John Curl's Blowtorch preamplifier part II - Page 3304 - diyAudio
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Old 20th January 2013, 12:44 AM   #33031
SY is offline SY  United States
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Quote:
Originally Posted by simon7000 View Post

The 6K is where the ESL of the .01F capacitor begins to make a significant difference. It affects total weighted value of the noise.
First, nonsense- try looking at the datasheets for modern aluminum electrolytics. What's the 6kHz impedance of a 10,000u/25V cap made today (no 1968 data, please)? What is the noise voltage that this represents after taking into account the second issue: if you want to take things up another octave, you also have to change the weighting factor in the Fourier series.

I've shown explicitly that your estimate of output noise is incorrect. If you want to keep moving the goalposts, feel free, I'm not playing that game. I hope that the deconstruction of your original analysis will alert anyone not up to speed on basic engineering to not take your calculations at face value. Honest, straightforward, easy to follow calculations show that the noise contributions of a regulated supply to modern IC opamps is ridiculously small.

I'm starting to think that all of this goalpost shifting is meant to distract from John getting egg on his face regarding his apparently false claim (it's gone well past a mistake when he won't address the simple technical issues) about 7th and 9th harmonics in competing technologies. You're better than that, I don't see why you need to play that game. John can take care of himself, he's not a kid.


http://www.epcos.com/web/generator/W...nformation.pdf

http://www.chemi-con.com/u7002/applications.php

http://www.eetimes.com/ContentEETime...2012_FINAL.pdf

http://www.cde.com/catalogs/AEappGUIDE.pdf
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Old 20th January 2013, 12:45 AM   #33032
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Originally Posted by john curl View Post
What I like best is the 1966 voltage regulators made by National. They were quieter than almost anything, today!
Cant find anything, you sure is 1966?
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Old 20th January 2013, 12:56 AM   #33033
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Quote:
Originally Posted by Kindhornman View Post
Frank,
The album is titled "The Doors". Elektra/Asylum This was my now departed wife's cd and it looks like it was one of those club produced cd's where you bought a bunch of cd's cheap. Perhaps that is part of the problem. It is utter trash.
Haven't got, but the company and time matches the others I have. I'm sure the versions of the songs match between different disks, no-one was being paid to do fiddly remastering back then ...

Frank
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Old 20th January 2013, 01:05 AM   #33034
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Originally Posted by Kindhornman View Post
It isn't so much the top end that makes it sound unbalanced, it is the midrange and the bass section that is what I will describe as thin, lacking of warmth in the vocals and almost no lower bass to speak of.
I listened to a copy of 'Riders on the storm' from this compilation. It is exactly what i described plus the fact that the original tape is obviously killed by age.
While the curtain of the vinyl (that i have) is removed, you can hear a lot of details witch were hidden; like the saturated take of the piano and one of the guitar, the blunders of play and mixing etc... The original vinyl was scrambled, that brought a lot of nice mystery. Now everything is too much separated and sound really poor.
Notice the cymbals had lost all their dynamic and body, compared to the vinyl (magnetic tape demagnetization). All this need really to be re-masterized with a lot of processing, and, like the original Beatles tunes from the same years, will never reproduce the magic it had at this time.
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Last edited by Esperado; 20th January 2013 at 01:07 AM.
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Old 20th January 2013, 01:17 AM   #33035
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Christophe,
I'll accept that explanation as more than probably correct. I may have the vinyl original to compare the dynamics and the frequency response. It just isn't worth worrying about, though I did grow up with this music and wish that I could listen to the songs, but not with this cd. So you are saying that the remastered Beatles albums are also having the same problems with old master tapes, that is a shame. I guess I better listen to one of the cd's before I get one of the newer compilations. You could probably make my old Revox sing, but I'm not sure what I would do with it anymore.

Steven
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Old 20th January 2013, 01:21 AM   #33036
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How about the old LM723 for a reg? Looks like the noise is better that a 317.
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Old 20th January 2013, 01:25 AM   #33037
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Originally Posted by kgrlee View Post
The AD797 is used as a MM & MC preamp. It is entirely inappropriate for this purpose. The surrounding circuit degrades the usual Lo Z MC cartridge noise by at least 10dB. There is a similar degradation for MM cartridges but due to the choice of AD797.

AD797 is appropriate for only one type of rare MC cartridge but then the gain structure is completely wrong.
Actually, I had always thought Scott perhaps had a secret agenda while designing the AD797, in that he wanted a better opamp for the first stage of an MC-preamp. Very low voltage noise, and enough drive capability to use very low value feedback resistors at low levels. Plus effortless high gains. This is just based on specs.

Based on actual build experience, it also works very well for MM as far as noise and distortion go. To test a new power supply scheme, I made a MM preamp (because I have a MM in my turntable) with passive RIAA, with AD797 as the first stage. It does very well, with the only problem being that it is like gluing a stick of dynamite to your woofers. The thing is the high input bias current, which on 47KOhm leads to a very different DC offset than when the 1K MM element is put across the input. This times 30dB amplification provides quite a voltage spike if something disconnects. For MC the low input impedance makes this much less of a problem I would think.

In that sense I understand why JC has such a low gain factor for the AD797 in the MM-mode.

I agree with you that switching these low level signals to allow the first stage to be used with both MM and MC is probably not what I would do, but perhaps it works with a lot of care.

What I don't understand in the scheme JC posted is why the input and output impedances of the 2134's used have not been matched. The specsheet explicitely mentions this should be done for best performance. Just to take the inverting opamp for output 2. Feedback R is 10K with G=1, non inverting input straight to the ground. Why not take a much smaller feedback R and match the impedance by connecting noninverting input to the ground through a matching R. Thus, the noise performance would not have to suffer. I am sure Ti does not put stuff like that in application notes for no good reason.

Last edited by vacuphile; 20th January 2013 at 01:28 AM.
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Old 20th January 2013, 01:30 AM   #33038
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Steven, remember too that all those records were made to sound good on the Am radio stations you listened in your 'transistor'. That explain why no deep basses etc...
And it is terrible, for us: we compare our actual listening, with all the musical knowledge and exigence we acquired with years, versus the feelings we remember we had at this time.
The doors were kids, as us, at this time .
Brought in full light, the garden of our childhood look so little, today. :-)
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Last edited by Esperado; 20th January 2013 at 01:33 AM.
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Old 20th January 2013, 01:34 AM   #33039
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Quote:
Originally Posted by SY View Post
First, nonsense- try looking at the datasheets for modern aluminum electrolytics. What's the 6kHz impedance of a 10,000u/25V cap made today (no 1968 data, please)? What is the noise voltage that this represents after taking into account the second issue: if you want to take things up another octave, you also have to change the weighting factor in the Fourier series.

I've shown explicitly that your estimate of output noise is incorrect. If you want to keep moving the goalposts, feel free, I'm not playing that game. I hope that the deconstruction of your original analysis will alert anyone not up to speed on basic engineering to not take your calculations at face value. Honest, straightforward, easy to follow calculations show that the noise contributions of a regulated supply to modern IC opamps is ridiculously small.

I'm starting to think that all of this goalpost shifting is meant to distract from John getting egg on his face regarding his apparently false claim (it's gone well past a mistake when he won't address the simple technical issues) about 7th and 9th harmonics in competing technologies. You're better than that, I don't see why you need to play that game. John can take care of himself, he's not a kid.


http://www.epcos.com/web/generator/W...nformation.pdf

United Chemi-Con

http://www.eetimes.com/ContentEETime...2012_FINAL.pdf

http://www.cde.com/catalogs/AEappGUIDE.pdf
SY

I show all the calculations. Your's are plain wrong. I posted real measurements. You can quote sims without showing the work. You quote ESR then list more paper. I have shown a measurement of a .01F capacitor and the noise.

So all you need now is a sim of listening and liner notes to read.

Your theory that I am spoiling your personal attacks on JC speaks volumes about you.

PS Your first reference supports a .01F capacitor rising impedance as low as 3K! So does the 4th cite. The other two refer to filtering switching power supplies.

Last edited by simon7000; 20th January 2013 at 01:44 AM.
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Old 20th January 2013, 01:39 AM   #33040
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Well, gentlemen, I would have to disagree ... the tape may have degraded but the digital has brought out detail which was "hidden", which are exactly the signs I look for. It means that the sound has not been "polluted" by being fiddled with by over enthusiastic remastering engineers, who are going to "fix up" the sound -- that's the last thing I'm interested in!

This is where I start - use the "poor" qualities of that transfer to point to where the deficiencies exist on my side of the equation. As things progress the picture becomes clearer and clearer - it won't sound like a nice cuddly, AM radio, vinyl veiled version of the song, but it will sound like real muso's doing their thing in the studio. And that's what appeals to me: I have stripped back to precisely what was captured by the recording technology of the time.

So then if I want a warming, fireside version of the tune I can just chuck in a bit of DSP to season it as appropriate, from my side of the experience. But it will be much harder to do that if I haven't got the underlying sound correct, or if it's been fiddled with by someone with a different agenda ....

Frank
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