[lokie]

Can someone discuss the downside of PXLLO circuits? I've been given conflicting views. A lot of people here at AC seem to have no problems. But I was told..." Typically sub signals are filtered at 18-24dB/octave, not the 6-12dB seen in the passive designs. The insertion losses with the passive filters are a pain to deal with especially when dealing with higher roll-off rates."

I would like to implement a 80Hz high pass filter for the main speakers and through another out in my 2 channel preamp, use EQ and seperate amps to power 2 seperate IB manifolds w 2- 15" woofers each.

Picture- An example of the high pass  PXLLO circuit I want to use between pre and main amps.



 

[nicoch]

is a nice if you can mod the input caps of amp for  the xo ,is normal in the tube amp .
you can use a coil too for 12db  or you can diy active line level jfet xo as Pass B5
the amp without the bass will work a lot better....

[richidoo]

If you plug the reflex ports in your main speakers, then your 1st order filter will add to the natural (sealed) rolloff of your speakers to make something like 12dB/oct. HP slope depending on the F3 of the mains. If you can set your OB subs to match that slope and xo freq then you should be sittin' pretty. Hopefully your sub amp can be adjusted to 12dB slope.

But if you find the HF distortion of the sub intruding on the clarity of the mid - upper bass of the mains too much, then you need to increase the sub slope to 24dB/oct, and likewise increase the HP to 24db/octave with an active 4th order filter. You might just wanna use an active crossover filter board with HP and LP that will ensure the phase between the filters remains aligned throughout the xo band.

BTW If you later decide to try a 2nd order PLLXO filter for your mains, make sure you use a real physical resistor for R2, don't rely on the amp's input impedance to act as R2, because some amps will oscillate without a real resistor in the HP filter for R2.

Edit: forgot to add that if your IB speakers are located behind your mains, then you have to delay the mains by ~1mS/foot to time align the mains and subs. It will sound smeared bass if not time aligned.

[lokie]

I am using a Eico HF-60 as  a mains amp. Please elaborate how you would implement caps or resisters.

A cap calculator can be had here   http://www.pronine.ca/capimp.htm

Attached is the schematic.

[lokie]

I see you can't enlarge the schematic.

Here's a link:   http://www.vintagevacuumaudio.com/schematics-manuals/eico/eico-hf-50-hf-60-schematics.pdf

[nicoch]

try different xo  start 0,1 to down

[lokie]

Awesome. Thanks for your efforts. You're a Prince

Just so I have this correct... change the C9 and C10 from .25 to .1 and adjust from there?

So if I wanted a higher xover point, I would try a .09 and below? And reverse for a lower xover point?

[nicoch]

yes if real impedence is 100k with 0,01 start cut 6db from 150hz ....

[lokie]

150hz is too high. I'm thinking 80hz.

According to the calculator... I should use .02. Which doesn't seem right considering there's a .25 cap in there now.

[Davey]

There's absolutely no (good) reason for you to fool with your Eico amplifier to achieve this objective.

You should implement a simple CR filter outside the amplifier but fairly close to the input jacks.  (Just a small project box like the one you posted above.)  This has the advantage of easy fine-tuning of a shunt resistor value so you can use standard value capacitors.  It also has the advantage of allowing you to easily increase it to a second-order filter should you so choose.

The KISS method here is much easier/better/safer.

Dave.

[lokie]

here's absolutely no (good) reason for you to fool with your Eico amplifier to achieve this objective.

You should implement a simple CR filter outside the amplifier but fairly close to the input jacks.  (Just a small project box like the one you posted above.)  This has the advantage of easy fine-tuning of a shunt resistor value so you can use standard value capacitors.  It also has the advantage of allowing you to easily increase it to a second-order filter should you so choose.

The KISS method here is much easier/better/safer.

Dave.

Dave-

Have you done this yourself? What crossover point were you shooting for? What kind of subwoofer?

How do you increase it to second order?

Thanks

[nicoch]

There's absolutely no (good) reason for you to fool with your Eico amplifier to achieve this objective.

There's absolutely good reason ie avoid another caps in series with signal ....great reason

thanks dave 

[nicoch]

lokie  6db is smooth transition if you want xo at 80 you must start to 150..btw have fun, test some caps...when you find the right one I can suggest a good sound one
no need 12db filter