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Modifying AA crossover to cross at 4500hz


geoff.
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Most of the suggested/most used mods have been curved by Bob, Al, or John Warren. When people start doing things that haven't been tested, you have no idea what you are hearing. I got bit by this in a bad way once.

 

The tweeter section of the AA is behind the 13uF capacitor (in series). We have a lot of curves/plots for that filter. When you change the crossover point AND the alignment, I just think it's probably safer to make it a true parallel filter -- and get the tweeter leg behind the 13uF. Notice this is how all of the filters are after the AA.

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None of you reading this at home can see this, but the lightbulb above my head is flickering brighter...

 

A great deal of what I have read on here over the years is starting to gel. Some days are better than others.

 

If I am NOT using K-77s I really don’t need an 18db per octave cross to the tweeter do I?

 

This is why the A/4500 was not designed as an AA/4500?

 

 

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2 minutes ago, geoff. said:

If I am NOT using K-77s I really don’t need an 18db per octave cross to the tweeter do I?

 

This is why the A/4500 was not designed as an AA/4500?

 

 

Pretty sure I pointed this out on the first page..

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20 minutes ago, geoff. said:

If I am NOT using K-77s I really don’t need an 18db per octave cross to the tweeter do I?

 

This is why the A/4500 was not designed as an AA/4500?

 

 


Using a higher order passive crossover is a designer or personal preference. For brevity, we’ll leave out electronic crossovers for this discussion.

 

Using a higher order network could be to maximize power output. Another reason could be to limit driver interaction or both. 
 

Keeping the “out of band” energy from overlapping into the adjacent passsband is the main reason for a crossover. Some people prefer steeper slope networks than others. Obviously, there is cost to consider as well as the steeper networks quickly add up to a lot of parts. 
 

Phase and group delay also play a part in the final design, but that is another conversation. 
 

 

 

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@jjptkd, from the majority of comments over the years regarding crossovers the AA always seems to hold it’s own.

 

I honestly thought I would be missing out on the magic if I strayed from the venerable AA crossover. 

 

The very same magic is in the A/4500. Just crossed lower to the tweeter, with less parts. 

 

Now, what of this swamping resistor mod that seems to garner a lot of positive reviews.

 

Is this something that would improve upon an A/4500?

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24 minutes ago, geoff. said:

Now, what of this swamping resistor mod that seems to garner a lot of positive reviews.

 

Is this something that would improve upon an A/4500?

I'm honestly no expert here and not familiar with that mod-- I just happened to modify a pair of type B's some time ago and researched these early crossovers quite a bit on this forum at that time, especially in relation to the A55-g / k-55v mid drivers and the CT-120 tweeters.  

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1 hour ago, Deang said:

 

The tweeter section of the AA is behind the 13uF capacitor (in series). We have a lot of curves/plots for that filter. When you change the crossover point AND the alignment, I just think it's probably safer to make it a true parallel filter -- and get the tweeter leg behind the 13uF. Notice this is how all of the filters are after the AA.

 

I think you meant to say make it a true parallel filter -- and get the tweeter leg in front of the 13uF. The 13uF doesn't touch the signal going to the tweeter, it and the mid-horn driver now appear in parallel with the whole tweeter and woofer circuits, like most crossovers.

 

My theory is profit, why waste a high pass filter when it's already there, just add upon it with filters with a higher roll-off frequency.

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On 12/5/2021 at 5:47 PM, geoff. said:

Now, what of this swamping resistor mod that seems to garner a lot of positive reviews.


The swamping resistor has a benefit in the following situation;

1. You want to move away from the factory (AA / A / E, etc. The swamping resistor can be added to a lot of networks. This is not a full list) network which is only 6dB/octave high pass on the midrange and implement a steeper high pass slope say 12dB or higher.

2. The swamping resistor also sets a continuous load for the midrange crossover, so you can now use the T2A taps to attenuate the midrange without messing with crossover components. Just move taps and the crossover will stay the same. 
3. One small downside to the swamping resistor is now you have to isolate the tweeter crossover and possibly use an L-pad for attenuation. A small price to pay for being able to quickly dial in the midrange level. 
edit 4. If using a single ended tube amp or an amp that needs a fairly constant impedance, the swamping resistor will smooth out the impedance curve.
 

I like the autoformer as a level component, but have no problem using L-pads either. Both are just tools. 

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On 12/4/2021 at 4:56 PM, Dave MacKay said:

I didn't think that I could run a DSP with my setup.

the miniDSP is one HUGE improvement in sound quality  ,it's like discovering new speakers ,super tight bass , clear crystal HF and mids , if you're  streaming digital files   DSP is a whole new experience  ,  SS class D amps are as low as 25-30$ or multichannel for 100$  , so quite affordable these days-

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1 hour ago, 000 said:

the miniDSP is one HUGE improvement in sound quality  ,it's like discovering new speakers ,super tight bass , clear crystal HF and mids , if you're  streaming digital files   DSP is a whole new experience  ,  SS class D amps are as low as 25-30$ or multichannel for 100$  , so quite affordable these days-

This may be the wrong place to ask but ...

 

Would you please share a bit about what equipment could be used and how one would set up the DSP?

 

I'm especially interested in what one could use (that doesn't cost an arm and a leg) to replace both the input section (streamers, etc.) and the amp section of a receiver. I'd like to experiment with having a DSP replace my crossovers, but I'd like to do so without a spending thousands.

 

I've purchased a UMIK and have played with REW but I'm really just fumbling around with it.

 

If this should be raised in a separate thread, I'll create one.

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It easy to spend thousands. 

It is perplexing since it is an investment and some individuals don't like the outcome. 

 

My suggestion is to buy something inexpensive and try it out. If it is a failure, then you can sell the box and recoup some of your money. For instance you can buy a Behringer DCX 2496 (new about $350 and used about $250). If you were in the US, I could sell you a NIB unit for a decent price. The DCX is not the last word in quality, but it is quite affordable and certainly more than enough to get your feet wet. There are other alternatives including the MiniDSP (although they do not have digital inputs).

Good luck,

-Tom

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