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Old 15th January 2013, 09:15 AM   #1
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Default 2.1 active crossover + amp build

Hi all.

I've started working on an 2.1 amplifier. The idea is to have active crossovers for all the speakers, summing for the sub. There will be a total of 5 amplifiers (tda7294 i think): 2 for left (mid + high), 2 for right (mid + right), 1 for sub.

The basic idea was to have all of these built on the same PCB with a whole ground plane for all the pieces (crossovers and amps). I will post pictures with schematics & pcb's as I move forward.

Questions from the start:
1. Is it a good idea to have them all on the same PCB or should I try to have them like modules?
2. Should I first low pass the inputs and them sum them, or sum them then low pass the signal?

I am sure I'll have lots of questions during the process but hopefully I'll be able to finish this up nicely.

Thanks,
Adrian
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Old 15th January 2013, 09:44 AM   #2
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On 2 (without speaking from experience) I would say it would be better to sum them after low passing, simply because it will give you more isolation from your high pass signal (ie less chance of your summing causing stereo crosstalk on your high pass stereo channels. Of course the downside is you then need to implement stereo low pass circuits...

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Last edited by wintermute; 15th January 2013 at 09:46 AM. Reason: add downside.
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Old 15th January 2013, 11:39 AM   #3
AndrewT is offline AndrewT  Scotland
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Use an MFB low pass filter.
It is inverting and can accept two inputs.
It both filters AND adds.
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Old 18th January 2013, 12:35 AM   #4
gman76 is offline gman76  United States
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adrian, sounds interesting, sorta like what I was thinking about doing. By 2.1, do you mean you'll have an amp for the sub? I thought most subs these days have a plate amp. And you have 2-way bookshelf speakers? (a mid/bass and a tweeter?) I have a few different 2-way speakers to target. I'm thinking of designing a plate amp that has active filters with adjustable xo freq and drives a 50W low freq and 20W high freq. Not sure how fancy I was to get with filter alignments and time delay correction. I've been reading Rod Elliot's articles about passive vs active crossovers, and it all makes a lot of sense (how passive have many shortcomings and cause a lot of problems if not designed properly).
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Old 18th January 2013, 06:54 AM   #5
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yes gman, I'll have 2 2way bookshelf (midbass + tweeter) and a sub. I'll use the sub a little higher then regular (somewhere around 200Hz) since it's hard to get a good midbass driver without a lot of money but that shouldn't be a problem.

I'll post pictures of the circuit and the PCB design as it's now soon.
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