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Old 27th September 2012, 02:56 AM   #21
benb is offline benb  United States
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I quoted a few posts and wanted to add to some off-topic banter (at least the phrase "double-blind test" on this forum doesn't get replaced with a "censored!" smilie or get the poster banned), but I've wondered something for a lot of years now, and it's perhaps pertinent to ask now that tape recording is gone as a commercial activity, and before the idea becomes totally lost to the confines of dead trees (and PDF scans with "RDH4" in their filenames).

Magnetic tape recording uses (or used) an ultrasonic "AC bias" to linearize the tape magnetization curve and eliminate the horrible "zero crossing" distortion that results without it. Transformers aren't anywhere nearly as bad in this respect, but the magnetization curve is still there, even in the best audio transformers. An ultrasonic "bias," perhaps added by a third winding, could effectively make this distortion go away, or reduce it by one or two orders of magnitude. The bias signal could be isolated from the input and output by putting a parallel L-C trap in series with each winding.

Has this ever been done before? Are there any negatives other than the extra circuitry? I wonder if this might add some low-level wide-band noise from the domains switching at perhaps slightly different magnetization levels each time.

Have I ever asked about this before? It's been in the back of my mind for perhaps ten years or so.

Years ago I heard a recording - actually, two recordings from the same microphone at the same time, one was with the mic's output directly to a preamp input. The mic was also connected to a Jensen 1:1 audio transformer and then to the same model preamp for the other recording. It took me a few times of listening and comparing the two recordings, but once I knew what to "listen for" I could fairly easily hear the difference.
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Old 27th September 2012, 04:18 AM   #22
BudP is offline BudP  United States
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benb you will want to communicate with John Attwod here

ClariSonus - Clear and enjoyable sound

John has looked at your question and has an amplifier that he explored some of these territories with. Ask, he will be delighted someone cares.

As for the "sound" of core material. Well. Commercial manganese iron, the M series of grain and non grain oriented metals, is all done with power transform at about 440 Hz or thereabouts. Depends upon chemistry, thickness and annealing correctly. So, except for controlling the rise time involved in supporting fields between primary and secondary antennas, it is right out of the equation. This is not true of 45/55% nickle, which will still transform power out to approximately 3.5 kHz. This was the material of choice in the old days of telephones.... you know, the black plastic thingys in some museums? 80% Nickle is good to about 10 kHz and metallic glasses can do 28 kHz. That rise time issue will make even double blind testing defeat-able as it is audible as an increase "softness" to leading edge information, as you transit from amorphous to M50 right across the 20 to 20kHz range. Still, not a big deal.

The real difference in how audio transformers perform comes from the coil and it's construction and how the B Field antenna events are handled, to a degree. The real tell is how much of the capacitive coupling area, vs volume of distributed capacitance you can use with a given core material. You might take note of amorphous core output transformers not having concentric windings as a guide.

And the final areas of interest involve not assuming the coil is a lumped parameter of any sort and that core can be used in such a manner that it will passively self demagnetize. Thereby making the polarization caused by saturation a moot point. Changes in these parameters make rather large differences in perceived audio characteristics and will definitely defeat a double blind test.

Bud
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Last edited by BudP; 27th September 2012 at 04:20 AM.
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Old 27th September 2012, 07:08 AM   #23
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hi, please one question for transformer :

it 's true that a current DC offset can cause transformer saturation?
if it 's true that for all transformers or just some special materials
permalloy or something?
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Old 27th September 2012, 08:42 AM   #24
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Yes, it can. Push pull transformers are usually designed to sustain several mA of DC current (5 - 10mA). This is true for all materials, higher permeability -> lower tolerance to DC offset, and opposite.

Air gap, either fixed, distributed or quasi-distributed. is used to prevent saturation under DC offset.
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Old 27th September 2012, 08:50 AM   #25
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therefore ..a DC offset 1,7 volt in superpermalloy transformer is highly damaging: (: (
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Old 27th September 2012, 10:20 AM   #26
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The influence of DC offset measured in A/turns-cm, or A/m, and resulting flux density B, not V.
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Old 27th September 2012, 11:53 AM   #27
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how I misure it ?

plaese help my.
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Old 27th September 2012, 12:40 PM   #28
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You have to learn basic theory first.
There is a plenty of material out there covering these issues.
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Old 27th September 2012, 01:00 PM   #29
DF96 is offline DF96  England
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Remember when talking about transformer cores and distortion that the core, to a first approximation, only sees the difference between primary (turns x current) and secondary (turns x current). This is why we can make a (fairly) linear transformer from a (fairly) non-linear core. This is quite different from a tape head or the tape itself.
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Old 27th September 2012, 02:40 PM   #30
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Quote:
Originally Posted by LinuksGuru View Post
You have to learn basic theory first.
There is a plenty of material out there covering these issues.
I assumed that it is not a simple thing .....
so .... 'do not know' what to do if you connect or less
* my dac to the preamp input transformer superpermalloy

thanks luigi
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