Hi,
high OL gain/tons of (global) feedback seems to me like cruising a Ferrari at pedestrian speed by pushing the throttle and the brake maximal at the same.
Speed -or rather slowliness- will be stupendously constant .... but it'll sound terrible
... besides one appearing to be quite foolish.
If I were to build a scientific instrument where certain 0-digits count I'd choose the feedback path without doubt ..... but my ears aren't scientist
jauu
Calvin
high OL gain/tons of (global) feedback seems to me like cruising a Ferrari at pedestrian speed by pushing the throttle and the brake maximal at the same.
Speed -or rather slowliness- will be stupendously constant .... but it'll sound terrible
... besides one appearing to be quite foolish.If I were to build a scientific instrument where certain 0-digits count I'd choose the feedback path without doubt ..... but my ears aren't scientist
jauu
Calvin
Good point.
Class aB amplifiers with massive feedback is not for wacky designs.
There is nothing wrong with feedback, it is definitely the way to go.
An op amp changes its output so the + and - inputs are always at the same potential. That's it. Any deviation from this = distortion. So if you connect a feedback network then the output will track the input in proportion to the feedback network gain, or beta. This has obvious limits, which we all know.
Back when tube circuits were losing market share but still evolving, the focus was on building "modern" circuits with as much feedback as possible. The constraints were considerable because of the output transformer compared to today's circuits. Some of the tube amps from the early 60s were really good, with clear sound and good high frequency response. I can tell you, some of those amplifiers were pretty practical even by today's standards; decent power (35 watts/channel was typical), full bandwith at half power (lame by today's standards but 12 clean watts at 20 kHz into almost any tweeter is plenty unless you're trying to drive rats out), clean sound with good highs, and they still sounded a whole lot better than the transistorized equipment back then. The global feedback amplifiers was so much better than the old amplifiers; so much more consistent, much clearer sound. I wish I still had my old home built unit.
Back when tube circuits were losing market share but still evolving, the focus was on building "modern" circuits with as much feedback as possible. The constraints were considerable because of the output transformer compared to today's circuits. Some of the tube amps from the early 60s were really good, with clear sound and good high frequency response. I can tell you, some of those amplifiers were pretty practical even by today's standards; decent power (35 watts/channel was typical), full bandwith at half power (lame by today's standards but 12 clean watts at 20 kHz into almost any tweeter is plenty unless you're trying to drive rats out), clean sound with good highs, and they still sounded a whole lot better than the transistorized equipment back then. The global feedback amplifiers was so much better than the old amplifiers; so much more consistent, much clearer sound. I wish I still had my old home built unit.
I think the first transistorized amplifiers were terrible designs like boldly converting tube stuff to solid state.
For instance, amps with two transformers, one at the output and one driver at phase splitting. I did make such a contraption, yes sound came out of this. I even made a similar version to make a 27 Mhz transmitter, yes it outputed a couple of HF watts.
Or, Class B amps with terrible Xover distortion, underbiased to avoid thermal runaway.
At that time of the first power bjts ( germanium ) I made a class A amp, that was something not to be shy with cult tube amps.
It took several years to understand how to use solid state right.
To make it short, let's compare tube amplifiers with the first Class A solid state amplifiers, I bet they they were as good.
For instance, amps with two transformers, one at the output and one driver at phase splitting. I did make such a contraption, yes sound came out of this. I even made a similar version to make a 27 Mhz transmitter, yes it outputed a couple of HF watts.
Or, Class B amps with terrible Xover distortion, underbiased to avoid thermal runaway.
At that time of the first power bjts ( germanium ) I made a class A amp, that was something not to be shy with cult tube amps.
It took several years to understand how to use solid state right.
To make it short, let's compare tube amplifiers with the first Class A solid state amplifiers, I bet they they were as good.
Hi,
Mark, of course are there no throttles and I certainly know of the limitations of a analogy ... indeed there´s not much wrong with the concept of feedback .... its just that the concept of global feedback seems to have its flaws.
Real time error correction??? Looollll .... rather its´s error amplification with a gain of almost OL (that is global feedack)
Df You brought it to the point ... I´m foolish and I´m happy about it
Just one Q: Could You please name the engineering concept our hearing is based upon?
That would make my day
jauu
Calvin
Mark, of course are there no throttles and I certainly know of the limitations of a analogy ... indeed there´s not much wrong with the concept of feedback .... its just that the concept of global feedback seems to have its flaws.
Real time error correction??? Looollll .... rather its´s error amplification with a gain of almost OL (that is global feedack)
Df You brought it to the point ... I´m foolish and I´m happy about it
Just one Q: Could You please name the engineering concept our hearing is based upon?
That would make my day
jauu
Calvin
That's exactly what they were.
Interesting. I made a class AB germanium power amplifier with input/output transformers. It wasn't that bad.
What were they and are there any still around? Heat is a real killer of solid state electronics.
Yet another hilarious thread. You would think an EE text was a book of necromancy sealed by Satan himself.
That's what it looks like to a lot of people.
I've been called Wizard my whole life. Coincidence?
I was wrong, the CD I was testing it with was the culprit of "the nervous sound". It's pretty flat, not sure without bandwidth testing but seems a bit attenuated in the higher range. It doesn't seem to make piercing treble unless it is adjusted to.
Definitely going to be a nice bass amp or sub driver.
I also changed the 4.7 uf electrolytic input cap with a Wima 2.2uf. Changed the input low bandwidth filter from about 1.5hz to 3.5hz. deep cut huh ? Mucho overkill on the input cap.
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