Why does this opamp have a diode on v+
Q1) The diode is there because it drops the Vdd on IC6 by about a volt (whatever the Vt of the diode is).  That means IC6.2 is only feeding a maximum of +8V into IC5.1
Q2) Will it matter?  I suspect so, but define &quot;matter&quot;.  Guitar pedals like to throw diodes into random places because it causes or ameliorates &quot;clipping&quot; which creates non-linear effects on the output audio spectrum.