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Dudeisms

Looking for some help with AA crossovers..

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I have a pair of 77’ LA Scalas with AA crossovers. I’m looking for some recipes of sorts.  I’d sorta prefer to just modify the AA’s if at all possible.

 

1. How do I cross the squawker to the tweeters at 4500hz? (I have b&c be120’s and SMAHL on the way, I know doing this to K77’s could zap them).

 

2. I’m pretty sure that if I wanted to attenuate the squawker I would move the tap on the original T2A from 4 to 3 and swap out the 13uf for 6.8uf in order to only attenuate the squawker.  Am I right?  Thoughts?

 

3. Is there a way to both change the XO point from 6,000 to 4,500 AND to attenuate the squawker?  Thoughts?

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What *I* would do (and have done) is to replace the caps with the best film and foil caps my wallet would tolerate, swap out the squawkers for solder terminal K-55-V (or Allen A-55Gs) and leave the crossover points alone.  The reason is, both the K-77-* and DE-120s have a response hump that the AA tweeter circuit smooths out.  If you change the tweeter circuit, you will have trouble replicating that built-in EQ.  To help with phasing and driver overlap, you can add an inductor to the squawker circuit to make it a bandpass.  With the DE-120s you can defeat/remove the KLiP diodes in the tweeter circuit.  You can also physically align the tweeter and squawker voicecoils by placing the tweeter on top of the cabinet.  That is the largest time misalignment in the system.  I have not done it, but a large gauge woofer inductor, perhaps even an air-core, *might* increase the woofer's output a tinch, at the risk of changing the woofer/box/horn "Q" and slightly changing its frequency response. 

 

If your squawkers seem too loud, you have a room problem you should address.  Mine tested +/- 4 db in my old theater room and did not have a midrange emphasis. 

 

Attached is my actual schematic.  I am using Hovland Musicaps.  The .35 uH inductor is an air-core.  I moved the tweeter circuit input in front of the squawker cap 20+ years ago because it is "traditional" design and I didn't fully understand how Mr. Paul's design worked.  Taking the tweeter off after the squawker cap adds a "knee" in the tweeter curve giving additional protection to the tweeter from bass notes. 

 

1384901678_TypeAAJohnLaScalasR1.thumb.jpg.00cef1f72de6b12869355036bd5fbbc6.jpg

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20 hours ago, Dudeisms said:

I have a pair of 77’ LA Scalas with AA crossovers. I’m looking for some recipes of sorts.  I’d sorta prefer to just modify the AA’s if at all possible.

 

Here's a possible recipe!  This will give you roughly a 3rd order Butterworth high pass to the tweeter around 4500Hz and a first order low pass to the squawker around 4500Hz as well.

 

I changed John's schematic (thanks John!) to show the new ingredients.  I don't have an AA crossover to test, however.

 

I agree with moving the tweeter filter away from tap 5 as it creates a series connection with the main high pass capacitor.

 

 

Quote

1. How do I cross the squawker to the tweeters at 4500hz? (I have b&c be120’s and SMAHL on the way, I know doing this to K77’s could zap them).

 

Add 500uH inductor between T2A and squawker.

Add 1uF capacitor in parallel with first 2uF capacitor to get a 3uF capacitor.

Add 6.8uF capacitor in parallel with second 2uF capacitor to get a 8.8uF capacitor.

I'd leave the 245uH inductor alone.  The ideal 210uH inductor will not make that much of a difference.

 

Quote

2. I’m pretty sure that if I wanted to attenuate the squawker I would move the tap on the original T2A from 4 to 3 and swap out the 13uf for 6.8uf in order to only attenuate the squawker.  Am I right?  

 

You are right!

 

Quote

3. Is there a way to both change the XO point from 6,000 to 4,500 AND to attenuate the squawker?  Thoughts?

 

I believe this will work, but I always reserve the right to be wrong.

 

Mike

 

 

AA-4600.jpg

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What *I* would do (and have done) is to replace the caps with the best film and foil caps my wallet would tolerate, swap out the squawkers for solder terminal K-55-V (or Allen A-55Gs) and leave the crossover points alone.  The reason is, both the K-77-* and DE-120s have a response hump that the AA tweeter circuit smooths out.  If you change the tweeter circuit, you will have trouble replicating that built-in EQ.  To help with phasing and driver overlap, you can add an inductor to the squawker circuit to make it a bandpass.  With the DE-120s you can defeat/remove the KLiP diodes in the tweeter circuit.  You can also physically align the tweeter and squawker voicecoils by placing the tweeter on top of the cabinet.  That is the largest time misalignment in the system.  I have not done it, but a large gauge woofer inductor, perhaps even an air-core, *might* increase the woofer's output a tinch, at the risk of changing the woofer/box/horn "Q" and slightly changing its frequency response. 
 
If your squawkers seem too loud, you have a room problem you should address.  Mine tested +/- 4 db in my old theater room and did not have a midrange emphasis. 
 
Attached is my actual schematic.  I am using Hovland Musicaps.  The .35 uH inductor is an air-core.  I moved the tweeter circuit input in front of the squawker cap 20+ years ago because it is "traditional" design and I didn't fully understand how Mr. Paul's design worked.  Taking the tweeter off after the squawker cap adds a "knee" in the tweeter curve giving additional protection to the tweeter from bass notes. 
 
1384901678_TypeAAJohnLaScalasR1.thumb.jpg.00cef1f72de6b12869355036bd5fbbc6.jpg

Hi John, What does the .35mh inductor to the squawker do? Also if I lift the tweeter to make this knee... does it change or effect values of anything else?


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