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hummmmming toroidal transformers

They are rated for 230V. 250VA each at 18-0-18V.

Incoming mains is 247-249V AC this afternoon at 50Hz.
That, right there, is your whole issue: your transformer cores are likely running into saturation: they are being run 9%+ over nominal voltage.

Try a bucking transformer to knock > 20VAC off the input voltage and see if that helps. You won't need much, a transformer with a single 24VAC/2A secondary of any kind will be more than enough -for the full power output capability of the system, and more. If you are into DIY, you might have something comparable in the bits box already - even 20v/1a will tell you what you need to know without compromise.


For everyone else, the issue with hairdryers is the common use of a single diode to give a 'lower power' setting - which makes it a c. 1kW, half-wave rectified load and so dumps a massive amount of even-harmonic distortion* on the distribution in your house... an utter mess that out to be outlawed (but it is v cheap and effective to manufacture.)


* this is actually what is usefully-meant by 'DC on the mains'- there really isn't, beyond a couple of tens of mV. 'DC filters' like the one pictured way above are really addressing this 'low frequency, even harmonics' issue.
 
That, right there, is your whole issue: your transformer cores are likely running into saturation: they are being run 9%+ over nominal voltage.

Try a bucking transformer to knock > 20VAC off the input voltage and see if that helps. You won't need much, a transformer with a single 24VAC/2A secondary of any kind will be more than enough -for the full power output capability of the system, and more. If you are into DIY, you might have something comparable in the bits box already - even 20v/1a will tell you what you need to know without compromise.


For everyone else, the issue with hairdryers is the common use of a single diode to give a 'lower power' setting - which makes it a c. 1kW, half-wave rectified load and so dumps a massive amount of even-harmonic distortion* on the distribution in your house... an utter mess that out to be outlawed (but it is v cheap and effective to manufacture.)


* this is actually what is usefully-meant by 'DC on the mains'- there really isn't, beyond a couple of tens of mV. 'DC filters' like the one pictured way above are really addressing this 'low frequency, even harmonics' issue.
Alleluia ! Running to my workshop now to grab a claw hammer to destroy my wife’s hair dryer !
 
Worked it out, it’s a combination of the higher input voltage and the transformer not having the saturation.
At 220v it’s just about audible, at 200v it’s silent.

I think a pair of better quality transformers (or bigger transformer) rated for 230V will sort it. It may be better to spec it for 240V.
In the mean time, I'll see if I have a 50VA 24V or 12V transformer kicking around.

 
I think some trafo makers are telling fibs when they say their transformers are designed for 230V; I think they're 220V transformers with a few less windings on the secondary so the voltage are correct, but the core gets saturated a lot quicker than I'd expect.

My evening mains voltage is 245V, seems to go up during the day. I wonder if it's anything to do with the solar PV installations?
 
What do you guys suggest for replacement transformer?
Airlink, Canterbury Windings (has he retired?), Toridy seems popular, though they're in Poland.

Is it worth going for dual mono? At the moment it's a shared PSU.
 
Terry at Canterbury Windings is semi retired but still makes lovely transformers, all be it with a 5 week order time. Toroidy wouldn't give me a quote at the time as Brexit caused issues. Tiger Toroids in this thread might also be an option.
 
I spoke to Steve @ Tigertoroids.
He suggested going for the next sized up in terms of core size and provide a series of taps on the primary to cater for my higher-than average mains AC.
 
Is it worth going for dual mono? At the moment it's a shared PSU.

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.
 
I bought an old Rotel amplifier that had a loud hum. A fishie suggested checking the input voltage and mains voltage. Turned out the transformer was set at 220V and the mains was 240V as opposed to a nominal standard of 230V. Switching the 220V fly lead for the 240V one reduced the hum significantly, as well as the working temperature of the amp.

There is still some hum at times that I attribute to DC on the mains. I'm going to try isolating or damping the base of the transformer rather than trying a DC blocker. I've looked at replacing the transformer (an enclosed toroidal with a nice resonant flat base and four mounting bolts); however, finding a replacement that'll fit has proven too much of a challenge.
 
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.
 
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Great in depth sleuthing and explanation firestorm.

Be interested (when done) if there is any sonic uplift.

My F6 & M2 will probably be having ‘transformer upgrades’ in the near future.
I have a few other amps which might benefit from a looking at too.
 
I had 300va made in 400va core to cure hum and specific primary voltages option if 240 or 250, Goss banded and specified for reduced hum and heat in operation.Tiger toroids were very helpful and suggested a few options to cure it.
Hight recommend them as I have said before they are the supplier to Rega and Rega stuff I have had did not hum or get red hot
 
That, right there, is your whole issue: your transformer cores are likely running into saturation: they are being run 9%+ over nominal voltage. ...
I am sure this is the case here but I am puzzled.

For the last 26 years we have known that in the European "230 V" mains region the maximum allowed voltage is 253.0 V. That "230 V" is a label for the real specification rather than its description. The maximum applies everywhere in the region AFAICS. My probably naïve engineering brain tells me that this is what you design a "230 V" region transformer for.

I am very unfamiliar with the design of transformers and their limits. However, I guess that for obvious historical reasons UK is the region's worst offender for in practice reaching close to the maximum. So is it correct to assume some/all transformer manufacturers might decide to cut the corner rather than design a device that's quiet at the region's maximum allowed voltage? If so, how does one select a transformer that will deal quietly with the UK. Look for one with a "240 V" rating I assume as in the post above, rather than a "230 V" label?
 
I am sure this is the case here but I am puzzled.

... Look for one with a "240 V" rating I assume as in the post above, rather than a "230 V" label?

For many applications the humming doesn't do any harm. For us, the golden ear crowd, any extraneous noise is regarded as interference and definitely not welcome.

You may get problems if the downstream components or SMPS has been designed without sufficient tolerance for possibility of incoming 253V AC.

So if your application demands quiet transformers, get it specced with a larger core and more turns to lower the flux density.
 


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