Name that opamp! - Page 1
Forum section: electronics / projects

author: iampoor
author_rank: Frequent Contributor
timestamp: March 26, 2014, 07:57:22 am
content: So long story short, I have had the oppourtunity to work on some good sounding, yet hoky, audio gear.Take a look at the website if you dont believe me....http://www.davisound.com/ToolBoxes.html#TB9Anyways, everything this guy builds is simple and point to point (except for the "masterpiece" modules) which comprise his gain blocks/opamps. Alot of circuits are done "dead bug" style on home etched single sided material too...etc. Ill get some pictures next time.Anyways, Im trying to figure out what opamp is in his custom potted 'masterpiece" modules, and he lists the specs on his sitehttp://www.davisound.com/MasterPieces.html"ELECTRICAL SPECIFICATIONS FOR HOUSE IC USED IN MP-1, MP-2, MP-3:Frequency response, (as-is, un-compensated, unity gain, .777 V RMS input ) ... flat to 10 MHZInput Noise Voltage at 1KHZ - less than 4 nanovolts per stageTypical Supply current - 12 mATHD at unity gain, per inverter stage less than .001%Slew Rate 12 V/uSMaximum Supply Voltage 48 voltsMinimum Supply Voltage + 9 voltsSuggested supply voltage + 45 VoltsLifespan- unknown - absolute minimum expected performance ...under less than ideal thermal conditions - 20 years ...Theoretical performance under ideal conditions - 1,000 years!"Any thoughts of what chip it may be? Im sure the manufactures datasheet doesnt say they will last 1000 years.

author: GK
author_rank: Super Contributor
timestamp: March 26, 2014, 08:06:55 am
content: Probably an NE5534.QuoteWell that's exactly what you want for maximum EMI/RFI immunity and electrical safety.

author: Anks
author_rank: Frequent Contributor
timestamp: March 26, 2014, 08:58:40 am
content: For the price it better be good. Ive worked in the pro sound industry for many years and yes the gear looks good but will probably ware quickly and not be up to the the quality you get from Klark Tecknik, Square 1, Lake etc.

author: fcb
author_rank: Super Contributor
timestamp: March 26, 2014, 09:51:01 am
content: NE5534 certainly meets the criteria, except it depends on your definition of flat to 10MHz is. Also NE5534 is 30v max.My guess is OPA37 though.

author: GK
author_rank: Super Contributor
timestamp: March 26, 2014, 10:34:53 am
content: Assume the cheapest! NE5534's absolute maximum rating is +/-22V (Phillips and ON semi datasheets). Those potted modules could have zener regulation or similar as well. At a bare minimum they would need supply rail bypass caps.Once upon a time there was a supplier selling re-labeled DIP NE5534's at an audiophile premium (~$50 each from memory). If you order a large enough batch from some semi manufacturers, for a fee, they will happily label the parts with your own logo / part #.

author: dannyf
author_rank: Super Contributor
timestamp: March 26, 2014, 11:00:26 am
content: QuoteQuoteThose are impossibly nice specs,

author: dannyf
author_rank: Super Contributor
timestamp: March 26, 2014, 11:01:38 am
content: QuoteWhen you are dealing with golden ears, science + rational thinking are out, marketing is in.

author: GK
author_rank: Super Contributor
timestamp: March 26, 2014, 11:11:42 am
content: Voltage noise spec for the NE5534 is 4nV/sqrtHz. It will do 4nV input-referred noise when connected as a unity gain follower. However configured with gain the input referred noise will be higher due to the contribution of the feedback network impedance. 4nV is approx equal to 900 ohms.

author: macboy
author_rank: Super Contributor
timestamp: March 26, 2014, 02:19:03 pm
content: Quote from: GK on March 26, 2014, 11:11:42 amNote quite. A 900 ? resistor does have approximately 4 nV/sqrtHz of thermal noise density. That doesnotequate to 4 nV of noise, unless your measurement bandwidth is only zero to 1 Hz! If you use the audio band (zero to 20 kHz), then the total thermal noise of a 900 ? resistor (or a NE5534 unity gain follower) is approximately 4 nV/sqrtHz * sqrt(20000 Hz) = 566 nV.

author: GK
author_rank: Super Contributor
timestamp: March 26, 2014, 08:42:56 pm
content: Quote from: macboy on March 26, 2014, 02:19:03 pmUmm, "input referred noise" is always expressed in a 1Hz bandwidth at a specific center frequency. For example, 4nV @ 1kHz for the NE5534 (which also happens to be the quoted spec for that audiophile module). At LF it can be higher due to 1/f noise (particularly for jfet-input op-amps). I didn't say that the net noise in a 20kHz bandwidth would be only 4nV.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 26, 2014, 08:53:48 pm
content: Quote from: GK on March 26, 2014, 11:11:42 amThe important thing here is to keep it below 5nV/Hz^0.5 ... my ear can hear 5nV and up! Sounds really... digital...

author: GK
author_rank: Super Contributor
timestamp: March 26, 2014, 09:01:11 pm
content: Quote from: CaptnYellowShirt on March 26, 2014, 08:53:48 pmLOL.5nV sqrt-hz is approx -123dB ref a signal level of 1V rms in a 20kHz bandwidth (even lower A-weighted).A 747 jet engine at full bore at 100m is ~ 120dB while a quite listening room back ground noise is around maybe, I dunno, 20 or 30dB. You are claiming to hear a mouse farting at your feet with your head stuck in the back of a jet engine.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 26, 2014, 09:10:26 pm
content: Quote from: GK on March 26, 2014, 09:01:11 pmPleaseeee.... no one could hear such a thing!...that is unless they're listing to it though spider-spun, 100% matter free, headphone wires. You've heard of platinum? Well these are made from un-platainum -- its just like platinum, only its 4 times as expensive.

author: macboy
author_rank: Super Contributor
timestamp: March 27, 2014, 01:11:13 pm
content: Quote from: GK on March 26, 2014, 08:42:56 pmThere is no need to debate. The noise specification of any amplifier or other analog system is usually given as nV/sqrtHz, but never simply nV @ some single frequency. Due to 1/f noise, there is a rise in the noise density (which implies the something 'per' something) at lower frequencies, so they usually include one or two additional noise density specs at lower frequencies and/or a noise density vs. frequency graph. If the bandwidth is >>10x the 'knee' of the 1/f noise, then it has no significant effect on the system noise calculation for that bandwidth.Here it is in black and white:

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: March 27, 2014, 11:07:54 pm
content: Quote from: macboy on March 27, 2014, 01:11:13 pmDo they even make spider-spun wires?

author: GK
author_rank: Super Contributor
timestamp: March 28, 2014, 05:27:16 am
content: Quote from: macboy on March 27, 2014, 01:11:13 pmWTF? Can you read for comprehension?Dannyf claimed that the quoted spec of "input noise of 4nV @ 1kHz" for that audiophile module was unrealistic. I simply pointed out that it was realistic/nothing remarkable and is in fact the exact same spec as for the NE5534. The NE5534 IS speced at 4nV @ 1kHz. What is so difficult to understand? And where did I say that ein is only ever specified/tabulated at single measurement frequency (not others besides 1kHz)?No, "4nV @ 1kHz" is not a complete noise characterization and in this particular case ignores 1/f noise, but that is completely besides the point I was making.And to reiterate, in op-amp datasheets, by established convention, input-referred noise IS always specified in a 1Hz bandwidth - it is nV/SQRT-Hz, not nV/SQRT-100kHz or nV/SQRT-5kHz. That's "Hz" as in just one. The noise plots Vs frequency typically given in op-amp datasheets, such as this (ONsemi NE5534).......show the input-referred voltage noise density in a1 Hz bandwidth(notice the label given to the vertical scale?) over a sweepedcenter frequency range(in this particular instance 10 Hz Fc to 10 kHz Fc)."4 nV/SQRT-Hz @ 1 kHz" given in the datasheet does not mean " 4nV/SQRT-1000 Hz", which appears to be your fundamental misunderstanding. It means that there is 4nV of noise in a 1 Hz brick-wall-bandwidth* bandpass centered on a "single" center frequency of 1 kHz. This is called a "spot noise measurement":FromMotchenbacher and Connelly, Low-Noise Electronic System Design, John Wiley & Sons, IncThe above text formed the theoretical basis for my homebrew noise measurement test set, specifically designed for characterizing the spectral noise density for audio amplifier stages over the range of 10 Hz to 20 kHz:http://www.users.on.net/~glenk/nts/nts.htm* This is theoretical. A brick-wall filter with a 1 Hz bandwidth also have a noise bandwidth of 1 Hz. In real life a measurement bandpass filter with non-ideal slopes will have a -3dB bandwidth significantly less than 1 Hz for a noise bandwidth of 1 Hz. The value of the ratio of -3dB bandwidth to noise bandwidth depends on the order of the filter. For a 1st order filter with a Gaussian response the ratio is 1.57:1. The ratio decreases for higher orders, which more closely approach the ideal response.

author: dannyf
author_rank: Super Contributor
timestamp: March 28, 2014, 10:58:56 am
content: QuoteIndeed.People just need to understand what a density function is.

author: dannyf
author_rank: Super Contributor
timestamp: March 28, 2014, 11:11:49 am
content: For those who don't understand density functions, I have an "audio-grade" ne5534 follower with noise < 0.000001pv, as evidenced by the datasheet.

author: GK
author_rank: Super Contributor
timestamp: March 28, 2014, 11:41:24 am
content: Quote from: dannyf on March 28, 2014, 11:11:49 amYou're exaggerating a bit. If your special NE5534 really did have only 4nV of noise for the square root of a 1000 Hz bandwidth, a 129pV ein (~7 times better than the best from either Linear Technology or Analog Devices) it would certainly be a remarkable op-amp.

author: macboy
author_rank: Super Contributor
timestamp: March 28, 2014, 12:42:58 pm
content: GK, you keep using units of "nV" for noise density, but nV does not specify noise density. You can't leave off theperpart of the units, or it doesn't make sense. You clearly approach the noise density thought process from a different direction than me, but in the end I think we both understand it well. Please, don't forget to use the nV/sqrt(Hz). Otherwise it is just a voltage not a density spec. What if I said that the noise in my system is 1 uV at 100 kHz, what would that mean to you? It should mean that when measured with a 100 kHz bandwidth (presumably zero to 100 kHz), the total measured RMS noise is 1 uV. It definitely does not mean that the noise density is 1uV/sqrt(Hz) at 100 kHz. If it did mean that, then the RMS noise at a 100 kHz bandwidth would be over 300 uV. Units are important to understanding; if you talk about noise density, use units that are meaningful to density.

author: dannyf
author_rank: Super Contributor
timestamp: March 28, 2014, 12:56:34 pm
content: Where is "opamp for dummies" when you need it?Fortunately, "Opamp for everyone" is as dumbed down so it may be a starting point for those density-challenged opamp gurus.They actually presented a simple, super-easy-to-follow numeric example there if the math and greek letters are too overwhelming for the gurus.

author: dannyf
author_rank: Super Contributor
timestamp: March 28, 2014, 09:10:18 pm
content: QuoteAgain, I am starting to take pre-orders for my audio-grade ne5534 follower with noise < 0.000001pv; I also take pre-pre-orders for my super-duper golden-ear grade ne5534 follower with noise < 0.0000000001pv.eevblog members are eligible for a 20.01% discount so hurry up!

author: G0HZU
author_rank: Super Contributor
timestamp: March 28, 2014, 09:40:58 pm
content: QuoteBrian

author: GK
author_rank: Super Contributor
timestamp: March 29, 2014, 01:03:30 am
content: Quote from: macboy on March 28, 2014, 12:42:58 pmWhen specifically discussing op-amp voltage noise density specifications (as in "4nV @ 1kHz") I can just talk in "nV" (or "pA" and/or "fA" for current noise density) as even the writers of datasheets often do because everyone who actually understands decades old and standardized conventions will know what I am talking about.Spectral noise density is noise in a 1 Hz bandwidth.Motchenbacher and Connelly is a good reference to have on the shelf. Go track down a used copy on Abebooks or something.

author: LukeW
author_rank: Frequent Contributor
timestamp: March 29, 2014, 11:31:57 am
content: Got to love that thermal noise density, it makes for such warm sound!I think too many people in this thread are trying to reconcile real technical engineering literacy with the world of audiophile bullshit, which is obviously futile.

author: dannyf
author_rank: Super Contributor
timestamp: March 29, 2014, 12:04:08 pm
content: And some people's apparently futile attempt at understanding density functions,

author: macboy
author_rank: Super Contributor
timestamp: April 01, 2014, 01:13:21 pm
content: QuoteYou are clearly not an engineer.That's the thing about "units".... unit means one. It's always one. It's kind of the point.

author: dannyf
author_rank: Super Contributor
timestamp: April 01, 2014, 01:31:06 pm
content: QuoteS/he may not be an engineer but s/he is definitely an "engineer",Apparently s/he is having lots of troubles understanding what a "density function" is.

author: G0HZU
author_rank: Super Contributor
timestamp: April 01, 2014, 03:03:04 pm
content: QuoteI think you can if everybody in the room is familiar with noise specifications and uses these terms on a regular basis.For example:QuoteThe quote above is from the OP's first post in the thread. It could/should have been presented better than this but to me that means the Vrms of the noise measured at a spot frequency of 1kHz (in a 1Hz bandwidth) is <4nV. I would be extremely surprised if anyone would interpret it any other way unless they were being deliberately silly or awkward.In my line of work (RF) it's common to measure noise power in a 1Hz bandwidth eg in dBm/Hz. This (1Hz bandwidth) spot measurement can be done at one frequency or as many spot frequencies as the user feels is necessary. It could be helping to characterise a noise source, or the noise floor of a receiver or the close to carrier noise on a synthesiser.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 01, 2014, 07:01:45 pm
content: I'm going to ask a dumb question after watching this guy's video.Where does the sqrt() part of the sqrt(Hz) come from? I realize this has a simple answer to it, but for whatever reason its escaping me now.

author: dannyf
author_rank: Super Contributor
timestamp: April 01, 2014, 07:19:24 pm
content: QuoteThe answer comes from "energy" - the energy distribution is inverse to that of frequency. So the "equivalent" voltage, is the rms voltage that would have generated the same energy, would be inversely proportional the the sqrt of f.You actually will never see that 4nv figure on the scope.

author: G0HZU
author_rank: Super Contributor
timestamp: April 01, 2014, 07:59:45 pm
content: QuoteI don't really work with nV/rootHz much. Because I work mostly in the RF domain I measure the power of noise (in a 1Hz BW) in dB relative to 1mW = dBm/Hz. Usually this is done with 50R test gear like a spectrum analyser.So someone who specialises in audio stuff can probably explain it better than me but see below:Try and (temporarily) think in terms of power. If you were able to measure the power of a (flat/white) noise source at 10kHz inside a 1Hz measurement bandwidth (centred on 10kHz) and you got something like 1nW in this little 1Hz slice then it's really easy to go on to calculate/predict the power you would measure if you looked in a 10kHz bandwidth because you simply multiply the power by 10,000 (because in a 10kHz bandwidth you have ten thousand 1Hz slices each containing 1nW of noise power) So the power in a 10kHz BW would be 1nW x 10,000 = 10uW. Easy.But it isn't that easy for voltage. Power is a function of V^2. So instead of multiplying the initial voltage figure of the noise source by 10,000 you would have to multiply by the square root of 10,000 to get the voltage for the 10kHz or 10,000 time higher bandwidth.If you watch the video again you can see he does this. He multiplies 40nV by the square root of 10,000Hz (= 40nV*100) = 4uV. He then factors in the less than perfect LPF and therefore multiplies by 1.57 to get about 6.28uV.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 01, 2014, 08:20:41 pm
content: I remember reading about all this some years ago, but I never work/think in these terms so it fades pretty quickly.In this case, is there a nominal 'load' the voltage spec is 'fed into' to think about it in terms of power or is it just the unity (1 ohm)?And I'm also assuming that these values are assume an incoherent noise source?

author: G0HZU
author_rank: Super Contributor
timestamp: April 01, 2014, 08:37:34 pm
content: I think I might be confusing you... I only gave the power example/reference to show how easy it is to calculate the power in a wider bandwidth.For another example of this, if you double the noise (measurement) bandwidth you will double the noise power you measure. This is quite intuitive.However, if you double the noise (measurement) bandwidth you don't get double the voltage when you measure the voltage at the higher bandwidth. The voltage will only go up by thesquare rootof 2 or 1.4142. Hope this helps...

author: GK
author_rank: Super Contributor
timestamp: April 01, 2014, 08:55:03 pm
content: Quote from: macboy on April 01, 2014, 01:13:21 pmYou really can't admit that you were wrong, and never had a coherent point all along, can't you?

author: GK
author_rank: Super Contributor
timestamp: April 01, 2014, 09:25:35 pm
content: Quote from: dannyf on April 01, 2014, 01:31:06 pmI think that you are suffering from a "density function".Quote from: dannyf on March 26, 2014, 11:00:26 amFor us non engineers, please explain exactly what is either so remarkable or "impossibly nice" about the above quoted op-amp specification.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 01, 2014, 10:05:49 pm
content: Quote from: G0HZU on April 01, 2014, 08:37:34 pmYou wouldn't be the first... today... or even in the last hour.Quote from: G0HZU on April 01, 2014, 08:37:34 pmSo I'm thinking this comes from the mathematics of adding (...summing, integrating, etc) incoherent phasors.

author: G0HZU
author_rank: Super Contributor
timestamp: April 01, 2014, 10:40:34 pm
content: Quote from: GK on April 01, 2014, 09:25:35 pmI doubt you will get an answer from dannyf... I haven't bothered to reply/comment to his posts on this thread.dannyf is like a little boy who likes to run up and shout "stupid person!". But he just runs away if you challenge him.

author: G0HZU
author_rank: Super Contributor
timestamp: April 01, 2014, 11:11:08 pm
content: QuoteDunno if this helps but I often use white noise to cross check my test gear here. I have a homemade high(ish) level noise source that puts out a pretty flat noise spectrum out to 180MHz.If I put it through a 2.8MHz high order LPF and into a decent (Anritsu) thermocouple power meter I can measure the total heating power of the noise energy inside that 2.8MHz bw.I can adjust the noise power to show -21dBm on the power meter via the 2.8MHz LPF. The power head works right down to a few kHz. This power level is 7.94e-6W and the Vrms should be 20mV in a 50R system.If I then feed the output to an old analogue true rms voltmeter terminated in 50R it indicates very close to 20mV (as expected) on the dialIf I then click down in 10dB steps via a precision attenuator I see (about) 6.3mV, 2mV, 630uV, 200uV and about 65uV on the bottom range of the voltmeter. The meter has a 20MHz BW and can see down to 10uV but it begins to read a bit high once you get down to a few tens of uV due to its own internal noise.So the power is falling by a factor of 10 (10dB) in each case but the voltage is only falling by the square root of 10 (= 3.16) in each case.If I return the attenuator to 0dB attenuation and measure the noise in a 1Hz bw using the noise marker on a decent spectrum analyser the analyser shows -86.0dBm/Hz at 1MHz.This is about 11.21uV in a 1Hz BW. To predict the voltage in the full 2.8MHz bandwidth we simply use our known method of multiplying 11.21uV by sqrt of 2800,000 to get 18.8mV.This 18.8mV is in pretty close agreement with the 20mV seen on the voltmeter. If I measured the true noise bandwidth of the high order 2.8MHz LPF the result might have worked out even closer but to get within about 0.5dB isn't a bad result especially when the various measurement uncertainties of my test gear are taken into accountNote: The attenuator is very expensive and extremely accurate (with a very low VSWR) over all of the 50dB range.

author: GK
author_rank: Super Contributor
timestamp: April 05, 2014, 03:52:39 am
content: Quote from: G0HZU on April 01, 2014, 03:03:04 pmOr just clueless.If a spot (center) frequency is specified it is obvious that any attendant voltage stated is rms noise in a 1-Hz bandwidth (as per convention), even if it is not followed with "sqrt-Hz". I mean, what else could it be? If a pedant wants to take me to task for not using strict notation, then fine, I am content to just roll my eyes, but giving a condescending lecture designed to infer that I don't know what I am talking about because I neglected to repeatedly restate the obvious is just playing like a dickhead.On Semi neglect the "sqrt-Hz" in some of their transistor datasheets, for example:The vertical scales are just nV/pA. However, even so the note is pretty much superfluous, they do specify the1-Hz measurement bandwidth in words. In a way though, that is probably a more logical approach to specifying the 1-Hz measurement bandwidth than by effectively saying that it is the square root of one, but someone unknowing couldn't infer from either of those graphs that the noise voltage/current increases in a wider measurement bandwidth by the square root of the bandwidth increase in Hz.Incidentally, 4nV at 1kHz is pretty run-of-the-mill for bipolar op-amp voltage noise performance; a far cry from "impossibly nice". The best op-amps do 0.9nV typ. (e.g. LT1115, ADA4898-X). The ADA4898-2 is a dual op-amp in a standard package. I'm not a IC designer, but if they can fit two 0.9nV op-amps on a single die I don't know why they couldn't put two 0.9nV input stages in parallel to make a single 0.64nV (0.9/(sqrt-2)) op-amp. It would have double the current noise and input bias current, but could still be a useful part for low source impedance applications.

author: dannyf
author_rank: Super Contributor
timestamp: April 05, 2014, 11:19:42 am
content: Wow, a week or so has passed and some people still struggle with density functions,

author: GK
author_rank: Super Contributor
timestamp: April 06, 2014, 12:20:27 pm
content: Quote from: dannyf on April 05, 2014, 11:19:42 amI don't know if this is your own special way of seeking help, but I should point out that persistently referring to oneself in the third person is typically a sign of some kind of psychological disturbance. Also, you have yet to answer my request, repeated again:Quote from: dannyf on March 26, 2014, 11:00:26 amFor us non engineers, please explain exactly what is either so remarkable or "impossibly nice" about the above quoted op-amp specification.Though I do know that I ask in vain. A probability density function cannot be applied for any possibility of dannyf posting something intelligent or insightful in this thread topic.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 07, 2014, 12:29:27 am
content: Quote from: GK on April 06, 2014, 12:20:27 pm

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 09, 2014, 05:24:29 pm
content: So I'm reading an academic paper today where the author claims a shielded DUT enclosure and preamp yield a "spectral voltage density S_u(f) of the background noise is 2x10^-16 V^2 s at 10 Hz."To confirm... that's a -16 as in 0.1 femtovolts.There's nothing special about his setup. Its a paper form the 1980's. He's using a 12bit / 20kHz A/D (controlled by turbo pascal ... ftw). Is there any way this is real? And if not, what mistake is he likely making?

author: dannyf
author_rank: Super Contributor
timestamp: April 09, 2014, 05:59:18 pm
content: QuoteThat's just a tad better than my NE5532 - which can be made to produce better noise figures than his.All it takes is rudimentary understanding of how "density function" works.

author: G0HZU
author_rank: Super Contributor
timestamp: April 09, 2014, 11:07:11 pm
content: Quote from: CaptnYellowShirt on April 09, 2014, 05:24:29 pmMessing around with low frequency VF opamps isn't really my thing but I can have a go at answering your question...If you look at the units you have quoted then the number does make sense.In my (RF) world I work in dBm/Hz for measuring the power spectral density of white noise. i.e. I measure the power of noise in a 1Hz bandwidth.NOTE:Power is a function of V^2The period of a waveform is measured in seconds = 1/F(Hz)So (in a 50 ohm environment) I could choose to convert the power spectral density units from dBm/Hz to (V^2)/Hz because I know I'm in a 50 ohm environmentor I could convert them to (V^2).s where s = 1 second = 1/(1Hz)or I could convert this again from (V^2)/Hz to V/rtHz by taking the square root of both the top and bottom terms which delivers familiar units for opamp users.Have a go at converting 2x10^-16 V^2 s across to V/rtHz to see if the number looks more familiar to you.Note: in your example above at 10Hz you are close to the typical 1/f knee/cutoff in the noise response of a typical opamp aimed at audio use. So in this region the noise response won't be flat as it won't quite be in the white noise region.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 09, 2014, 11:20:41 pm
content: Quote from: G0HZU on April 09, 2014, 11:07:11 pmSo ... 4.5 nV at whatever his FFT bin-width was.I'm familiar with power spectrums and the V^2 units. But not so much with the V^2-sec units. Is this a common way to express 1/f noise measurements?

author: G0HZU
author_rank: Super Contributor
timestamp: April 10, 2014, 12:10:53 am
content: It's late and I'm off to bed but I don't think you have worked that out correctly... Maybe if you posted a link to the paper in question someone could look at it for you.I'm afraid I really don't do anything with hifi audio so I'm not the right person to elaborate on any of this low noise AF opamp stuff.However, I did go through a phase of using low noise opamps for design work but this was with wide bandwidth £££ CFB type opamps for use in EW/ESM receiver design many, many years ago. eg as the final output stage for driving an ADC in a narrowband digital IF.I think the only low noise wideband VFB opamp I used for this type of receiver design was a 1.8GHz? GBW opamp with about 1nV/rtHz noise performance at 1MHz and an output IP3 of over +45dBm at a couple of MHz. These high cost/performance devices have high 1/f noise across the audio band but this didn't bother me as frequencies this low were out of band for me. So I was only ever interested in the white noise part of the noise graphs. eg I was interested in noise and linearity across a few hundred kHz to perhaps a few MHz. In their day this type of opamp was almost the perfect choice for my application but these days our receiver designs have digital IF bandwidths of 40-100MHz or more centred up at VHF. So opamps can't be used anymore...

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 10, 2014, 12:45:29 am
content: Quote from: G0HZU on April 10, 2014, 12:10:53 amWell this is just a math mistake. How's 14 nV / rtHz sound?