Advice for Linkwitz Orion system with Nelson Pass-style pre-amp and amp

[GRollins]

If you're going to build an active crossover, you're going to need isolation between stages, something you can tie a feedback loop around, something to offset insertion losses, and potentially add gain. This isn't all that difficult, conceptually. There have been numerous attempts at discrete opamps here, some more successful than others. You can swipe an existing design from another thread if you don't want to design your own. Better yet, steal the opamp out of Nelson's opamp paper and you're done.
Them what thinks chip opamps are the ticket can flip through a catalog and order in anything they want. I'd suggest something with a JFET input, though.
These days I'm going no gain and no feedback in my mid/upper active crossovers. Complementary JFET followers, self-biasing, used as buffers between filter sections. Works like a charm. You'll lose a smidgen of gain due to followers being less than unity gain and a bit to insertion loss, but it's about as pure and simple as you could ask for. It helps that I'm using first order crossovers for the mids and tweeters. You can cascade first order slopes to make a higher order slope, but it starts getting unwieldy; easier to go ahead and do a single discrete opamp and get it over with.

Grey

[Andersonix]

I asked Siegfried Linkwitz at tonight's lecture, and he has no problem with anybody making any changes or redesigns to the Orion ASP (analog signal processor), as long as it isn't being referred to as 'Orion.' (Would it be stupid to call it diyAurion?)

He also pointed out that his Pluto system (with sub) comes quite close in performance to the Orion, although with slightly shallower soundstage depth (but wider 'sweet spot'). That makes me think Pluto might be the place to start when it comes to bang for the DIY buck.

[rlim]

I would be interested in finding out how the number of gain stages can be reduced. For one, the opamps in unity feedback can be simplified to, say, a follower stage. But that's not exactly reducing the number of gain stages. Perhaps Mr. Pass can shed some light here.

Take SL's functional block diagram of the Orions' ASP as a conceptual study. Things that you see being repeated are the all-pass filter, 24db/oct HP, and 24db/oct LP. From a circuit standpoint, how would you reduce the 2-opamp 24db/oct filter to just one gain stage and still achieve the same response. This would be an interesting exercise, and for discussion purposes, we can just draw the traditional cascaded 12db 2nd-order filter w/2 opamps (low-pass, high-pass doesn't really matter), and see how it gets morphed into a single gain stage. I seem to recall that 3rd order filters can be done with just one gain stage. Just not sure about 4-th order without getting into insertion loss and possibly other issues related to gain and phase.

[JSprague]

Tosh should have naming rights, since it was he who confronted Sig. Bit... How about O'Brian (simplified circutry)ASP. Don't want anyone taking all this too seriously

[GRollins]

I confess that just looking at the "Orion ASP Function block diagram" gives me a case of the heebie-jeebies. So many opamps--and chip opamps, at that--must sum to several hundred transistors...just in the crossover. All told, there's probably a cumulative hundred thousand dB of negative feedback in there. Yikes! That's the very antithesis of the minimalist school of thought.
Yes, I realize that he's got a reason for all the various bits and pieces, but still...I can't help but think that maybe it would be better to mechanically offset the mid/tweeter drivers than to add yet more opamps to an already overly busy circuit.
Just me being silly again. You guys go on with your project.

Grey

[paulb]

For Grey's benefit:

Originally posted by Nelson Pass
...The Orion is a sifficiently good and interesting loudspeaker that it deserves any improvements that can be made in the electronics. Linkwitz appears pretty agnostic about "audiophile" issues in electronics, but then his focus is the speakers. He isn't averse to using "better" active electronics. The opamps in the Orion circuits can easily be replaced with discrete versions, and there may be some opportunities to simplify the system overall - I'll take another look at it.

Originally posted by Nelson Pass
I spent some time reviewing the (possibly earlier version of) electronics for the Orions, and it is clear that you can replace
something like half the gain stages with discrete op amps and buffers and get the same nominal functions.

[SY]

C'mon guys, get serious. This should be done either in the digital domain or with tubes.

Opamps. Sheesh.

[GRollins]

Paul,
I've seen what Nelson said, but I find Linkwitz's attitude strange--he goes to extraordinary lengths to attend to the most minute details in speakers--while compromising all the things he gains by using circuitry that sets his speakers back to the Stone Age. It just strikes me as odd. You would think that if he were that serious about the sound, he'd choose a better approach to all this eq/time domain/shelving/whatnot.

Grey

[apassgear]

Originally posted by SY
C'mon guys, get serious. This should be done either in the digital domain or with tubes.

Opamps. Sheesh.

Or start a new speaker project...

[Raka]

I find this conversation specially interesting, as I'm about to re-think the active filter of my dipole speakers, which are similar to Orion. But before that I have to measure again the drivers, so I have time to study what the alternative could be, alla Pass