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Old 9th March 2011, 05:13 PM   #10861
DF96 is offline DF96  England
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Would you care to explain how eddy current losses in the core produces added hiss?
As I said:
Quote:
any loss mechanism will contribute thermal noise.
I think the technical name for this is the fluctuation-dissipation theorem, but it is far too many years since I studied thermodynamics. To a first approximation you can calculate transformer noise by treating it as a perfect lossless noiseless impedance transformer, followed by an attenuator. The attenuator will both reduce the signal, and add thermal noise. The noise figure is equal to the attenuation. See any book on radio receivers.

This is not excess noise, as it is all thermal in origin. I am still waiting to hear of any sources of excess noise in a transformer.
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Old 9th March 2011, 05:15 PM   #10862
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Originally Posted by john curl View Post
Well, IF they are all different, then maybe we should sort out the 'better' ones for a specific application. For example, I need a 'great' MC transformer for very LOW LEVEL phono cartridges. Nothing else. I chose, almost a random, the Lundahl LL1931 or the LL1933 transformers, but I am open to anything, that MIGHT be better sonically, measurably, or cheaper with the SAME quality performance.
To my surprise and dismay, the Metglas version of the SAME transformer measured MUCH WORSE at 10Hz, at least 20 times worse! WOW! Can I use it? Joachim uses something similar in Metglas from the same manufacturer, and he has twice as expensive a phono cartridge than I have-$5,000 worth. He is a good listener, and a professional designer, should I go with his recommendation?
SY has a cheaper transformer (mumetal) from Sowter. SY likes his transformer and it is cheaper than either the mumetal or Metglas transformers from Lundahl. Should I change over to that transformer? We are still at the prototype stage, so it would be possible. Anybody COMPARE Lundahl with Sowter, subjectively? Nobody here has contributed anything here so far. In fact, nobody here has COMPARED mumetal with Metglas either, subjectively. What to do? I guess that I will just have to muddle on with what I have in front of me. '-)

"We are still at the prototype stage"

You are selling a $50,000 preamplifier and the MC phono stage is still at the prototype level? What will it cost when you actually get to the real thing?
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Old 9th March 2011, 05:16 PM   #10863
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Originally Posted by john curl View Post
Scott, if the Q of the transformer does not track the ideal with frequency, then noise is added. Extra resistance IS extra noise, why do you think the Q changes?
Why are you treating the transformer as if it were a resonant circuit?

se
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Old 9th March 2011, 05:18 PM   #10864
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This is all what the spec sheet says about the materials used:

The LL9226 core is our cobalt based uncut amorphous strip core. The transformer is housed in a mu metal can.
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Old 9th March 2011, 05:22 PM   #10865
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I'm at a loss to understand the engineering design approach. What do you folks do, pick a transformer out that you like and that's it? Don't you have to take into account the electrical characteristics of the source and the load including their variables?

How about an air core transformer since the ferrous core is a major contributor to distortion and then using mu metal to shield it from hum since the signal level is so low? While you're at it, how about a hybrid design that couples the transformer output to the rest of the preamp with an electronic buffer stage so that the load impedance on the transformer is fix and optimized. Shouldn't the cartridge manufacturer be the one to supply this for his specific cartridge? What adjustments are provided to compensate for variables in source impedance and output level?
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Old 9th March 2011, 05:22 PM   #10866
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Originally Posted by john curl View Post
To my surprise and dismay, the Metglas version of the SAME transformer measured MUCH WORSE at 10Hz, at least 20 times worse!
How can you compare Metglass to a laminated transformer while keeping all else equal? How can they possibly be the SAME except for the core material?

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Old 9th March 2011, 05:31 PM   #10867
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John,

I have tested interconnects, resistors, working on capacitors, even considering playing with a bybee. Why don't you just ask for samples from all of the manufacturers you are considering. It ain't gonna hurt to try. The best answer is I tried all of them, the measurements all varied in interesting ways and this is what sounded best to me.

I do have lost in digital memory somewhere the frequency response vs level for an inexpensive audio transformer. Response does change with level even when sourced and terminated with the matching resistance.

I use transformers in all of my sound systems, but I am pretty sure my experience listening to the finished system from 200 feet or more away is enough different from your use that it is not useful for you.

However even at 800 feet listening distance I can tell you cheap transformers do not sound as good as premium units.
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Old 9th March 2011, 05:36 PM   #10868
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Soundminded, I hate to say this, but you kind of have to choose a transformer, based on what you and your associates decide what is best. We are not just trying to meet a spec. here, and all transformers have different characteristics, beloved by their designers, so the company's marketing blurb will not tell you everything that you need to know. YOU HAVE TO LISTEN, AND LIVE WITH each transformer design to determine the best, overall, for your application.
Personally, 45 years ago, I listened to Triad and UTC, mostly. Then, I heard Sowter, when I was in England, in 1970, it actually had a different sound. How quaint. Then Jensen, and now Lundahl. And so it goes.
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Old 9th March 2011, 05:46 PM   #10869
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Originally Posted by DF96 View Post
I think the technical name for this is the fluctuation-dissipation theorem, but it is far too many years since I studied thermodynamics. To a first approximation you can calculate transformer noise by treating it as a perfect lossless noiseless impedance transformer, followed by an attenuator. The attenuator will both reduce the signal, and add thermal noise. The noise figure is equal to the attenuation. See any book on radio receivers.
Yes. So the question would be how would core losses compare to the losses resulting from winding resistances? I would guess that given a good quality, high nickel core, they would be pretty well swamped by the latter

Quote:
This is not excess noise, as it is all thermal in origin. I am still waiting to hear of any sources of excess noise in a transformer.
Rather like how I was waiting to hear how a photocell could be used to charge a capacitor?

se
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Old 9th March 2011, 05:48 PM   #10870
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Originally Posted by scott wurcer View Post
I'm having trouble picturing what you are describing. If the B-H curve had steps I would expect sudden changes in distortion components. And as we discussed before a step at 0 would mean below a certain input there would be no output.

Jan could/you send a copy? That might make it clear.
Try this:

http://www.linearaudio.nl/Documents/...ail%207125.pdf

Edit: I'm not saying this holds any water; I don't know enough about the subject to have an argumented opinion, and I know that some here think it's a heap of HM, but YMMV.

jan didden
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