Hi CJ,
You wrote
I just found out the struture of the "magical" Western Electric 111C, or whatever the famous model number is. It is a torroid core, of all things, with four seperate coils. Tape wound of course, not ferrite.
So mechanical geometry can be a factor when it comes to the sound of a transformer.
Thanks much for sharing the information. Do you happen to have or have access to any additional information about the WE transformer?
Like whether the separate sections are themselves subdivided (like the nice Beyer pic) or just one big layered section?
Like the material used in the core "tape"? Si Steel, Nickel, Nickel-steel, mu-metal, plain soft iron or nickel-iron alloy? Fairly thick or thin tape wound for the core?
Maybe estimated wire guages?
Any actual measures of the primary inductance?
I know I may be asking for the moon here, but I think the more we know about all the variables of "the good ones", the more our knowledge grows about how to select, spec, or design a transformer for any particular application.
I hope it's OK if I ask for this sort of information here, and hope this stimulates others to share what they may happen to know, even if none of you happen to have personally have first hand access to a WE or other really revered audio transformer. It does seem like there are a lot of knowledgeable and helpful folks around here who also have an interest in sorting out the complexities of the "simple" audio transformer. I appreciate you all sharing your knowledge and thoughts on this matter.
And Ted,
you said
Now we come to the interesting bit.... At the low frequency end, the performance limits are governed by the core material, the operating level and the winding resistance; the use of mu-metal in the core allows lower frequency operation, but when the core saturates, it does so suddenly, and audibly. more simple iron and the bottom end is smoother.
I think most people here would agree with you that this effect of core saturation and the many differences between various core materials, the overall size and structure of the core (including geometries as CJ called it), all have some role in how transformers transform audio signals, especially how they react when pushed a bit. I certainly agree that the saturation characteristic is an "interesting bit." I wish I understood it better.
I would find it most interesting personally if you would be willing to share any other insights or learnings you may have along the lines of what you know and/or have come to suspect are the effects of the various variables.
I feel like we are all too dependent on what the various engineers at transformer companies know about designing a good sounding transformer, or how they build custom and catalog-standardized designs because "that's the way we make those".
I wonder if at least some of the revered transformers may just be ones somebody who learned a bit about the sonics finally just lucked onto on that particular design, and/or perhaps something designed by someone who may not have passed on what he learned 40 or 50 years ago. So much concentration in the transformer field now seems to be on designing for where the volume is ... power supplies (mostly switching), still some microphone and line transformers, but I don't get the impression (correct me if I'm wrong) that there are many papers being published these days on the subtleties of audio transformer design. How to dodge using them, yeah. Maybe it's proprietary stuff, or maybe just no one really finds a place to brainstorm how to make sonically-pleasing transformers.
And here's my 2 cents worth ... we all know about the overall bass level decreasing as level increases and the transformer starts to saturate the core some. And that the satuaration is a form of soft limiting that generates harmonics. All that is undoubtedly true, even obvious. But we are passing complex waveforms through the transformer, and it seems to me, that when the low frequency level starts driving the core into saturation, that there must be some - probably complex and assymetrical - effect on the simultaneous transmission of the midrange frequencies "riding" on the saturating peaks of the (perhaps) fundamental or harmonically-related frequency of the sound passing through the transformer. Probably generating some second harmonic distortion of the midrange frequencies with a periodicity related to the frequency of the saturating peaks of the overall signal amplitude - or perhaps just the amplitude peaks of certain frequencies where the core is most subject - or perhaps suceptible, to saturation.
In any case, the soft clipping of gracefully saturating transformers is not the same sonically as electronic soft clipping, agreed all?
Thanks for the stimulating discussion.
"Tut, tut"s OK. <grin>
