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How to modify SMGa to Active Crossover?
How to modify SMGa to Active Crossover?
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Old 18th November 2017, 05:45 PM   #1
SanJoseMichael is offline SanJoseMichael  United States
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Default How to modify SMGa to Active Crossover?

I've got a set of Magnepan SMGa speakers that I'd like to biamp, but I'm pretty well clueless as to how to do it.

How to wire it for biamplificaton:
First, disconnect the existing crossover.
Then do I keep the inductor in parallel with the mid/woofer?
And keep the capacitor in parallel with the tweeter?

Then, when using an active crossover, what frequency makes sense to cross over at?

Thanks!
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File Type: jpg SMGaXO1.jpg (357.7 KB, 122 views)
File Type: jpg SMGaXO2.jpg (58.4 KB, 124 views)
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Old 18th November 2017, 07:00 PM   #2
planet10 is offline planet10  Canada
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How to modify SMGa to Active Crossover?
With passive bi-amping you need to separate the XO into 2 discrete XOs and drive each with its own amplifier. The passive XO is a series XO so a new XO configuration would be needed

With an active XO (real bi-amping) you eliminate the XO completely. The starting poing for setting your active XO is to get as close to the passive XO as possible (passive is 1st order).

dave
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Old 18th November 2017, 10:45 PM   #3
SanJoseMichael is offline SanJoseMichael  United States
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Dave -

Yes, real bi-amping, from pre to active crossover to two power amps, one for bass/mid and one for tweeters.

So, remove the passive XO from the Magnepans completely, and redo the speaker connections to allow direct connection from the each amp to each section of the SMGa's.

You said "The starting poing for setting your active XO is to get as close to the passive XO as possible (passive is 1st order)." How do I determine that? What might a guess of a good starting point be?

Thanks.

MG
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Old 18th November 2017, 10:52 PM   #4
SanJoseMichael is offline SanJoseMichael  United States
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Does this suggest 800hz?

1st Order / 6 db Butterworth Crossover Table
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Old 18th November 2017, 11:10 PM   #5
adason is offline adason  United States
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I would suggest minidsp. As a start. It allows you to change crossover frequency, slopes, delays, levels...on the fly, while listening. Its cheap too. Sounds ok, once you get all sorted out, you can upgrade. Plus its parametric eq, you can use it to correct room.
Just a suggestion, do what suits you.
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Old 18th November 2017, 11:13 PM   #6
planet10 is offline planet10  Canada
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How to modify SMGa to Active Crossover?
Quote:
Originally Posted by SanJoseMichael View Post
So, remove the passive XO from the Magnepans completely, and redo the speaker connections to allow direct connection from the each amp to each section of the SMGa’s.
Yes

Quote:
You said "The starting poing for setting your active XO is to get as close to the passive XO as possible (passive is 1st order)." How do I determine that? What might a guess of a good starting point be?
Manufacturer specs, reviews, email Magnepan.

dave
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Old 18th November 2017, 11:16 PM   #7
planet10 is offline planet10  Canada
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How to modify SMGa to Active Crossover?
Quote:
Originally Posted by SanJoseMichael View Post
Does this suggest 800hz?
You might be able to use text-book XO values as a 1st pass guess. You’d really need to have impedance plots of your speakers sans Cos to get more accurate impedance values.

dave
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Old 19th November 2017, 12:48 AM   #8
SanJoseMichael is offline SanJoseMichael  United States
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You guys are clearly more advanced than I am, but I ask the Tribal Elders and Wise Ones in order to learn.

Here's a very basic question: Is it worth it? I have read many places that bi-amping is worth exploring.

I am limimted in my equipment and $$ to upgrade much at this time, so my idea was this: CD Player/Aux into NAD 3225PE, Preamp out of NAD NAD 3225PE into active crossover, highs out of active crossover back into NAD 3225PE and speakers direct to Maggie tweets, lows out of active crossver into NAD 2100PE and speakers direct to Maggie lows/mid. (Alernately, into vintage Altecs, driven by Magnavox 8802 and 175).

I now drive the Magnepan SMGa speakers this the NAD 2100 PE alone, about 75 watts into 4 ohms to drive SMGa factory passive crossover speakers

Biamping suggests more power to the speakers. Active biamp = NAD 3225PE (About 30 watts into 4 ohms) for the high range, NAD 2100 (About 75 watts into 4 ohms) for the lows. Net difference: From 75 watts to passive crossover to 105 watts active crossover.

Or should I just sell off my old NAD stuff and get a Denon, Sony, Yamaha, Oinko, Pioneer AV reciever puting out about 140 to 150 watts (8 ohms), or find some 200W beast on Craigslist for cheap?
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Old 19th November 2017, 02:26 AM   #9
planet10 is offline planet10  Canada
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How to modify SMGa to Active Crossover?
Using the NADs is a fine approach. We sold a lot of NAD3020 with the promise of easy bi-amping in the future.

dave
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Old 19th November 2017, 03:45 AM   #10
kevinkr is offline kevinkr  United States
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How to modify SMGa to Active Crossover?
As others have alluded you need to remove all of the existing XO parts. The tweeter is somewhat fragile so the fuse should be retained.

I have include a simulation of the current XO response. Because the drivers look predominantly resistive the response is pretty close to text first order network amplitude and phase response.

First graph is just the series XO and drivers, the second is an overlay with a classic first order 2 way xo. There is no difference.

Looks like first order crossover at 800Hz would be fine.
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File Type: png smg1a.PNG (54.8 KB, 96 views)
File Type: png smg1a-2.PNG (55.9 KB, 87 views)
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