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Low-distortion Audio-range Oscillator
Low-distortion Audio-range Oscillator
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Old 7th November 2016, 01:56 PM   #5331
DNi is offline DNi  Switzerland
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Quote:
Originally Posted by EUVL View Post
Thanks. Already found those.

I was looking for details of Samuel's implementation and (measurement ?) results.
He mentioned in other threads he posted them somewhere at DIYA.
But the search tool did not lead me to the right post(s).

Patrick
I'm also not aware of any published performance figures for this filter. I've built one, but I'm just beginning to gather experience with it.
For information, using an RC generator as a source and a digital scope as the readout, I got more than 60dB of attenuation of the fundamental of 919Hz, the latter being the notch filter freq. of the filter with the nominal part values, i.e. without the tuning resistors.
I also improvised a tuneable version of the filter as per Fig. 1 of the Kuhn's paper using caps with 5% tolerance, and tested it at three frequencies in the tuning range around 1kHz in order to see whether the notch depth varies with frequency. Within the rather high uncertainty of the method, the notch depth remained around 40dB at all three frequencies.
With a due caution that these were only crude measurements, I would say that this is not a bad performance.

Regards,
Braca
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Old 7th November 2016, 04:12 PM   #5332
EUVL is offline EUVL  Europe
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> I can't post them but I can send them to you.

I'll send you my email address by PM.


Many thanks,
Patrick
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Old 7th November 2016, 04:40 PM   #5333
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by DNi View Post
You can find the Hall network theory at either of the two links below:
http://electronicdesign.com/analog/redis...ll-network
http://traktoria.org/files/radio/filter_...filter.pdf
The Traktoria link is better - there are small errors at the ED link.

As to the Gerbers, etc. you'll have to drop Samuel a PM.

Regards,
Braca
Using the corrected write up a simulation only gives a ~46dB notch, Rs = 0 and Rl = 10**9. What am I missing?

Using top picture all caps are .01u, R2 is two 5k resistors (k = .5) and R1 has to be ~13.2*5k not 10k to get a notch of ~45dB???
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Last edited by scott wurcer; 7th November 2016 at 04:56 PM.
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Old 7th November 2016, 05:30 PM   #5334
scott wurcer is offline scott wurcer  United States
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OK using the values for his lightbulb oscillator and wallking the two pots back and forth a few times I could get -60dB at exactly 1kHz. The values for the two lower resistors are fairly far apart. Still missing something.
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Old 7th November 2016, 05:38 PM   #5335
DNi is offline DNi  Switzerland
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Originally Posted by scott wurcer View Post
Using the corrected write up a simulation only gives a ~46dB notch, Rs = 0 and Rl = 10**9. What am I missing?

Using top picture all caps are .01u, R2 is two 5k resistors (k = .5) and R1 has to be ~13.2*5k not 10k to get a notch of ~45dB???
Referring to the notation in the schema enclosed, ratio of R1 to R2 must be 12 for optimal performance.
I'm also enclosing my LtSpice model of the filter.

Regards,
Braca
Attached Images
File Type: png Hall_Notch_Filter.png (18.4 KB, 353 views)
Attached Files
File Type: asc Hall_Notch_Filter.asc (1.6 KB, 22 views)
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Old 7th November 2016, 05:57 PM   #5336
DNi is offline DNi  Switzerland
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I've just completed the Groner filter by tuning it for a nominal frequency of 1kHz. The tuning is effected by soldering several extra resistors onto the pads provided on the board (I'll post the values if there is interest).
I connected the filter at the output of the 1kHz state filter oscillator mentioned previously, and obtained the waveforms of the first oscillogram enclosed. There is an attenuation of more than 60dB, but since there is also phase difference between the input and output, the oscillator and filter frequencies were apparently not in tune. Using the trimmers provided on the oscillator for fine tuning its frequency resulted in the second oscillogram enclosed. The phase seems to be right now, and the attenuation is at a maximum.
Taking the RMS input and output voltages at their face values results in an attenuation of 75dB.
Note that the filer and the oscillator are on the bench, no casings, BNC connectors, etc.

Regards,
Braca
Attached Images
File Type: png OscAndFilterOutOfTune.png (46.5 KB, 354 views)
File Type: png OscAndFilterInTune.png (59.7 KB, 350 views)
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Old 7th November 2016, 06:10 PM   #5337
scott wurcer is offline scott wurcer  United States
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Thanks it makes sense now, I had a different idea of what was meant by tuning range. Also there is some confusion about the ratios in the write up, R2 was drawn as the value of the pot not 1/2 of it and the factor is 12 not 13.2
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Old 8th November 2016, 02:02 AM   #5338
31697B is offline 31697B  Thailand
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Quote:
Originally Posted by davada View Post
It beats sitting down with an ohm meter and 100's of resistors.
there is no need for .001% tol.

-RNM
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Old 8th November 2016, 02:04 AM   #5339
31697B is offline 31697B  Thailand
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Originally Posted by DNi View Post
I've just completed the Groner filter by tuning it for a nominal frequency of 1kHz. The tuning is effected by soldering several extra resistors onto the pads provided on the board (I'll post the values if there is interest).
Using the trimmers provided on the oscillator for fine tuning its frequency resulted in the second oscillogram enclosed.

Regards,
Braca

Since this will be used for distortion measurements.... any distortion tests on filter??


-RNMarsh
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Old 8th November 2016, 03:00 AM   #5340
chris719 is offline chris719  United States
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Low-distortion Audio-range Oscillator
Bruce Hofer's presentation seems to indicate SMT thin film resistors of larger package sizes are good performers, esp the lower tempco parts. I believe at least one of OPC's "The Wire" headphone amp projects here used Susumu RG resistors and the measurements looked spotless. I'd try those in 1206 instead of MELF which I hate because they roll all over the damn place.
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