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Old 14th April 2008, 05:02 PM   #1
PWatts is offline PWatts  South Africa
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Default Miniature sub controller

Hi all,

Not sure whether the subwoofer or analog forum is more appropriate..
Just a quick display of a subwoofer controller I built for PC overkill sound system - a DIY 300W active subwoofer with a 80W power amp for the main speakers built-in as well, so the preamp output and speakers both connect to this unit. The surrounding circuitry and wiring is a bit rough (the thing was built in my student days), but I just wanted to upgrade the sub controller section. The main satellite speakers are Boston Acoustics Micro90's (fabulous things), and the sub is a Peerless SLS 8" unit in a 20l sealed box.

This little 100x45mm board houses a rectifier&regulators, opto-coupler and relay driver for a 12V input trigger at the left, and the actual controller part is the last small section at the right. For the important caps I used MKT's, the rest are plain 0603 & 0805 ceramics. IT contains 9 opamps (two quads and a single, OPA132 series) assigned to the following:

1&2) high-impedance input buffer for each channel to prevent crosstalk
3) left&right summer
4) 2nd order highpass filter, -3dB @ 17Hz; PC's often have nasty clicks and pops and rumble
5) 2nd order fixed lowpass filter, -3dB @ 110Hz
6) 2nd order adjustable lowpass filter, -3dB adjustable between 30-90Hz. It creates a sort of semi-4th order lowpass.
7) phase switch block
8) gain buffer
9) Linkwitz transform

There are two pots for frequency and volume, and two switches for phase and to bypass the Linkwitz Transform in event of a party or other situation where the volume might be damaging to the woofer.

It works fine and sounds just as it should, and measures just as calculated&simulated. The gain parameters had to be tuned a bit but the rest was plug&play. It is completely silent, not even the faintest buzz or hiss. Although hardly necessary it has a perfectly continuous ground plane at the bottom, mainly because it simplified routing. Given the size (the controller itself is only 40x40mm) and cost I'm quite happy.

The whole thing is controlled from another DIY project which houses a DAC and preamp (just need to finish the enclosure), but that will be posted later.
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Old 13th May 2008, 10:21 PM   #2
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hi there,

is this a kit or something you built yourself ?

-Dan
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