[LAU] M-Audio Audiophile Line Level Inputs

Folderol folderol at ukfsn.org
Tue Sep 18 15:12:36 EDT 2007

On Mon, 17 Sep 2007 23:58:36 -0600
"Bearcat M. Sandor" <HomeTheater at feline-soul.com> wrote:

> What makes a consumer level pre-amp different? I know some pre-amps "pop" and 
> i know quite a few subwoofers that "thump" when you first turn them on and 
> they never blow anything right? That would suggest that every time you are 
> turning on your Sony you run the risk of blowing something. Quite a few have 
> delays, but not all do.  

Some old valve (tube) amplifiers were vunerable to pulses due to
the back emf effects of output transformers and marginal stability.
Early transistors were delicate beasties and often worked at their
limits, so were also vulnerable. Unless you are using total crap, no
amplifier less than about 30 years old should have any problem at all
with pulses, DC shifts or raw mains stuffed up the input.

<pet peeve mode = "on">

Speaker manufacturers lie.

In case you missed that: Speaker manufacturers lie.

Most speakers have absolutely nowhere near their quoted power rating
(apart from PA etc.)

If you drive a *real* 50W speaker from a 50W amplifer, it is impossible
for any signal passing though the amp to damage the speaker.

'instantaneous power' is what they are quoting, a meaningless figure
invented by the marketing droids. It is supposed to be a 1 cycle and
the power is calculated from the difference between peak positive
voltage x current to the peak negative voltage x current. The
frequency of the signal and waveshape are usually NOT quoted.

Very occasionally they will be honest enough to give you an RMS
figure, but don't mention the frequency or duration.

The only trustworthy spec is *continuous* sinewave power with either a
given centre frequency or better still, 'full power bandwidth' 

<pet peeve mode = "off">

If your speakers and amplifiers are properly matched the amp should not
deliver any significant out-of-band power to the speaker, so should
have adequate low and high pass filters. Many do not.

I feel better now. I'll go and make a cup of coffee :)

Will J Godfrey

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