Pass X2 and negative feedback

[BRunenr]

Is the first version build entirely without negative feedback as Balanced Line Stage of SOZ, or is small amount of local feedback used, as in Aleph P 1.7?

Sorry for my bad english.

 

[GRollins]

By definition, the X topology is a feedback system. If you remove the feedback, it isn't "X" anymore.

Grey

 

[Petter]

I would not know, but my guess is that is uses the X-topology which relies on feedback.

Usually you can read up on such things in user manuals from www.passlabs.com

Petter

 

[BRunenr]

In user manual mr. Pass writes: "The first version used diferential Mosfet circuits operated without feedback." But I am unsure, if it means entirely without feedback or only without global feedback as in AlephP 1.7.

 

[Nelson Pass]

When I say "without feedback" I generally mean
no feedback loop, just degeneration if that.

When I say "no global feedback" I mean no loop from
input to output, although there might be local loops.

 

[BRunenr]

Thanks for explanation mr. Pass. I was interested in Aleph P circuit evolution.

 

[GRollins]

Apologies...I tend to think of X and "Super Symmetry" as synonyms, and since X is easier to type (I was born lazy, then had a relapse), I tend to use the one letter when possible.
Silly me.

Grey

 

[AudioFreak]

Grey that's why it was shortened to Su-Sy

Su-Sy is not a destructive form of feedback and should not be viewed in the same light as negative feedback.

 

[GRollins]

By my reckoning, the letter X only requires one keystroke, whereas Su-Sy takes five.
Ma pore widdle fingers can't take all tha' extra poundin'...

Grey

(Still doesn't excuse me for being mentally sloppy. Seems I'm missing a lot of details this week. I'll try to get some sleep and be back on track tomorrow...or the next day...or the next...)

 

[Petter]

Good and bad feedback

There is no such thing as good and bad feedback.

The X-circuits in the big power amps (which only licensees of Nelson Pass can use provided patent holds and no workaround can be found) employ local feedback to around a single voltage gain stage. This is very similar to basic op-amp theory (but most op-amps have multiple internal stages, and feedback around these have become universally detested in audio).

Feedback is a method to reduce noise etc. Degeneration is generally considered the "least harmful". The next level, I will call feedback around single loop for lack of a better name, and this is the method used in the X-series power amps.

Feedback free amplifiers are like Yeti's -- many have seen them, but nobody can produce one.

Petter

 

[Nelson Pass]

Actually, they are very easy to produce, but their sound
is not that popular commercially.