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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old 24th September 2017, 05:32 PM   #6971
RNMarsh is offline RNMarsh  United States
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Location: 2457 Cascade Trail; Cool, CA. 95614
Low-distortion Audio-range Oscillator
The particular model I ordered looks useable. However, its values and topology is also very useable if I need to make it even better. Might put in alum case.
The low-pass passive is not flexible with freq. But, I can truly get to the noise floor of -160dBv with the 725D and QA401 then.... no extraneous freqs showing. Just the DUT.

There is also a new gen put up in forum using 5534 with filtered output opamps as I suggested which in SIM looks great.

I would like to see that active filter improved (lower noise) and made more flexible for use with any generator at other freqs. Last year I showed a proof of concept using commercial filter (miniDSP) on a digital gen and how it really cleaned up a 16 bit gen. So, this needs more tuning and time on development to get its full potential realized.

But an active circuit with cap filter in fb path to also reduce the opamp thd which I also suggested and results are very interesting. If we cant come up with distortion cancelling method, this may be the next best solution. It also takes a burdon off the gen to be ultra low thd. Thus simplifying and lowering the gen cost.

I am taking off to Asia home as winter here is setting in... be away for 4 months. Today is a steak BBQ send off with family. But, I'll be Here still.


THx-RNMarsh

Last edited by RNMarsh; 24th September 2017 at 05:42 PM.
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Old 24th September 2017, 06:29 PM   #6972
EssB is offline EssB  United Kingdom
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Quote:
Originally Posted by RNMarsh View Post
There is also a new gen put up in forum using 5534 with filtered output opamps as I suggested which in SIM looks great.
Where is this output filtering ? I only see an SVO with 8 phase rectifier.
Simon
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Old 24th September 2017, 06:44 PM   #6973
grandsons is offline grandsons  Switzerland
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Join Date: May 2004
Location: Canton of Vaud,
I just finished to clean a Shibasoku AG15B oscillator.

few kHz, 1Vrms un-terminated (well terminated by 100k Panasonic input load), third harmonic.

Nothing to measure....
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Last edited by grandsons; 24th September 2017 at 06:50 PM.
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Old 24th September 2017, 08:27 PM   #6974
RNMarsh is offline RNMarsh  United States
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Join Date: May 2012
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Low-distortion Audio-range Oscillator
Nice. and 2H, pls? same?


THx-RNMarsh

Last edited by RNMarsh; 24th September 2017 at 08:29 PM.
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Old Yesterday, 08:02 PM   #6975
grandsons is offline grandsons  Switzerland
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Join Date: May 2004
Location: Canton of Vaud,
Here are the THD and THD+N measurement carried on my Shibasoku AG15B.

Analyser is Panasonic VP-7722A

Level 1Vrms on 100kOhm Panasonic input impedance

400HPF and 80kLPF engaged

cycles / THD+N / THD2 / 2Fo / 3Fo

10 /-112,5 /-135,7 / -140 / -140
100 / -111,7 / -134 / -140 / -140
1000 / -110,5 / -122,3 /-123 / -137,2
10k / -105,6 / -123,6 / -124,2 / -127,6

400HPF only
20k / -99,78 / -114,6 / -117 / -124,6
60k / -95,4 / -104,6 / -105 / -114,2
100k /-90,1 / -94,87 / -94,79 / -111,5

Anything I can do more?

This rescued Shibasoku from a bin looks good to me. I had trouble with noisy output level selector.

Any simple possible tweak?

PFB

Last edited by grandsons; Yesterday at 08:10 PM.
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Old Yesterday, 08:57 PM   #6976
grandsons is offline grandsons  Switzerland
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Join Date: May 2004
Location: Canton of Vaud,
I made an error in HPF vs frequency selection.

Level 1Vrms on 100kOhm Panasonic input impedance

80kLPF only engaged

cycles / THD+N / THD2 / 2Fo / 3Fo

10 /-108,3 /-119,2 / -128,2 / -133,9
100 / -108,9 / -121,4 / -120,7 / -140

400HPF and 80kLPF engaged
1000 / -110,5 / -122,3 /-123 / -137,2
10k / -105,6 / -123,6 / -124,2 / -127,6

400HPF only
20k / -99,78 / -114,6 / -117 / -124,6
60k / -95,4 / -104,6 / -105 / -114,2
100k /-90,1 / -94,87 / -94,79 / -111,5

PFB
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