From: mark_zacharias@labolgcbs.net
"Trevor" wrote in message
news:m6j1v2$h6k$1@speranza.aioe.org...
> On 11/12/2014 10:39 PM, Mark Zacharias wrote:
>> "Trevor" wrote in message
>> news:m6asds$39i$1@speranza.aioe.org...
>>> 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
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