Very interested in this thread as I sold the amp to 'firestorm'. I had some transformer humm but very very slight (far less than a Naim 250 I once had). I've been monitoring my mains because of this issue and my mains It floats around 228v and 235v so it seems that the 'off the shelf' transformers are not what we need. I have bought many many transformers over the years, bespoke for purpose always seems the way to go but cost is higher but worth it IMO. I recall I built amp using two 300VA IE jobbies and still to this day I swear, although generating some heat they sounded fantastic better than the toroid's I replaced them with for a case size reduction. I have some classic amps (Yamaha and Pioneer) from the 80's all using IE type transformers, their mains inlet tapings are marked 240/120. They run completely silent.
Using Meanwell SMPS units I had some concerns as it clearly states on the unit not exceed 220v supply voltage.....Some thing to do with the European Union or some such shite.
I built F5t's mono's and dual monos, I felt (at the time) there was no sonic benefit and I had just wasted a lot of time and money, others will tell a different story.
My setup and humming
The Aleph J sounds great driving the Ergo IC (Thanks to James for sharing his design and TheEliz for making them)
I can't hear the hum whilst the music is playing. I can hear it in-between tracks and it bugs me to have a constant 100Hz buzz, may be one of the downsides of developing a "golden ear" or may be just a 1st world problem.
The amp isn't that far away, it's in front of me about 1.5m away, with the speakers about 1m away - I use them near field.
The hum is audible from about 3m away.
DC Blocker
I bought a ready-made DC blocker and mains filter, it didn't make any difference.
re 220V, 230V, 240V
230V is a EU fudge to harmonise voltages across the bloc
"For many years, mainland Western Europe has used a mains electricity supply rated at nominally 220VAC 50Hz. The UK used 240VAC 50Hz.
Currently, ALL Western European supplies are classified 230VAC. In reality there is no 230VAC supply unless you create one locally. 230VAC was a “standard” created during European "harmonisation" to give a single voltage standard across Western Europe, including UK and Irish Republic.
Although the ideal would have been to have a single voltage there were too many political, financial and technical obstacles to reduce UK voltage to European levels or to increase European voltage to UK levels, so a new standard was created to cover both. This was achieved by changing the tolerances of previously existing supply standards. UK voltage to 240VAC + 6% and - 10% and European to 220VAC +10% and -6% (thereby creating a manageable overlap) and we would call these two combined 230VAC, despite the fact that nobody was intentionally generating at 230VAC!"
(source: Schneider Electric)
Basically none of the transformers are rated used in the UK or EU are running at the correct voltage.
In reality most equipment are powered by SMPS and won't be an issue. Older 50Hz transformer PSU should be ok with the tolerance.
EI and toroidal transformers
Toroidal transformers are more compact, cheaper to make, lighter offer better regulation and contain the magnetic flux better, much wider bandwidth, to many megahertz dependent on the core material.
For AC mains PSU most of the above is great, except the last characteristic, we just want the 50/60Hz stuff too come through, not the RFI and noise.
EI are not as good as toroidals, except that they have lower bandwidth, which is a good thing for a AC mains PSU.
There are other topologies, such as R core.
Why do my toroidal transformers hum?
The reason the transformers in my amp are humming is because they are saturated.
Some manufacturers are better at making toroidal that don't hum so much.
The level of humming that mine are exhibiting is due to :
1) Higher than regular AC mains - though very much with-in specifications
2) Intended use - they're general purpose toroids
3) Manufacturing tolerances
4) Closer than normal placement
My test results
I have used a VARIAC (I have a 2.4KW rated one) to adjust the incoming voltage from 200V to 255V).
At 1m distance, suspended on soft foam.
200V - totally silent
210V - just perceptible
220V - tiny bit more hum
230V - can hear it 2m away
240V - can hear it 2-3m away
250V - can hear it over 3M away
255V - it's angry now
(I did this with the secondary disconnected to avoid any accidents)
What do I do now?
1) Ignore it
2) Place it further away
3) Have toroidal transformer made for quietness
What's different?
1) The core size is larger, allowing more windings to be used in the primary and secondary and the flux density to be lower at all operating voltages.
2) Interwinding screen
3) GOSS band
4) Encapsulation
Number 1 is what makes the most difference to audible noise
2 and 3 helps with mains-borne RFI
4 makes it look pretty
The cost?
For low quantities, about 25% more compared to generic transformers.
So around £60 (+vat) for a 250VA transformer wound on a 400VA core with multiple primary taps to fine-tune the resultant voltage.
The cost is worth it in my eyes (ears), I know some of us can spend thousands on cables (I don't).
I'll be putting an order in for a pair of 400VA cored toroids with all the trimmings including a selection of primary taps.