The 2nd proto run of 10 UCI120s is now out for delivery with UPS so should have those very soon. The MAX9814’s have always worked perfectly for me, far better than some other IC options such as SSM2166/67. It does have the underpad + 3 ground pins (which are all properly grounded and reflow soldered on our boards), I suppose because the pkg is ridiculously small, but it’s packaged not unlike a 3W audio amp IC yet is using only a few mA, so that does seem like overkill. Definitely wouldn’t try hand soldering one.
Good point on the TP18 location next to the Insert I/O jack, which has 3 coupling and 2 bypass caps and ferrite beads but no resistor. I have added a 47K there on the sch. I had also made a few minor optimizations to the level detector circuit that’s also driven from that point.
I’ve done a good amount of analog design over the years but had not actually done a PCB layout, G1LRO did that for the UCI120, and while waiting for the new boards to arrive I decided to do a small accessory board on my own to test a new potential fully Class AB audio amp IC, try out some sweepable filters, and test some optimizations to the signal level LED circuitry. I was going to do just a small PCB module but then ended up going with the same form factor as the UCI120, thereby creating a matching accessory box that connects with a single 3.5mm aux cable, adds a 2nd speaker output, signal LED for the Spkr audio, and sweepable filters (variable 15-300 Hz HPF & 2-23K LPF). Finished the schematic and board layout in about 2-3 days work. Should have some of these boards in the next week or so.
The UCI120 is quite nice as a MAX9814 eval board even if you didn’t use the USB audio I/O. All the MAX9814 AGC option pins can be configured, which is not possible on the small modules, and the Insert I/O gives you a direct out.
There isn’t really room on the UCI120 enclosure panels to add the sweepable filter controls or the (internal DIP switch) AGC controls but I plan to do a larger version of the UCI120 at some point that brings all this out to the panels. Sweepable filters are not as useful on ASL as on HF but the parts cost to add them is around the $1-2 range, so there you go, and, it could have a switchable Aux In that would allow you to route an HF radio into audio path if you wanted to. I can now easily do many other similar concepts, such as something with a MAX9814, variable hi & low cut filters, and a variety of I/O jacks ie. basically a UCI120 + AAF3 but without the CM1xx. Below is simulation of the AAF3 frequency response at filters full open vs. closed, compared to the UCI120 speaker audio (fixed) response in red.
These are only 6dB/octave which keeps it very simple and inexpensive, but for a few $ more could support dual gang pots and 12dB/oct filters, though the design starts to get considerably more complex there if you want higher-order and variable optimized filter slopes eg. Butterworth response. At that point it might be more cost-effective and simpler to patch in some audio dynamics/EQ plugins into ASL. LADSPA/LV2 plugins could probably be patched into one of the channel drivers in a couple days work eg. Linux Studio Plugins Project