John Curl's Blowtorch preamplifier

[anatech]

Hi Nelson,

Are you certain you want to stand by that assertion?

Yes. By definition this is true.

An idea that can be constructed at no charge by many people counts as being sold. The retail price is zero, that's all. By that, the concept and principles become known to a larger number of people, and therefore known. The principles have impact. This you know well from your own work.

John's work is in the same league in so far that his concepts are brought forward. There were as many Blowtorch units sold as could be made I'm guessing. The Blowtorch builds upon Jon's earlier work (I didn't say it's the same!!). John has graciously talked about the circuit ideas and what he believes are important factors to consider.

Hi Grey,
If I keep all the fet cases in thermal contact through a heat sink, I get very tight matches by measuring vgs at set drain currents. Using devices from the same lot number ensures that they track very well across the current operating range. This is the only way to repair a Counterpoint using fets. Here, tight matching is extremely critical.

-Chris

[Nelson Pass]

Originally posted by anatech
Yes. By definition this is true.

An idea that can be constructed at no charge by many people counts as being sold. The retail price is zero, that's all. By that, the concept and principles become known to a larger number of people, and therefore known. The principles have impact. This you know well from your own work.

I understand your point. Having said that, I have ideas which
are not in circulation which have high value to me.

[anatech]

Hi Nelson,
I don't disagree. I like to think I have some good ideas too.

However.

If we leave this earth without revealing our brilliance to anyone else, those ideas are worth zero. I'll count further work based on those ideas as revealing those ideas to the masses.

-Chris

Edit: to clarify what I meant.

[john curl]

Nelson, what about that massless speaker of yours! Now that was something special.

[GRollins]

We stand at the precipice of another semantic argument:
Value to whom and how to judge such value?
Speaking only for myself, I would prefer that this thread not turn into a semantics thread.
I say this knowing full-well that I'm likely to end up with a mud fight once I start a thread on this amp I've been fiddling with. It has no global feedback--don't expect any argument on that--but is it "no feedback?" That will hinge on whether people define degeneration as feedback. This I do not relish.
So, really, can't we just sidestep this?

Grey

[john curl]

Grey, let us separate local from global loop feedback. Black did NOT invent local feedback, they MUST have known about it for decades before he wrote his paper. When MOST engineers say negative feedback, they mean feedback over several stages. Technically, this is incomplete, but so what? It is shorthand to describe a technique. Almost everyone uses SOME local feedback, AND it has real potential problems also, BUT not as many as does GLOBAL negative feedback. That is what we have found.

[anatech]

Hi Grey,

Value to whom and how to judge such value?

The parameters were specified. Re-read please.

I would prefer that this thread not turn into a semantics thread.

Where? You brought that one up recently.

It has no global feedback--don't expect any argument on that--but is it "no feedback?" That will hinge on whether people define degeneration as feedback.

It's been defined that local degenerative feedback is not considered feedback in a system sense. My understanding of the negative effects of feedback occurs when that feedback loop encompasses two or more power gain stages. Note my careful choice of words here. So maybe I defined a working example, something close enough to run with for the time being.

I start a thread on this amp I've been fiddling with. It has no global feedback--don't expect any argument on that--but is it "no feedback?"

Cool!
I'm listening to a pair of Cyrus Mono X amplifiers at the moment. I was talking to the designer in England (2004) before they existed as a product and got the first pair into Canada. No feedback and based somewhat on diamond transistor topology. Impressive sounding amplifiers. No feedback can be done, and done well.

Personally, I think the entire question of feedback or no feedback may depend heavily on the execution of the design and construction. The better these products become (the more accurate), the more similar they will sound to each other.

-Chris

[GRollins]

Originally posted by john curl

Grey, let us separate local from global loop feedback.

John,
I don't expect that you, Charles, or Nelson will have any problem with the degeneration, but you and I both know that there are others who might choose to take offense if I call the amp "no feedback." Should that come to pass...oh, hell, I don't know what I'll do...go camping and talk to the owls for a while, maybe. (I actually do a pretty fair imitation of a screech owl and am able to 'talk' to them. They will literally fly to me [probably a territorial defense mechanism being triggered] to check things out. I also happen to do a very good imitation of a barred owl, but they're not as prone to 'talking.' Screech owls will hoot back and forth with me for up to five or ten minutes. One of them got so distracted during a fly-over one night that he flew straight into a maple sapling. The tree was young and flexible and I don't believe the bird was hurt, but I'm sure it was a blow to the poor fellow's dignity.)
Chris,
I didn't mean you. I'm not aware of any reason why you would be bothered by the circuit. I could, however, give you a list of six or eight members who might be disposed to kick up a fuss about what is/is not feedback. I have no earthly idea what will happen if the simulation folks start in on it, but at least I don't anticipate a lot of hoo-rah about DC stability. They'll have to find something else to carp about.

Grey

[Nelson Pass]

Originally posted by john curl
Nelson, what about that massless speaker of yours! Now that was something special.

I would regret to have been recycled without the opportunity
to share more.

[Sigurd Ruschkow]

I once had a 1.5kg (appr 3lb) heavy solid brass knob made to my spec, and it feells great to turn this "Dolly knob" on my stepped ELMA rotary switch. Steps are not really "steps" anymore but more like a normal pot.

The 70mm diam knob you can see in the attached photo.




Sigurd

Originally posted by john curl
Please, fellow designers, I do not usually follow 'marketing decisions' except that the first CTC preamp had even BIGGER knobs than it has now. I called them: 'Dolly knobs' and I thought that they made the preamp look like it would tip over. They were reduced to 'MM knobs' in my preamp and all others. We are not unaware of marketing forces.