A parallel amplifier with the LM3886…

Gainclones or chipamps are a popular DIY-topic and I’ve done a couple of designs myself and assembled a few others as well. The only one of the “original” National semi amplifier IC’s that I haven’t really done anything with – and coincidentally the only one that’s still in production – is the LM3886.

But not any more, because I just finished a simple design with two LM3886s in parallel configuration. The circuit is built (mostly) according to the “PA100” design from the original National application note (AN-1192) and not the Jeff Rowland-derived PA150/BPA300 that has different configuration and of course a third IC per board.

The configuration with two parallel ICs gives full current output at +/-35V into 4 ohms where a single IC would otherwise be thermally limited, but of course the power is still modest. As I recently swapped my faithful Sonus Faber speakers for a set of Scansonic MB towers which have a fairly low impedance, that’s exactly what I needed though (not to mention that I had a 35V supply left over from another project 🙂 ). The two-chip configuration also means boards can be kept small (and cheap), and there’s still the option of using two boards per channel in bridge-mode to make a BPA200, although the supply voltage would have to be reduced – only the BPA300 will run at 35V rails in BTL-mode as well.

The boards worked first time on power-up and seem to be well-behaved (quick tests only though). I need to do a bit more testing and make some minor (mechanical) changes to the layout and then I’ll publish the project files 😀