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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old 14th September 2019, 02:30 PM   #7521
jan.didden is offline jan.didden  Europe
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Do you have experience with this type of paint?

Jan

Quote:
Originally Posted by Bob Cordell View Post
Faster settling time usually means more distortion. This is because the agc control circuit is a high-order nonlinear feedback system. The filtering needed to suppress the agc level detect rectification ripple introduces poles and phase lag, leading to instability in the agc loop. Some HP oscillators used to have a switch on the back where you could choose lowest distortion or fastest settling time for low frequencies.

Cheers,
Bob
That was what I thought. Mother Nature doesn't give anything for free, but she is willing to trade

A similar point is made in Samuel's paper.

Jan
Attached Files
File Type: pdf Samuel Groner low distortion oscillator design.pdf (1.84 MB, 52 views)
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Old 14th September 2019, 02:35 PM   #7522
phofman is offline phofman  Czech Republic
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No, it was just a handy link. Sorry for advertisement, it was not intentional. I was just surprised by the paint effectiveness in that rather sensitive soundcard.

A proper metal enclosure shields also magnetic field and is professional, but a plastic/3D printed enclosure with metalic paint or the poor-man's copper tape works too.
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Old 14th September 2019, 04:30 PM   #7523
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by jfetter View Post
<0.01% (<-80 dB) would have been decent in the 1980s. 2 ppm (0.0002%, -114 dB) is decent today, but not really low.

Victor's oscillator hits <-150dB. I have one of his oscillators in transit to me that's supposed to hit -155 dB (3rd harmonic), -160 dB (5th harmonic). -150 dB is 0.000003% or 30 ppb. That's low! State of the art in fact.

Tom
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Old 14th September 2019, 05:12 PM   #7524
1audio is offline 1audio  United States
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Low-distortion Audio-range Oscillator
Quote:
Originally Posted by diyralf View Post
Home made PCB is ready for drilling ...
TL062 has lower noise. Maybe I will find an even better one. Polyprops are not good enough. I am using PS.
The TL062 was originally the low power version with higher noise. The '072 was the low noise version 30 years ago.

I'm not sure how the noise at that stage will propagate through to the output. You could check in the simulation but I suspect its quite low. DC stability may be more important there.

Quote:
Originally Posted by jfetter View Post
Not sure about this one either ?
It does show schematic in assy manual. Cost much more than Hk assy.
At $80 but if the Hk board does not work out may look at getting this one.

1 kHz Oscillator
its not so bad. The light bulb AGC can work quite well. Probably some optimization and opamp selection could get very good results. If the circuit is low impedance enough it won't be too sensitive to radiated noise sources and will have a lower internal noise. The output should be a much lower Z pot, no need for a dual I can see. Use an opamp with lots of drive for that node and optimize the output at around 1/2 of the available supply range to start with.
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Old 14th September 2019, 06:53 PM   #7525
HpW is offline HpW
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Quote:
Originally Posted by diyralf View Post
Home made PCB is ready for drilling ...
TL062 has lower noise. Maybe I will find an even better one. Polyprops are not good enough. I am using PS.
Hmm, yes in mind this ones. But which brand do you use? While exits axial and potted with may one wire turned.. see pictures while consider to update my Victor LDO.

Quote:
Originally Posted by diyralf View Post
OPA1656: Nice new toy. Will give it a try after my Mouser christmas pack has been arrived.
Important will be the shielding as Victor already does. And finally the over all shielding to get ride of the un-pleased HUM pickup.

Additional things, if I would made a new PCB:

. using single opamp's (or using only one of the two) to avoid opamp channel cross talk's while we deal in the -150 dB regions

. The single OPA1655 do not exists (yet)...

. Output buffer for balanced and/or none-balanced operation
Attached Images
File Type: jpg ps-1.jpg (3.9 KB, 284 views)
File Type: jpg ps-2.jpg (4.7 KB, 279 views)
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Old 14th September 2019, 07:09 PM   #7526
diyralf is offline diyralf
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Balanced is more nosier than unbalanced. If the device is powered by battery, unbalanced is more advantageous as there can be no ground loop.
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Old 16th September 2019, 10:21 AM   #7527
HpW is offline HpW
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Quote:
Originally Posted by diyralf View Post
Balanced is more nosier than unbalanced. If the device is powered by battery, unbalanced is more advantageous as there can be no ground loop.
This is may your measurements! May show the detailed results.

Please also provide feedbacks about your agc mods, PS cap brand and resulting measurements

Hp
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Old 16th September 2019, 01:41 PM   #7528
jfetter is offline jfetter  Costa Rica
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Low-distortion Audio-range Oscillator
Quote:
Originally Posted by phofman View Post
No, it was just a handy link. Sorry for advertisement, it was not intentional. I was just surprised by the paint effectiveness in that rather sensitive soundcard.

A proper metal enclosure shields also magnetic field and is professional, but a plastic/3D printed enclosure with metallic paint or the poor-man's copper tape works too.
Yes it would seem so. But from my CISPR results I'm convinced we either do not have a full picture of 'fields' , 'radiated' vs 'conducted' or there is an error in the skin equation.
There is also a biophysics component not fully understood.

Steel seems to provide a good shield but aluminum is questionable. Copper appears best but the thickness is a factor. Silver, not enough information.
ie high quality Faraday rooms cost more than a waterfront house in Longbeach.

Not to hijack, this is an interesting subject and probably needs its own zine.
Attached Files
File Type: pdf CISPR_Guide_2016.pdf (497.4 KB, 44 views)
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Old 18th September 2019, 12:33 AM   #7529
vicnic is offline vicnic  Latvia
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First tests of the OPA1656ID.
Received 3 examples. Very similar. No significant differences in noise and distortions tests. Tests was made in comparison with the LME49720.
Attached pictures:
1) Noise test schematic (as I am using for the LME49720 selecting).
2) LME49720 (selected example with low noise) spectrum in low frequency range.
3) OPA1656 in the same range.
4) LME49720 spectrum in wide frequency range.
5) OPA1656 in the same wide range.
6) Distortions test schematic. 1kHz 2,5V RMS at input/output. Measurements was done via the passive notch.
7) LME49720 spectrum.
8) OPA1656 spectrum.
Congratulations and thanks to Texas Instruments for the very good new opamp!
Attached Images
File Type: png NoiseM.PNG (5.2 KB, 326 views)
File Type: jpg LME49720low.jpg (118.0 KB, 340 views)
File Type: jpg OPA1656low.jpg (116.9 KB, 329 views)
File Type: jpg LME49720wf.jpg (120.0 KB, 295 views)
File Type: jpg OPA1656wf.jpg (119.9 KB, 292 views)
File Type: png DistM.png (5.0 KB, 105 views)
File Type: jpg LM49720dist.jpg (123.5 KB, 116 views)
File Type: jpg OPA1656dist.jpg (123.8 KB, 102 views)
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Old 18th September 2019, 02:24 AM   #7530
rsavas is online now rsavas  Canada
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I find it hilarious that they show in the typical applications, "Preamplifier Circuit for Vinyl Record Playback With Moving-Magnet Phono Cartridges", Baxandall tone control, guitar balanaced XLR for a brand new opamp. = time warp, except for the soic-8
Good price too, winner, move over 5534
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