All interesting input.
What surprises me is that some people say their gear is dead silent. Others with the exact same gear experience hum.
Are conditions different?
Are people different? 
In my experience hum comes and goes. Every now and then I feel like I have found the cause. Then the hum comes back. You can imagine how frustrating that is after 10 years of experimenting.
Latest positive effect is getting rid of 2 custom made length of wireworld power cables.
Conditions are different. The hum usually is caused by some other device in the local electrical grid. A refrigerator, furnace, air conditioner, electric motor, compressor, etc. that is not correctly insulated, isolated, phased, or grounded. It could also come from another house with similar issues that is connected to a shared step down transformer.
We have a couple of 25kva isolation transformers connected to machines. You can feel them vibrate but they never give off an audible hum. They do give off a fair amount of heat.
iefbo,
The āMagnetostriction Effectā it is common in transformers. This effect is the result of magnetic materials changing shape when they are magnetized(magnetically loaded). With this being AC the transformer is constantly magnetically loaded and unloaded causing it to vibrate. I didnāt think this effect was common with hifi toroidal transformers since they donāt normally have a stacked metal core but usually instead use a ferrite core. I know it often occurs with large industrial step down transformers which DO have stacked metal cores. You can normally see these buzzing near your house, itās very common.
Many devices vibrate but usually at frequency too high/low to be audible(at least by humans). Like a tuning fork a system will be most audible at its fundamental frequency(which is unique to that specific system). This fundamental frequency is a function of geometry(which you canāt change), mass(which you canāt change) and stiffness. I would contact PS Audio before trying thisā¦but, you could possibly try very slightly tightening up the nut on the top of toroidal transformer since it will stiffen the connection of the transformer to the chassis. When you stiffen the transformer to the chassis you will not keep it from vibrating BUT you will move the systemās(your power regeneratorās) fundamental frequency out from the audible range and into an inaudible range. So you will no longer hear it. - Other options(again, I would contact PS Audio first) could be adding some type of vibration absorbing/damping mat under the transformer or simply encasing the entire transformer in a absorbing/damping material which both could accomplish with the same effect of moving the resulting vibration from the audible range to the inaudible range.
I would also look into āDC Offsetā, sometimes called āDC in the ACā. This is usually the result of unbalanced loads or flaws in the power distribution system. This can cause DC current flow in the transformers, making them run hotter and produce an audible, mechanical humā¦It may be worth looking into since you may have an actual issue with the power to/in your house.
Hope that helps,
Ryan
Yes conditions are different and people are different.
Some people do not hear so well so they do not hear the hum, but it is there.
Some people have their units placed within the room, that the frequency does not resonate as much, or it is not audible in the listening position. I had that in my previous house, i could hear the hum close to the P10, but not from my listening position. That does not mean it would hum less than it did now, just that the room was hiding it.
My P10 toroid had some hum (it still has but it is now buried inside resin). I have other transformer that hum, some quite a bit more than the one from ps audio, despite being much smaller ! They hum in any house, any time of the day. I have replaced the main part of humming transformers with new ones (better built and better encapsulated). Some vibrated so much that not even resin stopped them !
From my experience all toroids hum the bigger the louder. They can hum due to external conditions (ledās, eletric motors, etc) but that is an ADITIONAL hum to the one already present due to the size and property of a transformer.
Birger ,
Pot it ! Use Robnor PX700
I donāt understand āPot itā.
Is it the same as āDiscard itā?
No. To āpotā a transformer is to insert it in a āpotā and cover it with resin.
The Robnor PX700K is what i used. It is non conductive.
Just find a suitable 16cm aluminium pot (kitchen pots are excellent).
Remove the toroid from the P10/P15 and disconnect the cabling (my p10 had quick disconnect cables very easy).
Ok, well, I wonāt do that until the warranty has expired in 2.5 years from now.
Hi Ryan,
I used to have a humbuster from PS Audio, but that did not help so I sold it.
Is there a way to measure DC Offset?
Is there a way to measure other devices for poor insulation or other issues they might cause?
Hey saf,
Iām not as brave as you.
Do you think it would be a good idea to open up the P10 and tighten some of the screws? The ones holding the toroid in particular?
Thanks!
Hello
From my personal experience, i do not.
The toroid already is very well tightened . The problem is that it is a very big toroid and thus it need insulation. I have had toroids way smaller (160VA) that made more noise ! But those i sent them to the bin.
This one looks like a 600VA and ate least mine only had a center resin filled . No resin outside.
Even encapsulation is not all the same, as its construction.
I recently bought a couple of 160VA toroids for a power amp that are DEAD silent . I mean dead. They are truly magnificent.
I also bought a Keces P3 that has a lowly 100VA toroid (with resin) and it also HUMS.
So you see some are a piece of sh*** , and some are not.
I think manufacturers believe most of their clients wont bother with the hum or wont notice.
Yep, afraid you are right.
And letās be honest. It is subjective: some people hear it, some donāt ā¦ and some donāt care
Too bad we can not choose what category weāre in 
I can tell you what helped for me, although i understand not everyone is able to do so.
Besides the resin encapsulation , you can have your room treated.
I since added bass traps and ceiling absorbers in my room, the revererance droped a lot.
With that, the perceptible hum from toroids also droped.
But do bare in mind that i placed more than 20x panels in my room, measuring 60x120 cm !
This may be off-topic, in which case I apologize in advance. But since some of you here seem to be very familiar with toroidal transformers, I thought Iād ask.
I wanted to learn more about balanced AC toroidal transformers (Equi=tech, PLiXiR, Torus, etc.) - has anyone tried connecting one between the output duplex of a PowerPlant and a source component as a power conditioner?
My two P20s āregenerateā wall duplex AC into low-distortion, low output-impedance AC to feed my system, but they are still extremely sensitive to the quality of the input AC. So why not use a balanced toroidal conditioner to further filter out the residual DC and noise?
Potential effectiveness aside, doesnāt your postulation suggest placing a ābalancedā power conditioner ināfrontā of the P20ās?
Curious to read what others chime in withā¦
Regards.
Great question. As a side note I wonder if putting a filter in front of my P10 will have an impact on the HUM.
John, since you have 2 P20ās, could you try putting one after the other and see if there is any impact?
As my 230V P20s are rated for 2,000VA, a toroidal with adequate overhead will be the equivalent of 3,000VA and above. Such a unit would be over 110 lbs. in weight and of substantial size. Rather than two such units in my already cramped audio setup, I believe that it would be far more effective to place balanced toroidals AFTER the P20ās duplex outlet, as my source components a much more modest amount of power.
The most critical components (and the power consumption in watts) are: MSB Technology mono powerbase x 2 for the DAC (70W), Aurender W20 music server (29W), PLiXiR DC LPS x 2 for the SOtM network components (40W), and the Farad Super3 DC LPS (20W) for a SOtM USB peripheral. All together, these are less than 300W, and even with the generous overhead of 3x, less than 1,000VA, which can be split among multiple smaller units, say 400W x 2, or 120W x 4.
Hence, the short answer is that Iād rather let the two P20s provide the basically unlimited reserves of current into multiple balanced toroidals, offering the benefit of additional multiple isolation zones, which then feed the individual components and power supplies.
Back to my question - will the toroidals harm the P20s in any way when connected in this manner?
I donāt intend to ever connect two P20s in series. Not only are they tough to move, I have no space for them to be either stacked or placed side-by-side, and the benefits would likely not be worth the trouble/cost/inefficiencies.
So ā¦ I had an old power filter in the basement which Iām trying in front of the P10.
I know this is against the PS Audio recommendation, but Iāll give it a try.
First impression is good (hum seems to bee less present), but I have been fooled before about first impressions (see title of this topic!).
Iāll keep you posted about progress.
No, Iām not wondering about placing a Herculean 150 pound toroidal between the wall duplex and the P20, but rather, smaller (200-1,000W) balanced toroidal isolation transformers AFTER the P20ās output duplexes, to provide additional DC grounding and common-mode noise elimination for low-power source components.