Passive Line Level Crossovers

[GeorgeBoles]

Dear All,

I have been studying all the bits about active crossovers between my soon-to-exist pre-amp (BZLS) and some "home-made Alephs" ('cuz they won't be the real things). Then, it came to me this morning at 0400 ("Oh my goodness, its early"):

Why shouldn't my low-voltage, approximately "line-level" crossover be made passive, working with nice small and affordable components which can be as exotic as one wants, but a lot more affordable than the big things in a normal "speaker-level" passive crossover ... keeping with the philosophy of minimal components rather than strings of OpAmps, either normal opamps or DIY type?

1. Can anyone explain to me why this would be too complicated or less satisfactory than an active crossover.

2. Or is it in fact better?

3. Could it be "balanced" to match my BZLS and Aleph 30 or Aleph Mini or Zen 5, and what would that mean in this context, anyway?

Because if it COULD be passive, that would be a blessing, because I suspect that I will never want to see another power supply by the time I have finished building all this stuff. (I have to build the speakers too!)

Regards,
George

PS: I just read the Rushmore literature and it appears that the crossover for these is passive - (Designed with an XVR1 prototype, and implemented passive.) Is this correct?

[planet10]

A PLLXO can be implemented as RCs or as LCs. When using LCs the size of the inductors becomes very large and it is tricky to get good ones... marchand has one thou that one of these days i'm going to try.

http://www.marchandelec.com/xm46.html

For info on RC PLLXOs

http://www.t-linespeakers.org/tech/f...ssiveHLxo.html

When you are building amps for your speakers it is very easy to incorporate the above in the amp. For instance if you have a coupling cap between stages you can choose it to make one of the poles for your XO.

dave

[GeorgeBoles]

Thanks Planet.

1. Regarding the high inductance values if going LC, surely these are not as big as those in a passive speaker-level crossover. Having said that, the Marchand crossover has inductors of 1 Henry!! I would have thought that nearly impossible, but I will have to check up and do some maths.

2. Here is an admission of major ignorance on my part: With regard to crossovers, I thought that the number of "poles" related to the output of two speakers side by side. How does that relate to the number of "poles" of the crossover, or do the two things relate exactly to one another?

3. It does look as though 4th order crossovers might be a bit problematical, especially if I go LC. Perhaps 4th order for the tweeter/mid-range, and lower order for mid-range/bass driver.

Thank-you for the references to other information.

Regards,
George.

[planet10]

Originally posted by GeorgeBoles
1. Regarding the high inductance values if going LC, surely these are not as big as those in a passive speaker-level crossover. Are these doable as home-made devices using the myriad of formulae around?

The capacitance varies inversly as the load impeadance, the inductance as the load impedance. ie a 4 uF cap into an 8 ohm load crosses at 5kHz. increase the load to 16 ohms you only need 2 uF. Increase the load to 8k than you need 0.004 uF. The opposite is true with the inductor. increase the load by a factor of a 1000, and your 5 mH coke needs to be 5H.

2. Here is an expression of major ignorance: With regard to crossovers, I thought that the number of "poles" related to the output of two speakers side by side. How does that relate to the number of "poles" of the crossover, or do the two things relate exactly to one another?

A 1st order XO has 1 pole, a 2nd order 2 poles... every reactive component (ie L or C) adds a pole.

dave

[Jonathan Bright]

George with regard to "poles" in point 2 of your second post rather than being exact they are quite separate. Just keep the two ideas in quite different parts of your brain for now.
RE; point 1 "big coils". The good thing about low level stuff is that you don't have the need to make the DC resistance very low so while the numercial values in Henries is high the actual volume/weight/size/cost etc is comparitivley low because you aren't asking them to carry the sort of current that the Hi level x0ver does.
They other thing to think about is the way the sections will add up in a purely passive system. If you have an active system you can get good Butterworth shapes which I think are hard to do with repeated passive sections. I'm not a genius in this area but I think you are limited to Bessel types with passives unless you are doing resonant circuits and that will be a bit more hairy. Mind you some people swear by Bessels. But get a second opinion befor you take my word for it.

[Steve Eddy]

Originally posted by GeorgeBoles
1. Regarding the high inductance values if going LC, surely these are not as big as those in a passive speaker-level crossover. Having said that, the Marchand crossover has inductors of 1 Henry!! I would have thought that nearly impossible, but I will have to check up and do some maths.

1H is a piece of cake at line levels where you don't have to dissipate any power to speak of. The input transformers I use have a primary inductance of about 80H.

se

[Jonathan Bright]

George I notice that you are in the Great Southern Land and also that you can't be e-mailed. But if you contact me through my e-mail (click on my name on this post and get it from the profile) I think that a phone call might be profitable as there are a few things to sort with this one but they are straightforward and the idea is quite "doable".