Re: amplifier question

geezer <liveoak.nine@xxxxxxxxx> wrote:
Ok, I could only access the first two pages for some reason.
Since the issue appears to thermal runaway, isn't this pretty much
resolved by using MOSFETs as the output devices?

It's changed. Using MOSFETs doesn't eliminate the problem, but it does
make the design a whole lot easier and it does prevent the thing from
failing in a horrible and catastrophic "Phase Linear" manner.

Thing is, MOSFET output stages sound different than bipolar ones. Whether
this is a good or bad thing depends on taste.

And if you're building prototypes of a particular design using
transistors that would melt down in this way, wouldn't you just
purposely fry a few prototypes on your way to finding the limits of
that particular design? That doesn't seem too much like dark science,
not that I'm an EE or anything close.

That's called "cut and try" engineering, and it used to be the only way
to make absolutely sure. Still, no matter how well you design the thing,
some customer will find a way to abuse it that you never thought of.

For the most part, this is good enough, unless you're trying to design
the whole thing on a hybrid or monolithic chip where it costs thousands
of dollars to cut a prototype, or if you are trying to push the limits
of the technology.

But to be honest, all of the problems come from trying to push the limits
of the technology... but that's what you have to do to sell a product.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
.

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