Question about the Hollis Omnidrive and Digital Potentiometers

[wayland]

Very good catch on the digital pots (I'd been looking at the MCP4251 family https://4donline.ihs.com/images/VipMasterIC/IC/MCHP/MCHPS02708/MCHPS02708-1.pdf?hkey=6D3A4C79FDBF58556ACFDE234799DDF0 ), and you're right. 

But if I made it at that lower voltage level, and then ever happened to put eg. another gain stage or two in front of it in my pedalboard lineup, that'd overload it anyway, right?  Or is that not a problem as long as I bias the op-amps correctly and use the right resistances? 

Maybe I need to buy some pedals that already have digital pots in them, and see what they're using.  And since I think I already have some on the way, maybe I need to just wait. 

[antonis]

IMHO, in a ONMIDRIVE circuit, fed with 3.3V and Vref of 1.65V, more than half of circuit's resistors aggregate should be trimmers..

[ElectricDruid]

But if I made it at that lower voltage level, and then ever happened to put eg. another gain stage or two in front of it in my pedalboard lineup, that'd overload it anyway, right?  Or is that not a problem as long as I bias the op-amps correctly and use the right resistances?

It'd be up to you to decide what "maximum input level" you wanted, and then scale that down so the op-amps could handle it if you go for a number larger than 3Vpp or so. Plus you've also got to allow for gain within the circuit and think about where clipping occurs (and how much). Those considerations are typical for a drive pedal design, but at 3.3V it'll all happen just that little bit sooner!!

No, I don't think it's a problem. It's a factor you consider for the design is all.

[wayland]

OK, that works for me.  Thanks very much!  Looks like I have some circuit designing to do .  After some reading, that is. 

[wayland]

Regarding Op-Amps, would a MAX40078 work better then?