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Loudthud
diyAudio Member

Join Date: Nov 2007
Location: Near Dallas Texas USA
Quote:
 Originally Posted by Antoinel My simplistic interpretation of the output stage is: The top FET has a voltage gain of 1 [common drain]. The bottom FET has a gain which is greater than 1 [common source].
Although the output is taken from the source of the upper FET, it is operating in common source mode because the winding driving it gets it's reference (AC wise) from the output (source). Since the windings float AC wise, both top and bottom FETs operate in the same mode. Any distortion caused by non-linearity of the top or bottom FET circuits will affect the output symmetrically causing odd order harmonics.

Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Loudthud Although the output is taken from the source of the upper FET, it is operating in common source mode because the winding driving it gets it's reference (AC wise) from the output (source). Since the windings float AC wise, both top and bottom FETs operate in the same mode. Any distortion caused by non-linearity of the top or bottom FET circuits will affect the output symmetrically causing odd order harmonics.
Thank you Loudthud for your interesting analysis. It, and that of flg earlier now suggest that the upper FET is simply [and only] working as a modulated current source load to the bottom FET which is the [only] voltage gain device. Thus the math expression ZM used earlier relating voltage gain to the [bottom] FET's transconductance and load fits. This working scenario is palatable and digestible. I am happy.

 30th July 2012, 06:22 PM #443 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain yup output Jfet is either plain stupid or just careless - where load is connected ; all he cares/reflects is own internal impedance , as function of G vs. S modulation ; considering this - both Jfets (lower and upper one ) are behaving in identical way ......... correctly speaking - exactly opposite way - meaning - while one is decreasing internal impedance , other one is increasing internal impedance in same amount ; just look at them as on two variable resistors , working unison in opposite directions .......... and you'll forget on all common source/drain/blahblah hogwash (I'm anyway unable to remember meaning of that "common S/D/G" nomenclature .... it just don't blend with my way of thinking ) as remainder - quasi complementary is , by function , same as complementary I'm just (or "just" ) lacking in electronic vocabulary to express that __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM Last edited by Zen Mod; 30th July 2012 at 06:30 PM.
Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Zen Mod yup output Jfet is either plain stupid or just careless - where load is connected ; all he cares/reflects is own internal impedance , as function of G vs. S modulation ; considering this - both Jfets (lower and upper one ) are behaving in identical way as remainder - quasi complementary is , by function , same as complementary I'm just (or "just" ) lacking in electronic vocabulary to express that
Thank you ZM. It all coming together.

 30th July 2012, 06:26 PM #445 flg   diyAudio Member     Join Date: Jul 2005 Location: North East I thought ZM's math was regarding the reflected source impeadance seen by the output FETs looking back into the transformer? Which I thought to be about 35 ohms or so from the buffer x (the turns ratio) ^2 (1) = 35 ohms not 75? The xfrmr and the FETs probably like that? If you are going after some gain in the xfrmr, say 1:5.6, that would be 30 X (5.6^2) = 168 ohms. Now you are starting to see some source impeadance issues but, not really enough to worry about. This was all predicated on the fact that I was thinking there was something like a B1 arrangement on the input and I thought that would be about 35 ohms. I't not. It's a complementary buffer. So whats the output impeadance of that? 17 ohms? __________________ "It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.
 30th July 2012, 06:31 PM #446 Zen Mod   Official Court Jester diyAudio Member     Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain @ Antoinel ........ blahblah ......... serve and protect edited few lines above __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM
Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by flg I thought ZM's math was regarding the reflected source impeadance seen by the output FETs looking back into the transformer?
Sorry for injecting this confusion. ZM showed a thread even earlier than the one pertaining to the transformer [above] showing the relationship between the gain of a FET and its parameters plus load resistance etc. [e.g for for F5].

Zen Mod
Official Court Jester
diyAudio Member

Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
Quote:
 Originally Posted by flg I thought,,,,,,,,,,
take it easy ;

what's output impedance of sole (say that load up is plain CCS ) buffer 2SJ74 ?

it's 1/S+Rs

what's load impedance of sole (say that load down is plain CCS) buffer 2SK170?

it's 1/S+Rs

so - when you have those two together , as complementary buffer - where each one is CCS to other one , you have output impedance as (1/S+Rs // 1/S+Rs) = (1/S+Rs)/2 , if we assume that S of both are ~ same

so - if you have , say , 50 Ohms of output impedance of buffer (lazy and don't remember S of sissy Toshiba's) , when output current capability is divided to 2 secondaries , it's logical that each secondary is seeing double that - 100 Ohms
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

Last edited by Zen Mod; 30th July 2012 at 06:54 PM. Reason: ooked again what's up and what's down

Antoinel
diyAudio Member

Join Date: Jan 2012
Location: Pennsylvania
Quote:
 Originally Posted by Zen Mod @ Antoinel ........ blahblah ......... serve and protect edited few lines above
ZM: One liner replies may not be enough to teach DIYers and/or drive your point. Sometimes, the saying that Brevity is the soul of wit does not work well in/for technical matters. A clear math equation [like you showed earlier] may not cut it either. You pack a lot of technical/technology know-how. So please, be generous with your explanations; write, and write some more until there is no more for you to teach. You and us will feel enriched and satisfied in the end.

 30th July 2012, 06:52 PM #450 flg   diyAudio Member     Join Date: Jul 2005 Location: North East I would think it is logical to look at 1 secondary and say 50 ohms (1:1+1) Or the other. But a 1:2 connection (both is series) is 200 ohms??? I guess now and then, now being now, other's are dumber than ZM __________________ "It was the perfect high end audio product: Exotic, inefficient, expensive, unavailable, and toxic." N.P.

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