John Curl's Blowtorch preamplifier part II

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1/3 power is absurdly brutal, but it's what Atkinson likes to do, so one must be prepared.

There have been a number of products reviewed and tested in SP that failed during the 1/3 power preconditioning---even some touting fancy-tech heatsinks. Some old Harman automotive products had thermal throttleback, but if one wasn't careful sometimes it just made things worse.

Is it, Brad? If memory serves IHF standards stipulate that an amp must be run at 1/3 nominal power for 30 minutes before you start measuring its full rated power output.

I would expect Kindhornman to install quality amplification. This actually might work against him, given that with really good amps one's sense of loudness as sheer db SPL would produce the same quality, only louder. So it's easy to lose one's sense of being too loud, the typical problems would be absent, And which one of us, pray tell, who know all this will never be tempted to crank up the volume when the mood takes him?

Lastly, remember, there are all kinds of scary people out there, there's no telling who might try what. Never underestimate the damage potential of your customers.
 
Even the D'Agostino amps failed it. But for whatever people say about JA, he does at least try and give electronics a hard time, and if it blows up he tells people.

Just when I was ready to faint upon reading thet, I noticed that this happened due to a faulty protection circuit, it appears a vital component failed despite strict screening of incoming material testing.
 
Is there a better way to unsure an amp will be cooled enough and safe under all situations ?

That's a king size order. One unit may be used on Alaska, and another in Phoenix, Arizona, known as the hottest city in USA. Ambient temperature varies wildly, so there's also the issue of declaring normal operating conditions. Producing a realistic and honest data spec sheet is no easy job.

I need go no further than my own apartment. Winter temp is around 22 deg C and summer temp can easily hit 43 deg C, if not for the air con. At 43 deg C (app. 110 deg F), you can't hear youself think, let alone enjoy the music at ear splitting levels.
 
summer temp can easily hit 43 deg C

For naval design purposes, a hundred-year-wave is a statistical number/tool, but has little relevance to 24/7 operation.
Neither should a once in a hundred year temperature be.

A single preconditioning procedure for both 4 ohm and 2 ohm capable power amplifiers is not sensible imo.
1/3d is over the top for one category, 1/8th too light for the other.
 
What are you on about, Jacco? My mentioning of 43 deg C in sumer is not a one-off event, it happens every year for the lst 15 years ro so. Belgrade has a wicked temp chart amplitude all along, being on the borderline between a classic continetal climate with strong influence from both the Adriatic and Aegean seas.
 
Not a big problem in the audio range. You can hear the evils and cure them. It is at HF that the problem exists, where inductances produce their worst effects and where electronic is not able to deal with them without producing annoying IM.

This said, "both the path of least resistance but also the paths of least inductance" will be the same with star ground between several boards and no other loop.
Not a problem in audio. its the biggest cause of hum due to ground loops.... so I would say its a big problem
Power has to be supplied as twisted pair to different boards in a unit, hard to do with a star point, any digital in there instantly makes a star point redundant.
I only see a star ground point in audio, not in other areas of electronics (this is between boards within a unit)... Read the quote I put up regarding this form of star grounds
"The technique of a ground 'mecca' (a common point in the circuit to which all ground connections are tied) is often seen,
but it's a crutch; with a little understanding of the problem you can handle most situations intelligently."


http://hephaestusaudio.com/media/2009/11/Grounding-and-Layout-for-Audio.pdf
 
so I would say its a big problem
marce, please re-read what I said. I was talking of a specific problem: multiple power units and parasitic currents from AC flowing between their grounds once devices connected together.
I just said that, if you can have everything integrated in an unique box, the good solution is to rely all the grounds from the various PSUs to one point. And let those parasitic currents dancing as they want before this point ;-)
Then you will have: ground, +70V, -70V, +12V analog, -12V analog, +5V analog, +5V digital, etc... like from an unique power supply. And an unique reference as a good start.

After that, you do what you want with your grounds and shields inside and between the boards. And we all know it is not so easy and there is NO universal perfect and even best solution. Only good practices, like isolating large and low currents returns, digital and analog, and...avoid any loop.

Of course, no other equipment, connected to AC, sharing ground with this box. IE, optical or HF link only, or if absolute need, a symmetrical traditional input to reject common mode. No USB, as an example if its ground is not isolated ;-)
 
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Oh, I'm stupid. (About USB)
Who cares of the errors in the digital signals due to the parasitic currents, as long as they are under the thresholds and don't produce bits errors.
they will only affect clocks.
As long as the ground of the USB port will be directly connected this 'unique' ground reference point, and the signal re-clocked, no prob.
 
You cant star point digital....
I will reflect more on what you have wrote, in case we are at mixed purposes here.
Supplies though should go from the supply to the destination as a twisted pair, the )V should not go off to some star point and then to the board, it should follow the same route (and in close proximity) to the positive lead.
When I was referring to inductance and resistance I was referring to the way the return current tracks the signal, at dc it is the path of least resistance as the frequency increases it move to the path of least inductance, not parasitics added by wiring/PCB traces, I'll leave them for another day.
 
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Vuki,
Just take a look at the price of those KII speakers, not a consumer product in the least.


dvv,
thank you for the kind words and optimistic outlook for my end product. My concern is as said, the tendency for people to keep turning up the volume if they don't hear distortion, this can be a serious issue and i have encountered that and done it myself. The only solution that I have conceived of is if you could somehow limit the input voltage to the speakers to a set point of say 2V or thereabouts. I don't know how you do that but it would seem as good solution to me if it could be done. I don't want to under power the amplifiers, I don't want them to ever be able to clip so that would lead to the situation of people just trying to keep pushing up the level. There has to be a way without having to add a compressor/limiter circuit to the output amplifier I would hope. Again I am going to defer to the circuit designer on this type of question but it is an issue I am very aware of.
 
If you say so

(July 24, 2007, Belgrade : A record breaking temperature of 43 degrees celsius in the shade was measured in Belgrade on Tuesday. The previous record high was measured on July 4, 2000 at 40.5 degrees, the Serbian meteorological institute said)

One of he greatest mysteries in Serbia is how they make their temperture measurements, most of us have had external thermometers in our balconies, and we often wonder how they consistently measure less than we do from about 35 deg C upwards. And they never mak e areading od 45 deg C, because if they did, according to the law they would have to call the work day off. So, they simply never do, although frankly it rarely gets up that far., and if does, it's usually a one off event.

I am blessed by having a temp diff of +4...5 deg C internal vs external temp in my room, because two side walls and the ceiling are concrete in the sun until around 4 PM. I normaly have 4 deg C hotter inside, which should explain why in a three room apartment I have three air cons. The one in my room is switched on in early June and is switched off in late September. It truly earns its keep.

Much the same goes on in Greece. This summer, they publically announce 39 deg C, and my car's external temp says 42 deg C. I know it's not the heigth of perfection, but it's certainly not that much off.
 
I just tried out my low noise amplifier. A few tweaks to the original design. Input amps are now LME79740 and second stage NE5532.

Shown are the input shorted, with 10, 100 & 1000 ohm terminations. Powered by 9 volt batteries and no case. Should be able to improve this by at least 3 and maybe 6 db!

ES
 

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I have three air cons.
Some questions, by pure curiosity.
Is-it possible to live without pain when temp goes higher than 37-39% and no air flow ?
When you reach such terrific temps, where-are they by night ?
In those situations, what is your temps in your rooms ?
I remember myself, freezing in the hotels in Qatar, while you could cook an egg on car's hoods outside ;-)
 
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