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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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AlanP
Joined: Mar 11, 2014 Posts: 746 Location: New Zealand
Audio files: 41
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Posted: Sat Jun 06, 2020 10:25 am Post subject:
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Might be easier to just use a 10 giga-ohm resistor. Never used them myself, though, so don't know their details. |
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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Posted: Sat Jun 06, 2020 10:27 am Post subject:
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AlanP wrote: | Might be easier to just use a 10 giga-ohm resistor. Never used them myself, though, so don't know their details. |
yes I'm looking for sources of larger resistance now : )
maybe just a big chunk of some poor conduction material?
edit: OK, I see it's pretty easy to get 1 to 22 Gohm resistors... even 1 Tohm
With 44 Gohms (2 x 22Gohm) you get around 13mV of noise, not bad : )
With 1 Tohm you'd get 60mV, yumm! haha
I like avalanche noise but using resistors would be fun _________________ Fer
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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Posted: Mon Jun 08, 2020 4:38 am Post subject:
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Fernando wrote: | Would this be a reasonable start? |
no [ educational mode on ]. What would be the bandwidth given a 44Gohm source R and a 10pF input buffer capacity ? What happens if you load a 1mV voltage source with 1Tohm output impedance with an opamp with 1GOhm input impedance ? |
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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Posted: Mon Jun 08, 2020 4:48 am Post subject:
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elektrouwe wrote: | Fernando wrote: | Would this be a reasonable start? |
no [ educational mode on ;-) ]. What would be the bandwidth given a 44Gohm source R and a 10pF input buffer capacity ? What happens if you load a 1mV voltage source with 1Tohm output impedance with an opamp with 1GOhm input impedance ? |
Hey! thank you : )
I assume 10pF represents the input capacitance of the op amp...
A drastic R/C LP filter with -3dB at 0.36Hz? (44Gohm/10pF to ground)
Oh and yes the output impedance of such a resistor is giant too : (
even for a very high input imp op amp
disasta'
I trusted the unity gain buffer will take care of everything but ehmmm... no
How to pick up the noise with minimum degradation?
please enlight me : ) _________________ Fer
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Sven
Joined: Mar 10, 2017 Posts: 48 Location: Norway
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Posted: Mon Jun 08, 2020 9:20 am Post subject:
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Fernando wrote: | Would this be a reasonable start? |
No. Noise is a voltage. To amplify this voltage both ends of the resistor need to be connected to an amplifier. |
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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Posted: Mon Jun 08, 2020 12:55 pm Post subject:
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Sven wrote: | Fernando wrote: | Would this be a reasonable start? |
No. Noise is a voltage. To amplify this voltage both ends of the resistor need to be connected to an amplifier. |
Thank you.
One end to ground?
To both inputs of an op amp?
Or using two inputs of an inverting mixer? (two parallel inputs of same op amp)
Or using two op amps and mix them later?
any example or guide welcome
hope my ignorance is not too irritating 😅 _________________ Fer
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Fri Jun 12, 2020 5:54 am Post subject:
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While "thermal noise" is an interesting scientific topic, it has a varying effect depending on the material used. Carbon resistors will be one of the better noise generators hence why so many amplifier designers have stopped using them.
What you want is to pass current through the resistor. If the resistor is grounded, then there's no appreciable current flowing through the resistor. But this method of making a noise generator is not optimal. In fact, the noise in a diode or transistor is also caused by thermal physics, but the noise amplitude in some semiconductors is far larger than a resistor. The problem with transistor noise sources is that transistors have different noise characteristics per unit so one has to build a test jig and listen to different transistors until a "good" one is found. Problems can include weak noise signal and popcorn noise. Another problem of making analog noise sources is that even semiconductor noise is very low amplitude and thus needs a high gain amplifier to be useful. High gain amplifiers themselves are plagued by noise, but different kinds, the most common being mains hum pickup.
So if you just want decent noise, in the end, the best consistently high quality noise is generated digitally.
If this is just a tinkering experiment - well, have fun and let us know what the end result is _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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Fernando
Joined: Dec 30, 2006 Posts: 286 Location: Barcelona & Emporda, Spain
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Posted: Fri Jun 12, 2020 6:08 am Post subject:
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Thank you.
Yes zener or transistor noise generators are great. And I use a socket or breadboard to find the right ones, etc.
It's just that I'd like to try with a huge resistor, for fun and find it interesting.
I didn't expect to be so problematic, but since it is I will learn in the way to it.
The "problem" is that I need some help : ) can't do it by myself alone
> What you want is to pass current through the resistor. If the resistor is grounded, then there's no appreciable current flowing through the resistor.
. _________________ Fer
. Last edited by Fernando on Fri Jun 12, 2020 7:57 am; edited 1 time in total |
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JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
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Posted: Fri Jun 12, 2020 7:04 am Post subject:
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Got it.
Here is what I would try:
Code: |
+-------R4--+
+V | |
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R1 | | \ |
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+---||--R3-+--+ - \ |
| C1 | >---+-----> out
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R2 +---+ +/
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| GND |/
GND
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Pardon the ASCII-matic...
R1 would be 10K
R2 would be a resistor in megohms range
R3 should be at least as large as R2
R4 should be G (gain) times R3 depending on how much gain you want/need.
C1 something like .01 uF
It is best if R2 is the ONLY carbon resistor and all the rest are metal film.
The opamp should be one with high input impedance, such as TL07x.
A small capacitor may be needed across R4 to prevent oscillation.
No idea how much gain would be appropriate. It's possible it won't do anything at all.
However, the idea is to pass current through R2 which would develop a noise signal across it's terminals. Given enough gain (G), you might hear the noise signal. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
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Grumble
Joined: Nov 23, 2015 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Sun Jun 14, 2020 9:54 am Post subject:
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Make R1 also very high, like R2 and R3 because basically you have R1 in parallel with R2 and this wil lower your noise output.
Quote: | A small capacitor may be needed across R4 to prevent oscillation. |
Be careful, since this too will lower your noise output.
Better to have a power resistor very close to R2 to heat it up, you are looking for thermal noise, so increase the temperature and keep it at a fixed level, _________________ my synth |
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