Which topology for a subwoofer amp?

[Morse]

Hi everyone and thanks in advance for your help and suggestions!

I'm in the process of building a small subwoofer to go with my RS40-1197 (generic FE103's via Radio Shack) for the office. I'd like to get about 30wrms out of the amp and also use only parts on hand - no new purchases if possible.

Okay, I am torn between 2 topologies:

1. bridge a pair of TDA2030A's

OR

2. use a single TDA2030A to drive a PNP/NPN pair of transistors.

Unfortunately I don't have the "right" transistors for the circuit (BD907 and BD908) shown in the TDA spec sheet - how freely can I substitute in this application? I've got 2SA473's and their complement (2SB "something or other" - don't have my parts bins here for reference) in reasonable quantities. The NTE equivalents on these parts are NTE152 and NTE153.

Thanks again and all the best,
Morse

[Mr Evil]

Personally, instead of 1, I would use a single more powerful chip amp, such as TDA2040 or 2050, or one of the popular LM chips, since it is simpler and works out cheaper than buying two chips (the TDA2030 is not so great for sound quality either).

Or, rather than 2, I would use an op-amp driving a pair of transistors, as it will be cheaper and potentially yield higher quality. There are plenty of schematics around for doing such a thing, often to be found in the datasheets/application notes for op-amps. Generally, any pair of power transistors will do, either BJT or MOSFET (noting the higher bias voltage needed for MOSFETs). I've built many such circuits before, and they can go to very high powers with surprising sound quality.

Since you don't need much power, I would go for a chip amp so you get the advantage of lower component count and the various protection circuitry built into most chips.