Hello
I was just reading a friends copy of the August 05 EQ magazine. In the "Bang for the $$$
article page 62 I noticed repeated usage of the term "output attenuators" used when
talking about the ART SLA2 power amp. The controls on that amp or 99.9% of any
power amp do not attenuate the output level they only attenuate the input level coming
into the power amp front end and in no way reduce the amount of power the amp can
produce. If a power amp is rated for full output with a input signal of 1.25 volts reducing the
input level controls will only require more input signal to achieve the amps rated output. Setting
the controls to a certain position so no one will blow your speakers as referred to in the article is
not a real form of speaker protection, all someone would need to do is just turn up the mixer more
to compensate for a lower input level setting. The correct term to use would have been input level / input attenuator. I guess in a very crude sense you could turn down the input levels to such a low setting that even the highest output possible from your mixer, workstation ect. would not be able to drive the amp to it's full output. Setting the gain structure of a system up that way would seriously reduce the total operating headroom though.
I also question the set up used to do a A-B test between the ART amp and the Hafler amp using what was
referred to as a "JBL crossover box" to select between the two amps. Crossovers normally are used
to divided a full range input signal in to multiple output bands of low and high or low, mid and hi. or more depending on the unit and application at selected frequencies to crossover between the output bands.
Was the crossover used active or passive and what model was it. I am having a hard time trying to figure out how an accurate A-B listening test was done using a crossover as a switching device between power amps. True blind A-B listening test require that the amps under test are producing exactly the same output voltage as with even the slightest increase in perceived listening volume will sway many listeners in picking the louder amp or speaker depending on what is being tested or compared.
Just some questions from a curious reader and in no way affiliated with any products referred to
in the article.
Thanks for you time
Mike Caldwell
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Mike Caldwell
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