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sinsky
Joined: Aug 18, 2013 Posts: 4 Location: Poland
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Posted: Sun Oct 26, 2014 2:57 pm Post subject:
Chaotic shot noise generator proposition Subject description: Temperature coefficient random voltage generator |
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Hello everyone,
i've been wondering what happens to transistor on extremely high temperature operation - so I googled a bit and decided to do some tests.
Quote: | However, at sufficiently high temperatures the electrical difference between the n and p regions disappears and the p-n junction becomes ineffective in controlling carrier movement. This comes about as follows: as the temperature increases, the increased thermal energy ionizes significant numbers of the semiconductor atoms themselves (for example the Si atoms) in addition to the dopant atoms. This contributes additional electrons and holes in the conduction and valence and bands and, more important, results in approximately equal numbers of carriers in each band, independent of the doping, resulting in a condition called intrinsic. Since there are orders of magnitude more semiconductor atoms than dopant atoms, the influence of the dopant is overwhelmed at a sufficiently high temperature. The result is that the p-n junction becomes merely a fancy resistor that no longer controls the carrier flow, and leakage currents in devices can become so large that operation is disrupted. |
Yup. So if you heat transistor to high temperature (more than 300 deg Celsius) and decompose silicon junction, you’ll get variable resistor with chaotic behaviour. Adding resistor between emitter and ground will make voltage divider. Base is not connected.
So we have three-part noise generator able to make unpredictable sequence of noises
Circuit was connected to hi-Z input:
Heating the transistor case:
After holding transistor in flame for 10 seconds and cooling down it seems to have the same characteristics. Buffer made from burned transistor still worked nice…
Here is signal from node OUT recorded by Hi-Z input while heating up and cooling down transistor. Over some temperature (about 120-190 degree) it stops conducting.
When transistor achieves temperature of about 350 deg celsius (corner of case became slightly red) it starts to make chaotic oscillating sounds, its a sign that junction has changed its properties permanently. After cooling down it still can work, but huge random leakage currents are present.
BTW It’s sensitive to temperature changes - modulation is possible with heater resistor attached to case of transistor. It’s more stable at high temperatures, but stop conduct if it’s too hot.
Recording of damaged transistor generating random voltages:
https://soundcloud.com/sinsky-cuts/shot-noise
Bandpassed stable noise:
https://soundcloud.com/sinsky-cuts/tempco1
Oscillations during junction decomposition:
https://soundcloud.com/sinsky-cuts/tempco2
This noise generator can be used to add some grain to regular noise generator, would work great with drum generators (snares, hi-hats) and as trigger. As the transistor still conducts, some kind of random filtering and noise adder can be made (base is still working!)
I’ve also tested buffer made out of BC560 PNP transistor. It passes signal and add random noise bursts. Effects are very similar. Some low gain SI and Ge transistors are also waiting for temperature treating.
FYI: Paper about extreme temperatures transistor operation
http://www.extremetemperatureelectronics.com/tutorial3.html
Hope you find this interesting. Looking forward for feedback and your tests. _________________ sinsky Last edited by sinsky on Mon Oct 27, 2014 3:43 am; edited 1 time in total |
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DrJustice
Joined: Sep 13, 2004 Posts: 2114 Location: Morokulien
Audio files: 4
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Posted: Sun Oct 26, 2014 8:14 pm Post subject:
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Very cool experiment!
I like the tempco1 noise a lot. It sounds just like shortwave radio noise. What was the specific conditions to produce that?
BTW, the link ending in "shotnoise1" link should probably end in "shot-noise". |
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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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Posted: Mon Oct 27, 2014 5:51 am Post subject:
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very "uncool" experiment from the transistor POV
perhaps it would be more controllable and thus "reproducible" using power dissipation of the transistor instead of a lighter to toast it.
torting the transistor with high ( CB,EC avalanche) voltage instead of heat might cause other defects and sound different. Did you try this also ? |
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sinsky
Joined: Aug 18, 2013 Posts: 4 Location: Poland
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Posted: Mon Oct 27, 2014 7:45 am Post subject:
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@DrJustice: It was snippet from stable sequence recorded between one and another heating.. Unfortunately I cannot measure temperature inside the transistor Just need some time to make more precise recipe.
links fixed, thx.
@elektrouwe Thanks for hint, I think it's possible to control avalanche with current source, so I'll try make another circuit today. _________________ sinsky |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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sinsky
Joined: Aug 18, 2013 Posts: 4 Location: Poland
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Posted: Mon Oct 27, 2014 8:47 am Post subject:
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It produces noise also in room temperature. That 3-minute recording was made when transistor operated in 25 C. |
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DUBmatze
Joined: Feb 18, 2013 Posts: 150 Location: south Germaica (schwabilon)
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Posted: Mon Oct 27, 2014 9:10 am Post subject:
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PHOBoS wrote: | If it only produces noise when heated it's not really practical. | hehe .... today
we can ask dieter doepfer, maybe he add a gas pipeline for a bunsen burner to the eurorack modular system....
cool "project" btw!
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