Re: stereo amp cleaning

On 31 May, 01:35, "Mark D. Zacharias" <spamme...@xxxxxxxxxxxx> wrote:
Smitty Two wrote:
In article <J%f7i.62157$V75.33167@edtnps89>,
"Dave" <dspear9...@xxxxxxxxxxxxxxxx> wrote:

Has technology evolved so that a momentary crossing of speaker wires
could not destroy expensive output transistors?

It hasn't as much to do with technological evolution as it has to do
with intelligent design. Hasn't there always been good stuff and bad
stuff? A good design would allow you to hard wire the speaker leads
together and go fishing.

Sorry. From a technical standpoint, that is an idiotic statement, one that
has been made before, and disproven time and again. People like to make
statements like "This amp will drive a nail!" etc but it simply isn't true.
It is the nature of bipolar transistors, in fact any semiconductor, that
they cannot carry current much beyond their rating for more than a
split-second. The instantaneous current demanded by a short-circuit will
destroy ANY semiconductor output device unless that device is being so
limited that it cannot produce music, which is dynamic in nature. Any
protection circuit is there simply to protect the speakers from an amp
failure, and to protect the amp only if the overload isn't too severe. This
presumes that the sensing circuit will sense a large (but not TOO large)
current surge prior to total failure. Any circuit which would really protect
the amp from a short circuit would also protect it from the music.

Mark Z.

This is not always true.
The power supply can only supply so much current.
Any of my designs have MOSFETs that can take more than a shorted PSU.
By the time the MOSFETS have got anywhere near warm the fuses will
have gone.

www.ckp-railways.talktalk.net/pcbcad21.htm

.

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