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-   -   Quad 63 (and later) Delay Line Inductors (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors.html)

stokessd 10th March 2020 02:19 AM

That is very interesting, it seems that in your simulation, there isn't significant rolloff in the first few sections. That doesn't seem to follow what my ears are telling me, but I've never measured each section individually. To do it right, I'd have to do more than disconnect the sections, you'd need to replace the removed sections with an equivalent capacitance.

I could do that experiment with my test jig and a second uncharged mid panel. I have a panel test fixture (as seen here: SDS Audio Labs - Quad Electrostatic Loudspeaker Measurements) that would work well for such a test.

Sheldon

Hans Polak 10th March 2020 12:58 PM

Quote:

Originally Posted by stokessd (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6115551.html#post6115551)
That is very interesting, it seems that in your simulation, there isn't significant rolloff in the first few sections. That doesn't seem to follow what my ears are telling me, but I've never measured each section individually. To do it right, I'd have to do more than disconnect the sections, you'd need to replace the removed sections with an equivalent capacitance.

I could do that experiment with my test jig and a second uncharged mid panel. I have a panel test fixture (as seen here: SDS Audio Labs - Quad Electrostatic Loudspeaker Measurements) that would work well for such a test.

Sheldon

Thanks for replying.
However there are still a few points to clear.

1) The most obvious is that the LF impedance curve being strongly dependent on the level.
The only component to my feeling that can cause this effect, are the 12 delay line inductors.
If I had one, I could measure their behaviour at various levels with my vector network analyzer.

2) The other component is the used audio transformer, but without knowing the various parameters.
When you have the possibility, it would be great if you could measure:
1) the input inductance (L1=Ls+Lp) with the secondary open
2) input inductance (Ls) with secondary short circuited and
3) output inductance (L2) with the input open.
That would give me some important parameters of this trafo.

Hans

Hans Polak 10th March 2020 01:12 PM

1 Attachment(s)
Quote:

Originally Posted by MarcelvdG (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6115400.html#post6115400)
How do you model the inductor losses and parasitic capacitances?

The capacitances may be neglected with two identical trafo's correctly connected, see image below.
For the inductances see my question to Sheldon.

Hans

bolserst 10th March 2020 10:18 PM

1 Attachment(s)
Quote:

Originally Posted by Hans Polak (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6115963.html#post6115963)
However there are still a few points to clear.
1) The most obvious is that the LF impedance curve being strongly dependent on the level.

The LF impedance changes with signal level because the primary inductance of the transformer is a function of core permeability which increases with signal level until core saturation is reached. I have measured the inductance as a function of Vrms for a few frequencies and will post once I track down my measurements.

Quote:

2) The other component is the used audio transformer, but without knowing the various parameters.
I also measured step-up ratio and parasitics of the transformer(leakage inductance, winding capacitance, and resistance) and will post those as well.

For proper modeling of the HF roll-off behavior that stokessd mentioned, you would need to incorporate the losses intentionally introduced into the lattice inductors with shorted turns. You would also need to include the inherent winding capacitance in parallel with each inductor.

Peter Baxandall had a nice technical write-up of the ESL63 design, pages 179 – 194 of “Loudspeaker and Headphone Handbook”, J. Borwick, Ed., which is currently available for free preview on Google Books. Loudspeaker and Headphone Handbook - Google Books

Attached is a screen grab highlighting a couple sections related to your modeling effort.

Hans Polak 10th March 2020 10:59 PM

Quote:

Originally Posted by bolserst (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6116602.html#post6116602)
The LF impedance changes with signal level because the primary inductance of the transformer is a function of core permeability which increases with signal level until core saturation is reached. I have measured the inductance as a function of Vrms for a few frequencies and will post once I track down my measurements.


I also measured step-up ratio and parasitics of the transformer(leakage inductance, winding capacitance, and resistance) and will post those as well.

For proper modeling of the HF roll-off behavior that stokessd mentioned, you would need to incorporate the losses intentionally introduced into the lattice inductors with shorted turns. You would also need to include the inherent winding capacitance in parallel with each inductor.

Peter Baxandall had a nice technical write-up of the ESL63 design, pages 179 – 194 of “Loudspeaker and Headphone Handbook”, J. Borwick, Ed., which is currently available for free preview on Google Books. Loudspeaker and Headphone Handbook - Google Books

Attached is a screen grab highlighting a couple sections related to your modeling effort.

Thank you for your feedback.
I’m looking forward to see the results of your measurements.

Hans

Hans Polak 13th March 2020 03:08 PM

1 Attachment(s)
Sheldon,

In the calculation in posting #1, Z = wL was used instead of Z = jwL.
This gives a wrong outcome for L.
When simulating the values for V1 and V2 of resp 2.08V and 117mV that you measured, I get a value for L = 3.7 Henry.

Hans

Attachment 824652

bolserst 13th March 2020 03:40 PM

Your transient analysis wasn't long enough to let the DC offset die down, so the 117mV RMS valuse is erroneous. You would need to continue the transient analysis for a second or so and then only analyze the last few mSec. Alternatively, you could use AC analysis instead. Also, be sure to include the DC resistance of the inductors which is 5680 ohm, so Z = R + jwL = 5680 + jwL. Using the data posted, I calculate value of L = 2.651 H

Hans Polak 13th March 2020 04:56 PM

Quote:

Originally Posted by bolserst (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6119769.html#post6119769)
Your transient analysis wasn't long enough to let the DC offset die down, so the 117mV RMS valuse is erroneous. You would need to continue the transient analysis for a second or so and then only analyze the last few mSec. Alternatively, you could use AC analysis instead. Also, be sure to include the DC resistance of the inductors which is 5680 ohm, so Z = R + jwL = 5680 + jwL. Using the data posted, I calculate value of L = 2.651 H

Thanks a lot for giving Rser, this changes a lot.
Again using Sheldons values of 2.08V and 117mV, 1010 Ohm and 1Khz, I get 2.67 Henry.
I will integrate this Rser in my LTSpice diagram.

Hans

bolserst 13th March 2020 05:05 PM

7 Attachment(s)
Quote:

Originally Posted by bolserst (https://www.diyaudio.com/forums/planars-and-exotics/338927-quad-63-delay-line-inductors-post6116602.html#post6116602)
… will post once I track down my measurements.

Finally located the measurements I took back in 2016. Thank again to stokessd for letting me borrow one of the interface units he was purchasing. My main interest at the time was the transformer design, but took some additional measurements of the LC transmission line with the intention of working up a correlated LTspice model at some point, but it has been low my the priority list. Hopefully you will find the measurements sufficient for the purpose.

Attachment #1: The transformer primary inductance was measured for increasing input voltages applied directly to the primary(ie bypassing the 1.65 ohm resistors) showing the expected trend of increasing inductance with a sudden drop off as core saturation is approached.
Attachment #2: Parasitics were also measured. Step up ratio was 1:122 and nominal values of primary and secondary inductance are used. Note the unusually large leakage inductance and unusually small winding capacitance. Golfnut had posted some comments regarding why the transformer was designed this way.
About to take the ESL plunge
esl transformer.

Attachment #3: Transfer function of the unloaded transformer in red shows the expected peak where the leakage inductance resonates with the winding capacitance. The green line shows the response with the LC transmission line circuit is attached, but no ESL panels are connected. The orange line shows the response when 22pF capacitors are used to load the line.
Attachment #4, #5: Impulse response trends for the LC transmission line unloaded and then loaded with 22pF capacitors. Notice the increase in delay when capacitors are added.
Attachment #6, #7: Frequency response trends for the LC transmission line unloaded and then loaded with 22pF capacitors.

I can post a set of *.wav files containing the impulse responses if that would be helpful, just let me know.

***NOTE***
Meant to mention that the transformer output and LC line measurements were taken with a balanced HV probe having an input impedance of 2.7Mohm.

Hans Polak 13th March 2020 05:32 PM

1 Attachment(s)
In the version below of my LTSpice sim, I have made the following changes:

1: for the 12 Inductances: L=2.67H Rser=5680 Ohm and Cpar = 22p.
2: the first 6 HF sections are set to 12 x 44pF , giving a series value of 22pF.
3: I have changed the coupling factor of the audio transformer from 1 to 0.9998. Seemingly a small step, but this seems a correct value to take the serial inductance into account.

Although FR and step response are much better as before, I fail to get the impedance peak ar ca 23Khz of the real thing.

Hans


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