John Curl's Blowtorch preamplifier part II - Page 1237 - diyAudio
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Old 22nd May 2011, 03:31 AM   #12361
wayne is offline wayne  United States
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John I agree with you on try it and measure it and then give it a listen. A talented guy like you can find many solutions to a problem. One of the things I love is trying something that people say isn't good and finding out it was just what was needed.
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Old 22nd May 2011, 04:05 AM   #12362
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Right on, Wayne. I found the original article that contained the review of the ORIGINAL HCA-2200. It is in the April 1992 'Stereophile' pp. 203-209

It was done by Robert Harley, then at 'Stereophile' now senior editor of 'TAS'. He is very technical, certainly equal or better than most here. We spent a couple of hours talking together to and from the 'Stereophile' office and the airport. He DID notice the AD712 IC at the input, but apparently he could not give the amp a great subjective review, BECAUSE other amps immediately available, sounded better to him. He and I got along well, but he just had to tell it how it was, not like many think that magazine reviewers operate, as we regularly advertised in 'Stereophile', so how could he criticize anything?

He did NOT point out the IC as a problem, just the OVERALL SOUND QUALITY.

I, later, deduced it was the IC, and you know what? I stand behind my decision. It made having the same features more difficult to implement, but it got another review as a MK2 in a later issue, and got a B rating. Good enough for hi mid fi. The amp became VERY popular, and I use a version of it MYSELF, and am listening to it right now. Is it perfect? No. But it is darn good. The MODIFIED HCA3500 or the JC-1 is better, but it's OK. How do I know, because I used a Modified HCA-3500 for about 1 year before I accidently spilled a cup of coffee on it while it was operating, and I had to revert to the HCA2500, a slightly better version of the HCA2200, and I still use it, today.

Now I say all this because there are those who will think me some sort of 'guesser' when it comes to amp differences, but I don't have to be. The differences are apparent enough.

Last edited by john curl; 22nd May 2011 at 04:19 AM.
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Old 22nd May 2011, 08:16 AM   #12363
rowuk is offline rowuk  Germany
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Like with musical instruments, a successful amp design is the sum of the parts, the implementation in a particular system and ears that agree with what is given.

I don't think that there are many jazz fans out there that would argue with the statement that Maynard Ferguson was one of the finest trumpeters ever. I would not buy a recording of him playing any Mahler Symphony with the Chicago Symphony Orchestra however. HIs personal truth was elsewhere.

This is perhaps the issue here too. The feeble attempt to make JC, Bybee or anyone else someone that they are not. The idiotic attempt to evangelize them.

Those with an axe to grind often forget one very simple lesson: we all get ours in the end. If our life has been grudging, less show up to the funeral. The legacy dies much more quickly. If we have been of "service" to the community, our life goals are assimilated into the bigger picture of the next generation. We become immortal? Perhaps not, but we do get asked for interviews well into our retirement.

I think this too long thread could be divided into a couple of different ones. It sure would have been easier to read.
1) bit perfect repeatability
2) amp-part influences
3) getting good reviews
4) learning the hard way
5) don't believe anything you are told, half of what you see and 10% of what you are currently listening to
6) engineering vs artistry

I probably missed a couple. In the end, I am basically interested in getting as much enjoymant as I can for my investment (time, money, real estate, intellect). I would like to leave the decision of parts and topology to those that have developed those skills. Once I find the artisan who appeals to my sense of "good", a relationship is possible.

I never listen to bits. I listen to their symptoms.
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Old 22nd May 2011, 12:58 PM   #12364
DF96 is offline DF96  England
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Quote:
Originally Posted by simon7000
this was supposed to be an easy math problem!
Ah, did you rig the coefficients so that it comes out neatly, or there is a degree of cancellation? Otherwise there would be an infinite series, and this thread is already quite long without listing an infinite series!
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Old 22nd May 2011, 03:04 PM   #12365
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Quote:
Originally Posted by jam View Post
Mr.Curl did not start the thread so does not have ownership of it...........you could ignore him( a simple solution)..........but in his defense there seems a particular group that goes after him regardless, incessantly at that. If you disagree state you opinion and engage a discussion, if no conclusion is reached move on.

I am starting to feel that posting of cartoons (which I have been guilty of in times past) is more fruitful than this Bybee diatribe which attract trolls that suddenly appear out of the woodwork, invariably the same ones I might add.

Jam
Agreed.
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Old 22nd May 2011, 03:08 PM   #12366
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Quote:
Originally Posted by john curl View Post
Right on, Wayne. I found the original article that contained the review of the ORIGINAL HCA-2200. It is in the April 1992 'Stereophile' pp. 203-209

It was done by Robert Harley, then at 'Stereophile' now senior editor of 'TAS'. He is very technical, certainly equal or better than most here. We spent a couple of hours talking together to and from the 'Stereophile' office and the airport. He DID notice the AD712 IC at the input, but apparently he could not give the amp a great subjective review, BECAUSE other amps immediately available, sounded better to him. He and I got along well, but he just had to tell it how it was, not like many think that magazine reviewers operate, as we regularly advertised in 'Stereophile', so how could he criticize anything?

He did NOT point out the IC as a problem, just the OVERALL SOUND QUALITY.

I, later, deduced it was the IC, and you know what? I stand behind my decision. It made having the same features more difficult to implement, but it got another review as a MK2 in a later issue, and got a B rating. Good enough for hi mid fi. The amp became VERY popular, and I use a version of it MYSELF, and am listening to it right now. Is it perfect? No. But it is darn good. The MODIFIED HCA3500 or the JC-1 is better, but it's OK. How do I know, because I used a Modified HCA-3500 for about 1 year before I accidently spilled a cup of coffee on it while it was operating, and I had to revert to the HCA2500, a slightly better version of the HCA2200, and I still use it, today.

Now I say all this because there are those who will think me some sort of 'guesser' when it comes to amp differences, but I don't have to be. The differences are apparent enough.
John, it seems to me that some people here will not let themselves be confused with facts, their views will remain as they are, no matter what the facts are.
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Old 22nd May 2011, 04:02 PM   #12367
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Quote:
Originally Posted by DF96 View Post
Ah, did you rig the coefficients so that it comes out neatly, or there is a degree of cancellation? Otherwise there would be an infinite series, and this thread is already quite long without listing an infinite series!
Very good! Pure math would give an infinite series, but engineering math would recognize there is a floor beneath which additional terms are not required. I set my design goals at 160 db S/N. So any term smaller than exp-8 can be ignored. I did not include any phase shift in the terms and for this case we can cheat and assume the amplifier has no bandwidth limit or time delay.

So to break things down what is the amount of the original signal and the feedback signal that would be present at the amplifier when the feed back was set for a gain of 10. You can cheat and assume the gain is infinite and not correct for the problem set gain of 1000, as that error does not have significant effect on the final results.

The feedback reduction network and the limit of exp-8 will keep the answer from being too long.
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Old 22nd May 2011, 05:27 PM   #12368
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Quote:
Originally Posted by SY View Post
I think Bruno Putzeys put that canard to rest pretty thoroughly in his Linear Audio article.
Mr Putzeys also stated some time ago that's it's either use as little as possible negative feedback, or a gazillion of it.

Which is in-line with control systems theory, there can often be more than one optimal solution.
Mr Putzeys also mentions control systems theory in the LA article, for non-logistics folks : same-same as feedback stuff in electronics, exact same formulas and symbols, but much more elaborate.
(at control systems I and II, it was the teach that was totally spaced out, could stare at the wall for 15 minutes without speaking, like he smoked serious weed during each coffee break)

Differential equations' universality totally mesmerized me for years, i've yet to witness a non-compliant science area.
For electronics not to totally comply to control systems theory, as a singularity, now that would be something, far out.

(Oh dear, that late already. Back to stuffing lots of weed in bags, otherwise no more time for a decent smoke afterwards )
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Last edited by jacco vermeulen; 22nd May 2011 at 05:30 PM.
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Old 22nd May 2011, 06:24 PM   #12369
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I think that global negative feedback is great IF the open loop bandwidth is higher than the useful bandwidth. However, that is seldom the case, except for the original JC-2 line amp, or the CTC Blowtorch. That is the 'secret' to my success!
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Old 22nd May 2011, 06:46 PM   #12370
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> IF the open loop bandwidth is higher than the useful bandwidth

That's a good one !
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