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Author Topic: lamination material for transformers and chokes  (Read 9717 times)

maxdimario

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lamination material for transformers and chokes
« on: December 11, 2006, 11:32:28 pm »

Apart from the wire and winding techniques, lamination or core material has a marked influence on the sonic end-result of transformers and chokes.

I was wondering what sonic characteristics different metals have, not considering the various winding methods.

nickel? iron? mu-metal? what are the metals available today for transformers and what is their sonic signature?

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dcollins

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Re: lamination material for transformers and chokes
« Reply #1 on: December 12, 2006, 01:34:44 am »

maxdimario wrote on Mon, 11 December 2006 20:32

Apart from the wire and winding techniques, lamination or core material has a marked influence on the sonic end-result of transformers and chokes.

I was wondering what sonic characteristics different metals have, not considering the various winding methods.

nickel? iron? mu-metal? what are the metals available today for transformers and what is their sonic signature?




Oh, yes.

Absolutely.

DC

maxdimario

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Re: lamination material for transformers and chokes
« Reply #2 on: December 13, 2006, 10:36:36 pm »

hmm..
does that mean I can make my own transformers with any old laminations and they will do just as well?

It's relatively easy to copy windings.
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Oliver Archut

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Re: lamination material for transformers and chokes
« Reply #3 on: December 13, 2006, 11:28:50 pm »

Hello Max,

what about the sound of a transformer?

The sound of a transformer is mostly in the metal. Why? That is a kind of difficult question.
Here is one good example, what we refer to as Mu-Metal today was original developed by the Magnetic Shield corporation and is a loose world for anything that has to do with audio transformers, magnetic shields, etc.
Even Mu-Metal is today a registered trademark, there are several manufactures that offer a generic version of it.
The original Mu-Metal composition is

C 0.015
Mn 0.50
P 0.005 max
S 0.001 max
Si 0.30
Cr 0.02 max
Ni 80.20
Mo 4.85
Al 0.01 max
Co 0.02 max
Fe Balance

but most of the so called generic version and alternatives have slightly different trace elements that make the technical specs nearly the same but the overall audible sound is sometimes very different.
In my trials over the years in dealing with audio transformers the smoothness or harshness is given by the type of raw metal that is used for the lamination/transformer.

All additional high mu metal that are available today are based on the 80Ni/15Fe the rest even chromium, molybdenum or cobalt.
What the best alloy is, that is open for debate because the shape of the lamination is the 2nd most important part, where sometimes two types of the same lamination but from two different manufacture (cut different) can sound like day and night.

Best example is the early V72 units made by Maihak, they used Krupp lamination vs. the standard Siemens ones. There is a distinct difference in the upper mid range....

The situation about transformer cores is pretty dark today because there is hardly any manufacture left that offers audio grade "Nickel". Here in the US there is Magnetic Metal and BMI left that still offer off the shelf lamination, but from the 200 or so classic x-former lamination 90% of all are special order and sometimes not available at all.

It is pretty much like the electron tube, a specialty market product....

Best regards,
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Oliver Archut
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maxdimario

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Re: lamination material for transformers and chokes
« Reply #4 on: December 14, 2006, 08:49:17 am »

So the metal in the laminations makes a big difference.

the smoothness in the top end is a result of lamination material.

I imagine it's difficult to measure?

I remember that the v76s has a different core material for the HPF inductor to reduce distortion in the lows as well.. right? I think you mentioned nickle there.

can slew-rate and overshoot be altered by the core material?

why is the nickle today not up to audio standards as you say? is it a question of purity?
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Oliver Archut

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Re: lamination material for transformers and chokes
« Reply #5 on: December 14, 2006, 09:51:04 am »

Hello Max,

as I pointed out in my last post, in order to get your core material as you desire (some of it is still available) you have to special order it. Minimum of most manufacture for a custom run to your specs is about 1 Ton, that is a bunch of audio transformer for a small to medium size company.

There are companies that offer standard US lamination, lets say you make a Pull Tech output x-former, you call up you lamination distributor and tell him that you need Permalloy C, the product specialist looks it up and tells you that they have it in stock, but what you get is just a similar alloy that measures (nearly) the same... You wind your x-former to original specs and when you test it, you figure out that the Pull Tech sound is not there at all, maybe similar....


The same applies to nearly all audio x-former and when a companies does not exist anymore that makes the raw material than it is very difficult to get an identical "new version".

The slew rate and overshoot are a direct result of winding technique. A transformer with a 3 dB rating in the 40 to 10ooo range produces can produce up to 90 degree phase shift at the corner frequency for 1dB loss. So overshoot and slew rate are a direct result of a poorly designed x-former (or sometime a cheap one).
Winding location and wire size are a factor for resonances as well a the mounting hole position and size of the hole.

There are hardly any transformer design books available, the ones that are do not cover the sound issue at all, so experience and trial and error are the best ways to get what you want.


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Oliver Archut
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mikepecchio

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Re: lamination material for transformers and chokes
« Reply #6 on: December 28, 2006, 11:51:38 am »

Oliver,

Do you know of any historic cores that were made from more than one alloy? for instance building up a stack by alternating 2 different lams. this seems like it might be an easier way to tweak the performance for some desired effect.

mike
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Oliver Archut

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Re: lamination material for transformers and chokes
« Reply #7 on: December 28, 2006, 01:35:09 pm »

Hello Mike,

using more than two laminations was quite the standard durring the 1950s. Best known are the x-formers used by RCA as well as Westrex/Western Electric.
Mostly Mu Metal with plain steel, the Mu metal gives you the inductance the steel the max. level, but mixing laminations also increases your stray field as well as resonances.

The audible difference is also quite high, just by alternating 2/2 or 4/4 or even 2/4, etc. Biggest problem to get two laminations types that are identical, because there are different (stamping) tools for NI/FE than plain old steel types, so that the alternating can fire back on you.

Best regards,
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Oliver Archut
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KevinCarter

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Re: lamination material for transformers and chokes
« Reply #8 on: December 28, 2006, 04:23:53 pm »

Lundahl uses the two material interleaving technique currently for some of their cobalt amorphous core transformers, like the LL1544A.
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Kevin Carter
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Oliver Archut

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Re: lamination material for transformers and chokes
« Reply #9 on: December 29, 2006, 12:08:20 am »

Here is a pretty nice pic of a RCA x-former where Radio metal and silicon steel was used to reduce the resonance of the radio metal in the audio range. Because some type of laminations resonate on certain frequencies at high inductance the mixed approach was used. At the same time the stacking factor of the lamination helps to reduce the low end saturation.



index.php/fa/3946/0/
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Oliver Archut
www.tab-funkenwerk.com

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maxdimario

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Re: lamination material for transformers and chokes
« Reply #10 on: December 29, 2006, 09:49:46 pm »

excellent!
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mikepecchio

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Re: lamination material for transformers and chokes
« Reply #11 on: January 02, 2007, 02:05:23 pm »

what kind of core material would you choose if you desired substantial harmonic distortion that increases with falling frequency? steel, right?

also, for maximum LF extension, for an equal core size, would you choose 10k:10k or 600:600 (or lower) type construction?  assume all the surrounding conditions are optimised specially for each case.

mike
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Oliver Archut

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Re: lamination material for transformers and chokes
« Reply #12 on: January 02, 2007, 05:10:24 pm »

Hello Mike,

you have to be a bit more clear, there are several issues that happen in the lower frequency range, mechanical distortion in the alloy, dampening distortion of the bobbin/potting component, electrical distortion interacting with magnetic resonances.

If you are looking just for a harmonic distortion at 60Hz, etc. you can trigger it with placing (stacking factor) the steel lamination in the area where the low frequency are most present (a magnetic core is not linear all throughout the window). and/or the type of steel lamination (M6, Dynamometal, etc.)

For your 2nd question there is no general answer, because it depends on several aspects of the audio device.
The same approach that works on an output transformer will most of the times not work on an input, etc.
Also biggest issue by changing the low end cut off point is that whatever you do to increase the low end you will change the high end cut off too! Sometimes changing the winding technique, and core material at the same time will get the trick done extending the low end without changing the high end.

Hope that answers your question...


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Oliver Archut
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mikepecchio

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Re: lamination material for transformers and chokes
« Reply #13 on: January 02, 2007, 06:06:26 pm »

Hi Oliver

Thanks for the reply.  Im not talking about a particular application.  I know how to select a transformer.  Think of it this way: The application I have in mind would be considered "interstage", with tightly defined conditions on input and out.  operating level is flexible and can be adjusted to suit the transformer. I just need galvanic isolation and good LF response.  comprimising HF response if OK. any idea if a 10k:10K or 150:150 device is going to have an edge achieving extended low end?  which is easier for a transformer winder to make?  

mike
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maxdimario

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Re: lamination material for transformers and chokes
« Reply #14 on: January 02, 2007, 08:43:15 pm »

I think that is probably the result of a combination of things..

a 600:600 transformer can also operate as a 5K:5K transformer if the design permits it, I believe.
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