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Old 1st June 2004, 10:42 AM   #1
matjans is offline matjans  Netherlands
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Default xover question; will this work?

hey guys,

finally finished my desktop-speakers for use with my laptop. THey're using visaton frs-8 drivers (dirt cheap and not that bad) and go down to about 100 hz so i decided i needed a small sub. Finished that too; picked up a second hand vifa pl18w009-8 (yay!) pretty cheap and put it in a 15 liter vented box.

And now, the xover. I decided on an active linkwitz/riley filter at about 110-120 hz and came up with this:

Click the image to open in full size.

top and bottom blocks are highpass filters for stereo speakers, mid block starts off with a summing amplifier. last two opamps are the lowpass filter. In front of the summing amp are 2 100k resistors. First opamp in the top and bottom block use 100k to ground on the inputs.

Assuming that i can work out the correct values for the filters with rod elliott's l/r calculator (yay for rod!), is the rest of this schematic correct? In other words; will this work?

what kind of signal-level loss can i expect after the lowpass section? I presume that with the highpass section signal loss isn;t that bad.
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Old 1st June 2004, 11:22 AM   #2
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The schematic shows all op-amps connected as unity-gain buffers, so within the pass-band of each of the filter paths, the gain wil be close to unity.
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Old 1st June 2004, 11:40 AM   #3
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Depending on the power amp used for the sub, you may need a little more gain in the low pass section. You could easily achieve this around IC4. Looks fine otherwise.

Cheers
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Old 1st June 2004, 11:52 AM   #4
moamps is offline moamps  Croatia
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Hi,
Use inverted opamp topology for summing amp.(+in connected to ground).
Regards
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Old 1st June 2004, 11:59 AM   #5
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Good point.

For the inverting summer, R3=R9=R10 for unity gain from each input. R10 will now need to go between pin 5 and pin 2 of the op-amp.

Don't forget this will invert the phase of the LP section, so you'll have to swap over the connection to the woofer.
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Old 1st June 2004, 12:01 PM   #6
matjans is offline matjans  Netherlands
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moamps: why inverted?
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Old 1st June 2004, 12:21 PM   #7
moamps is offline moamps  Croatia
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Hi,
Inverted topology is used for correct summing function without influences in channels crosstalk.
http://hyperphysics.phy-astr.gsu.edu...opampvar5.html

Regards
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Old 1st June 2004, 12:29 PM   #8
matjans is offline matjans  Netherlands
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ah, right on. nice link!
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