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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old 6th April 2018, 04:30 AM   #7081
davada is offline davada  Canada
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suzyj what's the deal with the immaculately clean workshop?
Or was that just for the photo?
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Last edited by davada; 6th April 2018 at 04:41 AM.
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Old 10th July 2018, 12:20 PM   #7082
Armand is offline Armand  Norway
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Default Victor's oscillator measured

I just bought a 1kHz oscillator from Victor and made a notch filter to measure it using an R&S UPV Audio analyzer.
Here it is at 2V RMS with a passive notch that has -10dB at 2kH and -5dB at 3kHz.
Adjusting for the 10db drop from the notch and the signal of 2V (+6dBV) this translates to 2 order of: -153,5dBV + 10dB - 6dB = -149,5dB.
3 order is: -155+5-6 = -156dB.
Very nice result indeed.

Please note that the distortion we see can be from my notch filter using C0G capacitors, so the actual distortion migh well be even lower.
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Old 23rd July 2018, 02:24 AM   #7083
alexcp is offline alexcp  United States
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Low-distortion Audio-range Oscillator
Default GB for Samuel Groner's passive notch filter

Some time ago, Samuel Groner mentioned he designed a fixed frequency passive notch filter for very high resolution distortion measurements. With his blessing, I just started a little group buy for the PCBs for that filter. Please join!

Last edited by alexcp; 23rd July 2018 at 02:29 AM.
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Old 1st August 2018, 09:13 AM   #7084
RNMarsh is offline RNMarsh  United States
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Here is an interesting digital approach..... with LP filtering and the high number of bits used, should be ultra low distortion and very repeatable and precise:

DASG - Digital Audio Sine Wave Generator


THx-Richard
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Old 1st August 2018, 10:04 AM   #7085
Edmond Stuart is offline Edmond Stuart  Netherlands
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Nice !
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Old 1st August 2018, 10:33 AM   #7086
DNi is offline DNi  Switzerland
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The precision and repeatability are definitely there, but the THD would be that of the PCM1794 DAC that he uses, i.e. -108dB at best.


Regards,
Braca
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Old 1st August 2018, 10:48 AM   #7087
RNMarsh is offline RNMarsh  United States
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use a different DAC.

-RM
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Old 1st August 2018, 11:32 AM   #7088
simon7000 is offline simon7000  United States
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As I think has been mentioned the ultra low distortion method is to use two D/A converters. One is used to produce the test signal the other is scaled much lower and provides a correction signal.

As deriving the correction signal should be below the resolution of an FFT analyzer a series of lock-in amplifiers can be used as the system is digital a sine/cosine master clock can run the entire system. The limits would be how many harmonics you set up to measure and the ultimate limit would be clock stability.

With the speed of processor chips you could probably build such a gizmo with decent high frequency range and a minimum of hardware parts. Software would get interesting.
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Old 1st August 2018, 12:27 PM   #7089
Bob Cordell is offline Bob Cordell  United States
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Quote:
Originally Posted by RNMarsh View Post
Here is an interesting digital approach..... with LP filtering and the high number of bits used, should be ultra low distortion and very repeatable and precise:

DASG - Digital Audio Sine Wave Generator


THx-Richard
Who is the author/designer of this?

With its digital audio outputs it could be especially useful in testing digital input audio equipment, including digital input class D power amplifiers. In those applications the quality and limitations of its DAC don't matter much.

Cheers,
Bob
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Old 1st August 2018, 01:22 PM   #7090
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by Bob Cordell View Post
Who is the author...
The site says Uwe Beis, some pretty impressive work.

Best wishes
David
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