math help requested
Thanks for the suggestions.
I need help with the math to understand a 230V/7V 25VA power transformer is similar impedance to 2500:8 output transformer.
Thanks for the suggestions.
I need help with the math to understand a 230V/7V 25VA power transformer is similar impedance to 2500:8 output transformer.
Size has its drawbacks. Ask your preferred winder to make you a series feed 5K transformer with 100H of inductance gapped for 40mA and sized for 20W of output. Also require that the transformer is no more than -1dB at 25kHz when driven by a 1.6K source.
This arrangement is perfectly possible in parallel feed. In series feed, you'll just annoy your winder with such a request.
audiowise,
Prms = ((peak I squared) x R)/2
Prms = 40mA squared x 5000 Ohms/2
Prms = 4 Watts.
Is the reason to ask for a 20 Watt transformer so that it can output 4 Watts all the way down to 20Hz?
And with 3.98nF distributed capacitance, and rp 1600 Ohms, that is -3dB at 25kHz.
Even if there were no leakage inductance, -1 dB requires no more than 1.99nF (1,990 pF). And that 1990pF capacitance is the total capacitance of the output transformer in parallel with the choke.
Prms = ((peak I squared) x R)/2
Prms = 40mA squared x 5000 Ohms/2
Prms = 4 Watts.
Is the reason to ask for a 20 Watt transformer so that it can output 4 Watts all the way down to 20Hz?
And with 3.98nF distributed capacitance, and rp 1600 Ohms, that is -3dB at 25kHz.
Even if there were no leakage inductance, -1 dB requires no more than 1.99nF (1,990 pF). And that 1990pF capacitance is the total capacitance of the output transformer in parallel with the choke.
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You have 4 options with a toroid depending on whether you have the primaries in series (115 + 115) or parallel (115) and the secondaries in series (7 + 7) or parallel (7). From this, you develop the turns ration.
So if you use the primaries in series (230) and the secondaries in parallel (7) you develop a turns ratio of (230/7) * (230/7) = 32.86.
The impedence ratio is the square of the turns ratio.
32.86 * 32.86 = 1079
Multiply the expected output impedence of 8 ohms by the impedence ratio giving 8638.
To get 2.5k, use the primaries in parallel.
(115 / 7 ) * (115 / 7) * 8 = 2160
If your secondaries were 6 volt
(115 / 6 ) * (115 / 6) * 8 = 2938
Your choice is between too high or too low.
If you are looking for a 5K transformer, the primaries in series and 9 volts in parallel works well.
(230 / 9 ) * (230 / 9 ) * 8 = 5225
More on transformer ratios etc
https://www.electronics-tutorials.ws/transformer/audio-transformer.html
Hopefully, my calculations are correct.
ray
I don't have to ask. I calculate the transformer including the core size...otherwise one cannot design anything.
100H for 1.6K driving 5K gapped transformer are not necessary. 50H easy and more than enough.
You can do that easily for parafeed but you ABSOLUTELY need it to shift RESONANCE down which does not exist with gapped transformer and is present here because of the capacitor. And this also means that is worse with 2 different and unwanted hysteresis loops, additional and different types of losses and zero crossing.
Then you have the additional plate load...another choke or CCS, doesn't really matter. It is another imperfect additional device....
25KHz is poor for a relatively small transformer. You should really talk about 50KHz minimum.....
I could get better bandwidth in a 7Kg SE transformer for 814 or 845 with a rather simple geometry....and better is possible of course without much trouble. Just more expensive. This is not generic statement I designed and had made this transformer for a member in this forum....
5.8K, 50H, 110 mA DC current some 28 KHz @-1 dB from memory....cheaper than Sowter's parafeed transformers and including professionally carried out safety test for use at high voltage.
That's your twisted impression I am sorry. I never said or meant anything like that. You are only trolling here. Try to write something useful and objective sometime....
45,
Magnetism as a whole is a rather poorly conceptualized subject and DC biased magnetization is certainly not an exception. No wonder you are discombobulated...
Unfortunately, that is not the case. An air gap does not compensate for core material deficiencies. Anyway, signal transformers in particular, should be equipped with an air gap. The C-core makes provision for a well defined air gap.
The non-magnetic air gap acts as a dielectric insulation. By reducing permeability and inductance, it enhances power and frequency handling capability, dampens resonance, promotes a more coherent magnetic polarization and flux alignment with the external field and a more rigid coupling between forces, but it does not prevent saturation as stated in standard textbooks. Some degree of hysteresis and saturation is an integral part of magnetism. A higher reluctance mitigates the tendency for saturation, but no size of "saturation gap" can provide a cure for the adverse effects of the biased core flux disease.
Even a small DC current causes a high asymmetric magnetization (hysteresis loops) and saturation of the core, leading to increased flux distortion, increased noise-hum generation, increased harmonic distortion and increased residual magnetism. Resonant, high frequency, unipolar amplitudes arise in conjunction with strained transitions as a natural balancing action, accompanied by large inductive magnetizing currents. When impedance vanishes, the rapid DC energization of the core results in a random, slowly decaying saturation - like in the case of inrush current.
You are worrying about the wrong things. A resonant-transient transition with high harmonic content are the attributes of the low-loss, highly grain-oriented core materials having high intrinsic instability, high magnetic permeability and high saturation flux density.
¤
High quality transformers cannot be manufactured inexpensively. Stay away from toroidal transformers.
Magnetism as a whole is a rather poorly conceptualized subject and DC biased magnetization is certainly not an exception. No wonder you are discombobulated...
Unfortunately, that is not the case. An air gap does not compensate for core material deficiencies. Anyway, signal transformers in particular, should be equipped with an air gap. The C-core makes provision for a well defined air gap.
The non-magnetic air gap acts as a dielectric insulation. By reducing permeability and inductance, it enhances power and frequency handling capability, dampens resonance, promotes a more coherent magnetic polarization and flux alignment with the external field and a more rigid coupling between forces, but it does not prevent saturation as stated in standard textbooks. Some degree of hysteresis and saturation is an integral part of magnetism. A higher reluctance mitigates the tendency for saturation, but no size of "saturation gap" can provide a cure for the adverse effects of the biased core flux disease.
Even a small DC current causes a high asymmetric magnetization (hysteresis loops) and saturation of the core, leading to increased flux distortion, increased noise-hum generation, increased harmonic distortion and increased residual magnetism. Resonant, high frequency, unipolar amplitudes arise in conjunction with strained transitions as a natural balancing action, accompanied by large inductive magnetizing currents. When impedance vanishes, the rapid DC energization of the core results in a random, slowly decaying saturation - like in the case of inrush current.
You are worrying about the wrong things. A resonant-transient transition with high harmonic content are the attributes of the low-loss, highly grain-oriented core materials having high intrinsic instability, high magnetic permeability and high saturation flux density.
¤
High quality transformers cannot be manufactured inexpensively. Stay away from toroidal transformers.
Sorry this a forum where a lot people with different degrees of knowledge read and write so one tries to reply in a simple way.
Still wondering?
The air gap does compensate for core deficiency by reducing permeability and making the hysteresis loop thin and linear within the range of use. That's why the size increases for a given application.
Saturation is not happening in properly designed transformer.
The asymmetry is precisely what prevents zero-crossing and reduces Barkhausen noise due to rapid change of size of magnetic domains. This happens all the time in un-gapped transformers. Barkhausen noise in Fe-Si is AUDIO noise.
The rest of what you write about impedance vanishing etc.. it's total non-sense.
Really? Do you know what a tube does when the load is resonant one with 180 deg phase shift at low frequency? You really have no idea about what is needed to make a good amplifier.
High quality transformers are also toroidal. Not my usual choice but they are just fine.
Finally you are still neglecting that capacitors have similar issues as well and are almost invariably overlooked and there is an additional imperfect plate load.
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Sorry, I don't think they are fine. They are always low quality, inherent by their design approach. No one until today has managed to make proper windings on a toroid core. And by proper windings I mean layer wound transformers. Its impossible with toroid transformers.
So what you write is the usual "I have heard and a I have read this and that" story. Talk is cheap in an audio forum, my friend. If you go to top notch transformers, you won't find ANY toroid type there. You can just find them in the low quality section of audio signal transformers. All top notch transformers are layer wound types with the usual winding gimmicks, that couldn't be applied to toroids due to their nature of ring shape.
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I was so sure that this name would have been told to me, right now in the next post.
Yes, I do have heard of him. A very good salesman, but he's riding a dead horse.
And he may find enough people who don't know how any good audio transformer is being made. Every day, someone is waking up and decides to buy an output transformer. Some of them, those who are uninformed and believing his sermons, will buy his transformers. But for the informed people with knowledge, this is way out of their mind. And with more than one good reasons, in practice, not written in clever marketing books.
Yes, I do have heard of him. A very good salesman, but he's riding a dead horse.
And he may find enough people who don't know how any good audio transformer is being made. Every day, someone is waking up and decides to buy an output transformer. Some of them, those who are uninformed and believing his sermons, will buy his transformers. But for the informed people with knowledge, this is way out of their mind. And with more than one good reasons, in practice, not written in clever marketing books.
Surprisingly for me Lundahl chokes actually sound very good, both as PS or plate load.
The very best i have used were wound by diyaudio member AE50. He uses amorhous and nano cores and OCC wire. Multi sectioned.
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