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Old 19th October 2012, 02:53 PM   #741
KSTR is offline KSTR  Germany
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Hi,

looks like Samuel was right and the shown results were unreal in terms of absolute levels. The synced averaging and the AP graphing methods are to be taken with a grain of salt (and there are still some real and annoying bugs in the control software), especially for less experienced operators like me.

==> Forget the previous plot I posted in #730.


----:----

I measured again, now with traditional spectrum averaging (128x) and results are way more realistic now. The differences between the DUTs, though, remain fairly constant.

Two pcs. of Viktors' 1kHz Osc were tested, I see a slight increase of LF noise vs AP Genmon and the SG505 but the harmonic purity is outstanding and seems to be consistent.

I also looked at settling after a level change, at high level settings it settles quite fast while a the low end (at 300mVrms) it bounces up and down a little for some seconds.
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File Type: gif AP_GENMON vs SG505 vs 2xViktors @ 1kHz, 2.7Vrms.gif (33.0 KB, 235 views)
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Old 19th October 2012, 03:15 PM   #742
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Thanks very much for revising the measurements--that looks valid now!

The exact performance of the SYS-2722 depends a bit on the age, as later units have certain improved subcircuits. The one I'm using has around -135 dB (analyzer) and probably -140 dB (generator--measured with passive notch filter) 2nd and 3rd harmonic residual at 1 kHz.

So in your plot the distortion for Victor's oscillator could well be from the analyzer.

Samuel

PS: Yes, the synced average mode is tricky. Hardly ever use it therfore.
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Old 19th October 2012, 03:19 PM   #743
dimitri is offline dimitri  United States
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I concur with KSTR, I got very similar results with two units.
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Old 19th October 2012, 04:03 PM   #744
coluke is offline coluke  Italy
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Quote:
Originally Posted by Samuel Groner View Post
PS: Yes, the synced average mode is tricky. Hardly ever use it therfore.
It seems that in the previous plot there was no actual signal to sync on both for Victor's and AP's internal generator (or signal level was by far too low to get a stable sync) - I must admit the first plot was almost frightening

L.
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Old 19th October 2012, 04:38 PM   #745
KSTR is offline KSTR  Germany
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Follow up with the 10kHz version.

The AP genmon trace again has higher 2nd and 3rd, above that it's in the noise.
Viktors' is better in 2nd and 3rd harmonic but some 4th is visible too.
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Old 19th October 2012, 04:39 PM   #746
1audio is offline 1audio  United States
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In my experience long averaging (5,000,000 point 10 averages) even crystal controlled sources can drift enough to degrade the measurements. You can see the harmonics moving from bin to bin with successive measurements.

Is the AP oscillator stabilized (disciplined)? It shows less close in phase noise than Victors.
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Old 19th October 2012, 04:43 PM   #747
KSTR is offline KSTR  Germany
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Quote:
Originally Posted by Samuel Groner View Post
The exact performance of the SYS-2722 depends a bit on the age, as later units have certain improved subcircuits. The one I'm using has around -135 dB (analyzer) and probably -140 dB (generator--measured with passive notch filter) 2nd and 3rd harmonic residual at 1 kHz.

So in your plot the distortion for Victor's oscillator could well be from the analyzer.
Our AP is about two years old, is that late enough?
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Old 19th October 2012, 04:50 PM   #748
coluke is offline coluke  Italy
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Quote:
Originally Posted by 1audio View Post
It shows less close in phase noise than Victors.
Yeah - I was wondering about Victor's phase noise and THD+N. A full spectrum comparison betweem AP's and Victor's would be interesting.

L.
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Old 19th October 2012, 07:33 PM   #749
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Quote:
Originally Posted by Samuel Groner View Post
I quickly measured distortion of a small (10r cold resistance) lamp I had around (NOS replacement for Tek 7k scopes) and I've not been able to find any voltage coefficient effects. With 0 dBu across the lamp, distortion (pure 3rd) was -100 dB at 5 kHz. This falls at exactly 20 dB/decade, e.g. at 500 Hz I measured -80 dB. No flattening out at high frequencies was detectable--above the audio band distortion drops below the SYS-2722 residual.

So far it looks to me that all I've seen is pure thermal stuff. It's surprising at what high frequencies one still sees them. Perhaps there are lamps with different behaviour. I'll check if I find another one to measure.

Samuel
Well it was a long time ago, I remember -90dB at 10kHz and got the same THD with any op-amp. Maybe I convinced myself that that was all there was to it. I first saw this stuff in the 60's in an obscure text that used this oscillator to demonstrate the use of Volterra analysis.

I do know the non-linearity only stabilization works but have not exhaustively studied all the details. In thinking about the lightbulb, there still is in a way two effects the average power setting the resistance and the residual distortion at frequency. It might not matter that they are both thermally induced.
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Last edited by scott wurcer; 19th October 2012 at 07:45 PM.
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Old 19th October 2012, 08:33 PM   #750
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I repeated my measurements of Victor's oscillator with notch filter, to attempt to clean up some of the noise I was getting previously from a sloppy test jig. Pretty impressive results - All I could detect with 1.76V output was the 2nd at -139dB below fundamental, and that's barely detectable. This is 0.000011%, that's four zeroes.

During amplifier testing I noticed the oscillator does not care to be loaded down with your circuit, so I put this signal into Pete Millet's soundcard interface, which has a gain of 2, and balanced line driver output.

Then I get 2nd at -122dB below fund, and 3rd at -131dB below fund. That's about 7 times as much distortion, but still quite usable for testing amps and preamps.

I can provide calculations if anyone questions my numbers, knowing the notch filter gains the 2nd by 31dB and the 3rd by 35dB.

Jensen transformer should be coming this afternoon, so I will get some readings to compare.
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File Type: jpg 1.7V output.jpg (121.7 KB, 192 views)
File Type: jpg SC-3.76V out.jpg (122.3 KB, 183 views)
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