I wasn't referring to harmonics of the mains frequency no, even those are an issue if they go high enough in frequency. I was thinking about general mains noise which is often induced on the mains by (nowadays ubiquitous) switching power supplies with their own oscillators running from ~30kHz into the 100's of kHz. The input rectifiers in an SMPSU also contribute bursts of HF noise as they switch off at the mains frequency. Of course commercial SMPSUs contain some filtering to mitigate this but it doesn't eliminate it completely. SMPSUs are subject to EMC regulations for conducted mains noise in the region ~10kHz to 30MHz.
It's usually the opposite.
EI cores have strict window dimensions, which limits how much copper can you fit there; toroids are way more relaxed in that aspect.
I think that is probably 20-200KHz noise on the mains waveform coming from switching supplies. My experience is that the voltage noise on the secondary waveform is rarely an issue (with good circuit routing) but the ultrasonic noise is usually radiated into circuits from the leakage flux of the transformer or mains wires if they are not run together.
The noise can also be coupled through the electric field, in which case the mains wiring and transformer should be shielded, but if the transformer has significant leakage inductance a capacitor across the secondary can attenuate this as well. However if that leakage inductance couples through the air, you multiply your coupled flux noise by many times in order to achieve this...
The noise can also be coupled through the electric field, in which case the mains wiring and transformer should be shielded, but if the transformer has significant leakage inductance a capacitor across the secondary can attenuate this as well. However if that leakage inductance couples through the air, you multiply your coupled flux noise by many times in order to achieve this...
I've tried smallish toroids (30VA or so) as output trafos, with custom low voltage primary (30VAC) from a mains transformer vendor. The bandwidth was just about adequate for the bass/mid of an active speaker, somewhere around 4kHz I recall.
Dears,
I appreciate very much that this post got many qualified responses.
Also appreciate criticism on my views, if I knew how to solve this I wouldn't ask 😊. I'll like all replys here, sure it's not only me with this issue, everyone here is using power toroids.
PS, I read Rod Elliots articles on this subject few times.
For interest, here are 2 empirical tests I did early this morning (I can do only try - error tests as I'm not scientist in this subject):
Mains DC in my house is negligible :this is DC after 120k resistor and 10mf capacitor:
But my mains is going around 238 volts.
Secondly, in front I connected small 50VA 18 VA secondary transformer as step down that is effectively reducing supply mains to buzzy big toroid to cca 217 V.
This made my sealed 600VA trafo going much more quiet, very ok, but still possible to hear.
Than I connected another ( infamous for buzz) 600VA toroid garbage that is laying around, buzz iz also there but reduced a lot, almost usable.
Summary:, my empirical test shows reducing mains voltage is taking buzz down, with cost of efficiency naturally.
Potting trafo also helps a lot, even many say it's not curing of the cause but symptom.
As per picture above, seems I have no DC problem to worry about.
I would support you (members with scientific background and experience in this subject) to bring this question to resolution. Just buying trafos from reliable source is not full answer, but cure. Diyers like to understand what's happening.
I appreciate very much that this post got many qualified responses.
Also appreciate criticism on my views, if I knew how to solve this I wouldn't ask 😊. I'll like all replys here, sure it's not only me with this issue, everyone here is using power toroids.
PS, I read Rod Elliots articles on this subject few times.
For interest, here are 2 empirical tests I did early this morning (I can do only try - error tests as I'm not scientist in this subject):
Mains DC in my house is negligible :this is DC after 120k resistor and 10mf capacitor:
But my mains is going around 238 volts.
Secondly, in front I connected small 50VA 18 VA secondary transformer as step down that is effectively reducing supply mains to buzzy big toroid to cca 217 V.
This made my sealed 600VA trafo going much more quiet, very ok, but still possible to hear.
Than I connected another ( infamous for buzz) 600VA toroid garbage that is laying around, buzz iz also there but reduced a lot, almost usable.
Summary:, my empirical test shows reducing mains voltage is taking buzz down, with cost of efficiency naturally.
Potting trafo also helps a lot, even many say it's not curing of the cause but symptom.
As per picture above, seems I have no DC problem to worry about.
I would support you (members with scientific background and experience in this subject) to bring this question to resolution. Just buying trafos from reliable source is not full answer, but cure. Diyers like to understand what's happening.
If you put a very small transformer on the right table, it can make a lot of noise. If you take it in your hand the noise is gone and you have to hold it at your ear to hear anything. This is, beside from low quality and DC the next option for loud buzz.
Anyway, measuring DC must be done over time, as it is something that is never has a constant value.
Anyway, measuring DC must be done over time, as it is something that is never has a constant value.
Can you use a variac to further reduce the supply voltage and lower the buzz to negligible level?
Since the core size has increased by 20%, is it possible to increase the number of turns in the winding?
Magnetostriction can also cause some noise. Sometimes a transformer needs to be soft mounted, or at least mounted in a way that it does not flex the mounting panels. I saw a transformer mounted in a metal "tray" in an Onkyo amp, I wonder if this is why.
Menno van der Veen (who Jan Didden interviewed a few months ago) has been using toroidal OP transformers for years. I think his first design was published in Elector over 20 years ago. They may not have the ultimate performance compared to EI audio transformers, but they still perform very well and have good power bandwidths. See Susan Parker’s designs as well for some very unique and elegant designs.
https://www.mennovanderveen.nl/index.php/nl/
https://www.mennovanderveen.nl/index.php/nl/
Hope you notice it's an idiom.
Maybe lost it in translation. 😊
Here 🙂
Frank Sinatra is not actually saying he will sit in front of a typewriter and write a "paper" novel but that "he has-a lot-to-say" about his Love.
Same as Brian Gladstone has a lot to say about Toroids 😊
Glad he offered to share his experience with us 👍🏻
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I guess the idea is to leave windings the same, and get core working at a lower flux density, which will improve losses, regulation, and lower buzz.
Besides that, larger cores allow for lesser turns.
Dears,
Regarding power trafos buzz:
Thanks again to all for good suggestions!
Last couple of days I did some testing in my house with various toroids, few from my own orders to supplier, few from commercial amps. VA rating from 300 to 1,600VA. Results are all the same regardless the trafo in question:
As mentioned before; toroid made for British market with 240V primary and commercial EI trafos with welded plates have significantly much less buzz than other toroids.
When I think of it, those buzzy toroids are in best case made for 230V, and in worst case for 220V primary, makes sense?
Regarding power trafos buzz:
Thanks again to all for good suggestions!
Last couple of days I did some testing in my house with various toroids, few from my own orders to supplier, few from commercial amps. VA rating from 300 to 1,600VA. Results are all the same regardless the trafo in question:
- DC in mains; I increased number of diodes by making 3 x bridge rectifiers in series on my DC blocker: no result at all!. Thanks for many pointing at this problem, but it seems its not an issue in my case, measurements also confirm that.
- I reduced mains voltage; and that works well even it is not eliminating problem completely. I don't have Variac unfortunately, instead I made buckling transformer exactly as Rod Elliot described here in picture 4: https://sound-au.com/articles/buck-xfmr.htm . This brought mains voltage to approx 217 Volts (instead of almost 240V that I normally have) and the noise in al tested trafos is much less, acceptable but not completely eliminated.
As mentioned before; toroid made for British market with 240V primary and commercial EI trafos with welded plates have significantly much less buzz than other toroids.
When I think of it, those buzzy toroids are in best case made for 230V, and in worst case for 220V primary, makes sense?