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Old 11th March 2013, 06:39 PM   #1831
klewis is offline klewis  United States
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[3rd round] AN67 Ultra-low THD 10kHz sine oscillator PCB Group buy. - Discussion Page 10 - diyAudio

The measurement was taken using Dick's active twin T fundamental null filter, fed to an HP3562, screen capture via HPIB VEE. Dick and I have discussed wether the 2nd H is from the twin T or oscillator. You will need to ignore the THD calc.

I don't know if the AN67 would be happy being switched between different frequencies. It's twitchy to get started oscilating, once set it seems fine. My plan is to have a few of them each set for different frequencies.

Ken
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Old 11th March 2013, 09:58 PM   #1832
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by RNMarsh View Post
Did I mention the THd of the KH-4402B with 2-opamp upgrades and a couple tuning adjustments is a really nice .0001% at 10Hz and .00013% at 1Khz and at 10Khz is .00015% THD+N. at 1volt into high Z. ?

If you just need a nice, clean oscillator that is flexible in output and frequencies.... it does very well.

[With the oscillator opamp changed out (LT1486 was used). No instabilities or weirdness with the opamp change.]

Thx-RNMarsh
BTW - the thd+n does not change with load of 600 Ohms at any freqs. :-)
The 2h is -122 and 3h is -124dB at 1v/1KHz into 600 Ohms. KH4402B noise floor is -130dB. 100KHz BW. [Ref 1KHz amplitude is -110/10dB/div]

KH4402B.jpg


Thx-RNMarsh

Last edited by RNMarsh; 11th March 2013 at 10:09 PM. Reason: >-120
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Old 12th March 2013, 01:50 AM   #1833
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
BTW - the thd+n does not change with load of 600 Ohms at any freqs. :-)
The 2h is -122 and 3h is -124dB at 1v/1KHz into 600 Ohms. KH4402B noise floor is -130dB. 100KHz BW. [Ref 1KHz amplitude is -110/10dB/div]

Attachment 335449


Thx-RNMarsh
These are some impressive results especially at 10kHz. The LT1468 is nice little op amp.
What output level does the oscillator run at. Have you tried lowering/raising the osc level to study the effect?
The LT1468 has astonishing low distortion in an SVO when operated below 3Vrms and minimal load.

Cheers,
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Last edited by davada; 12th March 2013 at 01:53 AM.
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Old 12th March 2013, 02:25 AM   #1834
RNMarsh is offline RNMarsh  United States
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Seems I cant add numbers today.... Full Scale of -110db =1 v output from monitor port and another -22-24dB would be -132 and -134dB. It's noise floor is about -140 -145dB. Very close to my lower limit of testing. Got to work on that :-)

I use that opamp in everything... including the osc in the 339A. It seems to be better than its specs. The KH4402B output is variable up to several volts. I havent measured its max output... what ever the specs say it is, no doubt. Hold on .... I get about 6.5v rms from the 50 ohm output into 600 ohms. At that level, the THD+N is a little lower (better S/N) at .00008%.

The stock buffer opamp/output circuit is still in place! Its my NOS favorite osc as the thd doesnt change with scale selection/range and level to any significant degree.
Of course the ShibaSoku oscillator has lower noise floor and thd but not by much any more. It's THD+N is still 10dB better.

Thx-RNMarsh

Last edited by RNMarsh; 12th March 2013 at 02:41 AM.
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Old 12th March 2013, 02:35 AM   #1835
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
Seems I cant add numbers today.... Full Scale of -110db =1 v output from monitor port and another -22-24dB would be -132 and -134dB. The noise floor is about -145dB.

I use that opamp in everything... including the osc in the 339A. The KH4402B output is variable up to several volts. I havent measured its max output... what ever the specs say it is, no doubt. Hold on .... I get about 6.5v rms from the 50 ohm output into 600 ohms. At that level, the THD+N is a little lower (better S/N) at .00008%.

The stock buffer opamp/output circuit is still in place! Its my new favorite osc as the thd doesnt change with scale selection/range and level to any significant degree.
Of course the ShibaSoku oscillator has lower noise floor and thd but not by much any more.

Thx-RNMarsh
Hi Rick,

I meant the oscillator not he output of the unit.

For example the 339a osc runs at 9Vpp. The output is variable by attenuation.
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Old 12th March 2013, 02:47 AM   #1836
RNMarsh is offline RNMarsh  United States
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Oh I see. It runs high... +10 and -10 peak or 20v peak to peak on schematic. I didnt probe it to see exactly. Nor attempt to change the level... just tune for lowest thd.
Note the opamp has a discrete complementary output driver stage added onto it.

I think it is safe to say now that the Harmonic levels shown by Demian of the harmonics of his ShibaSoku generator is actually that of the ADC system.
The 2H and 3h are running at .00003% or less (noise) from the AD725D analyzer display reading. Right down there with Viktor's levels.... you can use his generator to gauge the ADC system accuracy.

-RNM

Last edited by RNMarsh; 12th March 2013 at 03:16 AM.
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Old 12th March 2013, 02:49 AM   #1837
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What is the difference in the circuitry between the KH4400 and KH4402? The controls are slightly different but I did not see anything really significant.
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Old 12th March 2013, 02:52 AM   #1838
davada is offline davada  Canada
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Originally Posted by RNMarsh View Post
Oh I see. It runs high... 20v peak to peak on schematic. I didnt probe it to see exactly. just tune for lowest thd.
Yes I got that. Have you tried varying this level to study the effect?
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Old 12th March 2013, 03:24 AM   #1839
RNMarsh is offline RNMarsh  United States
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What is the difference in the circuitry between the KH4400 and KH4402? The controls are slightly different but I did not see anything really significant.
I reported on this a few days back somewhere. The entire unit is different EXcept the choice of IC for the oscillator. That remained the same. I have one of each oscillator ($$) just to see what could be done for myself and for the DIY'er and when stock, the 4402 is 6 db lower across the board. It allowed the spec to be 1/2 of the 4400. But its still a lot of work/changes for 6dB. This is consistant with the work on the 339A... most improvement was found in changing the osc IC and lowering system noise thoughout [and bad quality parts]. I didnt go further, as davada did.
On the 4402, just osc and tune up parts.

-RNM

Last edited by RNMarsh; 12th March 2013 at 03:29 AM.
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Old 12th March 2013, 03:24 AM   #1840
RNMarsh is offline RNMarsh  United States
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Yes I got that. Have you tried varying this level to study the effect?
No I have not. Took a detour at the 725D exit off ramp. .

Last edited by RNMarsh; 12th March 2013 at 03:34 AM.
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