It’s NOT in the provided code, but in the Mozzi library you download
And speaking of - you should download the Mozzi library via its git repository rather than via the Arduino download manager. The last release is many years old.
This is what the edit looks like on my end but I use a different build environment (platformIO)
Wow, didn’t know you could do all that!
I just bought a few resistors from Mouser with the exact figures and hoped for the best. (since Mouser isnt cheap, I bought just a few)
What you wrote about chaining multiple resistor values is interesting. How do you do that in practice? Do you simply bind their leads with solder?
Good thing you told me that! It wasnt clear to me at all.
So do you have to enable HIFI mode manually as it off by default?
about resistor replacement: there are calculator tools like this, or ask your preferred search engine for some thing like “resistor combination calculator”
Another quandary:
If the BOM says “4.7u Electrolytic Capacitor” and the board and schematics display it as non-polarized (as in disc capacitor), should I assume it’s a mistake in the BOM?
Yup, one thing you can do is simply do is solder two components together to treat them as a single one, here’s an example with diodes instead:
A good read how resistance and capacitance combine:
(Matthew’s blog belong in everyone’s bookmarks - tons of knowledge (and strong opinions) there)
and yes, you need to edit the mozzi_config.h header, it defaults to STANDARD_PLUS:
(having to edit a vendor library is a very idiosyncratic way of providing configuration options, but that’s how they do it)
That 4.7µF cap is a coupling capacitor to avoid DC offset. It’s common for such capacitors to specify a polarized electrolytic cap but disregard the polarity. Not a good idea in theory, but it works in practice, so everyone does it. If you can source a non-polarized cap it would be better.
Thank you very much for the excellent replies.
Gotta say I didn’t know what to expect when initially posting here, as I thought that maybe this was a strictly Kosmo format users club. Happy to discover that this isn’t the case.
You are going to screw your project to a 20cm panel and use big jacks, right?
If not you are on your own form here on…
just kiddin’ 
Belive me, I’d LOVE to start using panel sizes that make sense, but my rack is 3U, so hopefully in the future.
You think it will grow when it gets older ? 
For certain values of “everyone”.
That’s what I prefer to do when faced with an electrolytic cap that sees both polarities.
But in this case the polarized cap is okay. It’s being used to AC couple the output signal, which before that point is 0 to 5 V. That means the voltage drop is always positive, and so a polarized capacitor with the + lead toward the resistor and the - lead toward the output will have the correct polarity.
What’s critical with R1 and R2 is not their values individually but their ratio: You want it as close as you can get to 128. With a handful of 1% 499k and a handful of 1% 3.9k and a multimeter you should be able to find two that are within 0.1%, let alone 0.5%, of that ratio — and a handful of 1% resistors is cheap compared to one 0.1% resistor, and the ones you don’t use can be saved for use in other projects. You can use two 1M in parallel, or 200k and 300k in series, to get 500k, and those being E24 values will be cheaper than 499k, but note that 500k/3.9k = 128.2 which is more than 1% too high.
R6 is marked “0.5%” in the schematic too, but I’m pretty sure it in fact is not critical.
Another question; there’s an LED footprint on the board, but it has 4 holes. I imagine that it’s for some RGB LED that I don’t have. I do have regular 2-lead LEDs, and I don’t mind the color changing too much. (I assume it’s for visual feedback to know which VCO mode is selected.) Can I just put any old LED? and if so, which holes should I be using and how do I know where the long lead goes? (there are no polarity indicators on the silkscreen)
Presumably that’s this
You could use 3 single LEDs. The long leads go to pads 1, 3, 4 and the short leads would connect together to a wire going to pad 2. Presumably the pads are labeled in order from one end or the other but which end? Use a multimeter to see which pad connects to ground, that’s pad 2.
Worth noting that as drawn, the RGB LED used is common cathode. Some are common anode instead. If you buy some for this project, double check you get the correct type.
