[Mark Zacharias]

"Trevor" wrote in message
...
On 11/12/2014 10:39 PM, Mark Zacharias wrote:
"Trevor" wrote in message
...
On 10/12/2014 11:21 PM, Mark Zacharias wrote:
In my experience the manufacturers are simply trying to reduce the
number of warranty repairs to some extent by specifying the higher
resistance. In truth, with a bit of common sense applied at the volume
control side of the equation, a four-ohm speaker will work just fine
with any solid state amp or surround receiver of even minimal quality,
such as Pioneer, Sony, Marantz, Denon, Kenwood, etc PROVIDED as I say,
some common sense is used and the user isn't trying to use the thing as
a sort of mini-PA system.

Problem is, people connect all sorts of speakers, even for example car
stereo speakers wired in unusual, often incompetent ways, then expect
to
be able to blast away for hours on end.

Yamaha, for example, knows full well that one of their power
transformers will not have a failed thermal fuse in the power
transformer in the absence of customer abuse - playing the thing at a
very high level, probably with low impedance speakers (or combinations
of speakers) for an hour or two more or less continuous.

Therefore, they will only cover ONE power transformer under warranty.
The warranty servicer is expected to educate the customer that a second
transformer won't be covered.

In fact, the newest Yamaha's will "rat out" the user by recording how
high the volume was for more than one minute and how many times. This
info is accessible in the service menu.


Amazing isn't it that a manufacturer can incorporate watch dog
electronics in a receiver, but not simply a more sophisticated
protection circuit to prevent damage in the first place!
I'd be looking elsewhere if that's the case.




Oh, they have protection circuitry all right. Lots of triggers all
monitored by the microprocessor. Problem is, since music can be
extremely dynamic in nature, and since transistors can be destroyed so
quickly, any circuit that would absolutely prevent damage to output
transistors caused by abuse, would also protect the amp from being able
to produce music at any decent level.


Rubbish. Transistor protection of SOA has been standard in many amps for
decades, and power outputs are now so high that only the *really* cheap
stuff has any problems providing "decent levels" into any normal speaker.
In any case we were talking about the transformer.



Some manufacturers are now monitoring temperature of the power
transformer as well, but I've already seen one where the transformer was
not saved from the internal thermal fuse opening.

So the protection circuit was inadequate, hardly surprising for many cheap
designs.


They're getting better, though - I'm seeing fewer and fewer blown
channels due to abuse these days.

Right, it's just not that hard these days. Some manufacturers will always
choose to cut corners however. And some do it deliberately as part of
their planned obsolesence :-(


Trevor.




So-called SOA protection has always been imperfect at the VERY least. When a
solid state (lets just say consumer grade) amp runs into a short circuit,
it's at best a toss-up whether it blows before the protection can kick in.
Add to this that a consumer will keep trying repeatedly even when the
protection does trigger, a major failure is very often the result.

mz