John Curl's Blowtorch preamplifier part II

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When I did instrumentation for astronomy from 1968 to 1985, I used a single-ended system for a spectrometer, and went to great lengths to avoid noise contamination, particularly important in the often-hostile environment of the observatory. Single-ended was best for front-end noise of the charge preamps. But many wise people counselled going differential, certain that extraneous noise would dominate any system and my carefully-optimized preamps would come to naught. Pete Stockman, who was interviewing for a tenure-track position at UCLA, also insisted that they had learned the hard way at Kitt Peak that you simply had to go differential wherever possible, regardless of any "3dB" deficits in noise performance.

Of course the consumer standard is mostly single-ended, and the equipment is often galvanically isolated (or used to be, before the migration to evil switchmode supplies). So if you are fortunate the whole shooting match gets lashed together through the common connections. Although you still have the opportunity to pick up magnetic field interference, positioning of cables can usually alleviate this. If however your circuitry "looks out" at the world, i.e. with poor E-field shielding, you can get back into trouble, as from the perspective of a high-Z node thus exposed, it sees a potentially large voltage, often of order one-half the mains voltage, since things run from transformers are capacitively coupled to the mains.

If you have the unfortunate situation of equipment hard-grounded to the mains safety ground, typical for computers for example, then the situation gets hairier. Bill Whitlock talks of his discovery that the primary cause of a difference in potential between safety grounds in a system is usually unequal inductive coupling from currents in the hot and neutral conductors to the safety ground, in conduit. He's had to get electricians to twist together said hot and neutral conductors and reinstall in conduit to suppress this. He has also expressed his opinion that the vast majority of line conditioners and other such things achieve their primary improvement in a system by enforcing a cluster of equipment be all plugged into the nearly-identical-potential safety grounds of the accessory's outlets. So he thinks you should save your money and buy a plugstrip.

As you can imagine, he's also a skeptic about a lot of other things :D


Brad
 
I think that for short runs, balanced input is over-rated. The very NATURE of the potential noise pickup shows that it is the low Z magnetic component of the E/M wave that cannot be shielded easily. Then balanced in will pick up the magnetic component equally on both input signals and cancel it with the common mode rejection.
 
Bill Whitlock ..... has also expressed his opinion that the vast majority of line conditioners and other such things achieve their primary improvement in a system by enforcing a cluster of equipment be all plugged into the nearly-identical-potential safety grounds of the accessory's outlets. So he thinks you should save your money and buy a plugstrip.

This is also an important component of long-term performance and reliability. Modern electronics is quite fragile when repeatedly exposed to the EMP of natural and man-made worlds, and short antennas are the first line of defense. Anybody who's seen the insanely failure-prone HDMI connections of the home theater world in action soon gets fanatical about such things.

Thanks,
Chris
 
diyAudio Member RIP
Joined 2005
This is also an important component of long-term performance and reliability. Modern electronics is quite fragile when repeatedly exposed to the EMP of natural and man-made worlds, and short antennas are the first line of defense. Anybody who's seen the insanely failure-prone HDMI connections of the home theater world in action soon gets fanatical about such things.

Thanks,
Chris

I still find it hard to believe that the HDMI connector was adopted as such --- even for consumer applications in which, once installed, there is not going to be a lot of plugging and unplugging. When AP was presenting about their new line of analyzers, one of my questions from the floor was how were they going to deal with the unreliability of the HDMI jacks, particularly when the instruments were being touted as suitable for production testing? They looked a tad sheepish, as evidently this problem had occurred to them.

Perhaps, after years of being excoriated, someone decided it was time to produce a connector that would make us wax nostalgic for the good old days of the RCA? :rolleyes:
 
I still find it hard to believe that the HDMI connector was adopted as such --- even for consumer applications in which, once installed, there is not going to be a lot of plugging and unplugging.

Perhaps, after years of being excoriated, someone decided it was time to produce a connector that would make us wax nostalgic for the good old days of the RCA? :rolleyes:

To add insult to injury, they operate off a supply voltage of 1.8 VDC. Very small (in the real world) differences between "grounds" pop 'em like a toy balloon.

One scary thing about the modern world is that professional standards are driven by consumer standards, instead of the other way around.

Thanks,
Chris
 
As usual I suspect the war machine had much to do with it long before idle chatter and Al Jolson.

Actually WWI was before the military really used much communications technology. Field telephones were of course wired and most radio communications was by Morse code. AM radio really only started around 1905 and was suspended in most places for the war. keep in mind during the first world war radio transmission across the Atlantic Ocean was not reliable.

One of the military contributions was the use of the 50 Ohm coaxial cable. The military came to the conclusion the lower voltage on the coaxial lines allowed the use of greater power. Now if you have ever seen the old coaxial lines they were based on standard copper water pipe! The high power stuff was 3" copper pipe with either a 1" or 3/4" inner pipe depending on impedance. Some of the original spacing insulators were gutta percha. It had holes to pass the dried air used as a dielectric. The air needed to be dried for marine use, which was the most important user of the wireless at first.

Now as anyone who has built an antenna knows 75 ohms is much easier to couple to an antenna. But back then 1 Mhz was getting up there in frequency. The international distress frequency was 500 Khz. So things that you would recognize as transformers could be used for the 50 ohm system.

After the war it was the talkies that drove larger sound systems. AM radio also had a foothold and so radio manufacturers started as there was now a market. For some funny reasons people didn't buy radios until there were radio stations. My "great" relatives all mentioned at some time their parents who sold radios in their store though it was a passing fad.

You may recall the US was unprepared for World War Two. Charles Lindbergh was one of the most well know isolationists at that time.

Although we had started to gear up via the lend lease program it was not until after Pearl Harbor that the country got serious. Also there were those (In particular Irish-Americans) who only wanted to go to war with Japan.

World war two was the real start of what we now call the Military Industrial complex. Remember companies like Ford stopped making cars and only made war material. After the war they went back to the auto business. It was specialty companies that stayed with the military along with folks who had a good idea and found the military interested in producing it.

If you look at consumer production it almost seems that 1950 was the year that followed 1938!

Now everyone knows that the second war fostered digital electronic computers, Radar, Sonar, FM radio, Nicad batteries, and much of the real start of the electronics age.

But Rice and Kellog at GE published how to build a modern loudspeaker in 1924. Certainly not a military project!
 
Actually WWI was before the military really used much communications technology. Field telephones were of course wired and most radio communications

My litany of random factoids looks different i.e. Manual of Wireless Telegraphy, A. Frederick Collins, 1906. I have a friend whose grandfather worked for Simplex Wire and Cable and he swore by transformer coupled 45's into a speaker installed into a closet door as baffle. He mixed work and pleasure.

I missed the anti-Japanese sentiment of the Irish American community, who would have figured. I hope this is not "Gangs of New York" as historically accurate stuff.
 
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My litany of random factoids looks different i.e. Manual of Wireless Telegraphy, A. Frederick Collins, 1906. I have a friend whose grandfather worked for Simplex Wire and Cable and he swore by transformer coupled 45's into a speaker installed into a closet door as baffle. He mixed work and pleasure.

I missed the anti-Japanese sentiment of the Irish American community, who would have figured. I hope this is not "Gangs of New York" as historically accurate stuff.

I go by tales my great uncles told of their service in WWI. Such as fixing field telephones. The carbon microphones were not effectively sealed so as the moisture got in they stopped working. German carbon grains were the roughest, English in between and the French a much finer powder. So for telephones used by Americans when US carbon wasn't available, they had to mix the German and French powders to get one that worked well for their system.

Then the tales about transatlantic communication were most interesting. As there ware telegraph cable between the UK and US that was the secure method of communication, but it seems there were suspected spies in the telegraph office. So the solution was to use women. Don't ask me why!

Then there were ships stationed at sea used as relay stations for wireless messages.

The first AT&T transatlantic success used hundreds of tubes in parallel. That was in 1915.

Now the Clark transmitter was the basic unit used for field wireless telegraphy. It used among other parts a coherer and leyden jars for capacitors. As it used an open vibrator to step up the voltage it was unreliable from dirt and moisture. It also require a long wire antenna. As explained to me you could throw the D'n thing farther that it would send.

(D'n was the more popular word as the French pro ladies of leisure had some influence on the use of the F word at the time.)

I am in theory named after a great aunt who died in the UK during her WWI service. I have a copy of the letter with a photograph of her grave after the marker was changed.

If you ever see one of those movie pans of the military cemetery where they show the markers of the different religions buried together, they were not war time accurate. Everybody got a cross marker. They only got changed if you wrote back and they had the time to place a straight marker.

As to the hifi system with a pair of 45 tubes, I don't know when they were introduced but I suspect that was well after 1924.

The Navy standard transmitter tube of the 1920's was the A-P. Of course a radio crew back then was three men. The range of a radio-telephone was at that time several hundred miles. The receivers had advance to the regenerative design. So there really was significant progress.
 
My grandfather blew taps for the Raindow Division, lots of that needed in WW1. I inhereted no musical talent, so it goes.

I assume you meant the Rainbow division. A great uncle was an ambulance driver there.

He got upset with me when he told me that and I wasn't impressed. In my prior experience it was a no-no to shoot medical aid workers. Turns out that was a result of WWI. After the battle the ambulance drivers would take their horse drawn ambulances out to pick up the dead and wounded under fire! It seems the Germans invented snipping just to shoot ambulance drivers. A fact I only learned latter.
 
Many thanks to Linear Systems for the 25th anniversary sample pack. It was good to see John Hall even though I bore the news that ADI's original person in charge back in the old Micropower days had passed away years ago. Now I can eval the whole FET line for audio use.

I hope Ron Quan was not offended that I chose not to discuss "business". I do hope he tests some modern devices and updates his results even if they are not to his liking.
 
We had snipers in the civil war, and so it goes nothing good comes of this.:smash:

Wiki has a nice article about sniping.

Seems the WWI Germans started using scopes in organized squads. It was the Brits who first used gilly suits.

And it was the Americans who started the process. We used rifles during our revolution and the Brits used muskets.

(For those unfamiliar with the distinction a rifle is called that because the barrel is rifled or cut with a spiral groove to cause the bullet to spin, increasing accuracy. A musket had a slightly larger bore than the bullet and was faster to load. So when the European Armies stood in lines and shot at each other loading speed was important. The Americans who hunted for food needed accuracy. The Brits thought it was poor manners when the Americans would hide behind trees and shoot them.)
 
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