The astonishing step up in the Duo GT’s performance owes itself to many factors and refinements, but it is centred on the application of Avantgarde’s iTron current drive amplification. Nearly all audio systems are built around voltage amplifiers. Yet it is current that actually drives loudspeaker and makes the noise. We all rely on the simple fact that V=IR – meaning that if we increase or amplify voltage, that increase will be tracked by current. But that tracking comes with a degree of lag and disconnection, discernable rise times on leading edge response and overshoot on peaks. In contrast, a current amplifier operates like a tap, simply responding to signal demand by asking “how much and when?” Current amplifiers trace signal input far more accurately, respond more quickly and with less overshoot than their voltage driven cousins. Which is why they are so widely used in control and instrumentation applications. That exactingly machined faceplate on your amplifier or DAC – it was almost certainly cut on a CNC machine and the cutter head was almost certainly controlled by a current amplifier. This is not some strange, mystical or barely understood new amplifier technology. It and its results are all around you.
But if current amplification is so accurate in operation, why don’t all audio amplifiers employ it? Because it comes with two limiting factors that make that impossible. The filter networks that form the crossover in conventional passive speakers operate on voltage input. They are effectively invisible to a current drive – making current amplifiers incompatible with the vast majority of speakers on the market. In order to work, current drive mandates an active crossover.
The second (potentially catastrophic) limitation that disqualifies current drive from general audio applications is that you cannot let it see a driver’s fundamental resonance – otherwise that resonance answers the question “How much?” with the answer, “More than you’ve got!” Given that the low-frequency output of all commercial loudspeakers depends on extending below their bass drivers’ fundamental resonance – often exploiting that resonance in the process – and it is impossible to generate serious low frequency output using a current amplifier.
But Avantgarde found itself in a unique situation. Not only did the extraordinary efficiency of their horn-loaded speaker systems make them ideally suited to exploiting the speed of response that comes with current amplification, their speakers already employed active bass. So, for all those asking, if current amplification is so wonderful, why don’t more companies use it, the answer is, because they can’t. In fact, the remarkable audio performance of current amplification is pretty much limited to this one, specific situation. Does the iTron amplifier package on the Duo GT trounce the performance of something like the Ongaku? Absolutely. Exactly the same as it’s going to trounce pretty much any other conventional, voltage amplifier – with this speaker! So for dealers and end-users, it’s not so much a case of this affordable amplifier buries the expensive one you own/I just sold you. It’s simply that this particular speaker, along with the Trio G3, has emerged to offer a unique solution – an opportunity you’d be well advised to consider seriously.
