John Curl's Blowtorch preamplifier part II - Page 3390 - diyAudio
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Old 31st January 2013, 02:12 PM   #33891
Bonsai is offline Bonsai  Taiwan
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"I would like to return to this post. After a week of listening tests, I would like to emphasize that the preamp based on AD797 with buffered output sounds great. It is extremely transparent with fantastic resolution and in the same time it is not aggressive. I mostly listen to classical philharmonic orchestra music when evaluating audio component. DGG Beethoven symphonies sets conducted by Harnoncourt and Gardiner are great through this opamp. No muffling, no blending, no rounding and also no aggressiveness. Hats off."

Why the re-conversion to integrated opamps again PMA? People argued at length on this thread some time ago about the glories of discrete . . .
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Old 31st January 2013, 02:15 PM   #33892
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I would like recommend a wonderfully recorded CD.

Telemann in Major by Pratum Integrum

Great for system evaluation.
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Old 31st January 2013, 02:17 PM   #33893
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'BUFFERED OUTPUT' PMA, This is not how it is normally used. Please show me the buffer, if you will? Did you compare it with an AD825 with the SAME BUFFER?
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Old 31st January 2013, 02:28 PM   #33894
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Default When Is An Opamp Not An Opamp....

Quote:
Originally Posted by john curl View Post
'BUFFERED OUTPUT' PMA, This is not how it is normally used. Please show me the buffer, if you will? Did you compare it with an AD825 with the SAME BUFFER?
+1

More so the whole implementation... please.

Thanks in advance, Dan.
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Old 31st January 2013, 02:35 PM   #33895
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Back to Slot's book 'Audio Quality' I am having trouble with my scanner.
However, on p. 52 "The effect of the response sounding brighter or shriller than when the characteristic is straight [flat frequency response] starts when the roll-off is more than 6dB/octave."
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Old 31st January 2013, 02:36 PM   #33896
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Quote:
Originally Posted by RNMarsh View Post
Regarding roll-off frequencies ---> group-delay is still important to keep under a certain threshold. Dean Jensen (Jensen Transformer founder and designer) made his fame by winding his transformers for low group-delay distortion (esp. at low end).... little known at the time.
Actually the transformers that Deane sold under the Jensen brand were transformers designed and built by Ed Reichenbach, formerly of Altec, then with his own company, Reichenbach Engineering. Jensen was originally billed as "Jensen Transformers by Reichenbach Engineering." Deane later split from Ed, taking the engineering with him and having them wound by another company.

And it wasn't at the low end that Deane was focusing on but rather the high end, where the transformer's parasitics combine to create a resonant circuit.

Finally, the transformers are made to have more or less a 2 pole low pass Bessel function (to give the best group delay) by way of external RC networks.

Edit: Here's a photo of Ed Reichenback and his wife, Betty, wearing their "Jensen Transformers by Reichenbach Engineering" satin jackets:

Click the image to open in full size.


se
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Last edited by Steve Eddy; 31st January 2013 at 02:56 PM. Reason: Add photo
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Old 31st January 2013, 02:49 PM   #33897
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Quote:
Originally Posted by john curl View Post
'BUFFERED OUTPUT' PMA, This is not how it is normally used. Please show me the buffer, if you will? Did you compare it with an AD825 with the SAME BUFFER?
No, I will not.

But output buffering, though different from mine, is shown in the AD797 datasheet, and was shown here few weeks ago. Datasheet image attached. Once again, my buffering scheme is different.

AD825 is not that transparent and does not have such good resolution - probably for the reason it is very noisy. But AD825 sounds "nice" (= equalizing).
Attached Images
File Type: png AD797_buf.PNG (26.8 KB, 162 views)
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Old 31st January 2013, 03:01 PM   #33898
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With AD825, I get +14dB more output noise than with AD797, integral over 20Hz - 20kHz, unweighted.
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Old 31st January 2013, 03:03 PM   #33899
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I would rather say understandable - you have used a poor audio system for your test. 95% or maybe even more audio systems are poor, including so-called highend.
Pavel,

I am very much in awe for your uncanny capability to conclude which systems people have in their homes just by reading these posts - even more by your very astute knowledge that 95% of these systems are poor. That must have cost quite some time to listen to all of them and count them!

jan
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Old 31st January 2013, 03:08 PM   #33900
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Jan, it's evident from Sturgeon's Law.
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