Just to add fuel to the fire
Right David, I managed to download that on the PC so I had a good read and there are a number of points.
Firstly Antonio, the so called blind tests you mention were carried out 32 years ago, and do little other than highlight the unreasonable amounts of NFB being employed by early solid state amplifier designers to cover up switching distortion artefacts. Properly implemented NFB is benign, as can be proven by the fact that this "experiment" has not been reapeatable in over thirty years!
Secondly, Martin Colloms is a hifi reviewer. The article is little more than a list of subjective experiences, and as such I cannot take it seriously. After all, this is the same guy who thinks that the latest Naim CD players are groundbreaking. They are not IME, and there is certainly nothing in the way of objectrive data to support his opinion on those players.
Finally, it is entirely feasible that MC did indeed hear differences, but that he fails to recognise the reasons behind them and blames NFB simply because of a lack of understanding. Yes NFB reduces measureable distortion but it also reduces the output impedence of the amplifier and therefore increases the damping.
According to Dave Berning (who I consider to be a pretty clever guy)there is no universally correct amplifier output impedance. This is why Berning and the Cary in the article offer a means to adjust output impedance/damping on some models. Many system designers have known this for years, and damping adjustment controls were found on some amplifiers going back to the 1950s or before. The reason that there is no one correct output impedance is because the speaker is a mechanical system with inertia and its transient response is very much determined by the source impedance driving it. Each speaker design behaves differently, and it is usually desirable to achieve what's called "critical damping". If the mechanical system (speaker) is under damped, the cone will overshoot and ring in response to a step transient. If it is overdamped, it will undershoot and be slow to reach its proper position. Underdamping happens when the output impedance of the amplifier is too high, where as overdamping occurs when the output impedance is too low.
In terms of the bass reproduction, underdamping results in an overly warm resonant reproduction, and overdamping results in a overly dry and heavy presentation. Neither of these are correct. When the amplifier output impedance is optimum, the bass will have its most natural reproduction. A damping/feedback control on the amplifier lets the user best tune the speaker, and yes, the room acoustics enter into it as well.
Or of course that's what Dave Berning says but given that Martin Colloms performed his "test" using a highly overdamped loudspeaker (Wilson), it is highly probable that reducing the amplifier damping by reducing feedback would lead to increased life and better perceived timing. But not for the reasons he summises. Not because feedback in inherently bad for the reporduction of sound. In your case, you have increased the output impedence of your amplifier, introduced some frequency response irregularities, and possibly improved the damping of your single drive unit. But swap loudspeakers and you may well prefer the results with the feedback loop re-inserted.