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Old 10th August 2013, 12:20 PM   #1
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Join Date: Nov 2004
Location: NY, NY
Lightbulb Active Crossover PCB (pre) Group Buy

Hi All,

I've completed 2 stereo amp boards and power supply based on a group buy from years back. I'd like to do an active crossover before the 2 stereo channels to allow for bi-amping speakers. I've looked around and although there are a lot of schematics, I don't see many PCBs available for purchase so I was thinking of starting a group buy. I can organize it and probably complete the schematic and PCB layout if no one else is able to. Wondering if people are interested in a group buy such as this. I was thinking a single board with line in and two lines out filtered at the crossover frequency. If you want to do two speakers bi-amped then you would get two boards. I was also thinking of making it adjustable for the crossover frequency and have not looked into the order or type of crossover model yet. Please post with any interest. It would probably be limited to USA and Canada due to shipping.
Edit>> I can setup a web site for this too if it gets off the ground.
Edit>> So after researching and looking at my particular application and possibly others needs, I am thinking of including an AC to DC circuit for a low current transformer as well as a voltage regulator circuit. This would allow for powering the active crossover directly from your main transformer without any additional components. I'm thinking this would fit onto one small board with a header connector that would allow you to us the AC to DC circuit and voltage regulator for other purposes as well. Not much interest so far but I'll see if anything picks up.

Last edited by DSchmidt; 11th August 2013 at 09:01 PM.
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Old 15th August 2013, 04:16 PM   #2
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Could you post your schematic?
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Old 15th August 2013, 09:47 PM   #3
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Hi Fred,

Thank you for your post. I'll upload the schematic when I have it complete. As far as design criteria, I'm adjusting that so that there will be two channels of active crossover and one AC-DC power supply as well as a voltage regulator on one board whose preliminary size is 2 inches x 4.5 inches.
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Old 15th August 2013, 10:23 PM   #4
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Location: Upstate NY
A couple of things to consider-

Unless the drivers are flat almost two octaves past the crossover frequency, you will need EQ, and possibly different slopes on high pass and low pass filters. You can accomplish EQ a number of ways, adjustable Q, shelving filters, notch and peaking filters and Linkwitz transform to name a few.

Phase alignment is a must (at least according to Sigfried Linkwitz) - two ways to achieve this are with all pass filters and split crossover points.

Adjustable level - use a multiturn trim pot so that you can more easily set the exact attenuation you need.

Sallen Key topology sounds better than state variable to me. Some like multi feedback, I haven't tried it.

In a Sallen Key filter it is difficult to get a potentiometer to track well enough to allow even a single channel 2nd order filter adjustment. I suggest that you allow for swappable 1% resistors. Either a pluggable module or simply snap header sockets at the appropriate locations.

Allow plenty of room for quality capacitors. MKP caps sound better , but tend to be a bit bigger than MKT.

It sounds like you plan to use amplifier rails or at least the main AC for power. Check the maximum voltage of regulator chips. Most I know of are limited to ~35V. You can use a simple resistor or resistor and zener shunt pre-regulator to drop the voltage to something suitable for your regulator. Be aware of the dissipation and size your parts accordingly. Check your opamp data sheets for current draw.

Even with opamp crossovers, the quality of the power supply makes a difference. There your proposed board doesn't seem to have room for a discrete regulator, but check the threads for suggestions.

Watch cost - your competition is miniDSP. At around $110 enclosed it's awfully convenient. If your design ends up costing anywhere near that it had better offer a heck of a lot and sound an awful lot better.

Last edited by BobEllis; 15th August 2013 at 10:29 PM.
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Old 15th August 2013, 11:02 PM   #5
Jsixis is offline Jsixis  United States
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I'm watching and may be interested.
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Old 16th August 2013, 12:40 AM   #6
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The board Jens Rasmussen and I collaborated on is here: Active filter board GB If that meets your needs, I can order the number of boards you coordinate. PSU not included.
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Old 16th August 2013, 09:01 AM   #7
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Join Date: Nov 2004
Location: NY, NY
Default Thank you

Hi Bob,

Thanks for your post and helpful info. I'll check out the link you posted. I'll continue with the schematics but if there is not enough interest than I will have to shelve the project.

Edit >> Hi Bob, I checked out the link to the group buy post you posted but am having difficulty locating the files associated with the project, namely the schematic. Feel free to post here or provide a link. It seems as though I might be trying to reinvent the wheel, so to speak, so maybe we can just go with another group buy on the board you guys did. I can certainly make a website and organize.

Last edited by DSchmidt; 16th August 2013 at 09:12 AM.
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Old 19th August 2013, 12:38 PM   #8
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Default Schematics ...

Active Crossover

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Old 20th August 2013, 07:26 AM   #9
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Default Mini DSP

I checked out the MiniDSP that Bob mentioned and it looks pretty nice. I'd prefer an empty board to a completed unit but I might be going this route and just make a voltage regulator circuit to power it. Does anyone know of a board for a DSP on these forums?
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Old 29th August 2013, 10:28 PM   #10
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Default Upgraded Idea

Seriously thinking about doing a small DSP board and wondering if anyone would be interested in joining in. I'm looking at the Analog devices DSP chips. Right now I'm exploring the SigmaDSP chips.
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