John Curl's Blowtorch preamplifier

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john curl

john curl

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Joined 2003
I must say that Jon Iverson independently invented the complementary differential input stage about the same time that I did. I know that 40 years ago, I had started on a working design with the complementary differential input stage, and I still have the physical prototype today. Used it for years.
 
jan.didden

jan.didden

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Charles Hansen said:


Don't be so quick to jump to unwarranted conclusions.

I've heard his old stuff. I worked at a shop (as a repair tech) that was one of the very first Ampzilla dealers there was. (This was after he stopped selling the kit and decided to make it into a commercial venture.)

The Ampzilla was a very good amplifier in its day. In fact, it was probably the overall best sounding solid state amplifier until the Leach amplifier was developed a few years later. (And that's not quite fair, as Leach never built his amp. He just made the instructions, so each builder's version varied slightly due to the parts used -- some Leaches were better than the Ampzilla and some weren't.)

The Ampzilla was one of the first fully complementary amps out there. At that time there was an argument as to whether Bongiorno was first or whether Daniel Meyer (Southwest Technical Products Corporation -- SWTPC) was first with his (Tiger) series of amps in Popular Electronics that culminated with the Tigersaurus.

In truth, I think that John Curl was first. It's just that he didn't publish his designs until years later as retribution against Mr. Mark Levinson who didn't honor his agreements with John Curl.

Bongiorno also was one of the first proponents of the "servo", whereby the feedback loop includes DC gain to keep the offset to low levels. At the time, all of this sounded very esoteric and mysterious. We were all sure that JB was a brilliant designer.

And given that background, where I held him in such high esteem, is exactly why my opinion of him dropped a few notches after reading the Audio Amateur article in question. If I thought he was a know-nothing, it couldn't have dropped. But I did think he was was an innovator. But after reading that article I realized that he didn't know as much as he thought he knew.

That doesn't take away from his accomplishments. It simply changes my personal assessment of his contribution to the art of audio reproduction. It's kind of like movies. Everyone has their favorite movies, perhaps a top ten list. And maybe every once in a while you see a new movie that bumps one of the old ones out of the top ten. Or perhaps more to the point, maybe one of your top ten movies was a remake of something that you had never seen the original of. Then when you saw the original and understood that the remake was only a pale imitation, then maybe the remake dropped out of the top ten (and maybe even out of the top 100).

Everyone has their own assessment as to the contributors to amplifier design. And I don't think that anyone could dispute that James Bongiorno made a valuable contribution to that art. All I said was that my personal opinion changed after reading that article. YMMV.
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Charles,

I remember another article in AA by Walt Jung where he showed that JB's diff input stage was inherently unbalanced. Walt, IIRC, offered some design changes to rectify the situation, and the whole exchange became a bit nasty. You remember that one? Was that about the Ampzilla?

Jan Didden
 
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MikeBettinger

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janneman said:

I remember another article in AA by Walt Jung where he showed that JB's diff input stage was inherently unbalanced. Walt, IIRC, offered some design changes to rectify the situation, and the whole exchange became a bit nasty. You remember that one? Was that about the Ampzilla?

Jan Didden
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It was the Ampzilla kit review and if memory serves me one of the changes involved raising the degeneration resistors on the differentials from around 100 ohms to, I think, 10K. I'd have to re-read it.

The gist of the unpleasantness was that Mr. B thought his design was right to begin with.
 
jan.didden

jan.didden

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h_a said:
By the way, maybe not all of you are aware that Bongiorno is back building amplifiers:

http://www.ampzilla2000.com

Amusing reading especially
http://www.ampzilla2000.com/Amp_History.html

(I'm not going to make fun of his marketing claims by posting them here - go read them yourself. If you care, that is.)

Have fun, Hannes
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So he claims to have designed the Dynaco 400? My information says that Erno Borbely designed at least the output stage for the 400.

Jan Didden
 
john curl

john curl

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Joined 2003
Nelson, the JC-3 power amp was first designed in 1974 as a horn tweeter amp (4K and up) for a 3 way time compensated horn project undertaken by John Meyer (now Meyersound) and me. I gave an updated version to Mark Levinson in early 1975 to build. By June 1976, the credit for the design was given to George Mayhew, and not me, and called the ML-1. However, since I threatened to sue Mark Levinson for non-payment of royalties, he changed the name of the JC-2 preamplifier to the ML-1, and called the power amplifier the ML-2. By this time, George was gone and Tom took over the design. I never saw a penny for the power amp design, and Tom worked hard to change it enough that a lawsuit would be difficult, and to perhaps improve it in some ways. In it's final form, it contains all the original elements that I put into it that make it fast and successful, such as the complementary diff fet input stage, circuit breaker protection, 100V/us slew rate, 2N5686, or 2N5886 power transistors, complementary fet buffer, etc. and all that I was asking for was $10/unit. Mark had other plans for the money.
 
jan.didden

jan.didden

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john curl said:
[snip] In it's final form, it contains all the original elements that I put into it that make it fast and successful, such as the complementary diff fet input stage, circuit breaker protection, 100V/us slew rate, 2N5686, or 2N5886 power transistors, complementary fet buffer, etc. [snip]
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John, if I may, that circuit breaker protection, was that in the supply lines or at the mains side? Are these things quick enough in your experience?

Jan Didden
 
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MikeBettinger

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Joined 2006
VPIindustries.com
Charles Hansen said:


Don't be so quick to jump to unwarranted conclusions.

In truth, I think that John Curl was first.

Bongiorno also was one of the first proponents of the "servo", . At the time, all of this sounded very esoteric and mysterious. We were all sure that JB was a brilliant designer.

And given that background, where I held him in such high esteem, is exactly why my opinion of him dropped a few notches after reading the Audio Amateur article in question. I realized that he didn't know as much as he thought he knew.

That doesn't take away from his accomplishments. It simply changes my personal assessment of his contribution to the art of audio reproduction.
Everyone has their own assessment as to the contributors to amplifier design. And I don't think that anyone could dispute that James Bongiorno made a valuable contribution to that art. All I said was that my personal opinion changed after reading that article. YMMV.
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I'm not trying to argue or be negative here, just pointing out a different side.

My take on that article; Mr B. was defending his not so tweeko attitude and went through a litany of things he didn't agree with and comments on things he had read that he'd been itching to comment on. The discussion on the bridged output stages and and their topology was very superficial. He was trying for another Ampzilla success, I guess.

I thought the comments on output stages were interesting and his favorite of the group of four, I believe, is actually quite good sounding with no stability issues. He did mention building and working with all of them to draw his conclusion and choice for the amp in the article. A form of it was actually discussed here (under a different guise 6 months to a year ago), mentioned as the best sound output stage. As for his technical ability, take a look at the first Sumo 9, the Power or the Gold designs. As the saying goes, the fact that it works is no accident. They sound very good in some respects but are very "full" from input to output and suffer in low level resolution and purity because of it. I own a Gold and someday hope to strip it down to just the basics and see what it can do.

janneman said:
Charles,
I remember another article in AA by Walt Jung where he showed that JB's diff input stage was inherently unbalanced. Walt, IIRC, offered some design changes to rectify the situation, and the whole exchange became a bit nasty. You remember that one? Was that about the Ampzilla?

Jan Didden
Click to expand...

I pulled the article and read it during lunch today. Bottom line the offset adjust was unable to dial in the offset to zero. Walt devised an elegant solution, Bonjoirno started matching the diff amp transistors instead. Responded very nicely (I was surprised) to Walt’s page and a half expose, Walt was the on who lost his cool.


janneman said:
So he claims to have designed the Dynaco 400? My information says that Erno Borbely designed at least the output stage for the 400. Jan Didden
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Mr. B used the same (very close) output stage in the Ampzilla with a symmetrical input stage.


scott wurcer said:


Funny too the Sumo 9 IIRC used LF351's as the input with a class A output. They weren't servos they were the input.
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The biasing for the Class A output stage is what's unique in the Nine. Also the output transistors were extremely high gain (and discontinued in no time) Hence the more sedate Nine plus design.

FYI.
 
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