Subwoofer amp "stages" - in which order?

[m127]

Hi all,

I am building a closed box sub and an amp for that. The power amp will be based on National Semiconductor LM3886s. This is the easy part.
The more difficult part is the "preamp" section. I'd like to build the following stages:
- Input (high level also, + buffer)
- Volume control
- Phase control (at least a 0-180° switch)
- low pass filter (crossover)
- high pass filter (subsonic)
- Linkwitz-transform

I will use TL072 or TL074 opamps.

What I don't know is the order in which these stages should follow each other. (Input is ok to be the first 🙂 )
I have found a few projects and schemas around this topic but none of them is complete, so I will have to design a mix of them. Examples:
- The ESP/EAS controller seems to be good but I don't know if I can just simply add the Linkwitz circuit to the end.
- The ESP project 71 (the LT) doesn't contain a crossover. It is not mentioned where it should be inserted into the chain.

Maybe it is not a key factor where the amp stages are but it would be nice to have some complete cricuit schematics. Can anyone send a link?

 

[SY]

FWIW, my current xover/bass controller starts with a buffer, LPF, HPF with eq (no need for separate stages), phase control, volume control, output buffer. It's all implemented with opamps (horror of horrors!). The idea is to knock down the high frequencies early on, then handling the rest becomes much less critical. You might want to use something better than a TL07x for the output buffer- you don't need speed here, but current drive capability and low source Z are nice things to have. I use an LM310 in that slot, just because I had a bunch left over from a project in 1980.

I think Rane has their schematics online, and if I were to copy someone, they would be a pretty good place to start.

If you don't mind spending a little bit and forgoing the joy of soldering, I think the whole thing can be done much better digitally, with something like a Beringer.