John Curl's Blowtorch preamplifier

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#5,321
Hugo,
Actually I wrote some small C programs that generate the stimuli (need to be on exact FFT bin freqs. as well) and do the time domain averaging. The "test system" is basicly a ordinary 24/96 semi-pro soundcard. Data is played back and recorded with a standard audio software, and the results of the processing is fed into a FFT program. Not very comfortable, but works well if I need the resolution.

I guess current FFT-based test rigs will have this feature implemented, but that would need to be checked.

Earl Geddes has a thread on this topic (and actually made me try this).

- Klaus
 
#5,325
Interference measured at power amp output, caused by interconnects, and interference sources (mains, DVD player). Depending on signal cable, shielding and grounding, this was reduced more than 30x.
 

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#5,326
Mr.Cordell,

In this instance we are talking about interconnects.

You bring up some good points.

I was thinking of using four different cables for the test from some coax (rg-6 maybe) through Radio Shack and a couple of high end cables and maybe a flat conductor cable like Nordost. This should cover the gamut of what is out there.

Whatv peaks my curiosity is the Millinium cable that Mr.Curl's analyzer crazy.

I strongly agree that a standard needs to be defined on how the cables should be tested, to eliminate as many variables as possible, and this criteria should be agreed upon by all the testers.

Speaker cables should be tested next by the way Mr.Pass wote a great article on speaker cables years ago. I am not sure if it is still on his web site.

Regards,

Jam
 
#5,329
PMA said:


Usually we ignore something we do not understand.

http://en.wikipedia.org/wiki/RF

the first link goes to

http://en.wikipedia.org/wiki/Radio_frequency
Click to expand...


Yep...and being condescending about it only shows that you are the one who does not understand. So, once more for those who might have missed this in other posts (and John thinks he's the only one who has to repeat himself...huh!):
1) I live in one of the poorest states in the US. I frequently compare SC to a third world nation. Why? Because the comparison is apt. There just isn't much in the way of technology (you know, that stuff that puts out RF...) around here. There's a grocery store about five miles from my house...perhaps I should tremble at the thought of their florescent lights. Mmmmm...nah, I'll save that for next week in case I get bored.
2) I live in a house situated in a stone bowl twenty miles from town. There's no reception here for anything. My wife's cell phone doesn't work. None of the local radio or TV stations come in. We don't even have cable. Zip. Nada. We have two or three of the newer bulbs in the house, but they're not on when I'm doing things, which is to say late at night. I get 60Hz hum, nothing else. As if that's not enough, both my bench and listening room are in the basement, half-underground.
Short of putting out a big dish antenna and pulling in a signal from a satellite or a passing alien spacecraft, RF is pretty much a non-issue at my house, except as it relates to people on websites who think they know everything and everyone else knows nothing.

Grey
 
#5,330
SY said:
Yes, and he can answer or not, as he pleases. 😉
Click to expand...

Oh absolutely.

But he didn't just answer or not, as he pleased. Instead he pleaded with a moderator to essentially shut me up. Hence my response, mentioning that this was a public forum and my question perfectly legitimate.

From what I understand of his point, John believes that the AP's grounding and isolation are artificially good, i.e., better than one will encounter with real-world high end products (which often have lousy grounding since they're designed by philosophers rather than engineers). So one potential mechanism for cable differences is eliminated from the test.
Click to expand...

Well yes, the AP's output transformers would isolate it from external components and break any potential ground loops. But while I can see how ground loops can produce noise and other spurious bits, how does a ground loop cause the driving or the receiving circuit to generate harmonic distortion?

se
 
#5,331
It's an interesting question, but I saw it with my own eyes. And I saw the levels decrease when we added shielding. Maybe ground loops, maybe RF, I don't know.

Grey, you're one of the lucky few. Here in the Bay Area, almost everyone has gone over to CFLs. They are now mandated and subsidized.
 
#5,335
SY said:
It's an interesting question, but I saw it with my own eyes. And I saw the levels decrease when we added shielding. Maybe ground loops, maybe RF, I don't know.
Click to expand...

It seems according to John that what decreased was spurious noise, not the distortion. Which takes us back to how does a ground loop cause the driving or receiving circuit to produce distortion? If it doesn't, then it doesn't seem that isolation is what separates the AP from John's ST.

se
 
#5,339
SY, this is a quibble. Harmonics themselves, that FALL ON THE LINE, cannot be reduced by external shielding. However, thanks for the foil trick, it does work VERY WELL. Better that I would have first predicted. By the way I just removed some of that original foil that we put on a test lead, just today, and EUREKA! Big time distortion, but the foil won't fix it, I don't think, however, I should double check.
Adding grounded foil does NOT change things much, IF most of the external sources are turned off.
 
#5,340
I guess I wasn't clear enough. I'm agreeing with you, and just clarifying in language I know Steve will understand. The noise and the distortion pattern were two separate issues. The former was ameliorated by shielding, and the latter changed consistently as we changed cables.

Sometimes I feel like that scene from "I Love Lucy" where she has to interpret her husband's English to someone else.
 
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