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

91–100 of 110 posts

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

#91

Post by pontifier »

Excellent 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.

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

#92

Post by analog31 »

guenthert wrote: post #64
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.

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…

Indeed the LT1028 datasheet shows a BF862 JFET at the front end of a photodiode preamp using the LT1018.

The reason why we're at a plateau of op amp noise performance is that the current crop of chips are operating very close to the theoretical limit for both bipolar and JFET input devices.

Ironically I use a LT1028 in a homemade circuit for measuring the noise of things that are more noisy.

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

#93

Post by msds »

floxy wrote: post #90
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.…

>I believe that it's just plain Johnson noise from a resistive divider. Any reason for guitar pads couldn't use a capacitive divider in place of a resistive divider? (I have no idea what a guitar pad is)

Wouldn't the input impedance be annoyingly variable?

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

#94

Post by analog31 »

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?

For 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.

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

#95

Post by Renaud »

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.…

While not exactly for guitar, Phil’s Lab on youtube recently posted a low noise headphone amplifier design that's both over-kill in some ways and interesting and cheap to make.

https://www.youtube.com/watch?v=Z2GUoi63pJs

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

#96

Post by KeytarHero »

Zenst wrote: post #80
michael1999 wrote: post #68

Earlier quoted context omitted.

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.

Not exactly - Zoom stuff does a clever trick of using 2 ADCs at different gain levels (essentially the same way that HDR photography works), but ultimately it's still using fixed-point ADCs.

This isn't actually a new idea - I know Line 6 has been using it in guitar pedals since at least 2006. Of course, ADCs have gotten better since then - I doubt they were getting even 24 ENOB back then.

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

#97

Post by ipspam »

mgleason_3 wrote: post #37
cryptonector wrote: post #28

> And, of course, we can't change Boltzmann's Constant because Professor Boltzmann is dead[3]. Worth the read just for that punch line.

The pinnacle on a wonderful respite from the mire of politics and opinions that often invades hacker news.

You 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

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

#98

Post by YZF »

kazinator wrote: post #47
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.…

I was surprised to find that after replacing most of the op-amps in a ADA MP-1 pre-amp, most of that orientation-sensitive remaining buzz that you still get with humbucking pickups was seriously reduced. When I'm playing at a low volume, I can just mute the strings and put the guitar on a stand to get it to be quiet. On a high-gain program using the tube board and all. The reason for some of the buzz is that the circ…

IIRC that's where you'd use an instrumentation amplifier.

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

#99

Post by failwhaleshark »

On 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?

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

#100

Post by bsmith0 »

failwhaleshark wrote: post #99

On 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?

It's probably coil whine? https://en.wikipedia.org/wiki/Electromagnetically_induced_ac...
Post reply on HN