passive line level 500 Hz cross over..

[Harkness]

i have dreams of bi-amping my jbl's, but i don't want to introduce an active crossover into the chain.

has anyone tried making a passive crossover for the preamp output to divide the signal instead of using an active design? basically i'd like to replicate the N400 design but at line level..

i'm not too design savvy, myself.

[4313B]

has anyone tried making a passive crossover for the preamp output to divide the signal instead of using an active design?

No. Never heard of such nonsense.

[JuniorJBL]

Active would be line level hense electronic crossover.

[grumpy]

Harkness,
between sly responses and helpful intent, there is a solution along the lines you are asking. Using passive line level highpass or lowpass filters between your electronics implies that you know at least a bit about your driving and loading impedances (pre-amp out and amp input) or can make some assumptions. Will take some reading, after that you might want to try a calculation using 10K and 0.033uF if you want to experiment in increasing your savvy factor . -grumpy

[Mike Caldwell]

Hello
Yes it can be done and has been done. I worked with a PA system in the early 80's and it used custom built passive line level three way crossovers. I forget who built them, they were well done using inductors, caps and resistor. The system sounded very good, it was a total of 8 JBL 4550 cabinets, 8 2482 drivers on I think 2350 horns and a whole lot of 2402 bullets. Powered with Crown PSA's DC300's and D150's.
Desiging a passive line level crossover will be the same a designing a passive speaker level crossover, you will need the impeadance of both the output unit and the power amps input for design to be correct.

Here is a link to a site that can make the caculations for the design.
http://www.pvconsultants.com/audio/targetgen/pcdc.htm

It would be easier to go active but this could be a fun project.

Mike Caldwell

[Earl K]

Hi

i'm not too design savvy, myself.

- Then you should consider a custom solution from Marchand Electronics Inc.

- You'll need someone to "reverse engineer" the actual Fx points ( slopes ) for the N400 with your specific speaker loads in-place . Then that info will need to be translated into the higher working load impedances of your specific amplifiers . ( ie ; I feel it's a paying gig to get this all correct ) .

- Here is a mono channel, 4-pole ( 24 db/octave ) , 2-way filter ( line Level ) sold by Marchand .

- A couple of notes ;

(i) His design ( these are unbalanced ) uses a pair of load resistors to normalize to two different working circuit impedances. I imagine the reason is to be able to use "off the shelf" parts .

(ii) A standard 2-channel, 2-pole crossover is going to use the same amount of LC parts as is shown in the picture of the single-channel 4-pole crossover. What is needed is another card and set of terminal blocks . So you can extrapolate that info into some speculative pricing . The prices I've shown are now 2 years old ( 2004 ) .

(iii) Most important note . At these type high working impedances , one is dealing with inductors that are sized in "Henries" not milliHenries as is found in the N400 & other passives . So forget using air-core coils . Potted ferrite cores are going to be the only affordable game in town . ( I don't know where to buy these type of potted coils .) I've inluded a pic of a typical parts count for a 250hz , mono channel crossover .

[Harkness]

No. Never heard of such nonsense.

hmmm... really?

it occured to me that all i really need is a 500Hz high pass, as i could use the speaker crossover to separate the low end. yes, i would be running full range signal to the LF amp, but i don't think that would compromise performance much.

so, i'd need to know the output impedance of my preamp, and input impedance of my power amp to obtain the values of the caps and inductors?

[Harkness]

Hi



- Then you should consider a custom solution from Marchand Electronics Inc.

hey, cool post, thanks..

[4313B]

(i) His design ( these are unbalanced ) uses a pair of load resistors to normalize to two different working circuit impedances. I imagine the reason is to be able to use "off the shelf" parts .

Exactly, and amplifiers with their own level controls balance out the insertion loss. For instance, I used Luxman M-120A's in one such system. My line level high pass implementations were always single pole however.

[Earl K]

and amplifiers with their own level controls balance out the insertion loss. For instance, I used Luxman M-120A's in one such system.

- Yes,, I always forget to mention that one should use amps with level controls to make this stuff all work .

- Have you ever bought these potted ferrite core inductors in the Henry size ?
( If I know they are obtainable I'll keep on looking )

My line level high pass implementations were always single pole however.

Okay, that answers that .

- I don't use load resistors in my balanced single-pole passives . My Brystons 2BLP does not have a capacitor coupled front end / so there is no capacitor to capacitor math employed .

[4313B]

Nope, never have tried them. They look interesting enough. I want to say I've seen them in some B&O stuff but I could be wrong.

[Izzy Weird]

I'd be more concerned about the sonic performance of inductors than I would about (well designed) amplifier stages in an active crossover.

You can do a single pole (6 dB per octave) passive filter with an R (or two) and a C, but most people want steeper slopes.



Izzy

[4313B]

but most people want steeper slopes.

Fortunately I've never had that requirement.

Anyway, I'm tired of talking about this. Once again, it's the SOS. The questions never change. It's like an army of undead or something...

[Harkness]

aren't the N400 slopes single order on the low pass side and second order on the high pass side?

with an active crossover stage i'd be concerned with the added noise and sonic signature of the IC stages. good quality inductors are pricey i guess, but probably worth it.

[Izzy Weird]

My line level high pass implementations were always single pole however.

That's interesting, is that a preference based upon the performance of single-pole HP filters?

Izzy