electronic audio low pass / inversion stage for bridging

[Learnincurve]

Hi all,

I should begin by admitting that I know almost nothing about electronics so please forgive what might seem like lots of stupid questions. If you have the poatience please put me right using words of as few syllables as possible!

I'm wanting to build an active subwoofer. The idea is sketched out in the subwoofer forum. Part of this needs to be a stage that will split the signal, inverting half of it and not inverting the other, then feeding the to my low pass network which will balance the natural rolloff of the unit and give a flat response down to around 20Hz. I found a schematicf that looks fairly good ( http://home/new.rr.com/trumpetb/audio/009js.html). All I need to do is forget the high pass bit, and build two of the rest with the first op (TL082CP in the schematic) inverting one signal and not inverting the other. then connecting them in parallel.

Is this right so far?

Some questions:

1. What about input impedance? Do I need to take this into consideration in vew of the parallel connection?

2. Gain: The schematic isn't explained, but I would like the overall gain of each "half" to be 1. I know that the 3 pF cap and the 100K resistor across op1 control this but don't know the equation. How does leaving out the high pass circuit effect the overall gain?

3. Topology: Presumably there's a good reason for the order of the ops. By reversing the order I could get away with only one filter network, splitting the signal afterwards (1 TL074CN, and 2 TL082 CPs). I assume this would not be a good solution.

4. choice of components: I want the sound quality to be as good as poss. How do the suggested ops compare with others? In the 405's I ended up using NE 5534 (more available than a BB OPA604AP, both were recommended). What about stability issues with various ops at low gain?

I will also end up building high poass networks for the front pair as my speakers are good down to 43 Hz, and I don't know how they roll-off below that. Far better to controll the X-over at around 70 Hz.


If anyone has a schematic for a better circuit please let me know. Otherwiose I would be happy for any help here.


Many thanks!