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 Forum index » DIY Hardware and Software » Developers' Corner
Chaotic shot noise generator proposition
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sinsky



Joined: Aug 18, 2013
Posts: 4
Location: Poland

PostPosted: 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.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
So we have three-part noise generator able to make unpredictable sequence of noises Very Happy

Circuit was connected to hi-Z input:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Heating the transistor case:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

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…

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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:
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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.

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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
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PostPosted: Sun Oct 26, 2014 8:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

Very cool experiment! Very Happy

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

PostPosted: Mon Oct 27, 2014 5:51 am    Post subject: Reply with quote  Mark this post and the followings unread

very "uncool" experiment from the transistor POV Wink
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
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Location: Poland

PostPosted: Mon Oct 27, 2014 7:45 am    Post subject: Reply with quote  Mark this post and the followings unread

@DrJustice: It was snippet from stable sequence recorded between one and another heating.. Unfortunately I cannot measure temperature inside the transistor Sad 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.

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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Mon Oct 27, 2014 8:33 am    Post subject: Reply with quote  Mark this post and the followings unread

looks interesting but one thing is not really clear to me.
Does it only produce noise when heated (and then it's broken as a normal transistor) or do you heat it and afterwards
you can use it as a noise source ? If it only produces noise when heated it's not really practical.

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sinsky



Joined: Aug 18, 2013
Posts: 4
Location: Poland

PostPosted: Mon Oct 27, 2014 8:47 am    Post subject: Reply with quote  Mark this post and the followings unread

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)

PostPosted: Mon Oct 27, 2014 9:10 am    Post subject: Reply with quote  Mark this post and the followings unread

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....
Laughing

cool "project" btw!
props
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