512 -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 144 -128 144 -368 WIRE 144 -128 80 -128 WIRE 160 -128 144 -128 WIRE 272 -128 240 -128 WIRE 320 -128 272 -128 WIRE 448 -128 400 -128 WIRE 512 -96 512 -144 WIRE 1008 -96 1008 -384 WIRE 1008 -96 512 -96 WIRE -304 -80 -304 -128 WIRE -80 -64 -80 -128 WIRE -32 -64 -80 -64 WIRE 80 -64 80 -128 WIRE 80 -64 48 -64 WIRE 832 -64 720 -64 WIRE 1056 -64 832 -64 WIRE 272 -16 272 -128 WIRE 320 -16 272 -16 WIRE 448 -16 448 -128 WIRE 448 -16 400 -16 WIRE 832 -16 832 -64 WIRE 272 16 272 -16 WIRE 272 16 48 16 WIRE 720 16 720 -64 WIRE -304 32 -304 0 WIRE 128 96 128 80 WIRE -272 112 -352 112 WIRE -208 112 -272 112 WIRE 48 112 48 16 WIRE 96 112 48 112 WIRE 912 112 912 96 WIRE 432 128 160 128 WIRE 448 128 448 -16 WIRE 448 128 432 128 WIRE 512 128 512 -96 WIRE 512 128 448 128 WIRE 576 128 512 128 WIRE 704 128 656 128 WIRE 720 128 720 80 WIRE 720 128 704 128 WIRE 752 128 720 128 WIRE 832 128 832 64 WIRE 832 128 816 128 WIRE 880 128 832 128 WIRE 96 144 -80 144 WIRE 1056 144 1056 -64 WIRE 1056 144 944 144 WIRE 1168 144 1056 144 WIRE 1264 144 1168 144 WIRE -352 160 -352 112 WIRE 880 160 848 160 WIRE -208 176 -208 112 WIRE 128 176 128 160 WIRE 912 192 912 176 WIRE 704 208 704 128 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 848 256 848 160 WIRE -352 336 -352 240 WIRE -352 336 -432 336 WIRE -80 336 -80 320 WIRE -32 336 -80 336 WIRE 16 336 16 304 WIRE 16 336 -32 336 WIRE -432 352 -432 336 WIRE -352 352 -352 336 WIRE -208 352 -208 240 WIRE -208 352 -352 352 WIRE 704 352 704 288 WIRE -32 368 -32 336 WIRE -352 432 -352 352 WIRE -208 448 -208 352 WIRE -352 608 -352 512 WIRE -272 608 -352 608 WIRE -208 608 -208 512 WIRE -208 608 -272 608 FLAG -432 352 0 FLAG 1168 144 output FLAG -304 32 0 FLAG 848 256 0 FLAG 704 352 0 FLAG 912 96 V+ FLAG 912 192 V- FLAG 128 80 V+ FLAG 128 176 V- FLAG -272 112 V+ FLAG -272 608 V- FLAG -32 368 0 FLAG 800 -416 V+ FLAG 800 -320 V- FLAG 864 -256 0 SYMBOL voltage -352 144 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 -7 54 VBottom 2 WINDOW 3 37 50 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 -224 176 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 -37 23 VRight 2 WINDOW 3 -9 -3 VRight 2 SYMATTR InstName J1 SYMATTR Value J112 SYMBOL voltage -352 416 R0 WINDOW 123 0 0 Left 0 WINDOW 39 10 135 Left 2 WINDOW 0 10 0 Left 2 WINDOW 3 15 104 Left 2 SYMATTR SpiceLine Rser=0.1 SYMATTR InstName V2 SYMATTR Value 12 SYMBOL polcap -224 448 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 416 -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 496 -240 R0 SYMATTR InstName R9 SYMATTR Value 100 SYMBOL res -320 -96 R0 SYMATTR InstName R10 SYMATTR Value 1.5 SYMBOL pjf 48 -416 R90 WINDOW 0 -34 29 VRight 2 WINDOW 3 -9 -1 VRight 2 SYMATTR InstName J2 SYMATTR Value J175 SYMBOL OpAmps\\LT1057 912 80 R0 SYMATTR InstName U1 SYMBOL res 672 112 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 5.1k SYMBOL cap 752 112 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 68n SYMBOL res 688 192 R0 SYMATTR InstName R12 SYMATTR Value 13k SYMBOL res 816 -32 R0 SYMATTR InstName R13 SYMATTR Value 6.2k SYMBOL cap 704 16 R0 SYMATTR InstName C8 SYMATTR Value 10n SYMBOL OpAmps\\LT1057 800 -432 M0 SYMATTR InstName U3 SYMBOL res 832 -528 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R14 SYMATTR Value 10k SYMBOL res 992 -400 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R15 SYMATTR Value 10k SYMBOL res 656 -384 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R16 SYMATTR Value 100 SYMBOL schottky 112 -592 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 48 -320 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value BAT54 SYMATTR Description Diode SYMATTR Type diode TEXT -80 472 Left 2 !.tran 0 10s 2s startup TEXT -248 -640 Left 2 ;Edward Rawde's high purity sinewave oscillator. 22 Oct 2024

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john larkin 1 year ago

If you do build an ultra-low-distortion oscillator, how would you measure the distortion?

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Edward Rawde 1 year ago

I'd probably ask the designers of the circuit Bill Sloman referenced, how they measured -110dB

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I'd be happy with 70dB but I doubt that's achievable with the FET circuit.

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JM 1 year ago

If you actually need a low distortion oscillator look for Viktor Mickevic's designs on diyaudio. I've attached a schematic.

PK

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Bill Sloman 1 year ago

Put a spectrum analyser on the output and measure the harmonic content.

The number cruncher's version of that is to digitise the sine wave with the best A/D converter you can get, fit a sine wave to the data and average the deviations from that closely fitted sine wave.

Random noise will go down as you average over more cycles. The distortion won't.

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Bill Sloman 1 year ago

Two spikes inject even more high frequency harmonics into the circuit as a whole. Some of them may cancel.

There are other ways of measuring the amplitude of the output, and most of them inject less high frequency hash into the power supplies. Injecting high frequency hash into the op amp that is generating the "high purity sine wave" if particulary silly.

Active filters can have nasty problems when the noise they are being asked to reject is at a frequency where the op amp doesn't have much gain.

I've had some daft managers, but none of them was that daft.

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legg 1 year ago

If this was a real lab with real hardware and test equipment, I'd need to see your test settup, because that's usually the reason you get 'strange' test results.

1.5sec and 2sec plots both 'look' the same here - full of crud.

Different crud, depending on whether .jpg or bmp formats . . . ;-]

RL

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john larkin 1 year ago

The very best bulk metal foil resistors have voltage-resistance coefficients of a few ppm/volt. Most resistors are much worse.

Just the resistors can kill distortion specs. At low frequencies, self-heating and tempco can add distortion too; the old HP oscillators had that effect from the lamp filament.

DGMS on capacitor nonlinearity.

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Bill Sloman 1 year ago

I can't see any crud. And comparing the FFT's of the outputs of U2 and and the "filtered" output at U1, the third harmonic content is much the same.

Just for kicks, I added a third op amp - an LT1056 - as a unity gain follower on U2's output - on to drive R9 (in the same way that U3 drives R16) to keep the spikey rectifier drive current out of U2 - the op amp generating the "pure" sine wave.

It didn't make any difference.

My guess is that most of the harmonic content is from the 1mV sawtooth on the two FET gates which capacitatively couples into the FET conduction channel.

An opto-FET might do better.

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Bill Sloman 1 year ago

Metal film resistors aren't all that much worse than bulk foil resistors, and they are pretty cheap aznd widely available.

Not that you can cite an example

Pull the other leg.

The lamp filaments ran rather hotter.

The capacitors and resistors would have to remarkably bad to make much difference to a well-designed Wein bridge.

You've already got started on making an ass of yourself about resistor non-linearities. Making bizarre claims about capacitors is more of the same.

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legg 1 year ago

I'm curious. By 'seeing' crud - what measuring technique is being used?

Built-in LTspice FFT?

Would be easier to compare if the measurement 'method' was included in the sim. Then, at least the test method could be inspected for errors.

Distortion here is quite visible in the simple LTspice waveform viewer. If you can 'see' it, it's bound to be measurable above a milli-percentage. Yes-No?

RL

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JM 1 year ago

It seems that I have a problem posting encoded binariesto this group with my provider. Attached is a link instead.

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john larkin 1 year ago

Gosh, you keep getting nastier and crazier every year. Your only function now seems to be to generate childish insults aimed at most everyone.

Here's some C-V notes. Series AC-coupling caps, or caps used in filters, can introduce distortion too.

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It's sort of outrageous that most ceramic cap data sheets specify capacitance and voltage and hide the fact that you don't get both.

Film caps can have C-V effects too, and those can matter at PPM distortion levels.

One could make a parametric amplifier using cap C-V effect.

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JM 1 year ago

And that links to an incorrect schematic - the rectified output tap is connected to the wrong node. Might be other errors..

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Liz Tuddenham 1 year ago

Some ceramic caps make rather poor-quality contact microphones, so don't use them in audio pre-amps.

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John R Walliker 1 year ago

... but COG/NPO ceramics are very well suited to this application.

John

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john larkin 1 year ago

They tend to be small values. We use one 10 nF part. Digikey offers a

0.88 uF C0G for $29. Each!

I had some N4700s cooked up special, to temperature compensate an LC oscillator.

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High purity 1kHz oscillator

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