The short circuit current noise of a 10 Ohm rersistance is 40 pA/rt-Hz or ~6nA rms in the audio bandwidth. This is > 10^9 electrons rms, I also don't see the point in Dr. Hawksford's paper, the quantization behavior is far from any relevance here.
Scott, I don't doubt your figures, but it doesn't touch my question:
Can a input traffo transfer this level of information accurately - or will it just ignore it? As in 10^9 electrons will flow through the traffo's winding, but does it/can it change the magnetic domains (or whatever) enough to be ACCURATELY transferred to the secondary?
What is the lowest level we can expect a (let's say) a Jenson traffo to stop "working"?
Regards, Allen
Hi John,
Interesting post. I wonder whether you have ever tried that trick patented by Bruce Hofer of AP (and also used by Lundahl) to use a minuscule amount of pos feedback around the transformer primary to cancel the resistive part of the windings?
Not only does that cancel the lf distortion almost completely, I would expect (but I'm not sure about that part) that it would also lower noise?
(I can find a link if you'r unfamiliar with it)
jd
I think "no." But there IS one hole in my argument which I'll get to.
Let's start with the assumption that the signal being put into the transformer is clean. In the case of the spectrum I showed, the test signal has a THD in the 0.001% range. So we can discard the idea that the spectrum is "improved" by some sort of filtering effect at the input. The only thing the transformer can do is ADD harmonics; if it takes any away, they're in the <<0.001% range and would be swamped by the larger distortions downstream.
Now, in your hypothesis, there's a dead band at zero crossing. What's the effect of the dead band on the harmonic content of the input signal? Well, that depends on whether it's a sudden, sharp dead band or has some curvature. The former will be particularly rich in higher order odd harmonics. The spectrum of the latter will depend on the symmetry- either there will be a mixture of low order even and odd harmonics or just low order odd harmonics. This is completely analogous to quantization distortion in undithered ADC.
The spectrum I showed had only second harmonic, and THAT was a function of the second stage, as tube-swapping demonstrated. There appears to be no dead band.
In a real world preamp, using phono cartridges and vinyl discs (analog recordings!) as input rather than signal generators, any dead band problem would be minimized anyway- returning to my digital analogy, the noise provides dither, decorrelating the quantization from the signal.
Now, to the hole in my argument, and what I'll do to plug it. The hole is the RIAA network. Since my measurement is at the preamp output, there is effectively a 6dB/octave reduction in first stage distortion. I'll repeat the measurement, but take the signal off the first stage plate.
A high quality transformer core material such as Mu-metal will have an excitation current of zero. So theoretically the core doesn't "quit working".
John
Says who? Where? measurements? Sounds like an "every body knows" sort of old wive's tale to me, but doesn't fit any logic.
At one or two microvolts of signal? Maybe. At one or two nanovolts of signal? Unlikely. At one or two picovolts of signal? Flat out don't believe it.
There MUST be a quantum level of energy needed to flip the magnetic domains in the core, because this needs to happen for energy to be transferred from the primary to the secondary.
Every time I insert a traffo into an audio circuit I hear a loss of low level information - why, if not because of my concept? And it's far worse with a MC cart traffo (circa 300uV) than an interstage (circa 2V), and far less in a poweramp output traffo (circa 100V). Also core materials have different low level loss effects. Amorphous cores transmit far more low level info than a normal steel core, and I mean in traffos otherwise identical (Lundahl).
Regards, Allen
is this true?
The magnetic domains must flip for energy to be transferred through the transformer!
That is my theory and I'm trying to get confirmation /refutal of it.
I can clearly HEAR an effect that I can only explain in this way.
Regards, Allen
Pavel, the only integrated INA i have experience with is the INA163. A friend and i made a major efford to make it work including Battery PSU and lokal shunt regulators. The sound was fine at the end. Very dynamic and lifely but the limit are the internal 3kOhm feedback resistors. When you do not like to work with very high gain, noise performance is not ideal but you know that of cause.
Currently i am working on a balanced stage with a transformer at the input. I am trying to let the transformer only do between 6dB and 15dB of gain to have an extended high frequency response. The transformer i use has a primary DC impedance of 1.8Ohm. Another problem in transformers is, that they need a high primary inductance to work low in the bass. My Lyra Titan with 5.5 Ohm plus 1.8 Ohm of the transformer needs at least 100mH to go down to 20Hz. That makes the transformer core big because we need thick wire. A cartridge like the Eminent with 2 Ohm DC impedance makes life somewhat easier. See an alpha version of my input stage.
Currently i am working on a balanced stage with a transformer at the input. I am trying to let the transformer only do between 6dB and 15dB of gain to have an extended high frequency response. The transformer i use has a primary DC impedance of 1.8Ohm. Another problem in transformers is, that they need a high primary inductance to work low in the bass. My Lyra Titan with 5.5 Ohm plus 1.8 Ohm of the transformer needs at least 100mH to go down to 20Hz. That makes the transformer core big because we need thick wire. A cartridge like the Eminent with 2 Ohm DC impedance makes life somewhat easier. See an alpha version of my input stage.
I'm sorry, I probably should have said near zero. The DC magnetization for curve for Mu-metal begins at the intersection of the B-axis and H-axis so of course induction at zero Oersteds is zero Gauss. As for induction at picoOersted magnetizing force levels, I'll have to look that up. Remember, I said theoretically - I suppose it's up to the individuals with the most at stake to do the actual measurements. If you have a figure for number of turns and DC resistance of your SUT, then I may be able to tells you if there is any induction at microvolt levels. I'm also curious if the motor on a cutterhead or a cartridge is capable of this kind of "signal detection" since they are also electromagnetic devices, after all.
John
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Well, at last some useful input. Allen, have you made the comparisons between amorphous and mu-metal, yet, yourself? I have been fighting with myself with that decision. Is that why there are two almost identical Lundahl transformers in its catalog for highest quality MC cartridge transformers?
Stick to your opinion, on transformers and audio reproduction requirements, Allen. You and I work in rarified atmosphere of high end audio design. We HAVE to work with phono cartridges like the Lyra Titan, or even more exotic, because that is what OUR customers have or use. We also have to load them very accurately, because that is what our customers demand.
Transformers have been with us since the 1930's in a very serious way. Up to 1970 or so, we could get a number of quality transformers from UTC, Peerless, Sowter, etc. However, for me, each of these transformers had a 'signature' sound. As a working audio designer of professional equipment, 40 years ago, we used interstage and input transformers on a regular basis, and it was 'refreshing' to design them out of the loop, when we could. Could I have picked them out in a double blind ABX test? NO, but then nobody else would be able to either. You just have to live with them and have their sonic 'signature' soak into you, so to speak, IF you had that kind of sensitivity.
For me, for example, I appeared to have this kind of sonic sensitivity from an early age, first, in my selection of acoustic guitars. This is one reason why I went into the design of audio equipment. However, my sense of taste, in wine, for example is far from subtle, compared to many others, and I am sure that if they had to live with '2 buck chuck' instead of their favorite wine selections, they would be very unhappy folks. The rest of us might consider the extra cost of the 'good' wines to be not worth the cost and effort, unless we were very wealthy. It is the same with super good audio quality.
Many designers are impugned on this website for the the articles they have written on audio quality. So far 3 Ph'd's with University and research lab experience that been 'picked at' on this tread alone. This includes: Hawksford, Otala, and VandenHul. Why? If what they wrote in their articles decades ago was so awful, why not a huge protest at the time? At the same time, why do these Professors (at least at one time in their lives) not back down and correct their work? I know each of these people personally, and I always learn from them. Sometimes they learn (a little too much) from me, and I find my topologies used or discussed to others, by them. In any case, I have asked them point blank about any controversies and they have never backed off, even to me. Who are these 'critics' who don't teach engineering, publish papers in the field of audio design, or know or significantly correspond with the people they are impugning? What are they up to, and why do they do it?
Stick to your opinion, on transformers and audio reproduction requirements, Allen. You and I work in rarified atmosphere of high end audio design. We HAVE to work with phono cartridges like the Lyra Titan, or even more exotic, because that is what OUR customers have or use. We also have to load them very accurately, because that is what our customers demand.
Transformers have been with us since the 1930's in a very serious way. Up to 1970 or so, we could get a number of quality transformers from UTC, Peerless, Sowter, etc. However, for me, each of these transformers had a 'signature' sound. As a working audio designer of professional equipment, 40 years ago, we used interstage and input transformers on a regular basis, and it was 'refreshing' to design them out of the loop, when we could. Could I have picked them out in a double blind ABX test? NO, but then nobody else would be able to either. You just have to live with them and have their sonic 'signature' soak into you, so to speak, IF you had that kind of sensitivity.
For me, for example, I appeared to have this kind of sonic sensitivity from an early age, first, in my selection of acoustic guitars. This is one reason why I went into the design of audio equipment. However, my sense of taste, in wine, for example is far from subtle, compared to many others, and I am sure that if they had to live with '2 buck chuck' instead of their favorite wine selections, they would be very unhappy folks. The rest of us might consider the extra cost of the 'good' wines to be not worth the cost and effort, unless we were very wealthy. It is the same with super good audio quality.
Many designers are impugned on this website for the the articles they have written on audio quality. So far 3 Ph'd's with University and research lab experience that been 'picked at' on this tread alone. This includes: Hawksford, Otala, and VandenHul. Why? If what they wrote in their articles decades ago was so awful, why not a huge protest at the time? At the same time, why do these Professors (at least at one time in their lives) not back down and correct their work? I know each of these people personally, and I always learn from them. Sometimes they learn (a little too much) from me, and I find my topologies used or discussed to others, by them. In any case, I have asked them point blank about any controversies and they have never backed off, even to me. Who are these 'critics' who don't teach engineering, publish papers in the field of audio design, or know or significantly correspond with the people they are impugning? What are they up to, and why do they do it?
Anyway, i am dedicated to make a "good" phonostage with transformers. Provided i get the hum problem solved, the low noise of such circuits is a very attractive oportunity.
One question John : The inductance of the moving coil transformer will roll off the bass at a rate of 6dB / Octave. Does that help to suppress ultra low frequency distortion from warps ?
One question John : The inductance of the moving coil transformer will roll off the bass at a rate of 6dB / Octave. Does that help to suppress ultra low frequency distortion from warps ?
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