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Old 16th October 2009, 12:58 PM   #1
Vigo is offline Vigo  Sweden
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Default Two B1 and a crossover

Hi

I am thinking about building a B1 buffer.
The point is that i want to use active crossover to without having any op-amps.

Sow my thought is to use a passive volume control, then split the signal to one HP and one LP crossover. And after each crossover put a B1 buffer.

I want to do this to get everything in one box and to avoid op-amps and to avoid any passive crossover in my speakers.
Also i want to try the B1 buffer as a preamp

I planed to make the crossover from passive components.

Will this work?
Is it possible to put the crossover were i planed?

I am grateful for an help from people that know more about electronics then myself.
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Old 16th October 2009, 01:08 PM   #2
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Active crossover, with what? Do you mean an active filter because you have drawn a passive filter (surely) with a B1 afterwards?
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Old 16th October 2009, 01:40 PM   #3
Vigo is offline Vigo  Sweden
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Yes of course, you are right. It is not correct with active crossover.

A passive line lever corssover might be a better description.
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Old 16th October 2009, 03:09 PM   #4
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Look up Sallen Key filters in Wikipedia. They work great
with simple buffers.

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Old 16th October 2009, 06:14 PM   #5
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Quote:
Originally Posted by Vigo View Post
A passive line lever corssover might be a better description.
A buffered PLLXO. I still call these active as i define an active speaker system as any one with amplifiers for each speaker.

This same thing is in our queue, and as i understand, similar to the B2 (Nelson?)

dave
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Old 16th October 2009, 06:31 PM   #6
miksin is offline miksin  Finland
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Quote:
Originally Posted by planet10 View Post
A buffered PLLXO. I still call these active as i define an active speaker system as any one with amplifiers for each speaker.

This same thing is in our queue, and as i understand, similar to the B2 (Nelson?)

dave
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Old 16th October 2009, 08:22 PM   #7
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You also need another Jfet buffer at the input between the Volume Pot and Filter network.
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Old 17th October 2009, 10:32 PM   #8
Floric is offline Floric  Europe
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Hi,

I have a thing like that up and running for almost one year now. Topology:
- b1 - hp - b1 - high volume - b1
Input - Volume control <
- b1 - lp - b1 - low volume - b1
The high and lowpass are ordinary 2nd order PLLXO. The high- and low-volume are stepped attentuators with 1dB steps (up to -5dB). As B1 I used the schematic with dual supply ZenMod posted, just to save some capacitors. In the version now, I was lazy and used lm317/lm337 series regs.

Everything was built on stripe-board and it fits on two 16cm*7cm boards.

Sound great, I recommend it.

Did not use the Sallen-Key filters then because the simulation lead to a little less distortion with the passive filters (less important) and I was not sure if I could run unbuffered Sallen-Key filters with a B1. A buffered Sallen-Key would have caused even more B1s in the box (12 right now).

After some experience, I would try

volume - B1 - lp(Sallen-Key) - low-volume - B1

For every path. But i am not sure if it sounded even better.

Best regards

Flo
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Old 19th October 2009, 08:58 AM   #9
Vigo is offline Vigo  Sweden
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Thanks for all replays and ideas.

If i build a Sallen key filter do i need 3 B1 for each channel?
One before the filter one in the filter and one after the filter, or is it enough to have one before and one inside the filter?

it seam that i need one B1 between the volume control and the filters, would it work to only use one B1 and then split the signal to the filters. I guess the signal strength will be 3dB lower. But is there any other problems?
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Old 19th October 2009, 09:37 AM   #10
Floric is offline Floric  Europe
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Quote:
Originally Posted by Vigo View Post
Thanks for all replays and ideas.

If i build a Sallen key filter do i need 3 B1 for each channel?
One before the filter one in the filter and one after the filter, or is it enough to have one before and one inside the filter?
I would use three one after the volume, one for the filter, a kind of attentuation after the filter (>10kR) to keep some fexibility, and another b1 after that for the output. You would need that one if you need an attentuation. If you would omit it, th impedance of the attentuation should be very low (<4k). In my experience, the b1 does not like it that low, leads to a lack of bass.

Quote:
Originally Posted by Vigo View Post
it seam that i need one B1 between the volume control and the filters, would it work to only use one B1 and then split the signal to the filters. I guess the signal strength will be 3dB lower. But is there any other problems?
Splitting works, no loss of signal. Sometimes (layout etc.) it is of advantage to use a separate inut buffer for every signal-row. But you don't have to, the b1 is capable of driving two b1's (with sallen key).

Best regards

Flo
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