amplify 40kHz audio signal using TL082: first two stages are fine, but high noise from the third stage

No one is reading your sh_t any more. Quite telling that you have no clue how much of hot air bag you sound/ and appear.

Typical psycho-babble characteristic of a trite usenet troll.

Anyone can see from your sickening style of writing that you are a heap of crap and bs. Nah- you're a small banana trying to look like a bunch- pathetic really.

Not to worry- hard to imagine anyone with so much time on their hands that they waste it reading your trash.

All you have done is make some simple 4KTRB and BW estimates- and then stopped as usual. This is a good example of your propensity to blather some elementary factoid trash and then make no sense of it.

Really? The OP builds a chain with 115 dB gain and all you know how to do is elementary electronic input noise- pathetic really.

You have done no analysis worth noting as usual. How many times do you need to get your ass kicked before you realize you're less than third rate garbage- so far *all* of your product has been laughably weak, inaccurate, and worthless.

More troll psycho-babble....

Couldn't get into the program? Guess your obsession with reading comic books just wasn't enough preparation- ahhh- too bad.

Nah- you are in fact a little delusional sh_t programmer- a non- scientific programmer at that.

All psycho-trolls say that...

Incredible narcissism...

You're a complete nobody- go back to your messy hovel of a cubicle and drink your soda...

>

Fred, i don't care what they say about you! your ok in my book! :)

A correction, motivated by one of Fred's rare technical efforts apparent in this thread, is inserted below. The OP should take note of this. I have added a few other details and notes as well. There is also a little humor for those who do not take themselves way too seriously. (See "1.")

The need for this correction underscores the importance of peer review and the value of stating assumptions and showing enough of the analysis to permit it to be critiqued.

....

[Frequency response revised and moved.]

It has come to my attention that the 3 stages are not "like" as I had stated. The last stage has about 7.16 fewer dB of gain than derived in my pre-corrected analysis. Also, due to the improved loop gain in the last stage, (as compared to that earlier analysis), the

-3dB bandwidth is about 59 KHz (rather than the

49 KHz mentioned before), and well centered on the OP's 40 KHz signal. These corrections affect the amount of noise that should be expected at the final stage output, as detailed below.

The bandwidths will change with a transducer in place, due to the slightly higher loop gain that will produce in the first stage, so it would be premature to worry about noise bandwidth just now.

[The input noise still appears to be correct.] [Cut incorrect gain figures and calculation.]

With the OP's stated 200K feedback R (not the "like" 500K I mistakenly assumed), the gain is closer to 90 dB. This results from the ideal gain of about 94 dB (= dB(50 * 50 * 20)) with losses of .63 dB per stage for the HPF's, .97 dB for the first 2 stages due to their (low) loop gains of 2, and .17 dB for the last stage with its loop gain of 5.

The output noise density is then 20.5 nV/sqrt(Hz) * 10^(90.0/20) V/V = 648 uV/sqrt(KHz) Multiplying by the square root of bandwidth yields an expectable RMS output noise of 157 mV.

[Noise bandwidth adjustment unmentioned.]

I would bet good money on long odds that the first stage can be revised to bring the SNR up by several dB, once the input is better known.

[corrected in place:]

able to see the few mV to be expected at the

The comparisons suggested between the noise to be expected and the noise you see should be used only for limited purposes, such as deciding to proceed further along the noise investigation rather than looking for another source for the noise. [1] The way to finally evaluate noise should involve the measured gain of the amplifier, not its nominal gain.

[1. For example, suppose you had left an op-amp unconnected whose inputs just so happened to float together, and stay within about 15 uV of each other, (offset by Vos), such that the output was miraculously active for an observable length of time during the few 100's of mS before they both float to the rail, and if that op-amp was paired with the first stage, then, if you looked at the noise appearing on the final stage quickly enough, (within say, 200 mS and allowing some time for noise observation averaging), you might see several millionths of a dB of extra noise that: arises at the open input at the about the same level as the other stages have (which estimation includes input current noise); then appears at the output of that unconnected amplifier after a gain of about 40 dB; couples into the input thru the typical 90 dB of channel isolation; and competes (at -45 dB relative to the *real* noise sources) for a position as the top dog noise source. This would seem to be far-fetched in the cold light of day, but late at night, when demons are at play, who knows what can *might* [2] happen? ] [2. Here, "might" must be distinguished from the false certainty that plagues us all from time to time, some more and more often than others. ]

It is also worth noting that the above analysis predicts the RMS value of a random signal with a Gaussian amplitude distribution. It is common to figure on seeing 5 times more peak value, but if you want to calculate the actual rate at which your detector will false detect due to that noise, you need a more sophisticated approach based on the Gaussian statistics.

A good place for that filter would be after the first stage. If you use an active filter, that will be a necessity. If you use an LC filter, that will be prudent due to coupling considerations and noise performance issues.

P.S. to Fred: If you reply, please try to take a rational approach to this, or, failing that, come up with some new names and more imaginative invective. Your latest efforts have become so repetitious that they are really quite boring.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

Mainly just laughs here.

"Fred Bloggs" wrote [snip]

much of hot air bag you sound/ and appear.

Thanks, Fred. I appreciate that. When my style begins to please you, then I will start worrying.

[More typical FB crap cut.]

they waste it reading your trash.

So, I take it you have no way to substantiate. Just as I thought. You are a nasty fabulist.

as usual.

I went as far as was needed to explain the reported observation that brought the OP here. Going beyond simple would be a disservice at this point, for reasons you could figure out yourself if you thought about the OP's situation rather than your own aggrandizement.

trash and then make no sense of it.

I note that you have failed to show any particular way in which my analysis does not make sense. Telling. Whenever you are shown up, out comes a load of crap. Who do you imagine is fooled?

elementary electronic input noise- pathetic really.

More baseless assumption and conjecture. What real reason is there to believe that I could not have completed a full noise analsysis? (Try not to confuse your need to denigrate with "real" here, Fred.)

....

Translation: Fred cannot rationally refute.

If you are the ass kicker, and my unblemished ass has been the target, then your counting skills are bad.

product has been laughably weak, inaccurate, and

So you like to believe. What does it do for you?

....

I'm still not sure what program you refer to, but I never took any courses aimed at tecnicians, nor did I try to get into any such program. That you are able to conjecture that way is pathetic.

ahhh- too bad.

More fabulizing. Your percentages are getting very bad, Fred. Maybe it's time to check your assumptions. They are not working.

[More of the same cut for space.] [Fred's venture into psychoanalysis cut.] [More of the usual name-calling cut as redundant.]

I wonder how long it will take you to figure out that I will never take orders from you. That it has not yet occurred is quite telling.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

An almost purely technical post, after severe editing.

"Fred Bloggs" wrote [SNIP]

[snip]

What other noise analysis do you believe is relevant to what the OP reports seeing? Have you ever actually done any practical noise analysis, such that you can explain why "All you have done ..." should perhaps be considered the insult you surely intended rather than a comical and telling snipe?

(And before you reply, you may want to consider Fred Bartoli's post of 12:16 today where he makes a point relevant to your "snipe". He appears to know more about real noise analysis than you do.)

[invective gone]

I am unable to replicate your 115 dB figure. In fact, I believe it to be erroneous. Do you have any way to show how you arrived at it, or was it too ephemeral to permit that?

In other words, either prove it or make clear that it was one of your thin air productions.

[SNIP]

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

still

LOL . Youu should stop hoping that I'd answer a delinquent like a Bartholi!

I checked it. All wrong.

Not all wrong at all. His fundamental point, which you would do well to learn, is that the noise output of cascaded amplifiers with moderate gain will be dominated by the input noise of the first stage.

This principle, (in a more general form that applies to any set of gains), is known as the "Friis formula" or "Friis noise equation". I suggest you look it up, study a bit, then extend an apology to Mr. Bartoli.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

Hello Ken,

An LC would be pretty easy at 40kHz. However, it depends on what the OP wants to do. If he intends to do pulse echo with good range resolution it needs to stay wideband.

Regards, Joerg

Nope. Only the first stage matters, unless the design is completely screwed (which it isn't).

Competing for an LB award from FB?

--
Thanks,
Fred.

I read in sci.electronics.design that Larry Brasfield wrote (in ) about 'amplify 40kHz audio signal using TL082: first two stages are fine, but high noise from the third stage', on Fri, 18 Mar 2005:

I get 94 dB voltage gain from the OP's 50 x 50 x 20. Anything more complex makes my brain 'urt.

Am I turning into an analogue Genome?

--
Regards, John Woodgate, OOO - Own Opinions Only. 
There are two sides to every question, except 
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

I read in sci.electronics.design that Fred Bartoli wrote (in ) about 'amplify 40kHz audio signal using TL082: first two stages are fine, but high noise from the third stage', on Fri,

18 Mar 2005:

Only in France and Wales.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
There are two sides to every question, except 
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

devices

amplified

screwed

OK, so you're saying that the second and third stages noise matters. Well, lets do the really, hem..., advanced maths for you...

Have 3 identical stages with input referred noise en and gain G. The total output noise is : sqrt(G^2(en^2+G^2(en^2+G^2 en^2)))= en sqrt(G^2 + G^4 + G^6) the first term being the output stage contribution, the second one the second stage contribution and the 3rd one the first stage contribution. OK?

Now, you build an amplifier, isn't it? So G>1. You pay attention to amplifier noise so your signal is low level too. Thus you want your gain above few units. Say G=3. (note the OP wants its gain = 50)

Onoise = en sqrt(9+81+729) = 28.62 en

Now, I magically make the output noise disappear, as you say so well.

Onoise = en sqrt(81+729) = 28.46 en

Even better now: I magically make the second stage noise disappear

Onoise = en sqrt(729) = 27 en

Wow, that's an 'enormous' difference.

Now, let G = 50, as is the case here, redo the computations, and you, the amplifier noise expert, enlighten us about the _huge_ 3rd stage noise contribution.

the

function,

component.

then

let

what

Yeah, obviously look at the 3rd stage noise.

I agree on this, guy. This is really basic electronics, but this is still too advanced for you, like it seems some 1.35V low voltage voltage amplifiers.

You appear to be a bit out of juice, lemonhead.

--
Thanks,
Fred.

"Larry Brasfield" a écrit dans le message de news:W%G_d.37$ snipped-for-privacy@news.uswest.net...

Well, I won't be so sure...

--
Thanks,
Fred.

Larry Brasfield wrote: [...snip drivel...]

As usual we all see you doing a bunch of pussy factoid arithmetic, but what have you accomplished? You have hit a brick wall- absolutely no plan whatsoever to define or fix the noise induced threshold crossing problem. And that's because you don't know how...

Nah- you went as far as you could- and that wasn't to far...

Yeah- right- bullsh_t.

[...snip drivel from a drowning rodent...]

I am not here to educate you...

[...snip drivel from drowning rodent...]

This has been converted, via a process I will call the DERF transform [1]. This elision process conforms to accepted Usenet quoting practise with the exception that elided text is replaced by "[DERF]" and, where needed for grammaticality, short sequences with a '[]' pair are inserted.

[1. Application of a filter removing Dreck, Extraneousness, Redundancy, Foolishness.]

"Fred Bloggs" wrote >

Clever, Fred. Assuming you meant "too far", you seem to have understood my earlier made point that complicating the analysis beyond what significantly affects the result is a disservice to the OP. I do try to avoid "too far".

As for "[I] went as far as [I] could", yes, you've gotten it. I operated within that constraint except for my analysis of the dreaded "open JFET op-amp" effect. I hope you were able to follow that and enjoy the chuckle I did. (However, I doubt both clauses of that conjuction.)

Woops, I guess you were unable to understand that point. Was there any particular part of it that you had trouble with, or is the whole concept of engineering approximation something you find difficult to grasp? Maybe you are unaware of the Friis formula and its implications here. I admit to puzzlement in light of the awe you seem to induce in some folks here. Of course, that also puzzles me.

[DERF]

(Well, 1 down, 2 to go. I'm disappointed, having missed that "challenge" you mentioned elsewhere.)

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

This has been converted, via a process I will call the DERF transform [1]. This elision process conforms to accepted Usenet quoting practise with the exception that elided text is replaced by "[DERF]" and, where needed for grammaticality, short sequences with a '[]' pair are inserted.

[1. Application of a filter removing Dreck, Extraneousness, Redundancy, Foolishness.]

"Fred Bloggs" wrote >

I agree. However, your pretense that there is some additional relevant noise analysis that you cannot divulge for anti-educational reasons is educational itself. Unfortunately, it's not an education I need.

[DERF]

(Well, 2 down, 1 to go. I'm disappointed, having missed that "challenge" you mentioned elsewhere. I guess, given your veracity, it must be coming up.)

-- Larry Brasfield email: donotspam_larry snipped-for-privacy@hotmail.com Above views may belong only to me.