John Curl's Blowtorch preamplifier part II - Page 2957 - diyAudio
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Old 19th November 2012, 10:02 PM   #29561
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Anyone got measurements of a real Blowtorch on the usual common or garden tests?

.. and also the new fangled Hirata tests and the PIM test announced at the latest AES?

I'd ask about Blind Listening Tests too but the designer objects ... so pls message me in secret. Even non-blind will do.
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So that we are clear, I know and you know what the behavior will be, but the neophytes who lurk here deserve to be clued in. And I was perfectly serious - I am interested whether the simulations will show the parasitic oscillation.
I've some success in getting my own circuit analysis package to simulate some of the stuff Baxandall reports in the Baxandall papers But this is only linear stuff and I dunno how easy it is to get LTspice to do the same thing.

BJTs only and I dunno about FETs.
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Old 19th November 2012, 10:23 PM   #29562
fas42 is offline fas42  Australia
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Must be my weird sense of humour or something ... the combination of the avatars in the first 2 posts of the previous page strikes my funny bone ...

Sorry!!

Frank
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Old 19th November 2012, 10:43 PM   #29563
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Good point Nelson Pass. 100 ohm or so resistors would need to be added, but it still WOULD be quieter than my original design.
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Old 19th November 2012, 10:48 PM   #29564
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The CTC Blowtorch measures relatively poorly, because there is no global feedback loop. It has an open loop bandwidth over 100KHz, however, and that is important (at least to me). Hirata? What do YOU know about the Hirata test? Ever try it? I have. This amp has no mechanism to trigger Hirata distortion.
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Old 19th November 2012, 10:49 PM   #29565
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by Wavebourn View Post
PFB by current causes negative impedance, plus filter on input causes some boost below Fs. What is different in this article, a language: they mixed electrical correction with mechanical formulas.
Either you were in a hurry to answer or you didnít read it

It is OK to enjoy what you have done in the past or now but consider the case that there might have been other people too who were technically literate, innovative and productive.

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Old 19th November 2012, 11:05 PM   #29566
RNMarsh is offline RNMarsh  United States
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Default Motional Feedback gore -

Modern voltage amplifiers driving moving coil loudspeakers work successfully on the assumption that the Z is roughly constant over the entire freq range. However, this is not the case and although damping factor can minimize the affects, this is one of the causes of coloration.

Placing the speaker in the feedback (as I described), via a sensing resistor that monitors the current, the output of the speaker will be proportional to the amplifier input and independent of variations in the speaker Z. It makes a fairly good approximation of the geometric mean [(in/out)^1/2] The results are quit impressive with even low-medium quality speakers.
Thx- RNMarsh [high-feedback designs are encouraged, if stable]

Try it.

Last edited by RNMarsh; 19th November 2012 at 11:26 PM. Reason: more guts and gore
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Old 19th November 2012, 11:18 PM   #29567
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Originally Posted by fas42 View Post
The end result is a coke can sized system which can bowl people over with its "big" sound ...
At the time we were exploring double moving coil (one front, one back) to study servos, we had to deal deal with several parameters, i'd like to submit to your thoughts.
Increase of frequency range where it need maximal excursion of speakers greatly reduce available power handling by it.
Added retro-action signals decrease it too, amp side, during transients.
At low level, according to Fletcher & Mudson curves, you add a lot of power for low frequencies you don't hear at this level.
We chose to forget about that, and thought it was better and simpler to use a better driver.
The added damping here was of great benefit.

At high level, and not trying to increase basses bandwidth, the system is power consuming, need to multiply the power in amp if you don't want to add distortion. You need too a loudspeaker witch can handle hight peak levels (we destroyed some).
Reasons why we abandoned the idea.

Now, reconsidering all that together, if i should try-it again, i'll do with an overkilling power system, like 1KW amp, and some big diameters hight efficiency speakers able to afford-it.
With a benefit due to the better damping of their heavy cone.
I would not try-it with a single resistance, where direct signal and error signal are mixed, neither double coils in the same magnets for same and other obvious reasons.
I believe the best solution to get the position of the membrane would be an optical system with a mirror on the cone, and a laser or so. (no adding mass, absolute position).

At the end, it is very complicated, and, as traditional loudspeakers can give enough listening pleasure, and because i'm old and lazy...
May-be the market is old and lazy too, reason why servos were never adopted as the standard solution ?
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Old 19th November 2012, 11:27 PM   #29568
RNMarsh is offline RNMarsh  United States
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Default Try it.

Quote:
Originally Posted by RNMarsh View Post
Modern voltage amplifiers driving moving coil loudspeakers work successfully on the assumption that the Z is roughly constant over the entire freq range. However, this is not the case and although damping factor can minimize the affects, this is one of the causes of coloration.

Placing the speaker in the feedback (as I described), via a sensing resistor that monitors the current, the output of the speaker will be proportional to the amplifier input and independent of variations in the speaker Z. It makes a fairly good approximation of the geometric mean [(in/out)^1/2] The results are quit impressive with even low-medium quality speakers.
Thx- RNMarsh [high-feedback designs are encouraged, if stable]

Try it. You might be pleasantly surprised. Listen. measure. Any draw-backs to the cost/perf or other?

Last edited by RNMarsh; 19th November 2012 at 11:30 PM.
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Old 19th November 2012, 11:29 PM   #29569
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Quote:
Originally Posted by gpapag View Post
Either you were in a hurry to answer or you didnít read it
Why do you think so? I even downloaded the PDF and read it.

Quote:
It is OK to enjoy what you have done in the past or now but consider the case that there might have been other people too who were technically literate, innovative and productive.
...and that other people used similar approaches. Before the patent application, during te patent application, and after the patent application. PFB by current was used, EQ was used, both described in articles and used in commercially available gear. This particular patent combines both EQ and PFB by current, and adds the description in mechanical terms.

It is one of valid ways to go, by patenting particular combination of particular solutions, when solutions using each of 2 approaches, and the same combination of 2 approaches, but realized differently, were used before, or after the patent application.

Here is an example: http://www.triodeel.com/heathw6.gif
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Old 19th November 2012, 11:31 PM   #29570
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Quote:
Originally Posted by RNMarsh View Post
Modern voltage amplifiers driving moving coil loudspeakers work successfully on the assumption that the Z is roughly constant over the entire freq range.
Actually this is successful cos speaker designers assume the amp is Lo Z.

If they assumed something else, they would design speakers differently as they did in da old days. The original Rice & Kellog is a good example.

Mr. Marsh's -ve resistance trick does good things for modern speakers but the response will not be as the speaker designer intended. Might be worse, might be better.

Last edited by kgrlee; 19th November 2012 at 11:34 PM.
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