The Marantz PM7000 core that I just measured uses a copper GOSS band. If you pick the transformer up and rotate it’s position in the amp housing you can hear the hum level come up (headphones on the speaker output). It’s a good quality component - also vacuum impregnated and no or very little mechanical noise. There are large mag fields associated with EI transformers. A torroid has almost no field and if you put a GOSS band on it it is very, very quiet. I have a Phono stage about 7 cm away from a 500 VA (low flux density) power transformer without noise problems.
I worked in Japan for 5 years with companies like Sony, Panasonic etc supplying IC’s. They are driven by cost and an EI is cheaper to make than a torroid and that’s the reason they still dominate in high volume consumer electronics.
Lower EI in-rush currents of course also make sense in this market. But a lot of stuff is SMPS anyway.
Low pri-sec interwinding capacitance is important to keep common mode noise coupling across the transformer in-Check.
I measured the CM bandwidth of a 500 VA torroid and it was flat from about 40Hz to 3 MHz (limit of my generator) which makes sense, since it’s just a c. 500 pF capacitor.
The normal mode bandwidth by the way was 40 Hz to 60 kHz. EI won’t be as wide as this in normal mode, but CM will be the same as the torroid.
I am curious who supplies something like that.
Maybe some audiophile oriented company introducing something "new"? (like for example Audio Note who came up with a c-core transformer made with three c-cores; really hilarious
).A dual bobbin EI transformer simply does not offer an advantage over a UI transformer (which are meant for dual bobbin transformers).
my comments are based on the hundreds of ss amps of japanese manufacture that came by my shop for repairs over the years, i am done repairing amps now..m
the better ones will have both the mu metal shields and belly bands....
the first time i saw belly bands in a power traffo was around 1960 in a popular electronics magazine that feature a receiver using germanium power transistors...
yes, traffo orientation in any amp with EI's is very critical compared to toroids...
but mind you, Mark Levinson using two 1kva+ toroids tweaked the orientation of their traffos for minimal noise by light rotation on their axis...
toroids have such a wide bandwidth owing to its very tight coupling so that noise from power line primary are easily coupled, but there are ways to mitigate those...
nowadays, i employ techniques found in ATX psu and TV sets to filter out line noise, passive power factor corrections....common mode chokes, NTC in series with the line, an MOV across the line and after the fuse, and primary winding RC damping...
the better ones will have both the mu metal shields and belly bands....
the first time i saw belly bands in a power traffo was around 1960 in a popular electronics magazine that feature a receiver using germanium power transistors...
yes, traffo orientation in any amp with EI's is very critical compared to toroids...
but mind you, Mark Levinson using two 1kva+ toroids tweaked the orientation of their traffos for minimal noise by light rotation on their axis...
toroids have such a wide bandwidth owing to its very tight coupling so that noise from power line primary are easily coupled, but there are ways to mitigate those...
nowadays, i employ techniques found in ATX psu and TV sets to filter out line noise, passive power factor corrections....common mode chokes, NTC in series with the line, an MOV across the line and after the fuse, and primary winding RC damping...
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I am curious who supplies something like that.
Maybe some audiophile oriented company introducing something "new"? (like for example Audio Note who came up with a c-core transformer made with three c-cores; really hilarious
A dual bobbin EI transformer simply does not offer an advantage over a UI transformer (which are meant for dual bobbin transformers).
i do use dual bay bobbins in my EI power traffo build, 1 3/4 in cl x 3 inch stack..
sectioning as mention in RDH 4 reduce capacitance by a factor of number of sections, in this case 2.....
I guess you mean one bobbin with a partition halfway.
With dual bobbin I mean two separate bobbins, one on each leg of a UI or c-core.
yes....
with UI, the very wide distance between coils made for low interwinding capacitance if indeed the primary and secondary are on each leg of the U...
but if you did your UI in such a way that each leg had 1/2 primary and 1/2 secondary atop of each other, then no advantage is gained imho...
except perhaps lower magnetizing currents owing the long magnetic path lengths..
the possibility of using bigger wires owing to a bigger winding window than an EI...
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Exactly the same as EI transformer except that pieces of steel sheet are cut in the form of letters M and D.
i doubt it, the way many japanese amplifier traffos are made with nylon bobbins wherein you can separate the primary coil from the secondary coils, that way it is easy to separate them....i have converted several japanese standard, 100vac primary traffos to 230 volts easily... i never see any screens aside from a belly band...
It looks like this: (source: Waasner Elektro Blechteile)
So it is not a lossless geometry.
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Thanks Tony I may try that. I presume I would have to remove the tape? I use a soft start circuit with NTCs that are shorted with a relay after a delay.
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I unscrewed the transformer and rotated it to check the radiated fields. The point is EI’s have much worse mag fields than torroids.
Most commercial transformers come vacuum impregnated. But if you have an old transformer it may not be.
You could find a local winder and ask them to do it for you - how old is the transformer?
i can trade off efficiency over temp rise and long term reliability..
this means operating at lower flux densities...
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