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Can you explain why the 1kHz square wave being this shape

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Posted on July 2, 2024 at 03:43:57
Eric Chan
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Posts: 391
Joined: October 31, 2001



Folks,

I have designed an interstage using amorphous core, 3200 turn : 3900, 4 section primary, 3 section secondary

The 1kHz square wave I obtained seems to have some odd phenomenon, the red circled shoot up.

Normally the mind overshoot should only happen in rising edge, but now it appears in falling edge. Can someone kindly explain why

Thanks in advance

 

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RE: Can you explain why the 1kHz square wave being this shape, posted on July 2, 2024 at 05:42:06
ivan_terrible
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 That's a digital scope.
What you see is the digital representation of a square wave.

There may be some ringing/resonance in there but it's irrelevant.

 

RE: Can you explain why the 1kHz square wave being this shape, posted on July 2, 2024 at 06:25:24
cellailuca
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Location: Roma
Joined: January 27, 2021
 It is a visual artifact due to hi-res (interpolation) filter.
There is also pre-shoot on the falling edge...


Omnes feriunt, ultima necat.

 

RE: Can you explain why the 1kHz square wave being this shape, posted on July 3, 2024 at 02:49:50
Eric Chan
Audiophile

Posts: 391
Joined: October 31, 2001



Hi both,

The original photo showed my transformer supplier measuring the out put of the cutom made interstage and the output show overshoot and ringing in the falling edge, which is strange and I do not know the reason

I am doing an experiment here at home using lundahl interstage, as shown, the falling edge does not have any overshoot and ringing. I use also, well, the so called digital oscilloscope.

Is there something wrong with custom inyerstage or something else. The overshoot and ringing in rising edge are explainable, but how to interpret the overshoot of falling edge?

 

RE: Can you explain why the 1kHz square wave being this shape, posted on July 3, 2024 at 07:59:03
Triode_Kingdom
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Posts: 10199
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 I don't think there's enough resolution to see what the falling edge is actually doing. How does it look at 10X that sweep?

 

RE: Can you explain why the 1kHz square wave being this shape, posted on July 3, 2024 at 09:19:06
Eric Chan
Audiophile

Posts: 391
Joined: October 31, 2001



Hi TK,

Does it look better

Pretty strange it happened in falling edge

 

Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 3, 2024 at 09:35:46
Ralph
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Location: Minnesota
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 FWIW that's how the spark is generated for a spark plug in a car. You put a current through a transformer and then shut it off. When the field collapses, a spike is generated that is large enough to jump the gap of the spark plug.

I'm not used to seeing this in audio transformers though, even if the 'scope is digital. Usually you just get ringing on the leading edge. At any rate, the ringing can be reduced by loading the output of the transformer. I suspect that spike will go away to once the transformer has a load.

 

RE: Can you explain why the 1kHz square wave being this shape, posted on July 3, 2024 at 09:43:57
cellailuca
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Posts: 289
Location: Roma
Joined: January 27, 2021
 I suppose because of the different level of deviation of the frequency response of the two DUT from ideal (gaussian response).
The device with the steepest out of band attenuation will exhibit the worst ringing and overshoot.

Omnes feriunt, ultima necat.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 4, 2024 at 01:02:45
Eric Chan
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Posts: 391
Joined: October 31, 2001



I have found this post

 

You can model your transformer..., posted on July 4, 2024 at 10:14:04
cellailuca
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Posts: 289
Location: Roma
Joined: January 27, 2021
 ...and find out the reason why.


Omnes feriunt, ultima necat.

 

resistor added but it is still a mystery for falling edge having overshoot , posted on July 4, 2024 at 22:27:11
Eric Chan
Audiophile

Posts: 391
Joined: October 31, 2001



Resistor 750 ohm added,mitigated, but falling edge still have overshoot

I seldom see falling edge having a overshoot

Can someone give a hint

 

I think this might help, posted on July 5, 2024 at 05:39:31
cellailuca
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Posts: 289
Location: Roma
Joined: January 27, 2021



I have just played a bit with some tentative values in the above LTspice model (based on the one of my previous post).
Depending on the rise and fall time of the 1 KHz squarewave (1 microsec) and on the capacitive coupling (1 nF) between primary and secondary I am able to replicate your experimental waveform.
So I recommend to model your HW before wasting your time.


Omnes feriunt, ultima necat.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 14, 2024 at 05:09:54
walge
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Posts: 140
Location: roma
Joined: September 25, 2008
 With a good ss amplifier you can test it in reverse mode.
Try to use Arta or Spectralab software with a good sound card 24bit / 192 kHz so you can see a lot of things.
The secondary acting as primary must be drive with a nominal Z as 8 ohm connected to ss amp
The primary acting as secondary must be closed with the nominal Rp of tube.
P.e. 700 ohm for 300B
In this way you can test the trafo for a great range of voltage; take a care on input sensitivy of audio card, ypu need round 40dB of attenuation.
not so complicated
And leave the simularion that are far for real world, it is fantasy


Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 15, 2024 at 12:58:58
Best audiotransformers
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 But what do you expect when you do a reverse mode measurement? Shouldn't it be the same? Besides, most "good" ss amps don't go beyond 100kHz, so what's it worth?

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 15, 2024 at 13:29:23
walge
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 With a good ss amp you can check a wide range of signals to get the max swing possible mainly in the bass region
You can't do this because it is impossible to have the right generator with the right Z
In a s.e. With 300B( example) to have 8 volt on 8 ohm you need almost 200 Vrms in the primary with Z of 700 ohm

Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 15, 2024 at 23:50:08
Best audiotransformers
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 There is nothing wrong to use a 300B to test a 300B transformer. And it is even better because you directly have the right bias and the right pre-magnetisation for the transformer.
For PP transformer it is better to use a variac (or on the primary or on the secondary). A ss can be broke if the transformer saturates.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 00:03:48
walge
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 The reason is to test the OT only without tube.
In the bass region ( where the Z tend to go lower for the limit of L ) and high region( parasitic) you see also the distortion of the tube and not how the OT works for a wide range of driving voltage.
And is not possible to get a high swing free of Thd to drive standard the trafo
It is a strong test for the entire stuff, iron + architecture

I have dozen of different test to show how OT respond at great signals; in the mid region normally it works perfect with low distorion.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 01:18:58
Best audiotransformers
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 I consider distortion measurements on (output)transformers not very usefull.
The distortion depends highly on the source output impedance for for low signals it also depends on the core material.
You don't get any valuable information the way you measure.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 03:33:08
walge
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Posts: 140
Location: roma
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Hi

In attach some test on three different trafo with different power
Backward mode

Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 04:06:18
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 There is no schematic how you measured it, any resistors?

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 04:58:56
walge
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Location: roma
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In attach the basic set up
The ss amp drive the secondary acting primary through a resistor, in this case 6 ohm
On primary acting seconday there is a load with a partitor to check the signal

Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 07:26:43
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 I guess that you know that the resistor is part of the distortion measurements, in other words, changing the 6 Ohm resistor value will change the thd.
This is not an industry standard measurement so for me it is pretty useless.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 08:49:47
walge
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 If it is not compliant with the industry is not a problem

I will check in this way
Even the R could be part of dist measurement it is linear and not non linear as tube

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 10:59:11
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 The problem is that your method is wrong. What you present has nothing to do in a real tube amplifier with a real tube with a different impedance,

When i look at the frequency plots of the 3 transformers you posted earlier i think they all look horrible. I didn't even know that Sowter makes so bad transformers... Is it broke?
You didn't use a bias current, also a big mistake, and i mean a big big big mistake speacially when you try to measure thd with your method.

At last, if you post measuruments from brands like Sowter and Hammond, don't use the brand name only, post the exact type, both brands make a lot of different transformers. Is the thirth brand some local brand?

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 11:32:23
walge
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 It seems that you are the same person banned 5 times in DIY forum
The method is always the same
And, as always, you haven't any fact to show us, only words.
I hope the administrator will read this post


Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 11:54:59
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 Walter, your method is always the same, you present your methods as being the Truth, but without any scientific evidence. As with other topics on other forums, you simply ignore scientific articles by Patridge, one of the great legends in transformer technology, simply because you want to tell your own story. What a shame.
And now you're complaining about what? Because my knowledge is better than yours? Please don't be so childish.

btw, you have to explaine the Sowter transformer too because Sowter has no information on there site which explains this kind of measurements. I think you are a liar.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 16, 2024 at 23:11:17
walge
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Location: roma
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 If it is not compliant with the industry is not a problem

I will check in this way
Even the R could be part of dist measurement it is linear and not non linear as tube

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 17, 2024 at 10:04:16
Best audiotransformers
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 Your choice of the resistor value makes the current distortion a lot bigger.
The current is also in the transformer so not liniair.

Read Radiotron designers handbook for the theory (or Partridge).

And yes it's a problem if you presents results on an open forum like this. At home you can do what you like, no one cares.
You should place a warning that the results are not very usable because of a different "standard" (and read also wrong* standard).

* no bias = wrong for thd and power measurements. Even frequency response could be different but that depends on the design.

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 17, 2024 at 10:27:56
walge
Audiophile

Posts: 140
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 Don't worry

Be Happy

Walter

 

RE: Is that a spike caused by collapse of the magnetic field as its switching?, posted on July 17, 2024 at 10:38:17
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 thank you Walter, the same for you. Please next time good arguments based on good and profen theory

 

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