Rev3 Feedback & Suggestions

While assisting vendors in developing commercially viable iterations of this hardware design, we've addressed some concerns that I'd like to share for others: ## USB Host voltage The Rev3 design only supplies about 4.2V to the Teensy. Without an external powered hub, this is inadequate for many devices to connect directly. To quote Paul from Discord discussions: > If you change R128 to get more voltage (which does bring USB host voltage up), you should also increace R116 and R117 so MIDI OUT current remains approx 5mA when driving the expected MIDI IN circuit of 220 ohms and 1.25V optocoupler LED. > Indeed I chose R128 and R129 for about 4.25V. This is at pretty much the low end of the range USB devices can use (and expected if running from an unpowered USB hub). The 4.25V choice was motivated by desire to reduce the power draw from the Eurorack +12V power. > If you're ok with higher overall power usage, perfectly fine to adjust R128 for voltage up to 5.25V. Just remember 4.25V powers MIDI OUT, so adjust R116 and R117 ## Audio input/output gain-staging I recommend changing resistor values (R101 / R102) to reduce input gain to avoid distorting the PCM chip... 31.6K is tuned for 10Vpp (+/-5V), so something like ~15K would better accommodate 20Vpp Eurorack signals, maybe smaller for 24Vpp. Likewise, you might want more gain at the output stage. (I'm not sure what to alter for increased output gain...) ## Trigger inputs By default, in Rev3, TR1-4 and CV1-4 share the same jacks, which I'd rather not have on any of the final designs. They should be broken out, with extra pulldown resistors (100K) in parallel. The PCB design allows for this, with extra pin headers and traces that can be cut... ALA successfully squeezed 4 extra jacks on the same 10hp front panel! Flexible Input Mapping in the firmware provides a workaround to avoid collisions, but it can still be confusing. More forum discussions here: https://modwiggler.com/forum/viewtopic.php?t=280365