There are no metal oxide/metal junctions that change from conducting to not over a 1 or 2 milli-volt span. Fermi levels, activation energies, bandgaps, whatever they all often have those pesky exponential relationships with temperature as well as values in the volt range.
Your plot shows about 50mV per div, a typical microphone has 20mV at 94dB SPL so why is there no output? You grind a bad connection back together by working the two halves around, no need for any exotic explaination. Same thing with corroded batteries.
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Several things confuse me.
1. Was your caliper calibrated? Digital or analog.
2. What was room temperature? Is the caliper TCE the same as the diode TCE? stainless is 166 ppm/C, silicon about 4, molybdenum 3.3, copper 16, aluminum 25..if ya gonna measure, do it right...
2. Why do you call a diode that is .123 inches by .064 diameter small??? A 1N4148 chip is .008 inches thick, and .012 by .012 inches..
3.. Why do you call .203 by .104 big?? The one on my desk is 3.5 inches wide and 8 inches long, weighs 11 lbs. ""you call that a knife??...now...that's a knife...""
Any schematic of the setup??
Cheers, John
Thanks, interesting. The first two have little detail, the third has too much (for me)?
We probably don't hear Barkhausen noise in our audio transformers, where coils of wire are deliberately coupled to ferromagnetic materials. Therefore we are extremely unlikely to hear it in small loops of wire loosely coupled to a relatively distant ferromagnetic case. So I conclude (as I expected) that Barkhausen noise is not the source of any problems with steel cases.
We probably don't hear Barkhausen noise in our audio transformers, where coils of wire are deliberately coupled to ferromagnetic materials. Therefore we are extremely unlikely to hear it in small loops of wire loosely coupled to a relatively distant ferromagnetic case. So I conclude (as I expected) that Barkhausen noise is not the source of any problems with steel cases.
If you ask me, I would say that most of the transformer's noise can be traced back to Magnetostriction induced strain.
I would also add that the effect of Barkhausen “noise” is not as gross as one that can be measured in a typical environment. (I’ve seen both cooled and uncooled Barkhausen noise probes in environmentally controlled R & D labs and I’ve seen liquid helium cooled Barkhausen noise probes in industrial environment. In every case, the signal was heavily noise reduced through software plus through data normalisation using various other sensors which simultaneously sensed different physical phenomena .)
I would also add that the effect of Barkhausen “noise” is not as gross as one that can be measured in a typical environment. (I’ve seen both cooled and uncooled Barkhausen noise probes in environmentally controlled R & D labs and I’ve seen liquid helium cooled Barkhausen noise probes in industrial environment. In every case, the signal was heavily noise reduced through software plus through data normalisation using various other sensors which simultaneously sensed different physical phenomena .)
Magnetic Issues
Hi all,
Interesting discussion. I have an experience with an effect I observed in aeons past. It mainly applied to low-inductance high-speed record heads, although similar effects could occur with gapped coils like those used in some audio circuitry.
Our high-speed duplicators sometimes recorded a frying-bacon like noise which we traced to certain individual heads of only certain ferrite types. I was able to reduce or eliminate the noise by lapping the head gap with diamond lapping film. We concluded that what we were hearing was the dynamic inductance modulation due to oscillation of microscopic ferrite particles in the gap. This was verified by using a high-speed current probe in the feed to the bias tank, and observing small spikes on the head side of the tank. These heads were very low inductance (20uH if I remember correctly), due to the fact that the speed-multiplied audio band was 1.28KHz to 1.28MHz, with an 8MHz bias frequency. It is probable that with the gapped inductors used at audio frequency, the modulation due to small particles in the gap may be several orders of magnitude lower and unnoticeable.
On the shielding issue currently under discussion: high-sensitivity magnetic pickups by their very purpose require much more magnetic shielding than do most circuitry. In our quest to lower the noise floor of our low-speed tape reproducers we found a solution that worked for us: enclosures machined from 1/4" aluminum to provide structural rigidity, and to space an inner shield from an outer shield. The inner shield was custom formed and annealed from mumetal, the outer shield was soft iron. The principle was to use a material which had more gradual saturation characteristics for the outer shield in order to reduce saturation effects. The inner shield was then a very high permeability, high performance shield which was therefore less challenged. Oh yeah, a critical factor was spacing ALL 60 Hz transformers and chokes as far away from the shield as possible (duh). You can learn a lot about magnetic shielding by listening to a high-sensitivity head while you try different shields and component spacings. I preferred to finalize designs in this way (another duh?).
One characteristic of magnetic materials which often goes unconsidered is the shape of the saturation knee. This one characteristic was largely responsible for the sound and increase in distortion products of the different tape formulations as they entered saturation, and we tried all of them over the years. I applied this concept to the application of different shielding materials.
Just another ancient technique from a old fart...
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
Hi all,
Interesting discussion. I have an experience with an effect I observed in aeons past. It mainly applied to low-inductance high-speed record heads, although similar effects could occur with gapped coils like those used in some audio circuitry.
Our high-speed duplicators sometimes recorded a frying-bacon like noise which we traced to certain individual heads of only certain ferrite types. I was able to reduce or eliminate the noise by lapping the head gap with diamond lapping film. We concluded that what we were hearing was the dynamic inductance modulation due to oscillation of microscopic ferrite particles in the gap. This was verified by using a high-speed current probe in the feed to the bias tank, and observing small spikes on the head side of the tank. These heads were very low inductance (20uH if I remember correctly), due to the fact that the speed-multiplied audio band was 1.28KHz to 1.28MHz, with an 8MHz bias frequency. It is probable that with the gapped inductors used at audio frequency, the modulation due to small particles in the gap may be several orders of magnitude lower and unnoticeable.
On the shielding issue currently under discussion: high-sensitivity magnetic pickups by their very purpose require much more magnetic shielding than do most circuitry. In our quest to lower the noise floor of our low-speed tape reproducers we found a solution that worked for us: enclosures machined from 1/4" aluminum to provide structural rigidity, and to space an inner shield from an outer shield. The inner shield was custom formed and annealed from mumetal, the outer shield was soft iron. The principle was to use a material which had more gradual saturation characteristics for the outer shield in order to reduce saturation effects. The inner shield was then a very high permeability, high performance shield which was therefore less challenged. Oh yeah, a critical factor was spacing ALL 60 Hz transformers and chokes as far away from the shield as possible (duh). You can learn a lot about magnetic shielding by listening to a high-sensitivity head while you try different shields and component spacings. I preferred to finalize designs in this way (another duh?).
One characteristic of magnetic materials which often goes unconsidered is the shape of the saturation knee. This one characteristic was largely responsible for the sound and increase in distortion products of the different tape formulations as they entered saturation, and we tried all of them over the years. I applied this concept to the application of different shielding materials.
Just another ancient technique from a old fart...
Howie
Howard Hoyt
CE - WXYC-FM 89.3
UNC Chapel Hill, NC
www.wxyc.org
1st on the internet
The plot is after the amplifier. Typical Microphone signal for a dynamic mic on a stand with a normal voice at 18" is around a mv. Tapping pulses to a few hundred.
I have never seen the need to tap a condenser microphone.
Of course when the tapping works, it either means a bad solder joint or a dirty connector.
There used to be a lot of low cost phone plugs that had a bright shiny chrome like finish. These would over time get a duller oxide coat and stop working. Cleaning would work for a short time, but then they would stop working again. The decent techs would recognize the problem connectors and just change them for a better brand.
I still would like a defined experiment to repeat. In any case cold solder joints and cheap bad connectors are pathological problems not some inherent property of any connection.
I still say a repeatable rectifier/detector that efficient at mV levels would interest the radio astronomy community.
Will get to it. Paying work comes first.
Just finished recovering from network problems. Next week another Arena.
I wouldn’t mind if you were farting like you were doing above, all day long
Regards
George
While I wouldn't put it quite the same way I agree completely.
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