Right, that was the paper I had in mind but couldn't find.
As I understand it, the flux depends on the ampere-turns into the primary. In an unloaded xformer (which is the case for an audio power amp at zero-crossing) the current is only that resulting from the prim inductance, which is much lower than the current in operation. So, the unloaded xformer is nowhere near saturation, right? That's why, in my measurements, I don't see the dreaded saturation inrush. I think.
jd
Yes, though there's also copper losses to take account of. When unloaded the trafo has lowest copper losses (lowest load current) and hence the highest magnetisation.
I think its actually the other way around - for the reasons above. Since so little voltage is being dropped across the primary winding, the peak flux is highest in the unloaded case. But if its been designed well, that's not going to saturate the core.
Thanks for sharing those plots. I think in those, the inrush current is being dominated by the charging of the 33,000uF caps - the waveform has discontinuity near the zero crossing which I take to be a sign of the rectifiers. In the case of the first cycle, the primary copper losses will be relatively much higher (peak current 30A or so compared to around 7A fully loaded normal operation) so perhaps saturation of the core is avoided even when switching on at the zero crossing. That's my guess anyway...
back to resistors and the associates issues. This link http://conradhoffman.com/MML%20files/1_vref_p4.jpg to some info from a contributor to DIYAUDIO highlights a number of issues that probably influence the sound we get but are not usually considered. For example the usse of stress on a resistor affecting its resistance- if the PCB the resistor is mounted on is exposed to the acoustic field from associated speakers its conceivable that its resistance changes a little. That small change with be delayed by the acoustic delay in the space. If its change is enough to be audible (a big unknown) then the net effect could be a variable that makes pinning down the effect difficult.
Years ago I build a custom preamp that was acoustically sealed in 3/4" Delrin. It seemed to make a big difference. However sealing the cables was a major PITA and not for commercial application at the time.
Years ago I build a custom preamp that was acoustically sealed in 3/4" Delrin. It seemed to make a big difference. However sealing the cables was a major PITA and not for commercial application at the time.
[snip]In the case of the first cycle, the primary copper losses will be relatively much higher (peak current 30A or so compared to around 7A fully loaded normal operation) so perhaps saturation of the core is avoided even when switching on at the zero crossing. That's my guess anyway...
In the first cycle, the current is also only flowing during the rectifier open time only. Even in the first cycle, there's no current to speak of at the (zero crossing) switch on point. Which means there's no current due to xformer losses or magnetisation. I can't see anything else.
jd
It's like falling into a prepared cavity, ie negative pressure.
The remanance is tied to it but its more a molecular stressing thing. Think dielectric stressing residuals but in the electromagnetic sense tied to conductive metals, specifically of the ferromagnetics. I doubt you'll find much in the way of papers on this subject.
Try measuring a given suitable transformer as well as possible in a manner relating to the specific question at hand, and then cryo'ing the transformer. Then measure again. The result will differ slightly. Then you will have your answer, with regard to the desire to have it on paper as a realized number. Muse away (ponder) -it should be fairly obvious at that point. Using two transformers that can be disassembled, measuring both, disassemble both, cryo one set of laminates, put both back together and then use the uncryo'd unit as a control-measuring both. Just to be sure - for elimination of variables. If still unsure, swap windings. The change should follow the cryo'd core. Do this test specifically with laminates, not powder cores. A powder core in this test leaves questions, a laminate core leaves the whole thing at the inescapable single cause analysis point.
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A guy here measured initial inrush current of the transformer in his thesis:
http://www.mti.tul.cz/files/disertace_Miroslav_Novak.pdf
http://www.mti.tul.cz/files/disertace_Miroslav_Novak.pdf
When I placed resistors on a shaker table, the only type that showed problems were the carbon composition types.
Capacitors were a different story. Not surprisingly some of the ceramics could be used as guitar pickups.
Jan,
I take it you have the setup and the controls to do a decent chart of turn on - turn off versus starting surge. It seems to me it is probably easier to run the curves than to look for somebody's data.
I like to put a capacitor across the secondary of the transformer. I use a larger one than is needed for filtering and approaches a power factor corrector.
ES
Hi Ed,
It's not that I don't want to look for somebody's data. But there is a difference with a xformer with a resistive, inductive or other type of 'continuous' load, and a rectifier-capacitor load.
In the first case, when you shut off the xformer at an arbitrary point on the mains waveform, you will have some kind of remanent flux which may influence the start up surge as is described in several quoted papers.
But in the latter case, there is guaranteed no load current around zero crossing of the mains. So, if you consistently switch the xformer off and on during that zero crossing, as I do, there's no remanent flux to speak of, so there is no switch-on surge. The curves I posted confirm that.
jd
Yes,
But how much work is it for you to do 3 cases at 10 degree steps? That might even be worth an article!
I would like to return to a topic that many here have contributed to, that I think is unresolved by many. This is the nature of internal interconnects and connections inside of audio equipment of the highest quality. Here, I am talking about circuit board interconnections, solder and hookup wire, both balanced and unbalanced.
Let me give a little history as I have experienced it:
When I first started seriously messing with audio electronics, namely building electronics kits from Heathkit or Eico, and audio kits from Dyna.
First of all, the wire supplied was a cheap plastic wire, probably originally designed for doorbells. The insulation melted easily, and it was usually solid core copper. This was true throughout the '50's and '60's. In the early '70's, Mark Levinson converted to solid core Teflon wire. This was harder to use in production, but with special thermal strippers, it was practical.
Then, in the late 1970's 'wire differences' were discovered in France, and the search was on for the optimum interconnect wire. Japan seemed to leading in this, and Mogami became popular with ultra pure stranded copper wire, with a non-teflon coating, making it easier to work with. This should have ended our search.
However, some 'researchers' like VDH, Dr Hawksford, and Eves B Andre, (I am pretty sure was a lecturer at the Ecole Polytechnique in Paris and a wire consultant for the French air force) started to formulate different cables. In the USA, Bruce Brisson came up with a unique geometrical formulation, while the former researchers seemed to concentrate on material purity and insulation abberations.
Now, everyone has their own biases an preferences, and when it comes to hook-up wire, I found that VDH was the most practical, with linear crystal copper.
Hawksford went forth with popular articles on wire selection and he 'discovered' an unknown distortion at line level audio. VDH did his own independent research and found a low level distortion, in virtually all metal conductor cables. This is why he moved toward carbon in later years. Unfortunately, carbon is really, really hard to use for relatively short distances, and almost impossible to terminate. I have some samples, but they were shown to be impractical. However, I learned about 'wire handling' from VDH, that you do not want to bend or twist these wires any more than necessary, to minimize microcracking. Also that all pure copper or silver wires will become contaminated, if left in the open atmosphere, and degrade from their original pristine quality.
Bruce Brisson, working with Monster Cables developed his own unique geometry, that I must admit, sounds 'different'. However it is also difficult use in short lengths, and I have not used it much.
The debate between 'geometry' and 'purity' is very real between wire designers. You should hear them go at it, in a debate. I think that both can be important, depending on signal level, and length of the cable, in this case, very short as it is only internal hookup wire. More later.
Let me give a little history as I have experienced it:
When I first started seriously messing with audio electronics, namely building electronics kits from Heathkit or Eico, and audio kits from Dyna.
First of all, the wire supplied was a cheap plastic wire, probably originally designed for doorbells. The insulation melted easily, and it was usually solid core copper. This was true throughout the '50's and '60's. In the early '70's, Mark Levinson converted to solid core Teflon wire. This was harder to use in production, but with special thermal strippers, it was practical.
Then, in the late 1970's 'wire differences' were discovered in France, and the search was on for the optimum interconnect wire. Japan seemed to leading in this, and Mogami became popular with ultra pure stranded copper wire, with a non-teflon coating, making it easier to work with. This should have ended our search.
However, some 'researchers' like VDH, Dr Hawksford, and Eves B Andre, (I am pretty sure was a lecturer at the Ecole Polytechnique in Paris and a wire consultant for the French air force) started to formulate different cables. In the USA, Bruce Brisson came up with a unique geometrical formulation, while the former researchers seemed to concentrate on material purity and insulation abberations.
Now, everyone has their own biases an preferences, and when it comes to hook-up wire, I found that VDH was the most practical, with linear crystal copper.
Hawksford went forth with popular articles on wire selection and he 'discovered' an unknown distortion at line level audio. VDH did his own independent research and found a low level distortion, in virtually all metal conductor cables. This is why he moved toward carbon in later years. Unfortunately, carbon is really, really hard to use for relatively short distances, and almost impossible to terminate. I have some samples, but they were shown to be impractical. However, I learned about 'wire handling' from VDH, that you do not want to bend or twist these wires any more than necessary, to minimize microcracking. Also that all pure copper or silver wires will become contaminated, if left in the open atmosphere, and degrade from their original pristine quality.
Bruce Brisson, working with Monster Cables developed his own unique geometry, that I must admit, sounds 'different'. However it is also difficult use in short lengths, and I have not used it much.
The debate between 'geometry' and 'purity' is very real between wire designers. You should hear them go at it, in a debate. I think that both can be important, depending on signal level, and length of the cable, in this case, very short as it is only internal hookup wire. More later.
I worked in the high tech industry and we used litz wire for RF transformers, ribbons and even hollow, solid tubes for microwave. Today i am using litz wire designed by Spiral Groove. It is made from very many extremely fine wires, individually isolated. It is easy to terminate by overheating the soldering iron and is very flexible. I asume it has a poyethylen isolation because teflon whould not melt so easily.
For simpler equipment and prototypes i still use something that looks like bell wire. I is used by the telecom industry and i buy it for virtually nothing as scrap.
For simpler equipment and prototypes i still use something that looks like bell wire. I is used by the telecom industry and i buy it for virtually nothing as scrap.
As for solder i still prefer leaded. I think for DIY thats ok.
Friends of mine in Japan have tested lead free solder to be able to deliver their components according to ROHS. Just on the High End i have spoken to on off them. They tested around 30 varieties over a period of 2 years. They made short interconnects that where colour coded by a women that did the soldering. When they listened they did not know what solder had what colour. They found only one that sounded "benign" but still not as good as the solder they used before that had lead in it.
I myself are not that critical about solder. I care more if it is easy to use and the soldering points look decent. I simply did not find the time to investigate that matter further.
Friends of mine in Japan have tested lead free solder to be able to deliver their components according to ROHS. Just on the High End i have spoken to on off them. They tested around 30 varieties over a period of 2 years. They made short interconnects that where colour coded by a women that did the soldering. When they listened they did not know what solder had what colour. They found only one that sounded "benign" but still not as good as the solder they used before that had lead in it.
I myself are not that critical about solder. I care more if it is easy to use and the soldering points look decent. I simply did not find the time to investigate that matter further.
Joachim you are ahead of the topic, but I tend to agree with you. Most serious audio designers that I know have tried hard to find a lead free solder that they are happy with. Some have succeeded, to their satisfaction, but I will stick to a quality leaded SN62 solder as long as I can, maybe for the rest of my life. It would be just like having to design an auto engine that runs on alcohol. We know it can be done, but at what cost to actual performance.
When it comes to solder, I started, like everyone else with 60-40 leaded solder. Why, on reflection, they EVER made 60:40 solder, is beyond me. SN 63 is Eutectic, and therefore avoids bad solder joints, specifically a problem with amateurs. Why amateurs would be using 60:40 rather than 63:37 is a problem with indifference to success in soldering, rather than extra cost.
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