O.H. Schade(1938) meets MOSFET - Page 5 - diyAudio
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Old 8th November 2012, 01:15 AM   #41
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Quote:
Originally Posted by avincenty View Post
Just for fun, I traced some curves for the NTE451 JFET that show the effect of parallel feedback. It indeed works as advertized (on the curve tracer).
A characteristic of real triodes I do not see in any of those curve sets:
Curves on the right side tend to "lean over to the right", is not happening.

Smoking Amp had once hypothesized that a real triode is many in parallel
with slightly different parameters, especially cutoff. So a triode is average
of a set that diminishes in size. Skewing the average, "leaning to the right".

I could graph a pretty realistic lean out of 4 carefully selected non-leaning
Schade curves. It doesn't take an infinitely huge set to find some lean.

Unless your load line is all over the map (like maybe a real loudspeaker),
I don't think you will hear much lean-over driving a well behaved resistor.
It might only make sense in an output stage for mimicry of triode sound.

How much you want to nit-pick how a solid state triode should behave
like the real thing, or like an ideal thing? I found math of a diminishing
set interesting, no intentions of building it...

Last edited by kenpeter; 8th November 2012 at 01:28 AM.
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Old 8th November 2012, 01:48 AM   #42
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You don't find so much lean in triodes of flat parallel construction.

But in sloppy triode where plate wraps round shape of convenience,
you got lots of variation in the internal set. You get a lean-over...

Unlike perfectly Schaded fake curves, they diverge at higher current
(or crunch together at lower current) and not at all parallel anywhere.

This 12AU7 shows some lean-over...
Attached Images
File Type: gif 12AU7_Lean.gif (89.7 KB, 174 views)

Last edited by kenpeter; 8th November 2012 at 01:52 AM.
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Old 8th November 2012, 02:19 AM   #43
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Not all triodes have a pronounced lean. Still, a schaded jfet is not a triode
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Old 11th November 2012, 06:56 PM   #44
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avincenty and kenpeter: Thank you for your valuable comments. You are in touch with the various approaches of Audio Engineers, and DIYers to coerce electrons moving in solid state devices to mimick those in triodes. Fortunately, the power of the natural law "Structure -Property" Relationships always dominates as kenpeter alluded to.

Please go to post # 58 in the Thread [Pass labs Forum] by wrenchone entitled partly" L'Fake .... " In it I describe a schematic of a working amp [also attached here] which [IMHO] satisfies the requirements of Schade feedback; except that I used a bjt current source amp instead of a power FET. I am not making any claims about it sounding like a triode, a SIT or other device. Just sharing information; which I hope maybe useful to you.
Brgds.
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