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Multi-Way Conventional loudspeakers with crossovers

Altec 605a duplex crossover upgrade
Altec 605a duplex crossover upgrade
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Old 24th October 2017, 05:30 AM   #1
mrmky is offline mrmky  United States
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Default Altec 605a duplex crossover upgrade

Iíve been listening to these for about a year, they have the original crossover, I think itís a n-1600. Iíve been really curious about the Markwart crossover. Does anyone have before and after experience? They are in 1620 style caps, right at 9 cubic feet.
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Old 24th October 2017, 05:34 AM   #2
mrmky is offline mrmky  United States
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Someday Iíll even finish the cabs...
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Old 24th October 2017, 06:28 AM   #3
dotneck335 is offline dotneck335  United States
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The BEST thing you can do with those beautiful old Altecs is BI-AMP them. BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1
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Old 24th October 2017, 05:18 PM   #4
John Busch is offline John Busch  United States
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The 2 crossover options for the 605 on Jeff Markwart's site are very good. Used one of the (slightly modified) for an Open Baffle design I presented at the Lone Star Audio Fest a few years back. The systems performance was very well received. Sounded wonderful. Coherent. Smooth. Well resolved.

For the Open Baffle application, I used the simpler of the two presented.

The only caveat is you need the best low pass inductor you can afford / find. With that 15" woofer section playing well into the midrange, a crappy inductor really degrades the system performance.
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Old 24th October 2017, 10:01 PM   #5
WBS is offline WBS  United States
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Altec 605a duplex crossover upgrade
I just built the Markwart crossover for my 604-8Gs in 9 cubic ft. cabs and it added a sense of spaciousness and clarity to the speakers. However it didn't improve the bass as I had hoped it would and it didn't completely do away with the annoying congestion and peaks that occur in the crossover region.

I'm beginning to think my room is too small for these to really shine. That said, dotneck is absolutely correct. The best sound I've gotten out of these was when I bi-amped them when they first arrived. But it still wasn't as exciting as I'd hoped when I bought them.

If you decide to build Jeff's crossover the best price I found on copper foil air core inductors was here at Erse.
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Old 24th October 2017, 10:06 PM   #6
kaputt is offline kaputt  Germany
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I use GPA 604s. The lowpass is important and I have the best results with a huge cored inductor with a DCR of .07R and low ESR shunt cap. Air core inductors don't cut it here.
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Old 24th October 2017, 10:14 PM   #7
WBS is offline WBS  United States
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Altec 605a duplex crossover upgrade
That's interesting. Jeff Markwart highly recommends foil air core for his Altec crossover upgrade. Are you using GPA's 604-H crossover?
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Old 25th October 2017, 10:08 AM   #8
kaputt is offline kaputt  Germany
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No, I started with GPA's crossover, then built a Markwart crossover and currently use a modified version of that Markwart without the shelving filter and an autoformer to attenuate the compression driver.
I also took out the loading cap of the compression driver which didn't change anything in my perception of the mids/highs but did a lot for bass. Less "muddy, one-note" and more distinction. In less audiophile speak: the overtones that make the specific sound of an instrument did more of their thing.
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Old 25th October 2017, 02:58 PM   #9
mrmky is offline mrmky  United States
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Thanks for all the feedback! I hadn’t ever thought of an active crossover and bi-amping, I might have to try that after I have some extra amps kicking around. I think I will probably go the passive route first. To my ears they sound pretty good now, but I can’t get it out of my head that they could be better....
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Old 25th October 2017, 06:03 PM   #10
WBS is offline WBS  United States
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Altec 605a duplex crossover upgrade
Quote:
Originally Posted by kaputt View Post
No, I started with GPA's crossover, then built a Markwart crossover and currently use a modified version of that Markwart without the shelving filter and an autoformer to attenuate the compression driver.
I also took out the loading cap of the compression driver which didn't change anything in my perception of the mids/highs but did a lot for bass. Less "muddy, one-note" and more distinction. In less audiophile speak: the overtones that make the specific sound of an instrument did more of their thing.
Thanks for sharing your experience. I'm currently trying to overcome the muddy bass you referenced as well as fatiguing mids. Would you be willing to share your schematic?

By loading cap do you mean the 6uF C4 in the Markwart schematic? Did you keep all resistors as designed? Finally, where did you insert the autoformer? and what are its specs?

Ultimately I plan to bi-amp when I complete my Pass VFET kits but that will take a while. Until then I'd love to optimize the performance of the 604s with a passive crossover that will make them sing.
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