A Audio and hi-fi forum. AudioBanter

Go Back   Home » AudioBanter forum » rec.audio » Pro Audio
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

overvoltage on audio circuits



 
 
Thread Tools Display Modes
  #31  
Old November 6th 19, 12:01 AM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 457
Default overvoltage on audio circuits


wrote:

------------------

Bewa this troll is e REAL lunatic

>
> Please go into this in greater detail. My understanding is that when
> using amplifiers, especially audio, the noise figure is a function of
> the application - impedance levels, feeback and other external circuitry,
> closed loop gain setting. etc. Therefore NF is usually not specified on
> the data sheet
>


** Noise figure is widely used in electronics, predominately in RF circuits but also in low noise audio where connection to a transducer is is the game.

It does appear on many data sheets for BJTs and JFETs.

Eg.

https://pdf1.alldatasheet.com/datash...MI/2N4403.html

See figure 9 showing a set of curves for Ic, resistance at the input and NF.

For 1mA and 500ohms the NF is under 1dB at 1kHz and beyond.

At lower currents, the best noise figure is at much higher resistances.

See link for published project of mine originally posted 20 years ago.


https://sound-au.com/project66.htm

It matches or outperforms the SSM2017.

FFS go away dickhead.


....... Phil









Ads
  #32  
Old November 6th 19, 09:42 PM posted to rec.audio.pro
[email protected]
external usenet poster
 
Posts: 16
Default overvoltage on audio circuits - Noname.jpg (0/1)

On Tue, 5 Nov 2019 15:01:55 -0800 (PST), Phil Allison > wrote:

>
> wrote:
>
>------------------
>
>Bewa this troll is e REAL lunatic
>
>>
>> Please go into this in greater detail. My understanding is that when
>> using amplifiers, especially audio, the noise figure is a function of
>> the application - impedance levels, feeback and other external circuitry,
>> closed loop gain setting. etc. Therefore NF is usually not specified on
>> the data sheet
>>

>** Noise figure is widely used in electronics, predominately in RF circuits but also in low noise audio where connection to a transducer is is the game.
>
>It does appear on many data sheets for BJTs and JFETs.


This is widely known. It is also widely known that it is difficult to specify a NF for an amplifier, or even supply curves for NF, because of all the
different permutations of external circuitry for all the various applications. NF came up because you said you calculated a best source resistor for
NF for the OPA by dividing the input voltage noise density by the input current noise density. I asked you to explain this since these noise densities
are independent and are noise and current SOURCES and are modeled as such. They do not obey E=I x R and do not define a resistance.

And again, you snipped out my request for an explanation, shown below-

1) please explain the physical significance of dividing the input voltage noise density by the input current density.
2) please explain how the 3.3Kohm source resistor you arrive at by doing this improves the noise or any
other performance parameter. please show calculations showing lower numbers than those above
3) Since the SSM has a higher input noise current density and would therefore give a lower resistor for
this calculation, does this mean better amps have higher input noise current densities?
4) As mentioned earlier, if I use a Darlington follower on the OPA inputs and lower the input noise current
density to 5pa, would you now use a 3.3Mohm source resistor?

The ratio of an amp input voltage noise and current noise densities does not define a "input noise resistance" from which you can calculate anything.
They are independent sources and have to be used independently to calculate noise and NF. There is a concept of "equivalent input noise resistance",
but it is a much more complicated calculation invoiving other elements. The amp's input impedance for all AC signals including noise, as seen by the
source (i.e., at the amp input), is is given by the dynamic input impedance speced in all amp data sheets, and is given in the OPA case by Rb'+ (beta
x (kt/qIe) + RE) x2, (ignoring parasitic caps which are significant at higher frequencies) and it is this number you would use for determining the
loading of the source or, if needed, for impedance matching.

Putting in a 3.3K resistor as you want will not give best noise or NF but will increase noise several fold.

http://www.ti.com/lit/an/slyt470/slyt470.pdf see page 25 and 26


And once again you resort to name calling. However, I'm getting calibrated. Apparently this has been going on for decades and you just have a
non-magnetic personality, to say things in a nice way.


>https://pdf1.alldatasheet.com/datash...MI/2N4403.html
>
>See figure 9 showing a set of curves for Ic, resistance at the input and NF.
>
>For 1mA and 500ohms the NF is under 1dB at 1kHz and beyond.
>
>At lower currents, the best noise figure is at much higher resistances.


Expected. Input impedance is a function of transistor operating conditions and beta. The impedance
is higher at low currents and goes down as current is increased. It is easier to specify NF in the case
of a single transistor amplifier, but notice that even in this case, NF cannot be given as a single number,
it is given in a series of curves for different operating conditions.

>
>FFS go away dickhead.


There you go again. What's the deal? Did your mommy not hold you enough when you were a baby? You can't
get it up anymore? You can get it up but have no outlet because you drive off women within 10 minutes? Are you off your meds?
What??? You can't possibly be a happy person. It's sad you have to go through life this way.

Have you ever tried smiling and giving compliments? You might be surprised at how you feel afterwards.
  #33  
Old November 6th 19, 11:24 PM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 457
Default overvoltage on audio circuits - Noname.jpg (0/1)

wrote:

---------------------


> This is widely known. It is also widely known that it is difficult
> to specify a NF for an amplifier,


** Not true.


> please explain how the 3.3Kohm source resistor you arrive at by doing this improves the noise



** It does no such thing, I made no such claim.


> Since the SSM has a higher input noise current density and would therefore give a lower resistor for this calculation, does this mean better amps have higher input noise current densities?


** JFETs have very low noise currents so noise voltage dominates with low input resistances.

> The ratio of an amp input voltage noise and current noise densities does
> not define a "input noise resistance" from which you can calculate anything.


** So there is a big hole in your imaginary knowledge.

>
> Putting in a 3.3K resistor as you want will not give best noise
> or NF but will increase noise several fold.
>


** Of course - lowest noise is with a dead short.

NF is tested with a real input load and is a figure of merit in dB for that condition. So many dBs more noise than if the amplifier were noise free.

So there will always be a resistor value that minimises the noise rise in dB.

Why do I have to explain this concept?


>
> >https://pdf1.alldatasheet.com/datash...MI/2N4403.html
> >
> >See figure 9 showing a set of curves for Ic, resistance at the input and NF.
> >
> >For 1mA and 500ohms the NF is under 1dB at 1kHz and beyond.
> >
> >At lower currents, the best noise figure is at much higher resistances.

>
> Expected.


** It is the same claim you disputed before.

What happened to the link to Project 66 ??

My published design with full tech details.

To much for you puny brain ?


> >FFS go away dickhead.


>
> There you go again. What's the deal?


** You are a lying idiot.

If I had your name I would make a very strong complaint to TI.

See if you really work there and in what role.

Coffee boy maybe?

Work experience kid ?

Nasty little ****, whatever the fact.


.... Phil

  #34  
Old November 7th 19, 07:23 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,656
Default overvoltage on audio circuits - Noname.jpg (0/1)

Phil is known to have some odd notions about noise, but I am assuming that
we can all agree on the same basic statements:

1. For high impedance, current noise is dominant, whereas for low impedances,
voltage noise is dominant.

2. Microphones are primarily low impedance, with output impedances of
microphones being lower than 500 ohms and input impedances of preamplifiers
being in th 500 ohms to 5k ohm region.

3. NF attempts to combine voltage and current noise, but is normally specified
on the datasheet in a way that is not useful, because the impedance is
seldom at a useful value, and the assumption is made of source/load
impedance matching which is almost never the case for a microphone
interface.

4. All the GkTB equations we were forced to memorize in school are useful at
RF but not useful in a mismatched low frequency world.

Now, Phil has in the past displayed extreme reluctance to believe that 1/f
noise is significant in these systems, and believes that pink Boltzmann noise
is the only issue. It is futile to attempt to demonstrate otherwise to him.

Marshall Leach's article is a very good introduction to the system and
presents basic noise analyses of several transformered and transformerless
microphone preamps:
https://leachlegacy.ece.gatech.edu/p...ransformer.pdf
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #35  
Old November 7th 19, 07:43 PM posted to rec.audio.pro
Scott Dorsey
external usenet poster
 
Posts: 16,656
Default overvoltage on audio circuits

Ralph Barone > wrote:
>
>I was under the impression that electromigration was only an issue in
>modern microprocessors and other ICs built using nanometer scale
>transistors. I would assume that an op amp is built with huge transistors
>(and huge traces) in order to achieve low noise, and would therefore be
>relatively immune to electromigration damage.


I think it's a matter of scale and voltage. So it's an issue at low voltages
with tiny transistors, but at higher voltages (and really 15V isn't that
high) with larger transistors. I think it's also a matter of the shape of
the metallization traces, with sharp angles promoting migration.

That said, if it were that big a problem I'd be seeing LM709s and LM301s
starting to fail by now, right?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #36  
Old November 7th 19, 08:07 PM posted to rec.audio.pro
[email protected]
external usenet poster
 
Posts: 16
Default overvoltage on audio circuits - Noname.jpg (0/1)

On Wed, 6 Nov 2019 14:24:19 -0800 (PST), Phil Allison > wrote:

wrote:
>
>---------------------


> To much for you puny brain ?


>> >FFS go away dickhead.

>
>> There you go again. What's the deal?

>
>** You are a lying idiot.
>
> If I had your name I would make a very strong complaint to TI.
>
> See if you really work there and in what role.
>
> Coffee boy maybe?
>
> Work experience kid ?
>
> Nasty little ****, whatever the fact.


OK, took a few posts, but now I know what I'm dealing with. There can be no rational discussion here, just insults and name calling from an "audio
expert" in place of technical rebuttal. From google, this has apparently been going on for decades. I feel sorry for you, it must suck to be you.

Over and Out.




  #37  
Old November 7th 19, 08:40 PM posted to rec.audio.pro
Mat Nieuwenhoven
external usenet poster
 
Posts: 42
Default overvoltage on audio circuits

On Thu, 31 Oct 2019 10:08:18 -0400, wrote:

>On Wed, 30 Oct 2019 20:33:11 -0700 (PDT), Phil Allison > wrote:
>
wrote:
>>
>>--------------------
>>
>>
>>> Also, bipolar amps don't use large devices to reduce noise.

>>
>>
>>** Discrete op-amps use paralleled BJTs at the inputs and fairly high current levels to get voltage noise down low as possible.
>>
>>Enlighten us -
>>
>>what magic trick do integrated ones use instead ?
>>

>
>Without getting too wordy, main components of bipolar noise are shot noise, which is a noise in the collector current and goes as the sq rt of emitter
>bias current, the thermal resistor noise of all resistance at the base of the signal input bipolar devices, and the IR voltage noise developed at the
>base by the shot noise divided by transistor beta times base resistor value. Increasing bias currrent increases shot current noise at the collector
>and base, so low noise bipolar amps tend to be biased at lower currents. Base resistance is a function of the area and the length of the current path.
>Since the depth of the resistor path in an IC is fixed by the fab process, one way the area and length are optimized is by using long, skinny min
>width emitters with base contacts the same length as the long emitters and on both sides on the emitters. Usually the device will have multiple long
>emitter stripes so that each long base contact in between the emitter stripes serve both emitters on each side, reducing base resistance by 2. True, a
>larger device could continue to reduce base resistance, but other performance parameters must be met so base resistance is minimized by transister
>geometry rather than brute force size. Not sure why discreet amps would use high currents for low noise. Shot noise is independent of process and
>increases with current. Perhaps they practically eliminated all base resistance so there is no thermal or base shot noise component. They woud still
>have the collector shot noise to deal with.Possibly they dealt with it with more transistors and more power eslehwere in the design. Don't know. ICs
>don't have the luxery of having the unlimited power and cost available to high quality hifi stuff. Of course, amp designs with high power output
>drive must use large transistors and high bias currents, perhaps this requirement reflects through the entire design.
>
>I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
>22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.



Impressive specs. Is this an enhanced version of the OPA1622?

Mat Nieuwenhoven


  #38  
Old November 7th 19, 10:31 PM posted to rec.audio.pro
[email protected]
external usenet poster
 
Posts: 16
Default overvoltage on audio circuits

On Thu, 07 Nov 2019 20:40:08 +0100 (CET), "Mat Nieuwenhoven" > wrote:

>On Thu, 31 Oct 2019 10:08:18 -0400, wrote:
>
>>On Wed, 30 Oct 2019 20:33:11 -0700 (PDT), Phil Allison > wrote:
>>
wrote:
>>>
>>>--------------------
>>>
>>>
>>>> Also, bipolar amps don't use large devices to reduce noise.
>>>
>>>
>>>** Discrete op-amps use paralleled BJTs at the inputs and fairly high current levels to get voltage noise down low as possible.
>>>
>>>Enlighten us -
>>>
>>>what magic trick do integrated ones use instead ?
>>>

>>
>>Without getting too wordy, main components of bipolar noise are shot noise, which is a noise in the collector current and goes as the sq rt of emitter
>>bias current, the thermal resistor noise of all resistance at the base of the signal input bipolar devices, and the IR voltage noise developed at the
>>base by the shot noise divided by transistor beta times base resistor value. Increasing bias currrent increases shot current noise at the collector
>>and base, so low noise bipolar amps tend to be biased at lower currents. Base resistance is a function of the area and the length of the current path.
>>Since the depth of the resistor path in an IC is fixed by the fab process, one way the area and length are optimized is by using long, skinny min
>>width emitters with base contacts the same length as the long emitters and on both sides on the emitters. Usually the device will have multiple long
>>emitter stripes so that each long base contact in between the emitter stripes serve both emitters on each side, reducing base resistance by 2. True, a
>>larger device could continue to reduce base resistance, but other performance parameters must be met so base resistance is minimized by transister
>>geometry rather than brute force size. Not sure why discreet amps would use high currents for low noise. Shot noise is independent of process and
>>increases with current. Perhaps they practically eliminated all base resistance so there is no thermal or base shot noise component. They woud still
>>have the collector shot noise to deal with.Possibly they dealt with it with more transistors and more power eslehwere in the design. Don't know. ICs
>>don't have the luxery of having the unlimited power and cost available to high quality hifi stuff. Of course, amp designs with high power output
>>drive must use large transistors and high bias currents, perhaps this requirement reflects through the entire design.
>>
>>I designed a decent low noise op amp a few years ago, the OPA1662, 3.3nv/rtHz noise densisty. -124db distortion, total noise+distortion 0.00006%,
>>22MHz GBW, 22V/uS SR, Sig/noise 95db, voltage gain 114db, and ..... 1.5ma power draw total.

>
>
>Impressive specs. Is this an enhanced version of the OPA1622?
>


No, this was a new design. It's a two stage amp with a modified Monticelli stage for the output. I designed it about 9 years ago. It's been on the
market quite awhile. I was actually working remotely for Burr Brown just after TI acquired them. All of the support work, product definition, customer
visits, characterization, etc., were done in Tucson by BB (now TI Tucson), but it's manufactured by TI in Dallas. Don't know anything about the 1622.
I stopped doing work for TI in 2014 and haven't kept up. Looking at the dates on the TI web site, the 1622 was announced around 2016, 5 years after
the 1662, so with that and looking at the 1622 block diagram, it might be that the 1622 is a modified 1662, but I have no idea.
  #39  
Old November 7th 19, 10:32 PM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 457
Default overvoltage on audio circuits - Noname.jpg (0/1)

Scott Dorsey wrote:
-------------------
>
> Phil is known to have some odd notions about noise,


*** Nah, that is not one tiny bit true.


> but I am assuming that
> we can all agree on the same basic statements:
>
> 1. For high impedance, current noise is dominant, whereas for low impedances,
> voltage noise is dominant.
>


** Yes. JFET inputs have negligible current noise.



> 2. Microphones are primarily low impedance, with output impedances of
> microphones being lower than 500 ohms and input impedances of preamplifiers
> being in th 500 ohms to 5k ohm region.
>


** Yes, sources like MC picks are only a few ohms yet is it still possible to make god pre-amps for them without out transformers.


> 3. NF attempts to combine voltage and current noise, but is normally specified
> on the datasheet in a way that is not useful, because the impedance is
> seldom at a useful value, and the assumption is made of source/load
> impedance matching which is almost never the case for a microphone
> interface.


** False. With a mic-pre you simply specify the ratio in dB between the measured (audio band) noise with a 150 to 250ohm load and the calculated Johnson noise.


>
> 4. All the GkTB equations we were forced to memorize in school are useful at
> RF but not useful in a mismatched low frequency world.


** False. Johnson noise is dominant in any resistive source situation.

>
> Now, Phil has in the past displayed extreme reluctance to believe that 1/f
> noise is significant in these systems,



** And he is dead right too.

>
> and believes that pink Boltzmann noise
> is the only issue.



** LOL there is no such animal.

Johnson noise is White - equal energy in equal bandwidths.


> It is futile to attempt to demonstrate otherwise to him.



** Naturally, cos that would be impossible.


Oh dear, the old " proof of some nonsense I am claiming is hidden in this massive link somewhere" trick.

No way.



....... Phil


  #40  
Old November 7th 19, 10:35 PM posted to rec.audio.pro
Phil Allison[_4_]
external usenet poster
 
Posts: 457
Default overvoltage on audio circuits - Noname.jpg (0/1)

wrote:

-------------------------

>
> > Too much for you puny brain ?

>
> >> >FFS go away dickhead.

> >
> >> There you go again. What's the deal?

> >
> >** You are a lying idiot.
> >
> > If I had your name I would make a very strong complaint to TI.
> >
> > See if you really work there and in what role.
> >
> > Coffee boy maybe?
> >
> > Work experience kid ?
> >
> > Nasty little ****, whatever the fact.

>
> OK, took a few posts, but now I know what I'm dealing with.
>



** I figured you out even quicker - sunshine.

A fake, a liar and know nothing fool.

One of thousands infesting all of usenet.

It was evident to me English was not your first language.

And clear thinking your last.



...... Phil

 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Overvoltage protection Alex Pogossov Vacuum Tubes 17 July 14th 11 08:06 PM
FA: Vintage Audio Tube Circuits Book WeBu Tech 3 July 7th 04 06:36 AM
FA: Vintage Audio Tube Circuits Book WeBu Vacuum Tubes 1 July 7th 04 06:36 AM
FA: Vintage Audio Tube Circuits Book WeBu Marketplace 0 July 6th 04 01:17 AM
FA: Vintage Audio Tube Circuits Book WeBu Marketplace 0 July 6th 04 01:17 AM


All times are GMT +1. The time now is 07:29 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Copyright 2004-2019 AudioBanter.
The comments are property of their posters.