DIY Active crossover !!!!

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.

zztop

Member
2002-05-26 8:45 pm
I think an active crossover could solve a lot of my troubles!!!!
Should be easy to go to my trusted hi fi vendor and buy a 3 way active crossover ( even if 2 is enought ) paying a lot of money.

But it's "only" a filter!!!!

Somebody has a good idea for building a 2 way active crossover.

I tryed to do something with a pair of uA741 op-amp but without good results.

What are the things to take care?
 
Passive active xover

Why not implementing an active system using different order passive filters at the input of each power amplifier?

The only problem such a system would have is the passive filter voltage loss, but nowadays that is not really such a big problem with solid state amplifiers.

We could get rid of the active parts in a crossover filter, and probably for good.

Any other thing against such a system?


Carlos
 
Re: Passive active xover

carlmart said:
Why not implementing an active system using different order passive filters at the input of each power amplifier?

Implemented with Rs & Cs you max out at 2nd order, but it gets a bit droopy. Passive Line Level XOs. If you do it with C, L, R you can go to town. Vinylsavor has had some practical experience.

dave
 

zztop

Member
2002-05-26 8:45 pm
May be a passive xover should be easyer to build, but, and maybe i'm wrong, the values of capacitors are higt, and i have to use elecrolitic unpolarized capacitors.

A lot of people that i know , me too ,don't like this because

- this capacitor must have a very low inductance value so they aren't easy to find and maybe are more expansive ( but this is the smaller problem)

- What about dimensions and matching accuracy?

- With an active xo i can easy change the freq

About followers, i'm shure that their sound is better than op-amp, but only if tey are well matched and i think it's not easy.

Lanz
 
Passive crossover

>May be a passive xover should be easyer to build, but, and maybe i'm wrong, the values of capacitors are higt, and i have to use elecrolitic unpolarized capacitors.

Quite the opposite: you can get away with most electrolytics and use film types, particularly on the high pass filter that goes to the mid and treble amps.

>- this capacitor must have a very low inductance value so they aren't easy to find and maybe are more expansive ( but this is the smaller problem)

You may need higher value caps on the sub amp really.

>- What about dimensions and matching accuracy?

Film types can be obtained in up to 1% matched pairs. You also need precision parts if you want a quality active xover.

>- With an active xo i can easy change the freq

It certainly is, as long as you use a pot to do that. If you use resistors or caps the problem is the same.

>About followers, i'm shure that their sound is better than op-amp, but only if tey are well matched and i think it's not easy.

Nowadays it's very easy to get precision parts, and even you can match them yourself using your own meters.

But the question raised for not being advisable to use higher than 2nd order passive filters might be important.

Still couldn't talk to anyone that tried both and can comment about the difference.

Using a stronger signal on the preamp, in the order of several volts, and a higher power amp might compensate for signal drop on the passive parts.


Carlos
 
Peter Daniel said:
I was thinking about doing this with Alephs.
Can one implement 3rd order filter with Aleph circuit by placing additional crossover components in a feedback network?

Losing a stage is usually a good thing.

Doing an entire 3-pole filter in a feedback loop sounds kind of scary.

I'd put it between 2 active stages. 1st order is just change the size of the coupling cap.

Using just RC, usually you only see one or two poles between active devices. You can push it to 3 poles but make some sacrifies.

3rd-order.gif


An LCR filter on the other hand...

dave
 
3rd order crossover

http://www.globalnode.com/users/stevenr/spkrs/

I think you will find that inductor values become HUGE for load impedances that a preamp can reasonably drive. I don't know why the big objection to an active filter with a couple of followers.
Smaller capacitors sound better than larger caps also. I built a Fourth oder L-R with mosfet followers that sound great. Inductors have sonic signatures that are as audible as caps for non aircore inductors required for line level crossovers.
 
Peter Daniel said:
So how would you implement previous examples with LCR type filters? I never tried this approch yet.

Other than 1st order i haven't tried it either. Vinylsavor has reported good results using a 2nd order sandwiched between two transformers.


3rd0rder-LCR.gif


Use the active stages of your choice. Just use standard values loading into R. In the low pass you have to worry about DC.

dave
 

zztop

Member
2002-05-26 8:45 pm
I tryed to do some simulation with P-Spice for the both solution, active and passive.
Maybe it doesn'n tell me how they play but some think should be done:

- Phase choerency is aggranted by active xo near the cross freq ( such as said inside the rod elliot site ) wile with passive i measured a 180° phase shift. I could invert the connection but....

- to tune the active one i can modify the values of resistors with a very low loss of signal ( using trimmers to get the right values), with passive xo i need to change the R-L-C values ( i can modify the resistor value only but what will appen to signal)

- in simulation i measured a -3 dB loss of signal with a 8 th order filter ( about )

- The global freq reponse is flat whith the suggested filter in ESP site
 
planet10 said:

An externally hosted image should be here but it was not working when we last tested it.

Use the active stages of your choice. Just use standard values loading into R. In the low pass you have to worry about DC.

is this preferable to a PLL XO (2nd order)?

do we put the C-L-C or L-C-L before the bias resistor (replace coupling capacitor with the L-C-L or C-L-C network)?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.