WAW / FAST build ?

[ton def]

I have a pair of Alpair 7 and sdx7 that I bought several years back. I would really like to start a build with these. I would likely need to use a passive x-over,as I have no dsp or experience with them. Any plans or examples of this ? I have seen planet 10's ,but I do not quite understand PLLXO. Thank you

 

[Cal Weldon]

PLLXO is less expensive. Hopefully Dave can chime in soon.

 

[planet10]

PLLXO is less expensive

And really easy to build. Do you have 1pr SDX7 or 2?

dave

 

[Bob Brines]

Consider DSP and bi-amping. The price of admittance has gone down seriously in the last couple of years.

Bob

 

[ton def]

And really easy to build. Do you have 1pr SDX7 or 2?

dave

I have one pair of sdx7. Is your design adaptable to use only one sdx7 per speaker ?

 

[ton def]

Consider DSP and bi-amping. The price of admittance has gone down seriously in the last couple of years.

Bob

Yes, that would probably be the best way to go.... But I am not knowledgeable with that technology ( and cash limited ) .

 

[planet10]

I have one pair of sdx7. Is your design adaptable to use only one sdx7 per speaker ?

Sure. It makes a passive XO possible, but the A7 may need padding down.

dave

 

[ton def]

Sure. It makes a passive XO possible, but the A7 may need padding down.

dave

By padding down the a7, do you mean attenuation for spl equalization or limiting current to it ?

 

[planet10]

Reducing its SPL.

A point to keep in mind is that by the time you sort passive parts their cost will very likel be in excess of what a 2nd amp (something like a TDA2116 or 18 would be fine) & PLLXO will cost.

dave

 

[chrisb]

I don't think the question as to how PLLXO is implemented has actually been described, this primer is as good a place to start as any, and includes an excel calculator to determine component values.



TLS.org | Passive Line-Level Crossover


In short, it can be as simple as a pair of resistors and very low value caps at the input of each amp - they can even be soldered directly at the input jacks with a bypass switch for full range.

Dave: note that the link to Alex's website on the bottom of BSC page is now 403

 

[tuxedocivic]

That single SDX7 will want a massive coil. I know first hand. And it's not very sensitive. It's rated as an 8ohm driver, but I think it's minimum impedance is something like 9ohms, and most 8ohm drivers have a 6ohm minimum, or thereabouts. The high impedance will require a very large inductor. Go price out a 8mH inductor and then price out a minidsp or PLLXO.

 

[ton def]

That single SDX7 will want a massive coil. I know first hand. And it's not very sensitive. It's rated as an 8ohm driver, but I think it's minimum impedance is something like 9ohms, and most 8ohm drivers have a 6ohm minimum, or thereabouts. The high impedance will require a very large inductor. Go price out a 8mH inductor and then price out a minidsp or PLLXO.

A first order Butterworth at 250 hz calls for a 5.2 mh coil. I have several of that size or larger,that were used for passive auto subs. The large cap values are something else again.If I do go passive I will have to use electrolytics.Somebody needs to put out a " digital x-overs for dummys " book .

 

[ton def]

I don't think the question as to how PLLXO is implemented has actually been described, this primer is as good a place to start as any, and includes an excel calculator to determine component values.



TLS.org | Passive Line-Level Crossover


In short, it can be as simple as a pair of resistors and very low value caps at the input of each amp - they can even be soldered directly at the input jacks with a bypass switch for full range.with.
Dave: note that the link to Alex's website on the bottom of BSC page is now 403

This is most likely what I will do down the road. I have a Sure 2x100w amp board to experiment with. I can't tell what values they are choosing for the resistors. what is this k and w ??

 

[tuxedocivic]

If you already have the coils, sure, then it makes sense. I'd go second order personally. R will be about 16ohms at 1khz, check the value required to suppress that 20db in your calculator and you'll see why.

 

[chrisb]

This is most likely what I will do down the road. I have a Sure 2x100w amp board to experiment with. I can't tell what values they are choosing for the resistors. what is this k and w ??

If the highlighted above refers to the values shown on the PLLXO page, "k" would refer to Kilohms, and the "w" would likely reference wattage rating of the resistors. Funny that is,- I've read that page numerous times, and have used the linked calculator spreadsheet as well, and never noticed the lack of a value for the "w". As the V/A levels present at line levels will be very small, I'd imagine you could easily get away with 1/4W at the most. That, and the fact that the load seen by the filter ( amplifiers' input impedance) is orders of magnitude higher than any loudspeaker, is why the component values and associated cost are so much lower than when calculating high ( speaker) level filters.