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Old 21st September 2011, 06:23 PM   #271
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Here is a comparison between Fets and BJTs :
http://www.cco.caltech.edu/~musiclab...er-acrobat.pdf
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Old 21st September 2011, 06:33 PM   #272
bcarso is offline bcarso  United States
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Jawohl! Boyk and Sussman is a great paper, and particularly notable for Boyk allowing that bipolars might not be so bad after all (if you recall, Jim had T shirts made that stated "Digital Finishes What The Transistor Began").

Now to test their simulations with real parts...
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Old 21st September 2011, 06:33 PM   #273
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Each of the 8 differential DACs has an output impedance of about 800 Ohms, but if you use the ESS9018 in stereo mode, like in the Buffalo2, you have about 195 Ohms, and 16mAp-p signal current max riding on top of 8mADC wehn using 0 Ohm load. In mono mode, the ESS9018 has its DACs in parallel giving twice the stereo mode current.

AFAIK, most people are using the ESS9018 in either mono mode or stereo mode.



Quote:
Originally Posted by EUVL View Post
Joachim,

The ES9018 has a low output impedance of about 800R.
So let's go as far as we can and aim to do Zin < 1R.
Since it is CEN, the PNP & NPN are in parallel for the signal.
That is why I chose E153 as current source (15mA bias), so that Zin is about 0R8.
This has the same function as your BF245 with trimmer.
E153 are widely used in Japan for powering LEDs.
I am sure Davide would be able to get them if necessary.

I was hoping to get zero DC offset by perfect matching.
Anyhow, the schematics demonstrates how it can fulfill all the functional requirements.



Patrick
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Old 21st September 2011, 08:41 PM   #274
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bcarso, yes BJTs degenerated to the same Gm as J-Fets have less distortion nominally.
That is mostly because they have much more Gm to burn to begin with. Still some prefer the sound of Fets for other reasons
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Old 21st September 2011, 08:44 PM   #275
EUVL is offline EUVL  Europe
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> Still some prefer the sound of Fets for other reasons

Absolutely.

If Gm and / or THD is everything then audio would be simple and DIY would be dead boring.




Patrick
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Old 22nd September 2011, 12:19 AM   #276
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It´s not so much the amount of Gm but the shape of it that is important for low distortion plus the correct topology that takes advantage of the Fets gain curve.
See the simulations on a circuit i designed with only one pair of Fets with EUVLs matching trick and my current mirror with cascode. We got -95dB, mostly 2nd harmonic with a gain of 60dB without any loop feedback.
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File Type: png Naked_Truth_MC_Mirror_with_Cascode_2.1.TSC_-_thd2.png (143.3 KB, 830 views)
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Old 22nd September 2011, 04:45 AM   #277
EUVL is offline EUVL  Europe
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What is the (current) signal amplitude ?


Patrick
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Old 22nd September 2011, 06:15 AM   #278
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Here is the datasheet´s information about the ESS9018 analog outputs.
In Stereo mode, you have 4X the currents, and in mono mode, 8X.

50-100mADC idle would be good to have for stereo mode.

Quote:
Originally Posted by EUVL View Post
What is the (current) signal amplitude ?


Patrick
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File Type: gif ESS9018 Analog Output.gif (12.4 KB, 783 views)
File Type: gif ESS9018 Analog Output Note 1.gif (6.1 KB, 774 views)

Last edited by staccatiss; 22nd September 2011 at 06:19 AM. Reason: Added Note 1 image
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Old 22nd September 2011, 07:30 AM   #279
EUVL is offline EUVL  Europe
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The question was to Joachim for what current signal he used in his simulation. (I read 0.1mA.)
Nothing to do with ES9018, the datasheet of which I have under NDA.

Also I wonder how distortion changes with signal amplitude ?


Thanks,
Patrick
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Old 22nd September 2011, 03:17 PM   #280
EUVL is offline EUVL  Europe
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One of you sent a email and wanted to purchase a apir of my IV's.
Thank you for your interest.

I do not sell them as finished circuits, but you may wish to consider subscribing for an evaluation kit which will make life somewhat easier for you to build them.

See :

SEN / CEN All JFET IV Converter Evaluation Pack


Patrick
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