The coercive magnetic field strength is related to the current flow and the number of turns, not the voltage.
The engineering approach is to specify a core with low enough coercivity and high enough saturation to handle whatever the cartridge can throw at it. Then any source of noise should be identified and the critical circuit isolated from it with adequate shielding to achieve the predetermined S/N ratio specification. It is hard to see why this is a problem for electrical fields since this is done routinely with rf stages that operate at much lower signal levels. The shielding from magnetic fields that induces noise is where mu metal comes in. The entire transformer should be wrapped in it. It is the only way to keep external magnetic fields from reaching the core.
Does an air gap not break up the magnetic path in the core, making it less efficient and thereby resulting in a reduction in effective permeability?
se
How large a voltage? A warp might have a frequency of half a hertz. If the arm is bobbing up and down by a centimeter and we make ridiculous high assumptions about the stylus displacement, the velocity is 2cm/s. For a typical MC, that's 0.1-0.5 mV (-12-15 dBV), best case. Probably lower, since this worst-case assumes that the magnetic field isn't falling off a centimeter away from the coil rest position. The cartridge is likely to have distortion, but will the transformer at that voltage? Or a more realistic case for a bad warp, maybe 10 times lower (-30-35 dBV)?
<1uV relays
Here's one and there are many, BT Low Thermal Reed Relays -MEDER electronic[backId]=2773
Here's one and there are many, BT Low Thermal Reed Relays -MEDER electronic[backId]=2773
That will depend on saturation treshold of the core, mass of the core (Afe) and number of windings.
I can't speak for other transformers but if your model is correct (and I have no reason for doubt) I am sure my step-up transformers will not go into saturation under these circumstances.
It seems to me like a review of Maxwell's equations, their underlying principles, and how to apply them in engineering solutions to field problems is in order. Should be child's play...for someone trained as a physicist. A little more difficult but still doable for someone who is an electrical engineer. I'd pay special attention to Gauss' law of magnetism and Ampere's law.
John,
10 Hz at what amplitude?
Did you hear any difference between these transformers playing warped records?
Scott,
I was wondering about your reaction to that line. A relay that has not been used may have a film form on the contacts. It can be out gassing from plastics used in the construction, junk in the air around it or whatever. (Think of the film that forms on the inside of your automobile's windshield.) If you apply a very low (nv level) to these dirty contacts they will not conduct until the voltage rises enough to burn through the film. In this case the magic level is spec'd to be 100uV. After that level is reached then the film is punctured and lower level voltages will pass. If the contact stops seeing voltage the film will grow back and another application of the "clearing" voltage will be required. How long they stay clear is one of the interesting questions.
This is all well covered in the older literature, I haven't looked to see what is on the web, but this was an active area of research around '95. Oh yeah I mean 1895! Continued until the 1930's, only rarely encountered today as most small signal contact makers know how to handle the issue. That is why bi-furcated gold plated over silver contacts are the norm for small signal relays. Of course Western Electric developed their own alloy for lower cost and harder for longer life.
ES
Yes that is a useful relay for not introducing additional voltage due to temperature differences in the metals used in it's construction.
I found it interesting that in the article the Pass preamp used thin film surface mount parts to avoid that issue.
Crimped end resistors seem to have a number of issues with that and with the voltage discontinuity you seem to not believe in. My inquiry may show that it is possible for the end caps to show the same problem as dry switch contacts. I.E. they don't conduct until a clearing voltage occurs, then they work perfectly until dry aged again.
Agreed. Thermally compensated latching reed relays seem to be a good choice.
http://www.digikey.com/Web Export/S...witchingLowMicrovoltsSignals.pdf?redirected=1
Thanks for the input, Pieter, it has been very informative. However, I don't really want to set up a turntable in my lab and measure worst case warp output at the moment. I once had a REAL problem with it, decades ago, trying to take a snapshot of a raw phono cartridge output, so I had to add a high pass filter. Let's just say that if I can measure significant 10 Hz, then 1/2 Hz is going to be even more difficult. And who is talking about saturation, in any case? Just distortion.
Many of last night's posts split to new thread. http://www.diyaudio.com/forums/everything-else/185033-testing-listening-split-blowtorch-ii.htmlScott,
Note the use of a sealed switch for these low level signals, keeps contamination out! But it turns out there is still new design work on switch contacts.
So these relays can get below 1uV of "Noise" that would be -126 re CD full output. So with a 24 bit CD playing a soft passage say -40 (A slow) from a loud passage recorded with 30 db of headroom would have even this products noise down by -56!
So an ordinary switch obviously would have enough thermal offset noise to not just matter but clearly reduce the "Air" obscure "Microdetails" and just plain destroy the musicality of the reproduced signal! ES
Since the grid is virtually nothing but crimped connections, I guess we should give up.
Another thing if your micro-volt level rectification is repeatable there are radio astronomers that would kill to have it.
ED, you really need to start including masking effects in these numbers.
Since the grid is virtually nothing but crimped connections, I guess we should give up.
Another thing if your micro-volt level rectification is repeatable there are radio astronomers that would kill to have it.
Real crimpers actually use enough force to get a cold weld! Amp used to do informational papers on this when they had to convince folks to give up soldering!
Micro-rectification...Grrr ain't no evidence, done the test, don't mix fairy tales with morality plays!
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