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Old 27th August 2009, 03:39 PM   #1
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Question ??? Output Transformer - Silicon Steel or Amorphous

Hi, Tube folks,

Currently there are 2 major flavors of audio output transformers (both SE and PP) - with silicon steel and amorphous cores.

Amorphous cores are ferromagnetic alloys based on iron (73.5%), silicon (13.5%), boron (9%), niobium (3%) and copper (1%)). Depending on the type of heat treatment after quenching they may have a rectangular (Br/Bs = 0,2-0,9), linear or circular hysteresis loop. They allow to build smaller transformers with given power rating with lower losses, high saturation flux (up to 1.56 Tesla), etc.

The question is - which one would you suggest? Different people state different things - some say only silicon steel (because of higher distortions of amorphous cores - IMHO a somewhat unproven statement), other say "I DON’T EVER WANT TO GO BACK to silicon steel".

Any suggestion(s) are greatly appreciated.

Last edited by LinuksGuru; 5th May 2013 at 12:02 PM.
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Old 27th August 2009, 06:40 PM   #2
kmaier is offline kmaier  United States
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I don't want to appear as being too biased on the subject, but here's a link from the US distributor's site who imports the Hashimoto line of transformers:

http://tube-amps.net/Technical_Aspects.htm

They purposely avoid permalloy and amorphous cores and have some explanations as to why they use Orient Core Hi-B steel. The company has a long history (aka Sansui) and I would note that the quality of their current product line in excellent in every detail.

Regards, KM
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Old 27th August 2009, 07:05 PM   #3
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Originally Posted by kmaier View Post
I don't want to appear as being too biased on the subject, but here's a link from the US distributor's site who imports the Hashimoto line of transformers:
http://tube-amps.net/Technical_Aspects.htm
They purposely avoid permalloy and amorphous cores and have some explanations as to why they use Orient Core Hi-B steel. The company has a long history (aka Sansui) and I would note that the quality of their current product line in excellent in every detail.
Regards, KM
Thanks for the link, Kmailer! Orient Core Hi-B is an enhanced silicon steel with lower loss. So, its still a silicon steel, and not another type of material.
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Old 27th August 2009, 07:13 PM   #4
kmaier is offline kmaier  United States
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Quote:
Originally Posted by LinuksGuru View Post
Thanks for the link, Kmailer! Orient Core Hi-B is an enhanced silicon steel with lower loss. So, its still a silicon steel, and not another type of material.
Yes it is... an enhanced directional silicon steel.

Regards, KM
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Old 28th August 2009, 12:32 AM   #5
BudP is offline BudP  United States
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The issue is not just the steel.

Amorphous core has excellent characteristics. The BH curve, saturation induced polarized core moment, until H goes opposite phase and the mag field crashes through zero to catch up, think zero crossing distortion here, is greatly reduced. Unfortunately you end up having to limit the E Field coupling to allow enough leakage inductance and distributed capacitance to keep the frequency response from forming a high Q resonant peak at 36 kHz or so. The core is also active out to about 18 kHz in a direct power transform function.

M6 or M3 commercial grade silicon steel does not have the BH curve, saturation induced polarization release of amorphous core. This causes a higher level of cross over distortion. This can be mediated with proper construction techniques that are the antithesis of those used for power transformers. Once implemented the two cores have very similar back wave performance.

The commercial core does benefit from allowing a far more efficient capacitive coupling scheme to be used, without encountering the resonance peak problems than beset amorphous core. This state of affairs also allows a lower dielectric constant material to be used as the dielectric barrier across all antenna events in the coil, meaning all events.

The difference in sonic’s is interesting. An amorphous core OPT for PP will be very clear, have great transient response and excellent tonality. However, they are somewhat one dimensional in that most of the fine gradient detail that provides internal note structure and makes transient noises into musical events, has been stripped away by the lack of E Field coupling and the higher dielectric constant materials used in the coils, essentially half of the information must be lost to avoid frequency response peaks.

An M3 commercial core, properly constructed for audio purposes, will sound slightly softer than an Amorphous core transformer. There is after all more distortion, and when comparing 99.997% correct signals (Amorphous) with 99.993% correct signals (M3), this is what you should expect. However, there can be a great deal more internal information made available, for all musical signals, because you do not have to throw away half of the signal and the antenna event is actually encouraged during it's E Field portion.

In addition the M3 and M6 core are basically only providing a ferrous bounding box for the coil antenna event above 400 Hz. The material still responds but the losses are so high, with extended frequencies, that it neither adds nor subtracts to the signal passing from coil to coil, so long as that core construction issue has been dealt with. Neither amorphous core not M3 core is "better", they have differing strengths, and when both are used properly either will provide superb audio, within the limitations found above, and their pricing will be about the same too. An M6 core unit, with more distortion and only slightly less information, without quite the refinement of either of the other materials, is a much less expensive alternative, with very few drawbacks.

Bud
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Old 28th August 2009, 01:02 PM   #6
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Originally Posted by BudP View Post
The issue is not just the steel.

Unfortunately you end up having to limit the E Field coupling to allow enough leakage inductance and distributed capacitance to keep the frequency response from forming a high Q resonant peak at 36 kHz or so. The core is also active out to about 18 kHz in a direct power transform function.

An amorphous core OPT for PP will be very clear, have great transient response and excellent tonality. However, they are somewhat one dimensional in that most of the fine gradient detail that provides internal note structure and makes transient noises into musical events, has been stripped away by the lack of E Field coupling and the higher dielectric constant materials used in the coils, essentially half of the information must be lost to avoid frequency response peaks.

Bud
Thanks a LOT, Bud! I never expected SO comprehensive reply. I did not understood entirely mechanism of loss of information in amorphous core. So, your suggestion is to use M3 silicon steel? Do you have any info about Orient Core Hi-B silicon steel used by Japanese companies?

I found that some Luxman audio transformers have frequency response 10Hz - 100,000 KHz, not 100% sure, it may be a seller mistake. What kind of material they used?
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Old 28th August 2009, 04:58 PM   #7
kmaier is offline kmaier  United States
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Published specs can be misleading unless they have some detail around the spec, meaning... what was the power level used, how they drove the transformer (dc current/imbalance for PP or dc current for SE), etc. I'm using a Hashimoto H-507S with a 45 DHT design. Published spec is out to 100KHz within 3dB. The amp does measure -1dB at 50KHz at 1-watt output and about 35ma of current in the primary winding. The circuit is zero-feedback and I use the 5K tap for the primary winding and the 16-ohm tap on the secondary. Measured distortion for 50KHz @ 1-watt is actually lower than 1KHz @ 1-watt.

Regards, KM
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Old 29th August 2009, 03:29 AM   #8
jlsem is offline jlsem  United States
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When you are talking about crossover distortion, you are referring to push-pull output transformers, correct?

John
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Old 29th August 2009, 04:01 AM   #9
BudP is offline BudP  United States
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Not entirely no. B/H curve saturation occurs even in SE OPT's, though not to the degree that it occurs in PP, due to the typical gap.

Core gap in E/I transformers is also the problem with an E/I SE OPT, the larger the gap the longer it will take for core polarity to catch up with the back wave of the driving signal. C core gaps are driven on both sides of the gap thus eliminating most of this latency, their drawback being the nonlinear flux created in the window, by having a gap in the center of the winding

For the most part, core is your enemy in signal transformers, above 400 Hz, even with amorphous core. If you construct an E/I core with the same distributed gap that works so well in PP E/I core, the core will actually help by passively demagnetizing on the back wave, after a saturation peak has polarized the core. This method actually works so well that it is dangerous to use it without a gap, in a SE OPT.

The same sonic values hold true, as in PP, between amorphous core and M3 E/I core, though i don't find them as noticeable.

Probably the two best providers of custom designed amorphous core SE OPT's are Intact Audio and Tribute Audio. O-Netics, the company I work for, is the only provider of partial self demagnetizing E/I core structures that I know of. I am sure there will be others in time, we do tend to pirate from one another as occasion permits.

Bud
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Old 29th August 2009, 02:01 PM   #10
jlsem is offline jlsem  United States
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But in a single-ended transformer, the core never demagnetizes (i.e., the field never collapses) because of the ever constant DC component. The AC signal manifests itself as minor AC loops along the DC magnetization curve. The AC loops may breech the the upper left hand quadrant of the BH graph with a large signal but the incremental permeability remains constant, so there is very little distortion and no "crossover" distortion to speak of.

John
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