Robust amplifier or " idiot fest ", Andrew ? Some manufacturers recomend to their boxes rather velding machines ( I can't show which ones, but we all know them... 😉 )...
Kevin,
The original AKSA was based on a Bailey design of the sixties, but finished looking a lot like the Citation 12, in which NP had a hand. It used asymmetric bootstrapping, miller compensation, phase lead and charge suckout, and a twin AC path in the feedback network. These are quite sophisticated techniques, and miller comp is widely used today.
The 55W handled loads down to 3.5R with ease, the 100W down to 2.2R. In fact source impedance was very slightly negative. Many hundreds were sold; if you care to examine the reviews at my forum you will see absolutely no unhappy customers.
You will not have seen schematics for my latest design, the Lifeforce. This is more modern than most would realise, and delivers scintillating performance an order of magnitude superior, again, see the forum. Like anyone passionate about his craft, I have a deep and comprehensive knowledge of the history of the technology as well, and so I read your comments with amused disbelief. But what is important, I believe, is that my designs are developed as much subjectively as objectively, which gives me a musical advantage. Power supply design and component choice are very important, as is layout.
Thank you for your post,
Cheers,
Hugh
The original AKSA was based on a Bailey design of the sixties, but finished looking a lot like the Citation 12, in which NP had a hand. It used asymmetric bootstrapping, miller compensation, phase lead and charge suckout, and a twin AC path in the feedback network. These are quite sophisticated techniques, and miller comp is widely used today.
The 55W handled loads down to 3.5R with ease, the 100W down to 2.2R. In fact source impedance was very slightly negative. Many hundreds were sold; if you care to examine the reviews at my forum you will see absolutely no unhappy customers.
You will not have seen schematics for my latest design, the Lifeforce. This is more modern than most would realise, and delivers scintillating performance an order of magnitude superior, again, see the forum. Like anyone passionate about his craft, I have a deep and comprehensive knowledge of the history of the technology as well, and so I read your comments with amused disbelief. But what is important, I believe, is that my designs are developed as much subjectively as objectively, which gives me a musical advantage. Power supply design and component choice are very important, as is layout.
Thank you for your post,
Cheers,
Hugh
Fanuc
---the old fashioned miller cap - which delays NFB.---
The idea that NFB suffers from delay is often seen in some popular subjective reviews and defended by some guys of the anti-feedback community.
More technically biased people say the feedback signal is delayed in the amp path by a negligible value of less than 100 nS.
Then a natural question which comes to mind is : what value of delay, voluntarily introduced in the feedback path, should have deleterious effects on the stability of an amp and/or should become audible ?
---the old fashioned miller cap - which delays NFB.---
The idea that NFB suffers from delay is often seen in some popular subjective reviews and defended by some guys of the anti-feedback community.
More technically biased people say the feedback signal is delayed in the amp path by a negligible value of less than 100 nS.
Then a natural question which comes to mind is : what value of delay, voluntarily introduced in the feedback path, should have deleterious effects on the stability of an amp and/or should become audible ?
Hi Hugh,
---The 55W handled loads down to 3.5R with ease, the 100W down to 2.2R. In fact source impedance was very slightly negative---
Have you an explanation from where the negative impedance comes from ? I've sometimes seen that.
---The 55W handled loads down to 3.5R with ease, the 100W down to 2.2R. In fact source impedance was very slightly negative---
Have you an explanation from where the negative impedance comes from ? I've sometimes seen that.
Hi Bob,
---Yes, to the extent of my memory, but I don't recall if he showed multiple spectrum analyzer plots for different values of NFB.---
Baxandall's diagrams are not really spectrum analyser plots as we often see now, but very similar because you can draw them from his data. They show the amount of harmonic components H2 to H6 with a varying amount of NFB around a Fet and a bipolar devices.
---Yes, to the extent of my memory, but I don't recall if he showed multiple spectrum analyzer plots for different values of NFB.---
Baxandall's diagrams are not really spectrum analyser plots as we often see now, but very similar because you can draw them from his data. They show the amount of harmonic components H2 to H6 with a varying amount of NFB around a Fet and a bipolar devices.
Forr,
Yes, I believe a high impedance feedback path - it leads to the inverse, the conjugate, at the output.
It was a side effect of the strange fb network I used, rather a good one, I thought.....
Cheers,
Hugh
Yes, I believe a high impedance feedback path - it leads to the inverse, the conjugate, at the output.
It was a side effect of the strange fb network I used, rather a good one, I thought.....
Cheers,
Hugh
Bob Cordell said:
Baxandall's analysis, IIRC, was done on a single common source stage. But there was a follow up, by another WW frequent author. I'll see if I can find it when I get home this weekend.
Jan Didden
Edit: Didn't see Forr's post while I was posting...
Cheever's paper also presented some calculated and tested
data on harmonic spectra vs feedback for very simple amplifiers.
😎
data on harmonic spectra vs feedback for very simple amplifiers.
😎
Hi Jan Didden,
I would be very interested to see the follow up of Baxandall's work. Baxandall series consisted of six articles and, sadly, was never finished. I plan to scan them all because I think it is a study which is very fundemental and not at all outdated, many people would be aware of it.
The other article on the feedback theme I know was by Cathode Ray and Ivor Brown but I did not get every issue of Wireless World since the first I bought in 1978, with Baxandall's and Linkwitz's articles in it.
Hi Nelson Pass,
Cheever's pictures are the replica of those published by Baxandall in 1978.
Hi Hugh,
Same as you, I found some negative impedance while experimenting some amp circuits, I think one of them had the effect related to a cascoded VAS.
I would be very interested to see the follow up of Baxandall's work. Baxandall series consisted of six articles and, sadly, was never finished. I plan to scan them all because I think it is a study which is very fundemental and not at all outdated, many people would be aware of it.
The other article on the feedback theme I know was by Cathode Ray and Ivor Brown but I did not get every issue of Wireless World since the first I bought in 1978, with Baxandall's and Linkwitz's articles in it.
Hi Nelson Pass,
Cheever's pictures are the replica of those published by Baxandall in 1978.
Hi Hugh,
Same as you, I found some negative impedance while experimenting some amp circuits, I think one of them had the effect related to a cascoded VAS.
Hi Mikeks,
Me too, though having them on paper, I'am interested to have the articles in the .pdf form.
Thanks.
Me too, though having them on paper, I'am interested to have the articles in the .pdf form.
Thanks.
Hello Mikeks,
Could you please send us a copy of the Baxandall .PDF. I've heard of the article before but never come across it.
Kevin.dabson(@)gmail.com - Please remove the brackets ()
Thanks
Kevin
Could you please send us a copy of the Baxandall .PDF. I've heard of the article before but never come across it.
Kevin.dabson(@)gmail.com - Please remove the brackets ()
Thanks
Kevin
Fanuc said:
Actually I was wondering there how easy it is to get articles from E&WW that were from the 70's. There is some others I am interested in, but I've never seen them listed on that EW website.
