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Changing taps on autotransformer – effects on the xo circuits

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There has been some confusion on changing tap points on an xo to alter the attenuation. Some people say not to do this, that would require a complete re designing of the xo and others have shared no concerns and make tap point changes. Both groups of people are respected in their fields so which is right?

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I have tried several taps on my Crites 3636 autotransformers without changing anything else on my Super Heresys.  I don’t recall which tap they’re on now but they are several dB down on the squawkers and they sound great.

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9 hours ago, Alexander said:

There has been some confusion on changing tap points on an xo to alter the attenuation. Some people say not to do this, that would require a complete re designing of the xo and others have shared no concerns and make tap point changes. Both groups of people are respected in their fields so which is right?

 

Well, you can't just change the setting unless you change the capacitor value or use a swamping resistor on the midrange. I wouldn't call that "a complete redesign" - just a small modification which is required to keep the crossover point the same. 

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The change to the autoformer tap changes the downstream impedance.  If you are using a 6db electrical crossover, you end up doubling or halfing the capacitor value as you double or half  the impedance.

Refer to Crites 3636 autoformer specs for the impedance multiplier.  https://critesspeakers.com/3636atz.pdf

 

Of course measure to insure the impact on the driver is as in theory and if you don't know the specs of the autoformer but apply what Dean has pointed out.  You'll likely not hear any significant difference.

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A paper explaining the theory behind the use of an autotransformer and swamping resistor to allow adjustable attenuation of drivers in a crossover network.

(by Al Klappenberger) is here - http://www.alkeng.com/dload_xo.html

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12 hours ago, DizRotus said:

I have tried several taps on my Crites 3636 autotransformers without changing anything else on my Super Heresys.  I don’t recall which tap they’re on now but they are several dB down on the squawkers and they sound great.

Same here. I'm one tap down in number from what Claude originally suggested.  Sounds awesome

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Without a change in capacitor value or a swamping resistor across the driver, you’ve changed the crossover point. 

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I am quoting here... this is what happens to the crossover profile when you drop that tap to try and attenuate. 

 

35478114886_7c2020e1fb_h.jpg

 

It creates a 'bark' in the profile...

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6 hours ago, mopardave said:

Same here. I'm one tap down in number from what Claude originally suggested.  Sounds awesome

Before I changed that tap, the mid driver a 55m sounded very distorted when I put my ear up to it. After changing tap the mid sounded very clean and clear.   When I stood back listening the speaker sounded much better.

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On 3/21/2020 at 6:58 AM, Wirrunna said:

A paper explaining the theory behind the use of an autotransformer and swamping resistor to allow adjustable attenuation of drivers in a crossover network.

(by Al Klappenberger) is here - http://www.alkeng.com/dload_xo.html

Thank You for the link

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Some of us find the sweet place is right in between the two using the 3636 autotransformer.

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