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Old 30th June 2013, 08:39 AM   #771
AndrewT is offline AndrewT  Scotland
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The LPF will have some attenuation effect on interference getting into the chips.
Reductions in the levels of VHF will reduce the the IMD. Some of that IMD is heard in the audio band. That reduction in IMD will not show in the scope of the audio signal nor show in the Vac noise measured at the signal.
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Old 30th June 2013, 12:30 PM   #772
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Originally Posted by owdeo View Post

No doubt some will dismiss these findings as delusional, psycho-expectational drivel, and for that reason I'm not going to speculate which change made the difference, but I'd thought I'd share my findings anyway
In general, your perceptions about SQ are remarkably close to my, so I am inclined to think that there must be some truth to it. And since we never met there is no way of influencing each other in any way.
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Old 30th June 2013, 12:53 PM   #773
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Recordings that Roy DuNunn did for Contemporary Records in the late 50's are considered by many, including me, as non plus ultra! Think for the moment, several condenser microphones from Germany, a few pots, direct to a valve tape recorder, and post production consisting of German built EMT echo plate, and that's it. That's as far away from linear as one can imagine and yet the sound of it is unsurpassed. Without any intention to make anything unsurpassed he achieved it. Just an improvisation.

The Search for Roy DuNann | Stereophile.com
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Old 2nd July 2013, 01:27 AM   #774
owdeo is offline owdeo  Australia
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Quote:
Originally Posted by AndrewT View Post
The LPF will have some attenuation effect on interference getting into the chips.
Reductions in the levels of VHF will reduce the the IMD. Some of that IMD is heard in the audio band. That reduction in IMD will not show in the scope of the audio signal nor show in the Vac noise measured at the signal.
Nice theory, sounds plausible. Any suggestions on how to test for this? A standard IMD two-tone test would not show it up presumably. With an f3 for this filter of about 16MHz, you wouldn't think it would be helping much unless I happened to live under a TV or FM broadcast tower (which I don't, I'm at least 20km from the nearest). I'm tempted to increase the cap value to say 1nF, since I won't ever be feeding the preamp from high Z source.
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Old 2nd July 2013, 01:29 AM   #775
owdeo is offline owdeo  Australia
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Originally Posted by ivanlukic View Post
In general, your perceptions about SQ are remarkably close to my, so I am inclined to think that there must be some truth to it. And since we never met there is no way of influencing each other in any way.
Nice to hear this, thanks. Have you also built the Precision Preamp, or are you speaking more generally?
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Old 2nd July 2013, 02:57 AM   #776
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Quote:
Originally Posted by owdeo View Post
Nice theory, sounds plausible. Any suggestions on how to test for this? A standard IMD two-tone test would not show it up presumably.
I believe you're right in that a standard two-tone test won't show it. That's a high level test with large amplitude signals whereas the effects here are low-level. I reckon what you need as a stimulus is a high crest-factor multitone signal where no single tone supplies more than -80dB of the total energy. If such a broadband signal were created with spectral gaps in it, the amount of gap-filling probably will give some indication of the IMD.
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Old 2nd July 2013, 05:02 AM   #777
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Originally Posted by owdeo View Post
Nice to hear this, thanks. Have you also built the Precision Preamp, or are you speaking more generally?
No, I have not built it because I do not need "complete" preamp, but your comments about sound of opamp types are very accurate and consistent with my experiences. Therefore I think that your other comments are relevant too.

BTW, it seems interesting to me to build simplified (and less expensive) version of the new Precision, the one that Ian Finch hopes to see one day from Signal Transfer. I do not need balanced inputs, etc...
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Old 2nd July 2013, 05:41 AM   #778
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Originally Posted by redjr View Post

The problem is it now reveals the weakness in all my other mid-fi gear!

Rick
This is very important detail. I've noticed that whenever some specific form of distortion is highly reduced, some other form jumps out to replace it. So, when you lower THD distortion in preamp, some other distortion in source, or in power amp, or in loudspeaker jumps out to dominate. The best sounding equipment is the one that have a certain distortion composition in some lucky ratio, distributed in some specific way. It is my theory that some people prefer j-fet opamps because of higher noise that masks certain forms of distortion that is particularly annoying for them.

But if you ask me to say what is the lucky ratio, how much or how little of certain specific distortion gives subjectively satisfying results, I am unable to answer.
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Old 2nd July 2013, 09:58 AM   #779
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Originally Posted by ivanlukic View Post
It is my theory that some people prefer j-fet opamps because of higher noise that masks certain forms of distortion that is particularly annoying for them.
Hi ivanlukic,

I prefer JFET op amps in general, but especially at the front-end of equipment. I doubt it is because of noise masking of distortion, since they are quite adequately low in noise. Moreover, many circuits that people use may not be optimized for the very best noise, and even BJTs in those circuits with BJTs will have as much noise as a well-designed JFET-based circuit.

I believe that the higher RFI immunity of the JFET is partially responsible for the better sound. Bear in mind that the signal entering a BJT op amp goes into a forward-biased junction (base-emitter) eager to rectify. The signal going into a JFET op amp goes into a junction that is reverse biased (gate-source), sometimes by a volt or more, and much less close to the region where it might rectify.

Cheers,
Bob
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Old 2nd July 2013, 10:13 AM   #780
Mooly is offline Mooly  United Kingdom
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I would go along with the "rf theory" too. In fact, this has been put forward as one reason why bjt's (such as 5532 etc) might have earned a poor reputation. This noise could apparently be "demodulated" in a non linear way (think of an old fashioned RF diode demodulator/detector) wheras FET input stages are essentially immune. It seems a very plausible theory given that the 5532 and similar was extensively used in DAC I/V conversion and filtering, a location that invariably does have a lot of hf hash present. And it was precisely these kind of applications that were seeing big sonic gains when switching to FET devices.
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