Op amp circuit on the MPC6004 section of the Petal rev 5 schematic

Hardware Development
1

Hi,

I’m building up a supporting circuit for my Seed-based pedal. I’m using the Petal schematic as a reference for all the utility stuff like buffers and PSU. Somewhat new to this, though I have some experience through guitar amp design (those circuits are very simple though.)

Question is what’s up with U6C in the input buffer? It’s joining pins 9 and 8 and tying 10 to ground. Is this simply a good practice with multi-pack opamp ICs like the 6004, like to avoid noise? My pedal is mono, so should I do similar with the other unused opamp block?

Thanks!

Tim

2

To answer my own question: it’s necessary to tie down unused op amps in a multichannel package; having them floating causes weird voltage spikes and instability. TI has a nice primer here on it: https://www.ti.com/lit/an/sboa204a/sboa204a.pdf

So, that’s what they’ve done in the Petal.

3

yup, that’s exactly the reason why. I’ve built a bunch of guitar pedals based on the same Daisy Petal schematic, happy to answer any questions you might have.

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