That's a 1982 article. The VPI brick is an old hat by now. Do people still use them? They were everywhere at audio shows back then. I suspected it was mechanical damping and didn't know it uses steel laminations inside.
I'm not defending this type of tweako stuff but, in context, Stereophile simply republished a 1982 article when the magazine was still "underground" and small and this was before John Atkinson was the editor, who implemented the measurements & testings at the magazine. If this were published in recent years, I would like to see a follow up on a measurement page to investigate into why we hear or not hear a difference. Personally, at this point it's a waste of my time to wait for that to happen.
I'd suspect makers of thick and heavy cast iron skillets will reap the benefit when some measurement is published. 
Placing soft magnetic material on top of a (cored) inductor/transformer increases inductance. Maybe your power transformer is just not sized appropriately and the increased inductance of the core you placed on top of it improved regulation?
Can you ppost a circuit diagram of the involved device and give specs of the original transformer?
Can you ppost a circuit diagram of the involved device and give specs of the original transformer?
That would be great but as described no schematics no specs no confirmed results, just a vague report on something somebody might have said somewhere else.
Many degrees of uncertainty in the chain.
I have measurement setup on the bench, because of other loony thread: https://www.diyaudio.com/community/threads/power-conditioners-and-cords.391921/post-7199581
I hope we can agree that for any audible change, there must be some measurable change at the power supply output: voltage, harmonics distribution, noise, transient response, output impedance, load regulation …
Otherwise, we are in the voodoo realm of snake oil peddlers and only opinions and mystical hearing impressions can be thrown in either way. Just look at that Stereophile article. ‘Focus of the sound’ as an improvement. Really? 🤣
I’ve made an introductory check by placing another EI transformer of the same size, on top of the one used in the CRC power supply. They were 100 VA EI transformers and powered one was at 30 VA load. There is no point to attach any measurements as there was absolutely no change in output voltage, noise, ripple and harmonics levels. I can measure all above mentioned parameters but there is simply no point. As Osvaldo said, this is pure foolery.
I hope we can agree that for any audible change, there must be some measurable change at the power supply output: voltage, harmonics distribution, noise, transient response, output impedance, load regulation …
Otherwise, we are in the voodoo realm of snake oil peddlers and only opinions and mystical hearing impressions can be thrown in either way. Just look at that Stereophile article. ‘Focus of the sound’ as an improvement. Really? 🤣
I’ve made an introductory check by placing another EI transformer of the same size, on top of the one used in the CRC power supply. They were 100 VA EI transformers and powered one was at 30 VA load. There is no point to attach any measurements as there was absolutely no change in output voltage, noise, ripple and harmonics levels. I can measure all above mentioned parameters but there is simply no point. As Osvaldo said, this is pure foolery.
I bet you have no cast iron skillet to try. 😆
But seriously, presence of soft magnetic material close to cored transformer will change distribution pattern of stray field as Wayne said. May affect parts which uses ferromagnetic material such as leads to a desirable, detrimental, or non perceivable change. I'd recommend a transformer repositioning or a shield if proximity of massive soft magnetic material close to a power transformer has any perceivable effect.
But seriously, presence of soft magnetic material close to cored transformer will change distribution pattern of stray field as Wayne said. May affect parts which uses ferromagnetic material such as leads to a desirable, detrimental, or non perceivable change. I'd recommend a transformer repositioning or a shield if proximity of massive soft magnetic material close to a power transformer has any perceivable effect.
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So you didn't measure... but then how are you so sure there's no change in all those 'measurements'?
Do you not realise you are sounding like the very type of people you are decrying?
If you want to prove or disprove via measurements, then you also do the measurements whatever you may think to settle it for yourself in your own system.
Thank you Schiirrn, that was good information on the inductance increasing. I just took two Radio Shack model 273-1353 EI core transformers that are 12.6v-0-12.6v, 1.2A and measured the inductance with a Sencore LC75 capacitor-inductor analyzer.
One transformer – primary 622mh, secondary 29mh
With the second transformer placed against the smaller side of the first ones core. Short side against short side- primary 631mh, secondary 30mh.
This test was repeated many times with the same result. So there are some real measurements showing a true increase in inductance like you said Schiirrn.
Short side against short side has a greater increase in L that long side against long side.
Would not increasing the inductance choke out more of the line noise that could be incoming? Could the second transformer absorb some of the radiated field inductive kick when the diodes turn off?
Every time I have increased the size (weight, VA) of a power transformer feeding the same equipment the larger size has sounded better to me.
Ehm, WTH?
I clearly stated that I’ve made measurements of voltage, noise, ripple and harmonics. but there was absolutely no change. So, no point to attach them.
What I didn't measure are other parameters like transient response, output impedance, load regulation, as there was no point to continue.
Radio Shack transformers are some of the worst quality I’ve ever used. They run way the hell too just idling, indicating to me that they are run too close to saturation. It’s no wonder there is a lot of stray field and that any bit of neighboring iron will pick up some of the flux. It’s likely not enough to materially affect what’s going on between primary and secondary, but certainly between the primary and the outside world where you ideally don’t want any coupling.
Any high quality audio equipment is going to use transformers of much higher quality than those RS junkers, and therefore much less subject to coupling between the transformer and its environment.
Some small change of inductance is expected if enough iron is put in contact with transformer core. You could as well measure weight and observe that there was large change. Small increase in inductance doesn’t tell what happens with PS or amplifier output. That has to be measured.
Otherwise, only subjective listening impressions remain. I like to repeat that, after a bottle of exquisite beer, my systems sounds much better. I can’t measure why. 🙂
631mh vs 622 is a 1.44% increase. This may be true or not. Now, repeat the same measurements adding any other kind of element magnetic or not to compare: a screwdriver, the magnet of a speaker, , a battery, a scissor, a plier... Almost anything you put close to the core will affect leackage inductance. It's natural. But the amount of change will be negligible except when the magnet of a speaker is close to it because it really causes an important change in the magnetic flux lines path.
Seems to me that wg_ski's version of hell is bloody hot 🙂
You may request the use of intoxicant detector from your friendly neighborhood cop while adding bottles of sound enhancer. Note the point of diminishing return. 🙂
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This may be the next audiofoolery to sell. Buy I suspect some people will demand a barrel 😳 😲 🙄 .
Isn't subjective listening impressions the only thing that really matter in the end? We have our equipment to give us enjoyment thru listening to music.