Okay I have just finished assembling the board shown on the photo above (simple audio amplifier for my mom). The one with greeting for the forum members has one little mistake — after finishing it, I suddenly discovered that the used operational amplifier is badly balanced, because of which I had about 0.5 volts output voltage (while the expected value is exactly zero). So I had to add
extra resistors for balancing. And before starting to work on the 2nd channel, I opened my PCB IDE (DipTrace, as I already mentioned) and added those resistors. So it was easier to properly balance the second instance. Both boards work fine, but for the second one I had to use MJE13007 as output transistors. You may be wondering why. The answer is: I already used all of my TIP41/TIP31 transistors, which suited this purpose better. This was a surprise for me, otherwise I would have bought them many days ago. It is worth to mention that I had Russian КТ819Г transistors, which also suited this purpose perfectly, but there was a little problem: their pinout differs from TIP41C, which was supposed to be used. I had no mood to redo the whole board because of that, so I just put MJE13007, as I do not have anything else in TO-220 package (except some other Russian transistors, but they all have E-C-B pinout, not B-C-E).
Top view of both boards
Bottom view of the first board
Bottom view of the second board
Now need to wash away the remaining flux and mount the boards into a box (power source is ready as well). And then I’ll probably build a simple stereo expander (using 2 opamps or 2-in-1 like NE5532).
Ah, I almost forgot. I will need heatsinks. As this piece of crap will be run at low power, I will use heatsinks like
this one (already used for an UV LED, just showing).
(upd) found some TIP122s, which I also completely forgot about. They are darlington-type NPN power transistors. Nah, no mood to redo it, though the amplification of MJE13007 is only ~25, hope that’s enough
(upd2) will be easy to add a subwoofer channel with this cheap
lowpass filter from AliExpress
(upd3) this can also be useful soon