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Modifying AA crossover to cross at 4500hz


geoff.
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8 hours ago, jimjimbo said:

I build all of my Heritage crossovers to the AA configuration, with very good caps, new coils, new autotransformers.  I listened to the Crites A4500 a while back, and gave it about two weeks.  I much prefer the AA for the tonal balance (admittedly with my somewhat senior ears.....)

Are you specifically referring to belles, Scalas, and khorns, or do you put AA crossovers in heresies and Cornwalls? I don't understand enough about crossovers, but I always wondered why heresy and Cornwall crossovers were so different when the mid and tweeter drivers are the same between the five different models (of the early time frame).

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10 minutes ago, dtr20 said:

Are you specifically referring to belles, Scalas, and khorns, or do you put AA crossovers in heresies and Cornwalls? I don't understand enough about crossovers, but I always wondered why heresy and Cornwall crossovers were so different when the mid and tweeter drivers are the same between the five different models (of the early time frame).

Back in the early models they all used pretty much the same crossover; Type A for the big speakers, Type B for the Cornwall and type E for Heresy-- differences were in the autoformer taps and cap value changes to go with them. Later the type AA was introduced for the bigger speakers because the Type A ran the tweeter at basically full output no reduction and tweeters would blow, the type B and E didn't have this problem because output to the tweeter was reduced via autoformer. 

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4 hours ago, Deang said:

The AL-4 and AK-4 schematics are in the Crossover Schematic thread, which is pinned. Why not just build those?

 

That is not a bad idea. But was there not also the consensus that the AL-4 was less than desirable? I’ll have to look back in the archives...

 

Funny thing is I remember seeing all the threads on La Scalas and Klipschorns and glazing over because I never thought I would make it that far up the Klipsch ladder. But the seed was planted. And it has been a good crop! 

 

In my case though, I am already in possession of a pair of AA crossovers and if swapping a couple of capacitors is all it takes to see what they sound like it is a no brainer. I would probably still need to do something about the tweeter level relative to the midrange, the resistor or autoformer mod.

 

 

 

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55 minutes ago, dtr20 said:

Are you specifically referring to belles, Scalas, and khorns, or do you put AA crossovers in heresies and Cornwalls? I don't understand enough about crossovers, but I always wondered why heresy and Cornwall crossovers were so different when the mid and tweeter drivers are the same between the five different models (of the early time frame).

LS and Khorns

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One alternative may be to incorporate the old notch filer idea on the “aa” network. Measurements from ALK years ago demonstrated that the aa tweeter filter was “all in” at 5000hz, not 6000hz, albeit with a 1 or 2db output reduction from an “a” network. The old Max Potter notch filter, with  3uf capacitor and .1mh inductor, wired in parallel on the positive side of the midrange - after the autoformer, will alleviate the 8-9k midrange spike on the single plug k56 AND reduce the total midrange db output by about -1db from perhaps 2-3k onward. With a first order mid, this should generate an approximate acoustical crossover at ~ 5k. This may deliver a middle ground acoustical cross between an a/4500 (which suppresses the midrange 1-3 db further and through a greater range) and the “aa”, and without a tweeter change. Can you hear a change? Maybe. FWIW.

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So... if one wanted to simply make an A/4500 out of an AA you could just parallel the two existing 2uf capacitors, add the .5mH coil to the midrange and “cut out” the .245uH coil and Zeners from the tweeter circuit?

 

I feel like I just graduated kindergarden, duh...

 

I paid good money for a pair of A/4500s years ago and I have no use for these AAs until now.

 

And I REALLY like the A/4500s. 

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3 hours ago, geoff. said:

Now, on to the next question...

 

Sometimes I notice the overlap from the bass bin to the squawker, not in a good way.

 

Would this be the fix?

281DF2DE-8B0F-48C2-98A1-B979E16F9337.jpeg

 

That would only effect the woofer circuit, like if you wanted to cut less mids from the woofer not the other way around like you want.

 

If you want less bass in the squawker try lowering the 13uF capacitor to a 10uF.

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Another option for replacing the type AA (LaScala, Belle and Klipschorn crossovers), AL, AL-2, AL-3 (LaScala crossovers), the AK, AK-2, AK-3 (Klipschorn crossovers) and the AB or AB-2 (Belle Crossovers) is our special Type A/4500 crossovers.  More info about these crossovers here:

 

B&K Sound Type A/4500 Crossover

You have to get different tweets for the 4500.  Easy to build from Crites parts.

 

A-4500Hz brich brand
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There is also another option to move toward a 4500hz crossover point already done by Klipsch on the aa network: for a short time, Klipsch employed a revised aa network that inserted a .35mh inductor in the positive output after the autoformer to the squawker as a band pass filter. I’ve never measured this one, but Klipsch used it and must have found it helpful in achieving a ~5000hz crossover (published or not) with the aa tweeter filter. Again, FWIW

 

In terms of network differences, I think Dean has it right; Klipsch was all over the road on midrange attenuation (from 3,4 and 6db down) for many years with the LaScala while maintains a 6000hz crossover point and 105db sensitivity. Voicing differences? Sure, but which is “better” is all personal taste and room dynamics imho.

 

 

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10 hours ago, geoff. said:

Until now, I never really noticed how similar the A and AA crossovers are:

 

 

6B0578B2-B145-4005-9964-EBBA3039E2A2.jpeg

 

As an alternative to the Crites A4500 network, we can build on the AA network and modify it to use an 18dB/octave filter at 4500Hz (vs the 6dB/octave filter at 4500Hz on the Crites network).

 

The below schematic has not been built or tested by me, but only offered as a starting point for people like Geoff to experiment with. If any type of tweeter attenuation is needed, you cannot use a T2A autotransformer tap. You will need to use an adjustable or fixed type L-pad. 

 

2.7uF and 8.2uF values can be used for the capacitors. The values on the schematic are calculated values. 

 

The diodes are optional and I only showed them because they are included on the OE AA network.

 

18dB Tweeter Crossover_v1.0.0.jpg

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9 hours ago, geoff. said:

Now, on to the next question...

 

Sometimes I notice the overlap from the bass bin to the squawker, not in a good way.

 

Would this be the fix?

281DF2DE-8B0F-48C2-98A1-B979E16F9337.jpeg

 

I used an 80uF cap in the woofer circuit to roll off the woofer a bit faster. This improved the transition from woofer to midrange for me in my Lascala. 

 

Two 100uF = 200uF, which would be too much. Try 80uF.

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