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View Full Version : Guidance on bi-amplification of 250TIs



mtrump
08-14-2006, 07:47 PM
I have recently picked up a pair of 250ti limited editions. (I bought the pair of rights that was on ebay for those of you who keep track)

Anyway, since they are bi-amplifiable, I am looking for information on how to do them justice by doing it. I could not find 250ti crossover design drawing info that tells me what happens when I remove the tie bars on the back of the speaker.

Is the low pass element still in the line with the woofer?

Is there "high" pass elements still in line with the top end drivers?

Do I need to add an active crossover in front of my amps to replace the crossover pass functions?

Amplifiers I am gathering to play with include 2 separate adcom 555mkII stereo amps (rated at 200 w/channel and bridgable to ~600) and a pair of home made mono tube amps (built by my brother... estimate about 150watts each which sounded great on his 4311s)

some choices might be:

the tubes for the top end and an adcom for the woofers;
the two adcoms split, one for the woofers other for the top; or
bridge the adcoms to mono and just listen and forget the bi-amp concept.

the "bi-wire" concepts seems a sales gimmick to me as all it does is add a resistor in the crossover network (the wire from the speaker to the amp and back to the speaker is just seen (at best) as a small resistor in the crossover circuit).

I searched the forums but did not find anything, direction to a good thread would be helpful as well as any opinions.

thanks for your thoughts!

Robh3606
08-15-2006, 11:13 AM
Hello mtrump

Pictures would be a real asset so we can see exactly which one you have. From what I have seen these speakers are bi-wire not bi-amp ready, at least not in the traditional sense where you would use an active crossover. Can you post a picture of your crossover panel. If they are Bi-Amp ready they should have a Bi-Amp switch like the XPL-200A that bypass the required parts of the crossover. If the woofer is seperated electrically you still have the internal network in line so you could biamp them however you would not have an active crossover driving the amplifiers.

Rob:)

mtrump
08-15-2006, 07:41 PM
Thanks for the response!

the 250tis do not have a biamp switch as does yours. I have never seen a biamp switch on speakers before. Now I am really curious about seeing the circuit drawings for both!

first time I posted a picture hope it works. Note the tie bars are missing (original owner lost them).

Robh3606
08-15-2006, 07:55 PM
Thanks on the picture. Attached are the schematic for the XPL-200A and an L250TIBQ which is what I think you have.

http://manuals.harman.com/JBL/HOM/Technical%20Sheet/XPL200a%20ts.pdf


http://manuals.harman.com/JBL/HOM/Technical%20Sheet/250TiBQ%20ts.pdf

You can see the components the biamp switch takes out. How about some pictures of the speakers. We love looking at them!!:nutz:

Rob:)

mtrump
08-15-2006, 08:39 PM
I am amazed! how do you get to this info, the harmon site has no links to it that I could master.

Are you an insider?

Robh3606
08-15-2006, 08:43 PM
No they are listed on the site. You need to spend some time looking around we have a lot of information you just need to know where it is.

http://audioheritage.csdco.com/vbulletin/showthread.php?p=110700#post110700

These are all thanks to Techbot

Rob:)

mtrump
08-16-2006, 04:16 AM
I had poked around in these forums but got discouraged by the "Waiting for Giskard to scan and submit" and thought they were largely unpopulated. THe search engine didn't catch the attachments.

Know I need only figure out the circuit, what does bypassing the inductor in your circuit with the biamp switch do..... that the 250ti circuit does not.

Time for text books! or more irratating questions....

thank you

grasshopper

Robh3606
08-16-2006, 06:06 AM
Know I need only figure out the circuit, what does bypassing the inductor in your circuit with the biamp switch do..... that the 250ti circuit does not.

What it does is remove the lowpass filter on the woofer so without this in place the woofer would run with no passive crossover. It takes the caps out as well and only leaves the resistors in place.

Rob:)

mtrump
08-16-2006, 05:17 PM
Thanks Rob!:applaud:

Based on your input and looking at the circuits, I intend to try various amplifier configurations without fear of over heating or otherwise unintentionaly damaging a driver due to throwing too wide a frequency spectrum at it.

more things to play with!

if I were home more, I might just settle down and listen....

trumpy