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overvoltage on audio circuits



 
 
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  #11  
Old October 27th 19, 02:04 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,649
Default 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."
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  #12  
Old October 28th 19, 08:04 PM posted to rec.audio.pro
gareth magennis
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Default 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.
  #13  
Old October 28th 19, 10:39 PM posted to rec.audio.pro
geoff
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Default 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
  #14  
Old October 29th 19, 04:01 AM posted to rec.audio.pro
Phil Allison[_4_]
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Default 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
  #15  
Old October 29th 19, 05:31 AM posted to rec.audio.pro
geoff
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Default 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
  #16  
Old October 29th 19, 04:28 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,649
Default 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."
  #17  
Old October 29th 19, 08:19 PM posted to rec.audio.pro
gareth magennis
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Posts: 44
Default 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.

  #18  
Old October 30th 19, 01:40 PM posted to rec.audio.pro
[email protected]
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Posts: 608
Default 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




  #19  
Old October 30th 19, 01:43 PM posted to rec.audio.pro
[email protected]
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Posts: 16
Default 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.
  #20  
Old October 30th 19, 02:58 PM posted to rec.audio.pro
Ralph Barone[_3_]
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Posts: 40
Default 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.

 




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