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Old 15th October 2013, 01:15 PM   #1551
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Would single ended be possible? That is, k170 top/bottom and current source?
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Old 15th October 2013, 01:48 PM   #1552
EUVL is offline EUVL  Europe
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We'll publish in due course.


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Old 16th October 2013, 09:45 AM   #1553
heb1001 is offline heb1001  China
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Quote:
Originally Posted by EUVL View Post
For those interested, here is our quick-&-dirty prototype of a SEN IV for PCM1794.
You got this working yet? I never got around to trying your simple bias solution. Curious to know whether it's stable enough to perform well.
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Old 16th October 2013, 10:23 AM   #1554
EUVL is offline EUVL  Europe
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It is stable enough. That we have tested and the results are posted.
But we have not tested it on the DAC.

The original PCB needs the analog stage stripped and replaced first.


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Old 17th October 2013, 05:45 AM   #1555
Calvin is online now Calvin  Germany
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Hi,

The simple JFET ccs not only works stable, but may easily be trimmed after due warm-up and is probabely the lowest noise ccs one could us here.
The ccs will be the dominant noise source of the complete circuit!
I tested several ccs structures and the JFET remained choice no1 and I use it for years in my iv circuits for the PCM179x.
Just make sure that its heavily degenerated to achieve a high enough impedance, as too low inpedance values affect THD.
JFETs like the 4391 are also a good choice here, if one doesnt want to rely on obsolete parts.

jauu
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Old 17th October 2013, 06:01 AM   #1556
EUVL is offline EUVL  Europe
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Only the old Siliconix datasheet has a noise figure for the 4391 of 3nV/(sqrtHz).
All currently available ones (Philips, Fairchild, OnSemi) are not specified.

So 2SK369V and the like is still the better choice I think.
You can also use 2SK246BL and degenerate to 2mA or so.
Need to use 3x in parallel.


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Old 17th October 2013, 11:11 AM   #1557
Calvin is online now Calvin  Germany
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Hi,

The interesting part about the 4391 is its high idss of ~100mA.
That allows for a a large valued source resistor, making the ccs stiffer and less noisy. Paralleling devices to achieve suffuciently large dc-currents reduces Zout and increases noise again.
So I still think, that a single high Idss JFET is a prefferable choice.

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Old 17th October 2013, 12:28 PM   #1558
EUVL is offline EUVL  Europe
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Isn't it that random noise reduce by sqrt of n, where n is the number of devices in parallel ?
Else why should they bother in phono preamps ?


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Old 17th October 2013, 01:59 PM   #1559
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by Calvin View Post
Hi,

The simple JFET ccs not only works stable, but may easily be trimmed after due warm-up and is probabely the lowest noise ccs one could us here.
The ccs will be the dominant noise source of the complete circuit!
I tested several ccs structures and the JFET remained choice no1 and I use it for years in my iv circuits for the PCM179x.
Just make sure that its heavily degenerated to achieve a high enough impedance, as too low inpedance values affect THD.
JFETs like the 4391 are also a good choice here, if one doesnt want to rely on obsolete parts.

jauu
Calvin
Hi Calvin

I also think that the 4391 is a good option. As the 2SK369V is.

But you have to take a better look to the topology, please.

I have developed this concept of floating current source exactly to eliminate the noise from the current sources in a folded cascode. As the current source is floating, any current noise that is produced in the current source will have to return to the current source.
The impact of the current source noise in this topology is close to none.

Also the output impedance of the ccs is not a problem, the circuit works with low distortion even with a resistor as current source

The PSRR of this topology is also very high.

In the first image is the PSRR of one of the circuits we have, the other image is the distortion with a 150 ohms resistor as current source .
(simulating a pcm1794 at 7,8ma p-p).

sorry for not show all the circuit, but is under development.
Attached Images
File Type: png floating_psrr_2.png (49.7 KB, 448 views)
File Type: png floating_no_ccs.png (112.7 KB, 444 views)
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Last edited by smms73; 17th October 2013 at 02:06 PM.
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Old 17th October 2013, 02:14 PM   #1560
rsavas is offline rsavas  Canada
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Quote:
sorry for not show all the circuit, but is under development.
for public use or proprietary?
Interested to learn how to sim a I/V converter!! So more for me too learn in ltspice.
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