John Curl's Blowtorch preamplifier part II - Page 3583 - diyAudio
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Old 25th February 2013, 12:04 AM   #35821
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Originally Posted by Kindhornman View Post
With a good conjugate network at the terminals of the speakers that flattens the impedance curve and keeps the speaker from becoming a reactive load would you really worry about the damping factor being cut in half?
Right, but damping decrease a little waterfall time in the basses. Give a more "fast" sound ?
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Old 25th February 2013, 12:36 AM   #35822
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When I first started to work for Alembic, who did the PA and recording for the Grateful Dead, in 1970, I saw a DC300 parked in a corner. I was told by my associate that the amp sounded very 'weak' compared to its rated power. This we found was because of the extreme protection circuits that cut in very often. It should be remembered that this amp was originally designed for servos, both AC and DC. Audio was sort of an afterthought.
In 1977, John Meyer and I tested 4 amps for TIM(30) and published the results. The Crown and the new (at the time) solid state Audio research failed the test at 100W out. Two other amps passed.
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Old 25th February 2013, 02:30 AM   #35823
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The DC300 was pretty conventional for its time, but IIRC included an LM301 for the input.
The later bridged/stacked ones were called Macro something.
Yeah, the MacroTech amps were the ones with the grounded bridge output.
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Old 25th February 2013, 03:18 AM   #35824
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Originally Posted by john curl View Post
In 1977, John Meyer and I tested 4 amps for TIM(30) and published the results. The Crown and the new (at the time) solid state Audio research failed the test at 100W out. Two other amps passed.
I don't suppose it was this:
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Old 25th February 2013, 03:11 PM   #35825
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Somehow, my last response was lost. Thanks, Nelson Pass for giving me the more 'correct' version of what we measured 36 years ago. We did also measure the Electrocompaniet, (passed) and the Crown (failed) but these were not the amps that the magazine gave us to test. This test was TIM (100) that is the most stringent test that we could devise to include ultrasonic garbage as well. TIM (30) (10us r.t.) is a somewhat easier test, but it can be shown possible to generate its waveform characteristics without added ultrasonic interference or hard clipping from previous stages.
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Old 25th February 2013, 03:51 PM   #35826
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I heard the LHC is going to be fired up again and this time they hope to get the beam energies equal to a 747 in full flight.
Actually, that is the amount of energy stored in the superconducting magnets. When the interconnect solder joint failed, all that energy deposited in the liquid helium. The resultant pressure wave made the dipole magnets in the tunnel play leapfrog. They have to take a 2 year (estimate) time out to re-do all 10 thousand solder joints before they can try full energy.

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Yes that was news (thermocouple effects) to a quasi-client (work done as a tradeout for use of an Ap). His current shunt is 5 milliohms for measuring currents in voice coils under test.
How does he account for the self inductance of the resistor and the loop trapped magnetic field caused by the tap wires across the resistance?

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It's a test fixture for measuring voice coil d.c.r. under heavy drive by extracting the voltage drop due to a probe current while a large a.c. signal is driving the loudspeaker under test. But as well the fixture will provide r.m.s. current and voltage and true power (average of instantaneous i * v) in the manner of a Valhalla-like meter.

So, yes, the voice coil as part of the assembled and magnetized loudspeaker driver.
What an odd way of measuring the temperature of a coil of copper.

If they zero the shunt inductive pickup, they could see the resistance of the wire as a function of time in the sub millisecond range. Of course, it's only the end terminal resistance and will show only where the current is travelling within the wire..but it's better than nothing...

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It doesn't look like it could go into a product, but it still might be the only thing for a research project. They have one set up with a feedback cap (.03pF) and reset switch for use as a charge amp. To be fair these are pretty special and even require special bonding to accommodate the tiny geometry.
Smaller than .7 mil gold TC?? The smallest SiO2 caps I used were a quad set of .25, .5, 1, and 2 pf. They were used for tuning. I unfortunately had to measure them to 5% as part of incoming inspection sampling.

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Old 25th February 2013, 04:39 PM   #35827
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It is amazing how quiet it is when we put up work that we did over 1/3 century ago. '-)
I suspect this is because the technical level of many of my critics is not quite up to it.
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Old 25th February 2013, 04:47 PM   #35828
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Old 25th February 2013, 04:52 PM   #35829
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It is amazing
Mr Curl,

apparently it's of no consequence on how many legs you once stood, for the number of fingers you're now showing.
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Old 25th February 2013, 04:53 PM   #35830
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John,
The interesting question about these earlier results of the TIM testing would be why these other amplifiers did so bad in the test? Not that the results were incorrect, but what specifically caused such disastrous results say in the case of the Phase Linear amplifier. I remember the very early Phase Linear amplifiers again in pro-audio. What I remember of them was that they actually sounded good but that we had nothing but problems with the power supplies, at least that is what I remember about them. It could have been the extremely difficult loads being driven at the time and perhaps it was the reactive loads that did them in. How does your own design of the Blowtorch show up in this same testing?
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