68 Silicon chip Australia’s electronics magazine siliconchip.com.au
Want to unlock immense power from an audio amplifier and speaker?
You can combine this easy-to-build unit with a standard stereo amplifier,
such as our Ultra-LD series, to easily get 400W into a single 8-ohm speaker.
That’s about three times the power that amp would typically manage. With
the right amplifier, you could even get 1000W or more – per channel!Bridge-mode Audio
Amplifier Adaptor
Need Extreme,
Earth-shattering Power?
Need Extreme,
Earth-shattering Power?
BY NICHOLAS VINEN
L
et’s say you want to put on a rock concert. You’re
going to need thousands of watts of power,
and it’s a bit impractical to stack up dozens
of smaller amplifiers and speakers. What
you need is something BIG.
You could build a few of our
Majestic loudspeakers, described
in the June and September 2014
issues (siliconchip.com.au/Se-
ries/275). You would build these
using the alternative Celestion
FTR15-4080FD woofer, giving you
very sensitive speakers capable of being
driven at levels of up to 1000W.
So that’s the speakers sorted, but how
to drive them?
The most potent audio amplifier we’ve published is a
500W job, in August-October 1997 (siliconchip.com.au/Se-
ries/146). As is typical for power ampli-
fiers, it will produce its full rated power
output into a 4load. But the Majestic
speakers have an 8W impedance, and
so that amplifier module will only
achieve a measly 278W into
such a load.
That’s just not good enough!
The trick is to drive the
speakers in bridge mode. If
you build two of those ampli-
fiers, plus this little device, you
can drive a single Majestic speaker
with two of these amplifiers.
And because the speaker’s impedance is
effectively halved when being driven in bridge mode,
you will get that 500W figure from each. 500W + 500W
= 1000W. Rock on!
The way it works is simple. This Bridge Adaptor (often
called a BTL [bridge-tied load] adaptor) splits your audio
signal in two. One output signal is virtually identical to
the input, while the other is inverted.
So when you connect those outputs
to two audio amplifiers (possibly the