Ground referencing when working with opamps

[diy didi]

Good day.
My question relates to two circuits for overdrive sections for guitars. See attached.
In both instances the second opamp’s + input is directly connected to the output of the first opamp. I was taught that the + input should usually be ground referenced via a resistor.
How do these circuits get away with this and not using any resistor here?

 

[dr pepper]

Yes you cando that, a noninverting amplifier built with an op amp takes its input on the + terminal.
Your thinking you wouldnt do that to the same op amp, ie connect the + input back to the output.
At least you wouldnt do that for a non weird linear amplifier, you would do that if you wanted to build an oscillator.

 

[Nigel Goodwin]

Good day.
My question relates to two circuits for overdrive sections for guitars. See attached.
In both instances the second opamp’s + input is directly connected to the output of the first opamp. I was taught that the + input should usually be ground referenced via a resistor.
How do these circuits get away with this and not using any resistor here?

You were taught (or understood?) wrongly, it merely needs a DC reference to 'somewhere' - in this case it's the output of the previous opamp, which is most likely at 'ground' anyway, and is an extremely common connection.

 

[crutschow]

I was taught that the + input should usually be ground referenced via a resistor.

That's typical for an inverting configuration, but those op amps are connected as non-inverting amps.