| Re:.0
>How in a typical Amp would the power handling be distributed between
>these outputs.
A typical amp has just a switch for each of the output terminals to be
connected to the actual power amplifier; with some amps it may get a
little more involved due to load considerations, but the gist is that
there is just one power source delivering into one or two speakers (per
channel). Surround may be an additional low-power amp, but it's more
likely to be a phase-shift network of sorts, connected again to the one
power amp.
[*REAL* amps have just one pair of speaker terminals, slightly less
*Real* amps have two pairs (one left, one right); speaker selector
switches are considered No Added Value (if not heresy) :-) :-) ]
>I'm disappointed with the output power of the Main o/p to which my
>speakers are connected.
In what way? Just not loud enough? or does it distort easily when you
crank up the level? What level?
>Could I connect the speakers to both the Main and Aux
>outputs to up the output power. Is this a dangerous thing to do.
Depends on the way your amp is switched internally. Hooking both (+)
terminals (while leaving (-) separate) together will *USUALLY* not harm
your amp, but it will offer no additional power, as the lot is still
driven by one power amp.
>This is why I'm curious about the impedance of the output stages of
>Amps.
Power amps are designed as Voltage/Voltage amps; this means LOW output
impedance. The lower, the better generally as this means a high damping
factor, or in other words the speaker drive units follow the amp output
more precisely. But there are two limiting factors in amp parameters:
voltage swing and output current. Usually, these are kind of matched
for 4 or 8 ohm speakers. This doesn't mean that you can't use other
impedance speakers but only that you will hit one limit way before the
other, thus preventing you to get the specified power out of your amp.
>Will the principle of superposition apply. It will, if the
>outputs are high impedance looking from the speakers back in. That is,
... but they aren't, so, no. And, as said, they probably aren't even
separate amps.
One way of getting more power from one amp is to bridge them (in
another meaning of the word than yours), but this means dedicating both
channels to a single speaker so you'd have to get a second, identical
amp then. In this setup, you connect one speaker between the (+)
terminals of the left and right channel of one of the amps, and feed
one channel a normal, the other an inverted signal (some amps have a
provision for this). The other speaker is handled by the second
amp. You double the voltage swing across the speaker, and provided the amp
can deliver the current, output power will be fourfold.
What amp and speakers are you using? Sounds like a mighty inefficient
set if 80 watts can't get a decent sound level.
- Rik -
|
| Rik,
Thanks for the info. I have a pair of Kef Carlton III's connected to a
Technics 880 Class AA(?) amp. I bought it in '88 when I had more money
than sense and since then I've been trying my best to improve on the
setup. It was a Technics one step above Midi type system. I swapped the
original speakers for the Kef's and they were a great improvement in
quality but the volume is still a drawback.
The speakers have a relatively low sensitivity, 86dB/w @1m. However
before I got them I listened to them connected to a 100w NAD and they
were perfect right up to as far as I could handle. I guess the current
drive ability of the technics just is'nt up to it. Would this have
anything to do with them been Class A. The double A is just marketing
hype (which I fell for in my innocence) meaning that the stage before
the power stage (pre-amp) is class A as well as the output stage.
They use a trick to keep the output stage from overheating in that they
use some sort of delay in the signal path so that they sample the
volume and adjust the o/p supply rail voltage to keep up with the music
demands. from what I know now from reading this file, I'm sure that
this does terrible things to the dynmamic headroom and the delay surely
adds extra noise.
Oh well, I suppose I'll just have to go out and buy a decent amp,
thanks,
Joe.
|
| Bridging amps: take a stereo amp, preferrably with this feature built
in; if it is it should be mentioned in the manual, and two speakers.
Hook each of the speakers to one of the amps in such a way that it is
connected between the (+) terminals of the left and right channels. Now
you drive both channels with the Left signal, one channel direct, the
other channel inverted (this is accomplished by the 'bridged mono'
switch if the amp has one). Figure a sine wave being fed into the amp.
Now the left channel (+) terminal follows the sine (amplified, of
course), the right channel (+) follows the inverted sine: the voltage
at the right (+) terminal is the same as on the left (+) terminal, but
has a negative value. So the voltage across the speaker is twice as
large as when referencing between a single (+) and ground, and because
P = V�*R, P (power) gets multiplied by 4 (6dB sound level increase)
You do the same, using the other amp, for the Right channel.
A simple (but flawed) analogy is to figure two men tilting a plank. If
one end is held steady and the other moved up or down you are able to
achieve a certain angle. Now if the second man moves the other end down
while you move this side up, the angle gets steeper.
Clear?
- Rik -
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