John Curl's Blowtorch preamplifier part II - Page 3238 - diyAudio
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Old 9th January 2013, 12:15 AM   #32371
fas42 is offline fas42  Australia
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Originally Posted by morinix View Post
I maintain that it is the art of science.
Yes, that's a way to look at it. The technique that I use that I've found very effective, is to consider every system I come across as being "perfect", but it doesn't sound that way because it's handicapped by weaknesses, often quite silly and simple in nature. So, the trick is to isolate, identify each and every weakness and rectify it, one by one by one. Doing that has always worked, got me sound far more satisfying than the vast majority out there deliver ...

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Old 9th January 2013, 12:34 AM   #32372
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Originally Posted by simon7000 View Post
Scott,

So your distortion just from the feedback resistor could be -60 db.
I

Please actually produce this rather than make up these "adder" factors out of the air. Since there are plenty of PA's that measure in the -100's of dB's at full power under many different conditions, the burden of physical proof is on you, not some measurement of -120dB and then a shaggy dog story that makes it 60dB worse.
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Old 9th January 2013, 01:03 AM   #32373
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fas42,
I would sure like to know the mechanism at play that would give these slow changes over time that you are saying that you observe? So if you could actually measure this change in an amplifier caused by ultra-sonic or other vibrations over time, does that mean that this could be reversed by removing the vibration and the device would return to the previous state> Somehow I doubt very much that you have tested this hypothesis in any real manner, this sounds like a purely subjective result that you are stating as a fact. If what you are saying is true it would be both reversible and measurable over time. How about if you put the device suspended in a vacuum chamber and operated it that way, would the sound be different also over time from the normal state of having the device in the same room as the speakers? I truly believe that there is a difference in having spikes or feet under a speaker, the change in the surface area that the enclosure touches the floor and transfers energy into the structure. But I don't think that I have ever seen an actual measure of an amplifier changing output due to airborne vibrations affecting a component unless it was a component that could be vibrated and cause a measurable change, this would not take a long period of time to achieve the result. Let's hear your theory and proof behind these so called changes you have found over the years. RCA cables are notoriously poorly constructed and oxidation is the problem, but is there truly any other sonic difference if we are leaving out balanced signals between RCA and XLR terminated cables. If the impedance is not a problem what are you hearing, are you saying you hear the oxidation? Why wouldn't an XLR also be subject to oxidation over time?
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Old 9th January 2013, 01:45 AM   #32374
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Originally Posted by scott wurcer View Post
Please actually produce this rather than make up these "adder" factors out of the air. Since there are plenty of PA's that measure in the -100's of dB's at full power under many different conditions, the burden of physical proof is on you, not some measurement of -120dB and then a shaggy dog story that makes it 60dB worse.
Scott

There is a 3dB increase in thermal distortion for each halving of frequency so that is 9 db more for music than the test frequency. Then there is 6 db per doubling of power level that is another 12. Then there is the 6 db from the test method vs what you would get from using the same part in the high resistance side of a divider.

The sample shown was -100 when you add all the harmonics. So that would leave an Ohmite 1/4 watt resistor at -73. Now there are other makers who are worse and using a resistor 1/4 the value from the manufacturer's circuit you quoted would get you there.

Now the designer used the smallest wattage resistor in the most important place, so I suspect they were going for that. Of course if they just used one of the CC resistors marketed as "audio grade" that would get them there and then some.

If I find it I will post one of those plots. If you look at the folks who love CC resistors you will find some favorites have quite spectacular distortion plots. I am almost waiting for them to discover thermistors. Or has someone already used them in feedback loops?

But Scott you could have done the numbers yourself. It was never a secret that when CC resistors were dominant they couldn't be used in A/D converters much past 12 bits. N
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Old 9th January 2013, 01:48 AM   #32375
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http://www.tubecad.com/2007/12/23/Th...20Resistor.pdf

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Old 9th January 2013, 02:13 AM   #32376
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Originally Posted by Kindhornman View Post
fas42,
I would sure like to know the mechanism at play that would give these slow changes over time that you are saying that you observe?
Thanks for the thoughtful response, Kindhornman ...

Quote:
So if you could actually measure this change in an amplifier caused by ultra-sonic or other vibrations over time, does that mean that this could be reversed by removing the vibration and the device would return to the previous state> Somehow I doubt very much that you have tested this hypothesis in any real manner, this sounds like a purely subjective result that you are stating as a fact. If what you are saying is true it would be both reversible and measurable over time. How about if you put the device suspended in a vacuum chamber and operated it that way, would the sound be different also over time from the normal state of having the device in the same room as the speakers? I truly believe that there is a difference in having spikes or feet under a speaker, the change in the surface area that the enclosure touches the floor and transfers energy into the structure. But I don't think that I have ever seen an actual measure of an amplifier changing output due to airborne vibrations affecting a component unless it was a component that could be vibrated and cause a measurable change, this would not take a long period of time to achieve the result. Let's hear your theory and proof behind these so called changes you have found over the years.
Certainly no proof so far, I haven't the access to the right, sensitive enough gear to measure things, so my ears have to do the work in the meantime ...

In my experience the effect does not reverse if the mechanism causing the abberation is removed; perhaps if one waits long enough it will diminish in intensity, I haven't experimented sufficiently to say one way or the other. The simplest technique I've used to reset is to power down everything, wait and power up again.

Your experiment in the vaccuum chamber would work if the particular problem was due to external vibration; but if it was internally initiated, say from the power transformer vibrating at different levels, depending upon just about everything, then perhaps no.

My theory in this area, that has evolved over the years, is that seemingly subtle triboelectric mechanisms are behind a lot of these issues; it's not the answer to everything, but all experiments that precisely addressed this behaviour as a cause have given positive results.

Quote:
RCA cables are notoriously poorly constructed and oxidation is the problem, but is there truly any other sonic difference if we are leaving out balanced signals between RCA and XLR terminated cables. If the impedance is not a problem what are you hearing, are you saying you hear the oxidation? Why wouldn't an XLR also be subject to oxidation over time?
Most certainly you can hear oxidation, this was one of my first "discoveries". Drove me crazy until I said, to hell with it, I'm going to hardwire everything(!) ... and that solved that one.

As you say, RCA connectors are terrible things; XLR are by design much better. The ideal is a gas tight connection, and the XLR has a much, much better chance of achieving that, if well constructed, the metal on metal pressure would typically be much greater.

Frank

Last edited by fas42; 9th January 2013 at 02:15 AM.
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Old 9th January 2013, 02:36 AM   #32377
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I might just mention that my rough and ready system has the woofer/subwoofer literally 1 foot away, as the crow flies, from the CD player/system electronics, for reasons of getting reasonable integration with the stereo speakers, and laziness , and I run it at very high volumes. I wouldn't be game to do this on a normal setup, it would mangle the sound terribly, in the areas I worry about ...

Frank
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Old 9th January 2013, 04:01 AM   #32378
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Feedback resistors are CRITICAL. We have known this, for like, forever. Thanks Ed for bringing it up.
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Old 9th January 2013, 09:10 AM   #32379
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Originally Posted by john curl View Post
Just aircraft grade aluminum.
Blowtorch flies ?
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Old 9th January 2013, 09:19 AM   #32380
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Are you a comedian or an audiophile, Esperado?
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