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Old 15th November 2007, 05:34 PM   #31
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This whole thing goes back to the project I did with Mobile
Fidelity back in the early 90's. The cutterhead drive system
had a massive amount of electronics in the signal path for
the purpose of gain, equalization, and feedback. The op amps
dated back to the 60's and early 70's, and there was an
isolated piece of electronics for every function, much like SL's
modular circuits. The advantage of this of course is that you can
play around with these in isolation from each other. The
disadvantage is that you end up running the signal through a
lot of op amps - in the case of the cutterhead system, maybe 10
or so.

What I did with Mofi was to integrate all these things around
a single op amp, the LT1028. To be sure, all the values of
every part were dependent on the others, and it was not a
trivial task, but I was able to accurately reproduce the response
curves of the original circuits.

We would look to do the same with the response of SL's Orion
circuitry with fewer discrete stages.

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Old 15th November 2007, 05:44 PM   #32
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Lacking a detailed schematic I can only make educated guesses about what he's doing in the circuit, but it seems that he's using electronics to do things that I would attend to in the physical design of the speaker. His background is in electronics; I'd lay odds that he's not particularly adept at woodworking and seeks to overcome that electronically.

Grey
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Old 15th November 2007, 10:33 PM   #33
Variac is offline Variac  United States
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http://www.linkwitzlab.com/xo_eq.htm

The Phoenix is pretty much the same crossover he says..
scroll down a bit..
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Old 15th November 2007, 11:05 PM   #34
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Nelson,
Would it be possible to show us what you did with the Mofi 1-opamp circuit? It would help to generate some ideas here. I am not creative enough to figure out how one can combine the response of say an LR4 low-pass with an LR4 high-pass into a single opamp, or combining a notch filter with an all-pass. Hmm, maybe this in itself can be an article that you can post at your website?

Thanks.
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Old 16th November 2007, 02:16 PM   #35
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He's got a stage in there to roll it off at 140kHz? Okay, that one can go.
Jeez, he uses chip amps for his speakers and recommends anything from Doug Self to Rowland for customers. I guess if you put a signal in and one comes out, he's happy. Somehow, I had the impression that he was more performance oriented. It appears I was wrong. To be honest, the more I learn about his views the more I find myself wondering about the speakers.

Grey
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Old 16th November 2007, 02:51 PM   #36
Raka is offline Raka  Europe
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Grollins, so I now know that you haven't heard the Orions yet. Me neither, but my speakers are similars to his, with cheaper mids, and I have to say that are excelent to my ears.

Let's focus on the electronics, as I'm sure that there are a lot of people listening to this thread, really excited with the possibility of improving an already really good sound. I would be really happy if I manage to change my filter to a better one. That would be great.


What would you choose instead of the gain module in the ASP?

The active filter of the JohnK dipoles has less active stages, and he's always trying to save on that (placing the poles in the right place, for instance)
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Old 16th November 2007, 03:27 PM   #37
eLarson is offline eLarson  United States
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I think Mr. Linkwitz is of the "speakers-matter-most" school.
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Old 16th November 2007, 04:22 PM   #38
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Quote:
Originally posted by Raka


Let's focus on the electronics...


Precisely. You'll note that I have not said one word about his choice of drivers or cabinet design.
Let me put it this way...if you heard people exclaiming about the steak at a particular restaurant you might become interested. As a red meat sort of fellow myself, I know I would. Now, let's say that before actually eating at this restaurant, you peeked into the kitchen and saw frozen chicken nuggets being microwaved, instant coffee instead of ground beans, and dried soup mix. These things are not necessarily inappropriate for a chain fast food restaurant, but this particular restaurant is being portrayed as an upper class dining establishment. Hmmm... Does it necessarily mean that the steak isn't up to snuff? No. Perhaps the restaurant has a particular cook who handles nothing but steaks; who goes to the local butcher every morning and hand selects each steak that he will be cooking that evening; who then spritzes a light dusting of herbs and spices over each steak so that it enjoys an entire afternoon absorbing flavor; who then grills each steak to perfection; who then bastes each side with a last minute addition of garlic butter before allowing it to be served.
Perhaps.
But I think you'll admit that it's not bloody likely, given the way the rest of the kitchen is run.
Now, as for my suggestion to dump the 140kHz "RF filter," there's a curious blindness that afflicts many audiophiles in that they look at each component in isolation. If they do consider interactions, it's usually along the lines of "will component X drive component Y?" But there are other things to ponder.
Consider the lowly filter. If someone tells you that there's a 140kHz low pass filter in a piece of equipment, your thought process is likely to be something along the lines of "140kHz is seven times the 20kHz upper limit of human hearing, so that's okay...in fact, that's more than okay...I'll never hear it."
I'll approach this from two directions:
--140kHz isn't 'seven times the upper limit of human hearing,' it's less than three octaves above the upper limit of human hearing. By comparison, compare 20Hz to 140Hz. Suddenly it doesn't seem quite as far away. Given that many instruments (e.g. brass, percussion, piano, synthesizer) have harmonics that go well above 100kHz, this begins to get a little scary. Can you hear 100kHz? No, not as a discrete tone, but it matters in terms of getting the waveform right down below the nominal 20kHz limit (which is pretty arbitrary, anyway).
--My second point--and here I come back to something I alluded to above--is that you're not listening to Linkwitz's crossover in isolation. You're listening to it with a source, possibly a phono stage, a line stage, the crossover itself, and an amplifier...all in series. Now suppose each of those components rolled off somewhere in the 100-150kHz region. In that sense, they're all filters. People don't look at what happens in the passband of a filter. They think that 140kHz is some sort of absolute. It's not. It's the -3dB point. But if you take a moment to look at a normalized filter response, you'll see that it has an effect for a couple of octaves below the nominal -3dB point. Okay, so what's a tenth of a dB between friends? Who cares? Consider what happens when you cascade each of the pieces listed above, each adding a tenth or two to the total. What happened at 20kHz? It's not at all uncommon to see response at 20kHz down by as much as a dB or even two (You'd be surprised how many circuits only make it to, say, 50 or 80kHz, instead of 100kHz; I was being generous when I said 100-150kHz.)
I can't speak for everyone, but I don't much like the idea of having my top end response lopped off before the signal even gets to the speaker.
I repeat--dump the 140kHz RF filter. Go away. Gone. Bye-bye. The easiest way to begin improving this crossover is to remove the unnecessary parts and the ones that harm the signal. Only then can you begin blending the rest into something more reasonable.
What would I choose instead of chip opamps? That's an easy one: Discrete. For that matter, I've already said so at least two or three times above. So now I've said it again.

Grey
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Old 16th November 2007, 06:30 PM   #39
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Default O'Brian works for me too...

Mmmm, steak.....

Nice to have you onboard and working on the same discrete recipe, Grey!

SL doesn't read these forums, but said if we needed to communicate with him we could do so in the Orion users' forum.

Linkwitz is concerned with the basics: getting the loudspeaker to have a uniform polar response. (See his recent lecture here)
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Old 16th November 2007, 07:40 PM   #40
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Here is the thread about discrete opamps that plug in like chips...
Also a nice crossover:

Dual discrete opamp PCB in DIP8

MOX-like crossover and discrete opamp group buy
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