As I said:
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.
"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?
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?
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?
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?
se
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.
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.
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.
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.
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
Rather like how I was waiting to hear how a photocell could be used to charge a capacitor?
se
Try this:
http://www.linearaudio.nl/Documents/MvdV aes preprint low level xformer detail 7125.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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Quality factor can be used this way to model series or equivalent parallel loss (resistance) in an otherwise ideal reactance.
The lack of rigor is typical of AES papers, I find it hard to swallow that there are no definitive treatments for nano-Tesla permeability of matierials in the literature.
Well John, you might just have to actually listen to them. But I have a hint, that "may" help.
A couple of years ago when I was looking for commercially available 1:1 output transformers for a DAC, I tested a few. Jensen, Onetics, Edcor, Sowther, Radio Shack and some prototypes I had wound in Taiwan. Did not test Lundhal or Cinemag.
I put each pair (stereo) in an identical small white cardboard box. They were wired to a DB9 connector (think serial port). That allowed me to plug and play any transformer set to the DAC, which I had fitted with the male DB9 connector. The boxes were weighted so that I could not guess. I listened thru many sessions over several days and picked what I liked. The system worked for me.
Now the hint. I found that running impedance sweeps of the various transformers under little to no load revealed great differences. Not that you'd ever use them that way, so it shouldn't be valid - but. I found that the smoother that impedance curve, the higher I had rated them by sound alone. Don't know why, but it's what I found. Not proof of anything, but maybe worth a look, anyway.
But I have a hint, that "may" help.A couple of years ago when I was looking for commercially available 1:1 output transformers for a DAC, I tested a few. Jensen, Onetics, Edcor, Sowther, Radio Shack and some prototypes I had wound in Taiwan. Did not test Lundhal or Cinemag.
I put each pair (stereo) in an identical small white cardboard box. They were wired to a DB9 connector (think serial port). That allowed me to plug and play any transformer set to the DAC, which I had fitted with the male DB9 connector. The boxes were weighted so that I could not guess. I listened thru many sessions over several days and picked what I liked. The system worked for me.
Now the hint. I found that running impedance sweeps of the various transformers under little to no load revealed great differences. Not that you'd ever use them that way, so it shouldn't be valid - but. I found that the smoother that impedance curve, the higher I had rated them by sound alone. Don't know why, but it's what I found. Not proof of anything, but maybe worth a look, anyway.
I tried to confirm the predictions of this paper experimentally and didn't see the effect using a large output transformer with a very conventional EI core.
Thanks, Jan!
I'm afraid I was rather put off by it though.
He's talking about what's going on literally at the threshold of audibility.
From the introduction:
In this paper I give a simple but very effective demonstration of this reverse approach by using the well known audibility threshold curves of our ears. In this famous research the lowest SPL level per frequency was
determined that the ear just can notice. Below that level only the happy few with golden ears can hear, but most people will have a threshold level close to measured in those days.
Imagine what happens there: for instance we can just notice at 4kHz at a SPL level of -4dB, which even is less than the 0dB level of 20 uPa at 1 kHz. Now take a loudspeaker in mind with an efficiency of 90dB/W,m and calculate the power which the speaker needs to reproduce such a weak sound level at 1 meter distance. Be stunned by the amazing 4 x 10-10 Watts. The next understanding is that then the signal levels at the speaker terminals are extremely small as well.
...
A valve amplifier with output transformers needs to transfer such small voltages with great accuracy, because "watch the golden ears, they
even listen below this level".
This is just a load of nonsense.
Yes, we can just detect at -4dB, 4kHz, which is pretty amazing.
But we can ONLY do this after being seated in an anechoic chamber and left to acclimate for 15-20 minutes.
Yes, our range of hearing does extend from -4dB to above 120dB, BUT NOT AT THE SAME TIME!
You're NOT going to hear that -4dB 4 kHz tone even sitting in a quiet room let alone while listening to music at an average 80-90dB.
His premise is fatally flawed from the start and worrying about what's going on at the raw thresholds of audibility is just silly.
se
Ok. But of course an ideal transformer has no reactances. The reactances in a realworld transformer are parasitic.
So I'm not seeing how the losses as they relate to parasitic reactances says anything meaningful.
se
> But of course an ideal transformer has no reactances.
Are you sure about that ?
Transformer - Wikipedia, the free encyclopedia
Are you sure about that ?
Transformer - Wikipedia, the free encyclopedia
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