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-   -   overvoltage on audio circuits (http://www.audiobanter.com/showthread.php?t=141821)

gareth magennis October 24th 19 09:56 PM

overvoltage on audio circuits
 
Hi,

I have here a batch of SSL channel strips rack mounted.
The regulated PSU that came with them is marked +-18v but actually produces +- 21v with a 1A quick test load, with the adustment pots at minimum as they arrived, .
(I suspect these are 24v based supplies - they are modular linear ones made in USA i think, 2 x "18v" and a 48v phantom)

It seems the channel strips have been running with this supply at 21v for a long time now.

What could be the possible detrimental effects?


I have only had a quick peek inside the first one of eight, and noticed a bulging capacitor on the SSL dynamics card.

I would not power any of them up with this supply at present.


Cheers,


Gareth.

Phil Allison[_4_] October 25th 19 09:49 AM

overvoltage on audio circuits
 
gareth magennis wrote:

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

>
> I have here a batch of SSL channel strips rack mounted.
> The regulated PSU that came with them is marked +-18v but actually produces +- 21v with a 1A quick test load, with the adustment pots at minimum as they arrived, .
> (I suspect these are 24v based supplies - they are modular linear ones made in USA i think, 2 x "18v" and a 48v phantom)
>
> It seems the channel strips have been running with this supply at 21v for a long time now.
>
> What could be the possible detrimental effects?


** Very few, likely there is PCB level filtering of the DC supply via resistor and electros.

Many Soundcraft analogue desks had 68ohm resistors and 100uF caps fitted in each rail feed - so dropped a volt or two in order to remove residual noise from the external PSU.

Op-amps like the NE5532 are happier with 16 volt rails.



...... Phil



>
> I have only had a quick peek inside the first one of eight, and noticed a bulging capacitor on the SSL dynamics card.
>
> I would not power any of them up with this supply at present.
>
>
> Cheers,
>
>
> Gareth.



Scott Dorsey October 25th 19 02:26 PM

overvoltage on audio circuits
 
gareth magennis > wrote:
>
>I have here a batch of SSL channel strips rack mounted.
>The regulated PSU that came with them is marked +-18v but actually produces +- 21v with a 1A quick test load, with the adustment pots at minimum as they arrived, .
>(I suspect these are 24v based supplies - they are modular linear ones made in USA i think, 2 x "18v" and a 48v phantom)


Who made themm? If they are at 21V with a 1A load, they are likely failed and
might even be running full open.

>It seems the channel strips have been running with this supply at 21v for a long time now.
>
>What could be the possible detrimental effects?


Electrolytics will go bad. Can cause failures of semiconductors too, but if
they were going to fail they would have failed by now. If the equipment was
well-designed, they used 25V or 35V electrolytics and the lifetime will be
shortened a little bit. If it was poorly-designed they used 16V electrolytics
and the lifetime will be shortened a whole lot.

>I have only had a quick peek inside the first one of eight, and noticed a bulging capacitor on the SSL dynamics card.


They do that naturally, though. They are wear items. It's probably time
to replace them.

>I would not power any of them up with this supply at present.


21V isn't enough to worry a lot about but if the regulation in the supply is
not working properly, the noise floor will be impaired too.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

gareth magennis October 25th 19 11:58 PM

overvoltage on audio circuits
 
OK, thanks Phil and Scott, I somehow thought 21v would be a bigger problem that it apparently is.

Gareth.

Scott Dorsey October 26th 19 12:38 AM

overvoltage on audio circuits
 
gareth magennis > wrote:
>OK, thanks Phil and Scott, I somehow thought 21v would be a bigger problem that it apparently is.


Maybe, but if the supply is producing 21V, it might be producing noise too.

Incidentally, did you see SSL has introduced a low cost console at the AES
show? Well, it's $40k so it's not that low cost, but by SSL standards it's
low.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

gareth magennis October 26th 19 01:18 AM

overvoltage on audio circuits
 
Well I haven't scoped the supply as yet but will certainly do so.

Just stuck 20 ohms on each leg to find out what it might do, before connecting any module, and didn't like the overvoltage.


Gareth.

Phil Allison[_4_] October 26th 19 01:54 AM

overvoltage on audio circuits
 
Scott Dorsey wrote:

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

>
> Maybe, but if the supply is producing 21V, it might be producing noise too.
>
>



** FYI:

Just about the dumbest thing any console designer can do is fill up the modules with rail bypassing electros ( tants or otherwise) without series resistors.

Doing that injects wide band noise from the regulated PSU directly into the ground pattern and ribbon cabling - millivolts of the evil stuff.

Seen it done.


..... Phil

geoff October 26th 19 01:24 PM

overvoltage on audio circuits
 
On 26/10/2019 1:18 pm, gareth magennis wrote:
> Well I haven't scoped the supply as yet but will certainly do so.
>
> Just stuck 20 ohms on each leg to find out what it might do, before connecting any module, and didn't like the overvoltage.
>
>
> Gareth.
>



Sounds like a fairly random shonky empirical tack-on to me, rather than
a solid scientific 'good' firm supply. If you want +/-15V JUST DO IT.
iF YOU WANT +/-18v JUST DO IT. dON'Y DO SOMETHING ELSE AND STICK A
SERIES RESISTOR IN TO DO MAYBE WHATEVER DEPENDING ON WHAT HAPPENS. And
+/-24V- what's that all about ?

Ooops capslock. Too late to give a ****.

geoff

Scott Dorsey October 26th 19 02:59 PM

overvoltage on audio circuits
 
geoff > wrote:
>On 26/10/2019 1:18 pm, gareth magennis wrote:
>> Well I haven't scoped the supply as yet but will certainly do so.
>>
>> Just stuck 20 ohms on each leg to find out what it might do, before connecting any module, and didn't like the overvoltage.
>>

>Sounds like a fairly random shonky empirical tack-on to me, rather than
>a solid scientific 'good' firm supply. If you want +/-15V JUST DO IT.
>iF YOU WANT +/-18v JUST DO IT. dON'Y DO SOMETHING ELSE AND STICK A
>SERIES RESISTOR IN TO DO MAYBE WHATEVER DEPENDING ON WHAT HAPPENS. And
>+/-24V- what's that all about ?


I think he means he used a 20 ohm shunt resistor as a test load.
Not a series resistor.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

geoff October 27th 19 04:29 AM

overvoltage on audio circuits
 
On 27/10/2019 2:59 am, Scott Dorsey wrote:
> geoff > wrote:
>> On 26/10/2019 1:18 pm, gareth magennis wrote:
>>> Well I haven't scoped the supply as yet but will certainly do so.
>>>
>>> Just stuck 20 ohms on each leg to find out what it might do, before connecting any module, and didn't like the overvoltage.
>>>

>> Sounds like a fairly random shonky empirical tack-on to me, rather than
>> a solid scientific 'good' firm supply. If you want +/-15V JUST DO IT.
>> iF YOU WANT +/-18v JUST DO IT. dON'Y DO SOMETHING ELSE AND STICK A
>> SERIES RESISTOR IN TO DO MAYBE WHATEVER DEPENDING ON WHAT HAPPENS. And
>> +/-24V- what's that all about ?

>
> I think he means he used a 20 ohm shunt resistor as a test load.
> Not a series resistor.
> --scott
>



I was more referring to the claimed practice of SSL to stick a series
resistor in the power supply legs after regulation.

geoff

Scott Dorsey October 27th 19 01:04 PM

overvoltage on audio circuits
 
geoff > wrote:
>On 27/10/2019 2:59 am, Scott Dorsey wrote:
>> geoff > wrote:
>>> On 26/10/2019 1:18 pm, gareth magennis wrote:
>>>> Well I haven't scoped the supply as yet but will certainly do so.
>>>>
>>>> Just stuck 20 ohms on each leg to find out what it might do, before connecting any module, and didn't like the overvoltage.
>>>>
>>> Sounds like a fairly random shonky empirical tack-on to me, rather than
>>> a solid scientific 'good' firm supply. If you want +/-15V JUST DO IT.
>>> iF YOU WANT +/-18v JUST DO IT. dON'Y DO SOMETHING ELSE AND STICK A
>>> SERIES RESISTOR IN TO DO MAYBE WHATEVER DEPENDING ON WHAT HAPPENS. And
>>> +/-24V- what's that all about ?

>>
>> I think he means he used a 20 ohm shunt resistor as a test load.
>> Not a series resistor.

>
>I was more referring to the claimed practice of SSL to stick a series
>resistor in the power supply legs after regulation.


Oh, safety resistors! Yeah that's a good idea. It may degrade the sound,
but when capacitors short it dramatically reduces the collateral damage.
The SSLs aren't designed to sound great, they are designed to be convenient
and reliable. Philips was big on that practice too.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

gareth magennis October 28th 19 07:04 PM

overvoltage on audio circuits
 
Turns out that although the output buffer pcb (not SSL) has the 21v on its op-amps, all the SSL circuitry is somehow protected and is running at just over 19v, which makes me feel a lot better.

Gareth.

geoff October 28th 19 09:39 PM

overvoltage on audio circuits
 
On 29/10/2019 8:04 am, gareth magennis wrote:
> Turns out that although the output buffer pcb (not SSL) has the 21v on its op-amps, all the SSL circuitry is somehow protected and is running at just over 19v, which makes me feel a lot better.
>
> Gareth.
>


Duuno what opamps, but 5532 are specced at max +/- = 22V, so 21 OK and
19 more 'comfortable' if running lower actually offers any benefit.

But the 24V previously mentioned somewhere distinctly not good, unless I
misunderstood the context.

geoff

Phil Allison[_4_] October 29th 19 03:01 AM

overvoltage on audio circuits
 
geoff wrote:

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

>
>
> Duuno what opamps, but 5532 are specced at max +/- = 22V, so 21 OK and
> 19 more 'comfortable' if running lower actually offers any benefit.
>


** Console makers who tried to use that 22V spec back in the late 70s soon came a cropper. Any NE5532s ran very hot and most failed in the first year or so.

The PSU voltage on the ICs was soon dropped to 18V or even 15V to get cool operation eliminate failures.


FYI:

Only real service techs know this sort of ****.


...... Phil

geoff October 29th 19 04:31 AM

overvoltage on audio circuits
 
On 29/10/2019 4:01 pm, Phil Allison wrote:
> geoff wrote:
>
> -------------
>
>>
>>
>> Duuno what opamps, but 5532 are specced at max +/- = 22V, so 21 OK and
>> 19 more 'comfortable' if running lower actually offers any benefit.
>>

>
> ** Console makers who tried to use that 22V spec back in the late 70s soon came a cropper. Any NE5532s ran very hot and most failed in the first year or so.
>
> The PSU voltage on the ICs was soon dropped to 18V or even 15V to get cool operation eliminate failures.
>
>
> FYI:
>
> Only real service techs know this sort of ****.
>
>
> ..... Phil
>


Yeah +/- 18 the highest I've ever seen on anything. And +/- 15 more 'usual'.

geoff

Scott Dorsey October 29th 19 03:28 PM

overvoltage on audio circuits
 
geoff > wrote:
>On 29/10/2019 8:04 am, gareth magennis wrote:
>> Turns out that although the output buffer pcb (not SSL) has the 21v on its op-amps, all the SSL circuitry is somehow protected and is running at just over 19v, which makes me feel a lot better.
>>

>Duuno what opamps, but 5532 are specced at max +/- = 22V, so 21 OK and
>19 more 'comfortable' if running lower actually offers any benefit.


And.. a lot of people would run the 5532 at +/-24V, outside the rated
envelope. If you tried this, a lot of them would fail in the first week,
but after that they all seemed to keep running fine. I gather there was
some variation in the thickness of the oxide layers on the chip and the
ones that were a little thinner got selected out..

>But the 24V previously mentioned somewhere distinctly not good, unless I
>misunderstood the context.


If it was going to fail, it probably would have failed by now. I would be
much more worried that the supply issues will degrade the sound quality.
(I will refrain from implying that SSL equipment has poor sound quality
here because people are probably tired of my harping on that).
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

gareth magennis October 29th 19 07:19 PM

overvoltage on audio circuits
 
Hi Geoff,

the psu modules are off the shelf and these adjust between 21v and 28 or something, can't remember.
I just postulated that these may be 24v based supplies with adjustment.
Rather than 18v with adjustment I would rather have seen.

Gareth.


[email protected] October 30th 19 12:40 PM

overvoltage on audio circuits
 

>
> I was more referring to the claimed practice of SSL to stick a series
> resistor in the power supply legs after regulation.
>
> geoff


which is a very good design practice for any low noise design.

hint: what is the lowest noise you can get from an electronic regulator vs an RC filter circuit?

m





[email protected] October 30th 19 12:43 PM

overvoltage on audio circuits
 
On 29 Oct 2019 11:28:57 -0400, (Scott Dorsey) wrote:

>geoff > wrote:
>>On 29/10/2019 8:04 am, gareth magennis wrote:


>And.. a lot of people would run the 5532 at +/-24V, outside the rated
>envelope. If you tried this, a lot of them would fail in the first week,
>but after that they all seemed to keep running fine. I gather there was
>some variation in the thickness of the oxide layers on the chip and the
>ones that were a little thinner got selected out..
>
>>But the 24V previously mentioned somewhere distinctly not good, unless I
>>misunderstood the context.

>
>If it was going to fail, it probably would have failed by now. I would be
>much more worried that the supply issues will degrade the sound quality.


Electronic circuits have a mechanical wear-out mechanism caused by the momentum of the
electrons in the current flow moving the conductor atoms slightly if they collide. Over time,
enough atoms will have moved that a void will open in the conductor line, breaking the path
and the circuit. This electromigration is a very strong exponential function of current density
and temperature (among other things.) Circuits are designed to last ten years under speced
conditions. So, even if you get an amp that is at the high end of the manufacturing distribution
for breakdowns, running at higher voltages increases the temperature and exponentially reduces
the life. Depending on wafer process and circuit package, going from 18V to 24V could significantly
lower the life of the circuit by many years.

This mechanism exists in all electrical conductors, but is only an issue in microcircuits because the
conducting lines are so small and the current densities are therefore very high.

Ralph Barone[_3_] October 30th 19 01:58 PM

overvoltage on audio circuits
 
> wrote:
> On 29 Oct 2019 11:28:57 -0400, (Scott Dorsey) wrote:
>
>> geoff > wrote:
>>> On 29/10/2019 8:04 am, gareth magennis wrote:

>
>> And.. a lot of people would run the 5532 at +/-24V, outside the rated
>> envelope. If you tried this, a lot of them would fail in the first week,
>> but after that they all seemed to keep running fine. I gather there was
>> some variation in the thickness of the oxide layers on the chip and the
>> ones that were a little thinner got selected out..
>>
>>> But the 24V previously mentioned somewhere distinctly not good, unless I
>>> misunderstood the context.

>>
>> If it was going to fail, it probably would have failed by now. I would be
>> much more worried that the supply issues will degrade the sound quality.

>
> Electronic circuits have a mechanical wear-out mechanism caused by the momentum of the
> electrons in the current flow moving the conductor atoms slightly if they
> collide. Over time,
> enough atoms will have moved that a void will open in the conductor line,
> breaking the path
> and the circuit. This electromigration is a very
> strong exponential function of current density
> and temperature (among other things.) Circuits are designed to last ten years under speced
> conditions. So, even if you get an amp that is at the high end of the
> manufacturing distribution
> for breakdowns, running at higher voltages increases the temperature and
> exponentially reduces
> the life. Depending on wafer process and circuit package, going from 18V
> to 24V could significantly
> lower the life of the circuit by many years.
>
> This mechanism exists in all electrical conductors, but is only an issue
> in microcircuits because the
> conducting lines are so small and the current densities are therefore very high.
>


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.


[email protected] October 30th 19 04:01 PM

overvoltage on audio circuits
 
On Wed, 30 Oct 2019 13:58:13 +0000 (UTC), Ralph Barone > wrote:

> wrote:
>> On 29 Oct 2019 11:28:57 -0400, (Scott Dorsey) wrote:
>>
>>> geoff > wrote:
>>>> On 29/10/2019 8:04 am, gareth magennis wrote:


>>
>> This mechanism exists in all electrical conductors, but is only an issue
>> in microcircuits because the
>> conducting lines are so small and the current densities are therefore very high.
>>

>
>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.


Nope, electromigration has always been a concern and is one of the two most important reliability
issues in layouts. The other being electrostatic discharge. Huge traces is a relative term, microcircuits
are tiny.

Besides, large interconnect traces result in large parasitic capacitances which have a major impact on
AC charateristics (phase margin, BW, etc.), not to mention the impact on chip size and therefore
chip cost. Also, bipolar amps don't use large devices to reduce noise.

Phil Allison[_4_] October 31st 19 03:33 AM

overvoltage on audio circuits
 
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 ?



.... Phil


[email protected] October 31st 19 02:08 PM

overvoltage on audio circuits
 
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.



geoff October 31st 19 08:42 PM

overvoltage on audio circuits
 
On 1/11/2019 3:08 am, 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.
>
>


Is that better than a 741 ? ;- )

geoff

Phil Allison[_4_] November 1st 19 10:02 PM

overvoltage on audio circuits
 
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 ?
> >

>

--------------------------------------------------
>
> Increasing bias currrent increases shot current noise at the collector
> and base, so low noise bipolar amps tend to be biased at lower currents.



** FYI so called "shot noise" is not relevant to input devices operating over the full audio band. High frequency noise completely dominates.


> Not sure why discreet amps would use high currents for low noise.



** Then you are simply not very familiar with audio circuitry - as I suspected.

The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


> 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.



** Nice part - but with about 1uV of input noise.

With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.

Though obsolete, this op-amp set a bench mark for low noise audio.

https://www.analog.com/media/en/tech...016SSM2017.pdf

Note the fairly high supply current.


...... Phil


[email protected] November 2nd 19 07:25 PM

overvoltage on audio circuits
 
On Fri, 1 Nov 2019 15:02:56 -0700 (PDT), Phil Allison > wrote:

>>

>--------------------------------------------------
>>
>> Increasing bias currrent increases shot current noise at the collector
>> and base, so low noise bipolar amps tend to be biased at lower currents.

>
>** FYI so called "shot noise" is not relevant to input devices operating over the full audio band. High frequency noise completely dominates.


That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?
>
>> Not sure why discreet amps would use high currents for low noise.

>
>The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


What do you mean here by NF? Are you referring to noise factor or noise figure? Those are ratios, not impedances. NF in my world is the SNRout/SNRin,
it's a measure of extra noise to the signal added by a component. Matching impedances gets maximum power to the load, but that is not what is desired
here. A microphone generates a small voltage and can tolerate very little current draw without distorting. The object is to amplify the microphone
VOLTAGE without loading it, not maximize power delivered to the amp. The last thing you want to do is put 150 ohm load on the microphone input. BTW,
the YBM data sheet gives the diff input impedance as 1Mohm or higher, depending on gain setting, which is what I would expect.
>
>> 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.

>
>** Nice part - but with about 1uV of input noise.
>With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


How are you coming up with these numbers? They certainly do not agree with either the design results, application characterization, or with the
feedback from customers. Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think
that gives you?
>
>Though obsolete, this op-amp set a bench mark for low noise audio.
>
>https://www.analog.com/media/en/tech...016SSM2017.pdf
>


Well let's compare your "benchmark" with the OPA1662. Conditions do not perfectly match, but I've gotten them close.

YBM OPA1662

Total Harmonic noise distortion 0.008 0.00006 % conditions
input voltage noise density 107 3.3 nv/rtHz 1KHz, G=1
" 12 2.9 " G=10
" 2 2.7 " G=100
" 1 2.6 " G=1000
input noise current density 2 1 pa/rtHz 1KHz input bias current
25 1.2 ua wc
input voltage noise density corner (1/f noise) 70 8 Hz
THD+ noise 0.007 0.0005 % G=2, [RL=5K YBM, 2K OPA]
Slew rate 17 22 V/uS
sm sig bandwidth 4 20 MHz G=1
Ips 10.6 1.5 ma

Now lets calculate input noise value using the YBM data sheet procedure and comparing to the YBM results -
From the YBM data sheet --------
For a microphone preamplifier, using a typical microphone im-pedance of 150 ohms, from the YBM data sheet,
using En =sqrt {(1 nVvHz)2 + 2 (pA/vHz× 150 ohms)2 + (1.6 nV/vHz)2} we get the input noise as

YBM OPA1662
noise source en = (for G=1,10,100,1000) 107,12,2,1 3.3,2.9,2.7.2.6
in = 2 1 pa/rtHz
RS = 150 ohm, microphone source impedance 1.6 1.6 nv/rtHz
et = 1.6 nV/[email protected] 1 kHz, microphone thermal noise
for G=1000 1.93 3.0 nv/rtHz
and for G=100 2.65 3.1 "
and for G=10 12 3.2 " and for
G=1 108 3.3 "

>Note the fairly high supply current.


Indeed, but I don't think it has anything to do with low noise, in fact, the noise is actually quite hign for except for very high gain settings. The
fact that it goes down so rapidly at high gain settings has very little to do with bias currents and says that the noise gain loop has been tweaked.
Noise gain is usually tweaked in the customer application to give the user more flexibility since it can impact other parameters, but is often tweaked
in the circuit as well. Having an order of magnitude reduced amplifier BW also reduces noise.
>
>** Then you are simply not very familiar with audio circuitry - as I suspected.


Let me say a little about that. I have designed audio circuits for 30 years. One was selected by Electronics Design magazine as Product of the Year. I
have presented papers at the International Solid States Conference in NYC. I have 25 patents as individual inventor, not global group co-inventer as
some places do. My designs are in avionics, satellites, medical equipment, and one is currently in every battery powered Apple product. However, I
will bow to an obviously superior master. Please tell me about your honors and designs and explain why my unworthy OPA1662 seems to be purchased in
the millions by these equally clueless customers such as Shure, Pioneer, and Marantz.

You know what I think? I've noticed in past posts when someone posts seeking help, and they've misunderstood their application or made a mistake,
rather than offering assistance, you call them an idiot. People like that are usually the C students in college and have limited accomplishments at
work, and use forums like this to bully those who know even less. Here, rather than offering transistor theory to prove your point, you pull out an
old data sheet designed by someone else and say, "see, see, it has high currents and low noise" without any understanding of the circuit. I would have
been impressed if you had offered theory and knowledge new to me, but didn't happen.

So, once again, please tell me how you came up with 3.3Kohms as input impedance for the OPA1662. The only resistance of the amp that affects noise is
the actual parasitic resitance of the base diffusion resistor of the input bipolar transistor, which is about 20 ohms. The dynamic input impedance is
set by the AC path, doesn't affect noise, and is not calculated by dividing the input voltage noise density by the input current noise density, if
that's what you did, then shows an appalling lack of understanding. Also, explain to me the mechanism of how the high current levels of YBM reduced
the noise. Also explain why, at 14% of the current draw, the OPA eq input noise bests in a major way or matches YBM for all gain settings below 100.
While you're at it, explain why you appear to want a 150 ohm NF input resistance for the amp.



>..... Phil
>


Phil Allison[_4_] November 2nd 19 11:28 PM

overvoltage on audio circuits
 
wrote:

-------------------
>
>
> >** FYI so called "shot noise" is not relevant to input devices operating
> > over the full audio band. High frequency noise completely dominates.

>
>
> That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
> What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?
> >



** Whatever name you give it, the noise is essentially white and so rises with frequency being proportional sq.rt of the bandwidth.


> >> Not sure why discreet amps would use high currents for low noise.

> >
> >The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.

>
> What do you mean here by NF?


** Noise Figure.

> Those are ratios, not impedances.


** BJTs have noise figures in dBs that vary with the source resistance and current. There are optimum values for both giving the lowest NF.

Surely you have seen the curves published on data sheets.



> A microphone generates a small voltage and can tolerate very little
> current draw without distorting.


** Dynamic mics can deliver signals of a volt or so while condenser types output several volts.

Dynamic mics have a source impedance that is mostly restive and a typically couple of hundred ohms. The load needs to be a few times higher for best results.

A good mic pre-amp needs to have input voltage noise less then that of a 200ohm resistor when operating at high gain, like 1000 times.



> >> 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.

> >
> >** Nice part - but with about 1uV of input noise.
> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.

>
> How are you coming up with these numbers?
>


** You are asking some very strange things.

> They certainly do not agree with either the design results,
> application characterization, or with the feedback from customers.



** There is no disagreement with the published data, at all.


> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


** It gives you a good guide to the source resistance that gives the best NF.

Do the same for a JFET op-amp and you get about 1Mohm, cos the current is so low. 1uV of noise in the audio band is many times that of a 200ohm resistor.

Is that news to you ?


> >Though obsolete, this op-amp set a bench mark for low noise audio.
> >
> >https://www.analog.com/media/en/tech...016SSM2017.pdf
> >

>
> Well let's compare your "benchmark" with the OPA1662.
>



** The SSM part beats it easily cos it is actually dedicated mic pre-amp, with a single resistor for gain control.

Did you not read the heading on the data sheet ?

You would need three op-amps connected as an instrumentation amplifier to do the same job and it would then behave like the SSM with input noise increasing at lower gains.


> >Note the fairly high supply current.

>
>
> Indeed, but I don't think it has anything to do with low noise, in fact, the noise is actually quite hign for except for very high gain settings.


** Got news for you pal.

Having very low input noise only matters at high gain settings cos one adjusts the gain setting to get an output of about 1Vrms.

So the actual input signal is about 1mV at high gain and proportionally more at lower gains, defeating any input noise increases going on.


> The fact that it goes down so rapidly at high gain settings has very little to do with bias currents and says that the noise gain loop has been tweaked.



** The common mode resistor that sets the gain ADDS to the input noise.

Unavoidable with that topology and not important in practice.

YOU are simply not very familiar with audio circuitry - as I suspected.



> Let me say a little about that. I have designed audio circuits for 30 years.
>


** Makes you familiar only with your own designs.

Those which you have not seen remain a complete mystery.



One was selected by Electronics Design magazine as Product of the Year. I
> have presented papers at the International Solid States Conference in NYC. I have 25 patents as individual inventor, not global group co-inventer as
> some places do. My designs are in avionics,



** FFS - that is more than enough solo trumpet playing.

Mics and mic pre-amps are not your thing.

If you have not spent many years dealing with them, like I have, you are not going to know very much about them.


> Please tell me about your honors and designs and explain why my
> unworthy OPA1662 .........


** Where did I say anything like that ???

I said it was a "nice part", but with 1uV of input noise in the audio band.


> You know what I think?



** Not very interested, thanks.

Because you are now beginning to sound like a raving lunatic.

Why are you posting on a pro-audio usenet group at all ??

BTW:

I use my real name and identity here, while you do not.

Attacking me from a position of anonymity is cowardly in the extreme.


( rest of this pig's misconstrued and paranoid garbage snipped )




...... Phil

[email protected] November 4th 19 07:11 PM

overvoltage on audio circuits
 
On Sat, 2 Nov 2019 16:28:47 -0700 (PDT), Phil Allison > wrote:

wrote:


>> >** FYI so called "shot noise" is not relevant to input devices operating
>> > over the full audio band. High frequency noise completely dominates.


>> That's a surprise to me and many others as well, since shot noise is white noise and broadband, extending orders of magnitude beyond the audio range.
>> What is this "high frequensy noise" if it is not shot wde band noise or thermal wide band noise?


>** Whatever name you give it, the noise is essentially white and so rises with frequency being proportional sq.rt of the bandwidth.


Since you are an audio expert, I am surprised that you did not know ----

That shot noise is white noise
That the " High frequency noise that completely dominates" is known as thermal or Johnson noise
That either shot or thermal noise or both can be important noise sources depending on the application. Just because shot noise is not a factor in
your microphone case does not mean it's never important.

>> >> Not sure why discreet amps would use high currents for low noise.


>> >The idea is to get the best NF impedances down to around 150ohms for use with dynamic mics.


The dominant noise source in this app is the parasitic base resistance of the input biplor and is not a function of bias current.

>> A microphone generates a small voltage and can tolerate very little
>> current draw without distorting.


>** Dynamic mics can deliver signals of a volt or so while condenser types output several volts.


I'm sure you know that you want the diaphram to move as little as possible to keep the response as linear as possible and thus distortion low, thus it
will be putting out a small volatge.

> >> I designed a decent low noise op amp a few years ago, the OPA1662


>> >** Nice part - but with about 1uV of input noise.
>> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


>> How are you coming up with these numbers?
>> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


>** It gives you a good guide to the source resistance that gives the best NF.
>Is that news to you ?


Yes it is. I've never known anyone to do that before, let alone think it means anything. I could put a Darlington on the inputs, get the shot noise
down 0.005na/rtHz. Would you then come up with 3.3Mohms as meaning something?

>> >Though obsolete, this op-amp set a bench mark for low noise audio.


>> >https://www.analog.com/media/en/tech...016SSM2017.pdf


> >Note the fairly high supply current.


I'm glad we're back on point. I originally said that high currents and large devices were not needed for low noise in bipolars. You said I was wrong
and pointed to the SSM as proof. I suppose "high currents" and "large devices" are relative terms, so I'll say more. Shot noise increases with current
and is independent of manufacturing process and device size, period. Thermal noise is dominated in a bipolar by the parasitic resistance in the base
of the input device. Even with best layout geometry, the resistance can always be made smaller by increasing the emitter width (larger device).
However, in the 40V analog processes I'm familiar with, and all 40V processes will have similar resistivities to get the breakdown voltages, a bipolar
with a 1nv/rtHz thermal noise can be designed with dimensions about 200u x 200u. This is not a minimum size device by any means, but it's not exactly
huge, on the OPA design two of these devices together would take up 15% of the chip area, and it's a small chip. Had this size been used, the OPA
would have a 1nv/rtHz noise density spec. However, our customers told us 3nv/rtHz was quite adequate and they preferred lower Ips, better distortion,
and better AC. The OPA comes in a dual, and each amp uses 45mW, far lower than competing devices with similar specs. I suppose very old manufacturing
processes would have larger feature sizes, but even 15 or 20 year old processes wouldn't give monstrous devices.

> YOU are simply not very familiar with audio circuitry - as I suspected.


>> Let me say a little about that. I have designed audio circuits for 30 years.


>** FFS - that is more than enough solo trumpet playing.


I very, very rarely do that, and I could have said much more. I did so in this case to show the absurdity of your repeateded statements that I knew
nothing about audio. I don't feel the need to broadcast anything. My plaques and patents are in boxes, and my walls instead have posters. I also don't
feel the need to belittle anyone or call them an idiot.

>> Please tell me about your honors and designs and explain why my
>> unworthy OPA1662 .........


>** Where did I say anything like that ???


>I said it was a "nice part", but with 1uV of input noise in the audio band.


For the OPA I get 0.49uV input noise over the audio band, for the SSM I get 0.27uV. Both of these numbers give excellent S/N ratios, and it is likely
the better distortion of the OPA compensates for the extra noise so that the signal error of each is close. Be that as it may, the OPA was not
designed as a special purpose amp for this application, it is a general purpose op amp. Nevertheless, Shure buys it as a microphone amp for battery
powered applications.

> BTW:
> I use my real name and identity here, while you do not.
> Attacking me from a position of anonymity is cowardly in the extreme.


And I won't. I am under a non-dosclosure agreement. I probably said more than I'm supposed to already, I sure as hell am not going to have someone see
my name in a newsgroup and report that I am blabbing away secrets. Anyway, I could list any name and how would you know if it was real or not?

As far as "attacking" you goes, I said you had an attitude and often called past posters idiots when they were looking for help. You have several
times told me I know nothing about audio. I question what drives someone to be like that.

Phil Allison[_4_] November 4th 19 10:44 PM

overvoltage on audio circuits
 
wrote:

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

**This raving nutter needs dealing with.

>
> >** Whatever name you give it, the noise is essentially white and

> so rises with frequency being proportional sq.rt of the bandwidth.
>
> Since you are an audio expert,



** I am, and you are very clearly not.



> >> A microphone generates a small voltage and can tolerate very little
> >> current draw without distorting.

>
> >** Dynamic mics can deliver signals of a volt or so while condenser
> > types output several volts.

>
> I'm sure you know that you want the diaphram to move as little as possible
> to keep the response as linear as possible and thus distortion low, thus it
> will be putting out a small volatge.
>


** Absurd drivel.

You know less than nothing about microphones in actual use.



> >** It gives you a good guide to the source resistance that gives
>> the best NF. Is that news to you ?

>
> Yes it is. I've never known anyone to do that before,



** Proves you have no real understanding of input noise.

Just a plie of rote learned irrelevances.



>
> >> Let me say a little about that. I have designed audio circuits for 30 years.

>
> >** FFS - that is more than enough solo trumpet playing.

>
> I very, very rarely do that,


** But are just about to do it again.

How sickening.


> > BTW:
> > I use my real name and identity here, while you do not.
> > Attacking me from a position of anonymity is cowardly in the extreme.

>
> And I won't. I am under a non-dosclosure agreement.


** But see no obligation to NOT post wild bull**** on public forums ?

How fascinating.


> As far as "attacking" you goes, I said you had an attitude and often
> called past posters idiots when they were looking for help.


** And you're real sure they were not all idiots ?

How would YOU know that?

I doubt you have any way to tell.


....... Phil


[email protected] November 5th 19 09:43 PM

overvoltage on audio circuits
 
On Mon, 4 Nov 2019 14:44:22 -0800 (PST), Phil Allison > wrote:

> wrote:
>
>---------------------
>
>**This raving nutter needs dealing with.
>>
>> Since you are an audio expert,


>** I am, and you are very clearly not.


OK,, let's look at one of the few pearls of wisdom where you attempted to actually provide supporting calculations for one of your statements

YOU
>> >With 3.3nV and 1pA per rtHz of input noise, the best impedance is 3.3kohms.


ME
>> How are you coming up with these numbers?
>> Did you get them by dividing the input voltage noise density by the input current noise density? If so, what do you think that gives you?


YOU
>** It gives you a good guide to the source resistance that gives the best NF.
>Is that news to you ?


ME
>Yes it is. I've never known anyone to do that before, let alone think it means anything. I could put a Darlington on the inputs, get the shot noise
>down 0.005na/rtHz. Would you then come up with 3.3Mohms as meaning something?


YOU
>** Proves you have no real understanding of input noise.
>
> Just a plie of rote learned irrelevances.


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 and instead the equivalent voltage and current densities at the input are specified, which allows the user to determine the added noise of the
amp or gain block Since the voltage noise density and current noise density are caused by different mechanisms, they are independent and are treated
separately and their results added by superposition. So, as shown before,

For the microphone preamp app previously given, using a typical microphone impedance of 150 ohms, and choosing a gain of 1000, then

mic noise amp input voltage noise amp input current noise
density density density

SSM (1.6 nV/rtHz) (1 nV/rtHz) (2pA/rtHz× 150 ohms)

OPA (1.6 nV/rtHz) (2.7 nV/rtHz) (1pA/rtHz x {150+10/(10+1000)}

total input noise density

SSM = sqrt{(1.6 nV/rtHz)^2 + (1 nV/rtHz)^2 + (2pA/rtHz× 150 ohms)^2} = 1.96nV/rtHz

OPA = sqrt{(1.6 nV/rtHz)^2 + (3.0 nV/rtHz)^2 + (1pA/rtHz x [150+10/(10+1000)]^2} = 3.0nv/rtHz

and over the audio band the total input referred noise is SSM = 0.28nV OPA = 0.43nV

I think these numbers give the user everything he needs to determine the noise levels and noise added by the amp. However, you say the user needs to
consider NF and you say 3.3Kohms is the best source resistor for best NF for the OPA and you arrived at that number by dividing the input voltage
noise density by the input current density. So,

Now I have a few questions. 1) please explain the physical significance of dividing the input 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 current
density to 5pa, would you now use a 3.3Mohm source resistor?

Since you are an expert and I am not, so you say, perhaps you can explain Ohm's Law to me. See, I always thought Ohm's Law stated that the voltage
across an impedance (resistance) was linearly proportional to the current through it, and the constant of proportionality was the value of the
resistance. Since the input noise voltage density is due thermal noise of the parasitic base resistance,and the input current noise density is due to
the shot noise of the collector divided by transistor beta, and the component due to base shot noise times base resistance is negligible in this case,
then the input noise voltage and current are independent and uncorrelated. I don't think Ohm's Law defines a resistor in the case of independent
values for voltage and current. I always thought they had to be linearly related to define a resistance.

Please try to answer in a mature way and support your position with technical calculations or references. Try to provide a technical discussion. If
you have some knowledge new to me, I'd like to learn it. See if you can avoid deleting large parts of posts you find inconvenient and resorting to
insults and name calling and stating over and over that you are an audio expert and I'm not.

However, I don't really expect to get a rational technical answer to the questions I've asked. I hope I'm surprised, but based on your past responses
in this and other threads, I'm getting a picture of how you click. Look at this below

> How sickening.


>> I said you had an attitude and often
>> called past posters idiots when they were looking for help.

>
>** And you're real sure they were not all idiots ?
>
> How would YOU know that?
>
> I doubt you have any way to tell.


Is this the way you live your life? Did you not get enough love when you were little?





Phil Allison[_4_] November 5th 19 11:01 PM

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










[email protected] November 6th 19 08:42 PM

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.

Phil Allison[_4_] November 6th 19 10:24 PM

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


Scott Dorsey November 7th 19 06:23 PM

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."

Scott Dorsey November 7th 19 06:43 PM

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."

[email protected] November 7th 19 07:07 PM

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.





Mat Nieuwenhoven November 7th 19 07:40 PM

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



[email protected] November 7th 19 09:31 PM

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.

Phil Allison[_4_] November 7th 19 09:32 PM

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



Phil Allison[_4_] November 7th 19 09:35 PM

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



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