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Simple, no-math transformer snubber using Quasimodo test-jig
Simple, no-math transformer snubber using Quasimodo test-jig
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Old 17th February 2020, 08:46 PM   #1811
wgh52 is offline wgh52  Germany
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@Rinman

thanks sa lot for sharing! I am learning the optimum judgement at the moment, so please let me understand why for you the red curve 39Ohm and not the green curve 23Ohm is the optimum. In my judgement the red curve still shows some (small!) ringing which the green one does not...

Thanks and Regards,
Winfried
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Old 17th February 2020, 10:17 PM   #1812
Rinman77 is offline Rinman77
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Quote:
Originally Posted by wgh52 View Post
@Rinman

thanks sa lot for sharing! I am learning the optimum judgement at the moment, so please let me understand why for you the red curve 39Ohm and not the green curve 23Ohm is the optimum. In my judgement the red curve still shows some (small!) ringing which the green one does not...

Thanks and Regards,
Winfried
I am also only learning. But let me post the individual curves to see if you still feel the same way. First let me explain that I consider "properly snubbed" to be indicated by the flattening of the 2nd swing at the point where it originally dips below the zero line, as indicated in Figure 10 of the original Quasimodo and document, and as is reprinted in post 1807 by MJ himself. In his example the first swing remains intact, though greatly dampened, but it is the eradication of the 2nd dip that is used as the criteria for zeta=1. I have marked up the attached scans with this in mind.
Ron
Attached Images
File Type: jpg 49-Ohm.jpg (40.1 KB, 131 views)
File Type: jpg 39-Ohm.jpg (42.0 KB, 136 views)
File Type: jpg 23-Ohm.jpg (45.7 KB, 138 views)
File Type: jpg compare 3 scans.jpg (65.9 KB, 138 views)
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Old 17th February 2020, 10:26 PM   #1813
wgh52 is offline wgh52  Germany
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Hi Ron,

thanks for your prompt answer! The individual screenshots help clarify your point more obviously! I'm going to do some measurements soon and will do the analysis be screenshots as well, instead of "just" using the CRT trace itself.

Thanks,
Winfried
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Old 20th February 2020, 11:09 PM   #1814
wgh52 is offline wgh52  Germany
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Default Hard to find optimum case with R-Core from ZeroZone

Hello Folks,

after having done many successful snubber optimization measurements over recent weeks, always leading to textbook optimums, I have now come across transformers with puzzling ringing behavior, despite these transformers working flawlessly in their applications so far. The behavior is only seen with ZeroZone R-Cores (so far), Audiophone R-Cores behave as expected. Please see the screenshots below and my only question to the knowledgeable Transformer and Quasimodo experts is: Which R-value do I take for the transformer?

Thanks a lot for your kind advice!
Winfried

PS: Just to make sure: The test set up is identical to the "well working" cases, also the procedure followed is identical!
PPS: If this is the wrong thread to ask my question, please advise where I should post this. Thanks!
Attached Images
File Type: png ZZ01 2VDivn 10µsDivn R open.png (69.7 KB, 120 views)
File Type: png ZZ02 1VDivn 5µsDivn R 500Ohm.png (21.6 KB, 53 views)
File Type: png ZZ04 1VDivn 5µsDivn R 100Ohm.png (20.4 KB, 53 views)
File Type: png ZZ05 1VDivn 5µsDivn R 80Ohm.png (20.5 KB, 51 views)
File Type: png ZZ06 1VDivn 5µsDivn R 60Ohm.png (20.2 KB, 49 views)
File Type: png ZZ08 1VDivn 5µsDivn R 40Ohm.png (20.1 KB, 39 views)

Last edited by wgh52; 20th February 2020 at 11:12 PM.
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Old 21st February 2020, 01:30 AM   #1815
AllenB is offline AllenB  Australia
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Simple, no-math transformer snubber using Quasimodo test-jig
The above post has been moved here from the results thread.
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Old 21st February 2020, 01:36 AM   #1816
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Thank you Moderator! The author of #1814 was concerned (correctly!) that he put it in the wrong place.
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Old 21st February 2020, 01:26 PM   #1817
wgh52 is offline wgh52  Germany
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Thanks for moving my post to the right location!
I hope someone can make sense of the measurements and can give advice on how to handle the strange transformer response. My suspicion is that the measured transformer somehow may have two resonances, only one of which being compensateable by a snubber... The question "where is the optimum" in this case remains.


Thanks and Regards,
Winfried
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Old Yesterday, 03:52 AM   #1818
Rinman77 is offline Rinman77
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I have a total of 4 Hafler DH-200. Their stock EI core transformers have a single secondary with a CT. I earlier took Quasimodo measurements on one of these transformers, on only one of the two leads against the CT. I received a result of 39 Ω. I assumed the 2nd lead against CT would render the same result. Well today I took measurements on one of my other DH-200 transformers, but this time I measured both secondary leads against the CT--I obtained different results. Not hugely different, but different outside the range of error even given the subjective nature of choosing "flat" for zeta = 1. I then measured yet another one of these transformers and obtained a very similar result. So I will identify these transformers by the S/N on the amp. Again, these are all Hafler DH-200 amps with their stock EI core transformers.
  • S/N = 3211064
    • 2ndary 1a to CT: 28 Ω
    • 2ndary 1b to CT: 40 Ω
  • S/N = 3938020
    • 2ndary 1a to CT: 28 Ω
    • 2ndary 1b to CT: 42 Ω
  • S/N = unknown (tag is missing) (This is the one measured earlier)
    • 2ndary 1a to CT: 39 Ω
So perhaps the secondaries are consistantly wound in such a way that one side of the CT has less self-inductance than the other side. If so it makes sense to snubber them differently. Agreed?
But if someone is looking to these resutls, but doesn't have the means to measure for optimal snubbing themselves, I guess a resistor of value 35 should be OK for both pairs. Would this be good advice?
Thanks,
Ron
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Old Yesterday, 04:01 AM   #1819
The Peasant is offline The Peasant  Canada
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I have encountered this same difference in results with other EI core CT transformers, although the numbers were not quite as far apart as yours are. I assume that one secondary is physically wound over top of the other, resulting in a slightly different inductance for each one. I installed different values of snubber resistors for each winding as you suggest.

I also agree that about 35 ohms would be an acceptable compromise value if you are unable to directly measure a DH-200 transformer yourself.

Take care,
Doug
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Old Yesterday, 01:52 PM   #1820
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Quote:
Originally Posted by wgh52 View Post
... and my only question to the knowledgeable Transformer and Quasimodo experts is: Which R-value do I take for the transformer?
Suppose you had to choose a value all by yourself: which one looks best (or which one looks least bad), to you? and why?
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