Cool job Dave!
My hat is off to you!
A couple of notes....
The ADC inputs self-bias to 1/2 Vdd so if you want to silence the unused input channel, you should do it by connecting the inputs to ground via a couple of 10uF caps. If you want to be really complete, bypass those 10uF caps with a 0.1 or a 0.01uF film cap. Grounding the inputs with a DC ground will smoke the bias supply for the inputs.
The unused DAC outputs can be left floating. If you ground them, 1/2 of the output stage is going to overheat as it tries to sink power into the ground connections.
It's funny to note that your FemtoVerb is almost identical to the Alesis PicoVerb, except yours has more parts, is more polished, and is MUCH better suited to guitar. The Alesis PicoVerb is made for line level applications. (
read: almost useless unless it follows another effect)
I actually like soldering SOIC packages because it's faster and easier than through-hole devices. The secret is to use a pre-tinned set of pads on the board and to coat them with liquid or paste flux before soldering. If you do that you can simply re-flow solder the part in place. I start by holding the chip down with a finger and touching the iron to pin 1. The next pin to go down is the one at the opposite end of the package (
pin 11 on a 20 pin chip). With the first two down, all you have to do is to touch the iron to the rest of the pins to re-flow solder them into place. Wash the flux at the end and you're all set.
It's just too bad that you can't adjust the LFO speed for the built-in effects.
I guess that's what programming is for.
On clocking... The DSP uses a 12.288 MHz clock to generate an internal bit clock, a left/right clock, and a word clock. To decrease EMI/RFI emmissions, the ADC and DAC use the DSP word clock and an internal PLL to re-generate the bit clock locally. That way the clock lines run at 1/64th the bit clock frequency.
