• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

R-Core Output Trans from ICL

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
diyAudio Senior Member
Joined 2002
R-Core OPT

Hello Reinhard,

This is new info to me too.
Actually ICL (a Siemens subsidiary) is the company that host Softone Inc.'s website.

Softone, Inc.
11-5, Sakuradai, Aoba-ku, Yokohama, Kanagawa, 227-0061, Japan

E-mail address: audio@icl.co.jp
Facsimile : +81-45-989-4642

I suggest e-mailing them?

What is R core Output Transformer?
R core power transformers are now increasingly introduced for the high-end HiFi components because of its excellent technical advantages. R core is of non-cut construction and has excellent magnetic properties. The magnetic core used for audio output transformer has evolved from EI core, cut core, and to toroidal core achieving successful results to improve the performance of the transformer. R core has several advantages over toroidal core that has been evaluated as the best. In fact, R core enables further technical improvements of the audio output transformer. We have designed this R core audio output transformer and carried out the performance tests for final product. The product packaging is made by Kitamura Kiden Co., Ltd., an originator of the R core transformer.

Best regards,
diyAudio Senior Member
Joined 2002


No idea why they called it R-core.
The idea isn't new but to me at least it's the first time I actually see it implemented.
It does away with any possible stray fields between the EI iron sheets by forming an "amorphous" double U core.Any vibration is also removed by the same technique.

The only other company I know of that implemented the idea was
(is ?) Audiotekne from Japan.
You just need to know that the Audionote pricing looks like peanuts compared to theirs.
The materials they used were Superpermalloy combined with slowly annealed sliver wire.
All stages were transformer coupled.
Just the thing I'm sure you'd kill for.
Have a look at the R-core OPT :


Joined 2001
Paid Member
Re: R-Core

These OPTs were brought up on the JoeList a while back.

I quote Phil:
It is a modified toroid, formed in a "racetrack" shape, with two long straight center sections and two semi-circles on each end. In addition, the tape is shaped or tapered, very narrow at both ends, reaching full width in the center. This causes the core to have a circular cross-section after the tape is wound. A bobbin is then assembled around the core, just loose enough to turn freely. The bobbin is then turned while applying wire or foil, allowing the coils to be wound in a normal manner, but with the super small air-gap typical of a toroid.

Of course, there are a lot of situations where you want an air-gap, but it is perfect for a parafeed design, with its virtually zero-DC current. Also, there may be weird, unforseen advantages, because as a general rule, C-core trannys are very often reported to "sound better" than E-core trannys, even when they have the same air-gap. Certainly C-core and R-core trannys, which in many ways are VERY similar, have a grain that is always oriented in the "correct" direction, along the path of the magnetic lines. The magnetic lines in E-cores trannys, in contrast, must cross grain boundaries, although I think there are also some theoretical advantages for E-cores as well.

Now that I think about it, I guess the best description of an R-core is that it is a C-core with no air-gap (it never gets cut and lapped), and with a round cross-section, allowing a bobbin to be assembled around it, so that the coils can be normally wound.

and a few comments from dave slagle
i think calling it an ungapped C-Core is a fair asessment...

-it will have a slightly longer magnetic path than a toroid
-it will have a smaller Ac (core area) than a C-core, but the lack of gap may make up for that and then some.
-it has a round bobbin, so your dead soft wire isn't work hardened with the bends on a square bobbin
-i have no idea how the cores are made, but suspect phil is right with the slitting (the one i had was not machined round and you couls see the "steps" of the layers) so that pretty much requires fewer layres of thick materials to avoid slitting a mile of tape per trannie so eddy current losses may be problematic... i suspect going to a thinner material would get costly quick, and material waste from the slitting will also add to the cost (maybe the tape could be slit in a scrapless manner??)

i suspect their origin is for power trannies and the goal was to keep manufacturing costs down... they are much easier to wind than toroids, and don't require the assembly the C oe EI cores do... there is an additional cost for different tooling etc.. but once ammortized you will pay a bit more for the core, but will make it up in other savings???

Someone on that list bought some, but hasn't reported any findings yet.

Re: Re: R-Core

Hi dave,

You have pretty much covered it and I would also like to add a few things:

The R core has advantage of lower copper losses. This is due to
the coils optimal circular shape with proper layer winding. Toroids
really lose out in this regard with very poor filling factor.

Another advantage over toroid is better RF isolation or smaller
bandwidth if wound with ES shield. ES shield for Toroids have
to be wound on like a coil and as such have a certain inductance
which renders them not very effective at frequencies above a few
100k. With the R core (as with EI or C) the ES shield can be made
1 winding of sheet copper with very low effective inductance.

Obviously EI wound with split bobbin would probably have the
best RF isolation but conversly has very poor regulation... no
free lunch!

I have priced R cores locally some time ago but they were not
price competitive with any other types however this may not be
an issue with hi end applications.

Best regards,

Terry Demol
I've been using the R-cores from Kitamura as power transformers for some time now. They sound pretty good, AC powerline garbage that causes other transformers to hum, buzz or vibrate doesn't bother them, and there have been no failures to date (and I've used several hundred of them). The only thing possibly against them is that for a given VA rating, they are somewhat larger than a good toroidal would be (Ulveco gets my vote here).

I haven't put them to use as output transformers, but at least I can vouch for their performance as power trannies.

hth, jonathan carr
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.