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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old Yesterday, 04:04 PM   #7761
1audio is offline 1audio  United States
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Join Date: Mar 2004
Location: SF Bay Area
Low-distortion Audio-range Oscillator
The AP uses a state variable filter with feedback for its notch I believe. That makes it easy to get a very small attenuation for H2. And easy to tune via a multiplying DAC.
Otherwise you need a jillion relays to have enough resolution.
The B&K passive notch filter has a correction for harmonics but with 20 dB insertion loss. I have not had the patience to reverse engineer it and the manual has no circuit info, quite unusual for B&K in that period.
I think it would be trivial to sweep and store a loss/phase curve of the filter and apply it to a measured distortion.
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Old Yesterday, 06:21 PM   #7762
HpW is offline HpW
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Join Date: Mar 2002
In the old beginning days I had a HAMEG HM8027 THD Analyzer. This HM8027 required the HM8000 ground module for operation as with other nice bargain modules at the old times.

There was 3 freq. ranges to select and one button to tune close to the fundamental until the device locked/snapped to the fundamental. Had a 0.01 % lowest reading & calibration and an output of residual filtered fundamental as the harmonic's... The used TL074 could be replaced with lower noise opamps.

While I do not have them anymore, interesting would be to measure the noise & THD of this residual signal. Whether the circuit is good enough for LDO measurement.

In other words, the HM8027 is obsolete but the service manual with full circuit is still around the internet.

just a from the old days...
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Old Yesterday, 11:39 PM   #7763
Vovk Z is offline Vovk Z  Ukraine
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Join Date: Oct 2011
Location: Kyiv
Low-distortion Audio-range Oscillator
Quote:
Originally Posted by vicnic View Post
Xonar Essence has the CS5381. The same as my Xonar D2 has. This chip is one of the best.
What the residual harmonics you can measure with your Essence? What is the input signal level (dBFs) in the best linearity region of your card (when the residual harmonics become invisible)?
I have very average results, nothing interesting to show. Second question - I haven't measured that. And now I am far away from my PC.
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Old Yesterday, 11:43 PM   #7764
Vovk Z is offline Vovk Z  Ukraine
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Join Date: Oct 2011
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Low-distortion Audio-range Oscillator
Quote:
Originally Posted by s3tup View Post
Averaging won't change a thing, unless it's synchronized and is performed in either vector FFT or time domain. Then it will reduce noise only, like 20-30dB of noise reduction.
Any averaging that reduces harmonics is faulty
I am talking about noise, of cause.
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