This is pretty much possible. On the other hand, it shows that the TI part might be, in the same setup, much more prone to parasitic impedances and to shielding than the competitive parts with BJT input.
LM4562 is also produced in the TO-99 package. Will it behave the same?
Glad to hear we agree on this. Would these TI part properties be critical in a real world audio applications, with gains in the 1-10 range?
I don't think the metal can would behave better, but likely worse (if you don't cut the legs to a minimum).
To split hairs: if the 10k feedback and 10k divider R were a lot smaller, their attenuation would be precisely a factor of two and not be loaded down by the 100k. The noise gain without that additional attenuation would indeed be given by the Rf/Rdiv + 1 expression, which would be a factor of 10,001 presuming sufficient loop gain. But that 100k + 10ohm loads the 10k - 10k network, and conversely the network impedance of 2.5k adds to the 100k. So when all is said and done, the noise gain is 86.4452dB, a factor of 21,001.94 to that many places. This also assumes that the input impedances are high relative to the network impedances, and that the effective output impedance of the op amp is low relative to the 10k etc.
If one wanted precisely 80dB noise gain, eliminate the 10k - 10k divider and use a 99,990 ohm feedback R directly from output to inverting input, again mindful of a small and frequency-dependent effect due to the op amp output impedance.
Of course all of this is absurd for the purposes of the experiment, except perhaps the roughly 6dB added due to the divider.
My first sentence is a relevant technical explanation, and since you have denied its basic meaning at least 3 times, I see evidence that you are impossible to educate.
Here is a relevant independent resource:
Thevenin Equivalent Circuits
Did you say something qbout 41 years of professional engineering experience?
Must have been 1 year, 41 times 'cause the basics of equivalent circuits (which this is) would have been taught to you early in the second year.
A) The test circuit is a magnified version of the real world, but with only roughly controlled Rf injection.
B) The test circuit is pathological because not best practice (because unshielded).
C) Only ranking order of compared commercially available monolithics matters anyway. None of us (except maybe one) get to make 'em ourselves.
To each their own. I vote C, and much thanks for the work.
Chris
B) The test circuit is pathological because not best practice (because unshielded).
C) Only ranking order of compared commercially available monolithics matters anyway. None of us (except maybe one) get to make 'em ourselves.
To each their own. I vote C, and much thanks for the work.
Chris
Sounds like some probes/antennas and a decent RF spectrum analyzer would be illuminating. The synchronization with the 100Hz mains suggests something in the vicinity, although it is puzzling that the detection effect, if that is what it is, appears on just one half-cycle.
I had convectured that simple mains sine waves (and nothing is ever really simple) are enough impetus to produce the effect. Raises the question of rectification vs. overload. Everyone is talking about input non-linearities, and for good reasons, but could we be seeing downstream overloads in (proprietary) architecture? Not the tiniest clue personally.
Much thanks, as always,
Chris
The hand-waving effect (no joke here) suggests something really high frequency, such as diode reverse recovery spikes resonating with a rather low inductance (i.e. not transformer leakage inductance). The brute force method of suppressing those is a fairly good-sized capacitor across the given diode, which pushes the resonant frequency down to where it no longer propagates well. But this is not good for conducted noise from the mains.
And there are rectifiers with a better-controlled reverse recovery, so-called soft-recovery parts.
In a stepped-variable-gain amp I did many years ago, and which used a fairly yucky op amp with a MOS front end, the CA3140, I had a board in the same enclosure with the rectifier diodes and filter caps. There was enough snap from the diodes to require some snubbing, I think it was 10nF in series with 30 ohms across each diode. Otherwise there was an audible line harmonic buzz. And the gains were not that high, but the through-hole boards had pretty good-sized loop areas, and the impedances weren't all that low either.
Thanks for clearing up that (ma)lingerer. There's so much noise in the modern world that we'll never lack for injection, and more thanks to PMA for such a clear test.
Now if we'd only go back to the True Path and build op-amps with 12AX7 diff-inputs, the way Lord Philbrick intended, we wouldn't be punished this way for our many (and varied, and tiresome) sins.
Much thanks, as always,
Chris
Do you have an opinion on the question of whether or not a modern equal to the Telefunken metal work of that era is possible? Some folks say that the world just gets better and better (as long as you live in the First World, anyway), and other folks say that specialized proprietary technologies can be lost and impossibly expensive to recover.
Lots of smart people in China, and some infrastructure - could the Telefunken 12AX7 be built today? A side note: McIntosh model Mc240 amplifiers ran these at 430 volts anode to cathode and I've seen lots of original examples still measure just fine, these many, many decades later.
Thank you for any thoughts,
Chris
Lots of smart people in China, and some infrastructure - could the Telefunken 12AX7 be built today? A side note: McIntosh model Mc240 amplifiers ran these at 430 volts anode to cathode and I've seen lots of original examples still measure just fine, these many, many decades later.
Thank you for any thoughts,
Chris
Last edited:
Yes I remember the 240 use, quite remarkable.
I don't know about re-creation, but an outfit I'm aligning with has spoken of making tubes in the US.
You've been trying not to hint about this for a while, haven't you? Must be killing you, so SPILL.
Or not, if you're just a weenie. (Or simply loyal to your group.)
Thanks, as always,
Chris
It's not the top priority for them right now. The first will be another product that will make audio right out of the box. I am close to finishing the design of the electronics portion as we speak.
I am under heavy-duty NDA about nearly everything so I really do have to remain restrained. In exchange for that taciturnity I am to be generously compensated. And things are fairly well-funded for a change.
Engineers in particular have a bad habit of talking about things besides Thevenin equivalents and base spreading resistances.
There are probably a number of technologies that have been lost. A specific and important one is the metallurgy for the ultrastable resistors. The alloy and process for making it apparently have been lost so the existing supply is all there is. I gather the issue is that the guys who figured it out retired/died and the details were lost. It seems this happens with low priority products regardless of their real importance.
My understanding is that TI is shutting down the National line the LME parts were made on so they are all destined to be discontinued. Apparently TI does not have a place they can move it to. I gather it is a very highly tweaked linear process. The designer was a wizard they brought in from Japan.
It would be interesting to see if the LME49990 has the same "sensitivity" as the LME49710.
I suspect that those who have a high RF environment and do measurements get the same result. Reminds me of my long time career at LLNL. Nuclear weapons design can become a lost science as well. Sr Physicist have to personally train Jr physicists as its all in the head with little published. Takes many years of mentoring. All it takes is one guy die ... like happened when I was there--- the most knowledgeable 'trigger' designer died suddenly. Most that is known in most fields never gets into print. Thus, the African saying.... when a man dies a library burns to the ground.
THx-RNMarsh
Just come to my house and you can test anything for RF susceptibility, a radio tower with every type of transmitter from FM to microwave. Comes through on any poorly designed device, tv's to cell phones to audio. Withing 100 yards line of site. Makes my cell phone just about useless except for text messaging at home.
- Status
- Not open for further replies.