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Old 27th November 2010, 02:10 PM   #31
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Hey John,

not thomas but he did help me with this a number of years ago. Essentially you need to add an additional resistor (R25) above the .126u 68K combo and lower the value of the 45mhy inductor.

dave

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Old 27th November 2010, 03:24 PM   #32
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Quote:
Originally Posted by Vinylsavor View Post
Hi!



A while back I shared a design of a full function preamp with RC RIAA phonosection on AA. I call it the Octal preamp. It uses 6SL7/6N7/6SN7 tubes.
If there is interest, I'll open a thread about it and post the schematics

Best regards

Thomas
Thanks, I am always interested in seeing stuff like this. I had gotten it in my head that I wanted to try one using the 12A_7 series of tubes just for giggles. I can't find the latest version of the schematic right off hand but it is essentially like this with a 12AY7 instead of 12AT7 for the lower element of the mu-follower.

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File Type: jpg SmPhonoOutput12AT7.jpg (28.5 KB, 471 views)
File Type: jpg SmPhonoSchem12AT7.jpg (134.7 KB, 473 views)
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Old 27th November 2010, 04:25 PM   #33
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Hey guys,
This an example of compensation that I simmed. The filters are from a Neumann 1974 cutter. It will still be approximation as Neumanns is 2nd order. If you have Daves chokes, Lundahls or a EQ-2L you can adopt it. The blue is uncompensated.
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File Type: png neu.png (43.6 KB, 96 views)
File Type: png neucurves.png (89.9 KB, 92 views)

Last edited by revintage; 27th November 2010 at 04:28 PM.
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Old 30th November 2010, 12:59 AM   #34
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hey lars,

surely a few value tweaks can fix the minor drop at 5-6khz. In some circles that -0.2dB would surely make the results unacceptable :-)

dave
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Old 30th November 2010, 05:29 AM   #35
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You can borrow my test signal (please return it after you done!):

http://wavebourn.com/gallery/riaa/Re...Sweep-RIAA.wav
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Old 30th November 2010, 07:30 AM   #36
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Hey Dave,
You can stay well below 0,1dB with 45mH, this has been showed at your place. What I now showed was an example of the difference between Neumann and std. Will surely be aproblem to do it IRL due to component-tolerances.

Below is another sim that shows the differences between std and Neumann. The *.asc is also in a thread at your place. Blue is Neumann-corrected. Now check tolerance .
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Last edited by revintage; 30th November 2010 at 07:36 AM.
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