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Old 26th November 2012, 12:28 AM   #891
davada is online now davada  Canada
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This is TP8 compared to TP9
The notch filter output and set level output respectively.
The levels are about the same but notice the cancellation of the 3rd H.
This is not good.
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File Type: png TP8.PNG (64.3 KB, 201 views)
File Type: png TP9.PNG (62.7 KB, 170 views)
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Old 26th November 2012, 02:20 AM   #892
davada is online now davada  Canada
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Default Wrong test point

It seem I was measuring off the wrong test point TP8 and TP9.
These test point are post distortion amp levels.

Here is 1Vrms input and 3Vrms input straight off the notch filter output.
These level are at +10dBV scale.

The notch filter has added to the second and third harmonic level.

This is not bad but still not as good as Dick Moore's Twin T.
Attached Images
File Type: png Notch 1Vrms.PNG (58.1 KB, 163 views)
File Type: png Notch 3Vrms.PNG (57.4 KB, 157 views)
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Last edited by davada; 26th November 2012 at 02:23 AM.
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Old 26th November 2012, 03:12 AM   #893
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by davada View Post
It seem I was measuring off the wrong test point TP8 and TP9.
These test point are post distortion amp levels.

Here is 1Vrms input and 3Vrms input straight off the notch filter output.
These level are at +10dBV scale.

The notch filter has added to the second and third harmonic level.

This is not bad but still not as good as Dick Moore's Twin T.
Is this on a stock unit or modified in certain ways?
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Old 26th November 2012, 03:22 AM   #894
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Quote:
Originally Posted by jackinnj View Post
Referring to this article: Injection-lock a Wien-bridge oscillator

EDN Glen Brisebois - October 31, 2012

Injection-lock a Wien-bridge oscillator | EDN
Read the comments, Jim Williams was surprised by the results. I have a nice red bulb going right now the settling is much slower than the standard lamp which by theory indicates better distortion. AD797 and AD844 work fine but a NOS OPA627 never settles in amplitude, I will report tomorrow.
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Old 26th November 2012, 03:39 AM   #895
davada is online now davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
Is this on a stock unit or modified in certain ways?
Hi Rick,

The oscillator has the channel modulation trim pot and the parallel cap value increase.
The notch filter op amp was replaced with a jfet type of poor quality for this job.
But the notch depth under certain conditions is better or the same.
I think the OPA1641 is a better choice for the notch amp.
Otherwise it is a stock unit. I have the 001 option with mine but that shouldn't make any difference for this. It's just an extended range option.

The result is almost as good as Twin T.

The spectrum should look better with some averaging applied but like I said the unit have is in beta and I can't add averaging right now.
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Last edited by davada; 26th November 2012 at 03:44 AM.
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Old 26th November 2012, 05:56 AM   #896
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Default Two 339A monitor out spectra

These are taken from the monitor output; this 339 has not been cal'd in some time -- more than a year. Even so, at last cal I used two oscillators to verify the accuracy of the output levels for distortion readings down to -90dB, and I have no reason to think they are in any way inaccurate.

The input is from the 339 osc. at 1kHz, at 1VRMS, with a high-Z load of the analyzer only (not into 600 ohms), which means that the monitor output's 0dBV level of 1VRMS full-scale is referenced to 1VRMS at the 339 analyzer input (in analyzer mode, the THD read about 0.0013% with all filters in, but the actual THD of the osc. is more than 20dB lower).

The first plot is the full-scale signal at 0dBV, even though I've raised the plot 10dB to show the floor -- note the 0.0dB RMS reading in red. The 400Hz HP filter is in, the two LP filters are out -- they are noisy and have distortion even though they do clean up the meter readings. Note the 2nd H at about -94dB, and the 3rd H at about -86dB (I'll go back and turn the 400Hz HP off, too, and see if that changes anything -- I've just always left that in).

The second plot is the monitor distortion output with the distortion range set to the max sensitivity of -80dB, so the plot's 0dBV level is actually -80dB. The notched fundamental is about -35dB = -115dB. The 2nd H is about -100dB, and the 3rd H is about -111dB. I don't know where the high Hs are coming from -- I really don't want to tear the 339 open just now, as I'm bring a Fluke 343A DC voltage standard back to life. Davada may figure it out for us....
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File Type: jpg 339A-1k-1V-mon.jpg (94.1 KB, 150 views)
File Type: jpg 339A-1k-1V-notch.jpg (94.7 KB, 67 views)
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Old 26th November 2012, 06:30 AM   #897
1audio is online now 1audio  United States
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It would seem that the Level control generates 10% distortion, second harmonic only. That is way higher than the Silonex claims and more than I would have expected. You would have a pretty small signal at that node so I think some other factor could be contributing. How much ripple is on the LED drive (TP3)?
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Old 26th November 2012, 08:11 AM   #898
RNMarsh is offline RNMarsh  United States
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The Monitor output opamp is X100 to get the F.S. null level of 10mV up to 1 V. I wonder how good this opa is on noise and distortion at x100?
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Old 26th November 2012, 04:45 PM   #899
1audio is online now 1audio  United States
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Unless something is very wrong X100 or 40 dB should be in the .01 % THD or less region even with a 741.

A diagnostic check would be to kill the LDR (Pull the FET to off, negative) and drop in a resistor, 50 Ohms or so, in parallel with the LDR to get X100 from the stage. Try returning the resistor to several possible "optimum" grounds to see which has the lowest harmonic contribution.
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Old 26th November 2012, 05:38 PM   #900
davada is online now davada  Canada
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Quote:
Originally Posted by 1audio View Post
Unless something is very wrong X100 or 40 dB should be in the .01 % THD or less region even with a 741.

A diagnostic check would be to kill the LDR (Pull the FET to off, negative) and drop in a resistor, 50 Ohms or so, in parallel with the LDR to get X100 from the stage. Try returning the resistor to several possible "optimum" grounds to see which has the lowest harmonic contribution.
Hi Demian,

The x100 is a stage just before the meter amp and is down stream from the auto set level.
The auto set level never sees this much gain since the input range selector and nag indicators keep the level within the 3.162Vrms FS for the most part.
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