Hi Peter, It looks like the electrolytic cap that popped was C4 or C7 ->I am following Jmej's circuit that on this schematic above.
How would this be wired on your original breadboard using electrolytic caps these are the C12 and C13 on Eric Archer's schematic except he used regular caps.
I think I set up the caps in that section with the wrong orientation causing one to pop.