On 28/01/14 10:56, Dave Plowman (News) wrote:
In article ,
John Williamson wrote:
Another alternative would be to install a 100 volt speaker system with
independent volume controls in each room, but that would mean buying a
new amplifier,and some matching transformers and volume controls.

I've used a 100 v line transformer I had lying around to adjust the level
of a speaker fed from a normal low impedance amp. It worked rather better
than a pad. It had five level taps on it - but it would be a bit of luck
if it gave the amount of attenuation wanted. Pads always seem to upset the
bass end - even on speakers which aren't exactly Hi-Fi.

+1

You can use a transformer to adjust power output via taps without
upsetting the impedance - but resistive pads are not good for bass units.

As part of my essays into reproducing 'valve sound' for guitar
amplifiers, artificially raising the output impedance of the power
amplifier was routine.

The good old Vox A30 amplifier has an output impedance of some 80 ohms.
Driving an 8ohm pair of loudspeakers, the effects are dramatic.

Massive bass resonance, about the bottom A on a guitar, plus overall
treble boost as the rising impedance of the speaker voice coil (a lot of
leakage inductance in a voice coil) is no longer a significant effect in
reducing treble output. Boom an chink we used to call it.

Also all other resonances in the paper cones and cabinets are much less
well damped, so the sound comes 'alive' with the sound of - well wood
and paper!

The amplifier loudspeaker and cabinet are the 'sound box' of an electric
guitar and give it an interest and colour it otherwise lacks. Hifi it
aint. But it isn't intended to be, either.



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