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Multi-Way Conventional loudspeakers with crossovers

GPA 604 adventures
GPA 604 adventures
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Old 28th December 2017, 09:58 AM   #1
c_door is offline c_door  Italy
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Default GPA 604 adventures

Hello,
I've just bought me a used pair of GPA 604-8H-II in pristine condition, along with the original N 604 8A xover filters.
Compared to my Troels' DTQWT drivers, these things are huge !
I put them in an open baffle (JE Labs style) and hooked to my Pass F5 monos.
At first, the speakers where mounted behind the panel, leaving a 40mm tunnel in front of them.
Big mistake. They were almost unlistenable with canned voices and muffled mids.
So I reoruted the boards as shown in pictures and mounted the salad bowls flush with the panel.
Far better. With some musical genres they play very nicely. The compression driver is in another league if compared to a dome.
Listening to a jazz trio is kind of mesmerizing.
But, they are (very) far from perfection. Image is low, bass is lean and human voices still need a correction.
Overall, my DTQWT's are better speakers, more able to cope with many music genres, although they miss the magic of the big coaxials.

So, time for some questions to the experts.
As a first upgrade I want to try this Jeff Markwart's filter:
Great Plains Audio 604-8H-III - Great Plains Audio
I'm going to build it with Jantzen's Air Cores and Cross-Caps. Then maybe in future the caps will be replaced with better ones.

I don't understand the attenuators schematics. I'd like to replace them with resistors, swapping them until I find the correct value.
Where I have to place a resistor for HF eq? Left side of L2 to C3, or right side of L2 to C3 ?
About MF eq I guess that the resistor goes from between R1-R2 to R3, right ?
Which range of values to allow let's say five steps of attenuation ?

Then I'll be back for suggestions about a proper cabinet style. Stonehenge, MLTL.. a lot of fun to come
Thanks in advance! Carlo.
Attached Images
File Type: jpg GPA and DTQWT.jpg (286.2 KB, 398 views)
File Type: jpg GPA_OB.jpg (457.3 KB, 392 views)
File Type: jpg GPA_back.jpg (645.1 KB, 389 views)
File Type: jpg GPA_filter.jpg (450.5 KB, 380 views)
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Old 28th December 2017, 12:40 PM   #2
KJ_Knowles is offline KJ_Knowles  United States
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Good for you! I once worked in a large electronics store that sold Altec, along with other classic and exotic lines (showing my age). The Stonehenge V was lusted after by many employees and customers alike. The 604 series drivers just seem to have an appeal all there own.

I occasionally consider building what the custom car community would call a Resto-Mod, a classic restored and improved with current technology. In my case would stick with the classic Stonehenge cabinet, but use up to date amplification and FIR filters. Just my idea, not suggesting you take that path. I look forward to seeing how things progress with your new treasures!

KJK
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Old 28th December 2017, 03:03 PM   #3
LineSource is offline LineSource  United States
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If you first select a cabinet and simulate your room placement, you will be able to construct the best crossover with just one investment.

A MLTL cabinet can be built/tuned to reduce many resonances better than the basic-big-box.

The popular 6041 studio monitor includes a bottom 416-8C woofer for both deeper bass, plus a midbass crossover frequency which allows a sealed box GPA 604 improved midrange clarity.

http://audio-heritage.jp/ALTEC/speaker/6041(3).jpg
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Old 28th December 2017, 06:12 PM   #4
planet10 is offline planet10  Canada
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GPA 604 adventures
Quote:
Originally Posted by c_door View Post
... suggestions about a proper cabinet style. Stonehenge, MLTL...
We have had a number of builds of the Woden Bison ML-TL with good results.

Click the image to open in full size.

dave
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Old 28th December 2017, 09:59 PM   #5
kaputt is offline kaputt  Germany
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Capacitors aren't that critical in the crossover, just pick good quality polyproplylene caps. Air core doesn't cut it in the low pass filter, a huge cored inductor with low DCR (below 100 mOhm) is the ticket for 604s. The shelving filter can be removed from the Markwart circuits.
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Old 28th December 2017, 10:13 PM   #6
multi is offline multi  Australia
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Open baffle is not for the 604 as they will not have much bass, they need large boxes at least 6 Cubic feet or more, for good bass. A friend of mine has his in 12 cubic feet boxes.
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Old 29th December 2017, 07:04 PM   #7
c_door is offline c_door  Italy
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Thank you everyone for the suggestions!
The ML-TL Woden Bison seems interesting, but it is damn big! Looks like a 300 liters plus the space under the bottom vent.
What if the port is moved to the front panel, and the driver placed closer to the top, keeping the same volume and inner structure ? Does it degenerate to a plain bass reflex, Altec 620 style, only bigger?
I'm not interested in squeezing the last hertz from bass response but, is the ML-TL concept far superior ?
By the way, I've moved the OB panels closer to the front wall, about 2,5ft. The mid-bass has improved, cello and upright bass are very enjoyable now.
I can't think of a simpler or cheaper speaker able to fill a smallish room with this kind of musical quality.

Last edited by c_door; 29th December 2017 at 07:08 PM.
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Old 29th December 2017, 07:12 PM   #8
planet10 is offline planet10  Canada
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GPA 604 adventures
Bison is actually smallish as far as 606 enclosures go. The vent can be moved to any of the sides (at the bottom). Those alternate drawings are supplied with the planset.

http://wodendesign.com/downloads/Bis...v82-071217.pdf

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Old 29th December 2017, 07:32 PM   #9
Cal Weldon is offline Cal Weldon  Canada
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GPA 604 adventures
Consider an Onken cabinet.

altec 604 in onken cabinet - Google Search
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Old 29th December 2017, 07:36 PM   #10
c_door is offline c_door  Italy
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Thanks a lot Dave for the plan.
If I'm not wrong, it is about 340 liters (12 cu ft) internal (gross). I would call it big!
I like the front panel width. I think that it fits better to the 604 unit than a slim Stonehenge enclosure.
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