Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

analog.com

Post reply on HN
Print view View original

71–80 of 110 posts

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

#71

Post by Gibbon1 »

bcaa7f3a8bbc wrote: post #16
klodolph wrote: post #15

My 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 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…

> the system noise is dominated by the first amplifier stage.

In radio receiver design you have an LNA, low noise amplifier, as the first stage. It's designed for low noise and to be linear. Idea is take the energy from the antenna and amplify it with as little noise and cross modulation as possible[1].

[1] If the amp is non linear you end up folding out of band signals into your band of interest.

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

#72

Post by fallingfrog »

klodolph wrote: post #66
guenthert wrote: post #64

Earlier quoted context omitted.

Uh, for a looong time already. The LT1028 was available in the eighties and afaik, still unsurpassed (in terms of voltage noise, it's unfortunately a sucker in terms of input current and current noise, so it's for low impedance applications only and it's fairly expensive). The cheaper OP-27 is also old and still available. The challenge is to find a low-noise OpAmp with high input impedance where earlier hybrids with…

Yes, I built a guitar pedal that was designed around JFET gain stages and the JFETs had to be sourced from a specialist. I wonder if they're still being made. Most of the discrete JFETs I see available are for switching applications.

I bought 4000 J201’s when I saw they were becoming obsolete, I still have most of them. But, I think there are better choices out there anyhow, that’s just what I’m used to using. They’re really easy to bias.

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

#73

Post by tedd4u »

exmadscientist wrote: post #53
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

Hew boy, don't click through to that site unless you have a few hours to check out all the custom LIGO part drawings …

Thanks for the link.

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

#74

Post by MegaDeKay »

Gibbon1 wrote: post #71
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…

> the system noise is dominated by the first amplifier stage. In radio receiver design you have an LNA, low noise amplifier, as the first stage. It's designed for low noise and to be linear. Idea is take the energy from the antenna and amplify it with as little noise and cross modulation as possible[1]. [1] If the amp is non linear you end up folding out of band signals into your band of interest.

The former bit is illustrated by the Friis formula.

https://en.wikipedia.org/wiki/Friis_formulas_for_noise

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

#76

Post by klodolph »

DiabloD3 wrote: post #32
wishinghand wrote: post #24

Earlier quoted context omitted.

That's really interesting. Is that a common design in headphone and other consumer amps?

It basically is now. He didn't invent the technique, but popularized it in inexpensive devices. The O2 has been surpassed by many great designs, but the O2 really did start that arms race.

It was also popular in the 80s, 70s, 60s, and yes, the 50s. Everything old is new. The real question is, "Why did people switch to single stage amps in the 1990s and 2000s?" The answer is that a bunch of chips appeared on the market around that time which could do everything.

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

#77

Post by cushychicken »

Chapter 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.

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

#78

Post by ChuckMcM »

I 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.

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

#79

Post by analog31 »

lisper wrote: post #63

One 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 da…

>>> I figured there was some hardware design trick that they hadn't taught me in my EE curriculum

https://patents.google.com/patent/US4744105A

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

#80

Post by Zenst »

michael1999 wrote: post #68
Zenst wrote: post #23

Earlier quoted context omitted.

I was messing about with contact microphones last year and very much akin area to guitar amps as high-impedance, so very much the same issues. If you run on batteries you will find it works best, as with anything mains, you will want a good ground. What I did find was that if you use peizo's back to back you can effect a balanced signal and that in itself helps immensely in eliminating much of the noise. You can also…

Wait. We have ADCs that produce floats now? That’s amazing.

Yip - not looked into any IC's, though kit with that functionality been trickling past couple of years and slowly picking up pace. https://zoomcorp.com/en/us/field-recorders/field-recorders/z... one example.
Post reply on HN