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Old 11th January 2012, 11:21 PM   #4271
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You can put coils in the gates and then 8 is the limit. I even managed a prototype with 13 Fets at the input. Sometimes it likes to work, sometimes not.
Ricardo, the "Loesch" circuit has the Fet at the bottom in the cathode chain of the ( top ) tube. That way the noise of the tube is not correlated with the noise in the Fet, just as in the Simplistic Salas. The top BC550 has 140 Ohm Rbe`, still it does not contribute much to the total noise of the circuit. The BC550 is common base so it only amplifies the voltage and not the current.
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Old 11th January 2012, 11:31 PM   #4272
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Joachim
Tanks for that SCH
I use a similar MC front end on my Salas Simplistic.

Just a couple more stages with J fets not Valves.

Suply of inversed polarity as I use 4 2SK170.

There are a couple of things In your drawing that I will try up
I have 33 Homs as source resistors and ommited the 25000U capacitor.
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Old 12th January 2012, 03:34 AM   #4273
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Bksabath, the Simplistic is not a folded cascode but a series cascode so schematic 4268 is not directly comparable. The Simplistic could be transferred into a folded cascode though.
33 Ohm as source resistor in an MC stage is rather high.
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Old 12th January 2012, 06:21 AM   #4274
gk7 is offline gk7
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Borbely did a cascoded FET/Tube phono input in 1997.
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Old 12th January 2012, 06:29 AM   #4275
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And Sonic Frontiers, and Manley, and Melos, and many Others

Regards,
Reinhard
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Old 12th January 2012, 06:33 AM   #4276
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The question is who did it first ?
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Old 12th January 2012, 07:59 AM   #4277
gk7 is offline gk7
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Probably HP or Tektronix (although not for a phono stage of course).
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Old 12th January 2012, 10:06 AM   #4278
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Just for completeness. This is a clone of the Arthur Loesch preamp.
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Old 12th January 2012, 10:29 AM   #4279
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Default Earliest hybrid cascode?

In
http://www.audiodesignguide.com/ba/prepsc.jpg
you can find downpage "Preampl. zero feedback by Bartolomeo Aloia" .
The diagram http://www.audiodesignguide.com/ba/prells.jpg
however is not easy to read. It is pre 1988.
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Old 12th January 2012, 11:06 AM   #4280
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Yes, Bartolomeo Aloia did BJT-tube cascodes and also Fet-tube cacodes, mostly with 3 elements in series like in your link. He called that Totem-Pole.
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