Biamp: Wich fc ?

[planet10]

Originally posted by Bill Fitzpatrick
Unless extenuating circumstances prevail, a passive network is the most practical and cheapest way to go.

Adding a separate amp for the tweeters still has the best potential for best sound...

Unless well planned and speakers well picked, a good passive XO is one of the hardest things to get right, and can present a really ugly load to the amplifier. With a complex passive & the low cost of some decent amps we are seeing, active can actually be cheaper in some cases.

I heartily recommend going active all the way.

dave

[Bill Fitzpatrick]

Cheaper my foot. The extra amp needed makes it more expensive and that doesn't count the crossover.

And it's just as hard to come up with the correct transfer functions with an active network as with a passive.

The load presented by a passive crossover is not that ugly.

I only use active for the high frequency crossover if I need to level match, tailor the curves in an unusual way or need a differential circuit.

[planet10]

Originally posted by Bill Fitzpatrick
Cheaper my foot. The extra amp needed makes it more expensive and that doesn't count the crossover.

Certainly sometimes it can. But when you can build a gainclone, a simple Class A amp, or a nice little 6BM8 amp for <$100 compared to good inductors & caps that can easily top that price wise. With clever engineering the XO won't add much to the cost. And you also have to factor in that you can get away with a less costly midrange amp.

And it's just as hard to come up with the correct transfer functions with an active network as with a passive.

But it is a lot easier to get the active one working right because you have a nice resistive load to work into and not a reactive speaker with back EMF and such. I'd say getting an active XO tuned right is probably 1 or 2 orders of magnitude easier. The tuning of an active XO can also be a lot cheaper then tuning a passive XO... a small cap & resistor vrs a big inductor & cap...

[QUOTEThe load presented by a passive crossover is not that ugly.[/QUOTE]

Any crossover is uglier than directly into the speaker. Unless you are using something like a simple cap in series with a well-behaved tweeter, i'd consider active the way to go, and even then if quality is your main concern.

dave

[Higo]

Raka:
I`m planning to use second order Butterworth in Sallen - Key topology.

According to Rod Elliot article about biamp and your comments I think that I have to change my speakers. I mean rebuild them from 2 ways to 3 ways.
I have to change the box or do you think that I can use the same? I never design a 3 ways system... . Any advice??

The tuning of an active XO can also be a lot cheaper then tuning a passive XO... a small cap & resistor vrs a big inductor & cap....

I`m totally agree with this. It`s easier to tunning the XOA

BR.
Marcelo

[Konrad]

I think we know start system design... triamp and aktive all the way. Personaly i belive IC amps in an fully aktive design beats amplifier and passive x-over speaker's.
The main reason i think is that speaker element's parameter varies with motion and is therfore a komplex load and have more than frequensy as a variabel to the filter. And that an amplifier is more suited for that job than any passive filter output ever can cope with.

[jackinnj]

i think that there are few things which benefit sound more than bi-amping or tri-amping. i have bi-amped Linn Kelidh's driven by a Linn Majik and a Linn Power Amp -- I was able to audition both the passive xovr version of the kelidh's and the active xovr version before I decided to go with the biamped version -- I also biamped a set of the KEF reflex speakers (KEFB139/B110 and Audax Tweeter) -- now disused collecting dust in the basement/laboratory. The quad GC I was building was to use active XO but I haven't gotten around to finishing it.

Speaking of designing XOVR's I again refresh the list with the link to the beta at Analog Devices:

http://www.analog.com/Analog_Root/st...er/filter.html

This is much more comprehensive than the design tool at Texas Instruments.

[planet10]

Originally posted by jackinnj
KEF reflex speakers (KEFB139/B110 and Audax Tweeter) -- now disused collecting dust in the basement/laboratory

A shame to have those wasting away... you can send them to me

More seriously, people are looking for those all the time... you'd fetch 200-300 on eBay for the B139s & B110s.

dave

[Konrad]

Made up a stat-var filter. Also made lovpas(30-600) and highpas (600-10K)freq adjustable. Then bass gain and mid Q adjustable.
At the end i figured it vise to add inverters at the same time. Then phase switch or balanced output is possible. Only one channel without power suply shown:

[jackinnj]

the state variable filter lends itself easily to use with the digital potentiometers from Analog Devices, Dallas etc. In fact, Analog Devices has one such circuit using the AD7528 Dual DAC:
http://www.analog.com/UploadedFiles/...68AD7528_b.pdf