Moderate feedback can sound great but generous ?
Ok is Papa
that say is part of topology
From BAF 2015 diy amp with IXFN Schade 50 in single-ended have DF= 12.5 at mid tap.
Negative feedback= 18 open loop= 38dB.
What is need for DF = 700 ?
ps: from specifications DF=200
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From BAF 2015 diy amp with IXFN Schade 50 in single-ended have DF= 12.5 at mid tap.
Negative feedback= 18 open loop= 38dB.
What is need for DF = 700 ?
ps: from specifications DF=200
That's a completely different amp and driven mostly single ended. The damping factor can be changed significantly with an easy tweak.
Whether it's 200 or 700, the audible difference between the two values in isolation is 3/5 multiplied by a number near zero. There are more interesting features with this amp. For me personally it's way down on my list of things to worry about.
I'm a little different, I'm not into the cloning thing, I like to get ideas from Papa and then try to kick start the right brain into action (it seems to start operating after a quality dump on the toilet.) No sh1t.
Without degeneration........
Could be complementary Jfet folded cascode for first stage. All voltage gain done by jfets. (like LSK preamp)
2nd stage toshiba mosfets connected like buffer/folower
3rd stage IXYS 40P50 and 48N60 Buffer/folower. (Patrick recommended)
According to Ixys datasheet @2A bias they have about 10S, two devices conducting in same time making 20S. Thats 50miliOhms output impedance without feedback. Then we need factor 5 feedback or 14dB to make that famous DF.
What do you think guys?
3rd stage IXYS 40P50 and 48N60 Buffer/folower. (Patrick recommended)
Patrick recommended 44N80P, I recommended 48N60P, pick what you like.
Papa may recommend something different but the examples above should be good enough.
That is a possibility.
Could be complementary Jfet folded cascode for first stage. All voltage gain done by jfets. (like LSK preamp)
I use to be a folded cascode worshipper for a long time, but when I compared the performance to Papa's BA3 and Sony front end, it wasn't really better (from memory) just a different way to skin the cat, and Papa's circuits have nice usable tweaks which I like.
I am in bed with the flu.
Mostly you are wrong. The Villars photo showed a mock up of the circuit
I used as an illustration of cascoded performance that I showed at BAF,
and is not related to the XA25.
...
From the description, I would guess that the XA25 might be essentially 1 phase of an XA30.8 with some PCF (positive current feedback) tweaks to get the high damping factor. The power dissipation and other specifications are consistent with this conjecture.
After looking more closely at the picture, I modify my last post to sugggest the output stage is using a complementary pair of "hocky-pucks". The XA25 might use a 2-stage front end very similar to 1 phase of the XA.8 series front end with cascode PCF. OTOH, the front end might use PFC more like that of the F7. I would vote for the former.
One other possibility coming in my mind reading the advertisement text is a circuit similar to the HPA int the front end, without IC of course, means J-Fet inputstage+Toshiba SK/SJ output tbuffer. So a very low output impedance could drive the common source output stage with the high input capacities.
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I think the text speaks of no degeneration, means for instance no source resistors in the outputstage similar to F6.
No "normal" feedback is not mentioned. I think there is feedback.
Current feedback is even mentioned!
O.k. I should read more carefully, you mention no feedback in the Frontend.
No "normal" feedback is not mentioned. I think there is feedback.
Current feedback is even mentioned!
O.k. I should read more carefully, you mention no feedback in the Frontend.
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Just barely, thank you.
I dropped a lot of weight, but seem to have avoided a secondary infection,
so I'll be fine.