Re: Op amps

[Adrian Tuddenham[_2_]]

Sean Conolly > wrote:

[...]
> For a benchmark I'm using the vernerable NE5532, which is acceptable in
> every way but the current draw....

Beware of strange behaviour when the battery runs down. I used an
NE5532 in an experimental instrument pickup; it brought the whole show
to a halt when it burst into audio oscillation.

It turned out that someone had replaced the battery just before the
show, but they had accidentally picked up an old one which was falling
rapidly in voltage. When the supply rails reached about 3v, one of the
internal stages began passing a signal which was the inverse of normal;
the external negative feedback loop became positive feedback and the
auditorium was filled with screaming oscillation at the full power of
the P.A. system.


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[William Sommerwerck]

"Adrian Tuddenham" wrote in message
nvalid.invalid...

> It turned out that someone had replaced the battery just before the
> show, but they had accidentally picked up an old one which was falling
> rapidly in voltage. When the supply rails reached about 3V, one of the
> internal stages began passing a signal which was the inverse of normal;
> the external negative feedback loop became positive feedback and the
> auditorium was filled with screaming oscillation at the full power of
> the P.A. system.

And the crowd loved it!

[Adrian Tuddenham[_2_]]

William Sommerwerck > wrote:

> "Adrian Tuddenham" wrote in message
> nvalid.invalid...
>
> > It turned out that someone had replaced the battery just before the
> > show, but they had accidentally picked up an old one which was falling
> > rapidly in voltage. When the supply rails reached about 3V, one of the
> > internal stages began passing a signal which was the inverse of normal;
> > the external negative feedback loop became positive feedback and the
> > auditorium was filled with screaming oscillation at the full power of
> > the P.A. system.
>
> And the crowd loved it!

Not at a folk dance evening, they didn't!


--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

[Sean Conolly]

"Adrian Tuddenham" > wrote in message
nvalid.invalid...
> Sean Conolly > wrote:
>
> [...]
>> For a benchmark I'm using the vernerable NE5532, which is acceptable in
>> every way but the current draw....
>
> Beware of strange behaviour when the battery runs down. I used an
> NE5532 in an experimental instrument pickup; it brought the whole show
> to a halt when it burst into audio oscillation.
>
> It turned out that someone had replaced the battery just before the
> show, but they had accidentally picked up an old one which was falling
> rapidly in voltage. When the supply rails reached about 3v, one of the
> internal stages began passing a signal which was the inverse of normal;
> the external negative feedback loop became positive feedback and the
> auditorium was filled with screaming oscillation at the full power of
> the P.A. system.
>

Wow - with the bench supply I've run the voltage down to the point that it
stopped working, but all I got was distortion before it stopped entirely.

Thanks for pointing that out,

Sean

[Adrian Tuddenham[_2_]]

Sean Conolly > wrote:

> "Adrian Tuddenham" > wrote in message
> nvalid.invalid...
> > Sean Conolly > wrote:
> >
> > [...]
> >> For a benchmark I'm using the vernerable NE5532, which is acceptable in
> >> every way but the current draw....
> >
> > Beware of strange behaviour when the battery runs down. I used an
> > NE5532 in an experimental instrument pickup; it brought the whole show
> > to a halt when it burst into audio oscillation.
> >
> > It turned out that someone had replaced the battery just before the
> > show, but they had accidentally picked up an old one which was falling
> > rapidly in voltage. When the supply rails reached about 3v, one of the
> > internal stages began passing a signal which was the inverse of normal;
> > the external negative feedback loop became positive feedback and the
> > auditorium was filled with screaming oscillation at the full power of
> > the P.A. system.
> >
>
> Wow - with the bench supply I've run the voltage down to the point that it
> stopped working, but all I got was distortion before it stopped entirely.
>
> Thanks for pointing that out,

It seems to be some peculiar combination of low voltage and a certain
range of supply impedance that causes it. It doesn't always happen, but
be aware that it can .

--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk