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

[Larry Brasfield]

[drivel snipped]

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.

As far as I can see, the OP is an electronics student
who simply needed to become aware of how noise
ultimately limits receiver performance. I offered to
review his detector and improve his preamp once
he shows the detector and provides a little more
data about the transducer. I have also indicated
that some sort pre-detection filter is likely to help,
but that depends on his existing detector as well as
the transducer bandwidth and what he is trying to
accomplish, yet to be known. I do not expect that
you can understand why that is a sensible approach,
but most normal folks would have no such problem.

And that's because you don't know how...

Another thin air production. I've built sonar detectors
that I doubt you could understand without my help, or
the help of some other competent analog designer.

(Well, that's all 3 posts alleged to contain a "challenge".
Maybe my news server dropped a post, as happens
once in a great while. I'll check Google news and see
if I can locate your "challenge" and post my answer,
one way or another. But I'm disappointed so far.)

 

[Ken Smith]

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.

It doesn't need to be truely wide band:

(1)
A burst of the 40KHz signal reflects off the far object and is received.
In the reciever, both the amplitude profile and the phase of individual
cycles can be used in the calculation.

So long as the amplitude profile is short enough in time that the timing
can be determined to within on cycle, the phase of the signal can be used
to fill in the digits below that. If the filter is reasonably stable, a
constant can be subtracted from the result to correct of its delay.

(2)
The 40KHz can be frequency modulated. The narrowness of the filter makes
the time between zero crossings change more slowly than in the transmitted
signal. A micro can look at the series of values of the period of the
signal. It can fit the numbers to a curve and determine when the curve
passed through a certain value. This will give a value that again is only
lated by a constant.

 

[Fred Bloggs]

Larry Brasfield wrote:
[...snip drowning rodent drool...]

Where's your workup on the 40kHz amplifier thread, fairy loudmouth boy?
Can't go any further with 4KTRB and some other simple-minded trash? We
are not surprised, windbag. You are one little superficial and worthless
moron.

 

[Fred Bloggs]

Larry Brasfield wrote:
[...snip a bunch of hot air from pretentious little pussy...]

Where's your workup on the 40kHz amplifier thread, fairy loudmouth boy?
Can't go any further with 4KTRB and some other simple-minded trash? We
are not surprised, windbag. You are one little superficial and worthless
moron.

 

[Fred Bloggs]

Larry Brasfield wrote:
[...yawn...]
Where's your workup on the 40kHz amplifier thread, fairy loudmouth boy?
Can't go any further with 4KTRB and some other simple-minded trash? We
are not surprised, windbag. You are one little superficial and worthless
moron.

 

[Pooh Bear]

Dear friends,

I am making an ultrasound signal receiver. The transmitter and receiver
is apart from each other about 6 meters. The circuit is powered by a 9v
battery. I used three amplifiers from two TL082. The reference voltage
(about 4.5v) is generated from voltage divider (two 100k resisters in
series). All amplifiers are in inverting input mode. First and second
stages are configured as: 10k input resister and 500k feedback
resister. The signal output in the second stage is very good. However,
the signal from the third stage (input res.= 10k, output res. = 200k)
is significantly corrupted by noise. Please give me some advice to
clean up the amplified signal.

To begin with, the inverting ampliifer configuration you're using is
inherently noisier than non-inverting.

You have a gain of 50 x 50 x 20 = 5000 x or 74dB. Any input noise will be
amplified by that amount ( plus you need to factor in the additional
thermal noise from your inverting configuration ). It's hardly surprising
it's noisy !

The input noise of the TL082 isn't great to begin with - try the TL072 for
a quick, simple improvement for example.

So - to summarise. Use the *non-inverting* configuration for lower noise.
Use quieter op-amps.


Graham

 

[Larry Brasfield]

The DERF tranform, applied here, is described earlier in this thread.

[DERF] Where's your workup on the 40kHz amplifier thread [DERF]?

Asked and answered. You may like repeating
yourself, but I find it too boring for words.

[DERF]

 

[Fred Bloggs]

Asked and answered. You may like repeating
yourself, but I find it too boring for words.

Nah- you didn't answer anything, little superficial dodger, just like
you haven't been able to answer a single OP. Your explanation is
unacceptable- it is a rodent dodge, something I'm damned sure you have
puuuuuuuulllenty of practice with. You're dropping it because you no way
in hell can go any further- you have nothing left. Anymore who expends
500 words on a bs 4KTRB answer is a total fraud. Looks like you're
crumbling, windbag- there's just nothing there.

 

[Larry Brasfield]

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.]

message
[DERF]

Amazingly, all 4 of the DERF criteria applied to that elision.

Fred, can you find anything worthwhile to post about?
With your probing and powerful intellect, surely you
can do better than we've been seeing lately.

 

[Larry Brasfield]

The DERF transform, applied here, is described earlier in this thread.

Asked and answered. You may like repeating
yourself, but I find it too boring for words.

Nah- you didn't answer anything, [DERF]

Nor did you answer, except with garbage.

you haven't been able to answer a single OP.

If you were as skilled at argument as you are
at unsubstatiated and baseless assertion, you
would be a force to be reckoned with.

Your explanation is unacceptable

Ok by me. Was there anything in particular, in the
way of technical ideas or facts, that you found
yourself unable to digest? (I imagine so! <g>)

[DERF]

 

[Larry Brasfield]

Hello Larry, Hi, Joerg.

So far I haven't seen that advantage that much. Very fast chips are usually very expensive, meaning they are out of budget for
many projects.

I think the cost of those parts will come down as
newer (and faster) fab lines come online and the
ones currently dedicated to higher margin parts
become available for "cheap" stuff.

On the discrete front there are lots of blazingly fast SiGe transistors. Even some really old regular ones can still run circles
around chips. An example is ye olde RF work horse, the BFS17A. It can ramp several milliamps in under a nanosecond.

For RF, the pad and trace capacitance can usually
be dealt with by incorporating it into the transmission
lines used as a matter of course. In that environment,
power is mainly a function of signal level. The power
I alluded to above is the power necessary to make
circuits work when the capacitance must be driven
at a higher impedance, typically much higher.

But there is often a case for chips. I must admit that I have used the uA733 a lot in the old days. That was because volumes of it
were built into VCRs so it became a cheap device. Whenever I use an IC I try my utmost to avoid a single sourced part. This is
because I have seen too many people including clients get zinged by that. Heck, I even flung a SMPS design to semi-discrete once
and even after a decade in production no PWM chip has come close in cost.

Designing for volume over years is a special challenge,
one which often precludes using the niftiest new parts.

In ultrasound apps I'd say that all but two of my front-end designs were discrete. The two that weren't used the AD603 which is a
marvelous chip but at around $5 it is too expensive for some designs.

I put a discrete amplifier in front of a predecessor
to the AD603. It added cost, but got the noise
down enough that management agreed with its use
in a moderately high volume circuit. Later, I found
out that a system level foulup had discarded about
6 dB of SNR after all my effort to glean a several
dB SNR improvement over what the IC could do.
(I won't go in the bureaucratic snafu behind that!)

Regards, Joerg

Likewise, and thanks.

 

[Fred Bloggs]

Amazingly, all 4 of the DERF criteria applied to that elision.

Oh the "elision" is it? Well- hoot-tee-doo, the little effete,
pseudo-sophisticated, narcissist is so damned special. Can you do
anything at all except shoot your mouth off? You don't know a damn thing
about detection circuits- you have been asked many times to finish the
circuit, and you not only refuse, but continue to brag about a
non-existent career. Where is the circuit, pretentious little
pseudo-intellectual?- Where is that circuit? And as long as we're on it,
where is that power supply? where is that algorithm, where is that
encoder, where is that derivation, where is this and where is that you
claim to know so much about and never have produced a thing- except a
bunch of hot air and bs. You are typical NG troll trash.

 

[Fred Bloggs]

For RF, the pad and trace capacitance can usually
be dealt with by incorporating it into the transmission
lines used as a matter of course.

Huh? Isn't that an original thought...

In that environment,
power is mainly a function of signal level.
Huh?

The power
I alluded to above is the power necessary to make
circuits work when the capacitance must be driven
at a higher impedance, typically much higher.

Which "above" allusion to power was that, phony boy- the previous sentence?

I put a discrete amplifier in front of a predecessor
to the AD603. It added cost, but got the noise
down enough that management agreed with its use
in a moderately high volume circuit. Later, I found
out that a system level foulup had discarded about
6 dB of SNR after all my effort to glean a several
dB SNR improvement over what the IC could do.
(I won't go in the bureaucratic snafu behind that!)

What a crock of shit- the little moron trumps the world again, huh? And
that's why you're a minor punk programmer who cleans the bathroom part-time?

 

[Fred Bloggs]

Larry Brasfield wrote:
[...snip pseudo-intellectual trash...]

The pseudo-intellectual troll Brasfield in troll mode will now proceed
to post 500,000 words of evasion rather than finish one simple
thread...typical third rate garbage.

 

[Larry Brasfield]

The DERF transform, applied here, is described earlier in this thread.

message [DERF]

Can you do anything at all except shoot your mouth off?

Yes. I can be brought to tears by your antics and posturing.

You don't know a damn thing about detection circuits

I am quite willing for you to believe that. Fortunately for
people who have paid me good money to design them,
my detection circuits do the job required of them and
have been copied into new designs done by others.

- you have been asked many times to finish the circuit,

The OP has not yet indicated any desire for a replacement
detector or review of his current detector. I have absolutely
no desire to engage in any more [1] effort along that path.
If my motivation was to prove something to you, I might
be inclined to get one or more of my detectors drawn up
in a suitable form for publication here. But, as you seem
completely unable to comphrehend, I am not the least bit
concerned about your low opinion. In fact, I treasure it.

[1. I have extended an offer to review the detector, and
given strong hints that such a review could be useful.]

and you not only refuse

For now, I decline for reasons stated.

, but continue to brag about a non-existent career.

Pure speculation, and false to boot. Delusional.

Where is the circuit [DERF]?- Where is that circuit?

["Where is " this and that cut.]

Fred, you completely misunderstand what I try to
accomplish here. And I do not think you can, even
when explained. But I will plant this little seed of
doubt in your overwhelming superiority complex.

I consider my job well done when a poster goes away
with his self esteem intact, more understanding than
he/she had before, and her/his presenting issue solved
to his/her own satisfaction. Whether this leaves you
with a better or worse opinion of me and my skills is
entirely immaterial to me. If anybody else reading is
naive enough to think less of me because of my effort
or yours, I consider that their problem, not mine.

You seem to think there is some kind of contest here.
What you seem unable to grasp is that I am completely
uninterested in the game(s) you like to play here.

[DERF]

 

[Fred Bloggs]

If my motivation was to prove something to you, I might
be inclined

Classic troll fallback- you have been pulling that one since you
arrived. You just love going off topic evasion, and upwards of 500,000
words of bs versus one single short on-topic post. You are a typical NG
fraud...

I consider my job well done when a poster goes away
with his self esteem ...

I can't believe anyone is so dumb they actually read you bullshit... go
away you are worthless.

 

[Fred Bartoli]

I read in sci.electronics.design that Fred Bartoli <fred._canxxxel_this_
bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote (in <423c21a6$0$22865$6
[email protected]>) about 'amplify 40kHz audio signal using TL082:
first two stages are fine, but high noise from the third stage', on Sat,
19 Mar 2005:
The appended 'isn't it' is characteristic of French ('n'est-ce pas?')
and Welsh English (not Welsh Welsh) spoken language. Note that the 'it'
in 'isn't it' has no referent in the preceding sentence, as in 'He's a
really tall man, isn't it?'

Thanks.
Obviouly, as you've spotted, the 'isn't it' was carelessly imported from
French. But now, following the example of Mr Jourdain, I'm very proud of my
new knowledge of Welsh English and I can find this 'isn't it' admirable.

I can even find more consolation into this by thinking that my bad (not so
much I hope) mix of French and English could be mistaken with some form of
erudition *cough*

 

[John Fields]

What you seem unable to grasp is that I am completely
uninterested in the game(s) you like to play here.

 

[John Fields]

I consider my job well done when a poster goes away
with his self esteem intact,

 

[Fred Bloggs]

Exactly- you can research his hypocrisy on sci.electronics.basics where
he was beating up on newbies all the time. He must be really dumb to
think we can't check up on that...