11 ms·
Resistor Noise Can Be Deafening, and Hard to Reduce (2007)
- zihotki 5y agoThe article, actually a single Q&A, is dated Sep 2007.
- Causality1 5y agoTo the best of my knowledge time-independent articles don't need a date stamp. I never see one on Wikipedia articles even if the last edit was years ago.
- IgorPartola 5y agoI am old enough to remember when naked Wikipedia articles were discouraged (or maybe even disallowed) on HN.
- zihotki 5y agoMy comment was only in regards with adding the date to the headline.
- jeffbee 5y agoI 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.
- JamesBryant 5y agoYou can find all the RAQ (Rarely Asked Questions) at:- https://www.analog.com/en/analog-dialogue/raqs/raq-issue-xxx.html https://www.analog.com/en/analog-dialogue/raqs/raq-issue-xxx... Where xxx (or xx or x - no leading zeros) is the number. Highest is presently 190. I wrote all the first ones, then I shared slots, and after I retired I just wrote the occasional one.
- OnlyOneCannolo 5y agoI binge-read the RAQs a few months ago. So much great information. Thank you! I also appreciated the consistent URL scheme because it let me easily scrape all the PDFs to read them offline. The one bummer is that the links at the end of the PDF versions seem to be broken now.
- zihotki 5y agoAnd 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?
- segfaultbuserr 5y ago> 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 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 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 https://news.ycombinator.com/item?id=6512288 198 points, 97 comments * The Basic Problem of Democracy (1919) https://news.ycombinator.com/item?id=21893486 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 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 https://news.ycombinator.com/item?id=7437643 387 points, 264 comments * War Is a Racket (1933) https://news.ycombinator.com/item?id=22012255 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 https://news.ycombinator.com/item?id=23035107 197 points, 39 comments * Claude Shannon Demonstrates Machine Learning (1952) https://news.ycombinator.com/item?id=25919006 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 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 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 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 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 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 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 https://news.ycombinator.com/item?id=4535611 273 points, 229 comments
- mattkrause 5y agoThe last line got a good chuckle out of me!
- ISL 5y agoIt is now partially incorrect, too. Now we can no longer change Boltzmann's constant not because he's dead (indeed, until recently, it was a measurable quantity), but because k_B is now defined as a part of the redefinition of the SI unit system in 2018. The value is 1.380649×10^{−23} J/K, exactly.
- JamesBryant 5y agoIt was correct when I wrote the RAQ in 2007. In fact I've been making the crack about 'not being able to change it because he's dead' in my lectures for at least forty years.
- StavrosK 5y agoIt's correct now too, since we can no less change the value now than before the redefinition (we can't change it in either case, and not because Boltzmann is dead), so the joke works fine!
- thaumasiotes 5y ago> k_B is now defined as a part of the redefinition of the SI unit system in 2018. > The value is 1.380649×10^{−23} J/K, exactly. Hmm. This is a trendy thing to do with SI units, indeed. But this definition makes me wonder if there are also definitions of the Joule and the Kelvin. If there are, it seems like they could easily conflict with this definition of k_B. And if that happened, we'd have to admit that k_B was a measurable quantity all along -- the only way to demonstrate a conflict in the definitions would be by measuring the quantity more accurately.
- minitoar 5y agoNot in SI. Kelvin is defined in terms of k_B. Joule is defined in several ways, eg force & distance.
- dekhn 5y agoYet another unexpected sighting of Boltzmann's tomb.
- OnlyOneCannolo 5y agoThey have a cool PDF cheat-sheet related to this which doesn't seem to be linked from the page. https://www.analog.com/media/en/selection-guides/Equation_Pullout.pdf https://www.analog.com/media/en/selection-guides/Equation_Pu...
- bcaa7f3a8bbc 5y agoFun 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/series10/Reid_DESCANSO_sml-110804.pdf https://descanso.jpl.nasa.gov/monograph/series10/Reid_DESCAN...
- madengr 5y agoSince the amplifier has both voltage and current input noise sources, there is an optimum source impedance that provides a minimum noise figure, and it’s not an impedance match. This is called a minimum noise match, along with associated noise contours where noise is traded off with impedance match. Also, the noise from an antenna is dependent on it’s efficiency and what it’s pointing at. Even if it’s input impedance is 50 Ohms, it can generate far less noise than the equivalent resistor.
- exmadscientist 5y agoI 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 https://dcc.ligo.org/LIGO-T0900200/public
- deleted 5y ago[deleted]
- carapace 5y agoNot really related (I think) but I was reading about "an electrical resistor that has no residual mutual- or self-inductance at high frequencies." The trick is to twist it into a Möbius strip! http://www.rexresearch.com/davis/davis.htm http://www.rexresearch.com/davis/davis.htm
- fallingfrog 5y agoI usually put a single 470 ohm resistor in line with the gate of a discrete jfet in common collector mode as the first gain stage in my projects. Once you boost up the signal voltage it’s way easier to maintain a good signal to noise ratio. The resistor is there to prevent the jfet from being burned out by over voltage on the gate, which is very sensitive to static electricity. But, I can easily hear the difference if I put a 10k resistor there instead. It’s really important to get that first gain stage really, really quiet, a discrete jfet has a better noise floor than an op amp or a regular transistor.
- klodolph 5y ago> ...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.
- adammunich 5y agoWhat is your favorite?
- klodolph 5y agoI 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.
- analog31 5y agoFor audio, it's hard to go wrong with the OPA1654 for DIY projects that are not cost sensitive. It draws a lot of current. For battery power I'm intrigued by the TLC2264 which, while having somewhat more noise, has very low operating current and rail-to-rail performance.
- guenthert 5y ago
- klodolph 5y agoMy only experience with this is building and designing guitar amps, which often have 80dB of gain or more, a.k.a., a pain in the ass amount of gain to deal with. It's not something on par with, say, radio astronomy, but it's still a lot of gain to deal with. Usually the main source of noise will be a 120Hz or 100Hz buzz, but with humbucking pickups and careful orientation of the guitar you can mostly eliminate that. The next source of noise will be a low-level white noise (sounds like a hiss), which is from the amplifier, and consists of a mixture of Johnson noise and shot noise. In older amps you may hear a louder hiss/crackle which is from old carbon comp resistors, which is an inferior type of resistor that produces additional noise through a different mechanism. If you're trying to record your guitar directly through a digital interface, you may run into clipping issues and have to enable the pad (a built-in attenuator). Unfortunately, my experience is that the pad often introduces an unacceptable amount of noise, and I believe that it's just plain Johnson noise from a resistive divider.
- bcaa7f3a8bbc 5y agoThe 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 significantly degrades signal-to-noise ratio, but adding the same noise after the first stage is often acceptable since the signal is much stronger now. To reduce noise, you move the noise-generating resistor away in an audio amp, or cryogenically cool the resistor in a radio telescope front-end. > One of the big claims for many audiophile op amps is lower noise. The chip manufactures make a big deal about it and audiophiles, not surprisingly, have jumped on the bandwagon. But, in reality, it’s often the Johnson Noise that limits the noise performance of a headphone amp, not the op amps. Johnson Noise is, literally, self generated noise that’s present in any resistor. The larger the resistor value, the more noise you get. Many DIY headphone amp designs have the volume control at the input to the gain stage. And it’s, at the lowest, usually 10,000 ohms. By comparison the O2 has 274 ohms in series with the input. That’s a huge difference in Johnson Noise. The way volume controls work, the noise is typically worst at half volume where you have 5000 ohms in series with the source and 5000 ohms to ground. So, at typical volume settings, you get a fair amount of Johnson Noise from the volume control that’s amplified by whatever gain your amp has. That noise typically exceeds the op amp’s internal noise. If you put the volume control after the gain stage its Johnson Noise is no longer amplified. And, as a bonus, the volume control at lower settings now attenuates noise from the gain stage. For more, see O2 Circuit Description and Circuit Design. > To put these numbers in perspective, referenced to the old 400 mV they’re –105.3 dBr and –108.2 dBr. On the exact same test, at half volume, the Mini3 had nearly 11 dB more noise and measured –94.5 and –97.5 dB. Noise of –113 dB below 1 volt is under 3 microvolts. [0] https://spectrum.ieee.org/tech-history/silicon-revolution/nwavguy-the-audio-genius-who-vanished https://spectrum.ieee.org/tech-history/silicon-revolution/nw... [1] https://nwavguy.blogspot.com/2011/07/o2-headphone-amp.html https://nwavguy.blogspot.com/2011/07/o2-headphone-amp.html
- peter_d_sherman 5y agoThere's a strange relationship between Resistance, Noise (audible and above the auditory spectrum, such as RF), and the concept of Impedance... I'll put a wager that future (or perhaps even current!) scientists are able to engineer complex waveforms such that the complex waveform effectively negates the resistance/noise/impedance -- effectively turning the resistor into a conductor -- but only for that specific complex waveform -- which very possibly would change over time... Also, future (and perhaps current!) scientists should be able to use an electrical signal of known characteristics -- to determine exactly what the complex impedance of the resistor/resistance element/impedance element -- in a circuit is, exactly... In other words, given one of the above things (complex waveform, complex impedance) -- derive what the other one is, from it...
- deleted 5y ago[deleted]
- ng55QPSK 5y agoAt my workplace one R&D engineer had the last lines printed out as poster (i guess the AD note is older than 2007)
- cryptonector 5y ago> And, of course, we can't change Boltzmann's Constant because Professor Boltzmann is dead[3]. Worth the read just for that punch line.
- mgleason_3 5y agoThe pinnacle on a wonderful respite from the mire of politics and opinions that often invades hacker news.
- ipspam 5y agoYou might be a candidate to join the Audiophile club ;) Just a couple hundred bucks a month for a decade, unlimited reading and real life trial and error, and infinite fun. Give it a consideration
- pfdietz 5y agoThe opening paragraph of Goodstein's "States of Matter": "Ludwig Boltzmann, who spent much of his life studying statistical mechanics, died in 1906, by his own hand. Paul Ehrenfest, carrying on the work, died similarly in 1933. Now it is our turn to study statistical mechanics."
- Applejinx 5y ago"…for as long as we can"? D:
- matthewdgreen 5y agohttps://en.wikipedia.org/wiki/Breeds_There_a_Man...%3F https://en.wikipedia.org/wiki/Breeds_There_a_Man...%3F
- Workaccount2 5y agoEhrenfest didn't just die similarly, he took his (disabled) son with him!
- jhallenworld 5y ago
- jbay808 5y ago> 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. Potentiometers are especially bad. If you want "good" resistors for noise-critical applications, I recommend metal thin-film resistors. They hardly cost any extra anyway. Also, in cases where resistors are used to set DC signals such as offsets and biases, you can add capacitors to filter the heck out of those lines to decrease their noise contribution.
- prpl 5y ago… and overspec them everywhere reasonable
- wellthereitis 5y agoGreat tips, thank you!
- xenocyon 5y agoElectrical 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 circuit as a whole. For noise critical applications you should do a noise analysis of the circuit as a whole rather than make ad hoc selections of components.
- jbay808 5y agoI 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.
- kazinator 5y agoShould say "Now that he's long dead, we could easily get away with changing Professor Boltzmann's constant, but it would be disrespectful".
- sunjain 5y agoIt 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 sound. Which is turning into quite a project.
- exmadscientist 5y agoIt 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.
- sunjain 5y agoThanks. 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.
- buescher 5y agoAnd yet, there is such a thing as a low-noise resistor, because thermal noise is not the only resistor noise. This application note, also from Analog, explains: https://www.analog.com/media/en/technical-documentation/application-notes/500824934643930414583807523874018494695982855668424783486554001060AN348.pdf https://www.analog.com/media/en/technical-documentation/appl...
- xbar 5y agoThanks. I will be sure to pay my respects at Boltzmann's grave the next time I am in Vienan.
- Footkerchief 5y agoThe underlying principle: https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise https://en.wikipedia.org/wiki/Johnson%E2%80%93Nyquist_noise
- FriendWithMoon 5y agoSimilar to what having permanent tinnitus sounds like. Take care of your ears!
- lisper 5y agoOne of my first jobs, which I got while I was still an undergrad (in the mid-80s), was designing amplifiers for fiber-optic sensors. I pretty much had no clue what I was doing so I just started futzing around with op-amps and realized very quickly that my signal-to-noise-ratio was much higher than was acceptable. I figured there was some hardware design trick that they hadn't taught me in my EE curriculum, but one day I decided to do the math on resistor noise and discovered that that was in fact my limiting factor and the only way were were going to get it to work was to either cool the first-stage resistor or to use a ridiculously high value because the gain goes up linearly with the resistor value but the noise only increases with the square root. We ended up with a ten gigaohm resistor, which was just enough to get the S/N ration we needed to make it work.
- analog31 5y ago>>> I figured there was some hardware design trick that they hadn't taught me in my EE curriculum https://patents.google.com/patent/US4744105A https://patents.google.com/patent/US4744105A
- fuzzfactor 5y ago>a ten gigaohm resistor Depending on the voltage across a resistor like that, you may calculate less than one electron passing through the resisitor per second. Without ceramic or teflon standoffs, the circuit board can often conduct better than the resistor, plus dust can also accumulate on the outside of the resistor and conduct better eventually, which is why they are often encased in glass, so they can be effectively cleaned during a maintenance cycle.
- lisper 5y ago> Depending on the voltage across a resistor like that, you may calculate less than one electron passing through the resisitor per second. If memory serves (this was a very long time ago) the output signal was a couple of millivolts, so it wasn't quite that bad. But one other thing that saved us was that we only needed a few hertz of bandwidth.
- deleted 5y ago[deleted]
- jeffrallen 5y agoIf you did not read to the last sentence, go back an do so. It's worth it.
- cushychicken 5y agoChapter 8 of The Art of Electronics, 3rd Edition is a great resource on electrical noise. The first section is almost exclusively about resistors and noise budgeting. Fun read. I should get back to it at some point. Lots of great tricks on bootstrapped filters, capacitive multipliers, precision transistor noise measurements with some outboard circuits fed into a spectrum analyzer.
- ChuckMcM 5y agoI read it more like a whine "don't blame our opamps, they better than resistors" :-) But it is something I've become much more familiar with building RF frontends for software defined radios. You want as much gain as you can get to pull in weak signals but keeping the whole thing noise quiet is really really hard.
- Unklejoe 5y agoI was watching an interview with Tom Christiansen (he owns Neurochrome, a company that makes very high-end DIY amplifier designs/kits, with THDs of 0.0001%). He mentioned something about how resistor noise can actually track with the low frequency portions of the audio signal due to the resistor literally heating up and cooling down as the current through it varies. I thought that was interesting. I knew that noise was proportional to heat, but I didn't realize the temperature could vary that quickly, but I guess it makes sense when you're dealing with tiny parts. There are probably also localized hot spots that have less thermal mass than the entire resistor as a whole. The interview is posted in this thread: https://www.audiosciencereview.com/forum/index.php?threads/the-intellectual-people-podcast-tom-christiansen-of-neurochrome.19946/ https://www.audiosciencereview.com/forum/index.php?threads/t...
- pontifier 5y agoExcellent article! I feel like I understand so much more about analog signals than I did before. It seems very obvious now, that if you want to have a high signal to noise ratio, you should get as much signal as possible, and keep your signal voltage as high as possible as long as possible before amplification. This fundamental resistor noise is something that I'm probably going to start seeing everywhere when I look at any analog signals, and will have to take into account when designing things.
- failwhaleshark 5y agoOn a tangent: acoustic noise. My HP 32SII made terrible resistor noises. Bzzzzzzz like some sort of bad tinnitus. I could also hear it on an HP 48G when I placed my ear up to it. Wouldn't it be possible to use SMT resistors and pot them in silastic to quiet them down?
- bsmith0 5y agoIt's probably coil whine? https://en.wikipedia.org/wiki/Electromagnetically_induced_acoustic_noise https://en.wikipedia.org/wiki/Electromagnetically_induced_ac...
- bcaa7f3a8bbc 5y agoUsually it's inductor coils and transformers, occasionally it's ceramic capacitors (all grades other than NP0 are microphonic, SMD or not), both problems are common in switched-mode power supplies, for example, powering the calculator LCD. I've never seen a singing resistor, very unlikely.