let us prepare to grapple with the ineffable itself
and see if we may not eff it after all -Douglas Adams
New DFM! Same great taste!
The "Sound Producing Amplifier Module" or "S.P.A.M." is hitting that point in it's life cycle where I can't really dedicate enough time to fufil orders, and still solder them all by hand. A good problem, to be sure. So as we hop from revision 5 straight to revision 7, I'm looking towards Designing For Manufacture. In the case of this amp, that means moving to mostly surface mount components.
I was mildly nervous that different tolerances and characteristics of surface mount components would affect the performance of the amplifier. Looking back, this is a silly thought. I made careful selection of components with all the same values. So despite the packaging, nothing really changed. Still, I felt it worth comparing the new prototype with the old rev.
I put put both amps on the bench, and hooked up an HP-35660a dynamic signal analyzer. There is about a 5db change in response from 64Hz to 1000Hz. Above 1000Hz the test goes a bit crazy, but all still within 10db. As you can see from the photos, the two amplifiers perform almost identically. I'm not really sure why I expected to see any difference, but I feel good to have gone through the effort.