My head hurts, I’ve been reading other peoples rantings about what makes the best audio amplifier, it’s not rocket science but does require an understanding of the laws of physics.
Firstly it is current not voltage that determines how far the cone or ribbon of a voice coil or ribbon speaker moves, as the current produced by a specific voltage varies with frequency, voltage drive will not produce an accurate representation of the original audio.
Secondly the inertia of a speaker can accurately be represented by the parallel LCR circuit used to simulate the resonance of a speaker.
Thirdly a high damping factor can reduce the amplitude of any overshoots and resonance produced on a high speed pulse input.
I used a resistor in series with the speaker back in the early 60’s when I modified a Radio & Hobbies (early electronics mag.) Playmaster Valve Amplifier and noticed a much cleaner audio result.
I worked on various solid state designs over the years eventually achieving the result I was after.
I recently decided to design a simple DIY project to demonstrate these facts and was surprised by the sound quality from a mediocre OP Amp.
The THD was improved by two orders of magnitude, and the bandwidth is now insane and completely stable even with a short circuit across the speaker.
The following circuit diagrams show the change required to convert a voltage amplifier to a current amplifier. Note:- the microvolt input required to zero the DC output before connecting the speakers.
To see the full specifications and complete DIY design visit my website at https://www.inja.com.au/diy.php
Note also :- speaker box design is different for current drive amplifiers. Start by mounting your driver in an infinite baffle and taking measurements.
The damping factor may appear at first glance to be low ie 1.2 ohm resister in series with the 8 ohm speaker. However when you divide this resistor by the open loop gain of the amplifier you get the real figure to divide into the 8 ohm speaker.