Input cap/Lowcut

[robkeeler]

If I put a lowcut filter (per Aaron's mods page) right after the input, do I also have to put a input cap to block possible DC from reaching my IC?

[Mike Burgundy]

I'm probably looking with my teeth here, but I can't locate the mods page.
Em, a low-cut filter? Are we talking about an inline cap of xx value? If that is so, then you already have DC blocking right there. Youre not isolating the opamp from DC, you're isolating the rest of the world from the opamps DC - it thinks (unless you use a bipolar supply - + AND - 4.5V) that 4.5V DC is actually ground. So with no signal applied, the inputs are actually at +4.5VDC.
If youre bridging that cap with a resistor however, the DC has a path through, so there's no blocking.
Generally, with stompboxes that use 0V as the negative supply, Vref=4.5V (virtual ground) and +9V as the positive supply, inputs and outputs of opamps sit at 4.5V. Usually the + input is held at this DC bias by connecting it through a resistor to Vref. The output will then be forced to 4.5V by the opamp itself. You want to isolate potmeters and in- and outputs from this, to avoid weird bias problems, unwanted crackle noise when turning a pot, and BIG booms when switching.
hih