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Old 27th September 2012, 04:38 PM   #31
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Quote:
Originally Posted by luigilamarca View Post
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
DAC output should not have any DC offset. If it has, it should be fixed, not the transformer.
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Old 27th September 2012, 06:20 PM   #32
DF96 is offline DF96  England
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He may be talking about a DAC chip (not a DAC box) which often have a DC offset. Often there is another pin with the same offset to use as a reference. However, this thread is about transformer cores not DACs. He has already been asking about his DAC in another thread.
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Old 27th September 2012, 08:15 PM   #33
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HI, I know i wanted , to know how does a transformer when superpermalloy and 'crossed by a dc offset
I do not want information about the dac.
this will damage the preamplifier
however the matter and 'complex for me,
* I do not think I'll have 'a solution,
Thank you for your help.
luigi
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Old 27th September 2012, 09:38 PM   #34
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I don't think 1.7V DC offset drive transformer into saturation. However, you can decrease current through the winding of transformer, just connect 1K - 5K resistor in series with primary.
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Old 29th September 2012, 04:49 AM   #35
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Quote:
Originally Posted by benb View Post
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.
The purpose of the AC bias is to overcome the coercive force of the material, so that, as a given grain of magnetic material on the tape approaches the head, it is gradually exposed to a larger and larger, then smaller and smaller, loop on its B-H curve. Ideally, this loop should probably reach saturation, or close to it, forcing the loop to be centered around zero. (A number of materials can retain an average magnetization despite being exposed to an unbiased AC field greater than the coercivity -- in other words, degaussing doesn't always work!) The recording signal now looks like a DC offset, so as the tape material comes out of saturation, or the loop shrinks, it's forced off center to the desired direction.

To do the same thing with a transformer, you can't simply add a high frequency bias, implying the voltage is relatively small. In fact, the voltage has to be high, very high, because the frequency is also high. The reason laminated anything (iron or otherwise) is not used above a few kHz is because, even for the thinnest strips and laminations, eddy currents dominate, permeability drops and the core looks like a resistor. Applying HV HF AC will melt any iron-cored transformer. Still, you could do this with ferrite, which will increase size considerably for the same LF performance.

The audio signal will act to alternately saturate the transformer at HF, most likely introducing various IMD, which *will* be noticable (because as I said before, saturation affects signals greatly; minor variations in an already-huge permeability are negligible).

The problem with the tape analogy is, the tape comes out of the bias field as it passes. A transformer core is kind of just stuck there, and any attempt to "improve" it will only result in far more power, weight, cost, effort and distortion than, for instance, adding another tube or two and actively improving the transformer, for real, with negative feedback.

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Old 29th September 2012, 05:55 AM   #36
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Great Topic !!

Funny I have been researching this stuff all week and some how I missed the thread!

I googled "THD vs core material".

Here are a few links that I have found that may be of interest,

Magnetic Metals Nickel Lamination, Electromechanical Assemblies and Custom Annealing Service

Audio Transformers By Cinemag Inc.

Audio Transformer Application Notes

http://cinemag.biz/application_notes/AN-104.pdf

The app note is particularly interesting.
Also I have not yet tried to contact any of the companys for prices yet.

jer

Last edited by geraldfryjr; 29th September 2012 at 05:59 AM.
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Old 29th September 2012, 06:22 AM   #37
Yvesm is offline Yvesm  France
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See also in the good old RDH4 (published in 1953) page 214 and next

Note than distortion is also a matter of the internal impedance of the generator (here, one or more tube).

Yves.
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Old 2nd October 2012, 04:39 AM   #38
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Default Radiometal......

Beacon Radio Ltd, Auckland, - now long gone - marketed many transformers. In a range of many P-P output transformers. This firm for the more popular designs provided three variations for each. The same winding construction was assembled with either silicon, super-silicon, or radio-metal laminations.

Beacon's catalogue disclosed primary inductance figures measured at 5 volts, 20hz - Examples:

10 watt/10,000 ohm 46, 110, 220 henries
15 watt/4000 ohm 18, 35, 70 henries
15 watt/10,000 ohm 50, 85, 180 henries

High inductance certainly provides extended bass response!! Distortion - ???

My last winding effort using a 60mm stack of radio-metal laminations (1.25inch wide) and intended to provide for 20+ watts at 3,000 ohms PP reveals a droop of 0.4db at 10hz and a HF droop of 1.15db at 40 khz. No resonances are apparent below 200 khz.

Both Bambini and Bernards published a "Coil and Construction Manual". There are no equations - just tables relating to a 1000 ohm example. Further tables provide arithmetical adjustments to modify.......

To use radio=metal laminations their figures suggest: (a substitution for silicon laminations):

Turns - divide by 1.3

Max power - multiply by 2.3

Mid-band losses - divide by 1.7

LF cut-off - equal

I am just a DIY winder upon a Chinese mandrel with an accurate counter. I don't even use the gearing provided - every turn by hand where I want it to be.....lovely.

ps - Follow Yves' section-layouts......

Graeme
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Old 2nd October 2012, 09:51 PM   #39
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Quote:
Originally Posted by MGH View Post
Thanks Yvesm and LinuksGuru for the info on radiometal, which appears to be commercially available as 45% nickel. I think the 55% radiometal AudioNote uses is their own formulation, as I can't find any information on it except on the AN site.
The resistivity of Radiometal is 55 microhm cm. I infer that Audionote is using that to name their alloy rather than nickel composition.

BTW - The ad copy is mostly mumbo jumbo, but have you read ads for speaker wire, USB cables and interconnects lately? These guys are tame in comparison.
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Old 2nd October 2012, 09:57 PM   #40
BudP is offline BudP  United States
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Quote:
BTW - The ad copy is mostly mumbo jumbo, but have you read ads for speaker wire, USB cables and interconnects lately? These guys are tame in comparison.
Or gotten involved in the EnABL or Electron Pool controversies, or the rotating triangle bar speaker? Or perhaps dipped into the After the Ariel thread from Lynn Olson? Lots more interesting and strange topics in this site.
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