using passive crossover before amps to active biamp?

[cowanrg]

hello everyone. im going a little slow building my MOX active crossover, so i had a thought. i already have matched stereo amps to passively bi-amp my front speakers. i was curious if i can remove the crossovers from the speakers, put them BEFORE the amp, and use them in place of the active crossover im building. would i really benefit from this? my speakers are pretty inefficient and power hungry (magnepan tympani 1D's).

i already have an outboard box i could use that will house the active crossover... so, if i just toss the guts of the current passive crossover in there, will it give me some of the benefit of the active crossover?

thanks!

 

[Bill Fitzpatrick]

Forget it - won't work.

 

[cowanrg]

any reason why?

magnepan actually sold early pairs of their tympani's with EXACTLY that. its a little box that is passive, has one pair of RCA's in, and two pairs out. it has full range in, and low and high out... it goes between the pre-amp and the amps. what is so different about that?

 

[Bill Fitzpatrick]

Because for the crossovers to work as they should the load on them needs to be the same as the speaker, 8 ohms or so. But if you load them that way your preamp won't be able to drive it.

 

[cowanrg]

interesting. if there any way to make a passive xover that can be driven this way, or does it have to be an active one?

 

[BobEllis]

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

 

[cowanrg]

cool, thanks! if i remember correctly, my speakers only have a 6db/octave 2-way crossover. so doing a simple passive line level xover would be easy and cheap. ill look into it. thanks again.

 

[cocolino]

http://www.t-linespeakers.org/tech/...assiveHLxo.html

This kind of RC-filters do not allow for steep(er) filter slopes as with CL-filters used in most "usual" passive crossovers.



It is possible though to use CL- filters in passive line level circuits when the load is lower than the 5k to 10kOhm loads as presented in the RC-filters from the link above (or as it is a common load value in many active crossovers too).
With let`s say 600 Ohms load the necessary big inductor values (up to about max. 100mH) for the LC-filters are still avaiable as small ferrite core inductors.
The load presented by this kind of passive filters may be to low to be driven properly by some preamps. with a wimpy output stage but with a suitable buffer (BUF634, LT1010 etc.) which can provide some "juice", this isn`t a problem.
Works fine!