Input buffer

[micahvdm]

Hey, I have a question about the buffer that you used for the inputs. I’ve built a knob style buffer for the input, but it’s not playing nice with 5v supply. What did you use for your input buffer?

[Randall (Admin)]

If by "not playing nice with the 5v supply", you mean noise, Yeah, I know all about that!  The 5v rail is likely to be extremely noisy.  Not just with typical ripple, but pop-corn burst noise.  Even a good low pass RC or LC filter won't help much.  I found I had to regulate the supply - kindof a bummer cuz you loose headroom to the voltage drop of the regulator, but the only other low noise solution I found was to battery power it.  Since it would be weird to require a battery in a digital multi-fx pedal, I used a  AMS1117-3.3 on the 5v rail with input and output caps.  For the buffer itself, I use this https://www.mouser.com/ProductDetail/579-MCP6292-E-P with unity gain (2 resistors, 2 capacitors per channel).  I tried 5 different dual op-amps and settled on that one because it was the quietest and supports rail-to-rail input/output which is important when you don't have headroom to spare.