Negative Feedback a deal killer?

I haven't read every post in this thread, but has anyone mentioned GLOBAL vs single stage feedback?
global, from output to input while other designs apply feedback at a single stage or a stage-at-a-time.
I can understand the time dependent nature of feedback, but can't that be helped by more....limited applications?

Hello H20Audio,

I have received reply from John Ulrick of Spectron - their chief designer:
============================================
Issue #1, stable driving a 0.1 ohm load. We can prove a Spectron amp will drive a 0.1 ohm load by providing lab data in the form of a oscilloscope graph of the amplifier driving a 0.1 ohm load. I will send a scope screen shot tomorrow [ I don;t need it - Dob].

Issue #2, driving the Apogee Scintilla speaker load. This is the issue of driving a low value complex load. The Spectron understand customers have chosen the Spectron amp because, for them we do drive their Scintilla speakers. There is a guy in, I think, Australia, who refurbishes Apogees that claims we do drive the Apogee speakers.
============================================
From me - Stereo Times reviewer Don Schaulis own Apogee speakers (don;t remember the model) and he gave Spectron spectacular review -http://www.stereotimes.com/amp013008.shtml

Cheers

Magfan,

Great question! I meant, but did not specify Global feedback.
Thanks for the responses, cat fights aside:)
Mike

Hello Athmaspere,

I have received reply from John Ulrick of Spectron - their chief designer. I sent him your first post as well:
==================================
"The above comments are only relative to analog circuits. It’s true that negative feedback in slow circuits with a –Z term in their transfer function have inherent ringing and do not enjoy the benefits of negative feedback. Spectron’s forward loop does not have any analog circuits, it’s digital with a propagation delay of .2uS. Engineering requires quantitative analysis. The first order look reveals some insight. Applying super-position theorem: The period of a 20KHz sine wave is 50uS. The ratio of the wave period to the forward loop propagation delays is 50uS/.2uS = 500 In simple terms, this means that the control loop can imitate 500 control vectors at shortest wave period of the input function."
===================================
Now, if you look midrange then the ratio would be about 5000:1 and for the bass 50000:1. So, while you are correct (in your 2nd post) that fast feedback is still not in real time - I would submit to you that in practical terms you can call it "nearly real time speed" it so fast!. While John mentioned here that the control loops used in Spectron are not analog but DIGITAL - you can read it in much greater details on Spectron web site.

I will not work as a mailman here anymore - if you want to discuss NF with John or Simon - take it to them, directly.

Cheers,

"50us/0.2us = 500" ?