The airDRIVE Paradox

Re: The airDRIVE Paradox

Postby Ted Fletcher » Tue Mar 20, 2018 11:32 am

AS a further update (March 2018), We now have transconductance amplifiers (current mode, airDRIVE) in production and actually in stock at major retailers here in the UK!
But, there is no 'song and dance' about it yet, we introduced a version of a new design of mine which succeeds in converting a class 'D' power amplifier into a transconductance amp. We put this amplifier into the 'main' signal path of our Orbitsound P70W loudspeaker, but without telling anyone!
The intention was to see if the Great British Public would spot the difference.... it is quite startling, and to gain experience with these amplifier types in production numbers.
The results are not exactly shattering..... the problem is that our airSound loudspeakers sound pretty good anyway and the improved fidelity, although really noticeable, can't be discussed openly with the customer or we would give the game away.
So to round it off, what I originally called 'airDRIVE' is actually a version of a transconductance amplifier, modified to overcome a couple of foibles of the system, namely a tendancy to some nasty peaks at resonance and a naturally rising HF response. All Orbitsound P70W units have this amplifier.
It's very likely that we shall introduce these amplifiers generally throughout future product ranges; the advantages are very real. :o :)
Ted Fletcher
 
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Joined: Tue Feb 12, 2008 2:06 pm

Re: The airDRIVE Paradox

Postby Ted Fletcher » Tue Mar 20, 2018 3:11 pm

A word of caution to anyone interested in the details; the marrying up of a transconductance amplifier with a loudspeaker is far from simple, The acoustic loading of the driver in its enclosure has a significant effect on the instant impedance of the voice-coil; a factor to remember is that sound is produced as a function of acceleration of the cone movements which is a result of changes in the currents in the circuit. all this means that the voltages appearing on the output terminals of the amplifier are not representative of the acoustic output!
On a previous post I inferred that a loudspeaker driver is 'damped' by a low amplifier output impedance (damping factor). Just to be clear, this is only the case at or near the resonant frequency of the driver in its enclosure. The requirement for a super-low damping factor is one of the myths of the audio business. :roll:
Ted Fletcher
 
Posts: 475
Joined: Tue Feb 12, 2008 2:06 pm

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