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Old 19th March 2013, 02:28 AM   #8661
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Frans and i are working on the current conveyor input stage for the balanced Paradise.
We got the peaking away ( this it not a big deal because it is over 10MHz ) and distortion is really low. Frans bootstrap is really cool. It balances the current also in both legs better.
So far distortion comes out at a bit more then -120dB, only second for the single ended case. Parallel symmetric-balanced there should virtually be no distortion because that suppresses the second. I am excited.
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Old 19th March 2013, 02:47 AM   #8662
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Stefano, i have drawn up a posible solution.
Comes in 10 minuts.
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Old 19th March 2013, 03:04 AM   #8663
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I think this circuit will work. For clarity i took out the cascodes over the J-Fets.
What is cool is that the input signal of the cartridge is driven from both sides to both inputs of the OPA1632. In common source and over the source followers in common gate.
I think we are set. We can use the Vd input of the OPA1632 as servo.
I will show you how that works soon. It has to be a common mode servo.
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File Type: jpg Masterpiece first draft.jpg (34.5 KB, 180 views)
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Old 19th March 2013, 03:08 AM   #8664
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Here is the Twisted Pear Retro phono.
It also uses the OPA1632 and shows the way to servo.
I think this is for high output MC or MM. For low output MC it is too noisy but the servo is cool.
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File Type: pdf retro_schematic.pdf (34.6 KB, 89 views)
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Old 19th March 2013, 02:18 PM   #8665
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this is extremely interesting!

I will have to build a little prototype I guess and see how it works.
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Old 19th March 2013, 02:24 PM   #8666
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Just a quick comment after having looked at the datasheet for the differential OP AMP.
It looks great distortion wise, the only thing is that, at least for a phono, the noise floor is 1.3nV/sqrHz.
Can we look for something even lower noise?
Do you think it exists?

I will look for as well.
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Old 19th March 2013, 02:54 PM   #8667
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I aslo never implemented a shunt RIAA.
How much gain will you think the differential OP AMP should provide? and how much gain should it reasonably be expected from the input stage?
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Old 19th March 2013, 02:55 PM   #8668
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I will move this subject to the MasterPiece so that we can keep this separate from the developments of the Paradise.
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Old 19th March 2013, 02:56 PM   #8669
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The input stage with the Infet super Fet defines the noise.
Say the output resistors of the first stage are 300 Ohm.
The Opa1632 has around 75 Ohm noise impedance so you see that the noise contribution of this chip is minimal IN THIS CIRCUIT.
To use the OPA1632 as the sole input stage, that is another story.
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Old 19th March 2013, 02:59 PM   #8670
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I will tell you more Stefanoo.
Yes, lets move it.
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