In article ,
Nick J. wrote:
Hello,
My amplifier/speakers have recently started playing funny buggers. It's
a Cambridge Audio A5 biwired in to a pair of Eltax Liberty 3+.
The speakers appear to have become out of phase somewhat or somehow --
not entirely out of phase, but enough to be noticable (and annoying).
I've ensured that all the cables are of the correct polarity.
How are you detecting this and identifying it as a phase problem?
It's also developed a strange frequency shift -- there's a big mid
"hole" in the left hand speaker, which seems to have transferred itself
in to the right speaker -- consequently, there's some audible distortion
from the right speaker, which seems not to be going as low or high as
the left speaker.
Having one speaker develop a frequency-response oddity can also make the
other sound odd in the opposing manner.
The amplifier pre-out and tape-out do not exhibit this problem when
monitored through an additional headphone amplifier.
I've also noticed that the amplifier is not as loud as it used to be --
a comfortable listening volume used to be on the third notch up. Now it
needs to go to the fifth for a comparable level. No matter how hard the
amp is driven, it just doesn't seem to get loud.
Does anyone know what it might be? I have no spare amplifier or
speakers to investigate individual apparatus here. At the moment, I'm
suspecting the amplifier's PA stage to be knackered -- unless a faulty
crossover in one of the speakers could be causing the effects throughout
the system?
The changes in 'phase' and frequency response sound to me more like a
problem with a damaged cross-over or speaker unit than with the power amp.
(Strictly speaking, not a 'cross-over' if you are biwiring, but the speaker
will still have networks of components between its input terminals and the
actual speaker units. A component here may have failed, or a lead come
adrift.)
What happens if:
1) You swap over the speakers. Does the change follow a speaker, or stay
with a given amplifier output? This should help decide where the problem
resides - speaker or amp.
2) Just listen to one speaker, and then the other, in isolation? Does one
sound OK and the other not? Use something like mono radio as the source for
this if you can.
I don't know the design of the A5, but I am not sure what amplifier fault
would give the changes in sound you describe. Usually, when a power amp
goes wrong the result is silence or very noticable distortion. The amp
might be producing excessive d.c. and this is annoying the speaker. To
check you can (carefully!) disconnect and reconnect the speaker lead with
the amp on but no music playing. If this produces a loud thump or crack
even when the amp has been on for some time it implies some d.c. is
present. (Do this with care to avoid accidentally shorting the leads which
might do damage.)
Slainte,
Jim
--
Electronics
http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc
http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio
http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc.
http://www.st-and.demon.co.uk/JBSoc/JBSoc.html
Amp/speaker issues
Linear Mode
