BoM diet

Earlier today, I went through another round of email discussions with one of our informal advisors, a truly gifted Eurorack designer. He kept poking holes in our new design, until all that was left resembled a fishnet. And once again, it’s going to bring some major improvements to our project.

Among other things, his main grief was that we were wasting close to a third of our Bill of Materials on a peripheral feature: our 128 oscilloscopes. This is due to the fact that we were planning to use the AD7606, an 8-channel 16-bit analog-to-digital converter costing over $15. And because each of our submodules now has 16 analog ports, we would need 16 of these, costing a not-so-cool $240.

There are three main problems with this component in relation to our design: First, 16-bit sampling is overkill, while 12-bit would be plenty enough. Second, what makes this converter so expensive is that it supports simultaneous sampling across all 8 channels, while multiplexing of the channels would be good enough for what we need. Third, if we go for multiplexed 12-bit sampling, we can use a 16-channel ADS7953, which costs just $5. As a result, we would shave over $160 off our BoM. Not bad…

Another piece of feedback was to replace the Lumberg 1502 03 by the PJ301M-12, which is 6 times cheaper, and does not require milling the PCB (plain holes are fine), and doesn’t wiggle when it is wave-soldered. Since we need 128 of them per module, this will save us another $80 in parts, and a few bucks in faceplate processing, not to mention the fact that we could prototype our faceplate with nothing more than a drill press…

Conclusion: our BoM went from over $800 to less than $550.

Thank you sensei, thank you!


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