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Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

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Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#51

Post by kazinator »

sobriquet9 wrote: post #45
bcaa7f3a8bbc wrote: post #16

Earlier quoted context omitted.

The experienced and mysterious audio engineer "NwAvGuy" [0] praised the virtue of using two gain stages and moving the volume control away from the first input to reduce Johnson noise in audio amplifier designs [1]. It's a good example of how the basic principle applies both to mundane audio and cutting-edge science: the system noise is dominated by the first amplifier stage. Adding some noise before the first stage…

It's relatively easy to make a headphone amp quiet because its input is typically already quite strong. Noise is more of a problem for microphone preamps, guitar pickups, etc., where the input signal is weak.

Bingo. In any piece of music gear that is after the guitar/mic preamp, where it is working with line level signal (a higher voltage than consumer audio line level, by the way), it hardly matters where you put the volume knob. If you design it halfway well, it will be quiet as a mouse.

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#52

Post by exmadscientist »

sunjain wrote: post #44

It is surreal that this article showed up now. I am going back and forth currently with our electric utility company. They upgraded capacitor pack on the pole by my house. And these new ones are generating so much of this kind of low buzz sound, it is unbearable. I was researching into what generates this noise, and found this article very timely. Only solution is to move these, as nothing else can be done about this…

It is quite rare for capacitor banks to hum. Much more likely that you're hearing the magnetics (transformers), which indeed have reason to be where they are. Good luck.

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#53

Post by exmadscientist »

bcaa7f3a8bbc wrote: post #9

Fun fact: for the most demanding RF applications, namely, radio astronomy, the front-end low-noise amplifiers are indeed cooled to cryogenic temperature by liquid nitrogen. Here's how it's done at NASA for the Deep Space Network [0]. It's a long paper, see Chapter 4 Cryogenic Refrigeration Systems , PDF page 179 (text page 159). Also, nice photos in page 183 and 188. [0] https://descanso.jpl.nasa.gov/monograph/series…

I haven't crunched the numbers, but I seem to remember that LIGO has the RF guys beat in terms of requirements.

Fortunately for the rest of us, that meant they had to make some measurements, which they were kind enough to share: https://dcc.ligo.org/LIGO-T0900200/public

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#55

Post by jbay808 »

xenocyon wrote: post #42
jbay808 wrote: post #33

> In fact, a remarkably common response to a diagnosis of resistor noise is to seek a source of "good" resistors, with "good" being defined as without thermal noise. This is impossible. It's impossible to make a totally noiseless resistor, but it's also important to understand that all resistors are not created equal. Most resistors have noise levels that are orders of magnitude above the Johnson limit. Potentiometer…

Electrical engineer here. Thermal noise is the same for all resistors with a given R, regardless of their method of manufacture. You cannot have thermal noise either less or more than this, so it's not a Johnson "limit" but rather a definite value. You are correct that there are other sources of noise such as 1/f noise. But more importantly, the manner in which noise manifests in the end result has to do with the cir…

I think you "well actually"'d a bunch of things I specifically didn't say.

I use "Johnson limit" synonymously with "thermal noise limit" because they are the same, and it's the limit of how low noise can be after removing all other sources of noise.

Most people, if they even learn about resistor noise, will only learn about thermal noise. If they're lucky enough to identify a resistor as the noise troublemaker in a circuit, they might not have any idea that they can potentially cut the noise 1000x by changing the resistor from thick film to thin film, with no other design changes, at the cost of one cent. It's not common knowledge, as illustrated by the fact that an article like this, dedicated to the topic of resistor noise, doesn't even mention it. And instead laughs at someone even considering to look for a "good" resistor as though it were superstition.

In fact, thick film resistors are far more common, so if you're in the situation where you're reading this article because you have a noisy resistor in your circuit and don't already know about Johnson noise, you almost definitely don't know about current/flicker noise, and since you got here because of a noisy resistor in the first place, a "good" thin film resistor is overwhelmingly likely to be the cure.

I'm not advocating ad hoc selection of components to reduce noise any more than selecting ad hoc components to reduce cost. A noise analysis can help you find the problem but won't help you solve it if you think your only option is to change the resistor's value, rather than its type.

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#56

Post by sunjain »

exmadscientist wrote: post #52
sunjain wrote: post #44

It is surreal that this article showed up now. I am going back and forth currently with our electric utility company. They upgraded capacitor pack on the pole by my house. And these new ones are generating so much of this kind of low buzz sound, it is unbearable. I was researching into what generates this noise, and found this article very timely. Only solution is to move these, as nothing else can be done about this…

It is quite rare for capacitor banks to hum. Much more likely that you're hearing the magnetics (transformers), which indeed have reason to be where they are. Good luck.

Thanks. Indeed those are transformers, upon further digging(for some reason, I think of transformers as big, these are not big but boy they emit this low-buzz sound). And indeed it has been very challenging to have them moved, because as you said they probably picked this location based on a reason.

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#58

Post by segfaultbuserr »

zihotki wrote: post #48
jeffbee wrote: post #11

Earlier quoted context omitted.

I don't know how this one made it, but if there's an Analog Dialogue article on the front page of HN weekly for the next five years it will still barely scratch the surface of all the treasure that's buried in that archive.

And that's only the AD, if we add old articles for the last century from other sources, the HN will be flooded over. But would be they news?

> if we add old articles for the last century from other sources, the HN will be flooded over.

HN has been doing it for... I think a decade already? The situation so far looks good to me.

* “Corn-Pone Opinions” by Mark Twain (1901)

https://news.ycombinator.com/item?id=10822133

127 points, 56 comments

* Five Hundred and Seven Mechanical Movements (1908)

https://news.ycombinator.com/item?id=19968114

798 points, 147 comments

* G.K. Chesterton: The fallacy of success (1909)

https://news.ycombinator.com/item?id=6512288

198 points, 97 comments

* The Basic Problem of Democracy (1919)

https://news.ycombinator.com/item?id=21893486

206 points, 189 comments

* Why I Quit Being So Accommodating (1922)

https://news.ycombinator.com/item?id=14418877

866 points, 316 comments

* Why I Never Hire Brilliant Men (1924)

https://news.ycombinator.com/item?id=7437643

387 points, 264 comments

* War Is a Racket (1933)

https://news.ycombinator.com/item?id=22012255

336 points, 181 comments

* A Mathematical Theory of Communication (1948) [pdf]

https://news.ycombinator.com/item?id=23035107

197 points, 39 comments

* Claude Shannon Demonstrates Machine Learning (1952)

https://news.ycombinator.com/item?id=25919006

209 points, 51 comments

* Three-dimensional model of electricity consumption in Manchester (1954)

https://news.ycombinator.com/item?id=25959571

135 points, 31 comments

* Kurt Gödel's Letter to John von Neumann (1956) [pdf]

https://news.ycombinator.com/item?id=19281633

183 points, 85 comments

* An Algebraic Language for the Manipulation of Symbolic Expressions (1958) [pdf]

https://news.ycombinator.com/item?id=14885779

171 points, 12 comments

* America's Cult of Ignorance (1980) [pdf]

https://news.ycombinator.com/item?id=14778856

169 points, 113 comments

* How does a gas pump know to shut itself off? (1981)

https://news.ycombinator.com/item?id=24741029

384 points, 390 comments

* Will cable TV be invaded by commercials? (1981)

https://news.ycombinator.com/item?id=22977448

288 points, 354 comments

* Have You Ever Tried to Sell a Diamond? (1982)

https://news.ycombinator.com/item?id=4535611

273 points, 229 comments

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#59

Post by jhallenworld »

bcaa7f3a8bbc wrote: post #9

Fun fact: for the most demanding RF applications, namely, radio astronomy, the front-end low-noise amplifiers are indeed cooled to cryogenic temperature by liquid nitrogen. Here's how it's done at NASA for the Deep Space Network [0]. It's a long paper, see Chapter 4 Cryogenic Refrigeration Systems , PDF page 179 (text page 159). Also, nice photos in page 183 and 188. [0] https://descanso.jpl.nasa.gov/monograph/series…

The reverse problem is interesting. Consider Voyager 1- its high gain antenna is pointed essentially directly at the sun, a powerful wide-band noise source. How does it detect anything from earth? The DSN has to outshine the sun within the tiny S-band window that Voyager listens to: 20 kW and 62 dB antenna gain.

https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_e...

https://ipnpr.jpl.nasa.gov/progress_report/42-175/175E.pdf

Re: Resistor Noise Can Be Deafening, and Hard to Reduce (2007)

#60

Post by klodolph »

adammunich wrote: post #49
klodolph wrote: post #19

Earlier quoted context omitted.

> ...a discrete jfet has a better noise floor than an op amp or a regular transistor. This used to be true, but you can get really good low-noise op amps these days.

What is your favorite?

I don't really have a favorite op amp. There are so many good ones. Some audiophiles like to swap out op amps and talk about how good different ones sound, but I think that's a bunch of hogwash. If you believe that choosing the right op amp for an audio project has an impact on the sound, I'm the wrong person to ask about it.

There are some exceptions, like if you need a microphone preamp with 60 or 80 dB gain, but I have no experience in that area.

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