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Some other Source Follower Configurations
Some other Source Follower Configurations
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Old 27th August 2008, 04:25 PM   #21
lineup is offline lineup  Sweden
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generally, using current source instead of resistor
will measure better = lower THD
and lower 2nd and often less other lower order harmonics

Now, it has been told many times in different amplifiers
that resistor loaded can give a more pleasing sound (at resonable low 2nd, of course. Not like 1% !!!)
... even if the hi-fi factor in terms of Lowest THD
is not as high as for current sources.

For example Hugh Dean AKSA 55 uses resistor loading of input LTP + good old bootstrapping.
Instead of 2 CCS current sources in those places.
At least if I have been informed correctly.

Lineup
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Old 27th August 2008, 06:29 PM   #22
EUVL is offline EUVL  Europe
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> is the Taylor CS possible with sureaMBs version of the Dao?

In theory yes. The circuit will work.

Read Nelson's article on Zen V9 regarding triode loadline, and you will understand why I cascode the way I did on the original DAO circuit, using MOSFETs.

No idea whether you get the same triode characteristics with a LU1014 Cascode and if so at what bias. Perhaps someone can Spice it and let us all know.



Patrick

PS I am not claiming that the LU1014 cascode is better or worse. I just don't know, not having tested it on breadboard.
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Old 27th August 2008, 06:57 PM   #23
audiotux is offline audiotux  Germany
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thanx Patrick for the answer .
the question was beside triode loadline ,
only if its possible or not , not
claiming its better than the orginal DAO .

Jürgen
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Old 27th August 2008, 08:03 PM   #24
EUVL is offline EUVL  Europe
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Perhaps a few more remarks on the same topic.

To use the LU1014 as the cascode device, you are dissipating something like 320mA x 20V in that device alone, which equals 6.4W. It will probably survive, but will run much hotter than the gain device itself. You might wish to reduce the rail voltages to say 12V.

In addition to that, the cascode device will have a different curve than the gain device.

The graph shown here is a LU1014 measured with 1R source resistor and 12V applied. This is likely to be how the cascode device behaves.


Patrick
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File Type: jpg lu1014 no cascode vds 12v.jpg (10.3 KB, 4514 views)
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Old 27th August 2008, 08:06 PM   #25
EUVL is offline EUVL  Europe
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As you would expect, I have played with the idea of a simpler Cascode than enhancement mode mosfets as cascode.

This is the curve of a LU1014 with a DN2540 depletion mosfet and 1R degeneration. The gate of the DN2540 is connected to the lower end of the 1R resistor.

The DN2540 has a TO-220 package, making heat dissipation a bit more convenient.
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File Type: jpg lu1014 w dn2540 cascode 1r degeneration.jpg (9.2 KB, 4478 views)
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Old 27th August 2008, 08:09 PM   #26
EUVL is offline EUVL  Europe
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And finally, this is what I use myself -- a LU1014 with 2SK2013 cascode and 3R degeneration.

I am sure it is obvious which graph is more linear around 250mA.
Note that the X-axis is Vgs, i.e. the graphs are showing the characteristics of the gain device alone, and exclusing the degeneration resistor.


Patrick
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File Type: jpg lu1014 w 2sk2013 cascode 3r degeneration.jpg (9.4 KB, 3956 views)
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Old 27th August 2008, 08:15 PM   #27
lineup is offline lineup  Sweden
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nice comparison

the last attachment is the one to prefer
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Old 28th August 2008, 07:13 AM   #28
h_a is offline h_a  Europe
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Hi Patrick,

thanks a lot for the comparisons - very interesting und it's always fun to see some real numbers

So you dropped your usual 2SK1529 for the 2SK2013? It's a pity these are hard to get. Do you remember maybe wether there was a significant improvement over the 2SK1529?

Have fun, Hannes
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Old 28th August 2008, 09:41 AM   #29
Tom2 is offline Tom2  United States
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Patrick,

How about this circuit based on
fig 1 in your article. Just an idea.

Tom
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Old 28th August 2008, 02:10 PM   #30
lineup is offline lineup  Sweden
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one variant of this idea of yours, Tom2
has been used in Forssell All fet Op preamp
See here:
http://www.forsselltech.com/download...et%20Opamp.PDF

Forssell is most know for something with
HIGHEST POSSIBLE hi-fi TURNTABLE arm movement = Air born travel

It is also very well worth to look into Forssell Products:
http://www.forsselltech.com/products.shtml
Quote:

Rack Mounted Products
JMP-6 Six Channel Mic Preamp
SMP-2 Discrete JFET Mic Preamp New
FetCode Tube Mic Preamp
CS-1 Channel Strip
NSEQ-F Upgrade PCB

Class A Discrete JFET Modules
JFET-992 Discrete Opamp
JFET-993 Discrete Opamp
DLR-1 Differential Line Receiver
JMP-1 Transformerless Mic Preamp
Unity Gain Buffer Module
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