Ad797

audioPT · 29th October 2003, 10:43 PM

Hi!

Is the AD797 a good opamp to a phono preamp?

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

Regards

Pedro Martins

Peter Daniel · 29th October 2003, 11:51 PM

Seems like ML are using that chip in their phono module
http://www.marklevinson.com/image_li...7&productID=11

Peter Daniel · 29th October 2003, 11:54 PM

.

audioPT · 30th October 2003, 12:01 AM

So, I must design a good preamp!

Christer · 30th October 2003, 07:31 AM

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.

Elso Kwak · 30th October 2003, 09:28 AM

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)

peranders · 30th October 2003, 10:11 AM

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?

audioPT · 30th October 2003, 06:56 PM

Just enough to get the best sound of my Ortofon witch is in a Tecnhics SL1210MKII

Christer · 30th October 2003, 06:58 PM

MM or MC??

jwb · 30th October 2003, 07:19 PM

Hey peter, how come you always have so many pictures of Levinson equip?

29th October 2003, 10:43 PM	#1
audioPT diyAudio Member Join Date: Aug 2002 Location: Right here	Ad797 Hi! Is the AD797 a good opamp to a phono preamp? I've cheked id the datasheet that it has very low noise... Regards Pedro Martins

29th October 2003, 11:51 PM	#2
Peter Daniel diyAudio Member Join Date: Jul 2002 Location: Toronto, Canada	Seems like ML are using that chip in their phono module http://www.marklevinson.com/image_li...7&productID=11 __________________ www.audiosector.com “Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.” - JC

30th October 2003, 07:31 AM	#5
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	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. __________________ "Jitter clock: - - indicates product does NOT have this feature" From product spec. of a CD player

30th October 2003, 06:58 PM	#9
Christer diyAudio Member Join Date: Sep 2002 Location: Sweden	MM or MC?? __________________ "Jitter clock: - - indicates product does NOT have this feature" From product spec. of a CD player

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30th October 2003, 12:01 AM	#4
audioPT diyAudio Member Join Date: Aug 2002 Location: Right here	So, I must design a good preamp!

30th October 2003, 06:56 PM	#8
audioPT diyAudio Member Join Date: Aug 2002 Location: Right here	Just enough to get the best sound of my Ortofon witch is in a Tecnhics SL1210MKII

30th October 2003, 07:19 PM	#10
jwb diyAudio Member Join Date: Mar 2002 Location: San Francisco, USA	Hey peter, how come you always have so many pictures of Levinson equip?

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