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Old 13th December 2004, 08:31 AM   #1
muhy3 is offline muhy3  Australia
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Default Is this circuit correct?

I am new at active equipment and I just used linkwitz information to design this circuit. It is a "bandpass" crossover for my subwoofer. It features a buffer (first op-amp) then high-pass filter (17Hz) and lowpass filter (150Hz) both with 24dB attenuation.

I was wondering if this diagram is correct. Also I would like to build the power supply, could anyone provide me with a diagram suitable to power 5x LM833 IC's (I believe thats +/- 15V) at Vcc,Vce.

edit: resistor & capacitor values were calculated using an excel spreadsheet and are correct.
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Old 13th December 2004, 09:49 AM   #2
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Looks spot onto me. Might like to add a 33-100 ohm resistor at the output of the last op-amp to guard against capacitive loading by cable.

The power supply can be done with 7815/7915 or LM317/337 regulators. There's plenty of info on these if you look in datasheets or search here
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Old 13th December 2004, 09:57 AM   #3
muhy3 is offline muhy3  Australia
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Thank you for your help, I found a kit which costs $13, and considering the voltage regulators are $4 each, it would be easier to buy the kit and build it since it comes with all the components and PCB ready done.

As for capacitive loading, thank you once again; I never thought about that.
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Old 13th December 2004, 10:16 AM   #4
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Perhaps you need to look around for suppliers more. $4 is a lot for a regulator chip. In the UK they are only 50p (if that) ~ AUD$1.30
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Old 13th December 2004, 03:54 PM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
What level of damping are you aiming for?
Bessel, Butterworth? You appear to be cascading 2 pole Butterworth for a 4 pole Linkwitz Reilly?
This will require non equal caps.
Regards Andrew T.
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Old 13th December 2004, 08:06 PM   #6
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I have found this filter on the forum somewhere but I forget who posted it, sorry

It might help, or not.
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Old 14th December 2004, 12:54 AM   #7
muhy3 is offline muhy3  Australia
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Thank you for the circuit diagram, I already have a plate sub-woofer amplifier which does the mixing, gain and phase adjusting. However my design requires that I have a high-pass at 20Hz to limit excursion for the driver. Along with that, I also put the low-pass for better control as I feel some mid-bass frequencies are still getting through.

But thank you for the circuit diagram.
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Old 14th December 2004, 12:59 AM   #8
muhy3 is offline muhy3  Australia
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Quote:
Originally posted by AndrewT
Hi,
What level of damping are you aiming for?
Bessel, Butterworth? You appear to be cascading 2 pole Butterworth for a 4 pole Linkwitz Reilly?
This will require non equal caps.
Regards Andrew T.

The capacitors/resistors are marked as C and R as the program I designed this circuit in is used primarily for PCB netlist export with which I am still playing around. I did not number them as I haven't gotten around to doing that.

On the buffer i use 1uF capacitor, and 21.5ohm resistor.
On the first high-pass C1 & C2 are 330nF where as the 2nd stage they are both 150nF. Resistors are all different values and there is an overall 1:1 "gain" in this circuit as I did not want to alter that aspect of the signal.
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