Most Greedy Boy, of them all... or (there is no) DEFiSIT of Papa's Koans

[aoc]

Same for Papa's Wakoo DEFiSIT , only this time smaller voltage swing possible , 16Vpp input signal;

red - current through 8R load
green - current through mosfet (IRFP9140)
red - current through PapaSit

And what happened to blue?

 

[Zen Mod]

(typo , what else ....... red, green ,blue)

 

[Nelson Pass]

Perhaps you would be better off degenerating the P channel part.

 

[Zen Mod]

tried several days ago , nope

10 times higher THD , same spectra

 

[indra1]

I'm speculating here. Papa's comment could also imply a warning on stability which could be rock solid on your build with Koan sized heatsink and sane load but potentially blow up on some situations?

 

[Zen Mod]

I'm usually that one , giving Papa's comments one zillion and 15 possible meanings .

 

[Zen Mod]

interesting to mention - while both DEFiSIT and SEF amps are showing wakoo behavior , regarding currents through outputs - "normal" mosfet is working against both other output and load (other output subtracting current , up to clipping level , where it starts adding) .......... LuDEF amp is functioning in more common way - upper and lower output are working together , where their two smaller currents are summing in greatest current through load

now for that ......... I wish I was a fly on the wall , through time when Papa stumbled on DEFiSIT idea ..... luckily flies being creatures laughing silently

 

[indra1]

I learn a bit by plugging different load values (2, 4, 6, 16, 32, 600 ohms) and various p channels including 9140, single and double die laterals. Warning, hold your laughter down to avoid serious stomach cramp, some combinations exhibit really nice crap.
Previous experience with Sziklai output pairs showed that it is easy to get either a real nice, stable and super low distortion output stage or a real nice, stable and super low distortion oscillator. Something somebody somewhere relate to something usually consumed as dessert.

 

[Zen Mod]

I confess ....... I even tried Darlingtons yesterday .......

talking about sims , of course

 

[Nelson Pass]

It appears you have discovered the reason why Schade feedback is not
so popular for followers...

Going back to your schematic of post #193, we see that positive voltage at
the output increases the voltage across R6, driving the P channel output
Mosfet harder, so that it acts contrary to the work the N channel is trying
to perform, even without a load.

For this to work, the Schade feedback needs to be seen equally by both
Gates, an exercise I leave to your imagination.

 

[Zen Mod]

it is for some nice and lazy discussion - is it feedback , or "just" altering transfer characteristic of part itself ..... I mean - all the way from original papers of Herr Schade

anyway - I'm not loosing my sleep over anything more, regarding behavior of circuit - any possible tweaking reserved strictly to bench with real parts

what I'm finding most important is that I stumbled on exactly same behavior of output devices as you have with DEFiSIT



to repeat :

Same for Papa's Wakoo DEFiSIT , only this time smaller voltage swing possible , 16Vpp input signal;

red - current through 8R load
green - current through mosfet (IRFP9140)
blue - current through PapaSit


edit : easy to confirm on one-rail PSU - current modulation of PSU is greater than current ending through load

 

[Nelson Pass]

Assuming no Schade resistors in circuit, it looks like Mosfet has about 3 times
the transconductance of the SIT. SIT is roughly 1 S, so P channel Mosfet
is maybe 3 S.

Maybe you put some Schade resistance on SIT and see what happens.....



Or not.....

 

[Zen Mod]

Dunno Pa , just trying to translate what sim is showing

I'm pretty happy with DEFiSIT sound and I'm not so sure when I will have opportunity to steal it from living room (and measure some) - right now whoomping and roaring LOTR 3 Extended




edit : worth mentioning

- LuDEF amp is not showing that behavior , it's behaving .........

-SJDP DEF iteration is behaving

-last iteration or 2SK180 DEFiSIT is defisitly misbehaving

-Real McKay DEFiSIT is defisitly etalon of misbehaving

 

[Zen Mod]

.........

Maybe you put some Schade resistance on SIT and see what happens.....



.........

tried that sim and - as expected ........ in case of Part which is having already Schade effect intrinsically (Pass SIT-1) , if we connect same net as done to mosfet (10k-ish D to G and 1k-ish series to gate) , effect is Anti-Schade - increasing xconductance of part

so , further "Schade-ing" of triode-like part is possible through already known and boring methods - degeneration and cascode modulation




damn , I'm again doing all the work here ........... when I'm going to see my Glory Days ?

 

[indra1]

........... when I'm going to see my Glory Days ? ....

You can start by being a founder an audio company with catchy name like Iron Zen Lab or Babel Mod Audio. Being curator of a disposal facility is less likely to attract attention of reviewers.

 

[Zen Mod]

tnx to imdra , we came to (it seems) glorious idea of Iq sensing , with handy Hall effect IC

it is ACS723 family of chips

last few nights I was playing with sims and came to few conclusions :

-Babelfishing XA25 - swell , can't talk ;

-M2 iteration , called by Mighty Moi M25 .... :
-8Vpp/8R - better THD than M2
-38Vpp/8R - even more better than M2
-40Vpp/8R - wakoo more better than M2
-in heavier loads ( 4R, 2R) difference even greater in favor of M25

.......... now , none of Poor Greedy Boy DEFiSIT substitutions* is not having any benefit of using Hall IC, simply because I needed source resistor in best position , as tool of shaping THD spectra ..... so nothing easier than to implement direct optocoupler biasing scheme

*means LuDEF amp, SEF amp ; now I realized that I didn't check thoroughly SJDP DEF amp and 2SK180 DEFiSIT

will do that later .....

 

[needtubes]

Do you intend to build a prototype amp using the ASC723? That is an intriguing circuit.

 

[Zen Mod]

yup

though ..... I meant to ask indra - did he found some bigger cased buggers , with same characteristics .........

preparing one short list of special parts , to order ...... none of them being in regular stock of my usual vendors

as soon I finish that list , with ACS buggers too , I can start count 2 or 3 weeks to delivery

 

[Zen Mod]

no 2SK180 DEF , no SJDP DEF, with ACS chips

btw ....... made sanity (sim) check of 2SK180 based DEFiSIT , made with ACS chips

nada - not big enough (voltage) window between gates of 2SK180 and IRFP9xxx to keep current in sane bracket

same case with SJDP

so , conclusion - in this very moment , ACS chips are extremely interesting for wakoo XA25 approach - pair of mosfets sans source resistors , be it oldies or pucks

I really hope reality will follow simulation

 

[indra1]

... did he found some bigger cased buggers , with same characteristics .........

Sorry, have not found any, but I think some soic-8 to dip adapters like these and low temperature solder paste like these should help.