I……... Not positive those are opto's, but very possible…...
on the website…..
"New gain stages with auto bias…."
https://passlabs.com/products/preamplifiers/xs-preamps/xs-preamp
😀
You missed ceramic circuit board.
😎
I will use ceramic saucer instead…..😀😀

With this, I tihnk the old school Laterals used by Patrick in his pre might be real nice. Dont underestimate a balanced version of the LSk preamp. Both are bruisers and if the SE version of the folded is any indication, it is a very musical topology. Neither are lacking in my experience.
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I want to make my personal contribution to common confusion….
What do we see on picture?:
Rather close neighborhood of optocouplers and servo loop double OPV (OPA2604?) let me assume they work together.
On board they are located on negative supply side, and below SL-opamp we see 2 resistors (R5&R6) ea. 453E. These resistors are probably collector resistors of lower cascode.
Now we know from UGS-modules that absolute offset is adjusted on neg. supply side; normally there is a single trimpot between joining collector resistors (of lower cascode) and neg. supply.
Could it not be that - instead of this trimpot - Wayne has incorporated both opto couplers as SL-controlled variable resistors?
On positive supply side we see a trimpot (50E) and close to this 2 resistors (R15&R17) ea. 562E. I assume that these resistors are collector resistors of upper cascode and this trimpot is still responsible for adjustment of differential offset. May be this trimpot is still needed because regulation headroom of SL should be kept (or is) small.
And we also see that many resistor values have been decreased, e.g. only 75E as source resistors for TO220-mosfets, 475E as their gate stoppers, 22E as source resistors for input-jfets, cascodes are referenced with 10k/4k75, and collector resistors of casodes are now 562E & 50E-trimpot or 453E & optocoupler.
Interestingly also that all resistors seem to be European and not brown colored US types.
What do we see on picture?:
Rather close neighborhood of optocouplers and servo loop double OPV (OPA2604?) let me assume they work together.
On board they are located on negative supply side, and below SL-opamp we see 2 resistors (R5&R6) ea. 453E. These resistors are probably collector resistors of lower cascode.
Now we know from UGS-modules that absolute offset is adjusted on neg. supply side; normally there is a single trimpot between joining collector resistors (of lower cascode) and neg. supply.
Could it not be that - instead of this trimpot - Wayne has incorporated both opto couplers as SL-controlled variable resistors?
On positive supply side we see a trimpot (50E) and close to this 2 resistors (R15&R17) ea. 562E. I assume that these resistors are collector resistors of upper cascode and this trimpot is still responsible for adjustment of differential offset. May be this trimpot is still needed because regulation headroom of SL should be kept (or is) small.
And we also see that many resistor values have been decreased, e.g. only 75E as source resistors for TO220-mosfets, 475E as their gate stoppers, 22E as source resistors for input-jfets, cascodes are referenced with 10k/4k75, and collector resistors of casodes are now 562E & 50E-trimpot or 453E & optocoupler.
Interestingly also that all resistors seem to be European and not brown colored US types.
I would accept a full XP30 schematic and be happy to let you guys fight over Xs. Fortunately I will not need gain from pre.
How hard would it be to apply a servo to the ba3fe? It seems to be a nice way to eliminate output caps but isn't used very much around here.
Interesting thoughts. Not positive those are opto's, but very possible. Makes my head hurt to think about. Servo is probably both simple and another point o manipulation. Unity gain FE could setup interesting output. Transformerish. If your hallucinating, I'm the walking dead.🙂
Yes those are Opto's : L 1205 4N35...and the OA is OPA2604AP....have a hires photo.😎
That's a really nice op amp. Wonder if the whole things is run through it an the other parts are misdirection
.

naah
entire gain is made with optocouplers
everything else , including OP , is there just for misdirection
entire gain is made with optocouplers
everything else , including OP , is there just for misdirection

Lost me at double servo loop, if not earlier. Soudns like something out of a dc motor controller app. XP30 was so well reviewed, I am surprised he didnt sit ont his for a while. Wayne and Nelson are productive, arent they.
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It is a high bandwidth design, I fI had to guess, and is probably susceptible to instablilty if not laid out correctly. I would imagine the caps on the input are to limit bandwidth, but they could be there to eliminate DC interaction with the FE. Seems unlikely with the servos, but could be wrong.
naah
entire gain is made with optocouplers
everything else , including OP , is there just for misdirection![]()
That reminds me of a film that came out a few years ago with John Travolta....Maybe whole top circuit is misdirection....real one is below😀😎
Lost me at double servo loop, if not earlier. Soudns like something out of a dc motor controller app. XP30 was so well reviewed, I am surprised he didnt sit ont his for a while. Wayne and Nelson are productive, arent they.
Methinks Wayne and Nelson wanted to give Ayre and such a run for their money.😎
Show them who's boss. 😎
How hard would it be to apply a servo to the ba3fe? It seems to be a nice way to eliminate output caps but isn't used very much around here.
The real question is which is worse? The Servo or the Cap?
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