O.H. Schade(1938) meets MOSFET

revintage · 14th May 2009, 08:37 AM

Lately there has been quite a few threads covering the work of OH Schade 1938, http://www.clarisonus.com/Archives/T...er%20Tubes.pdf . He showed how a tetrode could get triode characteristics with the help of what he called "inverse-voltage feedback". While working as a triode the efficiency of the tetrode was still kept.

On the left is a tube SE in accordance to his suggestion. It has the same output impedance and distortion characteristics as if it had been triode-strapped but twice the output power! On the right the output device is substituted by a common MOSFET that according to Schades suggestion is feedbacked ca 20dB.

Seeing any similarity with a Zen

?

By the use of an IT there is a better chance of getting much better HF-bandwith. The example sims with a -3dB point in the region of 100kHz.

revintage · 14th May 2009, 08:41 AM

A MOSFET has pentode-like characteristics.

With shunt-feedback(inverse-voltage feedback) applied they change to triode-like.

But this old news for the most of you

!

Nelson Pass · 14th May 2009, 03:19 PM

Very Excellent.

revintage · 15th May 2009, 10:51 AM

So what happens if we adapt what Schade taught us to a JFET as buffer?

Works like wonders

!

Zout below 200ohms, together with low THD and acceptable bandwith (-3dB at well over 200kHz). Zin chosen to 10kohm. With 22kohm/91k bandwith is 100kHz.

But don´t try to a volume-pot at the input! Must be fed from a lowZ source.

MRupp · 15th May 2009, 11:06 AM

Very interesting buffer concept, but off course it inverts phase, so where you need this ... and it also looks pretty similar to the buffer in the alephono MC stage

revintage · 15th May 2009, 11:18 AM

Quote:

but off course it inverts phase

Is this a problem? If so, just shift plus and minus on your speaker terminals

.

MRupp · 15th May 2009, 12:21 PM

Not a problem at all (as long as you keep track of the number of times you change phase in your system and do not switch to and fro inverting / non-inverting stages), and it should be useful where you have a requirement to revert phase ....

Nelson Pass · 15th May 2009, 06:49 PM

Quote:

Originally posted by revintage
Zout below 200ohms, together with low THD and acceptable bandwith (-3dB at well over 200kHz). Zin chosen to 10kohm. With 22kohm/91k bandwith is 100kHz.

But don´t try to a volume-pot at the input! Must be fed from a lowZ source.

You don't need R10. This circuit works to provide a virtual ground at the
Gate of the JFET, so the input Z is 10 Kohm as shown. Actually you can drive
it with a range of source impedances, and adding a pot as high as 25K should
work fine.

kenpeter · 16th May 2009, 12:02 AM

HighZ lowZ, don't matter. As long as its stable with frequency.
It just becomes part of the feedback divider...

There's a nice photo of a curve trace for a similar circuit:
http://www.radiomuseum.org/forum/the...ate_triode.htm

The only difference, Trioderizer gate is battery biased.
A battery could last a long time, if its only biasing gate...
I imagine you would want to bypass with a good cap???

something weird with that link. You have to find it the hard way...

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The Trioderizer - a solid state triode

chinsettawong · 16th May 2009, 03:40 AM

Very interesting!

Wachara C.

15th May 2009, 11:06 AM	#5
MRupp diyAudio Member Join Date: Dec 2003 Location: Frankfurt area	Very interesting buffer concept, but off course it inverts phase, so where you need this ... and it also looks pretty similar to the buffer in the alephono MC stage __________________ Martin Rupp

15th May 2009, 12:21 PM	#7
MRupp diyAudio Member Join Date: Dec 2003 Location: Frankfurt area	Not a problem at all (as long as you keep track of the number of times you change phase in your system and do not switch to and fro inverting / non-inverting stages), and it should be useful where you have a requirement to revert phase .... __________________ Martin Rupp

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14th May 2009, 03:19 PM	#3
Nelson Pass The one and only Join Date: Mar 2001	Very Excellent.

16th May 2009, 12:02 AM	#9
kenpeter diyAudio Member Join Date: Nov 2007 Location: Dallas	HighZ lowZ, don't matter. As long as its stable with frequency. It just becomes part of the feedback divider... There's a nice photo of a curve trace for a similar circuit: http://www.radiomuseum.org/forum/the...ate_triode.htm The only difference, Trioderizer gate is battery biased. A battery could last a long time, if its only biasing gate... I imagine you would want to bypass with a good cap??? something weird with that link. You have to find it the hard way... Forum » Technique, Repair, Restaurtion, Home construction ** » Home construction and general radio technique » The Trioderizer - a solid state triode

16th May 2009, 03:40 AM	#10
chinsettawong diyAudio Member Join Date: Jun 2006	Very interesting! Wachara C.