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Old 29th October 2003, 09:43 PM   #1
audioPT is offline audioPT  Portugal
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Hi!

Is the AD797 a good opamp to a phono preamp?

I've cheked id the datasheet that it has very low noise...

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Pedro Martins
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Old 29th October 2003, 10:51 PM   #2
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Seems like ML are using that chip in their phono module
http://www.marklevinson.com/image_li...7&productID=11
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Old 29th October 2003, 10:54 PM   #3
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File Type: jpg pho.jpg (22.2 KB, 1063 views)
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Old 29th October 2003, 11:01 PM   #4
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So, I must design a good preamp!
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Old 30th October 2003, 06:31 AM   #5
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Is it for an MM or an MC phono amp?

There has been some discussion recently on this in various
threads, and it seems many or even most would advice against
it for MM, but vote for it or a similar one for MC.

Op amps like AD797, LT1028 and LT1115 have very low voltage
noise. However, they are all bipolar input op amps so they have
a much higher current noise than, for instance, JFET input
op amps. For MC, the source impedance is usually so low that
the voltage noise is dominant, but for MM the source impedance
is much higher so the current noise can cause a noise voltage
many times higher than the op amps own voltage noise.
Basically, check the current noise of the op amp and multiply
with the source impedance and compare it to the voltage noise.
That is somewhat simplified, but gives you the idea of how a
particular op amp will perform.
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Old 30th October 2003, 08:28 AM   #6
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Smile Ad797

Quote:
Originally posted by Peter Daniel
Seems like ML are using that chip in their phono module
http://www.marklevinson.com/image_li...7&productID=11
Hi Peter,
In the good old days when John Curl and Tom Colangelo were with the Mark Levinson company they made only discrete circuits. At some point in time probably Madrigal decided to go for integrated circuits. It is my opinion that a better sounding circuit can be built discretely but it is more "hard work". This applies particularly to phono stages.
Why would Sonnya and I go through all the trouble to design a discrete opamp?
Jfet/bipolar PCB and Schematic (finaly)
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Old 30th October 2003, 09:11 AM   #7
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Default Re: Ad797

Quote:
Originally posted by audioPT
Is the AD797 a good opamp to a phono preamp?
Yes, it's rather good but it depends which goal you have, medium performance MM or super ultra high tech MC?
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Old 30th October 2003, 05:56 PM   #8
audioPT is offline audioPT  Portugal
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Just enough to get the best sound of my Ortofon witch is in a Tecnhics SL1210MKII
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Old 30th October 2003, 05:58 PM   #9
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MM or MC??
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Old 30th October 2003, 06:19 PM   #10
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Hey peter, how come you always have so many pictures of Levinson equip?
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